CHARACTERISATION OF A PIXEL DETECTOR IN BCD8 … Universita degli Studi di Milano FACOLT A DI...

Universita degli Studi di Milano

FACOLTA DI SCIENZE E TECNOLOGIE

Corso di Laurea Magistrale in Fisica

CHARACTERISATION OF A PIXEL DETECTOR INBCD8 TECHNOLOGY

Relatore interno:

Prof. Attilio Andreazza

Relatore esterno:

Dott. Mauro Citterio

Correlatore:

Prof. Valentino Liberali

Candidato:

Ettore ZaffaroniMatricola 845490

Codice PACS: 29.40.-n

Anno Accademico 2014-2015

Contents

1 Introduction 11.1 Semiconductor detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1.1 The depletion region thickness . . . . . . . . . . . . . . . . . . . . 21.1.2 The reverse current . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.1.3 The junction capacitance . . . . . . . . . . . . . . . . . . . . . . . 41.1.4 The Fano factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.2 The BCD8 technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.3 Radiation effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.3.1 Ionization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.3.2 Displacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.3.3 Effects on integrated circuits . . . . . . . . . . . . . . . . . . . . . 6

2 The KC53A chip 92.1 The pixels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.2 The amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102.3 The buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122.4 The current injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132.5 The pads and the biasing scheme . . . . . . . . . . . . . . . . . . . . . . . 142.6 KC53AA and KC53AB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3 Tests on KC53A passive pixels 173.1 Current vs. voltage measurements . . . . . . . . . . . . . . . . . . . . . . . 17

3.1.1 Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173.1.2 Protection diodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193.1.3 Connections and measurement . . . . . . . . . . . . . . . . . . . . 19

3.2 Capacitance vs. voltage measurements . . . . . . . . . . . . . . . . . . . . 203.2.1 Instrumentation and measurement . . . . . . . . . . . . . . . . . . 203.2.2 Data analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233.2.3 Estimation of the depletion depth and of a MIP signal . . . . . . . 24

3.3 Tests with radioactive sources . . . . . . . . . . . . . . . . . . . . . . . . . 273.3.1 The passive pixels test board . . . . . . . . . . . . . . . . . . . . . 273.3.2 Spectrum of 241Am . . . . . . . . . . . . . . . . . . . . . . . . . . . 283.3.3 Spectrum of 55Fe . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

3.4 Measurements with the X-ray tube . . . . . . . . . . . . . . . . . . . . . . 32

4 Tests on KC53A active pixels 374.1 Current consumption measurement . . . . . . . . . . . . . . . . . . . . . . 37

i

4.2 The test board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384.3 Output DC and noise levels . . . . . . . . . . . . . . . . . . . . . . . . . . 404.4 Measurements with current injection . . . . . . . . . . . . . . . . . . . . . 424.5 Comparison of the active pixels response . . . . . . . . . . . . . . . . . . . 44

5 Preparation for irradiation tests 515.1 Planned tests on KC53A . . . . . . . . . . . . . . . . . . . . . . . . . . . . 515.2 The KC01 chip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 515.3 Tests on KC01 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525.4 The KC01 test board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Conclusions 55

A Circuit schematics 57

B ROOT macros 63B.1 CV measurements macro . . . . . . . . . . . . . . . . . . . . . . . . . . . 63B.2 241Am macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

B.2.1 Macro to fit the spectrum peaks . . . . . . . . . . . . . . . . . . . 64B.2.2 Macro to perform the channel-energy calibration . . . . . . . . . . 66

B.3 55Fe macro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66B.4 X-ray tube macro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

Bibliography 72

ii

Chapter 1

Introduction

Hybrid semiconductor pixel detectors are used in many High Energy Physics (HEP)experiments to track charged particles trajectories. They usually feature complex readoutfunctions, both analog (amplifier, shaper, discriminator, etc.) and digital (zero suppression,sparse readout, data compression, serialization, etc.): this is possible since the sensor andthe electronics are located on separated devices. This separation is required because thesensor (a reverse-biased diode) and the electronics work at very different bias voltages: theformer requires tens or hundreds of volts, to achieve a thick depletion layer (150-300 µmfor standard sensors); the latter operate at about 2 V.

The two devices are connected by a bump bonding process: metallic bumps (In, SnPb,AgSn are commonly used materials) are deposited onto the pads of one of the devices,then it is flipped, aligned with the other chip and finally they are soldered. This processhas the advantages of being a mature technology and it is known to be radiation-hard,but it has the drawback of being expensive.1

One of the proposed alternative solutions for the ATLAS upgrade, in view of the HighLuminosity LHC, is to use a front-end chip where complex functions are implementedand a pixel matrix realized in a high-voltage, high-resistivity CMOS process, featuring apreamplifier, a discriminator and some logic integrated on each pixel [1, 2, 3, 6].

The pixel matrix and the front-end chip are AC coupled by capacitors obtained by facingpads of the two devices, which are separated by a thin dielectric material (glue): thissolution is called Capacitive Coupled Pixel Detector (CCPD) and it is expected to be lessexpensive since the bump bonding is not required [4].

In this work an HV/HR-CMOS pixel prototype, the KC53A, realized with BCD8 technol-ogy from STMicroelectronics will be studied.

1.1 Semiconductor detectors

A typical silicon detector consists of a reversely biased pn junction; the bias voltage formsa carrier depleted region with an electric field inside it, which will be the sensitive region

1The bump bonding process was about 1/3 of the module cost of the ATLAS first pixel detector.

1

2 Chapter 1

of the detector. When an ionizing particle crosses the detector, it creates electron-holepairs: the ones generated in the depleted zone migrate towards the collecting electrodes,inducing a current.

hole electron

Figure 1.1: When a charged particle crosses the detector, electron-hole pairs are created. Thesecarriers migrate under the effect of the electric field, inducing a current.

In an unbiased pn junction, electrons close to the separation plane diffuse from the n-typeside to the p-type one until equilibrium is reached (figure 1.2). This generates a potentialdifference (and consequently an electric field) between the two zones, called built-in voltageV0. In order to increase the depleted region thickness, the junction is reversely biasedwith an external voltage VB (it will be considered negative).

+ ++ ++++

- --

---

-

-

+

- +

+

+

++

++

+

+++

+ +

++

+

- --

---

-

- ----

---

---

--

+-

-holep type doping +

electronn type doping

0

Figure 1.2: Depletion of a pn junction. The depleted zone is highlighted in yellow. xp and xnare the depleted zone thickness (of the p-type and n-type semiconductor respectively).

1.1.1 The depletion region thickness

The thickness of the depleted region can be calculated, assuming a uniform dopingconcentration, starting from the Poisson equation for the voltage [13]:

d2V

dx2= −ρ(x)

ε(1.1)

where ρ(x) is the charge density in the depleted zone and ε is the dielectric constantof silicon. Being xp and xn the depleted zone thickness in the p-type and n-typesemiconductor, respectively, NA and ND the acceptors and donors numerical densitiesand e the elementary charge, the charge density is given by:

ρ(x) =

eND 0 < x < xn−eNA −xp < x < 0

Introduction 3

Furthermore, the total charge in the pn junction is 0, so the following relation holds:

NAxp = NDxn (1.2)

The boundary conditions for the Poisson equation 1.1 are:

E(x) = −dVdx

=

0 x = xn0 x = −xp

V (x) =

−VB + V0 x = xn0 x = −xp

in fact there is no electric field outside the depleted zone and the voltage is given by thesum of the built-in and the bias voltage. The solution of the Poisson equation can beeasily calculated imposing the boundary conditions and requiring the electric field at theinterface to be continuous:

V (x) =

− eND

ε (x2

2 − xnx) + eNA2ε x

2p 0 < x < xn

eNAε (x

2

2 + xpx+x2p2 ) −xp < x < 0

From equation 1.2 it is clear that the depletion region increases when NA ND (or whenNA ND): for this reason, silicon detectors usually have one side of the pn junctionmore doped that the other. Assuming NA ND the depletion region will extend in thep zone (xp xn) and its thickness will be:

d ≈ xp ≈

√2ε(−VB + V0)

eNA

Instead of the doping density NA, it is more useful to express the depletion thickness interms of the resistivity of the silicon ρp and the mobility of the carriers (µh for the holes,µe for the electrons); in the case of p-type silicon, the following relation is valid:

1

eNA= ρpµh

Using this relation, the depletion region thickness becomes:

d ≈√

2ερpµh(−VB + V0) (1.3)

1.1.2 The reverse current

A reverse-biased diode is ideally non-conducting. Actually a small current flows throughthe junction when a bias voltage is applied, producing noise and therefore fixing theminimum pulse height the sensor can detect.

The reverse current is produced mainly by minority carriers and thermally generated hole-electron pairs in the depleted region; it also depends on the surface chemistry, the presenceof contaminants and, of course, it is proportional to the area of the detector.

4 Chapter 1

The reverse current depends exponentially on the junction temperature: for a temperaturerise of 10 C, the reverse current triplicates, and so does the noise [13].

1.1.3 The junction capacitance

A pn junction is characterized by a capacitance which depends on the bias voltage. It canbe calculated considering a detector of area A with NA ND, so the depleted region isalmost completely contained in the p-type zone; the charge and the voltage in this regionare given by:

Q = eNAAd V =eNAd

2

2ε

where d is the thickness of the depleted region, and e is the electron charge. Thecapacitance is therefore given by:

C =Q

V= 2ε

A

d(1.4)

The capacitance can be expressed as a function of the bias voltage using equation 1.3 onthe previous page:

C =1√

µρ2εA2 (−VB + V0)

(1.5)

1.1.4 The Fano factor

The energy required to create an electron-hole pair is usually larger than the band gapenergy because, to conserve momentum, lattice vibrations are also excited (e.g., in siliconthis energy is Ei = 3.67 eV while the band gap energy is 1.12 eV). The number of carriersproduced by an energy deposition E is N = E/Ei. Since both electronic and latticeexcitations are involved in this process, in case of total absorption, the variance of N isgiven by σN =

√FN where F is the Fano factor (about 0.12 in silicon), so it is reduced

with respect to the poissonian variance σN =√N .

