Transcript A noiseless 512 x 512 detector for AO with kHz frame rates

Mid-IR photon counting array using
HgCdTe APDs and the Medipix2 ROIC
John Vallerga and Jason McPhate
Space Sciences Laboratory
University of California, Berkeley
Larry Dawson and Maryn Stapelbroek
DRS Sensors & Targeting Systems, Cypress CA
Photon counting
Count
(x,y,t)
Events
Threshold
Charge integrating
Q
V  sv
ADC
Events
 sEvents
Motivation for photon counting
Reduction of readout noise in infrared
imaging
Advantageous in applications where imaging is
not background dominated:
High frame rate (adaptive optics, interferometry)
Short integration times (Lidar etc.)
Low background (spectrophotometry, space based)
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Signal in presence of noise
1000 photons
100 photons
10 photons
8x8
Noiseless
35% QE
8x8 2.5 e- rms
90% QE
6x6 2.5 e- rms
90% QE
4x4 2.5 e- rms
90% QE
Imaging IR photon counting detector concept

Use an IR sensitive absorber with gain
– HgCdTe APDs
– Large arrays

Count events at the pixel level
– “Medipix2” CMOS ASIC
– 55m pixels, 256x256 format

Readout binary data at 100MHz fast (~1
kHz framerate)
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Avalanche Photodiodes (APDs)

Geiger mode
–
–
–
–

Biased above breakdown
High, saturated gain - easy to count
Long recovery time per event
Afterpulsing and higher background
Linear mode
– Biased near breakdown
– Lower gain -harder to count
– Distribution of pulse sizes - “excess noise”
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High Density Vertically Integrated Photodiode (HDVIP)
DRS Infrared Technologies
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HDVIP IR APDs from DRS

HgCd1-xTex with adjustable c

Electron induced avalanche

Ion-milled via allows backside readout

Linear gains as high as 1000 (c < 4.3m)

Excess noise ~ 1 !

Arrays have been fabricated (128x128)
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Gain vs. bias voltage
 = 4.3 m, 77K, 53 of 54 in array
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Excess noise factor



k=0, only electrons involved in amplification
Excess noise factor of 1.0 implies a deterministic
amplification process
Low noise factor allows a higher threshold in pulse sensing
electronics
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Medipix2 ROIC




Each pixel has amp, discriminator, gate & counter.
256 x 256 with 55 µm pixels (buttable to 512 x 512).
Counts integrated at pixel. No charge transfer!Previous Pixel
Amplifier noise 110 e- rms
Shut ter
Mask bit
Lower Thresh.
Polarity
Mux.
Clock out
Disc.
Disc.
logic
Input
Preamp
Disc.
Mux.
13 bit
counter –
Shift
Register
Upper Thresh.
Mask bit
Next Pixel
~ 500 transistors/pixel
Analog
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Digital
Medipix readout of semiconductor
arrays
Developed at CERN for
Medipix collaboration (xray)
radiography
tomography
mammography
neutron detection
gamma imaging
MCP readout
gaseous detectors
electron microscope
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Medipix2 readout architecture
• Pixel values are digital (14 bit)
3584 bit Pixel Column 255
3584 bit Pixel Column 1
3584 bit Pixel Column 0
• Bits are shifted into fast shift
register
256 bit fast shift register
32 bit CMOS output
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LVDS out
• Choice of serial or 32 bit parallel
output
• Maximum designed bandwidth is
100MHz
• Corresponds to 284µs frame
readout
HDVIP - Medipix2 Hybrid
Characteristics well matched:
HDVIP
64 m pixel (8x8)
Gain up to 1000
Backside output
Low dark current
Medipix2
55 mm pixel
Minimum threshold 900eFrontside input
10nA/pxl compensation
However
77K operation
IR sensitive
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Room temp. design
Very active chip
Test Setup

Simple test - drop Medipix2
chip into LN2
– Mounted on ceramic header
used for 350C tests
– Attached to brass heat sink
and copper cold finger
– Accurate diode thermometer
glued to header
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Ceramic Header & Thermal Testing
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Test thermal profile
LN2 Thermal test of MXR2 E07 on ceramic header
300
250
Temp [K]
200
150
100
50
0
15:00
16:00
17:00
Time
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18:00
Individual DACs vs. Temp.
PREAMP
IKRUM
1.4
2
1 .8
1.2
1 .6
1
1 .4
1
299K
170K
123K
101K
77K
0 .8
0 .6
0 .4
Volts
Volts
1 .2
299K
170K
123K
101K
77K
0.6
0.4
0.2
0 .2
0
1
0.8
0
1 4 2 7 4 0 5 3 6 6 7 9 9 2 1 0 51 1 81 3 11 4 41 5 71 7 01 8 31 9 62 0 92 2 22 3 52 4 8
1
13
25
37
49
61
73
85
DA C Value
97 109 121 133 145 157 169 181 193 205 217 229 241 253
DAC Value
DISC
THS
1.4
2
1.8
1.2
1.6
1.4
1.2
0.8
299K
170K
123K
101K
77K
0.6
0.4
0.2
Volts
Volts
1
1
299K
170K
123K
101K
77K
0.8
0.6
0.4
0.2
0
1
13
25
37
49
61
73
85
97 109 121 133 145 157 169 181 193 205 217 229 241 253
DAC Value
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0
1
13
25
37
49
61
73
85
97 109 121 133 145 157 169 181 193 205 217 229 241 253
DAC Value
Threshold Variation (noise)
299K
20000
18000
16000
14000
12000
10000
8000
6000
4000
2000
0
100
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150
200
250
300
350
400
Threshold Variation (noise)
98K
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
100
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150
200
250
300
350
400
Threshold Variation (noise)
77k-Reoptimized
5000
4500
4000
3500
3000
2500
2000
1500
1000
500
0
100
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150
200
250
300
350
400
Feasibility Test at DRS

Used existing 8x8 APD array mounted on fan-out
header

Wirebonded 8 APD outputs to 8 Medipix2 input pads

Hybrid assembly mounted on larger header

Large header mounted in test dewar
– Expect higher amplifier noise due to increased capacitance
– Use IR photodiode as photon light source to input light pulses
– Use photon-transfer curve to characterize gain and noise
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Medipix2 and APD array
Medipix2
APD array
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Wirebonds
Test Hybrid in dewar
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IR photodiode to illuminate APD
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Future work

Start/continue feasibility tests
– Quantify noise, gain and threshold sensitivity

Extrapolate results to realistic APD mounting
Investigate APD fabrication techniques onto
Medipix wafer
Model/simulate APD pixel to match Medipix

Seek funding to pursue full chip fabrication


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Summary
If successful, this effort could lead to a
sensor with:
–
–
–
–
–
HgCdTe QE (c < 4.3 m)
Large arrays (512 x n*256)
Zero readout noise
kHz frame rates or higher
Electronic shutter
Which should prove very useful for many niche
applications with low background in the IR
SPIE 2007 San Diego