Strain-enhanced Device and Circuit for Optical Communication System
description
Transcript of Strain-enhanced Device and Circuit for Optical Communication System
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Strain-enhanced Device and Circuit forStrain-enhanced Device and Circuit forOptical Communication SystemOptical Communication System
指導教授:劉致為 博士 學生:余名薪
台灣大學電子工程學研究所
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OutlineOutline Introduction
Optical Communication System Mechanical/Package Strain Technique
Strain-enhanced MOS Photodetector Strain-enhanced Transimpedance Amplifier 7Gb/s Transimpedance Amplifier SiGe HBT BiCMOS Active Inductor Summary and Future Work
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Optical Communication SystemOptical Communication System
MUX
CMU
Laser Driver
DFF
Q
TIA LA
CDR
DMUX
Optical Fiber
Data Input
Data Output
Photodetector & Transimpedance Amplifier (TIA)
System block diagram
Transmitter
Receiver
Medium
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Mechanical/Package Strain TechniqueMechanical/Package Strain Technique
Side view Top view
Mechanical setup (detector)
BiaxialTensile Strain
UniaxialTensile Strain
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Mechanical/Package Strain TechniqueMechanical/Package Strain Technique
O-ringto fix the substrate
Chip
Mechanical stress(at center)
Biaxial strain
r
Packagesubstrate
Package substrate Biaxial
compressive strain
Biaxial tensile strainChip
Mechanical displacement
O-ringChip
Mechanical stress(at centerline)
Uniaxial strain
Si strip
Si stripUniaxial
compressive strain
Uniaxial tensile strainChip
Mechanical displacement
Mechanical setup (circuit chip)
BiaxialTensile Strain
UniaxialTensile Strain
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Ramam & Electroluminescence spectra
Ramam spectrum EL spectrum
• The red-shift of Si-Si peak in Ramam spectra indicates 0.13% biaxial tensile strain and 0.35% uniaxial tensile strain.• The EL spectra of a MOS LED under tensile strain indicates bandgap shrinkage.
Mechanical/Package Strain TechniqueMechanical/Package Strain Technique
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Mechanical/Package Strain TechniqueMechanical/Package Strain Technique
Current change (%)At |VGS|-|VT|=1V
250nm node (L=240nm)
Compressive0.06% strain
Tensile0.06% strain
NFET
Uniaxial // channel
-4.3 10.8
Uniaxial ┴ channel
-6.9 2.5
Biaxial -6.2 8.7
PFET
Uniaxial // channel
5.5 -8.8
Uniaxial ┴ channel
-6.8 4.8
Biaxial 0.3 -0.9
Current enhancement in MOSFET
• The drain current is enhanced owing to the electron mobility enhancement.• NFET has enhancement under tensile strain, and PFET has enhancement under uniaxial compressive strain parallel to channel and the uniaxial tensile strain perpendicular to channel.
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OutlineOutline Introduction Strain-enhanced MOS Photodetector
Metal/Thin-oxide/P-Si Tunneling Diode Photodetector Responsivity Enhancement by Tensile Strain
Strain-enhanced Transimpedance Amplifier 7Gb/s Transimpedance Amplifier SiGe HBT BiCMOS Active Inductor Summary and Future Work
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MOS Tunneling Diode PhotodetectorMOS Tunneling Diode PhotodetectorI-V & C-V characteristics
I-V curve C-V curve
• At the negative bias region, the device can serve as a LED. When the gate is biased at the positive voltage greater than threshold voltage, the device can serve as a PD. • C-V indicates that the deep depletion in the NMOS tunneling diode is formed for the large positive gate bias.
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MOS Tunneling Diode PhotodetectorMOS Tunneling Diode Photodetector
Photo currentDark current
Interface defects
Δ EC
Δ EV
EC
EV
Al SiO2 P-Si
hv
EF
hv
Al SiO2 P-Si
EC
EV
Band diagram
Accumulation (LED) Inversion (Detector)
• The bandgap shrinkage enlarges the concentration of the electron in the bulk silicon, and since the tunneling process would not be the limiting factor for electron to go from p-Si to Al gate, the photo current increases. Namely, the responsivity is enhanced.
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MOS Tunneling Diode PhotodetectorMOS Tunneling Diode PhotodetectorMeasurement
Biaxial tensile strain Uniaxial tensile strain
• The dark current has almost no change under strain, and the photo current is enhanced gradually with increasing strain.
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MOS Tunneling Diode PhotodetectorMOS Tunneling Diode PhotodetectorResponsivity enhancement
12%
14%
• Uniaxial strain has potentiality to achieve higher strain gauge than biaxial strain.• The maximum of current enhancement is about 12% and 14% under biaxial and uniaxial strain respectively.