1.2 The BCD8 technology

BCD8 (Bipolar - CMOS - DMOS, version 8) is a 0.16 µm HV-CMOS technology thathas been used to build our sensor prototype. It is a combination of bipolar, CMOS andDMOS devices and allows to build low voltage and high voltage devices on the samewafer.

This technology is based on a p-epitaxial growth on a p− or p+ substrate, with theintroduction of a buried n-layer; the BCD8 technology is characterized by the main

Introduction 5

technology features of the standard CMOS platform, as Shallow Trench Isolation (STI),columnar poly-silicon, cobalt salicide and borderless contacts [8]:

This technology has been developed for the automotive industry, because it needs com-ponents that work at low voltage but must tolerate high voltage spikes (some tens ofvolts) generated by the turning on and off of inductive loads, such as electrical motors.Furthermore it is an appealing technology because it will be maintained for several years,due to the large volume production for the industrial applications.

1.3 Radiation effects

A particle detector must be radiation hard: in particular the pixel detector in ATLAS isthe innermost layer and for this reason it is exposed to a very high dose of radiations.2 Inthis section I will describe briefly the effects of radiations on integrated circuits [12]:

1.3.1 Ionization

A charged particle or a photon, interacting with the silicon lattice, can transfer energy toan electron, making it pass from valence band to conduction band and therefore generatingan electron-hole pair. Ionization is measured with LET (Linear Energy Transfer), definedby:

LET =dE

ρdx

where ρ is the density of the target material and dE/dx is the energy deposit along theparticle trajectory per unit length.

The number of generated hole-electron pairs Cnum can be estimated by integrating theLET on the particle trajectory:

LETtot =

∫dE

ρdxdx

then by dividing it by the energy required to create a hole-electron pair in that material(e.g., Ei = 3.67 eV in silicon and Ei = 17 eV in SiO2) and multiplying it by the density ofthe material:

Cnum =LETtot

Emρ

Ionization effects can be divided into two categories:

Temporary ionization effects are caused by pair generation in the semiconductor andby the resulting parasitic current.

2In HL-LHC, at an integrated luminosity of 3000 fb−1, it is expected a total dose of 1 Grad and aNIEL equivalent to 1016 1 MeV neutrons.

6 Chapter 1

Fixed ionization effects are caused by the trapping of carriers in insulators and causea shift in the device parameters.

1.3.2 Displacement

A particle, passing through a silicon lattice, transfers energy to the atoms. If the transferredenergy is greater than 20 eV, it can displace an atom, which may, in turn, displace otheratoms along its trajectory. These defects can act as traps for carriers and create energylevels within the bad gap of the semiconductor, altering its electrical properties. Since theprobability of transition between the two bands depends exponentially on the gap energy,these new energy levels increase that probability, leading to two different effects:

generation of carriers is dominant in the depletion region of pn junctions and inducesan increase of the inverse current, with a corresponding increase in the detectornoise and power dissipation;

recombination is dominant in a forward-biased pn junction and causes a reductionof the current intensity, due to charge loss. It also results in a reduction of thecollected signal generated by an ionizing particle.

Figure 1.3: Displacement effects: generation and recombination probabilities are increased dueto the creation of energy levels within the band gap.

1.3.3 Effects on integrated circuits

The damaging effects due to radiation can be divided into cumulative effects and singleevent effects: the former are related to the total dose absorbed by the integrated circuit(IC) and are due to the displacement effects and fixed ionization effects, the latter arecaused by the interaction of a single particle with the IC. Sensors properties are affected bycumulative effects only, while single particle interactions are critical for digital and controlcircuitry, which is not implemented in the test chip studied in this thesis. Cumulativeeffects can be divided into Total Ionizing Dose (TID) effects and Displacement DamageDose (DDD) effects; it is interesting to describe them on MOS transistors.

TID effects are caused by ionizing particles that create hole-electron pairs in the oxide layer

Introduction 7

of NMOS transistors.3 If the transistor is biased, an electric field is present and electronsmigrate towards the gate electrode (their mobility in SiO2 is about 20 cm2V−1s−1), whileholes move slowly (their mobility in SiO2 is 10−4÷10−11 cm2V−1s−1) towards the Si-SiO2interface, where they remain trapped for 103 ÷ 106 s: for this reason the trapped holescan be seen as a fixed positive charge which lowers the value of the threshold voltageof:

∆VOT = − e

COXNOT = − e

εOXtOXNOT

where e is the elementary charge, NOT is the density of holes trapped in the oxide, COX,εOX, tOX are the capacitance per unit area, dielectric constant and thickness of the oxidelayer respectively. This variation is negative for NMOS transistors.

gate

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + oxide

drain source

Figure 1.4: TID and DDD effects on a NMOS transistor: holes generated in the oxide are trappedat the SiO2-Si interface and electrons are trapped in the silicon due to the defects in the latticestructure.

DDD effects introduce defects in the lattice structure which can trap carriers; if these arelocated at the Si-SiO2 interface, they shift the threshold voltage of:

∆VIT = −QIT

COX

The sign of this voltage depends on the sign of the trapped carriers, therefore ∆VIT ispositive for NMOS transistors (the carriers are electrons) and negative for PMOS transis-tors (the carriers are holes). For this reason the overall threshold voltage shift is negativefor PMOS transistors and depends on the absorbed dose for NMOS transistors: the TIDeffects dominate at low dose while DDD effects dominate at high dose. Furthermorethese effects are different if the transistor is switched on or off during the irradiation. Aqualitative trend is reported in figure 1.5.

3This effect is not present in PMOS transistors because electrons don’t remain trapped at the Si-SiO2interface.

8 Chapter 1

Figure 1.5: Typical threshold voltage shift of PMOS and NMOS transistors as a function of theabsorbed dose D.

Chapter 2

The KC53A chip

Since the BCD8 technology has never been used to develop detectors for HEP, a pixeldetector prototype, the KC53A (see figure 2.1), has been developed in order to verifyif it can be exploited in this field also. This chip has been built on a higher resistivitysubstrate, with respect to the standard BCD8 one, in order to achieve a thicker depletionregion. In this chapter all the components of the KC53A will be described.

Figure 2.1: The KC53A. Only the pads and the MOM capacitors are visible, the remaining partbeing covered with dummy metals.

The KC53A chip contains twelve 250× 50 µm2 pixel sensors (the actual area of the diodeis about 240 × 40 µm2); four of them are passive sensors (in blue in figure 2.2), whichmeans that they consist of a diode with the cathode connected directly to a pad. Theremaining eight sensors (in yellow in figure 2.2) are active pixels: they contain an amplifierand a buffer, in addition to the diode. Only the buffer output is connected to a pad.

2.1 The pixels

The pixels of the KC53A consist of a diode between the p substrate of the chip (whichacts as the anode of all the sensors) and a buried n-well inside it (the cathode). The

9

10 Chapter 2

Figure 2.2: Simplified layout of the KC53A. This figure displays the active and passive sensors(in yellow and blue respectively) and the pads, with their numbering.

buried layer cannot be connected directly to the metal layers, so there are two rings ofn-type silicon, namely the n-iso and the n-well, above it: these two layers, beside allowingthe connection to the buried layer, insulate the p region above it from the substrate (seefigure 2.3).

The n-well of the passive pixels is connected directly to a pad, while in the active pixelsit is connected to the circuitry above the buried layer, which consists of:

• a PMOS transistor (which acts as a resistor) to bias the n-well;

• a capacitor to decouple the n-well from the rest of the circuitry;

• an amplifier and a buffer.

Figure 2.4 shows the complete electronic chain of an active pixel. The PMOS transistorused to bias the detector is 10 µm long and 500 nm wide and its gate is connected to adedicated biasing circuit in order to make it act as a high value resistor. The detectoris connected to the amplifier through a 500 fF Metal-Oxide-Metal (MOM) capacitor.The amplifier, in turn, is connected to a buffer and then to the output pad. For testingpurposes seven of the active pixels feature a current injection circuit realised with acurrent mirror.

2.2 The amplifier

The amplifier used for the active pixels is a single-ended amplifier in folded cascodeconfiguration (figure 2.5). This configuration has been chosen because, despite its lowergain, higher current consumption and higher noise compared to a telescopic cascode, theinput DC values can be chosen in a wider range and requires a lower supply voltage[14].

The biasing circuitry is needed to set the operating points of the transistors in the amplifier

The KC53A chip 11

Figure 2.3: A simplified cross section of the KC53A chip (not to scale). The dashed line separatesthe substrate (below) from the epitaxial layer (p-epi, above). The low voltage circuitry (PMOSand NMOS transistors) is insulated from the substrate by the n layers around it. The p stop isconnected to the substrate pad and insulates one sensor from the other.

Figure 2.4: The complete electronic chain of an active pixel.

Figure 2.5: The schematic of the amplifier.

12 Chapter 2

and consists of various current mirrors: the current depends on the dimensions of thetransistors and is set in order to have the desired voltage at the transistors gates (thePBIAS, NBIAS and NCASC nodes). The feedback part acts as a resistive feedback ofthe amplifier and is needed to set the desired input DC value, since the amplifier input iscapacitively coupled to the sensor [5].

