TECHNOLOGICAL PROCESSES FOR MICRO-HEATER AND MICRO-HOT-PLATE IN THE IMPLEMENTATION OF A MEM GAS SENSOR, J L GONZaLEZ-VIDAL1, ALFREDO REYES-BARRANCA2 Y WILFRIDO CALLEJA ARRIAGA3., 2ND INTERNATIONAL CONFERENCE ON ELECTRICAL AND ELECTRONICS ENGINEERING, MeXICO, D. F., 7-9 SEPTIEMBRE DE 2005, 440-443. IEEE CATALOG NUMBER: 05EX1097. ISBN: 0-7803-9230-2
In this work a microsystem fabrication process for a microheater (MH) and a microhotplate (MHP), as well as their electrical behavior, are reported. This microstructure consists of a SiO2 membrane supported by four cross shaped beams, and two layers of polysilicon (poly1 and poly2); poly1 forms the microheater and the poly2 layer works as a micro hot plate (MHP), whose function is to achieve a homogeneous temperature distribution all over the microsystem. Both poly1 and poly2 are separated by a SiO2 layer, isolating them electrically, and were patterned by lift off process. The microstructure or membrane is located over a micropit (IMP) that was made by etching the Si substrate with KOH for seven hours; a Si3N4 sacrifice layer was used for this purpose. Electrical contact for the layers was made evaporating aluminum and patterned by lift off also. Electrical measurements were made by applying a ramp from -1.5 V through 1.5 V and measuring the current through poly1 and poly2, with temperature as a parameter, changing temperature with 25 C steps, from room temperature up to 300C, heating and cooling. The temperature coefficient of resistance (TCR) for poly1 and poly2 was calculated.