Ultra-low noise HEMTs for deep cryogenic low-frequency and high-impedance readout electronics

In order to fill the gap of low-temperature and low-frequency noise field-effect transistors and to meet the needs in various experiments under deep cryogenic conditions, specially designed HEMTs with different gate capacitances have been fabricated and characterized at 4.2 and 77 K. At 4.2 K and with an appropriate gate capacitances, the obtained lowest input noise voltage at 1 Hz is 6 nV/Hz^1/2; the lowest input noise current at 1 Hz is about 3 aA/Hz^1/2; their white noise voltage is about 0.2 nV/Hz^1/2; and for switch applications, the channel resistance can be varied from about 10 Ω to more than 10 GO with a gate leakage current lower than 1 pA.