Optimizing the Structural Parameters of the Mechanical Sensing Element of a Microoptoelectromechanical Micro-g Accelerometer

The paper investigates a microoptoelectromechanical accelerometer that implements optical measuring transducer built on the optical tunneling effect. The article discusses the issues of micromechanical sensing element (MSE) optimization for an MOEM- accelerometer fabricated by silicon on insulator (SOI) technology. The results represent the requirements to the design to achieve a sensitivity of 1 μg m/s ² at a calculated eigenvalue of the MSE. The main parameters of the mechanical part of a MOEM-accelerometer affecting its sensitivity are dimensions, mass, resonance frequency and corresponding stiffness of the spring suspension. Following the Brownian noise that characterizes the accelerometer's sensitivity, the relations between the parameters are determined. Two designs of the MSE are considered according to the fabrication process. One design contains only a device layer; the second one implements a SOI-wafer basic layer as a weighting additive. The latter design occupies less area. To prevent MSE deflection stipulated by its larger dimensions and to increase the number of sensors fabricated from a single SOI wafer, MSE with additional mass are more reasonable to use. The MSE mass at an eigenfrequency of 10, 20, 50 and 100 Hz should exceed 0.01.10 ⁻⁶ kg, while at a frequency of 200 Hz, the mass should exceed 0.023.10 ⁻⁶ kg to comply with the requirement of minimal measurable acceleration of 1 μg m/s ² . Subsequent increase of the MSE mass at the same eigenfrequency decreases the thermal mechanical noise.