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
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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
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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
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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
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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.
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• 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
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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
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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
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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!