DIAPHRAGM DEFLECTION OF SILICON INTERFEROMETER STRUCTURES USED AS PRESSURE SENSORS

The influence of isotropic pressure on the mechanical properties of si licon diaphragms used in fiber-optical pressure sensors has been inves tigated by comparing experimental sensor output data with a simple the oretical treatment based on an analytical method and with a more rigor ous numerical treatment based on the finite-element method (FEM). The sensor structures are interferometers prepared in silicon by wafer bon ding. This method allows cavities to be prepared with accurately contr olled dimensions, bounded on one side by a silicon diaphragm. Optical interference occurs at the cavity when the devices are illuminated by light. The interference can be influenced by an external pressure pert urbation such that light flux reflected by the sensor body becomes a m easure of the applied pressure. Three different structures with differ ent diaphragm dimensions have been investigated. It is found that the analytical treatment can be used for rough estimates of sensor propert ies only for structures with thin diaphragms and for pressures up to a bout 2 bar. For accurate predictions and for thicker diaphragms, where the entire sensor body may be influenced by pressure, numerical metho ds must be used.