Micro-fabrication of Si-based optomechanical inertial sensors for cryogenic temperatures

Abstract

The design of next generation gravitational wave observatories considers operation at cryogenic temperatures to enhance their sensitivity by reducing thermal noise fluctuations. Inertial sensors are used on the observatory platforms to measure local seismic noise and counteract its effects by active control or subtraction in post-processing. Measuring the displacement of a test mass in a resonator system allows for creation of a compact accelerometer system. Currently, there are no commercial inertial sensors available that are capable of operating at cryogenic temperatures and providing the required sensitivities for gravitational wave observatories. Materials such as fused silica exhibit very low losses at room temperature. However, this changes significantly at lower temperatures. Unlike fused silica, the Q factor of crystalline silicon structures is expected to remain high at low temperatures, making it a likely candidate for use in these types of inertial sensors. We are working to fabricate compact mechanical resonators from Si wafers to test their mechanical response. Micro-fabrication consists of optimizing the photolithography and Bosch etching processes for through-wafer Si etching on a 280 μm, 500 μm, and 1 mm wafer. Successful etching on 280 μm wafers has been achieved. We report on the design, model, and fabrication progress of these resonators. © 2021 SPIE.