CMOS Sensor for AO. Backside-Illuminated, high QE, 3e- RoN, fast 700fps, 1760x1760 pixels CMOS Imager for AO with highly parallel readout

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1 CMOS Sensor for AO Backside-Illuminated, high QE, 3e- RoN, fast 700fps, 1760x1760 pixels CMOS Imager for AO with highly parallel readout Mark Downing, Johann Kolb, Gert Finger, Norbert Hubin, Javier Reyes, Olaf Iwert European Southern Observatory ESO ( Martin Fryer, Paul Jorden, Andrew Walker, Andrew Pike, Paul Jerram, Jerome Pratlong e2v technologies ltd ( Bart Dierickx, Arnaud Defernez, Benoit Dupont Caeleste, Antwerp, Belgium ( Philippe Feautrier, Eric Stadler Institut de Planétologie et d Astrophysique de Grenoble ( Jean-Luc Gach, Philippe Balard, Christian Guillaume Laboratoire d'astrophysique de Marseille LAM ( Downing SPIE Amsterdam

2 Outline Adaptive Optics Deployment of zero noise L3Vision CCD220 Next challenge WFS for E-ELT Specifications of the large E-ELT Wavefront Sensor Technology solutions investigated Results of Technology Demonstrators Wavefront Sensor Architecture and Design Downing SPIE Amsterdam

3 Adaptive Optics (AO) - removing the twinkle of the stars Deformable mirror compensates the distorted wavefront, achieving diffractionlimited resolution 4 1 Wavefronts from astronomical objects are distorted by the Earth s atmosphere, reducing the spatial resolution of large telescopes to that of a 10 cm telescope OFF 3 Control System computes commands for the deformable mirror(s) 2 Wavefront Sensor measures deviation of wavefront from a flat (undistorted) wave Downing SPIE Amsterdam 2012 ON 3

4 e2v L3Vision CCD220 OP 4 OP 3 OP 2 OP 1 Store slanted to allow room for multiple outputs. Gain Registers Gain Registers Store Area Image Area 240x µm Image Area 240x µm Metal Buttressed 2Φ 10 Mhz Clocks for fast image to store transfer rates. Store Area Gain Registers Gain Registers OP 8 OP 7 OP 6 OP 5 8 L3Vision Gain Registers/Outputs Each 15Mpix./s. e2v CCD220: Split frame transfer CCD 240x µm pixels 8 L3Vision EMCCD outputs < 0.1 e- RoN at 1,500 fps Integral Peltier for cooling to -45 C Downing SPIE Amsterdam

5 Deployment of CCD Science Devices in house 16 Std Silicon 4 Deep Depletion See poster Javier Reyes Thursday evening AO session An Overview Front-end of Analog AONGC Board and the ESO Adaptive Optics Wave Front Sensing Camera 7 Pre-series cameras complete and in use for Instrument Integration Production run of 18 cameras for VLT AO Facility (MUSE HAWK-I), SPHERE, and others will start soon. Downing SPIE Amsterdam

6 Commercially available Cameras using CCD220 Technology transfer NGC I/F Boards Technology transfer to industry Go along to booth # July See talk Philippe Feautrier Monday 15:50 pm session Advances in detector technologies for visible and infrared wavefront sensing CCD220 OCam Boards Downing SPIE Amsterdam

7 CCD220 Impressive (Measured) Test Results Requirement Measured Specification Frame Rate: > 1,500 fps >1,200 fps Read noise: at gain of fps < 0.1 e- < 1.0 e- Image Area Full Well: > 200 ke- > 5,000 e- Cosmetics: # of traps, bright/dark defects 0 < 25 Dark Current at 100fps -40ºC: < 0.02 e-/pix/frame < 0.04 e-/pix/frame Key goal specs are meet Deep Depletion (highly sought after for better red response) is working as well as standard silicon device. Next Step: Increase frame rate to 2,500 fps to extend use to E-ELT XAO (Extreme AO). Downing SPIE Amsterdam

