Study of Extended-gate FET-based Dissolved Oxygen Microsensor

• Main Authors: Ren-He Chen, 陳仁和
• Other Authors: I-Yu Huang
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/35847814733946304928

碩士 === 國立中山大學 === 電機工程學系研究所 === 100 === Water resource is one of the most important natural resources on earth. In recent years, due to the discharges of large industrial and domestic waste-water into the nature, water pollution problem is getting more and more serious and how to monitor the quality of water in real time has become a very important research issue. The dissolved oxygen is one of the critical indexes for evaluating the quality of water. Although the conventional dissolved oxygen detectors presented a high sensitivity and high accuracy, the high cost, large dimension, low capability of batch fabrication and real-time monitoring will limit their applications. In this thesis, an extended-gate field-effect transistor (EGFET) based dissolved oxygen microsensor is developed utilizing micro-electromechanical system (MEMS) technology. The gate voltages of EGFET under different concentrations of dissolved oxygen can be detected by the Cr/Au sensing electrode. To further enhance the sensitivity of the proposed microsensor, a polystyrene layer with very high permeation rate of the dissolved oxygen gas is adopted and coated on the surface of Cr/Au layer. The main processing steps of the presented microsensor involve four photolithographic and four thin-film deposition processes. The influence of the channel’s width/length ratio, source/drain geometry and polystyrene additional layer on the sensitivity of the EGFET based dissolved oxygen microsensor are investigated in this study. The chip size of the implemented dissolved oxygen microsensor is 11 mm×13 mm× 0.5 mm and the sensing area is 1 mm×1 mm. As the dissolved oxygen concentration varies from 2 ppm to 6 ppm, a very high sensitivity (35.36 mV/ppm) and sensing linearity (98.83%) of the proposed EGFET microsensor can be demonstrated. In addition, the response time of the presented dissolved oxygen microsensor is only about III 180~200 seconds, hence it is very suitable for developing a real-time monitoring microsystem.