Development of Diaphragm and Microtunnel Structures for MEMS Piezoelectric Sensors

This paper reports a novel method for fabrication of diaphragm along with microtunnels for various applications. Micromasking, grass formation, uniformity over the process wafer, notching, growth of thick silicon oxide masking layer, protection of microtunnel during diaphragm fabrication etc. are the major challenges in deep reactive ion etching (DRIE) of the existing silicon bulk micromachining process. The proposed fabrication technique solves these issues by proper selection of a stack of Al/SiO
₂
masking layers. Scanning Electron Microscopy (SEM) employed at intermediate fabrication stages shows that the microtunnel formed is smooth and pin hole free. The fabricated structures can be used in variety of applications such as pressure compensation in acoustic sensors, temperature compensation in integrated chips, liquid transportation in biological and chemical applications. In order to evaluate the device performance and practical applicability, investigations have been done on the device behavior as an acoustic sensor. Further, the deep cavity sealed with Pyrex glass and a sandwich structure on the front side with Al/ZnO/Al has been developed. This fabricated structure exhibits resonance frequency of 84kHz with high sensitivity of 58 μV/Pa.