SIMULATION OF A HUMIDITY-SENSITIVE DOUBLE-LAYER SYSTEM

Humidity-dependent swelling of polyimide layers on silicon membranes i s described. A simulation strategy using the finite element method (FE M) to predict the resultant deformation of the double-layer system is obtained. A humidity extension coefficient alpha(phi) is introduced an d determined by means of X-ray bending measurement and backward simula tion. The FEM is used to investigate the influence of possible technol ogical 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 compa rison of the results simulated by FEM shows a satisfactory agreement w ith experimental investigations.