The gain of the amplifier as a function of frequency is reported in figure 2.6: it has amaximum at about 1 MHz, and amplifies in the range 5 kHz÷ 200 MHz.

100 101 102 103 104 105 106 107 108 109−80

−60

−40

−20

0

20

40

60

Frequency (Hz)

Gain(dB)

Figure 2.6: Gain of the amplifier obtained from simulations [18].

2.3 The buffer

The buffer after the amplifier is necessary to drive the pad capacitance, so the outputsignal of the pixels can be measured with an external circuit. This buffer can driveabout 1 pF, for this reason the external circuitry connected to the output pads needs anextremely low input capacitance.

The buffer schematics is reported in figure 2.7 on the right: it consists of a source followerwith a NMOS transistor as a current source. The voltage VBIAS is set by a bias dedicatedcircuit.

The pad connected to the output of the buffer acts as a RC low-pass filter: since thevalue of the resistance is 750 Ω (see section 2.5) and the maximum value of the capacitiveload is 1 pF, the minimum cut-off frequency which can be obtained is about 212 MHz,which is outside the amplifying range of the amplifier.

The KC53A chip 13

Figure 2.7: The schematics of the injected current divider on the left and of the buffer on theright.

2.4 The current injection

To simulate the charge deposited by an ionizing particle, a current can be injected into then-well of seven of the active pixels (one of the active pixels has not the current injectioncircuit). Each injection pad is not connected directly to the n-well, but there is a circuitto reduce the injected current.

This circuit (figure 2.7, on the left) consists of a current mirror where the input NMOShas a multiplier factor of 103 (i.e., there are 103 NMOS transistors in parallel), so thecurrent drained by the output NMOS should be 103 times less: I2 = I1/103.

100 101 10210−2

10−1

100

I1 (µA)

I 2(µ

A)

Points from simulationPolinomial fitExpected behaviour

265 300 400 500 600 700 800

Vin (mV)

Figure 2.8: Current injected in an active pixel (I2) as a function of the current injected in theinput pad (I1) and as a function of the input pad voltage (Vin). The blue line shows the nominalbehaviour I2 = I1/103, the red points are from the device simulation.

This configuration has been chosen, instead of a simple capacitor, because it is expectedto allow a better control over the injected current, in fact it is possible to modify both the

14 Chapter 2

input signal amplitude and duration. This feature can also be used to extract propertiesof the amplifier if its output is not directly accessible, as in the practical applications inwhich a readout front-end chip is used.

Since the current necessary to simulate a particle crossing the detector is very small, withrespect to the normal operating conditions of BCD8 technology, it is necessary to operatethe transistors of the current mirror in the linear region; therefore the circuit does notdivide the current by 103, but by a value that depends on the injected current, which hasbeen calculated from simulations [18].

The simulated points can be fitted with a polynomial function, in order to calculate k(I1),i.e. the ratio I2/I1 as a function of I1:

I2 = (−9.4 · 10−6 µA−1)I21 + 0.012I1 + 6.3 · 10−3 µA −→

k(I1) = (−9.4 · 10−6 µA−1)I1 + 0.012 +6.3 · 10−3 µA

I1

2.5 The pads and the biasing scheme

The pads consist of a 160× 100 µm2 metallic surface on the top of the chip from which itis possible to connect the power supply and other external circuitry. Each pad (except theSUB pad) is insulated from the substrate with a structure similar to the pixels (n-well,n-iso and buried layer). The only difference is that here the n-iso layer is not a ring, butoccupies all the area of the pad (see figure 2.9).

Figure 2.9: Simplified layout of a pad. The n-well is connected to VDD, in order to form areverse-biased diode between the substrate and the n-type zone. The protection diodes and theresistor are not reported.

There are four types of them and each one is slightly different from the others:

IO pads these pads are used to inject current in the chip and read signal from it. Theyfeature two protection diodes each(one towards VDD and one towards GND) andare connected to the chip interior through a 750 Ω polysilicon resistor.

VDD and GND pads these pads are used to power the electronics on the chip; theyhave only one protection diode (VDD pad towards GND and vice versa) and noresistor.

The KC53A chip 15

SUB pad this pad is connected to the substrate, so it has no protection diode and noresistor. Furthermore, while the other pads are surrounded by an n-well, this onelays right over the substrate.

The schematics of the pads is reported in figure 2.10. The diodes and the resistor arerequired in order to protect the internal circuitry from unexpected voltage peaks, like inthe case of an electrostatic discharge (ESD).

Figure 2.10: Schematics of the four different types of pads.

The KC53A features 22 pads, reported in dark grey in figure 2.2 on page 10:

• four of them are connected to the cathodes of the passive diodes (D1 to D4);

• eight of them are connected to the outputs of the amplifiers (OUT1 to OUT8);

• seven of them are used for the current injection (IN1 to IN7, P8 have no injectioncapabilities);

• two of them are used for the power supply of the amplifiers (VDD and GND)

• one is connected to the substrate and it is used to deplete the pn junction betweenthe buried layer and the substrate (SUB).

The supply voltage inside the chip is delivered to the active pixels and to the injectioncircuitry with two metallic rings (one for VDD and one for GND, directly connected tothe respective pad), which enclose all the detectors. Every amplifier is connected directlyto the rings.

2.6 KC53AA and KC53AB

The KC53A has been produced twice (the KC53AA were delivered in July 2015, whilethe KC53AB in mid-January 2016) because of layout errors which have been found in the

16 Chapter 2

metal layers of the first version of the chip. The most important errors in the KC53AAwere:

• D3, VDD and GND nodes inside the chip were shorted;

• VDD pad was not connected to the VDD ring inside the chip;

• D4 pad was not connected to its n-well;

• some shorts and open circuits in the circuitry of the active pixels.

All these layout problems have been corrected in the second version of the chip, theKC53AB. However it has been possible to take advantage of some of the errors to makemeasurements impossible to perform on a perfectly working chip.

In particular it has been possible to measure the capacitance of a single pad, in order tocorrect the CV measurements of the passive pixels (see section 3.2).

The measurements described in the following chapters have been performed on theKC53AB, unless noted otherwise.

Table 2.1: List of the pads functions.

Pad number Function

1 GND

2 IN1

3 IN2

4 VDD

5 D2

6 OUT2

7 OUT1

8 IN5

9 OUT5

10 OUT4

11 D4

Pad number Function

12 OUT3

13 IN4

14 IN3

15 SUB

16 D3

17 OUT6

18 OUT8

19 OUT7

20 IN7

21 IN6

22 D1

Chapter 3

Tests on KC53A passive pixels

Measurements on passive pixels allow to characterise the behaviour of the sensor alone,without taking into account the performance of the circuitry of the active pixels. Thereverse current and the capacitance of the four passive diodes have been measured. Fromthe capacitance measurements it has been possible to check the depletion depth of thesensors. Moreover some tests with radioactive sources and an X-ray tube have beenperformed.

3.1 Current vs. voltage measurements

Current vs. voltage (IV ) measurements of passive pixels are necessary to estimate thereverse current flowing into the pixel sensors when no radiation hits the detector. Thesemeasurement can only be performed on the passive diodes, since they are the only oneswith the cathode connected directly to a pad.

3.1.1 Instrumentation

To reduce parasitic currents as much as possible the chip has been glued with non-conductive glue on a support and placed inside a probe station (figure 3.1). The probeswere used to contact the pads of the chip and consist of a metallic needle mounted on anarm and connected to a coaxial cable (see figure 3.2).

The current to be measured is very small (< 3 pA), so it has been necessary to usea Keithley 6517A electrometer, which is able to measure small currents with a 0.1 pAprecision. This instrument features a voltage generator, covering the range from −1000 Vto +1000 V, and a precision ammeter: these need to be connected inside the instrumentsetting the option METER CONNECT to ON. Furthermore the chip had to be kept in adark environment during the measurement to avoid the parasitic current generated bythe light photons hitting on it.

It has not been possible to guarantee a constant chip temperature nor to measure it andthis can slightly affect the current measurements (the chip was heated by the lamp of

17

18 Chapter 3

Figure 3.1: The probe station used for IV and CV measurements.

Figure 3.2: Detail of the probes contacting the pads of the KC53A.

Tests on KC53A passive pixels 19

the microscope used to place the probes); in order to minimize this effect, before eachmeasurement the chip was kept unbiased some minutes in the dark, to cool it down.

3.1.2 Protection diodes

The KC53A features some protection diodes inside it, which have to be taken into accountfor an IV measurement, since they may contribute to the reverse current. The schematicof the diodes inside the chip is reported in figure 3.4 on page 21:

black the sensor diode;

red protection diodes of the D pad;

green protection diodes of the GND and VDD pads (two diodes in parallel);

yellow protection diodes of the remaining 18 pads (so they are 18 couples of diodes inparallel);

blue the anode of this diode is the substrate, the cathode are the n-wells of the pads,which are, in turn, connected to VDD.

Figure 3.3: Connection diagram for IV measurements (left) and CV measurements (right).

3.1.3 Connections and measurement

The connection diagram is reported in figure 3.3 on the left. It is necessary to connectthe ground of the instrument to the GND and VDD pads in order to measure only thecurrent flowing through the sensors diode.

In fact, in this configuration VDD, GND and D pads are at the same voltage, so:

• no current flows through the protection diodes (red) of the D pad (their anode andcathode are at the same voltage);

• the current which flows through the blue, green and yellow diodes is not measured;

• the only measured current is the one which flows through the detector (black diode).

