Heterojunction field effect transistors (HJFETs) for a readout circuit of a cryogenically cooled far-infrared detector

Deep cryogenic field effect transistors (FETs) which are able to operate under liquid helium temperatures have significant advantages over conventional cryogenic Silicon- Junction-FETs or Si-metal-oxide-semiconductor-FETs as readout circuits of a far-IR focal plane array detector: simple operation, simple system structures, and large transconductance. We report the testing of an InGaAs-channel heterojunction field effect transistor (HJFET) operating at 4.2 K designed for a readout circuit of a cryogenically cooled far-IR detector. In this report, we present current- voltage characteristics, transconductance, low-frequency noise (LFN) characteristics, and the influence of the gate leakage current on the LFN characteristics of the HJFET. Input-referred noise voltage as low as a few hundred nanovolts at 1 Hz was measured for the HJFET with a 100 X 100 micrometers 2 gate area. We discuss further possibilities for the fabrication of HJFETs with an extremely small input current of less than 10 -15 A.