Hiroyuki Fujita

Photoresist-Assisted Release of Movable Microstructures

A simple but efficient technique to avoid the post-release adhesion problem of movable surface-micromachined structures is reported. A grid pattern of photoresist reinforces microstructures during wet etching of the underlying sacrificial layer followed by rinsing and drying. The photoresist is eventually removed by the dry process. This technique requires minimal modification to the original fabrication process while rendering batch process capability for the release of microstructures. The technique was employed to fabricate comb-drive microactuators and demonstrated considerable improvement in yield.

Microactuated self-assembling of 3D polysilicon structures with reshaping technology

This abstract proposes and experimentally confirms the automatic self-assembling of 3D polysilicon structures, compatible with both mass production and IC based surface machining. This technique combines an integrated actuation based on the scratch drive actuator (SDA), for the structure raising up, and the reshaping technology to obtain the permanent 3D shapes. Complex 3D structures have been successfully realised and their electrostatic actuation have been obtained. This self-building capability of 3D devices from silicon surface micromachining opens new integration capabilities and new application field for MEMS.

A three-dimensional shape memory alloy loop actuator

Shape Memory Alloy (SMA) actuators can produce large displacement/force and are robust against external overload. Their structure is simple because an SMA element serves as both structural and functional parts. This paper deals with deposition of thin films, heat treatment and patterning of titanium-nickel (TiNi) SMA. Microactuators have been fabricated by this process. Typical dimensions of the actuator were 10 /spl mu/m in thickness, 30 /spl mu/m in width and 800 /spl mu/m in length. They produced large displacement up to 300 /spl mu/m, and large force of more than 5 mN was generated thanks to the intrinsic recovery stress of the SMA. A three-dimensional SMA loop actuator unit composed of two SMA cantilevers is widely described. The dimensions of the loop actuator were 1000 /spl mu/m in length and 600 /spl mu/m in height. The loop actuator has been successfully operated. It features repeatable motion up to 20 Hz. The three-dimensional loop actuator is found to be very attractive to perform external work for MicroElectroMechanical Systems (MEMS).

A Reshaping Technology With Joule Heat For Three Dimensional Silicon Structures

This paper presents a new basic reshaping technology which is efficient to realize real three dimensional silicon microstructures. In this process, the elastically deformed polysilicon structure is annealed by Joule heating generated by the current passing through the structure. Plastic deformation occurs resulting in permanent three-dimensional shapes. The application of this basic process to different polysilicon structures is successfully performed. Some quantitative characteristics of the annealing effects are also investigated by means of structure deformation measurements.

Electroplated and Dry-Released Metallic Microstructures for a Lateral Tunneling Unit Application

This paper presents a new method of fabricating a lateral tunneling unit (LTU), by dry releasing of electroplated structures. An LTU is an integrated tunneling current sensing unit that has a tunneling tip and a linear actuator for moving the tip. The new fabrication method has many advantages over the existing polycrystalline silicon structure and hydrofluoric acid (HF) wet release method, namely, use of a metallic material, thicker structure, higher yield, and a safer, easier, and faster process. New LTUs and LTU-AFM probes were successfully fabricated by this method. Gold and nickel were used as alternative structural materials. The electrolytic polishing method was proposed as a new post-release processing and was used to fabricate sharp needles. The comb-drive actuator of an LTU was operated and the characteristics were measured; the results showed that this actuator has good linearity.

A Piezoelectric Quartz Microactuator for a Large Pseudo-Static Displacement

A piezoelectric quartz microactuator based on a new driving mechanism is reported. The actuator is fabricated by anisotropic etching of a Z-cut quartz substrate and operatred by means of piezoelectricity. The uniqueness of the actuator is that large static displacement is generated under AC volutage at the mechanical resonant frequency (8.5 kHz). Therefore, we call it a pseudo-static displacement actuator. The pseudo-static displacement is relatively large (40 µm), considering the size of the actuator (5 mm across). Furthermore, it is 20 time larger than the displacement in true DC volage operation.

Control of a micro tunneling unit under atomic force

We have previously reported the development and operation of a lateral tunneling unit (LTU), a micromachined device which can control the magnitude of a tunneling current passing through a vacuum gap by adjusting the distance of the gap. The amplitude of the actuator driving voltage necessary to vary the current certain range was much larger than the theoretically expected value. Its cause has been left unclear. We carried out experiments in the air and in ultrahigh vacuum (UHV), in order to determine the mechanism of the disagreement. The results of them indicated that an atomic force affects the behavior of the LTU. The estimated magnitude of the force was so large as not to be neglected compared with the actuation force of the LTU. We increased the rigidity and actuation force over 50 times and achieved stabilization. A guide to design a stable LTU and its controller will be given based on the experimental results.

A Threaded Wobble Motor A Micro Motor Generating Large Linear Displacement

SUMMARY This paper deals with the driving principle and the experimental demonstration of, a micro motor which can convert rotation into linear motion and generate large displacement. The motor is a wobble type one; its rotor and stators have screw threads. When the rotor turns, it moves linearly in the axial direction like a screw. The range of linear motion is limited only by the length of the rotor. The threaded wobble motor can be driven either magnetically or electrostatically. We have fabricated a magnetic version having a rotor of lmm in diameter and operated it successfully.