September 19 th 2012 – Oxford, UK

1. Emerging Research Topics in Advanced Solid-State Image Sensors David Stoppa stoppa@fbk.eu Fondazione Bruno Kessler (FBK) Center for Scientific and Technological Research Trento, Italy September 19th 2012 – Oxford, UK Topical Workshop on Electronics for Particle Physics – TWEPP 2012

2. Outline • Image Sensor Evolution • CMOS Image Sensor Technology and SoA • Conventional Imagers: solution to any problem? • Emerging Research Topics: • Time-Resolved Imaging: Single-Photon • Time-Resolved Imaging: 3D Imaging • Multispectral Imaging: Terahertz • Conclusions and future perspective Part 1 Part 2 Part 3

3. Image Sensors History

4. Evolution of “Image Sensors” Niepce Camera Leica (1925) Eastman “Kodak” 500BCE - 1816 1816 - 1900 Camera Mass Production No Storing Era! Film Storing

5. First (Electronic) Image Sensors • 1966 – Phototransitor array (Westinghouse) • 1969 – CCD, Smith and Boyle (BellLabs) • 1974 – 512x320 CCD imager (Sony) • 1983 – 1Mpixel CCD camera (TI) • 1985 – Color array (Hitachi) • 1987 – CCD Broadcast camera (NEC) • 1990 – Passive pixel array (Univ. of Edinburgh) • 1996 – 1Mpixel array (AT&T, JPL) • 1997 – CMOS Active Pixel • 1996 – 66Mpixel CCD (Philips) • 2002 – 14Mpixel CMOS (FillFactory)

6. CMOS Imaging Revolution In 2008 More MPC than Films: Digital Imaging Era

7. CIS Technology and State-of-the-Art

8. CMOS Image Sensor Technology • Pinned photodiode: • 1/10 dark current • Integration capacitance is small (floating diffusion) • Correlated-Double-Sampling -> no more kT/C • Sharing of in-pixel electronics

9. CMOS Image Sensor Technology

10. CMOS Image Sensors SoA Pixel Pitch CIS Technology Node Feature Size [um] Logic Gate Length Year S.-H. Hwang – Samsung

11. This is what we can rely on… • 65nm CMOS-CIS, Pinned photodiode: • Pixel pitch <1.1um • Global shutter, DR>80dB • Extra pixel-level circuitry (8um pitch): • Rolling shutter, DR>140dB • In-pixel Buried SF, High-Gain Column Amplifier and CMS: • PN<0.7e • Special Column-level ADCs: • UHDTV, 33Mpixel@120fps

12. “Conventional” Imagers: Solution to any problem?

13. Lifetime Imaging Source: Becker&Hickl Website

14. PET/MRI Scanners • Detector • A scintillator crystal converts the incoming gamma-rays into visiblephotons; • Photon “shower” hits the sensor spread in space, close in time;

15. 3D Imaging • We live in a three-dimensional world • We have 3D perception 2D 3D f(x;y)=(Intensity, Distance) f(x;y)=Intensity Capture for each point of the scene not (only) the intensity but the distance from the sensor

16. 3D Imaging: ToF D Target

17. We need image sensors with sub-nanosecond time resolution (all), and single-photon sensitivity (not for 3D)

18. How to achieve Single-photon sensitivity and sub-nanosecond resolution? CMOS Single-Photon Detectors (Part 1)

19. Photodiode, APD, SPAD • A SPAD is a photodiode biased beyond its breakdown voltage (Geiger mode) Photo-multiplication effect allows for SINGLE PHOTON DETECTION 20

20. SPAD Operation • Operation Loop: • 1. Entering the Geiger region at VB+VE (meta-stable point) • 2. Avalanche • 3. Quenching • 4. Recharging to 1 VE: Excess bias voltage

21. SPAD with a simple pn Junction? • At the edges (shallow junctions, microplasmas) high electric fields • Premature breakdown at the sensor periphery Active area!

22. SPAD with a simple pn Junction? Desirable active area Key point: guard-ring structure is needed!

23. SPADs in CMOS Technologies

24. GR#1: Low-doping Diffusion • In Deep-submicron high doping concentration, shallow implants • -> High DCR • Quasi-neutral field region at edges -> Long diffusion tail • Limited scalability • Require HV process A. Rochas at Al., Rev. Sci. Instrum., 2003

25. GR#2: STI and Retrograde NWell • Suitable for deep-submicron technologies • Compatible with any triple-well process • Non optimal scalability • Excellent DCR performance J. A. Richardson et al., Photonics Tech. Lett., 2009

