Wide Range Variable Capacitance Controlled by Electrostatic MEMs

Our study describes design of wide range variable capacitor controlled by electrostatic MEMs actuator. The capacitor consist of two 1000μm
²
doped polysilicon plates, which are aligned one above the other and separated by 0.5μm thick dielectric BaTiO
3
. High dielectric constant of selected insulator and a large area plates of the capacitor provides maximum capacitance of about 0.15μF (micro-farads). Moving the upper plate of the capacitor in a vertical direction quickly decreases the total capacitance by many orders of magnitude, linearly proportional to the distance between capacitor plates. Flexible wires attached to the capacitor could be connected to AC terminals of any tunable circuitry, such as resonance amplifiers or to the two terminals of voltage-controlled oscillators (VCOs). The movements of the varactor’ upper plate is provided by electrostatic actuator controlled by 1V to 5V DC voltage. The electrostatic actuator is designed to be a second capacitor positioned above the varactor and aligned to the vertical axis of movement. To solidify operation of the system the upper plate of the varactor is covered by epitaxially grown 0.5μm thick SiO
2
layer. On top of the insulating layer the well doped 0.5μm polysilicon plate (lower plate of the actuator) is deposited. The most critical point of proposed design is the suggestion to have the entire system below of the wafer surface, avoiding occupying the precious territory of integrated circuit. The potential fabrication steps using MEMs sculpturing technology are described.