Three-Bolometer Devices from CSO Run 1 :
Time Constants
Matt Gardner (Caltech)
Version: 9 December 2000
Acknowledgements
Christine Allen (NASA/GSFC) provided the bolometers. Jeff Groseth (Caltech)
glued and wirebonded the dies. Matt Gardner and C. Darren Dowell (Caltech) performed
all measurements.
Thanks also to C. Darren Dowell for feedback and guidance.
Apparatus
Cryostat: Caltech Barney Dewar, which is IR Labs HDL-10 with helium shield +
Chase Research single-stage 3He fridge. RFI filtered connectors with 1-4 nF capacitance.
Detector holder: Up to 6 each 10 mm × 8 mm dies attached with GE varnish to
fiberglass PC board with gold-plated copper traces. PC board screwed to Invar base and
covered with lid. Black paint on inside of lid. Invar base attached with screws and N
grease to copper cradle, which is attached to fridge coldhead with screws and N grease.
Eight each gold wirebonds (0.001”) provide electrical interface to each die. Calibrated
Lakeshore G.R.T. attached to PC board with screw and N grease.
Methods: Load resistors and JFETs inside dewar are used during measurements.
1) “Direct” -- Bolometer is biased with a square wave between (Vbias - V/2) and (Vbias +
V/2). Output response is amplified by a Stanford Research 560 preamp and displayed
on an oscilloscope for measurement.
Measurement Period: All measurements took place between 2000 Dec. 1 and
2000 Dec. 7.
All device models used herein are taken from “Test Report -- Three-Bolometer
Devices from CSO Run 1”, version 5, written by C. Darren Dowell.
Direct Measurement
For a given base detector temperature, device models can predict the bias voltage,
Vopt, which minimizes bolometer NEP at 0.03 Hz. Bolometer responses are measured for
Vbias/Vopt = .5, 1, 2, and 4 (the last value was omitted on Dec. 1) at several base
temperatures. The bias frequency is selected so that a full thermal settling of the
bolometer is visibly apparent before the next bias edge.
Sample bolometer responses from December 1 are shown in the figures below;
indicated in red on Figure 1 are the voltages measured for every observed response, while
measured times are shown in blue.
settle
VOS
Vrise
VOS / e
OS
Figure 1: Bias voltage (bottom) and response (top) of bare 5273.7200 T2 device at
Tbase = 502 mK, Vbias = Vopt, RL = 21.48 M; both signals are amplified by a factor of
100. Measured settle is 13.2 msec.
Figure 2: Same as Figure 1, except Tbase = 282 mK. Measured settle is 22.8 msec.
Table 1: Direct Measurement of Thermal Time Constants
Thermistor Type Bol. Loc. Date Tbase (mK) Vbias (mV) V (mV)T (mK) G (nW/K) e/ settle (ms)
5273.7200 T2 bare bolometer
mid
Dec. 1
282
15.7
3.92
310
0.118 1.066
33.2
5273.7200 T2 bare bolometer
mid Dec. 1
282
29.4
3.92
359
0.158 0.848
22.8
5273.7200 T2 bare bolometer
mid
Dec. 1
282
58.8
7.84
441
0.240 0.610
12.8
Die
5273.7200 T2 bare bolometer
5273.7200 T2 bare bolometer
5273.7200 T2 bare bolometer
mid
mid
mid
Dec. 1
Dec. 1
Dec. 1
397
398
398
21.6
45.1
88.2
3.92
3.92
7.84
417
459
528
0.215
0.260
0.345
0.903
0.758
0.627
29.2
14.9
10.1
5273.7200 T2 bare bolometer
5273.7200 T2 bare bolometer
5273.7200 T2 bare bolometer
mid
mid
mid
Dec. 1
Dec. 1
Dec. 1
501
502
502
37.3
74.5
147.1
3.92
7.84
15.69
521
561
635
0.336
0.389
0.500
0.896
0.769
0.649
37.2
13.2
12.2
5273.7200 T4
5273.7200 T4
5273.7200 T4
5273.7200 T4
bare bolometer
bare bolometer
bare bolometer
bare bolometer
mid
mid
mid
mid
Dec. 7
Dec. 7
Dec. 7
Dec. 7
283
283
283
283
16.5
30.2
61.3
119.5
1.03
1.03
1.03
4.06
301
349
456
567
0.144
0.187
0.300
0.441
1.212
1.214
0.657
0.515
N/A
27.0
8.0
6.1
5273.7200 T4
5273.7200 T4
5273.7200 T4
5273.7200 T4
bare bolometer
bare bolometer
bare bolometer
bare bolometer
mid
mid
mid
mid
Dec. 7
Dec. 7
Dec. 7
Dec. 7
384
384
384
384
20.4
39.7
80.6
160.0
1.94
1.94
1.94
2.88
405
446
528
638
0.243
0.289
0.390
0.545
0.961
0.820
0.625
0.531
17.2
14.8
7.6
4.6
5273.7200 T4
5273.7200 T4
5273.7200 T4
5273.7200 T4
bare bolometer
bare bolometer
bare bolometer
bare bolometer
mid
mid
mid
mid
Dec. 7
Dec. 7
Dec. 7
Dec. 7
505
506
506
506
33.9
68.8
136.8
272.6
3.91
3.91
3.91
5.78
526
569
650
773
0.387
0.445
0.562
0.765
0.901
0.764
0.630
0.552
NOTE: T, G, and e/ are derived from device models; cases where Vbias = Vopt are
shown in bold.
These same measurements were performed on several devices from wafer
5347.7500, as provided in 32-element test arrays by NASA/GSFC, in April 2000 (“PopUp Detector Test Report”, version 2, by C. Darren Dowell); of those devices, type
HGUNIT.2B are equivalent in design to the bolometers considered here. Comparing
these devices at Tbase ~ 300 mK and Vbias = Vopt, we findsettle ~ 4 and 25 msec for wafers
5347 and 5273, respectively.
We take settle to be a measurement of the bolometer thermal time constant, e.
Another appropriate time constant for device description is  = C/G, where C is the
bolometer heat capacity. Device models predict that for nearly all measurements here,
e/ < 1 (see Table 1); we assume that this ratio should be the same for both wafers at
similar Vbias and Tbase, and will therefore ignore its effects in further comparison.
Again considering Tbase ~ 300 mK and Vbias = Vopt, models predict G ~ .3 and .2
nW/K for wafers 5347 and 5273, respectively. If this were the only difference between
the two wafers, then wafer 5273 would have e larger by a factor of only 1.5. In order to
account for the observed time constant increase, devices from the current dies must have
4 times the heat capacity of those tested in April -- specifically, C ~ 1 and 4 pJ/K for
wafers 5347 and 5273, respectively.
10.0
11.3
8.5
4.6