Transcript Slide 1
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 MacKinnon and Joshua Ward Advisor: Prof. Mustafa Guvench Abstract: MEMS Resonator, wire bonded to a 44pin J-LDCC package MEMS Resonator chip 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 QuartzCrystal-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. The system we have developed employs LabView 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 LabView 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 LabView 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. Frequency Response of MEMS Resonator Magnitude(yellow) & Phase(blue) 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 Controlled Test System . Computer running LabView software Quartz crystal Monitor MEMR Controlled Test Environment HP 4194A Impedance/Gain Spectrum Analyzer GUI Window displayed by the LabView control program for MEMS Gas Sensor characterization Gas into Test Chamber GPIB Bus 1 2 3 4 5 Frequency from MEMR and QCM Bubbler 14 6 Thermocouple 7 MFCs Analog Voltages from MFCs to Monitor Flow Rates Gas Flows USB Bus 13 12 11 10 Analog Control Voltages to MFCs Gas Gas Carrier Gas Schematic diagram of the test system for MEMS Gas Sensor characterization 9 8 1) Actual Frequency from the MEMR attached to counter 0 of the Daq 3001 2) Actual Frequency from the Quartz Crystal attached to counter 1 of the Daq 3001 3) Voltage outputted from PID to heater. ON/OFF button to shut voltage output on or off from DAQ 4) Temperature set by user at start-up of the program, temperature the user wants the MEMR to reach 5) Actual thermocouple (TC) temperature reading 6) When pressed, will first turn all voltage outputs to 0 then stop the program 7) Graph of TC temperature over time, which is the temperature of the MEMR device. Graph is set to auto scale. Therefore, a slight difference in temperature will appear large. 8) Graph of voltage output from each MFC over time. This voltage can be correlated into the actual gas flow from each MFC. 9) Present time, in seconds, from the start-up of the program. 10) Actual voltage output from MFC, which can be correlated into the actual gas flow. 11) Voltage being outputted from the Daq 3001. 12) Voltage set by the user at the start-up of the program. 13) LED indicates when the Daq 3001 is outputting a voltage, which causes that specific MFC to start flowing. The ON/OFF button allows the user to shut the voltage OFF or ON to that specific MFC. 14) Graph of frequency of both the MEMR device and the Quartz Crystal on same graph.