Micromachines
　　Micro-machines, which are very much smaller than conventional machines, are expected to bring about dramatic technological innovation in many areas including plant maintenance and medical science. Recognising the future importance of micro-machines, the Agency of Industrial Science and Technology began work on micro-machines early on in the development of the field in 1991, with a 10-year Industrial Science and Technology Program entitled: "The Research and Development Project on Micro-machine Technology". In this project, we are studying nine selected core themes considered essential for developing practical and reliable micro-machines and covering processing, assembly technology, mechanism configuration, micro-operation, control technology, and evaluation technology.
　
　　Machines for producing micro-parts are far larger than the parts which are made, and this generates much wastage. The concept of the "Micro factory" was therefore developed in which production machines are made smaller - similar to the size of the product - in order to save energy, space, and resources. For example, a new micro-lathe was proposed which demonstrates the feasibility and effectiveness of this concept. Work will continue on developing basic component technologies, system technologies, and methods for evaluating the economic effects of micro factories.
　　Four of the nine research themes are described in more detail below.[220,233,234,238]
　
Direct wafer bonding at room temperature
　　Bonding technology is important in the fabrication of three-dimensional micro-structures and in realizing flexible fabrication processes using various combinations of materials. Application of bonding so far has been limited to simple silicon structures because most methods require heat and/or high voltage, both of which may damage the materials and microstructure.
　
　　A new method of bonding silicon wafers at room temperature has been developed. As shown in the Fig.1, the surfaces to be bonded are etched by Ar beam sputtering which creates a clean surface with high bonding capability. The surfaces are then bonded in vacuum, without prior exposure to the atmosphere, and bonding strength equivalent to bulk strength is achieved at room temperature. It is also not necessary to load the components in order to force them together during the bonding process. This method has significant advantages over conventional techniques.
　
　　A mesh pattern micro structure with 100μm line width was successfully bonded using the technique. The specimen fracture surface is shown in the Fig.2, and fracture from the silicon bulk indicates strong bonding. These results demonstrate the potential of the method for many different applications.[218,224]
　
Fig.1 Bonding in vacuum after Ar beam etching.
　
Fig.2 Bonding of micro structure after fracture.
　
　
Tensile tests of micro fabricated thin films
　　A novel tensile testing machine has been used to measure the mechanical properties of 0.5μm thick titanium films and 1.0μm thick aluminium films. The films are difficult to handle because they are so fragile and were fabricated in a protective silicon frame using semiconductor manufacturing technology. The test section was 300μm wide and 1000 - 1400μm gauge length. The specimens were gripped with a new device using a micrometer so that they could be easily mounted on the testing machine. Stress-strain diagrams were measured continuously at room temperature. The results showed that both titanium and aluminium thin films had smaller breaking elongation but larger tensile strength than pure bulk material at room temperature.[219,223,228,237]
　
Fig.3 Tensile Machine.
　
　
Micro fabrication using a micro manipulation System
　　Micro-manipulation technology has many potential applications, including microscopic surgery and the assembly of complete micro-machines from miniature components. We have developed a two-fingered micro hand based on sequentially arranged parallel mechanisms with six degrees of freedom. Precise manipulation of microscopic objects has been achieved using tele-operation control and an auto-focus microscope.
　
　　Assembly of micromachines from miniature components requires the application of adhesive drops which are smaller then the components themselves. These ultra-low volumes of adhesive are achieved by making use of capillary phenomena in a glass pipette. After heating and drawing a glass pipette to shape the tip, a glass fibre is inserted into it and a microdrop of adhesive created by pressurising. This simple technique does not require precise pressure control, and a micro-scarecrow only 25μm in height was successfully assembled as a demonstration.[231,232]
　
Fig.4 Micro scarecrow.
　
　
Micro-lathe development
　　A lathe much smaller than conventional machines has been developed. It comprises an x-y stage driven by laminated piezo-actuators, a main shaft driven by a micromotor, and a tool rest. It measures 32mm long by 25mm deep by 30.5mm high. The machine weights 100g and power consumption of the main shaft drive is approximately 1.5W. The lathe is approximately 1/50th of the size of the conventional lathe, 5000 to 10,000 times lighter, and the power consumption is reduced by a factor between 500 and 1000.
　
　　In tests, a brass rod 2.0mm in diameter was cut on the lathe. Surface roughness in the feed direction was Rmax=l.5μm, and the roundness was 2.5μm. The cutting accuracy is equal to or better than that of a conventional lathe. By using very small machine tools, production systems for small components and mechanical devices will become considerably smaller with concomitant savings in space and energy consumption.
　
　　We are currently working on a high-speed, high-precision spindle with integrated motor, an inching worm feed mechanism with improved accuracy and control, microposition sensors (encoders), and an integrated numerical control system - all of which are necessary for developing micro-machine tools. [220,233,234,238]
　
Fig.5 The micro-lathe.
　

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produced by General Research Counselor