photoconductor detector arrays for pac s iidr - estec

Photoconductor Detector Arrays 1

PACS IIDR 01/02 Mar 2001

Photoconductor Detector Arrays for PACS

IIDR - ESTEC

Stefan Kraft • ANTEC-GmbH • Germany

Günter Bollmann, Peter Dinges, Otto Frenzl, Marco Jasinski, Heidrun Köppen, Heribert Krüger, Claudia Popp


PACS IIDR 01/02 Mar 2001Overview

• Requirements & Specifications• Design Implications on Arrays

– Mass Budget– Thermal Budget– Vibration Load– Stress Mechanism / FEM analysis– Fore Optics / Optical Design– Detection efficiency

• Achieved Performance versa Spec– Detector Responsivity– Cutoff Wavelengths– Stress Uniformity / Variations in CW– Bias dependency– Uniformity of abs. Responsivity

• Summary


PACS IIDR 01/02 Mar 2001Impacts of Specifications and Requirements to Detector Array Design

# Item Specified Input parameters

1 Applicable IR-flux range (each pixel)

Transient behavior

1*10-15 (dark) 3*10-12 W nominal:

5*10-15 W/pixel 3*10-12 W

< 100 ms

Telescope

Photoconductor, NEP

2 Mass 5 kg Weight of materials

3 Thermal budget 600 / 800 µW FEE support, harness suspension, detector wires,

array suspension

4 Vibration load Input on optical bench: 15 g

Critical items: FEE and harness suspension

5 Mean quantum efficiency

> 30 %

Detector material, FEE, Cavity, Fore optics, Surfaces

6 Wavelength range high stress (R > 0.1Rpeak)

110 – 208 µm

7 Wavelength range low stress 60 – 130m

Detector material,

applied stress

8 Current sensitivity high stress (low stress)

10 A/W ( 3 A/W)

Detector material, cavity efficiency, fore optics

9 Uniformity cutoff wavelengths

c 200m 125 m <c < 130m

(c: 50% of peak)

Detector material, FEE, Cavity, Fore optics

10 Number of cycles >25 Design, gluing and coating techniques


PACS IIDR 01/02 Mar 2001Design Detector Housing

5x5 linear arrays arranged according to needs of acquisition mode for spectroscopy Light metal design (Al) - total weight ~ 6.6 kg Thermally isolated

Front view Side view



Red array

Blue array

Design Detector Housing

Optical path requires different arrangements of blue and red array

Red array rotated by 90°

Detectors are optically shielded from environment by light tight envelopes

Shielding structures coated by black paint



Light weight FEE thermally isolated from array Thin wire harness (Nano/micro connectors) High stability

Proper wiring concept (CDet < 2pF, dark current <5·104 e-/s) Low EMC impacts High degree of light tightness Good uniformity of responsivities Uniform cutoff wavelengths (CWs) Low variation of CWs

Design Detector Arrays

FEEbackside

Fore opticlight cones

Detec torstack incavity

Stresssc rew

Leaf spring

Coolingstrip to4 K level

Harnessw ires

Mic roconnector

Harnessw iresAWG 36

Nanoconnector

Mountingposts(K apton)

Detec tor AWG 40w ire channels

FEEfronts ide

Bridgingsubstrates

Harnesssubstrate

Proper stressing mechanism Low cross-talk (<0.1%) High collection efficiency High quantum efficiency


PACS IIDR 01/02 Mar 2001Design - Stress mechanism

• Maximum force: 800 N highly stressed

200 N low stressed

Spring travel: ~2 mm both types of modules

High stress module Low stress module

• Al alloy with strength of steel

• Design verified by FEM analysis

• Detector cavity remains stress free

• Controlled adjustment of stress possible

• Stress is predictable even after cool down


PACS IIDR 01/02 Mar 2001Mass Budget

Low Stress Array:• 50 g

High Stress Array:• 57 g

Harness: 3gFore Optics: 9g

FEE: 2g

25 Low Stress Arrays• 1.24 kg

25 Low Stress Arrays• 1.4 kg

50 Arrays 2.64 kg in Total



1.7 K

4 K

25 High Stress Arrays

P = 375 µW

2.5 K

4 K

25 Low Stress Arrays

111666 DDDeeettteeeccctttooorrr WWWiiirrreeesss (((SSSttteeeeeelll))) 444 CCCRRREEE PPPooossstttsss +++222 HHHaaarrrnnneeessssss PPPooossstttsss (((KKKaaappptttooonnn))) 222 HHHaaarrrnnneeessssss PPPooossstttsss (((KKKaaappptttooonnn)))

