Toshiki Hirano

Design, fabrication, and operation of submicron gap comb-drive microactuators

Making submicron interelectrode gaps is the key to reducing the driving voltage of a micro comb-drive electrostatic actuator. Two new fabrication technologies, oxidation machining and a post-release positioning method, are proposed to realize submicron gaps. Two types of actuator (a resonant type and a nonresonant type) with submicron gaps were successfully fabricated and their operational characteristics were tested experimentally. The drive voltage was found to be lower than that of existing actuators. The stability of comb-drive actuators is discussed. >

Dual-stage servo controller for HDD using MEMS microactuator

A MEMS microactuator provides a low-cost and high-performance solution to realize high track densities of HDD, because of the batch fabrication process and its clean mechanical characteristics. However, the servo system to control such a dual-stage system tends to be more complicated than a conventional HDD system. In this paper, a simple and efficient design method of a dual-stage servo controller for HDD applications is described. The experimental results of the track following control with the dual-stage actuator using a conventional VCM and a MEMS microactuator showed that the fourth-order servo controller can achieve a high bandwidth of more than 2 kHz.

High-bandwidth high-accuracy rotary microactuators for magnetic hard disk drive tracking servos

Reports on the design, fabrication, and testing of an electrostatic microactuator for a magnetic hard disk drive (HDD) tracking servo. The design requirements for a microactuator are investigated. These include high Z-directional stiffness, low in-plane stiffness, high structural aspect ratio, large output force, high area efficiency, low cost, and mass batch production. An area-efficient rotary microactuator design was devised, and microactuators were successfully fabricated using innovative processing technologies. The microactuator has a structural thickness of 40 /spl mu/m with a minimum gap/structure width of approximately 2 /spl mu/m. Its frequency response was measured and it was determined that it can be modeled as a second-order linear system, up to the 26-kHz frequency range. Moreover, the microactuator will enable the design of a servo system that exceeds a 5-kHz servo bandwidth, which is adequate to achieve a track density of more than 25 kilotrack per inch (kTPI). The microactuator/slider assembly was also tested on a spinning disk, with its position controlled by a PID controller using the magnetic position error signal written on the disk. An accuracy of about 0.05 /spl mu/m was observed when the servo controller was turned on. Continuous-time dual-stage servos were designed and simulated using the /spl mu/-synthesis technique. A sequentially designed SISO and a MIMO control design method have been shown to be capable of meeting prescribed uncertainty and performance specifications.

An integrated lateral tunneling unit

A micromachined device developed to perform displacement-controlled tunneling is described. Its performance was experimentally confirmed. The lateral tunneling unit (LTU), composed of a comb-drive actuator, a tunneling tip, and an opposing wall integrated on the same wafer was fabricated using surface micromachining with only one photomask. Integration of the tip and its opposing wall eliminated coarse positioning of the specimen, and realized a fully micromachined tunneling unit. The lateral configuration is easy to fabricate and suitable for integrating other structures such as an atomic force microscope (AFM) tip. The LTU can be used as an extremely sensitive position detector. Possible applications, such as an accelerometer and an integrated AFM/LTU chip, are discussed.<<ETX>>

MEMS milliactuator for hard-disk-drive tracking servo

This paper describes the design, fabrication, and operational characteristics of a MEMS milliactuator designed for servo tracking in a hard-disk drive (HDD). The actuator is designed to increase the bandwidth of an HDD tracking servo and pack more recording tracks on a disk. An Invar (low thermal expansion metal) electrode position process was developed to meet the thermal stability requirement. The electroplated Invars thermal coefficient of expansion is as low as 6.3/spl times/10/sup -6//K, which is almost half of that of pure nickel. For the plating mold pattern definition, a high-aspect-ratio polymer etching technique was developed. A high-aspect-ratio structure line-and-gap definition is required to achieve both a high directional stiffness ratio and electrode efficiency for the actuator. The etching technique described can etch through a thick (<40 /spl mu/m) polymer layer with an aspect ratio of 16:1 at an etch rate of <2 /spl mu/m/min. Low-cost/high-volume manufacturing is achievable by this batch fabrication technique. A milliactuator was fabricated and assembled with a suspension and a slider weighted at around 2 mg. The slider was successfully driven by the milliactuator while the slider was flying on a spinning disk. The operational characteristics (frequency response) of the in-flight milliactuator were measured, and the results indicate that the actuator is suitable for high-bandwidth HDD servo-tracking applications.

