Design of a passive photonic MEMS accelerometer compatible with fiber Bragg grating interrogators and a silicon photonics foundry platform

In recent years more and more aspects of our lives have started relying on data-driven technologies. Decision-making processes based on the extensive analysis of data are improving how we address as a society challenges in safety, health, sustainability and many other fields, with structural health monitoring, personalized medicine, and environmental assessment being a few notable examples. The development of sensing technologies has played a key role in the collection of these data, driven by continuous advancements in fabrication processes, materials, and sensor design. Nowadays accelerometers are mainly based on MEMS and piezoelectric technologies, relying on electronic readout and signal processing. Thanks to the increasing performance and decreasing cost of electronic components, accelerometers are being integrated into many different devices and systems, from smartphones to industrial machinery. However, the readout electronics pose a limit to the applicability of these sensors in certain scenarios. Electronic devices are inconvenient to use in environments where battery replacement is difficult, immunity to electromagnetic interference is needed, or multiple sensors with high multiplexing capabilities are required. Among the technological advances that have had an impact in the sensing technologies field, photonics stands out for posing possible solutions to these problems. Light propagating in guiding waveguides is highly sensitive to the external environment without requiring an external power source and is characterized by wide bandwidth, high signal-to-noise ratio, and immunity to electromagnetic interference. Integrated photonics could therefore enable a new generation of accelerometers, possibly removing the need for specific packaging or manual assembly by integrating the mechanical structure of the sensor alongside the readout photonic circuit. However, the development of integrated photonics is relatively new, with fabrication processes still being complex and expensive, and foundries lacking the possibility to release mechanical structures. Silicon photonics in this sense is a promising platform, given the maturity of the fabrication processes around silicon reached in the microelectronics industry. This thesis aims to add another step towards the development of such sensors, presenting the design of a single-axis passive MEMS accelerometer featuring an optical readout compatible with already existing interrogators built for fiber Bragg grating sensors. The mechanical and optical features of the sensor coexist integrated into the same device layer. The design is based on a silicon photonics foundry platform (IMEC’s iSiPP50G), following all the design rules with a few foundry-compatible post-processing steps required. Multiple design variations have been proposed to enhance sensitivity and address fabrication challenges. At the time of writing, the sensor is being fabricated. Once the fabrication is completed, the device will be the first generation of accelerometers on the platform, paving the way for a photonic integrated circuit combining multiple sensors interfaced to a single interrogator.