Three-Phase Electrostatic Rotary Stepper Micromotor With a Flexural Pivot Bearing

Electrostatic stepper motors, also known as synchronous variable-capacitance motors, operate by utilizing the electrical energy stored in the variable capacitances formed between the poles of their rotor and stator. We present the design, modeling, and experimental characterization of a three-phase rotary stepper micromotor that employs a flexural suspension of the rotor to avoid any frictional contact during operation, providing precise, repeatable, and reliable bidirectional stepping motion without feedback control. A monolithic micromotor with high-aspect-ratio poles and an integrated three-phase electrical network was fabricated in a standard single-crystal silicon wafer by combining vertical trench isolation and bulk micromachining. The experimental characterization of a prototype having a diameter of 1.4 mm has demonstrated a rotational range of 26° (±13°) at 75 V and a maximum speed of 1.67°/ ms. Half-stepping and microstepping operation modes were demonstrated with step sizes of 1/6° and 1/48°, respectively. The exceptional performance of the motor makes it suitable for use in hard-disk drives as a secondary stage actuator to maintain a constant orientation between the read/write head and the recording tracks.