8 Advantage of Multiplication Gain Downing SPIE Amsterdam

9 AO Detector needs for E-ELT Low Order AO Shack Hartmann Quad -Cell Extreme AO 2.5 khz ultra low-noise detector possibly reuse CCD220 Pyramid TipTilt Sensors Existing visible high performance detector (e.g. CCD220) IR WFS Other WFS Guiding IR TipTilt sensors NGS - Natural Guide Star NGS Ground Layer AO NGS Single Conjugate AO LGS - Laser Guide Star LGS Multi- Conjugate AO Laser Tomography AO Multi- Object AO LGS Ground Layer AO Large Visible AO WFS Detector See talk Gert Finger Monday 15:50pm session Evaluation and optimization of NIR HgCdTe avalanche photodiode arrays for adaptive optics and interferometry Downing SPIE Amsterdam

10 Large Visible AO WFS Detector needed to sample the spot elongation Sodium layer T ~ 10km Sodium Laser Guide Stars Frame rate ~1 kframe/sec require bright guide stars With natural guide stars only 1% of the sky is accessible Sodium layer at km altitude can be stimulated by Laser to produce artificial guide stars anywhere on the sky LLT Pupil plane Detector plane Distance from launch site H ~ 80km Predicted spot elongation pattern Downing SPIE Amsterdam

11 ¼ WFS image Natural Guide Star: 84x84 sub-apertures of 8x8 pixels NGSD Laser Guide Star: 84x84 sub-apertures of 20x20 pixels LGSD Downing SPIE Amsterdam

12 Location of Wavefront sensors on the E-ELT WFS adaptor Some instruments also contain WFS WFS adaptor detectors Deformable Mirror 38 m diameter WFS arms (contain WFS 65 m high detectors) Instruments Downing SPIE Amsterdam

13 Large Visible AO WFS Detector Top Level Requirements Parameter Specification Comment Array Format 1680x1680 pixels Up to 84 x 84 sub-apert. each 20x20 pixels to sample the spot elongation Pixel Size µm Large to simplify the optical design Wavelength nm (NGS) 589nm (LGS) QE > 80 % High Frame Rate 700 fps Fast, low latency; up to 1000fps with reduce performance RON < 3 e- rms Low read noise Storage Capacity < 4000e-/pixel Expect few photons Cosmetics < 0.1% bad pixels Good; very few bad sub-apertures Ease of use/compact size: low pin count; goal < 200 pins integral Peltier low power < 5W integrated read-out electronics - digital I/F preferred 27/06/2010 SPIE 2010: AO WFS Detectors 13

14 ELT WFS DETECTOR Multi-phase plan to progressively retire risk Design Study Design Study Retire Pixel Risks 2018 Technology Validation Development Testing/ Acceptance Technology Demonstrators Several Industrial Design Studies Many different technologies investigated Natural Guide Star Detector NGSD Most promising were CMOS Imager, APD array and orthogonal EMCCD Authorize Production Testing Retire Architecture/ Process Risks Laser Guide Star Detector LGSD Engineering exercise Testing Full size device meeting all specs. Authorize Production Production Phase 30 NGSD Science Devices NGSD Production LGSD Production 30 LGSD Science Devices Downing SPIE Amsterdam

15 ELT WFS DETECTOR Multi-phase plan to progressively retire risk Design Study Design Study Retire Pixel Risks 2018 Technology Validation Development Testing/ Acceptance Technology Demonstrators Natural Guide Star Detector NGSD Several Technology Demonstrators were built: All CMOS Imagers - judged most likely to succeed Searched for most suitable pixel and test various video processing/adc concepts Authorize Production Testing Retire Architecture/ Process Risks Laser Guide Star Detector LGSD Engineering exercise Testing Full size device meeting all specs. Authorize Production Production Phase 30 NGSD Science Devices NGSD Production LGSD Production 30 LGSD Science Devices Downing SPIE Amsterdam

16 ELT WFS DETECTOR Multi-phase plan to progressively retire risk Design Study Design Study Retire Pixel Risks 2018 Technology Validation Development Testing/ Acceptance Technology Demonstrators CMOS Scaled Down Demonstrator Natural Guide Star Detector NGSD Retire architectural risks by fab. ~ ¼ imager Authorize Production Usable for first light E-ELT AO systems Testing Retire Architecture/ Process Risks Laser Guide Star Detector LGSD Engineering exercise Testing Full size device meeting all specs. Authorize Production Production Phase 30 NGSD Science Devices NGSD Production LGSD Production 30 LGSD Science Devices Downing SPIE Amsterdam

