REDUCTION OF HEAT-LOSS OF SILICON MEMBRANES BY THE USE OF TRENCH-ETCHING TECHNIQUES

Silicon membranes are widely used for sensor applications because of t heir mechanical and electrical properties. Because of the high heat co nductance of silicon, they are often required for thermal insulation o f sensor devices like ps-sensing elements and electronic circuits. In the present paper a method to improve the thermal insulation of single -crystal silicon membranes is presented. SIMOX technology is employed for the fabrication of silicon membranes with a thickness of 5 mum, wh ere the buried oxide layer is used as a stop for backside etching. Thi s technique allows batch processing and is compatible to a standard CM OS process, so that electronic devices can be placed directly on the m embrane. Improvement of the lateral thermal insulation is achieved by etching trenches into the outer region of the silicon membrane and fil ling them with a thermally grown oxide. For a typical 600 mum X 600 mu m silicon membrane, the measured thermal resistance amounts to about 2 00 K/W. By the use of 18 trenches the thermal resistance can be increa sed to 1700 K/W (960 nm oxide). For comparison, a pure oxide membrane shows a thermal resistance of about 3500 K/W. These experimental data are in good agreement with simulations done by the ANSYS finite-elemen t program.