Modeling a MEMS Thermal Conductivity Pressure Sensor for the Evaluation of Glass Frit Vacuum Packaging

Developing an accurate model for MEMS devices and structures is a great asset for future design optimization and provides insight into experimental results. A thermal conductivity pressure sensor was microfabricated to evaluate the success of a glass frit vacuum packaging scheme. The sensor and the package dimensions present classical size effects that must be included in the model for accuracy. It was found that the experimental data correlates quite well with the developed model but with a few shortcomings. Introduction be capable of producing a hermetic seal. Portable power has been an important Intermediate material bonding is the optimal demand in our technologically advanced bonding method for the fuel cell and society. From laptops and cellular phones, thermophotovoltaic systems due to the to unmanned military probes and battle field constraints imposed by the device design electronics, high density compact power is and fabrication processes. Glass frit is the needed. The majority of current portable ideal material to use since it is relatively power sources are lithium-ion batteries but versatile, electrically insulating, and has they may soon fall behind on the increasing excellent reflow characteristics. demand for higher power densities. An A thermal conductivity pressure sensor attractive option is to take advantage of the consisting of a platinum heating element high energy to weight ratios associated with sitting on a silicon nitride membrane was combustible fuels. fabricated as a test structure. Power Fuel cell systems, microengines, dissipated in the resistor has a direct thermoelectric, and thermophotovoltaics are correlation to the pressure within the several power generation schemes that package and is used as the sensing utilize these fuels. Extensive work has been mechanism [1]. The device is designed to done on the fuel cell systems and permit a four-point probe measurement to be thermophotovoltaics but both require a taken after a successful bond. The purpose vacuum environment for efficient energy of the measurement is to determine whether conversion. Poor thermal isolation degrades the desired vacuum package was achieved or device performance substantially so a simple not. Developing an accurate model with a solution is to use a vacuum package to thorough understanding of the various heat minimize the heat loss. transport mechanisms involved will be very Methods such as anodic bonding, silicon useful for the interpretation of experimental fusion bonding, and intermediate material data. bonding with solder or glass frit is known to