Design of a Computer Controlled Test System for

Design of a Computer Controlled Test System for Automated Characterization of MEMS and QCM Gas Sensors University of Southern Maine Electrical Engineering Department Authors: Robert Mac. Kinnon and Joshua Ward Advisor: Prof. Mustafa Guvench Abstract: MEMS Resonator, wire bonded to a 44 pin J-LDCC package Micro-Electro-Mechanical-Resonator (MEMR) based gas sensors are being developed at the Microelectronics Research Labs of Electrical Engineering Dept. at USM. This project involves design and development of a computer-controlled test system to measure and characterize response of these devices to various gas mixtures and concentrations. MEMR resonance frequency is determined by the inverse of the product of its vibrating mass and its spring constant. Therefore, just like Quartz. Crystal-Microbalance (QCM) sensors, a Silicon MEMR device coated with a thin film of a polymer with gas absorption properties, responds to the presence and concentration of the gas to be sensed with a decrease in its resonance frequency. MEMS Resonator chip The system we have developed employs Lab. View as GUI software platform for interfacing, communication, data acquisition and control between a personal computer and the measurement setup via a GPIB bus and the USB ports. The Lab. View program developed communicates through a data acquisition unit, “Personal DAQ 3001” from IOTech, to achieve control in synchronization with the measurement, monitoring and recording of sensor response. Mass flow controllers (“MFC”s) are used to control the flow of the gases during the tests. The Lab. View program written measures and monitors the frequencies of both MEMR and the quartz crystal gas sensors, monitors and controls temperature of the MEMR device under test as it steps the concentration or composition of the gases via three MFCs. Finally, the program saves all the data being generated for later data processing and correlation to determine the response of the sensors under test to the gases used in the experiment. Computer Controlled Test System This project was done to satisfy the senior design requirements of the authors in Engineering. It was funded by grants from NASA/Maine Space Grant Consortium and USM Faculty Senate. . Computer running Lab. View software Frequency Response of MEMS Resonator Magnitude(yellow) & Phase(blue) Quartz crystal Monitor MEMR Controlled Test Environment HP 4194 A Impedance/Gain Spectrum Analyzer Gas into Test Chamber GPIB Bus Frequency from MEMR and QCM Bubbler Thermocouple MFCs Analog Voltages from MFCs to Monitor Flow Rates Gas Flows USB Bus Analog Control Voltages to MFCs Gas Carrier Gas Schematic diagram of the test system for MEMS Gas Sensor characterization GUI Window displayed by the Lab. View control program for MEMS Gas Sensor characterization