Cryogenic Low Noise Amplifier with GaAs JFETs

A SONY n‐type GaAs junction field effect transistor (JFET) can operate at deep cryogenic temperatures without exhibiting kink phenomena or hysteresis in its I‐V characteristics. Further the GaAs JFET has small gate leakage currents(⁠$<4.6×10−19A)$ and a minute input capacitance (0.037 pF). Moreover, even though the gate terminal of a JFET is surrounded by high‐impedance materials, the noise level does not increase and a low noise level of ∼500 $nV/Hz1/2$ at 1 Hz with low power dissipation (<1 μW) was achieved. We are currently developing operational amplifiers (Op‐Amps) and digital modules for cryogenically cooled high‐sensitivity photodetection systems. The GaAs Op‐Amp with an open loop gain of 2000 at a power dissipation of 6.5 μW has been developed.