Makoto Mita

A Scratch-Drive-Actuator array is fabricated in an inverted way. According to the applied square wave of ±90V from 100Hz to 100kHz, the inverted SDAs successfully conveyed an object placed on it to the designed direction. Since SDA is a microactuator with several ten μN of force and several ten nm of actuation step, the inverted SDA will be a key device of precise, powerful conveyance system over a large area.

Simultaneous visual control of tip position is indispensable for in-situ observation of nanoscopic phenomena at the tunneling gap. In this paper we propose a one-chip tunneling control device, which is small enough to load on a standard sample holder of the transmission electron microscope (TEM). Tunneling probes and micro actuators have been successfully integrated on a 2.4 x 2.4-mm(2)-chip by silicon micromachining technique. A pair of sharp silicon tips is obtained by the combination of stress-induced oxidation and selective etching of silicon oxide. Typical dimensions of the tips are 10 nm in radius and I mum in length with a 200-nm-initial gap. An electrostatically operated comb-drive actuator is used to close the gap with a voltage around 100 V. The tunneling tips are suspended over a through hole in the base substrate, and the tunneling gap can be observed by TEM. We found that clear images could be obtained without distortion or shift due to the driving voltage applied to the integrated actuator.

We have newly invented a micromechanism for precise position control, which is equivalent to that of an electrical digital-to-analog converter(DAC) of the R-2R resistor network. The micromechanical C-2C compliance suspension network has been fabricated on a silicon-on-insulator wafer by a micromachining technique. When N-bit digital driving voltages are applied to the micromechanism, cascaded electrostatic microactuators produce a set of displacements of +/-1 mu m. These displacements accumulate in the suspension network with binary weights to synthesize DAC-like displacement output. A traveling displacement of 6 mu m is obtained while the positioning resolution is 0.38 mu m in the case of 4 bit input. Resolution can be improved further by increasing the addressing size of the input.

With the promotion of SPM technology, scientific interest has expanded from visual observation of static nanometric structures to in-situ investigation of mesoscopic phenomena, such as quantized electrical conductance of atom bridges. Bringing two probes or more into a tunneling distance is needed to determine the transfer function of the nanometric specimen. Technical difficulties lie in reducing the tip radius and the total size of the tip-positioning mechanism. For this reason we have previously proposed lateral tunneling unit that is a tunneling probe integrated with an electrostatic actuator produced by silicon micromachining technique. Size reduction of the whole SPM systems was found to work in favor of improving the control accuracy of tip-positioning as well as suppressing the effects of thermal drift and external vibration. Based upon these results we have recently developed such one-chip STM (scanning tunneling microscope) which is small enough to be loaded in the chamber of the transmission electron microscope. A pair of pre-aligned sharp tunneling tips has been successfully fabricated by the combination of deep dry etching and stress induced oxidation of silicon. The mutual distance of the tips is controlled by using the integrated electrostatic microactuators. The device enables us to in-situ observe atom scale phenomena in the tunneling gap.