Evaluation of the orientation of thermal deformation in the surface-micromachined membrane of gas microsensors

Abstract

Within this paper we perform a simulation study of the 'bimetal' effects for the silicon-silicon dioxide membrane suspended in different manners. For this purpose, a commercial, COSMOS/M program working with finite element method has been used. We investigated the dependence of the value and orientation of the displacements of the bi-layer type membrane as a function of temperature, temperature gradient, geometrical dimensions, expansion coefficients and type of membrane support. The test structure for this simulation consists of a square SiO2 membrane of 100 X 100 micrometers 2 with 10micrometers for each layer. The connection of the membrane to the bulk silicon was performed by different manners as follows: (i) by four horizontal bridges, (ii) by four vertical legs or (iii) by its four edges. From simulation study, we have obtained the effect of the above variables on the value and orientation of the membrane deformation, as follows: a) The temperature and gradient temperature, layer thickness and rigidity of the material lead to modification of the value displacements of the membrane; b) Type of the membrane support lead to modification of the both value and orientation of t he deformation of the membrane. This study of the membrane deformation can be successfully used for designing a new gas structure based on surface micro machining and hopefully with low power consumption and predicted deformation.