26. SPAD-based Imagers: Megaframe Sensor (Digital) SPAD with analog readout

27. The MEGAFRAME Project www.megaframe.eu EPFL (E. Charbon), Univ. of Edinburgh (R. Henderson),STMICRO (L. Grant, J. Richardson), Univ. of Pavia (S. Donati),FBK (D. Stoppa) • Goal: Create a high-speed, CMOS-based FLIM image sensor • Use a single-photon avalanche diode (SPAD) and a TDC in every pixel • Eliminate scanning, gating/shuttering • Increase frame rate • Decrease exposure time, fit time • Move towards video-rate FLIM • Recover fill factor losses with microlenses

28. PixelArchitecture • 1.2V transistors • Two rings implemented: 50ps and 170ps delay

29. MEGAFRAME Sensors MF128 Sensor MF32 Sensor C. Veerappan et al., ISSCC’11 D. Stoppa et al., ESSCIRC’09 • 130nm imaging process • 160x128 array of pixels • 50x50um2 pixel • Pixel includes SPAD; 10b, 55ps TDC; 10b memory • Transistors: 45M

30. TDC Architecture Ring fine state • 1.2V transistors • Two rings implemented: 50ps and 170ps delay

31. On-chip Calibration • The TDCs are locked to that of an integrated PLL that contains a replica of the TDC ring oscillator • This provides global process, voltage, & temperature stabilization, when locked to a stable external clock

32. Jitter and Uniformity Blue laser Red laser TDCs Uniformity

33. Fill Factor Issue with SPAD Sensors [1] C. Niclass et al., ISSCC 2008 [2] C. Niclass et al., ESSCIRC 2008 [3] R. Walker et al., ISSCC 2011 [4] C. Veerappan et al., ISSCC 2011 [5] R.K. Henderson et al., IEDM 2010

34. Analog Approach Output: number of counts inside the observation time window Input photons Quenching circuit SPAD Gate Counter Observation window Analog pixel schematic diagram All n-MOS 12-transistor pixel (digital pixel requires hundreds of transistors) L. Pancheri et al. 2011

35. SPAD Sensor with Analog Readout Pixel pitch: 25um Fill factor: 20.8% Array size: 0.8 x 0.8 mm L. Pancheri et al. 2011

36. SPAD Sensor with Analog Readout Time-gating Performance Pixel output histogram 2 1 3 4 0 5 6 L. Pancheri et al. 2011

37. Time-Resolved Compact Pixels for 3D ToF Imaging (Part 2)

38. Phase-sensitive light detection Received Light Echo R(t) = K sin(ωmt–Δφ) Electrical Demodulation Signal G(t) = sin(ωmt) Iph(t)= K/2 [cos(Δφ) – cos(2ωmt – Δφ)] LP Filter DC Component

39. Demodulation pixel concept Demodulation signal 1x ΔVoutµ cos(Δφ) Δφµ TOF Cint Iph Received light

40. Demodulating detectors: • Photogate-based devices • Pinned photodiode devices

41. Basic PhotogateDemodulator VG2> VPG > VG1

42. Basic Photogate Demodulator VG2< VPG < VG1 • Electron transportspeedlimited by diffusion: • From Si substrate • From PG to D1 and D2

43. Electron diffusion time Few microns for high frequency modulation

44. Pixel electronics: basic readout • 1-tap pixel: 3T readout • Compact - high fill factor • Readout of 4 sequential frames is needed

45. Pinned photodiode demodulator • Available in CIS processes • 100% contrast in DC • Small bandwidth due to: • Lateral diffusion • Residual potential barrier between PD and FD V. Berezin, et al., US Patent 2003/0213984A1, 2003 D. Stoppa, et al., Proc. ISSCC, 2010

46. Pixel scaling • Small pixel size increases device BW • Larger pixel size recovered by binning [1] S.-J. Kim, et al., IEEE Electron Dev. Lett., 2010 [2] S.-J. Kim, et al., Proc. VLSI Symp., 2011 [3] S.-J. Kim, et al., Proc. ISSCC, 2012

47. Pixel size and resolution VGA QVGA [6] S.J. Kim et al., Proc. VLSI Symp., 2011 [7] L. Pancheri et al., Proc. ISSCC 2012 • [8] S.J. Kim et al., Proc. ISSCC 2012 • [9] W. Kim et al., Proc. ISSCC 2012 [1] R. Lange, IEEE J. Quantum Electron., 2001 [2] T. Oggier et al., Proc. SPIE, 2004 [3] T. Möller et al., Proc.1st Range Imaging Research Day at ETH, 2005 [4] S. Kawahito et al., IEEE Sensors J., 2007 • [5] L. Pancheri et al., Proc. SPIE 2010

48. “Imaging Waves” Terahertz Radiation Detectors (Part 3)

49. The THz Gap UV VIS IR uW, RF Radio X Ray Optics Electronics 100um 1mm H. Sherry et al., ISSCC’12

50. How to Detect THz? • CMOS QE<0.001% THz Radiation Micrometer Antenna