Design and calibration of an infrared position sensor

Abstract

An optical method for sensing lateral motion in silicon-based devices was developed and implemented. Using an infrared laser to illuminate the device and an InGaAs photodiode to detect the transmitted radiation, acquisition of the frequency component of motion has been demonstrated. A simple analysis of electromagnetic transmission through silicon was performed, along with an infrared characterization of pertinent materials. A lateral resonator was designed and fabricated to act as a calibration device for the optical position sensor. Using a coupled electro-mechanical solver, MEMCAD, the resonant modes were simulated and found to be in agreement with the analytical calculations. Upon completion of the device, it was found that motion was not optically detectable. Instead, an audible tone was heard when electrical stimulation was applied. The sound was analyzed and a first-order explanation was developed. Electrical testing and destructive examination of the resonator indicate that the device fabrication was not complete. Process developments and improvements to realize the desired design are discussed.