20 Chapter 3

The results of these measurements are reported in figure 3.5. The values of the reverse cur-rent are a few orders of magnitude smaller than the signal expected for a Minimum IonizingParticle (MIP) (see section 3.2.3), so its contribution to the noise is negligible.

The junction breakdown voltage has been also measured: all the passive diodes have it atabout −70 V, as expected from BCD8 technology.

3.2 Capacitance vs. voltage measurements

Capacitance vs. voltage (CV ) measurements of passive pixels are necessary to estimatethe capacitance of the sensors in order to validate the simulations; furthermore they canbe used to evaluate the depletion depth. These measurements, as the IV ones, can beperformed on the passive diodes only, since they are the only ones with the cathodeconnected directly to a pad.

3.2.1 Instrumentation and measurement

These measurements have been performed in the same conditions (probe station, darknessand ground connections) as those of the IV measurements. The instrument used is an HP4280A CV meter. This instrument allows to measure the capacitance at a fixed voltage(ranging from −100 to +100 V) with a precision of about 1 fF; a 1 MHz, 10 mV RMStest signal is used to measure the capacitance. The connection diagram is reported infigure 3.3 on the right.

Before performing any measurement it is necessary to calibrate the instrument: thecalibration is executed with all the cables connected and the probes slightly lifted, inorder to take into account every parasitic capacitance. This procedure must be repeatedevery time a probe is moved, because varying the relative position of the probes modifiesthe capacitance of the setup.

After each calibration the probes are lowered on the pads and the measurement isperformed. The results are reported in figure 3.6. D1 and D3 appear to have a slightlydifferent behaviour with respect to D2 and D4.

The KC53AA design has some layout mistakes, described in section 2.6; in particular theD4 and VDD pads are unconnected and this has allowed to measure the pad capacitance.The procedure is the same used for the working diodes, the only difference is that it isperformed on the D4 and VDD pads of the KC53AA. The results are reported in figure3.7.

Although the pads have a bigger area with respect to pixels, their measured capacitancevalue is smaller: this is due to the presence of the buried layer connected to groundbetween the pad and the substrate. They are therefore equivalent to two capacitors inseries, so the total capacitance is smaller.


Figure 3.4: Schematic of the diodes inside the chip.

−65 −60 −55 −50 −45 −40 −35 −30 −25 −20 −15 −10 −5 0−3

−2.5

−2

−1.5

−1

−0.5

0

VB (V)

I(pA)

D1D2D3D4

Figure 3.5: Voltage-current characteristic of the four passive diodes of the KC53A chip.

22 Chapter 3

−65 −60 −55 −50 −45 −40 −35 −30 −25 −20 −15 −10 −5 00

0.2

0.4

0.6

0.8

1

1.2

1.4

VB (V)

C(pF)

D1D2D3D4

Figure 3.6: Voltage-capacitance characteristic of the four passive diodes of the KC53A chip.

−65 −60 −55 −50 −45 −40 −35 −30 −25 −20 −15 −10 −5 00

5 · 10−2

0.1

0.15

0.2

0.25

0.3

0.35

0.4

VB (V)

C(pF)

D4 padVDD pad

fit

Figure 3.7: Voltage-capacitance characteristic of the D4 and VDD pads of the KC53AA chipand the fitted curves.


3.2.2 Data analysis

After subtracting the D4 pad capacitance values from the data of figure 3.6, they havebeen fitted with the following curve (see equation 1.5 on page 4):

C(VB) = CP +1√

k(−VB + V0)with k =

µρ

2εA2

where CP is a parasitic capacitance inside the chip, considered independent of the voltage,V0 is the built-in voltage of the diode, µ is the holes mobility, ρ is the substrate resistivity,ε is the silicon dielectric constant and A is the area of a pixel.

The expected value of k can be computed using the following values:

• ε = 1 pF/cm [7],

• ρ = (125± 25) Ω cm (from the specifications of BCD8 technology),

• µ = 450 cm2 V−1 s−1 [7],

• A = 240× 40 µm2;

and it turns out to be:

k = (3.05± 0.6) V−1pF−2

The fit has been performed with a ROOT macro (see section B.1), using CP , k and V0 asfree parameters. The results of the fit are reported in table 3.1, along with the estimatedvalue of the capacitance at VB = −50 V; the value χ2 = χ2/NDOF is also reported.

Table 3.1: Diode capacitance fit results.

χ2 CP k V0 C − CP(pF) (V−1 pF−2) (V) (pF)

D1 5.78 0.161± 0.001 3.26± 0.05 0.414± 0.007 0.079± 0.001

D2 11.4 0.125± 0.001 2.82± 0.06 0.46± 0.01 0.087± 0.001

D3 7.89 0.157± 0.001 3.22± 0.06 0.415± 0.008 0.081± 0.001

D4 11.8 0.126± 0.001 2.90± 0.06 0.45± 0.01 0.085± 0.001

The values of χ2 are greater than 1, probably because the curve used for the fit is atoo coarse approximation and doesn’t take into account voltage-dependent parasiticcapacitances. For this reason the errors on the parameters extracted from the fit havebeen multiplied by

√χ2 [7].

The values of k obtained from the fit are in good agreement with the expected value:this means that the characteristics of the substrate (ε, µ, ρ) are close to expectations.The value of the capacitance of the diodes are not in good agreement with simulations(the expected value is 500 fF [18]); this is probably related to the wrong value of thesensor capacitance in the development kit provided by STMicroelectronics, which is based

24 Chapter 3

on a lower resistivity substrate, so the most reliable values are the ones obtained frommeasurements.

The pads capacitance data have been fitted with the same function used for the pixels:the results of the fit are reported in table 3.2 and in figure 3.7.

In this case k is a parameter of difficult interpretation, since it is no longer equal to µρ2εA2

due to the presence of the buried layer between the pad and the substrate.

Table 3.2: Pad capacitance fit results.

PAD χ2 CP k V0(pF) (V−1 pF−2) (V)

D4 0.79 0.1217± 0.0003 50.7± 0.8 0.358± 0.006

VDD 1.12 0.1390± 0.0003 45.7± 0.7 0.381± 0.006

3.2.3 Estimation of the depletion depth and of a MIP signal

From the capacitance value it is possible to evaluate the depletion depth d using equa-tion 1.4 on page 4:

d = 2εA

C= (23± 1) µm (VB = −50 V)

The expected depletion depth at VB = −50 V can be calculated also with equation 1.3on page 3:

d ≈√

2ερµ(−VB + V0) = 23.8 µm

so the two results are in good agreement.

From the depletion depth it is possible to estimate the expected signal of a MIP: itsmean energy loss in silicon is about 0.3876 keV µm−1 [7] which corresponds to a chargegeneration of Q ≈ 2500 electrons in a 23 µm layer. The collection time can be estimatedfrom the holes speed (v = µE = µVB/d):

tcoll =d

v=

d2

µVB≈ 0.24 ns

So the current intensity would be:

I =Q

tcoll≈ 1.7 µA

Therefore, the expected signal of a MIP would be a 1.7 µA current pulse 0.24 ns long.


−65 −60 −55 −50 −45 −40 −35 −30 −25 −20 −15 −10 −5 00

0.2

0.4

0.6

0.8

1

1.2

1.4

VB (V)

C(pF)

D1fit

Figure 3.8: Plot of the voltage-capacitance characteristic of D1 after subtracting the padcapacitance and the curve obtained from the fit.

−65 −60 −55 −50 −45 −40 −35 −30 −25 −20 −15 −10 −5 00

0.2

0.4

0.6

0.8

1

1.2

1.4

VB (V)

C(pF)

D2fit


26 Chapter 3

−65 −60 −55 −50 −45 −40 −35 −30 −25 −20 −15 −10 −5 00

0.2

0.4

0.6

0.8

1

1.2

1.4

VB (V)

C(pF)

D3fit


−65 −60 −55 −50 −45 −40 −35 −30 −25 −20 −15 −10 −5 00

0.2

0.4

0.6

0.8

1

1.2

1.4

VB (V)

C(pF)

D4fit



3.3 Tests with radioactive sources

Some tests with radioactive sources have been performed at Politecnico di Milano; inparticular different spectra have been taken.

The radioactive sources used for the spectra measurements are:

• a 1 mCi 241Am source;

• a 0.04 mCi 55Fe source;

Figure 3.12: The passive pixels test board. The filtering capacitors and resistors are visible. Thechip is under the white cover, which protects the chip and can hold the radioactive sources. Thepreamplifiers sockets are placed on the bottom side of the board.

3.3.1 The passive pixels test board

To perform the measurements with radioactive sources I designed a PCB to hold the chipand four preamplifiers, one for each passive pixel; the VDD and GND pads of the chip areconnected to ground, in order to switch off the protection diodes. Furthermore this boardfeatures filters on the power supply of the preamplifiers and on the bias voltage.

The RC filter connected to the bias voltage features a time constant of τ = 1 MΩ ·10 µF =10 s, in order to make the voltage raise slowly and prevent damages to the chip; furthermore,there is the possibility to add a high-value resistor after the filter to measure the leakage

28 Chapter 3

current of the pixels. The preamplifiers sockets are placed on the bottom side of theboard, in order to keep the connections between the chip and the amplifiers as short aspossible.

I also designed a support to hold the board, to guarantee enough clearance for thepreamplifiers and a cover to protect the chip and hold a radioactive source at the sametime; these two elements have been 3D-printed.

The preamplifier chosen for this setup is charge sensitive preamplifiers with a 0.47 pFfeedback capacitor, followed by a voltage buffer with factor 2 multiplication. Its outputhas been connected to a pseudo-Gaussian shaping amplifier, providing an additional 410gain factor, and then to a multichannel analyser (MCA 8000A).

