STRAIN-SENSING CRYOGENIC FIELD-EFFECT TRANSISTOR FOR INTEGRATED STRAIN DETECTION IN GAAS ALGAAS MICROELECTROMECHANICAL SYSTEMS/

We have fabricated a strain-sensing cryogenic field-effect transistor (FET) from a GaAs/AlGaAs heterostructure containing a near-surface two -dimensional electron gas. The FET has transconductance 100 mu S and a small signal drain-source resistance 10 M Omega. The charge noise has a flat spectrum at high frequencies with magnitude 0.2e/root Hz and 1 /f noise corner less than 300 Hz. The piezoelectric effect couples str ess in the substrate to the electron density in the FET channel giving an electrical response to applied strain. Strain sensitivity was meas ured to be 2x10(-9)/root Hz, limited by FET noise. Integrated strain-s ensing FETs offer advantages for detecting small forces in GaAs/AlGaAs microelectromechanical systems. (C) 1996 American Institute of Physic s.