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D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
September 19th 2012 – Oxford, UKTopical Workshop on Electronics for Particle Physics – TWEPP 2012
David [email protected]
Fondazione Bruno Kessler (FBK)Center for Scientific and Technological Research
Trento, Italy
Emerging Research Topics in Advanced Solid-State Image Sensors
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
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
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Image Sensors History
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Evolution of “Image Sensors”
500BCE - 1816 1816 - 1900
No Storing Era!
Niepce Camera
Eastman “Kodak”
Film Storing
Camera Mass Production
Leica (1925)
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
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)
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
CMOS Imaging Revolution
In 2008 More MPC than Films: Digital Imaging Era
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
CIS Technology and State-of-the-Art
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
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
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
CMOS Image Sensor Technology
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
CMOS Image Sensors SoA
Year
Fea
ture
Siz
e [u
m] Pixel Pitch
CIS Technology Node
Logic Gate Length
S.-H. Hwang – Samsung
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
• 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
This is what we can rely on…
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
“Conventional” Imagers:Solution to any problem?
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Lifetime Imaging
Source: Becker&Hickl Website
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
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;
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
3D Imaging
Capture for each point of the scene not (only) the intensity but the distance from the sensor
• We live in a three-dimensional world• We have 3D perception
2D
f(x;y)=Intensity f(x;y)=(Intensity, Distance)
3D
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
3D Imaging: ToF
TargetD
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
We need image sensors with sub-nanosecond time resolution (all), and single-photon
sensitivity (not for 3D)
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
CMOS Single-Photon Detectors(Part 1)
How to achieve Single-photon sensitivity and sub-nanosecond resolution?
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Photodiode, APD, SPAD
• A SPAD is a photodiode biased beyond its breakdown voltage (Geiger mode)
Photo-multiplication effect allows for
SINGLE PHOTON DETECTION
20
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
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
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
SPAD with a simple pn Junction?
• At the edges (shallow junctions, microplasmas) high electric fields
• Premature breakdown at the sensor periphery
Active area!
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Desirable active area
Key point: guard-ring structure is needed!
SPAD with a simple pn Junction?
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
SPADs in CMOS Technologies
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
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 processA. Rochas at Al., Rev. Sci. Instrum., 2003
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
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
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
SPAD-based Imagers: 1. Megaframe Sensor (Digital)2. SPAD with analog readout
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
The MEGAFRAME Projectwww.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
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Pixel Architecture
• 1.2V transistors• Two rings implemented: 50ps and 170ps delay
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
MEGAFRAME Sensors
• 130nm imaging process• 160x128 array of pixels• 50x50um2 pixel• Pixel includes SPAD; 10b,
55ps TDC; 10b memory• Transistors: 45M
MF128 SensorMF32 Sensor
C. Veerappan et al., ISSCC’11D. Stoppa et al., ESSCIRC’09
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
TDC ArchitectureRing fine state
• 1.2V transistors• Two rings implemented: 50ps and 170ps delay
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
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
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Blue laser Red laserTDCs Uniformity
Jitter and Uniformity
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Ref. Array size
TechnologyPixel pitch
Fill Factor
In-pixel circuit
[1] 128x128 0.35um HV 25um 6%Inverter + active quenching
transistors (TDC at column level)
[2] 60x48 0.35um HV 85um 0.5% 2 gated counters
[3] 128x96 130nm CIS 44.6um 3.2%Time-Of Flight extraction
circuit
[4] 160x128 130nm CIS 50um 1% Time-to-Digital Converter
[5] 3x3 90nm CIS 5um 12.5%Inverter + passive
quenching (3T)
[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
Fill Factor Issue with SPAD Sensors
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
SPAD Quenchingcircuit
Gate Counter
Output: number of counts inside the observationtime window
Inputphotons
All n-MOS 12-transistor pixel
(digital pixel requireshundreds of transistors)
Analog pixel schematic diagram
Observation window
Analog Approach
L. Pancheri et al. 2011
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Array size: 0.8 x 0.8 mmPixel pitch: 25umFill factor: 20.8%
SPAD Sensor with Analog Readout
L. Pancheri et al. 2011
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Pixel output histogram
0
1 23
4
5
6
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0 2 4 6 8 10 12 14 16
Sig
nal [
V]
Time delay [ns]
1.1ns
2.7ns4.4nsGate width FWHM:
Time-gating Performance
SPAD Sensor with Analog Readout
L. Pancheri et al. 2011
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Time-Resolved Compact Pixels for 3D ToF Imaging
(Part 2)
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Phase-sensitive light detection
Received Light Echo
Electrical Demodulation Signal
DC Component
LP Filter
G(t) = sin(ωmt)
R(t) = K sin(ωmt – Δφ)
Iph(t)= K/2 [cos(Δφ) – cos(2ωmt – Δφ)]
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Demodulationsignal
Received light
Iph
Cint
ΔVout µ cos(Δφ)
Δφ µ TOF
1x
Demodulation pixel concept
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Demodulating detectors:
• Photogate-based devices
• Pinned photodiode devices
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Basic Photogate Demodulator
VG2 > VPG > VG1
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
VG2 < VPG < VG1
Electron transport speedlimited by diffusion: From Si substrate From PG to D1 and D2
Basic Photogate Demodulator
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Electron diffusion time
n
2DIFF
DIFF D
Xt
Few microns for high frequency modulation
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Pixel electronics: basic readout
• 1-tap pixel: 3T readout• Compact - high fill factor• Readout of 4 sequential frames is needed
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
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, 2003D. Stoppa, et al., Proc. ISSCC, 2010
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Pixel scaling
• Small pixel size increases device BW• Larger pixel size recovered by binning
Ref. Pixel pitch [μm]
Binning Contrast [%]
Mod. Frequency [MHz]
[1] 12 1 35 5
[2] 6 2x2 n.a. 10
[3] 3.65 4x4 52.8 20
[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
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Pixel size and resolution
QVGA
VGA
[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
[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
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
“Imaging Waves”
Terahertz Radiation Detectors(Part 3)
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
The THz GapX Ray UV VIS IR uW, RF Radio
100um 1mm
ElectronicsOptics
H. Sherry et al., ISSCC’12
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
How to Detect THz?
