Microfabrication and characterization of gallium arsenide membranes for force sensor applications

摘要

High-precision force sensors based on membranes of semi-insulating gallium arsenide with stable structures had been fabricated by micromachining. Their structural quality had been evaluated by high-resolution X-ray diffraction techniques. Free hanging membranes with thicknesses of > 2 ?m have been synthesized by utilizing photolithography, implantation and selective etching. Starting wafers were (100) n-type GaAs crystals with n = 3.5 × 101? cm?3. Implantation by 4 MeV N2? (dose ? 101? cm?2) produced N compensated semi-insulating GaAs with a resistivity of 10? ? cm and breakdown voltage of ~ 60 V. An ~ 100 ?m deep cavity below the membrane was produced by selective etching. A typical sensor was coiled shaped with five segments. The five-crystal X-ray diffractometer developed at NPL was employed in (+, -, +) configuration for structural characterization of the final device structures. A highly monochromated and well-collimated Mo K?? X-ray beam of very narrow lateral width (~ 10 ?m) was employed as the exploring beam. Specimens were studied in symmetric as well as in highly asymmetric Bragg geometries with (400) and (511) diffracting lattice planes, respectively. Crystalline quality, tilt between adjoining sensor segments and the level of stress in the specimens were determined.