Theoretical analysis of the effect of static charges in silicon-based dielectric thin films on micro- to nanoscale electrostatic actuation

Silicon-based dielectric thin films such as SiO₂ and Si₃N₄ are commonly used as insulation layers in electrostatic microactuators to protect the device from short circuiting if the electrodes are in contact. However, dielectric films can store bulk and/or surface static charges. In this paper, the effect that these static charges have on the force applied by an electrostatic actuator is analyzed. Based on a one-dimensional model, the electric field within the gap of an electrostatic actuator for a metal/gap/dielectric/doped silicon-layered configuration is calculated for three assumed charge distributions in the dielectric layer. A characteristic voltage is defined for the metal/gap/dielectric/doped silicon system with static charges, which is found to govern the interaction. It is found that when the applied voltage to the actuator is within one order of magnitude of the characteristic voltage, the real electric field within the gap can differ by many orders of magnitude from the electric field that is predicted without considering the static charges.