Patrick Breckow Chu

Nanoprecision MEMS Capacitive Sensor for Linear and Rotational Positioning

This paper presents a microelectromechanical systems (MEMS) capacitive position sensor for nanopositioning applications in Probe storage systems. The objective of the sensor system design is to develop a high-precision X-Y linear and rotational position sensor with a minimum sensor area and a large range of movements at high speed. To achieve this, first, a simple sensor noise model scalable with a sensor area was developed, in which all the parasitic capacitances are taken into account. Furthermore, a signal-processing solution was developed to compensate for the nonlinearities caused by rotational disturbances and, at the same time, to generate a rotational position signal for active rotation-control purposes. A MEMS capacitive sensor prototype was constructed with the design of a 13-mum pitch, a 300-mum peak-to-peak linear stroke, and a 3.46-mm2 sensor area at a 3-mum gap. The measured sensor noise was 0.2 nm 1sigma, which corresponds to 12 mudeg 1sigma for the fabricated prototype sensor, at 25-kHz bandwidth. Furthermore, the signal linearity was significantly enhanced by the proposed sensor signal processing, with a measured sensor signal nonlinearity of 0.78% for an 80-mum peak-to-peak stroke at 200 Hz. Finally, the capacitive sensor-based dynamic closed-loop X -Y linear and rotational position control of an electromagnetic scanner was successfully demonstrated.

Sliding Contact Micro-Bearing for Nano-Precision Sensing and Positioning

Applications involving sub-nanometer, relative, in-plane motion between two substrates require precise control of gap-spacing between substrates for, both position-sensing as well as for signal transduction between the substrates. A method of passive gap-spacing control using MEMS-fabricated rigid spacers is proposed. A model to design a low-friction and low-wear interface between the sliding substrates is developed. Prototype parts with hard-coated interfaces and with and without lubrication were fabricated and tested. Sliding friction coefficients of 0.1-0.15 or less and wear life of millions of sliding cycles were achieved on prototype parts. Better results are predicted for MEMS-scale devices.

Nano-Positioning of a Electromagnetic Scanner with a MEMS Capacitive Sensor

Abstract This paper presents the control design and experimentation of a prototype electromagnetic scanner with an integrated capacitive linear and rotational position sensor for small form factor probe storage. An array of probe heads is to be precisely positioned in X/Y linear and rotation directions so that high areal density (>1 terabit/in 2 ) and high data throughput can be achieved. The scanner has X/Y motion capabilities with a linear stroke of about 300 µm. It can also generate rotational motion with offset actuators to compensate for disturbances, mechanical tolerance and nonlinearities. System characterization, modeling, MIMO control design and simulation, and preliminary experimental results are presented. The feasibility of rotation control with the developed capacitive sensor and offset actuators is experimentally confirmed.

Head-disk spacing control for an advanced rotary tester

This paper discusses head-disk spacing (HDS) control for an advanced rotary tester (ART). With active control of HDS, the ART enables testing of individual recording head sliders and evaluation of novel magnetic recording processes with great flexibility. In this paper, system characterization and servo control design for the ART are presented. Various hardware and design issues are addressed and the corresponding solutions are provided. Simulation and experimental results show that the nominal HDS can be controlled to be within 10 nm with a standard variation of 1.5 nm.

Spinstand control characterization of an electromagnetic slider microactuator

Increasing areal densities in disc drives require high performance servo tracking systems to attenuate runout. High bandwidth, large stroke microactuators are used to improve positioning accuracy by eliminating disturbances at higher frequencies. This paper details modeling and servo control of an electromagnetic slider microactuator designed at Seagate and its promise as a solution for high accuracy tracking control. The device has passive high frequency windage disturbance attenuation due to its structure. Controller design is developed for a single stage spinstand environment to show the device effectiveness.