Design and fabrication of micromachined sensors on energy consumption measurement for premature infants

• Main Authors: Chien-Chung Wu, 吳建中
• Other Authors: Ching-Hsing Luo
• Format: Others
• Language: en_US
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/49131527925510712680

博士 === 國立成功大學 === 電機工程學系碩博士班 === 92 === Although the conventional indirect calorimeter is a valuable tool, its size and expense prohibits its widespread use in hospitals. Furthermore, its flow-through measurement technique dilutes the respiratory variations, and hence high-precision detection instrumentation is required. These limitations may be overcome by combining MEMS with CMOS circuit design technology to develop an innovative SOC biochip as the basis of a miniaturized energy consumption measurement system. Typically, the system is designed to operate with higher oxygen concentrations. Accordingly, the current thesis deals with the development of mircromachined oxygen sensors capable of sensing higher concentrations of oxygen at a lower operation temperature of 150�aC. The proposed gas sensors consist of a polysilicon resistor and a sensing metal-oxide film placed on a thermally isolated silicon-nitride membrane or bridge. The sensing film is a tin-oxide sheet, which has been doped with a low concentration of 2wt% Li. This thesis involves the development of three different types of oxygen sensors, which are distinguished from each other by the structure of their micro-heaters. The first type is a micro-heater on a silicon nitride membrane, the second type employs a membrane located on a thin silicon layer, and the third type uses a bridge membrane with a thin underlying layer of silicon. At an operating temperature of 150�aC, the power consumptions of these three sensors are found to be 24 mW, 223 mW and 1240 mW, respectively. The resulting experimental data indicate that the proposed oxygen sensors are capable of detecting oxygen with concentrations ranging from 21% to 50%, and that they exhibit a linear output behavior. At an operating temperature of 180�aC, the proposed flow sensor demonstrates a linear behavior over a range of flow velocity from 0-10 m/sec. Besides, this thesis develops an automated oxygen concentration control and measurement system which can simulate the miniscule respiratory variations of a premature infant and can subsequently establish a suitable oxygen concentration environment to ensure the infant’s well being. The proposed system can also automatically measure the properties of the oxygen sensors, including their resistance characteristics at different oxygen concentrations, the relationship between their sensitivity and the oxygen concentration, and the influence of working temperature and humidity upon their sensitivity. The measurement data is acquired locally and can then be transmitted to a remote PC via the Internet.