Integrated GaAs microsensors

Abstract

A b s t r a c tThe compatible integration of planar-processed microsensor structures with GaAs MESFET depletion-mode operational amplifiers is described.Basic low-noise differential amplifiers have been integrated with on-chip piezoelectric pressure sensors and accelerometers. A key design issue in this work is the fabrication constraint of forming both amplifiers and deformable microsensor structures on a common GaAs semi-insulating substrate. Circuits using 2.0 wm-gate FETs are formed in planar, direct, ion-implantation process. Main features of this process include a lightly-doped shallow channel layer, selective n+ contact layers, and planar isolation by proton implantation. A deformable microsensor structure using the piezoelectric thin film zinc oxide is formed over a micromachined air gap over the GaAs substrate. The circuit and fabrication issues of integrated GaAs microsensors are described and compared with equivalent implementations using silicon technology.