Capacitive Surface-Micromachined Pressure Sensors on Fused SilicaContributions to Micromachining on Fused Silica

Abstract

Capacitive absolute pressure sensors fabricated by means of surface-micromachining on fused silica are presented. The non-conductive substrate material eliminates all parasitic capacitances to the bulk. Fabricated prototypes are simulated with SPICE and a lumped components model is derived. Simulation data is compared to wafer and package level test results. Touch-mode hysteresis, sensitivity, and magnitude of capacitance are discussed. Processing on fused silica is covered in detail with a focus on surface micromachining. Substrate material related process challenges are addressed such as high film stress levels as well as viscose and elastic deformation. Analytic formulas for surface-micromachined circular plates are presented. Topography, stress, and a limited displacement magnitude are considered by means of normalization. The approach leads to a solution for plates in touch-mode. General characteristics of capacitive circular plate transducers in normal- and touch-mode are discussed.