Takahiro Kudo

Photo-induced preferential anodization for fabrication of monocrystalline micromechanical structures

Photo-induced preferential anodization (PIPA) for fabrication of monocrystalline micromechanical structures is presented. P-type silicon formed in an n-type substrate is preferentially anodized in an aqueous solution of hydrofluoric acid under illumination. This technology is based on anodization and the photovoltaic effect. In experiments, dependence on light intensity, HF concentration, and the ratio of the pn-junction area to the entrance area of the HF solution was investigated. It was found that porous silicon conditions depend on light intensity and HF concentration and that anodic current density provided by a pn-junction is the most important factor for controlling PIPA. A monocrystalline microbridge structure 1 mu m thick, 20 mu m wide, and 300 mu m long was formed using this technology.<<ETX>>

Differential Pressure Sensor With Micromachined Overrange Protectors

A differential pressure sensor which has protectors on both sides for overrange pressure is presented. There are two narrow gaps (-lpm) on both sides of a square diaphragm on the sensor. When the overrange pressure is applied, the diaphragm contacts the planes which face the narrow gaps and is protected from fracturing. The sensor also works as a high-pressure vessel and a hermetically sealed electrical feedthrough. An overhang structure was created to improve the strength of the bonded structure of a silicon chip and a pyrex glass base. These structures are integrated with a silicon sensor chip using micromachining technology. The measurement range of the sensor is f100kPa and the sensor withstands an overrange differential pressure and static pressure which are a few hundred times over the measurement range.