November 13, 2014 // Jean-Pierre Joosting

Physics and astronomy depend on being able to register a barely detectable electrical signal in the microwave regime to learn and make discoveries. A typical example of this was the discovery of cosmic background radiation that helped confirm the Big Bang theory. Another example is the detection of data from scientific instruments in space missions on their way to distant planets, asteroids or comets.

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Faint microwave signals are detected by transistor-based low-noise amplifiers. Researchers at Chalmers University of Technology have optimised indium phosphide transistors using a special process for this purpose. A spin-off company from Chalmers, Low Noise Factory, designs and packages amplifier circuits.

This is an electron microscope image of an indium phosphide high electron mobility transistor (InP HEMT). The region affected by the self-heating process is highlighted in the cross section of the InP HEMT. Credit: Chalmers University of Technology

"Cooling the amplifier modules to -260 degrees Celsius enables them to operate with the highest signal-to-noise ratio possible today," says Jan Grahn, Professor of microwave technology at Chalmers. "These advanced cryogenic amplifiers are of tremendous significance for signal detection in many areas of science, ranging from quantum computers to radio astronomy."

Using a combination of measurements and simulations, the researchers investigated what happens when a microwave transistor is cooled to one tenth of a degree above absolute zero (-273 degrees Celsius). It was thought that noise in the transistor was limited by so-called hot electrons at such extreme temperatures. However, the new study shows that the noise is actually limited by self-heating in the transistor.

Physics and astronomy depend on being able to register a barely detectable electrical signal in the microwave regime to learn and make discoveries. A typical example of this was the discovery of cosmic background radiation that helped confirm the Big Bang theory. Another example is the detection of data from scientific instruments in space missions on their way to distant planets, asteroids or comets.

Faint microwave signals are detected by transistor-based low-noise amplifiers. Researchers at Chalmers University of Technology have optimised indium phosphide transistors using a special process for this purpose. A spin-off company from Chalmers, Low Noise Factory, designs and packages amplifier circuits.

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Microwave amplifier noise limited by quantum particles of heat