Study On The Pressure Sensing Properties Of Cantilever-type Optical Ring Resonators

Silicon pressure sensor is one of the most widely used in all kinds of sensors. At present, the measurement range of domestic silicon micro pressure sensors with high precision is less than 1kPa and this kind of sensors urged in the industrial control, military equipment, medical equipment and other aspects of micro pressure measurement are basically rely on foreign imports. So it is significant to study the silicon micro pressure sensor with low measurement range and acquire the relevant technologies. Optical ring resonator based on silicon on insulator(SOI) is the core function unit of the integrated optical chip, it has high detection limit, which made it used widely in optical sensor with high sensitivity. Ring resonator integrated on cantilever has great advantages in the integration, sensitivity and measurement range when used as micro pressure sensor, therefore we design and study the pressure sensing structure of cantilever-type optical ring resonators based on SOI material.At first, the coupling transmission mechanism of ring resonator is introduced. Then the micro pressure sensing mechanism based on cantilever is detailedly analyzed combined with evanescent wave coupling principle in nano-scale waveguide, force-optical coupling effect and photoelastic effects. Meanwhile, the mechanical property of a cantilever beam is simulated and analyzed. Based on the characteristic parameters of ring resonator, this paper design the sensing structure and optimize it structure parameters for a high sensitivity of the sensor. The sensitivity of the designed sensor is analyzed and its theoretical value is 73pm/kPa. The dynamic range is 30 kPa. The ring resonator and cantilever are manufactured using micro electro mechanical systems(MEMS, Micro-electro-mechanical-systems) process, containing UV lithography, electron beam lithography, deep silicon etching, and reactive ion etching and so on. Main preparing process and parameters are introduced in this paper. The structure is characterized with atomic force microscopy AFM(atomic force microscope) and scanning electron microscopy(SEM, scanning electron microscope).Finally, the coupling testing system is built to test the transmission properties of ring resonator. The Q value of the ring resonator is 7.75×104 and the sensitivity of the sensor is 31pm/kPa. In order to optimize the performance of ring resonator, we apply thermal oxidation method to ring resonator for smoother waveguide surface. The result shows that the Q value of the ring resonator after thermal oxidation method is 1.2×105 and the sensitivity of the sensor is 48pm/kPa.