Electrostatic Rotary Stepper Micromotor for Skew Angle Compensation in Hard Disk Drive

Circular data tracks in present-day hard disk drives (HDD) are accessed by a read/write head mounted on a support arm, which is swung by a voice coil drive. The orientation of the head relative to a data track varies with the radial position of the track, causing an increase in data track misregistration and limiting the performance of HDD. We present a rotary micromotor which can be used as a secondary stage actuator to maintain a constant orientation between the head and the tracks during disk operation. This electrostatic stepper micromotor, bulk micromachined in a standard monocrystalline silicon wafer, uses flexure pivots to avoid any frictional contact of the rotor, providing precise, repeatable and reliable bidirectional stepping motion without feedback control. The experimental characterization of a prototype having a diameter of 1.4 mm has demonstrated a rotational range of 26deg (+/- 13deg) at 75 V, a resolution of 1/6deg in a coarse stepping mode and a maximum speed of 1.67deg/ms.