Smart Infrared Detector

1. Smart Infrared Detector • M. Denoual • mdenoual@ensicaen.fr

2. Outline • Infrared imaging systems context • Bolometer principle • What is smart ? • Integration • Heat balanced bolometer • Smart functionalities

3. Infrared imaging systems According to market research, the volume of sale of uncooled infrared imaging system exhibits a 23% annual growth rate. [Yole Development] Process control and monitoring Pedestrian detection Building diagnostic Examples of applications of uncooled infrared imaging systems Among infrared imaging systems, infrared imagers based on uncooled resistive bolometers represents 95% of the market. [Yole Development] Uncooled IR Cameras & Detectors for Thermography and Vision, Tech. & Market Report, 2010

4. Bolometer principle (1/3) voltage variation IR optical power thermal power temperature variation resistance variation absorbing layer thermal mass sensing element current biased

5. Bolometer principle (2/3) voltage variation IR optical power thermal power temperature variation resistance variation absorbing layer thermal mass sensing element current biased • Figures of merit of bolometers Responsivity Time constant Noise Equivalent Power noise responsivity • low Geff high R •  high time constant • R NEP • R -  tradeoff related to Geff

6. Bolometer principle (3/3) • Through materials: • absorption layer (  responsivity  ) • high TCR materials (VOx, aSi, LSMO,... 2-6%) •  responsivity  • And fabrication/design: • miniaturisation, membrane • Cth time constant   • Gth responsivity  and time constant  trade-off responsivity/time constant Gth≈10-6 - 10-7 [W/K]; τ ≈10-100 [ms] • Performance improvement sensor improvement

7. What is smart ? (1/2) • IEEE 1451.2 definition : smart sensors are sensors “that provide functions beyond those necessary for generating a correct representation of a sensed or controlled quantity”. • conditioning electronics • ADC conversion • communication : wire (SPI, I2C), wireless SENSOR MICROSENSOR integration SENSOR PREPROCESSING SMART SENSOR I SENSOR PREPROCESSING PROCESSING SMART SENSOR II

8. What is smart ? (2/2) • another aspect: control and diagnostic functionalities: smart functions • configurability, • adaptability, • measurement range selection, • compensation, • self-test, • … • derive bolometers into heat balanced bolometers • in first attempt to overcome the responsivity/time constant tradeoff approach similar to that for accelerometers “force-balanced” accelerometers analog device micro-accelerometer

9. Heat balanced bolometer (1/6) • Electrical Substitution (ES) principle: “whatever the physical nature of the power received by an element is, either optical or electrical, its thermal equilibrium temperature is the same” • Open-loop to closed-loop operation mode we can use Joule power to balance optical power and operate in closed-loop mode amplification electronics open-loop closed-loop  bolometer current biased  PFB1, Joule effect, defines the thermal bias point Tbias.  When optical power, Popt, is absorbed onto the bolometer, PFB evolves to keep the total amount of power constant.

10. Heat balanced bolometer (2/6) • Advantages of closed-loop mode • reduced time constant (wider bandwidth) • direct power reading • operation at a determined working point • linearization, wider dynamic range • feedback power variationopposite to • optical power variation

11. Heat balanced bolometer (3/6) • Advantages of closed-loop mode • reduced time constant • direct power reading • operation at a determined working point • linearization, wider dynamic range max αfor max responsivity room temperature transition edge material to improve sensitivity (LSMO) thermal working point optimization

12. Heat balanced bolometer (4/6) • Advantages of closed-loop mode • reduced time constant • direct power reading • operation at a determined working point • linearization, wider dynamic range G high open-loop independent of G sets the temperature at which the bolometer operates closed-loop

13. Heat balanced bolometer (5/6) • Advantages of closed-loop mode • reduced time constant (wider bandwidth) • direct power reading • linearization, wider dynamic range • operation at a determined working point • Also smart functions • measurement range selection • self test • self-identification • … since a stimulus is available

14. Heat balanced bolometer (6/6) Our way to do this : Capacitively Coupled Electrical Substitution (CCES) • Principle: separate the electrical and thermal working points according to frequency • Advantages: • easier to control • only one resistor • Requires extra-electronics • Digital modulation • linear feedback electrical working point thermal working point & feedback feedback Joule power bias power Popt+Pfb=cst

15. Smart function (1/9)Control: operating mode, time constant OFF input ON output • Experimental results • open  closed-loop mode operation input output closed-loop open-loop total power constant in closed-loop temperature constant in closed-loop • time constant reduction (up to 200 so far in our experiments) • direct power output

17. Smart function (2/9) Control: gain and working point • adjust the measurement range to the input signal • measure small variations around a continuous component closed-loop • Measurements with a macroscale bolometer and digital electronics and infrared 1mW LED

18. Smart function (3/9) Control: gain and working point • In the context of imaging, contrast enhancement

19. Smart function (4/9) Diagnostic: self-test output x diagnostic function: «is the sensor working or not ?» input input output output output input input open-loop self-test closed-loop self-test

20. Smart function (5/9) Diagnostic: self-identification output diagnostic function: «how is the sensor working ?» x • monitor the evolution of the system in time (aging) • extract system parameters to optimize the controller input Example of experiment performed to demonstrate self-identification functionality • P  Geff  R  and  

21. Smart function (6/9) Diagnostic: self-identification output x • monitor the evolution of the system in time (aging) • extract system parameters to optimize the controller input prediction error actual output applied input predicted output input output estimated parameters estimated parameters • model parameters • time constant • responsivity least mean square adaptative algorithm running in parallel with the measurement

22. Smart function (7/9) Diagnostic: self-identification output x input input pseudo random sequence real time estimated gain • R  pressure T=2225s, pump switched off Geff=Gconv+Gcond+Grad atmospheric pressure • Geff  R  ; vacuum 20 mTorr real time estimated time constant measuredoutput • 

23. Smart function (8/9) Diagnostic: self-identification RB1 RB5 RB2 • monitor aging of the device • compensate for process discrepancies • self-calibration RB6 RB3 RB8 RB7 RB4 RB9 RB are different due to process variations

24. Smart functions (9/9) Summary • Control: • operating mode • time constant • gain/measurement range • working point • Diagnostic: • self-test • self-identification • self-calibration • heat balanced bolometer  smart bolometer • next step is integration MCU: MicroController Unit 3 cm macro-scale setup

25. Integration sigma-delta interface solution • thermal working point setting • self-test, self-identification input Σ inputs CMOS 0.35 µm, 3.3V measure output • both the feedback and the analog-to-digital conversion feedback bitstream input measurement dynamic range selection

26. Integration co-integration, pixel matrix Released in September 2013: VDEC, Tokyo-University, Mita-laboratory MEMS-CMOS co-integration process

27. Conclusion Smart bolometer • not only a matter of integration • introduction of smart functionalities • smart functionalities make bolometer smart “A rose with a microcontroller would be a smart rose”. Randy Frank, Understanding smart sensors. smart sensor intelligent sensor

28. A team project Thank you for your attention