Finite-element analysis of rotor stability in an axial-drive micromotor

The effect of axial electrostatic forces on the rotor deflection of an axial-drive double-stator micromotor is studied with respect to the limits of stability against elastic rotor collapse using the finite-element method (FEM). Forces obtained from an electrostatic FE model have been applied to a structural FE model using the indirect coupled-field analysis approach. This technique may be applied to other MEMS structures with conducting components. A technical description is given of the design and the fabrication process of the axial-drive double-stator micromotor investigated. Two different axial rotor supports (bearing and bushing) are investigated. The results are discussed as a function of the applied voltage and rotor thickness considering polysilicon and aluminium as possible rotor materials. The effects on the stability of the rotor of supporting the rotor with an additional bushing, and of increasing the rotor thickness, are investigated quantitatively.