Design and Characterization of MEMS Thermal Converter

This paper presents design and characterization of a new GaAs based RF Microwave Power Sensor (RFMPS) microsystem. The main criteria for the RFMPS optimization are to keep the stable thermal distribution and minimize the thermal stress. The concept of absorbed power measurement is based on thermal conversion, where absorbed RF power is transformed into thermal power, inside a thermally isolated system. The Micromechanical Thermal Converter (MTC) spatial temperature dependences, thermal time constant and power to temperature characteristics are calculated from the heat distribution. The temperature changes induced in the MTC by electrical power dissipated in the HEMT (High Electron Mobility Transistor) are sensed by the integrated temperature sensor (TS). The temperature distribution over the sensing area and mechanical stress was optimized by studying different MTC sizes, and topologies of the active HEMT heater and temperature sensor

Micromechanical GaAs Hot Plates for Gas Sensors

This paper discusses the design, simulation and fabrication of new Micromachined Thermal Hot Plates (MTHPs) based on GaAs, which were designed for Gas sensors. High sensitivity and low power are expected for present metal oxide Gas sensors, which generally work in high temperature mode (which is essential for chemical reactions to be performed between molecules of the specified gas and the surface of sensing material). Because low power consumption is required, even for operation temperatures in the range of 200 to 500 oC, high thermal isolation of these devices are necessary. The problem can be solved by designing free standing micromechanical hot plates. Mechanical stability and a fast thermal response are especially significant parameters that can not be neglected. These characteristics can be achieved with a new concept of GaAs based thermal converter

Struktury MEMS pro mereni mikrovlnneho vykonu.

The thesis discusses the thermo-mechanical simulations performed with the aim to optimise the temperature distribution of the Microwave Power Sensor microsystem keeping the thermal stress as low as possible. The concept of the absorbed power measurement is based on 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 heater. A new technology of low stress polyimide has been used for MTC thermal isolation.By means of thermo-mechanical simulations we propose a GaAs MTC 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. The 3-D thermal and thermo-mechanical simulations were performed, using the Coventor Ware simulator.Available from STL Prague, CZ / NTK - National Technical LibrarySIGLECZCzech Republi