Concept for Manufacturing a Microoptoelectromechanical Micro-G Accelerometer

Abstract

The paper presents the schemes for manufacturing a microoptoelectromechanical (MOEM) accelerometer for measuring small accelerations. MOEM-accelerometer includes three subsystems: mechanical, optical and electronic. The mechanical subsystem includes an inertial body, mounted on a spring suspension in a case. The optical subsystem includes a laser, moving and fixed waveguides. The electrical subsystem includes a photodiode and electronic components. To measure microdisplacements that correspond to measured microaccelerations, an optical system based on the optical tunnel effect was used. The work considers the schemes of the optical transducer for linear and angular displacements of the mechanical subsystem. The moving waveguide together with the inertial body are combined into the mechanical sensing element that diverges in the case of acceleration. A technological process for manufacturing a MOEM accelerometer based on the “silicon on insulator” technology with additional layers of nitride and silicon oxide for optical functional elements is presented. Depending on the character of the movement of the sensing element, the functional schemes of the MOEM-accelerometer were developed with various changeable parameters: optical coupling length, gap, overlapping area between the moving and fixed waveguides. The article analyzes the advantages and drawbacks of the proposed schemes of accelerometers from the perspective of their manufacturing feasibility and the predicted accuracy. The highest sensitivity $(6.25 \times10^{6} \text{m} ^{\text{-1}}$) belongs to schemes with changeable gap between the waveguides. The dynamic displacement ranges of them is ± 80 nm. Lower sensitivity $(1.25 \times10^{6} \text{m} ^{\text{-1}}$) belongs to schemes with changeable overlapping area. The dynamic displacement range may reach ± 300 nm. Schemes with changeable optical coupling length possess the highest dynamic range which directly depends on a chosen optical coupling length and amounts to dozens of microns. The sensitivity of the last scheme also depends on the optical coupling length and amounts to $11.25 \times10^{3} \text{m}^{-1}$ for an optical coupling length of 44 $\mu$m and to $30 \times10^{3} \text{m} ^{-1}$ for an optical coupling length of 15 $\mu $m.