Ultra-low noise CryoHEMTs for cryogenic high-impedance readout electronics: Results and applications

Based on a long-term investigation of material growth and fabrication procedure, the cryoHEMTs (Cryogenic High Electrons Mobility Transistors) made at the CNRS/C2N (formerly LPN) are now in the process to fill the gap of the FET (Filed-Effet Transistor) for high impedance, low-power and low-frequency deep cryogenic readout electronics. Different input capacitance cryoHEMTs have been fabricated and characterized, and ultra-low noise voltage and noise current have been obtained at 4.2 K, e.g., the device with a gate capacitance of about 100 pF the noise voltage can be reduced to 6 nV/Hz1/2 at 1 Hz and 0.32 nV/Hz1/2 at 1 kHz, and its noise current varies from 20 aA/Hz1/2 at 1 Hz to 0.5 fA/Hz1/2 at 1 kHz. The device with a gate capacitance of 3.5 pF shows a noise voltage of about 0.25 nV/Hz1/2 and a noise current of about 2 fA/Hz1/2 at 1 MHz. By using these cryoHEMTs, significant progress has been made in deep cryogenic readout electronics and few examples will be shown.