Download - Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)

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Page 1: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)

Near-Infrared Detector Arrays

M. Robberto

(with several slides grabbed from J. Beletic, K. Hodapp et al.)

Page 2: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)
Page 3: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)
Page 4: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)
Page 5: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)
Page 6: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)

Intrinsic materials

material λc(m) Eg(eV)

AgCl 0.39 3.20

CdS 0.52 2.40

GaP 0.55 2.24

CdSe 0.69 1.80

CdTe 0.71 1.45

GaAs 1.35 0.92

Si 1.11 1.12

Ge 1.85 0.67

PbS 2.95 0.42

InAs 3.18 0.39

PbTe 5.0 0.25

PbSe 5.40 0.23

InSb 5.40 0.23

Pb1-xSnxTe <12.4 >0.10

Hg1-xCdxTe <12.4 >0.10

The bandgap depends on the temperature

0 ( <0)g gE E T

e.g. for InSb: Eg = 0.24 eV and β= -2x10-4eV

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NASA CDR 05-08-01

Extrinsic materials

P-type ◄ ► N-type

material λc(m) Eg(eV)

Ge:Au 8.27 0.15

Ge:Hg 13.8 0.09

Ge:Cd 20.7 0.06

Ge:Cu 30.2 0.041

Ge:Zn 37.6 0.033

Ge:Be 40 0.03

Ge:B 119.2 0.0104

Ge:Ga 120 0.01

Ge:Li 140 0.009

Si:In 8.00 0.165

Si:Mg 14.3 0.087

Si:Ga 17.1 0.0723

Si:Bi 17.6 0.0706

Si:Al 18.1 0.0685

Si:As 23.1 0.0537

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Page 9: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)

Homework 1

• Small fractional changes in x lead to large fractional changes in the gap energy. How well we need to control x at room Temperature to have a 2% uncertainty in response at cutoff for

– HgCdTe 1.72micron cutoff at 145K [WFC3]

– HgCdTe 2.5micron cutoff at 77K [ground based]

– HgCdTe 5micron cutoff at 35K [JWST]

– HgCdTe 10micron cutoff at 35K [NEOCAM]

• Among these, that is the most demanding material to grow?

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Page 11: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)

Cross-section of HgCdTe detectorp-on-n

P-on-N design

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PN junctionSemiconductor

EF = Fermi Level => ½ occupancy at high T

Page 14: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)

PN junction

N-typeP-type

Doped semiconductors

Impurities (doping) move the EF closer to the valence (P-type) or conduction (N=type) bands.

Page 15: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)

PN junction

N-typeP-type

P-N Junction

When the two materials are brought into electrical contact, the electrons and hole diffuse. Recombination occurs until the Fermi levels are in equilibrium.

Depletion or Space Charge region

E

Page 16: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)

Depletion Region

• Not Neutral: there is an electric field from the N-type (+ charged) to the P-type (- charged)

• Free (depleted) of mobile carriers: extremely low conductivity, or high resistivity.

• An insulator between two charge distributions is a capacitance.

• The development of the electric field eventually stops the diffusion: “built-in voltage” or “contact potential”

• The electric field facilitates the flow of charges in one direction and prevents in the other: diode

E

Page 17: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)

PN junctionReverse biased P-N Junction

Reverse bias: apply voltage with the same polarity of the contact potential

+ Voltage to the N-type

- Voltage to the P-type

makes depletion region wider and increases the resistance of the junction.

(but do not exagerate! => breakdown)

Forward bias: smaller depletion region, eventually no E: high conductivity

N-typeP-type

E+Eb

Page 18: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)

PN junction illuminatedReverse biased P-N Junction

Assume a photon is absorbed BY THE BULK MATERIAL on the P-type side, creating a hole-electron pair. They will eventually recombine. However, if the electron (minority

carrier in the P-type material), reaches the junction before recombination, it will be swept on the other side. There it becomes a majority carrier. It will be sensed out if the bias is

kept constant, or recombines with a hole and discharges the junction

If the bias is “floating”, the other original hole, a majority carrier in the sea of holes, will drift until recombination, calling an electron from ground. A current is generated in the

reverse direction with respect to the original one that set the junction.

(Same is true for photogenerated holes in N-type material).

N-typeP-type

Page 19: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)

PN junction illuminatedReverse biased P-N Junction

Assume a photon is absorbed BY THE BULK MATERIAL on the P-type side, creating a hole-electron pair. They will eventually recombine. However, if the electron (minority

carrier in the P-type material), reaches the junction before recombination, it will be swept on the other side. There it becomes a majority carrier. It will be sensed out if the bias is

kept constant, or recombines with a hole and discharges the junction

If the bias is “floating”, the other original hole, a majority carrier in the sea of holes, will drift until recombination, calling an electron from ground. A current is generated in the

reverse direction with respect to the original one that set the junction.

(Same is true for photogenerated holes in N-type material).

N-typeP-type

Page 20: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)

PN junction illuminatedReverse biased P-N Junction

Assume a photon is absorbed BY THE BULK MATERIAL on the P-type side, creating a hole-electron pair. They will eventually recombine. However, if the electron (minority

carrier in the P-type material), reaches the junction before recombination, it will be swept on the other side. There it becomes a majority carrier. It will be sensed out if the bias is

kept constant, or recombines with a hole and discharges the junction

If the bias is “floating”, the other original hole, a majority carrier in the sea of holes, will drift until recombination, calling an electron from ground. A current is generated in the

reverse direction with respect to the original one that set the junction.

(Same is true for photogenerated holes in N-type material).

N-typeP-type

Page 21: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)

Back to zero bias and beyond

N-typeP-type

P-N Junction

Eventually the junction is discharged but photons are still absorbed. The diffusion current pushes back to maintain the built-in bias. Dark and photocurrent therefore work in

different directions. An equilibrium is reached: saturation.

