On the use of GaAs MESFETs in the realization of low-frequency low-noise amplifiers for applications at cryogenic temperatures

Static characteristics and noise performances of selected dual-gate GaAs MESFETs at cryogenic temperatures are presented. Devices are operated with both gates interconnected, emulating in this way single-gate MESFETs with double gate length. With a biasing power of 360 mu W at 4 K A/sub f/, the 1/f noise coefficient is A/sub f/=3.8*10/sup -14/ V/sup 2/. When it is operated as a dual-gate device, A/sub f/ increases by a factor of four. The spectral power density of low-frequency noise at 4 K is two orders of magnitude lower than at 300 K. Transconductance at 4 K is 6 mA/V at V/sub DS/=0.6 V and I/sub D/=0.6 mA. Gate leakage current is lower than 10 fA below 100 K. Using these devices, a charge-sensitive preamplifier has been designed and tested. Detector matching capacitance is 8 pF. The minimum equivalent noise charge after semi-Gaussian shaping with tau =10 mu s is 20 RMS e/sup -/. The risetime is 16 ns, and the power dissipation is 7 mW.<>