Developing 3- -D Imaging D Imaging Developing 3 Sensors Sensors - PowerPoint PPT Presentation

Developing 3- -D Imaging D Imaging Developing 3 Sensors Sensors Problems and Technologies Problems and Technologies Silvano Donati Donati Silvano Department of Electronics, University of Pavia, Italy web: http://www-3.unipv.it/donati Coupling Phenomena and Applications, by S.Donati, Univ Pavia

Outline Outline • outlook to 3D applications • time ‐ of ‐ flight measuring technique • comparing PULSED and SWM approaches • developing the Photo ‐ demodulator in CMOS • measurements and conclusions

3- -D Imaging D Imaging 3 Today’s technology is ready to develop photodetectors for the three ‐ dimensional world !! 2D 2D adding distance information pixels describe pixels describe the intensity morphology pattern I(x,y) z(x,y)

typical applications typical applications • Homeland security • Navigation aids • Virtual reality • Robotics • Cultural heritage • Ambient assisted living

techniques for 3D imaging techniques for 3D imaging bulky, requires scanning • Triangulation short distance medium/low resolution very high resolution • Interferometry expensive, critical to operate Compact, may be scannerless Fast acquisition Large distance range • Time-of-flight Cost-effective (pulsed or SWM) Active (illuminator required) Ambiguity range limitation

Time- -of of- -Flight rangefinders Flight rangefinders Time Δτ SW (sine wave) Modulated PULSED D = c Δτ Δτ Optical Power Dt 2 Received Emitted Time

in most applications, to be interesting… … in most applications, to be interesting both PULSED PULSED and and SW SW 3 3- -D D developments developments both should entail: should entail: - integration of time integration of time- -of of- -flight pixel flight pixel - on- -board technology with the Silicon board technology with the Silicon on CMOS industry standard (and … … CMOS industry standard (and !!) technology cost !!) technology low- -cost low - minimum invasiveness (optical power) minimum invasiveness (optical power) - of the active illumination required of the active illumination required

analyzing Time- -of of- -Flight rangefinders: Flight rangefinders: analyzing Time pulsed vs vs SWM SWM pulsed 2 /D r 2 GP s = (S/N) P n 4L eq theoretically equivalent at the quantum limit at 1M receiver noise power = equal average power, P n d e r e s 1 mW t l e u p m e l e t but PULSED is less 1 μ W sensitive to stray light, 1k has some safety issues 1 nW equivalent power G P and requires more s (W) d e t a l u d h o p m a bandwidth to circuits. 1 r 1 pW W g o S p o t SW-modulated is short- distance, is about 3-D camera eyesafe, but has range 1m λ =0.85 μ m S/N = 10 D =100mm r ambiguity to circumvent 1k 10 k 100 1.0 10 normalized distance L/¦T (m) atm

other features of PULSED and and SW SW other features of PULSED - Pulsed 3 Pulsed 3- -D requires a fast (sub D requires a fast (sub- -ns) detector ns) detector - for operation on short distances, and very fast for operation on short distances, and very fast time sorters to measure the ns- -range time range time time sorters to measure the ns SPADs and Counters with TAC and Counters with TAC delay SPADs delay -this makes the pixel large and fill this makes the pixel large and fill- -factor low, factor low, - requiring a lens- -array for sensitivity recovery array for sensitivity recovery requiring a lens - SW works on moderate frequency (20 to 100 SW works on moderate frequency (20 to 100 - MHz) for 3- -D short range, and by incorporating D short range, and by incorporating MHz) for 3 a demodulator into the detector circuits are a demodulator into the detector circuits are greatly simplified, and fill- -factor is high factor is high greatly simplified, and fill

detour on the PULSED PULSED 3 3- -D D approach approach detour on the - in 3 in 3- -D, D, PULSED PULSED is a competitor to SWM is a competitor to SWM - but calls for a fast (sub- -ns) detector able to ns) detector able to but calls for a fast (sub resolve the sub- -ns propagation times of ns propagation times of resolve the sub short- -range applications range applications short - the the SPAD SPAD (Single Photon Avalanche Detector) (Single Photon Avalanche Detector) - is the suitable choice of photosensor photosensor is the suitable choice of - SPAD SPAD is compatible to fine is compatible to fine CMOS technology - CMOS technology - an an FET European Program pursued pursued - STREP European Program FET- -STREP development of a 120- -nm CMOS 3 nm CMOS 3- -D and fast D and fast development of a 120 spectroscopy imaging ( 32x32 32x32 and and 128x160 spectroscopy imaging ( 128x160 pixels) device – – the the MEGAFRAME MEGAFRAME project project pixels) device