In order to minimize the noise, it has been necessary to shield the board: in this way wemanaged to achieve about 35 mV RMS of noise at the shaper output, which correspondsto 57 channels of the multichannel analyser. This value might have slightly changed whenthe setup has been modified (e.g. when the radioactive source was changed or the setupmoved) due to a non-perfect shielding of the board.

3.3.2 Spectrum of 241Am

Americium-241 decays mainly, via alpha decay, in Neptunium-237.

241Am −−→ 237Np + α+ γ

Most of the decays populate an excited state of 237Np, which can emit 59.5 keV or 26.3keV γ-rays [11] and these produce two peaks in the photon energy spectrum. There areadditional peaks at 13.9, 17.7 and 20.7 keV due to L shell X-rays [9]. Other peaks cannotbe distinguished with our setup; the α particle is absorbed in the source sealing material,so it produces no signal.

To obtain the spectrum, the americium source has been placed on the dedicated supporton the PCB, so it was about 1 cm far from the detector, in order to maximize the countingrate. The spectrum measurement has been performed with a bias voltage of −50 V, andit lasted 9000 s. The shaping time of the amplifier has been set to 1 µs.

The obtained spectrum is displayed in figure 3.13 on the next page. The peaks have beenfitted with a Gaussian function:

f(x) = Ce−(x−µ)2

2σ2 (3.1)

The fit has been performed with a ROOT macro (see section B.2.1), using C, µ and σ asfree parameters. The results of the fit are reported in table 3.3. The χ2 value is alwayssmaller than 1, so the Gaussian curve is a good approximation for the peaks shape. Thestandard deviation of the fitted curves ranges from 45 to 76 channels (which correspondsto 27÷ 46 mV), in good agreement with the noise contribution calculated in the previoussection.


0 500 1000 1500 2000 2500 3000 3500 4000 4500100

101

102

103

13.917.7

20.7

26.359.5

Channel

Cou

nts

Figure 3.13: Spectrum of 241Am. The fitted Gaussian curves are reported in red, along with theenergy of each peak (in keV).

500 1000 1500 2000 2500 3000 3500 4000 45000

20

40

60

Channel

Ene

rgy(keV

)

Figure 3.14: Calibration function obtained from the 241Am data.

30 Chapter 3

Table 3.3: 241Am fit results.

Peak χ2 C µ σ(keV) (Counts) (Channels) (Channels)

13.9 0.006 223± 27 979± 14 66± 17

17.7 0.012 162± 18 1239± 9 61± 9

20.7 0.045 29± 3 1476± 26 76± 27

26.3 0.13 8± 1 1876± 13 67± 27

59.5 0.2 5.4± 0.7 4241± 6 45± 7

A channel-energy calibration has been performed using the fit results. The calibration isreported in figure 3.14; the resulting curve, obtained with the ROOT macro reported insection B.2.2, is:

Energy (keV) = (139.6± 0.6) · 10−4 · Channels + (0.27± 0.17) χ2 = 0.52 (3.2)

3.3.3 Spectrum of 55Fe

Iron-55 decays by electronic capture in Manganese-55.

55Fe + e− −−→ 55Mn

This decay produces K shell X-rays: their most probable energy value is 5.9 keV [9].

The source has been placed on the support in this case too. The spectrum measurementhas been performed with a bias voltage of −50 V and a shaping time of 1 µs. Thismeasurement lasted 3450 s, since the absorption coefficient of lower energy photons isgreater. This effect can be better understood if one looks at the X-rays absorptioncoefficient plot in figure 3.15: 5.9 keV photons are absorbed about 400 times more withrespect to 59.5 keV photons.

The obtained spectrum is reported in figure 3.16. As for the spectrum of 241Am, thepeak has been fitted with a Gaussian function (equation 3.1) using a ROOT macro (seesection B.3). Its mean value is (406 ± 9) channels, which corresponds to (5.93 ± 0.12)keV, using the calibration of equation 3.2, which is in good agreement with the expectedvalue. In this case the standard deviation of the fitted Gaussian is (51± 6) channels, ingood agreement with the previous noise assessment. The χ2 is 0.003, so the Gaussiancurve is a good approximation of the peak shape.

This measurement is particularly interesting because the energy deposit of a 5.9 keVphoton is comparable with the most probable energy deposit of a minimum ionizingparticle in 20 µm [7], so this demonstrates that the sensors built in this technology areable to detect MIPs.


0 10 20 30 40 50 60

100

101

102

103

Photon energy (keV)

Absorbp

tion

coeffi

cient(c

m−1)

Figure 3.15: Absorption coefficient for X-rays in silicon as a function of the photon energy [10].

100 150 200 250 300 350 400 450 500 550 600 650 700 750 800100

101

102

103 5.9

Channel

Cou

nts

Figure 3.16: Spectrum of 55Fe. The fitted Gaussian is reported in red, along with the energy ofthe peak (in keV).

32 Chapter 3

Table 3.4: Results of the fit.

τ χ2 µ σ σ(µs) (keV) (keV) (e)

0.25 0.006 17.8± 0.1 1.0± 0.2 304± 57

0.5 0.006 18.2± 0.1 1.0± 0.2 284± 53

1 0.006 17.7± 0.1 1.0± 0.2 296± 53

2 0.005 17.2± 0.2 1.1± 0.3 296± 83

3 0.005 17.1± 0.3 1.2± 0.4 335± 100

3.4 Measurements with the X-ray tube

Some spectra measurements have been performed with an X-ray tube produced by X-rayOptical Systems (XOS), which features a molybdenum anode, a maximum voltage of50 kV and a maximum current of 1 mA. We set the voltage to the maximum and thecurrent to 20 µA in order to avoid the pile-up (the rate of photons emitted by the tube isproportional to the current).

In this configuration five spectra at different shaping times have been taken, in order toevaluate the Equivalent Noise Charge (ENC) as a function of the shaping time τ . Thespectra are reported in figures 3.18, 3.19, 3.20, 3.21 and 3.22.

In these plots two peaks are clearly visible. The lower energy one is due to the K lines ofcopper at 5.9 keV (this metal is present on the shielding and on the board), the higherenergy one is due to the K lines of molybdenum at 17.5 keV (the anode of the X-ray tubeis made of molybdenum) [9].

These two fluorescence peaks rise over a continuum distribution from the bremsstrahlunggenerated by the tube. On the low energy side of each line there is a shoulder due toevents in which the energy deposited is not fully contained within the pixel (the sharingeffect): this effect is not negligible because the active region is quite small (40× 240× 23µm3), with a large perimeter to area ratio. In addition, hole-electron pairs, producedoutside the active region, may be collected by diffusion.

To model these effects, the 17.5 keV peak has been fitted with the convolution of aGaussian with the combination of a Heaviside step function (for the “plateau” beforethe peak) and a Dirac delta (for the peak) using the ROOT macro reported in sectionB.4:

f(x) = C1 exp

(−(x− µ)2

2σ2

)+ C2

[1− erf

(x− µ√

2σ

)]The results of the fit have been converted in keV with the calibration obtained from the241Am spectrum; their values are reported in table 3.4.

The ENC have been calculated subtracting the Fano contribution from the values of σ(in electrons) obtained from the fit:


ENC =

√σ2 − F µ

Ei

where F = 0.12 is the Fano factor and Ei = 3.6 eV is the energy needed to createa hole-electron pair in silicon (so µ/Ei is the number of the generated hole-electronpairs).

The resulting values have been plotted as a function of the shaping time τ . The resultsare reported in figure 3.17: it is clear that the ENC is minimum at τ = 1 µs.

The calibration obtained from the americium spectrum with τ = 1 µs is only approximatelyvalid for the spectra obtained with different shaping times, because the gain of theamplifier changes slightly at different values of τ . However this can be considered agood approximation since the energy of the peak varies less than 5% with respect to itsexpected value.

0.2 0.5 1 2 3150

200

300

400

τ (µs)

ENC

(e)

Figure 3.17: Plot of the calculated ENC as a function of the shaping time.

34 Chapter 3

500 1000 1500 2000 2500 3000100

101

102

103

104

17.5

Channel

Cou

nts

Figure 3.18: Spectrum of the X-ray tube obtained with a 250 ns shaping time. The fittedfunction is reported in red, along with the energy of the peak (in keV).

500 1000 1500 2000 2500 3000100

101

102

103

104

17.5

Channel

Cou

nts

Figure 3.19: Spectrum of the X-ray tube obtained with a 500 ns shaping time. The fittedfunction is reported in red, along with the energy of the peak (in keV).


500 1000 1500 2000 2500 3000100

101

102

103

104

17.5

Channel

Cou

nts

Figure 3.20: Spectrum of the X-ray tube obtained with a 1 µs shaping time. The fitted functionis reported in red, along with the energy of the peak (in keV).

500 1000 1500 2000 2500 3000100

101

102

103

104

17.5

Channel

Cou

nts


36 Chapter 3

500 1000 1500 2000 2500 3000100

101

102

103

104

17.5

Channel

Cou

nts


Chapter 4

Tests on KC53A active pixels

After having verified the proper functionality of the passive pixels, it is necessary totest the active pixels to evaluate the performances of their electronic chain. The currentabsorption of the circuitry has been measured and compared with simulations; then theresponse of a pixel to current injection and the uniformity of the behaviour of all theactive pixels in a chip have been tested. For the latter measurements a dedicated PCBhas been used.

