Pressure Sensor

Technology

STMicroelectronicsJay Esfandyari

Product Marketing Manager

Agenda• MEMS Technology

• Bulk Micromachining

• Surface Micromachining

• Pressure Sensor Technology

• Piezo-resistive Technology

• Principle of Design

• Pressure Sensor Specifications

• Design rules & System Integration

2

• Pressure Sensor Applications

• SensorTile

• Components of a

Development Platform

• Q & A

MEMS Technology• MEMS : Micro-Electro-Mechanical-

Systems

• Materials: Si, Poly-Si, GaAs, SiGe, Glass…

• Major Processes: Bulk machining & surface machining

• Physics/engineering: Piezoresistivity, capacitive…

• Applications: Bio, RF, Chemistry, Optical, Mechanical…

MEMS Structure

Taking advantage of mechanical AND electrical

properties of silicon

3

Bulk Micromachining

SubstrateEpitaxy

Glass

KOH Etch Mask

Micro-Channel

Micro-Mirror

Comb Fingers

Bulk micromachining structures: Wet/Dry Etching of Silicon substrate:

300um <L< 3mm

4

Surface MicromachiningSurface micromachining structures: Deposition and Patterning of sacrificial and

structural layers; 1um <L< 300um : Lateral dimensions

5

Pressure Sensors

Terminology

Atmospheric Pressure

(1 bar - 100Kpa – 14.5 psi)

Absolute Vacuum, Zero psia

Absolute

Pressure

Gauge

Pressure

Differential

Pressure

Differential

Pressure

Gauge

Pressure

Gauge

Pressure

Absolute Pressure sensor: Pressure is referred to 0 (absolutely empty); Only positive pressure values

7

Pressure Sensor Technology (1)Typical Conventional technology

Monolithic Silicon Back Die Etching

Glass bonding

Piezoresistive Resistor

diffusion

Full Silicon Pressure Sensor technology

Monolithic Silicon Cavity creation Cavity completed Piezoresistive Resistor

diffusion

Full Silicon Technology Advantages• Monolithic sensor: no need for wafer to wafer bonding to create the cavity

• High burst pressure - Intrinsic mechanical stopper

• High shock survivability

• Good temperature behavior – one temperature coefficient (only silicon)

• More robust and thinner sensor

8

Air cavity ~100um; Membrane 1mm thick

Air cavity ~1um; Membrane 300um thick

9

• Proprietary MEMS Processes used

to manufacture these sensors.

• ST Full Silicon Pressure Sensors’

main feature is an extremely thin

membrane above a hermetic air

cavity.

• ST Full-Silicon exploits piezo-

resistivity in Wheatstone Bridge

configuration to measure the

pressure applied on the

membrane.

Cavity

Membrane

N MONOSILICON

P+

P

FOX+BPSG

MEMBRANE

Pressure

VOID

POLY

PAD

METAL

P+P+

PASSIVATION

Piezo resistor

Pressure Sensor Technology (2)

Piezo-Resistive Technology10

• Piezo-resistivity: a change in the electrical resistivity of a metal or

semiconductor due to an applied stress

• All the materials show a piezo-resistivity effect: Si is the best.

• Four resistors are connected in a Wheatstone bridge configuration.

• Pressure variations change the bridge balance.

Internal Block Diagram of

a Pressure Sensor

MUX

Temperature

Sensor

AFE

&

ADCTemperature

Compensation

&

Digital

filtering

REGISTERS

&

FIFO

I2C

SPI

INT

DRDYInterrupt & reference pressure logic

• The sensor is calibrated at 3 temperatures and 2 pressures for

better accuracy• Trimming parameters are loaded at each start-up.

• No need for re-calibration in application.

Pressure

sensor

11

ST Pressure Sensors

Pressure Sensor20162011 2012 2013 2014 2015

LPS331AP

3 x 3 x 1mm

LPS25HTR

2.5 x 2.5 x 1mm

LPS25HBTR

2.5 x 2.5 x 0.76mm

LPS22HBTR

2 x 2 x 0.76mm

LPS35HWTR

3.5 x 3.5 x 1.8mm

LPS001WP

3 x 5 x 1mm

Full molded unique Package Water

resistanceCavity Package

4 Vent holes

with 20um

6 Vent holes

with 20um

2017

Ultra thin package

LPS33HWTR

3.3 x 3.3 x 2.9mm

Water

proof

12

Pressure Sensors – Major Specs. 13LPS331AP LPS25H LPS25HB LPS22HB LPS22HD LPS35HW LPS33HW

