Thesis Examination Committee
Prof Zhiyong FAN, ECE/HKUST (Chairperson)
Prof Man WONG, ECE/HKUST (Thesis Supervisor)
Prof Kevin CHAU, ECE/HKUST (Thesis Co-supervisor)
Prof George Jie YUAN, ECE/HKUST
Many industrial, automotive, and oil exploration applications demand measuring pressure higher than 200 MPa (or 2000 atmospheres). Micro-electro-mechanical systems (MEMS) refer to tiny electrical devices integrated with movable mechanical micro-structures that are realized using micro-fabrication technology. Conventional diaphragm-type MEMS pressure sensors have been widely used for many applications. However, they are not suitable for measuring pressure beyond 100 MPa due to the structural limitation of the sensing diaphragm.
For high pressure sensing, a bulk-type sensor having no fragile movable micro-diaphragm but instead utilizes the entire sensor die for pressure measurement is more desirable. A single-cavity bulk-type MEMS pressure sensor has been realized that converts the external hydrostatic pressure into a biaxial stress field acting on two orthogonal pairs of piezoresistors. The silicon anisotropic piezoresistance is optimized for the sensing performance. The fabricated junction-isolated bulk-type pressure sensor on -oriented substrate has been characterized to 200 MPa. However, the operation temperature is still limited due to junction leakage. An improved dielectric-isolated bulk-type sensor using oxide-refilled trenching techniques has been subsequently realized and tested up to 200 MPa and 225℃. Furthermore, with selective trenching for the relief of the transverse stress component, a bulk-type MEMS high pressure sensor has been realized on the more readily available -oriented silicon substrate as well.