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OutlineOutline Introduction Strain-enhanced MOS Photodetector Strain-enhanced Transimpedance Amplifier
Circuit Design & Simulation Bandwidth Enhancement by Tensile Strain
7Gb/s Transimpedance Amplifier SiGe HBT BiCMOS Active Inductor Summary and Future Work
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Strain-enhanced Transimpedance AmplifierStrain-enhanced Transimpedance Amplifier
Iin
Vout
VDD
VB
50Ω
Parasitic isolation Core Amplifier Output buffer
M1
M2
M3 M4
M5 M6
M7
M8
M9
M10
R1
R2
R3
R4
R5
I1
I2
I3
X
Y Z
Circuit schematic
Main Gain Stage Peaking Stage
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Strain-enhanced Transimpedance AmplifierStrain-enhanced Transimpedance AmplifierInductive peaking
L
R
CVin
Vout
12
RCsLCs
RLsg
V
Vm
in
out
1
)1(22
sms
msRgm
• For m = 0.4, the transfer function exhibits a maximum flat response with a bandwidth improvement of 70% compared to a simple common source amplifier. If m = 0.7, the bandwidth reaches its maximum value with 1.5dB peaking and 85% improvement.
fM
agni
tude
(dB
) m = 0.4
m > 0.4
m < 0.4M1
M2
M3
I1
I2
Rf
VB3
Zin
(τ= RC , m = L/R2C )
Active Inductor
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Strain-enhanced Transimpedance AmplifierStrain-enhanced Transimpedance Amplifier
f f
Main Gain Stage Overall Gain
Peaking Stage
Bandwidth enhancement
After strain After strain
8
7 8 7 8 7
1,gs
s sm m m m o
CL R
g g g g r
2262
2
2 nn
nnsm
Y
Z
ss
sRg
V
V
s
gsgds
gsgds
n L
CCR
CCL
106
1062
,)(
1
Active Inductor :
Peaking Stage :
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Strain-enhanced Transimpedance AmplifierStrain-enhanced Transimpedance Amplifier
1E91E8 1E10
20
30
40
50
60
10
70
freq, Hz
dB(G
ain)
1E91E8 1E10
-150
-100
-50
0
50
100
150
-200
200
freq, Hz
Pha
se
Frequency response & Stability
Magnitude response Phase response
2 3 4 51 6
500
1000
1500
2000
0
2500
freq, GHz
Sta
bFac
t1
1 2 3 4 5 6 7 8 90 10
0.05
0.10
0.15
0.20
0.25
0.00
0.30
freq, GHz
mag(D
elta
)
K factor Δ factor
Gain: 60dBΩBandwidth: 3.5GHzPeaking < 0.5dB
K > 1
Δ< 1
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Strain-enhanced Transimpedance AmplifierStrain-enhanced Transimpedance AmplifierInput-referred noise current density & Eye diagram
Input-referred noise current density
Eye Diagram at 3.125Gb/s, 20uA
HzpAI innoise /202,
Jitter < 20ps
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Strain-enhanced Transimpedance AmplifierStrain-enhanced Transimpedance Amplifier
Technology TSMC 0.18um RFCMOS
Supply voltage 1.8V
Transimpedance gain 60dBΩ
Bandwidth 3.5GHz
Input referred noise current
< 20pA/√Hz
Jitter < 20ps
Group delay variation < 65ps
Power consumption (core) 12mW
Chip Area 600*380 um2
Performance Summary
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Strain-enhanced Transimpedance AmplifierStrain-enhanced Transimpedance AmplifierMeasurement : Bandwidth enhancement
• Through 0.06% biaxial tensile strain, the characteristic of active inductor can be modified, thus improves the -3dB frequency.• The bandwidth enhancement is about 5.5%.
