SIMULATION OF A HUMIDITY-SENSITIVE DOUBLE-LAYER SYSTEM

Humidity-dependent swelling of polyimide layers on silicon membranes is described. A simulation strategy using the finite element method (FEM) to predict the resultant deformation of the double-layer system is obtained. A humidity extension coefficient alpha(phi) is introduced and determined by means of X-ray bending measurement and backward simulation. The FEM is used to investigate the influence of possible technological tolerances of layer thickness, coefficient alpha(phi) and chip-clamping on the behaviour of the system. For convenience an analytical equation for temperature- or humidity-induced deformation of bimorphs is presented, using the concentrated-element theory. Finally, a comparison of the results simulated by FEM shows a satisfactory agreement with experimental investigations.