Package size (mm)HCLGA 3x3HCLGA

2.5x2.5

HLGA

2.5x2.5

HLGA

2.0x2.0

HLGA

2.0x2.0

CCLGA

3.5x3.5

CCLGA

3.3x3.3Max Thickness (mm) 1 1 0.8 2 2.9

Numebr of Leads 16 10 10 10 10 10Supply voltage/IO voltage

(V)1.8 -3.6V 1.71-3.6V 1.71-3.6V 1.71-3.6V

Dynamic range (hPa) 260-1260 260-1260 260-1260 260-1260Absolute accuracy over

temp. (hPa)±2.0 ±1.0 ±1.0 (0.1 after OPC) ±4.0

Relative accuracy over

pressure (hPa)±0.1 ±0.10 ±0.10 ±0.10

Low power mode current

consumption (uA)6 4 (LPS25HB) 4(LPS22HB); 3(LPS22HD) 3

Ultra high resolution mode

current(uA)45 25

15(LPS22HB);

12(LPS22HD)15

Output Data Rate (Hz)1-25 1 - 25

1-75 (LPS22HB); 1-200

(LPS22HD)1 - 75

RMS noise (hPa_rms)0.02 – 0.45

0.03 without filter – 0.01

with filter0.0075 0.0075

FIFO No 32 levels of 24 bits each

32 levels / each of 40 bits

for Pressure and

Temperature

32 levels / each of 40

bits for Pressure and

Temperature

Temp. Comp. function PWL Quadratic for Pressure Quadratic for P & T Quadratic for Pressure

Temperature Accuracy

(°C)+/-2 +/-2 +/-1.5 +/-1.5

Vent holes (number/width) 1 / 400um 1/400um 4/20um 6 / 20um 1 / 300um 1/1.6mm

Pressure Sensor – Water Resistant

ST Water Resistant Pressure Sensor solution - 5 ATM & 10 ATM

LPS35HW SPEC:• Low Power consumption : 3uA

• 260 to 1260hPa absolute pressure

• Absolute Accuracy (after OPC) Typ. 1hPa

• Verified & Certified with 5ATM condition.• ISO22810 Horology Certified

• IEC60529 (IP Code) : IPx7, IPx8 certified

CCLGA-10L,

3.5 x 3.5 x 1.85mm

CCLGA-10L,

3.3 x 3.3 x 2.9mm

LPS33HW SPEC:• Same Electrical SPEC than for LPS35HW

• More robustness with full Metal LID

• Easier assembly in application with O-ring package shape

• Target Water Proof up to 10ATM

• No damage of 10ATM test in ST

• Final Verification will be planned by External LAB with

final LPS33HW

14

LPS22HB vs LPS25HBThe Smallest High Performances Absolute Pressure Sensor

15

A look

inside

Altimeter Barometer Weather StationIndoor Navigation

2.0 x 2.0 x 0.76 mm

59% Lower

Power

75% Lower

Noise

Mode@25Hz ODR LPS22HB LPS25HB

*

High Resolution 270 uA 660uA

Mode LPS22HB LPS25HB

High Resolution 0.75Pa* 3Pa*

1Pa = 0.01hPa = Equivalent 8cm altitude

50% Lower

TCO*

Mode LPS22HB LPS25HB

High Resolution 0.4Pa/’C 0.8Pa/’C

TCO : Temperature Coefficient of Offset

36% Smaller

PKG

Mode LPS22HB LPS25HB

HLGA Package 2 x 2 mm 2.5 x 2.5

mm

Noise and Current Consumption• LPS25HB

16

AvgP

(avgt=11)Conditions

Supply

current

RMS

noise

00ODR=1 Hz, Internal

avg=84 µA 125µbar

01ODR=1 Hz, Internal

avg=326 µA 70µbar

10ODR=1 Hz, Internal

avg=12810 µA 45µbar

11ODR=1 Hz, Internal

avg=51225 µA 30µbar

FIFO

AVGNo FIFO 2 4 8 16 32

AvgP RMS noise Icc

00 125µbar 85µbar 60µbar 40µbar 25µbar 15µbar 4 µA

01 70µbar 50µbar 40µbar 25µbar 20µbar 12µbar 6 µA

10 45µbar 35µbar 30µbar 20µbar 15µbar 10µbar10

µA

11 30µbar 25µbar 20µbar 15µbar 10µbar 8µbar25

µA

Noise and Current Consumption

• LPS22HB

17

Mode ConditionsSupply

currentRMS noise

Low NoiseODR=1 Hz,

LC_EN = 012 µA 20 µbar

Low CurrentODR=1 Hz,

LC_EN = 13 µA 65 µbar

EN_LPFP LPFP_CFG

Additional low

pass filter

status

Device

BW

RMS noise in

Low Noise mode

RMS noise in

Low Current

mode

0 x Disabled ODR/2 21 µbar 65 µbar

1 0 Enabled ODR/9 12 µbar 37 µbar

1 1 Enabled ODR/20 7.5 µbar 22 µbar

Power Consumption & RMS Noise18

• Power consumption – LPS25HB / LPS22HB • RMS Noise – LPS25HB / LPS22HB

Pressure

Average

RMS noise (Pa)