Array-driven ultrasonic microactuators

The authors present the design of an array-driven ultrasonic microactuator. Unlike a conventional ultrasonic motor, the array-driven ultrasonic microactuator consists of many distributed modules, using a concept similar to that of the distributed microactuator array. With a conventional ultrasonic motor, it is difficult to control an object locally and to obtain sufficient resolution of the rotor position and orientation without closed-loop control, since the motion of the rotor is produced by traveling waves on the whole diaphragm. However, an array-driven ultrasonic microactuator can control the motion with high accuracy even in open-loop control, because it can control the motion of each distributed module. It uses perpendicular motion, which is suitable for an electrostatic-force-type actuator. Perpendicular motions produced by two transducers in each module are mechanically transformed into circular motion, and a set of circular motions of the micromodules induces motion in the object.<<ETX>>

Silicon microprobing array for testing and burn-in

A silicon microprobing array made by the micromachining technique is proposed for testing and burn-in at the die level. The microprobing array is made on a silicon substrate to avoid misalignment caused by mismatching of the thermal expansion rates. The die to be tested is placed face down on the microprobing array surface, and compliance in the direction perpendicular to the substrate is realized by means of a membrane covering a microcavity in the silicon substrate. A microprobing array was successfully fabricated, and a basic contact experiment showed that it can establish good contact even at high temperatures. A contact resistivity of 0.5 /spl Omega/ was measured, and burn-in was successfully carried out at the die level.<<ETX>>

Operation of sub-micron gap electrostatic comb-drive actuators

Resonant and nonresonant operation of submicron gap, electrostatic, comb-drive actuators is reported. Using a single-mask process and a 4- mu m-thick phosphorus-doped polysilicon layer as the structural material, a resonant actuator and a nonresonant, linear actuator were fabricated and tested. Resonant displacement amplitude of +or-5.2 mu m was observed in a resonant actuator with 0.3- mu m gaps when an AC drive voltage of 11.5 V (peak) without bias was applied. Maximum displacements of 3.6 mu m were observed in a nonresonant linear actuator with 0.2- mu m gaps when a DC drive voltage of 11.1 V was applied. A postrelease assembly technique is used to position and fix the comb-drive suspension such that the drive electrodes of the nonresonant linear actuator are in the submicron gap region prior to the application of the drive voltage. Measured displacements of linear actuators with 0.2-0.65- mu m gaps show little hysteresis and observed performance parameters which are in good agreement with theoretical predictions.<<ETX>>

Sub-micron gaps without sub-micron etching

The authors present a processing technique consisting of polysilicon etching, thermal oxidation of polysilicon, and silicon dioxide wet-etching which results in the fabrication of operational, submicron gaps between the electrodes of side-drive actuators, without the need for submicron etching capability. As one example of an application of oxidation machining, this technique was used to define operational submicron gaps between the polysilicon electrodes of an electrostatic comb-drive actuator and a type of linear, side-drive actuator. Experimental results have verified the fundamental principle of the fabrication and indicate that it is possible to achieve operational gaps as small as 0.2 mu m with 10,000 AA resolution.<<ETX>>

Invar electrodeposition for MEMS application

Low thermal expansion metal such as Invar is suitable for MEMS application, where the dimension stability requirement is very high over a wide temperature range. Invar electrodeposition process was developed as a method to fabricate Invar structure. The effect of plating parameters were investigated to develop optimized Invar deposition process. The Invar film obtained in this research has the thermal coefficient of expansion as low as 6.3 PPM/K, which is almost half of that of pure nickel. The process compatibility to the rest of MEMS fabrication process was proved through the prototyping of a microstructure.