First Measurement of the Intrinsic Noise of a HEMT at Sub-Kelvin Temperatures

The increasing sensitivity of high impedance cryogenic detectors demands amplification stages closer to detectors to guarantee high performance. We have developed a cryogenic installation to measure the intrinsic noise, the gain, and the DC characteristics of HEMTs or MOSFETs at low temperature. Components under test are mounted in a helium cryostat containing a double stage ^3 He/ ^4 He sorption cooler to perform sub-kelvin measurements. In this work, we describe this installation and present the encouraging first results that have revealed a level of intrinsic input voltage noise of a HEMT, developed by CNRS/LPN, of 0.44 nV/sqrt(Hz) at 1 kHz at 480 mK (Cin = 100 pF).