P = 624 µW

P = 11 µW P = 202 µW P = 162µW

P = 7 µW P = 134 µW P = 108 µW

P = 249 µW

Thermal Budget


PACS IIDR 01/02 Mar 2001Vibration Load

• Static Load Test: 420 g @ RT on 2 posts ~ 200 g

Kompression Bending

Safety Factor (Calculation): 5

Clamped Fixed Clamped Fixed

Safety Factor (Calculation): 54


PACS IIDR 01/02 Mar 2001Design - FEM analysis

• Addition of cushion pads between detector and pistons reduces the pressure gradient considerably

• High centring accuracy necessary



Photographs

Ge:Ga crystal

Al2O3 isolator

Steel ballsegment

CuBe contact

Linear cone offore optic

Instrument Description

Schematic view of the linear photoconductor array design

• Mounting accuracy ~10 µm• Slit size 30 to 70 µm• Rotational mounting accuracy <5°



• Force transmittance from detector to detector

• Equalisation of non-parallel surfaces

• Minimisation of stress non-uniformity within detectors

• Optical shielding between the cavities in the detector channel via

the metal contacts

• Electrical insulation of the detector contacts from the housing and each

other

• Electrical contacts made by 70 µm Cu wires and 25 µm Au wires in

cavity

”Detector – metal contact – insulator – ball joint – metal contact” Block Design: Purposes

1 mm


PACS IIDR 01/02 Mar 2001Design - Fore optics

• Low surface roughness (<0.3 µm) obtained by electric discharge machining (EDM) for high reflectivity

• Coating with a 10µm thick Ni-Au layer ensures high reflectivity close to 1 as proven by measurements on flat samples

• 16 linear light cones• Optical cavities with

small apertures• Radial orientation to

pupil at 240 mm distance• Design optimised by optical

calculations



-0,5 0,0 0,5

0,4

0,5

0,6

0,7

0,8

0,9

1,0

Rel

. spa

tial d

istr

ibut

ion

y (mm)

Design impacts / biasing concept:• Slits unavoidable

• Polarisation dependence, glancing angle of impinging photon: Effective slit size is small

Experimentally verified by spectral responsivity

Performance Aspects - Photon Lossesy

Supported by ray tracing

Photon starting point: 240 mm from focus with 15 mm diameter (conditions of the optics in the instrument PACS)

High detection efficiency



= Pabs/(Pabs + Ploss)

• Ploss : Loss area inside cavity = entrance hole + slits (25 µm, 50 µm) + wires

• Pabs = 2(a+b)·h·(1-R) ·’ : Absorbing area

Abs. eff.: ’ = · L, Abs. coeff.: = 2.4 cm-1, Abs. length: L = 2.1 mm

Length: a = width: b = 1 mm, height: h = 1.5 mm, Reflectivity: R = 0.4

D hole P hole P (1) P (2) P loss (1) P loss (2) P abs (1) (2) Rel. Improvementmm mm2 mm2 mm2 mm2 mm2 %0,5 0,196 0,927 0,467 1,199 0,740 1,80 0,90 0,60 0,71 0,15

0,55 0,238 0,927 0,467 1,240 0,781 1,80 0,88 0,59 0,70 0,150,6 0,283 0,927 0,467 1,286 0,826 1,80 0,86 0,58 0,69 0,15

0,65 0,332 0,927 0,467 1,335 0,875 1,80 0,84 0,57 0,67 0,150,7 0,385 0,927 0,467 1,388 0,928 1,80 0,82 0,56 0,66 0,14

0,75 0,442 0,927 0,467 1,445 0,985 1,80 0,80 0,55 0,65 0,140,8 0,503 0,927 0,467 1,505 1,046 1,80 0,78 0,54 0,63 0,14

0,85 0,567 0,927 0,467 1,570 1,111 1,80 0,76 0,53 0,62 0,140,9 0,636 0,927 0,467 1,639 1,180 1,80 0,74 0,52 0,60 0,13

0,95 0,709 0,927 0,467 1,712 1,252 1,80 0,72 0,51 0,59 0,131 0,785 0,927 0,467 1,788 1,329 1,80 0,70 0,50 0,58 0,13

1,05 0,866 0,927 0,467 1,869 1,409 1,80 0,68 0,49 0,56 0,13

Slit 1: 0,05 mm (plus wire holes) 0,08Slit 2: 0,025 mm

Performance Aspects - Detector Efficiency


PACS IIDR 01/02 Mar 2001Measured Relative Responsivities

Good uniformity, close to expectation

R 20% @ 205 µm

QM 13 - Low Stress

0 50 100 1500,0

0,2

0,4

0,6

0,8

1,0 P14 P15 P16 P1 P2 P3

Rel

. res

pons

ivity

(m)

QM 2 - High Stress (re-stressed)

10 % level

0 50 100 150 200 2500,0

0,2

0,4

0,6

0,8

1,0 P14 P15 P16 L197 R202 P1 P2 P3

Rel

. res

pons

ivity

(m)

2 4 6 8 10 12 14 16190

195

200

205

C ( m)

