| With the development of Micro-Electro-Mechanical Systems (MEMS) technology, different types of pressure sensors, such as piezoresistive, capacitive and resonant pressure sensor, have been applied on automotive, aerospace, bio-technology, etc. The MEMS optical pressure sensor is a new type of pressure sensor which has gained more and more attention in recent years. The merits of the optical pressure sensor, such as small size, immunity to electromagnetism interference (EMF), high sensitivity and resolution, make it suitable for applications in extreme conditions with high temperature and high EMF, such as in space, desert, and oil drilling industry. Optical fiber and silicon waveguide pressure sensors are two major types of optical pressure sensor. Compared with the optical fiber pressure sensor, the silicon waveguide pressure sensor using CMOS process is more suitable for system integration and packaging. Most silicon waveguide pressure sensors are based on rectangular waveguide structure. The pressure-induced displacement of the diaphragm is read out with the change of light intensity. However, the performance of the pressure sensor can hardly be further improved due to the inherent non-linear relation between the light intensity and the pressure applied.In order to solve the nonlinearity problem of the rectangle waveguide pressure sensor and improve the performances, two types of Nano-Opto-Mechanical pressure sensors are proposed, designed and fabricated in this work; one is based on nano-scale ring resonator and another on Bragg structure with circle hole.1. In the ring resonator, the radius change of the ring resonator is used for sensing purposes instead of the effective refractive index change of the waveguide. This method not only solves the non-linear problem of the rectangle waveguide pressure sensor, but also optimizes the parameters of the pressure sensor and overcome the difficulties in P. K. Pattnaik’s design, such as the transmission power loss of the ring resonator and the high thickness of the diaphragm which bring up difficulties in fabrication.The software COMSOL based on Finite Element Method is used to simulate the displacement and stress distribution of the pressure sensor. The software Rsoft based on Finite Difference Time Domain is used to simulate the optical characteristics of the pressure sensor. Compared with the structure proposed by P. K. Pattnaik, the parameters of the pressure sensor are optimized. For example, the radius of the ring resonator is reduced by a factor of ten and the thickness of the diaphragm is reduced to one-third. Standard CMOS and MEMS process are used on the fabrication of the device. The full range of the pressure sensor is from0to60kPa. The sensitivity, resolution and hysteresis are1.47pm/kPa,1.36kPa, and less than2%, respectively. The achieved experimental results agree with the numerical prediction. The pressure sensor can be used to form an array structure with single optical layer to detect the pressure distribution in highly accurate measurement. The feasibility is verified by the simulation.2. To improve the sensitivity and resolution of the device, another new optical pressure sensor based on Bragg structure is designed. The new sensing scheme is based on the change of the resonant wavelength to detect the pressure on the diaphragm. The device is babricated by the standard CMOS and MEMS process. The experimental results show good linearity. The sensitivity and resolution of the pressure sensor are1.55pm/kPa and1.29kPa, respectively.The two new optical pressure sensors have different characteristics. The ring resonator pressure sensor is suitable for array structure because of the small size and simple structure. The ring resonator pressure sensor has potential applications such as shear stress displacement detection and pressure mapping etc. The Bragg structure optical pressure sensor has high sensitivity which could be applied in the pressure mapping of the diaphragm and biological applications and medicine. |
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