High Aspect Ratio Silicon MEMS Shutters for Stellar Sensing Applications

We propose the design and implementation of High Aspect Ratio Silicon Micro-Electro-Electro-Mechanical-Systems (MEMS) Shutters (HAR-SMS). The HAR-SMS were designed for stellar sensing applications. In addition, the proposed design will be easily utilized as an add-on layer between the optical sensing element, e.g. photodetector and the optical lens. The MEMS shutters can be integrated with optical sensing systems to reduce noise, e.g. dark current, flicker, 1/f, etc.  Detection of low intensity signals in space is an extremely challenging task. Stellar sensing requires sensitive sensors to detect low intensity optical signals. These photodetectors need to be in-flight calibrated in dark conditions in order to remove both inherent detection noise as well environmental noise. In order to perform such calibration, MEMS shutters may be utilized to physically close the aperture of the photodetection area to reduce unwanted radiation exposure. Shutters may also be used to physically close an aperture to protect detectors, thereby protecting sensing elements. In addition, shutters may be used as modulators to increase the Signal-to-Noise Ratio (SNR) of detectors. The key component for the in-flight live calibration, sensor protection and SNR improvement is therefore the implementation of such a transmissive optical shutter. The challenge is that the shutters require large aperture areas, fast dynamic response in the millisecond range, mechanical stability and reliability for space applications, and low power consumption, as well as operating in a wide temperature range, e.g. -200-200 °C. These stringent requirements make the current state-of-the-art shutters not applicable for space applications. For example, liquid crystal shutters are not fast enough and cannot operate in very low or high temperatures. In addition, the blocking spectrum is limited, making them limited for blocking unwanted multi-wavelength radiation. Existing MEMS shutters do not provide a large aperture area or a high frequency response. Out of plane MEMS shutters rely on hinges, which are not reliable for very large number of cycles (e.g. 10E10) and require high actuation power.   The HAR-SMS will be able to meet the US Navy’s needs. The proposed design is based on Single-Crystal-Silicon (SCS) Multiple Aspect Ratio Structures (MASIS) fabrication process to achieve large aperture areas with high aspect ratio structures for mechanical robustness and high frequency response. This fabrication process has already been demonstrated to produce MEMS shutters. In addition, the device will be CMOS compatible for future electronics integration.