Development of micro-hotplate and its reliability for gas sensing applications

This paper presents the development of a double spiral micro-heater and its reliability testing for gas sensing applications. The design and simulation of the micro-hotplate was carried out using MEMS-CAD Tool COVENTORWARE. The micro-hotplate structure consists of a 1.0 µm-thick thermally grown SiO2 membrane of area 600 µm × 600 µm over which a double spiral platinum resistor has been fabricated. A platinum resistor of 117 Ω is fabricated on SiO2 layer using lift-off technique. The platinum deposition was carried out using DC sputtering technique. The hotplate membrane release was accomplished by using both wet and dry etching of silicon. The temperature coefficient of resistance (TCR) of platinum as measured was found to be 2.19 × 10−3/°C. This value has been used to estimate the micro-hotplate temperature. The micro-hotplate consumes only 50 mW power when heated up to 500 °C. The results of reliability testing of fabricated device using pulse mode of operation, maximum current capability and thermal stability have been presented. The hotplate has been shown to continuously operate at 500 °C for more than 4 h and sustain maximum current of 23 mA and 130 cycles of pulse mode operation without any damage to the structure.