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Strain-enhanced Transimpedance AmplifierStrain-enhanced Transimpedance AmplifierCircuit layout & Die photograph
Die photo
Layout
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OutlineOutline Introduction Strain-enhanced MOS Photodetector Strain-enhanced Transimpedance Amplifier 7Gb/s Transimpedance Amplifier
Circuit Design & Simulation Measurement
SiGe HBT BiCMOS Active Inductor Summary and Future Work
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7Gb/s Transimpedance Amplifier7Gb/s Transimpedance Amplifier
R1
VB1
M1
M2
M3 M4
M5
R2
R3
L1
Rf
C2
Vout
C3
R6Iin
R4 R5
C1VB2
L2 L3
M6 M7
VB3
Parasitic isolation Core Amplifier Differential Output Buffer
Circuit schematic
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7Gb/s Transimpedance Amplifier7Gb/s Transimpedance Amplifier
1E6 1E7 1E8 1E9 1E101E5 1E11
-50
0
50
-100
100
freq, Hz
dB(G
ain)
1E91E8 1E10
-150
-100
-50
0
50
100
150
-200
200
freq, Hz
Pha
se
7 8 96 10
50
100
150
200
0
250
freq, GHz
Sta
bFact1
10 20 300 40
0.2
0.4
0.6
0.8
0.0
1.0
freq, GHz
mag(D
elta
)
Frequency response & Stability
Magnitude response Phase response
K factor Δ factor
Gain: 56dBΩBandwidth: 8GHzPeaking < 1dB
K > 1
Δ< 1
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7Gb/s Transimpedance Amplifier7Gb/s Transimpedance AmplifierInput-referred noise current density & Eye diagram
Input-referred noise current density
Eye Diagram at 10Gb/s, 20uA
HzpAI innoise /152,
Jitter < 15ps
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7Gb/s Transimpedance Amplifier7Gb/s Transimpedance Amplifier
S11 S12
S21 S22
Measurement : S-parameters
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7Gb/s Transimpedance Amplifier7Gb/s Transimpedance AmplifierMeasurement : Frequency response
Magnitude response Phase response
50)1)(1(
2
12212211
2121 SSSS
SZTransform function:
Gain: 57dBΩBandwidth: 6GHz
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7Gb/s Transimpedance Amplifier7Gb/s Transimpedance AmplifierMeasurement : Eye diagram
2.5 Gb/s PRBS 3.125 Gb/s PRBS
7 Gb/s PRBS
• Measured on PCB.• Equivalent input current ~ 50uA.• Eye can open well under 7Gb/s PRBS.• Jitter < 35ps @ 7Gb/s• The inductive characteristic of bond wire may help improve overall bandwidth.
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7Gb/s Transimpedance Amplifier7Gb/s Transimpedance Amplifier
Simulation Measurement
Technology TSMC 0.18um RFCMOS TSMC 0.18um RFCMOS
Supply voltage 1.8V 1.8V
Transimpedance gain 56dBΩ 57dBΩ
Bandwidth 8GHz 6GHz
Input referred noisecurrent
< 15pA/√HzSensitivity:
20uA/eye open
Jitter < 15ps < 35ps @ 7Gb/s
Group delay variation < 80ps < 90ps
Power consumption (core) 10mW 10mW
Chip Area 880*980 um2 880*980 um2
Performance Summary
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7Gb/s Transimpedance Amplifier7Gb/s Transimpedance AmplifierDie & PCB photograph
Die photo
PCB photo
PCB layout
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OutlineOutline Introduction Strain-enhanced MOS Photodetector Strain-enhanced Transimpedance Amplifier 7Gb/s Transimpedance Amplifier SiGe HBT BiCMOS Active Inductor
CMOS Active Inductor BiCMOS Active Inductor
Summary and Future Work
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SiGe HBT BiCMOS Active InductorSiGe HBT BiCMOS Active Inductor
Zin
V1 V2
-Gm1
Gm2
I2
I1
C 21 mmin GG
sCZ
M1
M2 M1
M1
M1
M2
M2
M2
M1
M1
M1
M1
M2
M2 M2
M2
Basic configuration of active inductor
Gyrator-C topology:
CS-CD type
CS-CG type
Two-transistor active inductor:
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SiGe HBT BiCMOS Active InductorSiGe HBT BiCMOS Active InductorProposed active inductor
CMOSBiCMOS
Type A Type B
RsLs
Cp
Rp
Zin 2
1
mp gR
1gsp CC
21
1
mm
os gg
GR
21
2
mm
gss gg
CL
M1
M2
I2
I1
I2
M2
Q1
Q2
M1
I1
I2
I1
I2
M2
Q1
Q3 VB3
Equivalent model :
1
2
o
gs
s
s
G
C
R
LQ
2121
212 1TT
gsgs
mm
psSR ff
CC
gg
CLf
CascodeBiCMOS Type A
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SiGe HBT BiCMOS Active InductorSiGe HBT BiCMOS Active Inductor
)))(CC((
)CCC()(
211gd1gs22
gd1gd2gs21
gddsmm
dsin sCggsg
sgsZ
eq
m
gs
m
gd
mm
gsgd
gsm
gdm
mm
gs
mm
ds
in R
g
C
g
C
gg
CC
Cg
Cg
gg
C
gg
g
Z
2
2
2
1
22
2
21
222
21
22
1
2
2
2
21
1
1
11
]Re[
eq
m
gs
m
gd
mm
gsgd
gdmm
gs
mm
gs
in Lj
g
C
g
C
gg
CC
Cgg
C
gg
Cj
Z
2
2
2
1
22
2
21
222
221
22
21
2
1
1
]Im[
M1
M2
I2
Zin analysis
Zin
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SiGe HBT BiCMOS Active InductorSiGe HBT BiCMOS Active Inductor
1M 10M 100M 1G 10G 100G-100
-80
-60
-40
-20
0
20
40
60
80
100
Zin
ph
ase
Frequency (Hz)
CMOS BiCMOS BiCMOS cascode
Frequency response of input impedance
Magnitude Phase
• For fair comparison, all the active inductors are designed with identical MOSFET size and power consumption. • BiCMOS active inductor has wider inductive range.• The phase of BiCMOS type rises at lower frequency and reaches the higher degree, which means BiCMOS type has much higher quality factor and less resistive loss.