• CMOS QE<0.001% THz Radiation
Micrometer Antenna
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Antenna…and then?
fT<300GHz for CMOS
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Solution 1: Antenna+uBolometer
THz Radiation
Antenna
Load
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
MUTIVIS project
Multispectral Terahertz, Infrared and Visible Imaging and Spectroscopy
Multispectral
optics
Cam
eracontroller
FP
Asensor
Scene
VisibleInfrared
Terahertz
Tunable narrow band Terahertz Source: 0.5-5 THz, =100 GHz
Imaging + spectroscopydemonstrator
THz radiation
Multisp. image
Camera
Source
Airport, train station, etc.
Field test in pilot application airport security
R & D Validation and Field Test
Imaging sensor
THz source
Demonstrator
proof of principle proof of principle development prototype prototype
technologicalmaturity
• BOSCH• CEA-LETI• FBK• Rainbow Photonics• Flughafen Zurich• ETH Zurich
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Pixel Architecture
• Visible: photodiodes in CMOS (400-900nm)• Infrared: bolometers above-IC (8-14m)• THz: antenna + bolometers above-IC (1-3THz)
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Sensor Architecture
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Hybrid Sensor Fabrication Steps
CMOS
productio
n
• Wafer production with special finishing• Wafer level testing & die level characterization
BOLO
process
• Additional wafer level steps• Wafer level testing, selection and dicing
Vacuum
packagin
g
• Selection of proper multispectral window• Packaging in standard IR vacuum package
System
integratio
n
• Low-noise supplies & reference• FPGA waveforms generation
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
• Propagation of waves through electron plasma [Dyakonov, Shur]
• Oscillation of electron density– Faster than current due to charge
transport– Resonant detection possible
• Solution of differential equations expressing charge in space and time
s
L
s
Lsh
Tk
qV
TkC
mqLjTk
qV
TkC
mqLjms
qVV
B
eff
BoxB
eff
Box
rfDS
2cos
2exp
21
1
exp2
1
1
422
2
222
20
222
20
2
2
Solution 2: All-CMOS THz Detector
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Fully CMOS THz Pixel
H. Sherry et al., ISSCC’12
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
THz Imager Readout
H. Sherry et al., ISSCC’12
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Fully CMOS THz Camera
H. Sherry et al., ISSCC’12
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Solution 3: Schottky diode
R. Han et al., ISSCC’12
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Conclusive Remarks on SPADs
• There are many applications requiring:
Single-Photon and Time-Resolved Imaging
• CMOS SPADs available in different technologies
• Performance improvements in the last 5 years
• More research groups on the subject
• Pixel pitch is shrinking, fill factor increasing
• New application domains on the horizon (PET, Lab-on-chip)
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Conclusive Remarks on 3D-ToF
• 3D Imagers are becoming more and more popular
• ToF techniques take advantage of:
- Improvements in the lighting industry (LEDs, SS-Lasers)
- CMOS Image Sensors technologies
- Increased interest from big players • Challenges for Portable Devices Market:
- Dramatic reduction of the power consumption
- Color 2D co-integration with 3D
- Outdoor operation
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Conclusive Remarks on THz
• THz Imaging is increasingly popular
• New detectors are under development:
- cost reduction
- reasonable pixel pitch to obtain scannerless imaging
• Still a lot of work to be done:
- lack of THz sources (at reasonable cost)
- difficult to find calibrated testing labs
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Thank you!
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
CIS technology: 1.4um pixels
Front-side CIS (Aptina)R. Fontaine - Chipworks
Back-side CIS (Fujifilm/Toshiba)R. Fontaine - Chipworks
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
3D-TOF with in-pixel PD-SD
R. Walker at Al., ISSCC’11
• Phase Shift is directly measured at pixel-level by event-driven PDSD;
• 128x96-pixel array implemented in 130nm CIS;
• s=160mm @ 2.4m
• Pixel Pitch 44.6um, FF=3%
• First implementation of “real” D-TOF: output data volume greatly reduced
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
ΔVout
Δφ
AMP
OFF
V0
V1
V2
V3
4 samples per pixel are needed
Phase shift measurement
02
13
VV
VVatanΔφ
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Mutivis Architecture
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
Lifetime Imaging Challenges
• Each pixel must be capable of:
- Detect light with Single-Photon Sensitivity - Measure the distribution of photons arrival time:
Range: 1n-100ns; Resolution: <100ps
• Main Issues:
- Pixel dimension and fill factor- Uniformity along the pixel-array- Power consumption- Very high time precision
D. Stoppa – TWEPP’12 – Oxford, UK – 19th September 2012
TOF Image Sensors Challenges
• Light is fast! c=3x108m/s 1cm=>66ps High Time Accuracy
• High Dynamic Range
• High Sensitivity (QE, FF)
• Scannerless 3D Imagers: pixel dimensions, uniformity, power consumption etc.
• Immunity to background illumination