Design of a Computer Controlled Test System for
MEMR Gas Sensor Characterization
Joshua Ward
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 are developing employs LabView as the software platform for interfacing, communication, data acquisition and control between a personal computer and the measurement setup via GPIB bus and serial ports. In the set up the gas or the analyte vapor to be sensed is mixed with an inert carrier gas to adjust its concentration. Flow rates and concentration level are determined by computer controlled mass flow controllers. The LabView program written, in addition to the gas mixing ratio, controls the injection time of the analyte and, synchronizes cycling of sample temperature with purging and gas injection in the test chamber. After each injection the program triggers all measurement instruments and gathers data to quantify and generate plots of sensor response vs. injected gas concentration and temperature.
Design of a Test System and Packaging of SOI-MEMS Resonators for High Temperature Characterization
Robert MacKinnon
Silicon-on-Insulator (SOI) Micro-Electro-Mechanical-Resonator (MEMR) devices are being developed by Prof. Guvench at the Microelectronics Research Labs of Electrical Engineering Dept at USM for frequency control and gas sensing applications in high temperature environments. These miniature devices, with dimensions smaller than a millimeter and with electrical contact pads less than 50 micrometers, are very difficult to handle and test as bare silicon chips. At room temperature they are tested with electrical contacts made to their contact pads with electrodes micro-manipulated under a microscope. However, such micro-manipulated electrical probing cannot be done in an environmentally controlled test chamber operating at elevated temperatures. In order to facilitate testing of these devices at high temperatures, we are first packaging them in ceramic chip carriers using ultrasonically bonded aluminum wire. The packaged devices are fitted to molybdenum heaters designed to bring the sample temperature as high as 350˚ C. The sample temperature is measured and controlled using thermocouples embedded in the heaters by computer interfaced PID controllers. LabView is being used as software platform to achieve temperature control in coordination with the automated electrical testing sequence of the GPIB interfaced instruments of the system.
An Experimental Setup to Characterize
MEMS Resonators and MEMS Resonator Gas Sensors