Pavg = 8 12.5

Pavg = 512 3

Pressure Average RMS noise (Pa)

Low Current Mode 2.2

High Resolution 0.75

LPS25HB

LPS22HB

Current Unit : uA

Lower Power

consumption

Low RMS noiseSmallest Size

LPS22HB

PCB Design Rules• PCB design rules

• The area below the sensor must

be defined as “keep-out” area.

• Mechanical stress coming from

PCB board should be avoided

• The whole package surface

should have minimum

temperature gradient

• Soldering

• LGA packages for pressure

sensor are qualified for soldering

heat resistance according to

JEDEC J-STD-020, in MSL3

condition.

19

• Surface mounting guidelines for MEMS

sensors in LGA package

• Any cleaning process has to avoid foreign

materials inside the sensing element holes

• Kapton sticker can be applied after the

soldering profile and before cleaning

How to Interface with the Device• Power supply: Separated Vdd and Vdd_IO lines (ultra low drop, low noise

LDO) & Supply voltage range: 1.71 to 3.6V for both, VDD_IO <= VDD

• The device is capable of communicating over 2 digital serial interfaces • SPI 3-wire(CS, SPC, SDI/O) or 4-wire (CS, SPC, SDI, SDO) & I2C (SCL, SDA)

with slave address selectable by SA0 pin

• Device setup and data acquisition is done by accessing registers of the

sensor

• INT_DRDY interrupt push-pull pin has programmable functionality (pressure

high, pressure low, data ready, FIFO interrupts)

20

Pressure

SensorMicro-controller

SPI or I2C

INT_DRDY

Pressure Sensor

Applications

Pressure Sensor Applications22

Weather station Altimeter and barometer

GPS applications Indoor navigation

DronesMan down detectionVacuum Cleaner

Smart Glasses

Smart Watch

Altitude23

• As altitude increases, atmospheric pressure decreases.

• Pressure drops by 1mbar approx. every 10 meters. Terminology is very

delicate for altitude.

• Sea level pressure is defined as 1013.25 hPa (or mbar)

• Pressure altitude - the simplest and widely used barometer (altitude) formula

comes from the US Standard Atmosphere, 1976 edition.

Altitude[ft]=(1-(Pressure[mbar]/1013.25)^0.190284)*145366.45

• Density altitude – is pressure altitude adjusted to non-standard temperature

and humidity

Advantages of Measuring Altitude

with LPS22HB•World’s smallest pressure sensor in production => small size

•LPS22HB is available in full-mold package with silicon cap and four 20µm holes guaranteeing sensor moisture resistance => water resistant

•LPS22HB relative accuracy of pressure measurement < 10 µbar

•Very low power consumption (e.g. 3µA in Low Power mode @1Hz ODR)

•Option to have “One shot mode” (triggered measurement on demand from MCU)

•1 µA in power down mode

24

Drones• The barometric pressure sensor is needed in drone application in order

to give an accurate position of the UAV height (Altitude Hold).

• Considering an ascend/descend speed of 5m/s:

5cm * With sampling rate of 100Hz, ascent/descent @10ms*5m/s=5cm

LPS22HD Sampling rate up to 200Hz

25

Personal Navigation Device

Loosely Coupled Kalman

Filter

3-axis Accelerometer

6-DOF IMU

GPS: • provide initial position, retrieve earth declination

angle and calibrate pedometer step length

• can not tell Heading when the object is not

moving and is not able to tell small height

variation

• Accelerometer: Tilt compensated compass

and pedometer step detection

• Gyroscope: Continue provide Heading when

compass gets disturbed

• Magnetometer: calculate magnetic

Heading and calibrate gyro sensitivity

• Pressure sensor: tell the floor difference

for indoor navigation

Ax, Ay, Az

3-axis Gyroscope

GPS Receiver

StrapdownInertial

Navigation or Pedometorbased PND

3-axis Magnetometer

Pressure sensor

ωx, ωy, ωz

Mx, My, Mz

Pz

λGPS, φGPS

λINS, φINS

λ, φ, Heading

26

Kalman Filter: Estimate and compensate gyro long term bias drift, output DR info when GPS is lost

SensorTile

DIME SIZED evaluation / development kit.

Sensors+BLE+MCU Eval Kit!27

SensorTile Cradle

HTS221 - STBC08 - Battery - SDCard

STEVAL-STLCR01V1

Q & A

Thank You!