X-Message-Number: 26073
From: "Basie" <>
Subject: The solid-state refrigerators 
Date: Sat, 23 Apr 2005 14:12:08 -0400

Chip-scale Refrigerators Cool Bulk Objects
Chip-scale refrigerators capable of reaching temperatures as low as 100
milliKelvin have been used to cool bulk objects for the first time,
researchers at the National Institute of Standards and Technology (NIST)
report. The solid-state refrigerators have applications such as cooling
cryogenic sensors in highly sensitive instruments for semiconductor defect
analysis and astronomical research.
This colorized scanning electron micrograph shows a cube of germanium
attached to a membrane. The four small light blue rectangles at the
midpoints of the membrane perimeter are chip-scale refrigerators that cooled
the cube and membrane to only a few hundred thousandths of a degree above
absolute zero.
Nanomaterial Yields Cool Results (July 5, 2004) -- A pinch of iron
dramatically boosts the cooling performance of a material considered key to
the development of magnetic refrigerators, report researchers at the
National Institute of Standards.
The work is featured in the April 25, 2005, issue of Applied Physics
Letters.* The NIST-designed refrigerators, each 25 by 15 micrometers, are
sandwiches of a normal metal, an insulator and a superconducting metal. When
a voltage is applied across the sandwich, the hottest electrons "tunnel"
from the normal metal through the insulator to the superconductor. The
temperature in the normal metal drops dramatically and drains electronic and
vibrational energy from the objects being cooled.

The researchers used four pairs of these sandwiches to cool the contents of
a silicon nitrate membrane that was 450 micrometers on a side and 0.4
micrometers thick. A cube of germanium 250 micrometers on a side was glued
on top of the membrane. The cube is about 11,000 times larger than the
combined volume of the refrigerators. This is roughly equivalent to having a
refrigerator the size of a person cool an object the size of the Statue of
Liberty. Both objects were cooled down to about 200 mK, and further
improvements in refrigerator performance are possible, according to the

The refrigerators are fabricated using common chip-making lithography
methods, making production and integration with other microscale devices
straightforward. The devices are much smaller and less expensive than
conventional equipment used for cooling down to 100 mK, a target temperature
for optimizing the performance of cryogenic sensors. These sensors take
advantage of unusual phenomena that occur at very low temperatures to detect
very small differences in X-rays given off by nanometer-scale particles,
enabling users such as the semiconductor industry to identify the particles.
The work was supported in part by the National Aeronautics and Space
Administration and NIST's Office of Microelectronics Programs.

*A.M. Clark, N.A. Miller, A. Williams, S.T. Ruggiero, G.C. Hilton, L.R.
Vale, J.A. Beall, K.D. Irwin, J.N. Ullom. Cooling of Bulk Material by
Electron-Tunneling Refrigerators. Applied Physics Letters. April 25, 2005

Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=26073