Optical Three-Axis Accelerometer with Vertically DRIE-Etched Micromirrors

The sidewalls of deeply etched silicon typically exhibit significant optical scattering losses caused by scallops, which severely degrade reflected or transmitted light. We propose a post-smoothing method utilizing a dilute potassium hydroxide (KOH) aqueous solution to smooth deep-etched silicon sidewalls. Post-Smoothing, the sidewall roughness decreased from tens of nanometers to below 5 nm, enabling the fabrication of optical-grade vertical micromirrors and vertical Fabry-Pérot (FP) cavities. By leveraging this advancement, we propose a three-axis optical accelerometer with excellent electromagnetic compatibility. The accelerometer adopts a typical comb-proof mass-beam spring structure similar to that of conventional capacitive accelerometers. The smoothed sidewalls of the proof mass create X- and Y-axis tunable FP cavities with the corresponding sidewalls of the frame, while the polished proof mass’s bottom surface as well as the BF33 glass structure forms a Z-axis tunable FP cavity. Clear FP interference spectra, observed in the experiment, demonstrate the low optical loss and high smoothness of the cavity surfaces. The measurement results show that the sensitivity variations in the three orthogonal directions (X, Y, Z) of this accelerometer were 0.19 μm/g, 0.13 μm/g, and 0.22 μm/g, respectively, (g=9.8 m/s²). This work eliminates high-temperature processes and is compatible with advanced packaging techniques, demonstrating significant potential for manufacturing and integrating various MOEMS (Micro-Opto-Electro-Mechanical System) sensors.