4.1 Current consumption measurement

The measurement of the current consumption is the first test performed on the activepart of the chip. It has been performed in a dark probe station with a Keithley 6517Aelectrometer, connecting 1.8 V to the VDD pad, 0 V to the GND pad and measuringthe current flowing through the chip. This current intensity has been measured on 20different chips and its mean value is 0.28 mA, its standard deviation is 0.01 mA. Thisvalue is in good agreement with the one obtained from simulations (0.272 mA, 0.034 mAfor each active pixel).

0.25 0.26 0.27 0.28 0.29 0.3 0.310

2

4

6

I (mA)

Figure 4.1: Distribution of the current consumption.

37

38 Chapter 4

The main source of current consumption is the circuitry of the active pixels: each amplifierrequires 9 µA to work, the biasing circuitry and the feedback a total of 25 µA.

4.2 The test board

To easily perform measurements on the KC53A chip I designed a PCB with an injectioncircuit for the active pixels input and a buffer for each output. Furthermore it features avoltage regulator to power the chip.

Figure 4.2: First version of the injec-tion circuit.

The board was designed to inject a current pulse inthe chip with a PNP transistor (see figure 4.2): wetested this configuration by measuring the voltageon an input pad of the chip and injecting a currentpulse. The result is reported in figure 4.4.

A negative spike is present, due to the capacitivetransmission of the falling voltage edge on the baseof the transistor, then the current injection starts.When the PNP transistor is switched off, the voltageon the input pad decreases very slowly: this is dueto the discharging of the NMOS gate of the currentmirror (see section 2.4) through its drain, since the

PNP transistor is off.

For these reasons we changed the configuration of the circuit using just a resistor (figure4.3). Now the negative spike and the long tail are not present because the gate of thecurrent mirror can discharge through the resistor, so it requires much less time (see figure4.5).

Figure 4.3: Final version of the injection circuit.

The test board contains 8 buffers too, one for each output. Unfortunately the noiseintroduced by the buffer and the board itself is too high, so they cannot be used to makemeasurements on the chip: it is necessary to use an active probe.

In the end the board can be used to easily power the chip (both 1.8 V for the CMOSelectronics and −50 V for the substrate) and inject a signal; to read the outputs it isnecessary to use an external probe. This board has been used to perform the measurementsdescribed in this chapter.

Tests on KC53A active pixels 39

Figure 4.4: Current injection through a PNP. The pulse generated by the function generator isreported in blue; the signal measured on an injection pad of the KC53A is reported in red.

Figure 4.5: Current injection through a 1 kΩ resistor. The pulse generated by the functiongenerator is reported in blue; the signal measured on an injection pad of the KC53A is reportedin red.

40 Chapter 4

Figure 4.6: The active pixels test board; the chip is placed in the center of the board ad isconnected to the power supply (top-left), the buffers, the injection transistor (around it) and tothe high-voltage power supply (top-right). The jumpers on the left are used to select the pixel tobe injected. There are two holes to place a 3D-printed protection (not shown). P6 and P8 arealways connected to an output, two of the remaining active pixels can be selected with a jumper(bottom-center).

4.3 Output DC and noise levels

The measurement of the output DC and noise levels of the active pixels is necessary tocheck if each amplifier and buffer-shaper are working as expected and if the noise is lowenough to perform measurements with radioactive sources. This measurement has beenperformed contacting each output pad with a 12C Picobrobe (by GGB Industries Inc.)connected to an oscilloscope, powering the chip and leaving any other pad floating.

It is necessary to use an active probe because the capacitive impedance connected tothe output of the chip must be smaller than 1 pF, otherwise the fast amplifier signalwould be slowed down too much by the probe load. The active probe we used features aninput capacitance of 100 fF and a bandwidth of more than 1 GHz. The results of themeasurements are reported in table 4.1.

The DC value is in good agreement with the expectations. Unfortunately the noise is toohigh to be able to perform any measurement with radioactive sources or beams, in fact a10 mV signal corresponds to a deposited charge of about 10 ke (see figure 4.13), which, inturn, is equivalent to a 36 keV energy deposit, while the most probable energy deposit ofa minimum ionizing particle is about 5-6 keV.

The noise spectrum of the active pixels signal has been also measured in this configuration.The results are reported in figure 4.7, along with the noise spectrum obtained with theprobe unconnected from the oscilloscope; the simulated noise spectrum is reported in4.8.


Figure 4.7: The measured noise spectrum of the eight active pixels. The spectrum obtained withthe probe unconnected from the oscilloscope is also reported (NC).

104 105 106 107 108 109

10−14

10−12

10−10

10−8

10−6

10−4

10−2

Frequency (Hz)

Noise( µV

/√H

z)

Figure 4.8: Simulated noise spectrum of the amplifier [18].

42 Chapter 4

Table 4.1: DC and noise values.

DC RMS PK-PK(mV) (mV) (mV)

OUT1 847 8.5 102

OUT2 795 8.6 83

OUT3 840 8.9 91

OUT4 855 12.1 116

OUT5 857 10.9 104

OUT6 859 8.8 86

OUT7 878 10.0 97

OUT8 883 8.4 86

The measured noise spectrum is about one order of magnitude greater than the simulatedone and features a wider bandwidth (the former starts to decrease after about 10 MHz,the latter after about 1 MHz). In the measured spectrum of some of the pixels a spike atabout 180 kHz is present: the explanation of this behaviour is unknown. The differencesbetween the two spectra can be related to the simulation with an incorrect value of thepixel capacitance (see section 3.2.2).

4.4 Measurements with current injection

Another test to verify the proper functionality of the active pixels is to inject a currentpulse through the input pad and measure the output signal of the amplifier; the activepixel chosen to perform this measurements is P5. To perform this measurement a pulsegenerator has been connected to the input connector of the test board, and then to anoscilloscope (with a 50 Ω termination) to monitor the injected pulses.

The output pads have been contacted with an active probe connected to the oscilloscopeand their signal has been averaged in order to reduce the noise. An example of themeasured signals is reported in figure 4.9.

Three measurements have been performed in this configuration:

• in two of them the injected current was kept fixed (3 µA and 5 µA) and the durationof the pulse was varied;

• in the last one, the duration of the pulse was kept fixed (100 ns) and the injectedcurrent was varied.

The amplitude of the averaged output pulse was measured; the results are reported,respectively, in figures 4.10 and 4.11 on page 45.

From the duration of the injected pulse t and its amplitude I1 it is possible to calculate


Figure 4.9: From the top: the shape of the injected pulse, the averaged output signal and theoutput signal.

the injected charge:

Q = k(I1)I1t (4.1)

where k(I1) is the dividing factor of the injection current mirror inside the chip whichdepends on the injected current (see section 2.4). The output pulse amplitude has beentherefore plotted as a function of the charge injected in the n-well (figures 4.12 and 4.13on page 46).

The relation between the pulse amplitude and the injected charge appears to be linearuntil about 40 ke in the tests with a fixed pulse amplitude and until about 60 ke in thetests with fixed pulse duration. This difference may be due to the inability of the circuitto amplify long signals: if the input signal is too long, the rise time becomes smaller withrespect to it, so part of the injected charge signal is not amplified (see figure 4.16 onpage 48); in any case the amplifier appears to have a linear behaviour on a wide range (40ke corresponds to a 144 keV energy loss, to be compared with the most probable energyloss of a MIP, which is about 5-6 keV).

The measured output pulse shape is not in good agreement with the simulations. Inparticular the simulated rise time and fall time of the pulse are greater than the measuredones: the rise and fall time with a 20 nA, 200 ns injected pulse are about 100 ns each(see figure 4.9), the simulated values, reported in figure 4.15 on page 47, are about 200ns (rise) and 800 ns (fall); furthermore the pulse shapes are different. The cause of thisbehaviour is unknown, but it will be studied in order to improve future versions of thechip.

44 Chapter 4

4.5 Comparison of the active pixels response

The current injection test has been performed on the remaining pixels also, in order toverify if they have the same behaviour: this measurement have been performed with afixed pulse amplitude, changing its duration, as explained in the previous section. Thepulse duration has been converted to injected charge using equation 4.1; this test hasbeen performed on three different chips and the results are reported in figures 4.17 onpage 48, 4.18 and 4.19 on page 49.

There is a huge variability among the behaviour of different pixels on the same chip (theresponse to the same injected charge can be different by one order of magnitude) and alsoamong the same pixel in different chips (e.g., one can notice that the maximum outputsignal of P4 is 215 mV in the first chip, 130 mV in the second chip and 50 mV in the thirdchip): this can be explained with a high variability of the parameters of the componentsinside the chip related to the building process itself.

Furthermore, the gain of all the pixels is smaller than the one obtained from simulations:this is probably related to the simulation with an incorrect value of the pixel capacitance.It may be also related to a wrong simulation of the current mirror, since it is not possibleto verify the actual injected current.


0 50 100 150 200 250 300 350 400 4500

20

40

60

80

100

120

140

t (ns)

Amplitud

e(m

V)

I1 = 3 µAI1 = 5 µA

Figure 4.10: Output signal amplitude as a function of the injected pulse duration (fixed current).

0 5 10 15 20 25 30 35 40 45 50 55 60 65 700

50

100

150

200

250

300

350

400

I1 (µA)

Amplitud

e(m

V)

t = 100 ns

Figure 4.11: Output signal amplitude as a function of the injected current (fixed duration).

46 Chapter 4

0 50 100 150 200 250 300 350 400 450 5000

50

100

150

200

250

300

350

400

Q (ke)

Amplitud

e(m

V)

I1 = 3 µAI1 = 5 µAt = 100 ns

Figure 4.12: Output signal amplitude as a function of the injected charge.