17 3T Pinned PhotoDiode VRST VSF Read Time reset 1 SF 2 select 3 select reset Exposure Time p + p-si n + Column bus PPD start and other at end of exposure, Column bus Simplest guaranteed to work, but requires two digital samples spaced in time; one at video chain must be very stable with low 1/f noise. V o +v n Sample reset v o +v n +v s Sample signal CDS = signal - reset Downing SPIE Amsterdam

18 4T Pinned PhotoDiode VRST VSF Read Time reset 1 SF 2 select select reset transfer 4 3 transfer Exposure Time p + p-si n + Column bus Column bus V o +v n v o +v n +v s PPD SN Solves the problem of two digital samples per frame, but relies on good charge transfer from photodiode to sense node; not known for large 24µm pixel. acds = two samples close in time Downing SPIE Amsterdam

19 5T Pinned PhotoDiode Wide Dynamic Range p + C 5 Low gain reset p-si transfer 4 VRST 1 n + SF VSF 2 select 3 Column bus Low noise obtained by using very high gain > 100 uv/e-, however, saturation occurs at 1V/100 uv/e- =10,000e- Solution is to have switched capacitor on sense node and sample twice; high gain (/low noise) then low gain. Unfortunately increases the capacitance and lowers the gain. Putting reset transistor on other side of gain switch restores high gain mode. PPD SN Downing SPIE Amsterdam

20 7T Pinned PhotoDiode for potential use with PULSED Laser guide star VRST VRST VSF 7 resetppd reset 1 SF 2 select Na Layer close open Gated Shutter sample 4 hold 5 transfer 6 3 p + n + p-si Column bus Rayleigh back-scatter PPD SH SN Laser Launch Telescope * Concept courtesy of Jim Beletic and Stefen Lauxtermann of Teledyne Downing SPIE Amsterdam

21 Specifications of the LGSD Physical characteristics Pixel array (reference pixels either side) 1760x1680 (880x840 pixels in NGSD) - 5x6cm requiring stitched design (max. reticle 25.5x32.5mm) Technology Thinned backside illuminated CMOS 0.18µm Pixel pitch 24µm Pixel topology Array architecture 4T pinned photodiode pixel 84x84 time coherent sub arrays of 20x20 (8x8 NGSD) pixels - LGSD image area size of 4x4cm Shutter Rolling shutter in chunks of 20 rows synchronous detection within a sub-array. Downing SPIE Amsterdam

22 Block Diagram of Full Size Device; LGSD 44 LVDS Serial Links Highly integrated Control Logic Y-addressing Control Logic Multiplexer/serializer 35,200 single slope Pre-amp Gain of x1/2/4/8 1760x1680 pixels 84x84 Sub-apertures each 20x20 pixels Pre-Amp Gain of x1/2/4/8 35,200 single slope Control Logic Y-addressing Control Logic All analog processing on-chip: programmable gain of x1/2/4/8 on the fly, correlated double sampling (CDS), Single slope Many rows processed in parallel to slow the read out per pixel and beat down the noise. trade study showed to be the optimum number Fast LVDS serial interface to outside world Simple digital interface power consumption similar to high speed drivers to transport the analog signal off chip better guarantee of achieving and maintaining low noise performance Multiplexer/serializer Natural Guide Star Detector (NGSD) 44 LVDS Serial Links scaled down demonstrator ~ ¼ of full size non-stitched Downing SPIE Amsterdam

23 Specifications of the LGSD Read out Number of rows read in parallel 40 (20 in NGSD) rows in parallel Number of ADC s Number of parallel LVDS channels Serial LVDS channel bit rate Frame rate Power dissipation Actual LVDS driver dissipation per channel 40x1760 (20x880 in NGSD) at 9/10 bits 88 (22 in NGSD) 210 Mb/s baseline, up to 420 Mb/s (desired) 700 fps up to 1000 fps with degraded performance 2 to 3 Gpixel/s = 20 to 30 Gb/s over 88 parallel LVDS channels < 5W, including the 88 LVDS drivers 6.0mW at maximum data rate. 4.5 mw in sub-lvds Downing SPIE Amsterdam

24 Specifications of the LGSD Performance Pixel full well Q FW > 4000 e- Linearity to full well < 5% Read noise including ADC < 3.0 e - RMS Image lag < 2 % Dark Current < 0.5 e-/pixel/frame Thought critical and need to validate QE Point Spread Function > 90% over the visible range BackSide Illumination (BSI) < 0.8 pixel FWHM Downing SPIE Amsterdam