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Reset

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Photon detection

Do you see the cross-talk/MTF problem?

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End of integration

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Reading out the generated charges• “Hybrid CMOS sensors”

• Indium bumps are aligned, squeezed and distorted to establish electric contact between detector layer and multiplexer: COLD-WELDING

• The addressing and readout electronics is built on Silicon. More standard technology (still >107 transistors).

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Page 42: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)

HAWAII-2: Photolithographically Abut 4 CMOS Reticles to Produce Each 20482 ROIC

Twelve 20482 ROICs per 8” Wafer

20482 Readout Provides Low Read Noise for Visible and MWIR

Canon 16mm x 14 mm

GCA 20mm x 20 mm

ASML 22mm x 27.4 mm

Reticle-Stitching: 2048x2048 ROIC

Submicron Stepper Options

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Page 44: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)

RSC Approach

H A W A I I - H A W A I I - 2 R G2 R G

H A W A I I - H A W A I I - 2 R G2 R G

• HgCdTe detector – substrate removed to achieve 0.6 µm sensitivity

HgCdTe Astronomy Wide Area Infrared Imager with 2k2 Resolution, Reference pixels and Guide Mode

• Specifically designed multiplexer– highly flexible reset and readout options – optimized for low power and low glow operation– three-side close buttable

• Two-chip imaging system: MUX + ASIC– convenient operation with small number of clocks/signals– lower power, less noise

Page 45: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)

HAWAII-2RG

Page 46: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)

Block Diagram

5 MHz column buffersfast normal shift register + logic

glow

and

cro

ssta

lk s

hiel

d

g low and crosstalk shield

Additional row of reference pixels for diagnostic purposes

2048 x 2048 pixel array(2040 x 2040 sensitive pixels)

4 rows and columns containing reference pixels

4 rows and columns containing reference pixels

serial interface

clock buffers

fast guide shift register + logic

Slow

gui

de s

hift

regi

ster

+ lo

gic

Slow

nor

mal

shi

ft re

gist

er +

logi

c

decoders for horizontal start and stop address

I/O Pads & output buffers

deco

ders

for v

ertic

al s

tart

and

sto

p ad

dres

s

• All pads located on one side (top)

• Approx. 110 doubled I/O pads (probing and bonding)

• Three-side close buttable

• 18 µm pixels

• Total dimensions: 39 x 40.5 mm²

Page 47: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)

Output Options

Slo

w s

can

dire

ctio

n se

lect

able

Single output for all2048 x 2048 pixels

(guide mode always uses single output)

Fast scan direction selectable

Single Output ModeSingle Output Mode

default scan directions

Fast scan direction individuallyselectable for each subblock

Separate output for each subblock of 512 x 2048 pixels

S

low

sca

n di

rect

ion

sele

ctab

le

4 Output Mode4 Output Mode

default scan directions

Page 48: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)

Output Options (2)Sl

ow s

can

dire

ctio

n se

lect

able

32 Output Mode32 Output Mode

Separate output for each subblock of 64 x 2048 pixels

Four different patterns for fast scan direction selectable

default scan directions

Page 49: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)

Interleaved readout of full field and guide window

Guide windowGuide window

Full fieldFull field

FPAFPA• Switching between full field and guide window is possible at any time

any desired interleaved readout pattern can be realized• Three examples for interleaved readout:

1. Read guide window after reading part of the full field row

2. Read guide window after reading one full field row

3. Read guide window after reading two or more full field rows

Page 50: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)

Pixel by pixel reset Line by line reset Global reset

Full field

Guidewindow

Pixel by pixel reset Line by line reset Global reset

Full field

Guidewindow

Reset Schemes

Page 51: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)

MIRI Detectors: Si:As IBC

• Extrinsic (vs. HgCdTe, intrinsic)

• Blocked Impurity Band (BIB) extrinsic (vs. “Bulk”)

Page 52: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)

READOUT INTEGRATED CIRCUIT (ROIC)

• 1024 × 1024 / 25 μm pixels

• 7 K Operation

• Source-Follower-per-Detector (SFD) PMOS input circuit

• Low Noise: 10 – 12 e- rms with Fowler-8

• Low Read Glow

• Low Power: < 0.5 mW

• 4 outputs with interleaved columns

• Reference pixels on all outputs mimic "dark" detectors

• Reference output averages noise from 8 "dark" reference pixels

• 2.75 second read time at 10 μsec per sample (100 kHz pixel data rate)

Page 53: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)

Time

Dio

de B

ias

Vol

tage

0.5 V

0 V

Res

et

Readout

Re

se

t

kTC Noise

Reset-Read Sampling

Page 54: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)

Reset Noise in Capacitors

Energy stored in a capacitor:

Noise floor energy:

E_n = ½kT

Noise Charge: E=En

Problem:

Calculate the Reset noise for JWST detectors, assuming: C= 50 fF, T=37 K

Page 55: Near-Infrared Detector Arrays M. Robberto (with several slides grabbed from J. Beletic, K. Hodapp et al.)

Time

Dio

de B

ias

Vol

tage

0.5 V

0 V

Re

se

t

Open Shutter Close Shutter

Readout

Re

se

t

Readout

kTC noise

CD

S S

ign

al

Double Correlated Sampling

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Time

Dio

de B

ias

Vol

tage

0.5 V

0 V

Res

et

Readout

Re

se

t

Readout

kTC noise

MC

S S

ign

al

Fowler (multi) Sampling

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Time

Dio

de B

ias

Vol

tage

0.5 V

0 V

Res

et

Re

se

t

Up-the-ramp Readout

kTC noise

MC

S S

ign

al

Up-the-Ramp Sampling