Reduction of heat loss of silicon membranes by the use of trench etching techniques

Silicon membranes are widely used for sensor applications because of their mechanical and electrical properties. Because of the high heat conductance of silicon, they are often required for thermal insulation of sensor devices like gas-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 fm, where the buried oxide layer is used as a stop for backside etching. This technique allows batch processing and is compatible to a standard CMOS process, so that electronic devices can be placed directly on the membrane. Improvement of the lateral thermal insulation is achieved by etching trenches into the outer region of the silicon membrane and filling them with a thermally grown oxide. For a typical 600 fm x 600 fm silicon membrane, the thermal resistance can be increased to 1700 K/W (960 nm oxide).