Pressure Sensors beyond Traditional MEMS. Appo van der Wiel MEMS and post processing Melexis

Transcription

1 Pressure Sensors beyond Traditional MEMS MEMS and post processing

2 Contents? Traditional pressure sensors Challenges MEMS-CMOS integration System evolution Pressure information unit Conclusion

3 Idea Design is a fab less semiconductor company with a turnover of about 200M Wafer In house Out sourced Probing offers a wide range Assembly of standard products and ASICs. Our business is system development including high volume production and testing for automotive applications Final Test Customer

4 Discrete pressure sensors (traditional) Process dedicated to sensor Few masks Specific passivation and diffusion External calibration circuit Calibration by customer Vexc.+ Vout + Vexc.- Vout-

5 Integrated pressure sensors (traditional) On-chip calibration After assembly Temperature compensation Compromise CMOS-MEMS process Backside processing Diffusions and passivation not dedicated to sensor Less silicon needed!

6 Discrete or Integrated? Traditional discussion Vexc.+ Vout + Vexc.- Vout- Both give real time pressure output Cost driven discussion Real estate Calibration costs Sensor performance

7 Traditional integrated sensor Calibration defined by hardware Not optimal when only a part of the temperature/pressure range is used Offset Ohigh O0 T0 = RT TH = C T Offset = O0+Oc(T-T0)

8 Example integrated sensor in 1 um CMOS Analog Membrane Zap cell Memory Digital

9 Challenges MEMS-CMOS integration Use standard CMOS process for piezo resistors and membrane passivation Back side processing How to prevent scratches on top How to protect the front side during KOH etching Back side alignment How to align at the CMOS pattern CMOS p-epi in conflict with electrochemical etch-stop

10 System Evolution Traditional system approach: The system converts and interprets the sensor signal Information processing outside the sensor Hardware defined calibration method New system approach: The system imports information from the sensor Information processing in the sensor Software defined calibration method

11 New System Approach Convert non compensated pressure and temperature signals into numbers Store calibration constants in EEPROM Use microcontroller to calculate output signal(s) based on the signals calibration constants Allow client to define output (EEPROM)

12 Gain Programmable calibration Gain Ghigh GH1 Glow GL1 G1 G0 TL = T0 TH T TL T0 TH T Gain = Glow(1 + GL1(T-TL)) with Glow = G0 and TL = T0 Gain = G0(1+G1(T-T0)) Gain = Ghigh (1 + GH1(T-TH)) with Ghigh = G0(1+G1(TH-T0)) Gain = G0(1+G1(T-T0)+G2(T-T0)^2)

13 Ghigh Gain G0 Glow Gain = Glow(1 + GL1(T-TL)) with Glow = G0(1 + G1(TL-T0)+G2(TL-T0)^2) Ghigh Glow Gain GL1 GL1 Gain = Glow(1 + GL1(T-TL)) with Glow = G0 and TL = T0 TL T0 TH T Gain = G0(1+G1(T-T0)+G2(T-T0)^2) G1 GH1 Gain = Ghigh(1 + GH1(T-TH)) with Ghigh = G0(1+G1(TH-T0)+G2(TH-T0)^2) TL = T0 TH T Gain = G0(1+G1(T-T0)) GH1 Gain = Ghigh (1 + GH1(T-TH)) with Ghigh = G0(1+G1(TH-T0)) System blocks MLX90809 MLX90810 MLX90809 & MLX90810 DSP Overvoltage & reverse voltage protection Pressure sensing element : piezoresistive Wheatsone bridge Vana SE1 Temperature sensor Programmable Coarse Gain (3 gain stages) + Programmable Coarse Offset OPA MUX Vana ADC 16 bits Micro controller Gain & Offset temperature compensation Analog & Digital Regulator and POR DAC 12 bits Broken wire detection Vext Ana driver Gain Vext Analog OUT SE2 Possibility of pressure lineariztion Plinear SENT driver Vext SE1, SE2, VEXT G(1+L1) ADC0 G Oscillator Rom FW G(1+L2) -Pnl 0mbar Pnl Programmable filter EE PROM Ram Pressure Slew rate control SENT OUT Ground

14 0.35 CMOS Pressure Sensor on a 200 mm wafer EEPROM Memory Micro Controller Membrane Temperature cell Analog

15 Pressure Info Unit Sensor output = System input The sensor always talks to the system Program the sensor to the system standard TPMS With temperature output With customer specific digital output format Altitude meter With reference pressure storage setting Conversion delta P to height Level metering Your application

16 Examples Pressure Info Units HVAC Power Steering Seat Occupancy Lumbar Pressure Barometric Absolute Pressure Manifold Absolute Pressure Turbo Manifold Absolute Pressure Exhaust Gas Recirculation, Secondary Air Valve Filter Control Fuel Rail In Cylinder Pressure Diesel Particle Filter Fuel Vapor Brake Booster Transmission Oil Crash Air Pressure Sensor Active Suspension

17 Success Angle Info Unit

18 What do you need? Traditional pressure sensor? Pressure signal Hardware defined calibration method Pressure information unit? Pressure / temperature calculation Programmed output format Pressure trigger Temperature reading What you want to program in the device Software defined calibration method