Planar Antenna-Coupled Hot-electron Microbolometer

1
Planar Antenna-Coupled Hot-electron Microbolometer
Shafinaz Ali1, Dan Mccammon1, Lance D. Cooley2,
Kari.L.Nelms1, John Peck3, Daniel Prober4, Dan
Swetz1, Peter Timbie1, Daniel van der
Weide3 1Department of Physics, 2 Dept. of
Materials Science and the Applied
Superconductivity Center, 3Dept. of Electrical
and Computer Engineering, University of
Wisconsin-Madison, Madison, WI 53706, 4Dept. of
Applied Physics,Yale University, New Haven, CT
06520
Fabrication The transition edge sensors are
fabricated by depositing a bi-layer of
Molybdenum(Mo) and Copper(Cu) on a Silicon wafer
coated with 1 micron Silicon Nitride layer via
electron beam deposition. The Mo layer is
deposited at 700 0C to optimize grain size and
structure of the Mo. The Cu layer is deposited
at much lower temperature. The TES shown in the
figure is a square device of 200 micron by 200
micron. We are now in the process of fabricating
much smaller TES devices ( 10 mm x 10mm) with Mo
layer 40 nm, and Cu 150 nm with Cu absorber
that adds an additional thickness of 23 nm.

ABSTRACT We describe a new type of bolometric
detector for millimeter and submillimeter
wavelengths. The detector is a variant of the
Transition Edge Sensor (TES), which has recently
been used to build bolometers. In this version of
the TES, we couple radiation from a planar
antenna to an absorbing normal metal film which
is electrically connected to a superconducting
thin film. The lateral dimensions of the absorber
and TES are 10microns. At low temperatures, the
thermal isolation between the electrons and the
lattice in the absorber and the superconductor
allows the electrons to heat up. We call this
device a Transition-edge Hot-electron
Microbolometer (THM). These detectors could have
numerous advantages for low-background
measurements in the far-IR, such as,
background-limited sensitivity, short time
constant, wide spectral range, immunity to cosmic
rays, low microphonic noise and simple readout
electronics. We are currently building a
low-frequency scale model of the planar antenna
to characterize microwave properties the system.
SCIENCE GOALS The millimeter and the
submillimeter of the electromagnetic spectrum
promise unprecedented discoveries for
astrophysics over the next decade. Future
measurements at these wavelengths depend
critically on the development of new detectors.
The proposed Hot-electron bolometers will be
particularly useful for the measurement of the
power and polarization of the faint sources, such
as the 2.7KCosmic Microwave Background (CMB)
radiation. The temperature fluctuations
(anisotropy) in the CMB are 1 part in 100,000 and
the predicted polarized signal from the radiation
is at least a factor of 10 times smaller.


Optical mage of a Mo/Cu TES
SEM image of a TES device. It shows the clean Cu
edge and overhang above Mo layer.
Development of highly sensitive bolometers and
advanced experimental techniques have made it
possible to measure the CMB anisotropy with much
higher precision (e.g. BOOMERanG, MAXIMA). To
measure the elusive polarization we need better
and more bolometers, because the current
conventional bolometers are not suitable for the
job. The proposed THMs are going to be much more
sensitive than the coventinal bolometers and
since they are produced by standard lithographic
techniques a matched array of THMs can be easily
fabricated. THMs can be easily coupled to planar
antenna via low-loss superconducting microstrip
transmission lines.
Simulation of a Slot Antenna Scale Model A
planar antenna coupled to a microstrip
transmission line was performed with commercially
available ADS software. A slot antenna
separated by a insulating layer with dielectric
constant 6 was coupled to a microstrip line.
We have built a microwave scale model of the
above circuit that is scaled in size by a factor
of 13 over the actual 90GHz circuit. The circuit
is fabricated by using standard printed-circuit
board etching techniques on a Duroid microwave
circuit board. The circuit is then laminated to a
slab of a dielectric material with e_r12.
Similar to that of silicon. We have conducted
reflection test of this circuit to verify the
computer model.
Theoretical Power Spectra of CMB Polarization, E
and TE cross-correlation. Temperature anisotropy
is shown to give the viewer some perspective.
Error bars are those expected for the MAP
satellite. (figure courtesy Wayne Hu)
Simulation result for a 90GHz slot antenna and
microstrip transmission line with 10
bandwidth.
RF and Thermal Design
Eccostok HiK
application observations of the 2.7 K CMB from
a cooled space telescope
microstripline
6 ?m
Nb microstrip Z0 10 W
Absorber
Nb radial stub
IRF from antenna
The mictrostripline is separated from the ground
plane by an insulating layer. The thin microstrip
that crosses the slot antenna has an impedence
that matches the antennas(20W). The rest of the
line is built to include a transition to the 50W
standard coax components for network analyzer.
Mo leads
Mo/Cu TES bilayer
The scale model test setup for planar antenna.
GAndreev
GWF
GAndreev
es
es
Possible design for low-background CMB
observations Cu absorber, 23 nm thick, V 6.2
(?m)3 R 10 W Mo/Cu TES, 200 nm thick, V 3.0
(?m)3
es
Gep
Lattice phonons

• Future Plans
• We plan to
• Build a double slot antenna scale model and
  conduct reflection and beam pattern tests, as
  well as tests to understand the power loss in
  substrate.
• Measure the electron-phonon coupling in newly
  fabricated microbolometers.
• Use Bismuth as an alternate absorber for THMs
• Integrate superconducting planar antenna ciruits
  to THMs.

Frequency ? 90 GHz, ??? 30 GHz Optical
efficiency (assume) ? 0.5 NEPPhoton 5.2 x
10-18 W/Hz1/2 Tbath Tphonons 0.050 K
Require GWF a 1/R gtgtGep Gandreev lt Gep R
Z0 NEPPhonon (4kBT2G) lt NEPPhoton ? Gep 10-11
W/K