GAAS-MESFETS AND MONOLITHIC CIRCUITS IN CRYOGENIC ENVIRONMENTS

We present the latest results of a research work started in 1986 in Milano, aiming at the optimisation of GaAs MESFETs and circuits for cryogenic readout of particle detectors used in experiment of high energy physics. For bolometric detectors we have been looking for low 1/f noise and good dynamic performance at 4 K. We want also fast speed with low white noise and high radiation resistance for the readout of liquid Argon calorimeters. An ion-implanted MESFET process was selected for the realisation of FETs and monolithic preamplifiers for the mentioned applications. The noise and dynamic parameters of the process have been determined for the first time at 4 K and 77 K. SPICE parameters have also been extracted. As a result of this work, monolithic low noise preamplifiers were designed and fabricated. The chips have been tested with a LAr detector at CERN, confirming the expected performance. Voltage-sensitive preamplifiers for 4 K have also been fabricated and will soon be evaluated. The performance of FETs and monolithic preamplifiers at cryogenic temperatures are reported.