CMOS SPAD parameters CMOS SPAD parameters μ m active diameter devices has been designed a 50 μ m active diameter devices has been designed a 50 in 120 ‐ ‐ nm CMOS with good performances of: nm CMOS with good performances of: in 120 40 40 Δ V=1.0 0.6 excess voltage (mV) 20 0.2 0 temp ( ° C) high probability of detection high probability of detection low dark counts rate low dark counts rate (35%@1- -V overdrive) V overdrive) (35%@1 μ m - μ (40 Hz for a 6- m dia dia.) .) (40 Hz for a 6

CMOS SPAD parameters II CMOS SPAD parameters II and, not less important: and, not less important: 50 ns low afterpulsing afterpulsing low sub- -ns time resolution ns time resolution sub (negligible @ T T ho >200ns) (negligible @ ho >200ns) (61 ps (61 ps rms rms) )

On- -board pixel processing board pixel processing On processing circuits processing circuits implemented by implemented by CMOS technology CMOS technology μ m - μ in a 50- m dia dia. pixel . pixel in a 50 area around the area around the μ m SPAD: - μ 6- m SPAD: 6 -active quenching active quenching - - premaplifier premaplifier - - TAC TAC - -comparator comparator - -8 8- -bit memory bit memory - Stoppa et al.: ESSCIRC 2009

the CMOS SPAD pixel… … the CMOS SPAD pixel the pixel, 50- μ m by side …and and the 32x32 the 32x32 array array … = A A ph /(A /(A qc +A +A ph ) ) chip, 4- -mm mm by by side side FF = chip, 4 FF (~ 0.02 in example above) (~ 0.02 in example above) Stoppa et al.: ESSCIRC 2009

fill- -factor recovery in factor recovery in SPAD fill SPAD 8- μ m A ph A ph A qc A SPAD qc quenching and/or sorting circuits achieved lens 5 array concentration 0.25 50 μ m 0.2 10 5 = A A ph /(A qc +A ph ) FF = ph /(A qc +A ph ) 0.15 FF 15 NA ~ 0.02 in example above ~ 0.02 in example above 10 0.1 15 20 μ m - μ 20 then we use a 50- m dia dia. . then we use a 50 25 0.05 30 lens- -array to concentrate array to concentrate lens C= 35 0 incoming optical power incoming optical power 0 -10 -5 5 10 Z ( μ m)

Example of 3D image pickup with the Example of 3D image pickup with the 32x32 SPAD array 32x32 SPAD array Accuracy: • 1mm (100 frames) Frame rate: • 1Hz 8-bit digital output

going back to SW- -modulated modulated… … going back to SW - the the SWM is attractive for 3 SWM is attractive for 3- -D if we can D if we can - simplify data analogue processing simplify data analogue processing - then, we are asked to devise a high then, we are asked to devise a high- - - efficiency photodetector photodetector, working with , working with efficiency shallow epi epi- -layer of a CMOS, low cost, layer of a CMOS, low cost, shallow standard industry process. standard industry process. - the answer has been a specially the answer has been a specially - designed, CMOS- -compatible, high FF, compatible, high FF, designed, CMOS photodetector demodulator demodulator photodetector

principle of SWM SWM telemeter telemeter principle of R(t) = K sin[ ω m t ‐ Δφ ] Received Light Echo LP I ph ( θ ) = K/2 cos( θ + Δφ ) M(t) = sin( ω m t + θ ) Filter Demodulation Measured LO Signal correlation function recovery of phase Δφ amenable to CMOS integration of the pixel: the detected demodulation signal I ph (t) is sampled on 4-phases θ periods of the local oscillator M(t) so as to supply I 1 = I ph ( θ =0°) , I 2 = I ph ( θ =90°), I 3 = I ph ( θ =180°) , I 4 =I ph ( θ =270°) , then we compute ⎛ ⎞ − I I ⎜ ⎟ Δ ϕ = 4 2 arctan ⎜ ⎟ − ⎝ ⎠ I I 3 1

let’s now have a look at sensor architecture o design of a new photo-demodulator o pixel design o array architecture

PDD, the Photo- -Demodulator Detector Demodulator Detector PDD, the Photo M1, M2: modulation electrodes D1, D2: collection electrodes first reported by: Van Nieuwenhove, et al., Proc. Symp. LEOS Benelux Chapter, 229-32 (2005)

more on the PDD more on the PDD output I M - I M by pulsing a current I M I ph (50 μ A typ.) between D1 M1 light M2 D2 + 3 V + 1 V + 3 V -1 V electrodes M1 and n p p n M2, we can switch c photocurrent I ph from +- output D1 to output I M output - I M D2. If current I M is a I ph sine wave, process is + 3 V + 1 V + 3 V -1 V n p p n a demodulation of the c detected signal (wow!) M1, M2: modulation electrodes, D1, D2: collection electrodes of the photo-demodulator detector (PDD)