1M 10M 100M 1G 10G 100G0
10
20
30
40
50
60
70
Zin
mag
nit
ud
e (
dB
)
Frequency (Hz)
CMOS BiCMOS BiCMOS cascode
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SiGe HBT BiCMOS Active InductorSiGe HBT BiCMOS Active Inductor
0 2 4 6 8 10 12 14 16 18 20-20
-10
0
10
20
30
Ind
ucta
nce (
nH
)
Frequency (GHz)
CMOS BiCMOS BiCMOS cascode
0 2 4 6 8 10 12 14 16-5
0
5
10
15
20
Qu
ality
facto
r
Frequency (GHz)
CMOS BiCMOS BiCMOS cascode
Inductance & Quality factor
Inductance Q-factor
• BiCMOS type has much higher resonant frequency.• Cascode will reduce the resonant frequency owing to its extra parasitics, but it provides higher inductance at high frequency and higher quality factor.
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SiGe HBT BiCMOS Active InductorSiGe HBT BiCMOS Active Inductor
5 10 150 20
-1E-8
0
1E-8
2E-8
-2E-8
3E-8
freq, GHz
Indu
ctan
ce3
2 4 6 8 100 12
10
30
50
70
90
-10
110
freq, GHz
Q3
5 10 150 20
-1E-8
0
1E-8
2E-8
-2E-8
3E-8
freq, GHz
Indu
ctan
ce3
2 4 6 8 100 12
10
305070
90110
130150170
190
-10
210
freq, GHz
Q3
5 10 150 20
-2E-8
-1E-8
7E-24
1E-8
2E-8
3E-8
-3E-8
4E-8
freq, GHz
Indu
ctan
ce3
2 4 6 8 100 12
10
30
50
70
90
110
-10
130
freq, GHz
Q3
Inductor characteristic tuning
I1 tuning
I2 tuning
VB tuning
I1 increasingI1 increasing
I2 increasing I2 increasing
VB increasing VB increasing
Inductance Q-factor
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OutlineOutline Introduction Strain-enhanced MOS Photodetector Strain-enhanced Transimpedance Amplifier 7Gb/s Transimpedance Amplifier SiGe HBT BiCMOS Active Inductor Summary and Future Work
Summary CMOS Image Sensor
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SummarySummary A novel metal/thin-oxide/silicon structure tunneling diode photo detector is
proposed. With biaxial or uniaxial tensile strain, the band-gap of bulk Si shrinks, resulting in higher electron concentration under identical exposure, thus the responsivity is enhanced. The maximum of responsivity enhancement under biaxial and uniaxial tensile strain are about 12% and 14% respectively.
A Transimpedance Amplifier (TIA) adopting active inductor is designed. Through inductive characteristic tuning by biaxial tensile strain, a 5.5% bandwidth enhancement can be achieved.
A 7Gb/s transimpedance amplifier fabricated with TSMC 0.18um CMOS process is proposed. The measured gain and bandwidth are 57dBΩ and 6GHz respectively. The eye can open well with operation under 7Gb/s PRBS.
A novel BiCMOS type active inductor is proposed. From simulation, it can be proved that BiCMOS active inductor can achieve higher quality factor and resonant frequency than CMOS type with the great help from SiGe HBT. However, the inductance value would be slightly lower.
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Future WorkFuture WorkCMOS image sensor
Replace with MOS detector
• The photodiode can be replaced with our MOS tunneling diode photodetector by connecting the gate of the diode to the source of transfer gate.
• The lower dark current(~3nA/cm2) and higher quantum efficiency (~80%) can improve the performance of the pixel, such as dynamic range and sensitivity.