Study On Preparation And Application Of Porous Silicon-Key Material In MEMS

Micro-Electro-Mechanical System (MEMS) was born in 1990's. It developed rapidly in the past 20 years. The technique in fabrication of Micro mechanical structure is the focus of MEMS research. As a new material applied in MEMS, Porous silicon (PS) displays the excellent advantage which other material cannot compare with when used as the functional and structural layer materials or sacrifice layer materials. This paper aims at the application of PS in MEMS. The research works are listed as follows:Study on the preparation of PS materials: Four methods were used to preparation PS with emphases on double-cell electrochemical etching. The control rules of the appearance and property for the PS layer such as the pore size, porosity and the PS layer deepness were studied. The wafer type, etching time and etching current density are the three main factors that control the etching. Among the four methods, double-cell electrochemical etching exhibits the minimum pore size, highest porosity and largest PS layer deepness, it also acquire best uniformity and flattest surface. In this way we can get nano-materials, etch P+<100>wafer 30 minutes with current density of 40mA/cm2, the result pore size is 5 nm.Study on PS used as functional layer and structural layer in MEMS ——the application of thermal isolation layer. The thermal isolation layer of thermal sensitivity systems must has high sensitivity of temperature change and low thermal wastage, PS with property of low thermal conductivity and large inner surface area can meet this requirements exactly. In this paper crystal silicon was used as reference materials. Comparing these two materials we got the result: The thermal isolation property of PS is much better than crystal silicon; furthermore, the higher porosity PS got, the better thermal insulation it achieved.Study on PS usied as sacrifice layer materials in MEMS. Using as sacrifice layer materials is another important application of PS in MEMS. We use electrochemical etching to achieve PS layer with several hundred micrometers deep that was use as sacrifice layer; after that, copper film with deepness of several micrometers was deposited on PS layer; Finally, PS sacrifice layer was removed by the mixed solution of 1% KOH and C2H5OH, then the structural layer was released and the simple micro-cantilever was achieved.