0 10 20 30 40 50 60 70 80 90 1000

20

40

60

80

100

120

140

Q (ke)

Amplitud

e(m

V)

I1 = 3 µAI1 = 5 µAt = 100 ns

Figure 4.13: Output signal amplitude as a function of the injected charge.


0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 21.34

1.35

1.36

Time (µs)

Amplitud

e(V

)

Figure 4.14: Simulated amplifier output corresponding to a 10 nA, 10 ns injected pulse [18].

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 21.3

1.35

1.4

1.45

1.5

1.55

1.6

Time (µs)

Amplitud

e(V

)

Figure 4.15: Simulated amplifier output corresponding to a 20 nA, 200 ns injected pulse [18].

48 Chapter 4

0 50 100 150 200 250 300 3500

50

100

150

200

t (ns)

t ris

e(ns)

P1P2P3P4P5P6P7

Figure 4.16: The rise time of the output signal of different channels (trise) as a function of theinput signal duration t. The input current is 3 µA. The line trise = t is reported as a comparison.

0 10 20 30 40 50 60 70 80 90 100 1100

50

100

150

200

250

300

Q (ke)

Amplitud

e(m

V)

P1P2P3P4P5P6P7Simulation

Figure 4.17: Output signal amplitude as a function of the injected charge measured on the activepixels (chip 1). The expected signal amplitude, obtained from simulations, is also reported.


0 10 20 30 40 50 60 70 80 90 100 1100

50

100

150

200

250

300

Q (ke)

Amplitud

e(m

V)



0 10 20 30 40 50 60 70 80 90 100 1100

50

100

150

200

250

300

Q (ke)

Amplitud

e(m

V)



Chapter 5

Preparation for irradiation tests

The irradiation tests are necessary to evaluate the radiation hardness of the KC53A. Thegoal would be to reach a dose of 1 Grad, i.e. the dose expected for HL-LHC; at the timeof writing is has not been possible to perform any irradiation test on the chip, so in thischapter I will describe the preparation of the planned tests only.

However, the radiation hardness of BCD8 technology has already been tested on anotherBCD8 test chip, the KC01. This chip contains an array of PMOS and NMOS transistorsof various dimensions. The results of the tests are summarized in this chapter.

5.1 Planned tests on KC53A

An irradiation with a proton beam at Laboratori Nazionali del Sud (LNS) in Catania,Italy has been planned. Our purpose is to irradiate the KC53A with a dose of 100 Mradand then to perform the characterisation of the passive pixels again, to verify the radiationtolerance of the chip.

To characterise the KC53A before, after and during the irradiation, the PCB designed forthe test with radioactive sources (see section 3.3.1), with some modifications, will be used.In particular it is necessary to short the input and the output of the preamplifiers socketsand not to mount the filters on the different power supplies, in order to keep parasiticseffects as small as possible.

5.2 The KC01 chip

The KC01 chip contains four rows of 1.8 V transistors of different types, layouts anddimensions:

• the first row contains six linear PMOS transistors;

• the second row contains six linear NMOS transistors

• the third row contains five PMOS Enclosed Layout Transistors (ELT);

51

52 Chapter 5

• the fourth row contains five NMOS ELTs.

The transistors in each row have the gate and the body in common.

Every transistor is insulated from the substrate: the PMOS transistors are built on an-well and their gates are connected to a p+ region in the n-well, the Diode ProtectionCathode (DPC) which is needed to protect the gates oxide during the fabrication. TheNMOS transistors are built on a p-well surrounded by a n-ring, which is connected to apad, and their gates are connected to a n+ region in the substrate with the same purposeof the DPC.

The insulation for both types of transistors is achieved by biasing the substrate at alower voltage with respect to the n structures around them (it can be biased until about−50 V).

Figure 5.1: Top view of a linear transistor (right) and a ELT (left).

5.3 Tests on KC01

The KC01 has been irradiated with a 62 MeV proton beam at LNS up to a 32 Mrad dose.The transistors have been characterized before and after the irradiation: in particular thedrain current IDS as a function of the gate-source voltage VGS has been measured.

The data have been fitted with the following curve:

IDS =

0 VGS < VthI0 + gm(VGS − Vth)2 VGS > Vth

in order to extract Vth and gm of each transistor. The results of the fit of a linear NMOSis reported in figure 5.2 [17].

The obtained results are very preliminary, since only one chip has been tested, but it hasbeen possible to notice that Vth increased of about 15% for most of the linear transistorsand of more than 25% for most of the ELTs. The transconductance, instead, varied

Preparation for irradiation tests 53

Figure 5.2: Fit of the IDS vs. VGS for an NMOS transistor [17].

less than 5% for most transistors. From this first measurements, it appears that thelinear transistors are more radiation hard than the ELTs, even if the latter are designedspecifically to be more radiation tolerant [17, 12].

5.4 The KC01 test board

In order to facilitate the characterisation of the KC01 in future test beams, I designedtwo boards to perform measurements of IDS as a function of VGS at a fixed VDS. The firstone contains only the socket to hold a 68 pin JLCC package with the KC01 bonded insideit (figure 5.3), the second one contains some headers to select the transistor to test andthe circuitry to measure the drain current (figure 5.4). The two boards can be connectedwith three 10-wires flat cables, so it is possible to perform measurements also when thechip is irradiated.

To test a transistor is necessary to place five jumpers:

• three to select its gate, drain and source,

• one to connect the body of its row to the power supply,

• one to connect the n-ring or the DPC of its row to the power supply.

Furthermore it is possible to power the linear transistors and the ELTs at different voltages.The current measurement is accomplished with a 50 Ω resistor connected in series withthe drain. One of its terminals is connected to a non-inverting amplifier realised with aOP184F op-amp; the feedback resistors have been chosen to have a gain of 2: the output

54 Chapter 5

of the amplifier Vout is therefore proportional to IDS

Vout = 2 · 50 Ω · IDS

Using this board it will be possible to perform measurements from the control room ofthe radiation facility during the irradiation of the chip.

Figure 5.3: Board with the socket to hold the KC01 chip.

Figure 5.4: Board with the amplifiers and the headers to select the transistor to be measured.

Conclusions

In this thesis I have studied the properties of the first CMOS radiation detector realizedin the BCD8 technology by STMicroelectonics.

The tests on the passive pixels have demonstrated that the pixel design used in KC53Acan have good performances in particle detecting. In particular the IV tests have shownthat the reverse current is a few orders of magnitude smaller than the expected signal ofa MIP, the CV measurements have allowed to estimate the depletion depth and to verifythat the substrate resistivity value is in good agreement with expectations. Finally, themeasurements with radioactive sources have shown that a good output signal is producedand can be measured, even with a non-completely optimized acquisition chain.

The tests on the active pixels have demonstrated that their electronic chain is not suitableto detect an ionizing particle signal because the noise is too high (the RMS of the noisecorresponds to a energy loss of 30÷ 36 keV). However, tests on a single active pixel haveshown that the amplifier features a good linearity until a injected charge of more than 40ke; unfortunately its gain is not reproducible among the different pixels on a chip noramong the same pixels on different chips and it is always lower than expectations. Thedifferences among the pixels can be explained with a high variability of the parametersof the components inside the chip, related to the building process itself. The low gainis probably related to a bad simulation of the sensor capacitance, which conditions thesimulation of the amplifier.

The irradiation tests are at a very early stage, so at the moment no final results areavailable. With future tests we expect to be able to characterise the radiation hardnessof detectors in BCD8 technology.

Finally an improved version of the chip integrating a better amplifier and a tunablecomparator, in order to have a readout chain that can be interfaced with the currentATLAS pixel readout chip [15, 16], is being designed.

55

Appendix A

Circuit schematics

The schematics of the PCBs designed for this work are reported in this appendix, in thefollowing order:

• the passive pixels test board, used for the radiation sources measurements (section3.3);

• the KC53A test board, used for the tests on active pixels (sections 4.3, 4.4 and 4.5);

• the two boards for the tests on KC01 (section 5.4): the support board and theboard to perform measurements.

57

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Appendix B

ROOT macros

The ROOT macros used for the fits performed in this work are reported in this ap-pendix.

B.1 CV measurements macro

This macro reads the voltage and capacitance values from a file (two columns: voltage in Vand capacitance in pF) and fits them with the function described in section 3.2. It printsthe fitted parameters, the χ2 and displays a plot. It has been used for the pads capacitancefit also, by changing the initial values. To be executed with root fitCV.C.

//file name: fitCV.C#define EX 0.001#define EY 0.0014

Double_t funct(Double_t *x, Double_t *par)

return par[0]+ 1/TMath::Sqrt(par[1] * (-x[0]+par[2]) );

/*paramenters:0: C_P1: k2: V0*/

void fitCV() TF1 *function = new TF1("fit", funct, -60, 0, 3);//initial valuesfunction->SetParameters(0.1, 3, 0.5);

function->SetParNames("C_P (pF)", "k", "V0 (V)");

//data file name here

63

TGraphErrors *graph1 = new TGraphErrors("D1-CV.txt");

//set the errors on the measurementsfor (int i = 0; i < 61; i++)

graph1->SetPointError(i, EX, EY);

TCanvas *c1 = new TCanvas("c1","CV",200,10,700,500);c1->cd();

graph1->Fit("fit", "R");graph1->Draw("A*");function->Draw("LSAME");

double chisq=function->GetChisquare();double ndf=function->GetNDF();double chisqdf=chisq/ndf;cout << "Chisquare: " << chisq << "/" << ndf << " : " << chisqdf << endl;

B.2 241Am macros

B.2.1 Macro to fit the spectrum peaks

This macro reads the bins content of the spectrum from a file and fits five Gaussian peaks.Then it prints the fitted parameters, the χ2 and displays a plot. To be executed withroot peaksAm.C.

