Multiplexed
RF-SET Readout Amplifiers
for Superconducting Detector Arrays
T
homas Stevenson,
Orbital & NASA/GSFC, Code 553, Greenbelt, MD 20771
Fernando Pellerano, NASA/GSFC, Code 555, Greenbelt, MD 20771
Carl Stahle, NASA/GSFC, Code 553, Greenbelt, MD 20771
Robert Schoelkopf, Ken Segall, Applied Physics, Yale University, PO Box 208284,
New Haven, CT 06520-8284
INTRODUCTION:
Several types of superconducting detectors are being
developed for NASA applications, including transition edge sensors (TES)1,
superconducting tunnel junctions (STJ)2, and photon-counting direct
detectors (SQPC)3.
Despite the complexity of cryogenic operation, such detectors are desirable because of
capabilities such as single-photon spectroscopy, or
extreme levels of sensitivity, which cannot be obtained with uncooled detectors.
Large format detector arrays will be
facilitated by sensitive, fast, compact, low-power, multiplexable, on-chip
amplifiers. For high
impedance detectors such as the STJ and SQPC, the Radio Frequency Single
Electron Transistor (RF-SET) seems to be an ideal readout amplifier.
RF-SET:
Single electron transistors (SET) are cryogenic quantum-effect devices which
utilize quantization of charge on a small conducting “island” to yield a very
high performance electrometer (
Fig. 1 )
SETs are the electrostatic “duals”4
of the better known SQUIDS, which are the most sensitive magnetometers and
current amplifiers5.
With picowatt power dissipation and sub-femtofarad input capacitance,
SETs are well-suited as on-chip amplifiers for detectors with high resistance
and low capacitance.
In an RF-SET6(
Fig. 2), an rf readout technique is employed to give
amplifier bandwidths as large as 100 MHz.
When an SET is connected to a high-frequency tank circuit and a carrier signal
applied at the resonance frequency, the reflected power is modulated by
signals at the SET input gate.
Wavelength Division Multiplexing (WDM) of 20 - 50 amplifier outputs on one coax
can be done by placing RF-SETs with different resonance frequencies in parallel. TWO-CHANNEL WAVELENGTH DIVISION MULTIPLEXING: We have successfully demonstrated the first two-channel wavelength division
multiplexing of RF-SETs using discrete components wirebonded together (
Fig. 3).
The rf power reflected from
the parallel combination of the two tank circuits had nulls near two
well-separated resonance frequencies (
Fig. 4).
By applying carrier waves at those two frequencies and monitoring the
amount of reflected power for each, the input charge signals on each of the
two SETs were reconstructed (
Fig. 5).
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LITHOGRAPHIC TANKS:
Planar 3D electromagnetic modeling software (SONNET
7) was used to design the circuit elements to minimize unwanted
cross inductance and capacitance, and to give the desired resonance
frequencies and impedance transforming properties.
For example,
Fig. 7 shows a calculation of the capacitance matrix of
the pad array. The capacitance of
a pad dominates the total capacitance of its tank circuit.
Calculations indicated that independent WDM channels with negligible
cross coupling would be obtained if bonding pads used for tank circuits
were alternated with pads tied to ground.
We tested this by measuring the reflection coefficient of
tank circuit arrays in the superconducting state (
Fig. 8).
We found excellent qualitative agreement between the data and a
parametric model assuming no cross couplings.
Values derived for capacitances, inductances, and frequencies agreed
with SONNET predictions to about 10% or better. CONCLUSIONS:
ACKNOWLEGEMENTS:
REFERENCES:
We have made progress in miniaturizing tank circuits to
allow larger arrays of multiplexed RF-SETs.
On optically patterned substrate chips for our next generation
prototype submillimeter detectors (
Fig. 6), we have integrated a set of
inductor coils and bonding pads which form tank circuit arrays when connected
together with wire bonds. Each
chip has sixteen inductors.
We have demonstrated the wavelength division multiplexing
concept for RF-SETs, and have
shown that we have the rf engineering tools and fabrication technology for
scaling up the number of multiplexed channels.
WDM will be a valuable multiplexing technique for applying RF-SETs as
on-chip readout amplifiers for superconducting detectors.
We thank Peter Wahlgren, Abdelhanin Aassime, and Per
Delsing of Chalmers University for SET fabrication.
This work was supported by internal GSFC Director’s discretionary
funds, NASA Explorer grant NAG5-8589, the NASA Cross Enterprise Technology
Development Program, and equipment funds from the Jet Propulsion Laboratory.
1. K.D. Irwin, Appl. Phys. Lett.
66,
1998 (1995); K.D. Irwin, J. Appl. Phys. 83,
3978 (1998).
2. S. Friedrich et al., Appl. Phys. Lett.
71,
3901 (1997); K.J. Segall, Ph.D. Thesis, Yale University, 2000;
K.J. Segall
et al., Appl. Phys. Lett., to appear 2000.
3. R.J. Schoelkopf, S.H. Moseley, C.M. Stahle, P. Wahlgren, and P.
Delsing, “A Concept for a
Submillimeter-Wave Single Photon Counter?”,
IEEE Trans. Appl. Superconductivity, 9,
2935 (1999).
4. K.K. Likharev, IEEE Trans. Magnetics,
MAG-23, 1142 (1987).
5. J. Clarke, Proc. of the IEEE
77, 1208 (1989).
6. R.J. Schoelkopf et al., “The Radio-Frequency Single-Electron
Transistor (RF-SET):
A Fast and Ultrasensitive Electrometer,” Science
280, 1238 (1998).
7. SONNET ®, Sonnet Software, Inc., 1020 Seventh North St.,
Suite 210, Liverpool, NY 13088, USA.