Pixel position


PACS IIDR 01/02 Mar 2001Cutoff wavelengths and variations highly stressed QM arrays

Uniform mean cutoff wavelengthsRelation between RRT and CW (pressure)

Low variations within one array

0 2 4 6 8 10

195

200

205

FiFi

720 N/mm2

On purpose(760 N/mm2)

Mean

CW

(µm

)

QM # - HS1 2 3 4 5 6 7 8 9 10

0

5

10

15

Specification

PACS QM

FiFiVariation ofcutoff wavelength

(µ

m)

QM # - HS


PACS IIDR 01/02 Mar 2001Cutoff wavelengths and variations low stressed QM arrays

Uniform mean cutoff wavelengths Low variations within one array

12 14 16 18 20 22 24122,5

125,0

127,5

130,0

132,5Specif ication limits

Mean

CW

(µm

)

QM # - LS12 14 16 18 20 22 24

0

1

2

3

4

5

6

7

8FO not optimised

Mean

Variation ofcutoff wavelength

(µ

m)

QM # - LS



0 2 4 6 8 10190

195

200

205

Min Max

CW

(µm

)

QM # - HS

Status Min-Max Cutoff Wavelengths QM arrays

12 14 16 18 20 22 24

125

130

135 Min Max

CW

(µm

)

QM # - LS

Initial specification limits

Specification limit FM: CW > 200 µm @ 40 mV


PACS IIDR 01/02 Mar 2001Bias dependence QM 10 - Pixel 2

0 50 100 150 200 250 3000,0

0,2

0,4

0,6

0,8

1,0

1,2 U15mV U30mV U43mV U49mV

Rel

. res

pons

ivity

(µm)0 10 20 30 40 50 60

190

195

200

205

210 CWQM10

C (µ

m)

UB (mV)

Higher stress Higher CW Lower Bias Break Through Voltage

Higher Bias Higher CW

Lower stress means less risk of detector breakage Specification close to optimum


PACS IIDR 01/02 Mar 2001Relative spectral responsivity - absolute uniformity

EM 6

TIA measurement ANTEC

T = 1.9 K

High stress (700 N)

Ubias = 30 mV

EM 5

T = 2.5 K

Low stress (62 N)

Ubias = 100 mV

0 50 100 150 200 2500

2

4

6

8

10

12

Ideal responsivity QE() = const

30% totalvariation interval

P14 P15 P16 P1 P2 P3 P7 P8 P9 EM5.P7

Res

pons

ivity

(A/W

)

(m)


PACS IIDR 01/02 Mar 2001Dependence of the DC signal (responsivity) on RT resistance

Measured detector output signal UDC during operation as a function of the RT resistance of the Ge:Ga crystals - no stress applied

UDC ~ Current sensitivity1/R ~ Doping density

280 300 320 340 3600

1

2

3 QM1 QM2 QM3 FitUDC (V)

R ()

FM LSFM HS

A linear fit derived from the data points gives a slope of -0.0339V/

Sensitivity increases with decreasing resistance

Selection of crystals with variation of less than 15 (35) should give less than 10% (25%) variation within one array (whole array)



# Item Specified Input parameters Achieved with EM/QM Requirement fulfilled

1 Mass 5 kg Materials < 1.5 kg per array EM housing: 0.42 kg per array

( ) Housing not included

2 Thermal budget 600 / 800 µW FEE support, harness suspension,

detector wires, array suspension

Design/analysis

~300 µW per array

( )

Heat load to housing not included

3 Vibration load Input on optical bench: 15 g

Critical items: FEE and harness

suspension

Design: 20g safety factor >5

( ) - static

Vibration tests in prep

4 Wavelength range high stress (R > 0.1Rpeak)

110 – 208 µm 50 – 225 µm ( )

5 Wavelength range low stress

60 – 130m

Detector material,

applied stress 40 – 150 µm ( )

6 Current sensitivity high stress (low stress)

10 A/W ( 3 A/W)

Detector material, cavity efficiency, fore

optics

12 A/W @ 40 mV bias

3.5 A/W @ 100 mV bias

( ) Improved

Detector Material for FM Arrays

7 Uniformity cutoff wavelengths

c 200m 125 m <c < 130m

(c: 50% of peak)

195 m < c < 200m 125 m <c < 130m

(c: 50% of peak)

( )

Goal FM: c = 205 µm @ 40 mV bias voltage

8 Uniformity of responsivity 30 % < 25% (ANTEC) Verification at MPE/MPIA planned

( )

9 Mean quantum efficiency ( applicable flux range)

> 30 %

Detector material, FEE, Cavity, Fore optics

Tests ANTEC, MPE:

~ 35% Verification at MPIA planned

( )

10 Number of cycles >25 Adhesive, coating Several cool downs performed during testing

TBC Cycling test in prep

Summary: Specifications fulfilled

photoconductor detector arrays for pac s iidr - estec

Documents