Study On Dielectric Character Of SiO₂ Under Applied Stress

Due to dielectrostriction,the dielectric property of dielectric will change under stress.As dielectric,SiO₂ films present in many MEMS and integrated Circuits,so the change of dielectric property affect the performance of capacitor components.Though some literatures referred this effect from the theory or experiment,there was no theory that can directly calculate the change of dielectric constant with stress and the relationship between the thermal SiO₂ dielectric is unclear,so as the dielectrostriction in SiO₂ films,which will research in this paper.The dielectrostriction coefficient reveals the degree of strain effect on the dielectric property.Start with a single relative dielectric constant in isotropic materials and linear relationship between dielectric susceptibility and the stress,the formulas of the dielectrostriction coefficient of isotropic dielectric under nonconstrained and constrained conditions have been derived,include M₁₁ and M₁₂.The coefficient was related to the initial dielectric constant,Young's modulus and Poisson's ratio.To measure the dielectrostriction coefficient M₁₂ and M₁₁,different load of pressure, lateral stress,longitudinal stress were studied,and the corresponding structure of MEMS thermal SiO₂ capacitor were designed,along with the pressure chamber,3-D stage,the capacitance was measured by LCR meter.For different SiO₂ capacitor structure,the formulas of the capacitance change under different stress state formula were derived to analyze the dielectric changes of thermal SiO₂,the dielectrostriction coefficient were measured.In order to avoid the capacitance was repeatedly polarized by AC,a DC charge/ discharge capacitance measuring system was designed based on FPGA.Make use of ADC and LCD resources on SPARTAN-3E development board to play a parallel,high-speed characteristics of FPGA,the charging voltage were sampled in equal time interval to achieve a capacitance measurement function,dielectrostriction was attempted to study by FPGA.The formulas derivation of dielectrostriction coefficients provides a way to further study dielectrostriction in isotropic dielectric.The experiments and the FPGA measurement systems are efforts for studying dielectrostriction.