//file name: peaksAm.Cvoid peaksAm()

gROOT->Reset();float y;float stepx=1.;float x=-stepx/2.;Int_t iiy,ii;

FILE *f;

//data file name heref=fopen("Am-50V-9000s.txt","r");

TH1F *gg = new TH1F("gg", "Am-241", 8192., 0.,8192. );

TF1 *g1 = new TF1("13.9", "gaus", 930., 1070.);TF1 *g2 = new TF1("17.7", "gaus", 1180., 1345.);TF1 *g3 = new TF1("20.7", "gaus", 1440., 1580.);TF1 *g4 = new TF1("26.3", "gaus", 1820., 1950.);TF1 *g5 = new TF1("59.5", "gaus", 4180., 4310.);

64

gStyle->SetOptStat(0);gStyle->SetOptLogy(1);

while (fscanf(f,"%f", &y)!=EOF) iiy = y;x+=stepx;gg->Fill(x,y);

gg->SetAxisRange(0.1, 2000, "Y");gg->SetAxisRange(0, 4500, "X");

gg->Fit(g1,"R");

double chisq=g1->GetChisquare();double ndf=g1->GetNDF();double chisqdf=chisq/ndf;cout << "Chisquare: " << chisq << "/" << ndf << " : " << chisqdf << endl;

gg->Fit(g2,"R");

chisq=g2->GetChisquare();ndf=g2->GetNDF();chisqdf=chisq/ndf;cout << "Chisquare: " << chisq << "/" << ndf << " : " << chisqdf << endl;

gg->Fit(g3,"R");


gg->Fit(g4,"R");


gg->Fit(g5,"R");


gg->Draw("HIST");g1->Draw("SAME");g2->Draw("SAME");g3->Draw("SAME");g4->Draw("SAME");

65

g5->Draw("SAME");

fclose(f);

B.2.2 Macro to perform the channel-energy calibration

This macro performs a linear fit to find the channels-energy calibration curve. To beexecuted with root calibrationAm.C.

//file name: calibrationAm.Cvoid calibrationAm()

TF1 *function = new TF1("fit", "pol1", 960, 4500);

function->SetParNames("q", "m");

//array with the fitted values of the peaks (in channels)Double_t x[5] = 979, 1239, 1476, 1876, 4241;//array with the energy of th peaks (in keV)Double_t y[5] = 13.9, 17.7, 20.7, 26.3, 59.5;//arrays with the uncertainitiesDouble_t ex[5] = 14, 9, 26, 13, 6;Double_t ey[5] = 0.1, 0.1, 0.1, 0.1, 0.1;

TGraphErrors *graph1 = new TGraphErrors(5, x, y, ex, ey);

TCanvas *c1 = new TCanvas("c1","CV",200,10,700,500);c1->cd();

graph1->Fit(function, "R");graph1->Draw("A*");function->Draw("LSAME");

double chisq=function->GetChisquare();double ndf=function->GetNDF();double chisqdf=chisq/ndf;cout << "Chisquare: " << chisq << "/" << ndf << " : " << chisqdf << endl;

B.3 55Fe macro

This macro reads the bins content of the spectrum from a file and fits one Gaussian peak.Then it prints the fitted parameters, the χ2 and displays a plot. To be executed withroot peaksFe.C.

//file name: peaksFe.Cvoid peaksFe()

66

gROOT->Reset();float y;float passox=1.;float x=-passox/2.;Int_t iiy,ii;

FILE *f;

//data file name heref=fopen("Fe-50V-3450s.txt","r");

TH1F *gg = new TH1F("gg", "Fe-55", 8192., 0.,8192. );

TF1 *g1 = new TF1("fe", "gaus", 360., 510.);


while (fscanf(f,"%f", &y)!=EOF) iiy = y;x+=passox;gg->Fill(x,y);

gg->SetAxisRange(0.1, 2000, "Y");gg->SetAxisRange(100, 1000, "X");

gg->Fit(g1,"R");

double chisq=g1->GetChisquare();double ndf=g1->GetNDF();double chisqdf=chisq/ndf;cout << "Chisquare: " << chisq << "/" << ndf << " : " << chisqdf << endl;

gg->Draw("HIST");g1->Draw("SAME");

fclose(f);

B.4 X-ray tube macro

This macro reads the bins content of the spectrum from a file and fits the peak withthe function described in section 3.4. Then it prints the fitted parameters, the χ2 anddisplays a plot. To be executed with root peaksX.C.

//file name peaksX.C#include "TMath.h"

67

Double_t fit(Double_t *x, Double_t *par) return par[3] * (-(erf(x[0] - par[1])/sqrt(2)/par[2]) + 1)/2 +par[0] * exp(-(x[0] - par[1])*(x[0] - par[1]) / (2*par[2]*par[2])) ;

/*parameters:0: gaussian constat1: mean2: sigma3: erf constant*/

void peaksX()gROOT->Reset();float y;float passox=1.;float x=-passox/2.;Int_t iiy,ii;

FILE *f;

//data file name heref=fopen("X-50V-1us.txt","r");

TH1F *gg = new TH1F("gg", "X rays", 8192., 0.,8192. );

//uncomment the suitable definition//TF1 *g1 = new TF1("g1", fit, 850., 1320., 4); //250ns//TF1 *g1 = new TF1("g1", fit, 850., 1340., 4); //500 nsTF1 *g1 = new TF1("g1", fit, 850., 1300., 4); //1 us//TF1 *g1 = new TF1("g1", fit, 900., 1250., 4); //2 us//TF1 *g1 = new TF1("g1", fit, 900., 1250., 4); //3 us

g1->SetParameters(300, 1210, 150, 150);

g1->SetParNames("C1", "mean", "sigma", "C2");


while (fscanf(f,"%f", &y)!=EOF) iiy = y;x+=passox;gg->Fill(x,y);

gg->SetAxisRange(0, 3500, "X");

gg->Fit("g1","R");

double chisq=g1->GetChisquare();double ndf=g1->GetNDF();

68

double chisqdf=chisq/ndf;cout << "Chisquare: " << chisq << "/" << ndf << " : " << chisqdf << endl;

gg->Draw("HIST");g1->Draw("SAME");

fclose(f);

69

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[2] I. Perić, C. Kreidl, P. Fischer, Particle pixel detectors in high-voltage CMOS tech-nology—New achievements, Nucl. Instr. and Meth. in Physics Research SectionA617(2010)576–581.

[3] I. Perić et al., High-voltage pixel sensors for ATLAS upgrade, Nucl. Instr. and Meth.in Physics Research Section A765(2014)172–176.

[4] I. Perić, C. Kreidl, P. Fischer, Hybrid pixel detector based on capacitive chipto chip signal-transmission, Nucl. Instr. and Meth. in Physics Research SectionA617(2010)576–581.

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[6] A. Andreazza et al., R&D Proposal on CCPD with HV/HR-CMOS,https://espace.cern.ch/project-INFN-HVR-CCPD/Shared%20Documents/PROPOSAL%20HVR-CCPD.v1.1.pdf

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[9] R. D. Deslattes et al., X-ray Transition Energies, (version 1.2, 2005). National Instituteof Standards and Technology, Gaithersburg, MD. Online available: http://physics.nist.gov/XrayTrans.

[10] C. T. Chantler et al., X-Ray Form Factor, Attenuation and Scattering Tables, (version2.1, 2005). National Institute of Standards and Technology, Gaithersburg, MD. Onlineavailable: http://physics.nist.gov/ffast.

[11] M. S. Basunia, Nuclear Data Sheets 107, 3323 (2006). Online available: http://www.nndc.bnl.gov/chart/decaysearchdirect.jsp?nuc=241AM&unc=nds

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https://espace.cern.ch/project-INFN-HVR-CCPD/Shared%20Documents/PROPOSAL%20HVR-CCPD.v1.1.pdf

http://physics.nist.gov/XrayTrans

http://physics.nist.gov/XrayTrans

http://physics.nist.gov/ffast

http://www.nndc.bnl.gov/chart/decaysearchdirect.jsp?nuc=241AM&unc=nds

http://www.nndc.bnl.gov/chart/decaysearchdirect.jsp?nuc=241AM&unc=nds

[12] V. Liberali, M. Riva, A. Stabile, Design Approaches for IC Radiation Hardering,Prospettive Economiche e Strategie Industriali, Convegno Nazionale AEIT, Milan,2011.

[13] W. R. Leo, Techniques for Nuclear and Particle Physics Experiments, Springer-Verlag,1987.

[14] P. E. Allen, D.R. Holberg, CMOS Analog Circuit Design, 2nd ed., Oxford UniversityPress, New York, USA, 2002.

[15] The ATLAS IBL collaboration, Prototype ATLAS IBL modules using the FE-I4Afront-end readout chip, JINST, 7 (2011) P11010.

[16] The ATLAS IBL Collaboration, The FE-I4B Integrated Circuit Guide, version 3.2,December 30, 2012.

[17] S. Passadore, Study of Pixel Detectors in BCD (Bipolar-CMOS-DMOS) Technology,Master Thesis, University of Milan, 2015. Online available: http://www.infn.it/thesis/thesis_dettaglio.php?tid=9961

[18] Data provided by E. Ruscino and G. Gariano, INFN Genova.

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http://www.infn.it/thesis/thesis_dettaglio.php?tid=9961

http://www.infn.it/thesis/thesis_dettaglio.php?tid=9961

CHARACTERISATION OF A PIXEL DETECTOR IN BCD8 … Universita degli Studi di Milano FACOLT A DI...

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