Authors: J. Jakovenko, M. Husak and T. Lalinsky
Affilation: Czech Technical University in Prague, Czech Republic
Pages: 606 - 609
Keywords: MEMS, optimization, GaAs
This work discusses the thermo mechanical simulations performed with the aim to optimise the temperature distribution of the Microwave Power Sensor (MPS) microsystem keeping the thermal stress as low as possible. The concept of the absorbed power measurement is based on a thermal conversion, where the dissipated or absorbed RF power is converted into the thermal power, inside a thermally isolated system, so called the Micromechanical Thermal Converter (MTC) device. A new MTC approach uses a GaAs with an active HEMT (High Electron Mobility Transistor) heater. New technology of low stress Polyimide has been used for MTC thermal isolation. By means of thermo-mechanical simulations, we propose a GaAs Micromechanical Thermal Converter design and a layout of the active sensor elements (HEMT heater and a temperature sensor TS) placed on the MTC structure. Spatial temperature distribution (thermal time constant, thermal stress and displacement and the power to temperature characteristics are calculated from the heat distribution. These findings are compared with results of thermo-mechanical measurement of real micromachined MTC devices. Three design concepts of the MTC have been proposed: cantilever, bridge and island structure. Using FEM simulations, the layout of HEMT transistor, temperature sensor and the MTC shapes and dimensions were optimized. The analyses were performed for both vacuum ambient and non-convective gaseous medium around the MTC structure.