Transcript Development of Ge JFETs for Deep

SPIE - Astronomical Telescopes and Instrumentation
Development of Ge JFETs
for
Deep-Cryogenic Preamplifiers
Hawai’i, August 2002
R. R. Ward and R. K. Kirschman
GPD Optoelectronics Corp., Salem, New Hampshire, U.S.A.
M. D. Jhabvala
NASA Goddard Space Flight Center, Greenbelt, Maryland, U.S.A.
R. S. Babu
Ball Aerospace & Technologies Corp., Boulder, Colorado, U.S.A.
D. V. Camin and V. Grassi
Physics Department of the University and INFN, Milan, Italy
ASTRO-E Preamp Assembly
~1.2 K
~18 K
~120 K
The Problem
• Sensor at ~1 K, Preamplifier at ~100 K
• Long Wires
– Parasitic capacitance and resistance
– Microphonics
– EMI pickup
• Heat Transfer to Sensor
• Extra Power
• Mechanical Complexity
A Solution
• A Transistor That Can Operate at ~1 K
A Solution
• A Transistor That Can Operate at ~1 K
• We Proposed the Ge JFET
(Junction Field-Effect Transistor)
Technical Goals for Ge JFETs
• Operate at Any Temperature, ~1 – 300 K
• Very Low Low-Frequency Noise
– Equal to best Si JFETs at optimum temp (~120 K)
• High Input Resistance/Low Input Current
• Tailorable Input Capacitance
• Low Power
• Integrable
• Available, Standard and Custom
Why Ge?
• Ge JFETs Operate Well
to Lowest Temperatures (~1 K)
• Both n-Channel and p-Channel JFETs
• Texas Instruments Ge JFET
• Ge Is an Elemental Semiconductor
• Ge Technology Is Sufficiently Developed
Ge JFET Cross-Section (n-channel)
Passivation
N Epitaxial Layer
P+ Implant
N+ Implant
Au-Sb
S
Gf
D
P+ Ge Substrate
Gb
Backside Metalization (Au)
Ti-Au
Ge JFETs
~1 mm
Conduction vs Temperature
3.5
3
2.5
Si JFET (2N4416)
2
I
dss
(T)
1.5
Si JFET (U310)
Idss(300)
1
0.5
0
0
50
100
150
Temperature, T
200
(K)
250
300
Conduction vs Temperature
3.5
3
Ge JFET, Vds = 0.5 V
2.5
Si JFET (2N4416)
2
I
dss
(T)
1.5
Si JFET (U310)
Idss(300)
1
0.5
0
0
50
100
150
Temperature, T
200
(K)
250
300
Conduction vs Temperature
3.5
Ge JFET, Vds = 1.0 V
Ge JFET, Vds = 0.5 V
3
2.5
Si JFET (2N4416)
2
I
dss
(T)
1.5
Si JFET (U310)
Idss(300)
1
0.5
0
0
50
100
150
Temperature, T
200
(K)
250
300
DC Characteristics
DC Characteristics - 4 K
DC Characteristics
DC Characteristics
Noise Characteristics
Noise Voltage - 77 K
Noise Voltage vs Power - 77 K
Noise Voltage vs Power - 77 K
Noise Voltage vs Temperature
Noise Voltage vs Temperature
Noise Voltage - 4 K
Summary
• Successfully Fabricated Ge JFETs, n- and p-Channel
• Provided Evaluation Ge JFETs to Potential Users
• DC Characteristics Good at All Temperatures down to 4 K
• Turn-On Threshold at 4 K (T<~20 K)
• Achieved Low Noise down to ~30 K
• Noise Higher than Desired at 4 K
Plans
• Adjust Parameters to Extend Low Noise to ~1 K
• Reduce Noise at All Cryogenic Temperatures
– Match that of Si JFETs at higher temperature
• For Both n- and p-Channel