Electronic Tongue System with Chlorine Appetite

• Main Authors: Febus ReidjG.Cruz, 古福博
• Other Authors: Wen-Yaw Chung
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/69333055714358334402

碩士 === 中原大學 === 電子工程研究所 === 96 === Monitoring the chlorine level of water within the proper range ensures that the quality of water is safe for human consumption. A microelectronics solution is hereby presented to offer an electronic tongue system with a so called chlorine appetite, a system that can measure the concentration of chloride ions (pCl) in aqueous solutions. A front-end full-custom analog readout circuit was created as interface for the chloride ion sensor which was connected in extended gate field effect transistor (EGFET) structure. Since the electrochemical characteristics of EGFET and ion sensitive field effect transistor (ISFET) are similar, with the EGFET providing the advantages of disposable sensor and of transistor isolation from the chemical environment, the readout circuit of ISFET was tested for EGFET application. This research showed that the architecture of ISFET bridge-type floating drain source follower (BFDSF) that provides constant voltage constant current (CVCC) operation to sensor functions properly not only for ISFET pH sensing but also for EGFET pCl sensing. HSPICE simulations and proto-board module tests had confirmed that BFDSF can be used as a readout circuit for ISFET with 54.69 mV/pH sensitivity from pH2 to pH12, as well as for EGFET with 28 mV/pCl sensitivity from -0.70pCl to +1.70pCl. Another part of this research was the implementation of back-end semi-custom digital sensor data processor. A module that determines the unknown pCl value based on the input data that represents the voltage generated from the readout circuit and on the predefined calibration data, was made using the conquer-and-divide scheme of binary search. The portable binary search module accommodated both the two-point and three-point calibration systems. Simulations had confirmed the correctness of binary search scheme for two-point and three-point calibration methods. Both the analog readout circuit and the digital sensor data processor used the TSMC 0.35m 2P4M CMOS technology. Moreover, this research started with the preparation of chloride ion sensor by depositing a 4-L drop of synthesized chloride ion sensitive membrane (PVC-DOS-ETH9033-TDDMACl) onto a 2-mm by 2-mm window of indium-tin-oxide (ITO) film on a slide glass substrate. This sensor (PVC-DOS-ETH9033-TDDMACl/ITO/Glass) was connected to a commercial CD4007UB MOSFET to form the EGFET structure so as to study its sensing characteristics. In addition, the CD4007UB was also characterized to extract its important electrical parameters which were used in simulations and chip implementations. With the availability of the basic design blocks of chloride ion electronic tongue system, and with their possible application to other ion sensing system, this research provided a step closer in realizing a portable multi-ion detection system for water quality monitoring and lab-on-a-chip applications.