New concept of lateral GaAs field emitter for sensor applications

Abstract

We present a novel lateral field emitter structure for sensing applications, which is based on GaAs. According to the Fowler–Nordheim theory, the emitted current depends exponentially on the distance between the cathode and the anode. Hence, this effect is predestined for sensing of vibration, acceleration, and pressure. We have designed and fabricated a lateral field emitter structure consisting of two wedges vis-à-vis. They are etched anisotropically in n+-doped epitaxial GaAs. One of the wedges is released by front side bulk micromachining to form a flexible cantilever. This cantilever contains the seismic mass of the accelerometer. The sensing principle is based on the following effect. The electrical field strength at the cathode is already very strong at relatively low cathode–anode voltages due to the geometrical parameters: (i) the low radius of the emission wedge, its radius of curvature is much smaller than 50 nm and (ii) very small distance between the cathode and the anode. Acceleration or vibration causes the cantilever to bend, so that the distance between the two wedges varies accordingly. This causes a modulation of the electrical field strength at the cathode and leads to a modulation of the emission current. The proposed sensor has the advantage of high sensitivity combined with a good temperature insensitivity. Classical beam theory was applied to define the geometrical parameters and the corresponding deflection of the cantilever.