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:
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.
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.
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. .
MEMS Resonator chip
MEMS Resonator, wire bonded to a 44-pin J-LDCC package
Frequency Response
of MEMS Resonator
Magnitude(yellow) & Phase(blue)
Computer Controlled Test System
Controlled Test
Environment
Computer running
LabView software
GPIB Bus
MEMR
Gas into Test Chamber
Gas
HP 4194A Impedance/Gain
Spectrum Analyzer
Carrier Gas
Gas Flows
MFCs
USB Bus
Quartz crystal Monitor
Analog Control Voltages to MFCs
Analog Voltages from MFCs
to Monitor Flow Rates
Frequency from
MEMR and QCM
Bubbler
Thermocouple
GUI Window displayed by the LabView control program for MEMS Gas Sensor characterization
Schematic diagram of the test system for
MEMS Gas Sensor characterization