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Photoconductor Detector Arrays for PAC S IIDR - ESTEC Stefan Kraft • ANTEC-GmbH • Germany Günter Bollmann, Peter Dinges, Otto Frenzl, Marco Jasinski, Heidrun Köppen, Heribert Krüger, Claudia Popp. Overview. Requirements & Specifications Design Implications on A rrays Mass Budget - PowerPoint PPT Presentation
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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
Photoconductor Detector Arrays 2
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
Photoconductor Detector Arrays 3
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
Photoconductor Detector Arrays 4
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
Photoconductor Detector Arrays 5
PACS IIDR 01/02 Mar 2001
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
Photoconductor Detector Arrays 6
PACS IIDR 01/02 Mar 2001
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
Photoconductor Detector Arrays 7
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
Photoconductor Detector Arrays 8
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
Photoconductor Detector Arrays 9
PACS IIDR 01/02 Mar 2001
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
Photoconductor Detector Arrays 10
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
Photoconductor Detector Arrays 11
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
Photoconductor Detector Arrays 12
PACS IIDR 01/02 Mar 2001
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°
Photoconductor Detector Arrays 13
PACS IIDR 01/02 Mar 2001
• 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
Photoconductor Detector Arrays 14
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
Photoconductor Detector Arrays 15
PACS IIDR 01/02 Mar 2001
-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
Photoconductor Detector Arrays 16
PACS IIDR 01/02 Mar 2001
= 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
Photoconductor Detector Arrays 17
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
Photoconductor Detector Arrays 18
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
Photoconductor Detector Arrays 19
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
Photoconductor Detector Arrays 20
PACS IIDR 01/02 Mar 2001
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
Photoconductor Detector Arrays 21
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
Photoconductor Detector Arrays 22
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)
Photoconductor Detector Arrays 23
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)
Photoconductor Detector Arrays 24
PACS IIDR 01/02 Mar 2001
# 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