25 Technology Validator - TVP In a nutshell: All features of NGSD/LGSD 60x60 pixels, Same pixel and ADC driving 1200 (60x20) ramp > 700 frames/sec Downing SPIE Amsterdam

26 TVP optimises pixel deisgn VRST VSF Optimize the pixel design to find best trade between image lag, linearity, gain, and noise (white and 1/f) by testing: reset transfer select 3 pixel variants with different transfer gate and transistor geometries; different threshold voltages of the nmos transistors; extra implants to improve image lag. p + p-si n + Column bus Pinned photodiode p+ implant p implant transfer gate reset select Downing SPIE Amsterdam

27 TVP - All key performances validated All key performances validated < 3.0e- RMS Full well > 4000 e- Conversion gains > 100 µv/e- Image Lag < 0.1 % Best pixel and implant levels fed into the NGSD phase. Column ramp Not tested in TVP:? Massive parallelism? Array of LVDS serial IO? Back Side Thinning Back Side Illumination Downing SPIE Amsterdam

28 Pixel designed for best centroiding TCAD simulations Y / center X Downing SPIE Amsterdam

29 Yaddressing Corner Corner Yaddressing Yaddressing Corner Corner LGSD Tentative Stitching Plan 10.56mm 10.56mm 10.56mm 10.56mm 20.16mm 10.08mm 5.28mm Corner Yaddressing Corner 10.56mm Reticle View 20.16mm 20.16mm Corner Yaddressing Yaddressing Corner Downing SPIE Amsterdam

30 Yaddressing Corner Corner Yaddressing Yaddressing Corner Corner NGSD anticipates scaling to LGSD 10.56mm 10.56mm 10.56mm 10.56mm 20.16mm 10.08mm 5.28mm Corner Yaddressing Corner 10.56mm Reticle View 20.16mm 20.16mm Corner Yaddressing Yaddressing Corner Downing SPIE Amsterdam

31 Video Chain single slope ADC reset 4T pixel transfer 4 VRST 1 VSF select 2 3 Column bus Pre-Amp + - Gray Code 9/10 Comparator + - D A Q Clk Double Latch D B Q Clk Sync 110MHz DDR Parallel to Serial p + p-si n + x1 x2 x4 x8 Copy LVDS Out Ramp Single slope ADC chosen for robustness, excellent low noise and linearity (DNL). Good compromise between speed, precision, power consumption, and area occupied video ramp comparator output Gray code offset reset signal Latch code Downing SPIE Amsterdam

32 Random address Control Read out Random address Control 88x42 Sub-Apertures North Half-Array Center line Subaperture row addresses (1 of 42) 88x42 Sub-Apertures South Half-Array 20 sets of row select lines per SA reset, select transfer 20 lines per of pixel 20x20 pixels per SA 4T 24um pixel Subaperture row addresses (1 of 42) ADC Ramp Gain ADC Gray Code BUS Copy D 20 rows of bias pre-amp with gain of x1/2/4/8 settable SA by SA 20 rows of comparators (35,200) 20 rows of Registers A 20 rows of Registers B Q D Q Timing, clocks and biases LRC40 Checksum Calculator 110MHz Clock DDR Sync Parallel to serial LVDS Outputs Downing SPIE Amsterdam

33 Solution to drive 210 MHz clocks over 4cm in a stitched design Capacitive load Capacitive load Capacitive load Capacitive load Skew is minimized by using a Clock Tree to distribute signals < 0.25ns Fast clock 3/4 Secondary clock line 1/4 Fast clock Primary clock line Downing SPIE Amsterdam

34 Summary Preparation work for our next challenge, the E-ELT, is well advanced. ESO has formed a good partnership with e2v and Caeleste. Multi-phase, progressive risk reduction development plan should guarantee that devices are available on-time that meet specifications. Measured results from the TVP have clearly validated the CMOS imager approach. The best pixel design that meets the requirements has been found and is being used in the NGSD. The schematic design of the NGSD is complete and layout has started. Fabrication is scheduled for late autumn with devices available early next year. Downing SPIE Amsterdam

35 Thank You This work has been "partially funded by the OPTICON-JRA2 project of the European Commission FP7 programme, under Grant Agreement number " Downing SPIE Amsterdam