Design of a silicon photonic microphone

Abstract

In a world increasingly dominated by technological advancements, the demand for high-quality microphones has never been more present. Seamless speech recognition and the development of userfriendly hearing aids remain significant challenges. State-of-the-art micro-electromechanical system (MEMS) microphones are reaching their bottlenecks in terms of thermo-acoustic noise, caused by the acoustic resistance of the parallel plate capacitor. This constrains the achievable signal-to-noise ratio (SNR). This thesis presents a novel solution to address these challenges through the application of silicon photonics technology in the development of a silicon photonic microphone. Silicon photonics is a technology that uses silicon as an optical medium to create photonic systems with sub-micrometre precision, which can be used to create ultra-sensitive sensing devices. The optical sensors are fabricated on standard silicon-on-insulator (SOI) wafers, allowing for seamless integration with the precise and cost-effective complementary metal-oxide-semiconductor (CMOS) process. The optomechanical
sensitivity of the proposed microphone is derived for three different cladding materials that could be deposited on the wafer in the fabrication process. The thermal acoustic noise of the microphone is quantified. As the integrated photonic circuit does not require a backplate the design potentially reduces the thermal acoustic noise of current microphones by 44 %. The optimized design for the laboratory setup that is considered for this thesis can theoretically result in an SNR of 73.1 dB, which is roughly 5 dB more than the current state-of-the-art microphone technology.