Recently DNA molecules have been focused on as electronic elements in the field of nanometer-scale electronics. One of the fundamental issues in this research area is the development of methods to measure accurately an electrical conductivity of DNA wire. The DNA tweezers we have recently developed have a great advantage of measuring
the electrical current passing through DNA wire. In this paper, we investigated the electric conduction of lambda DNA molecules covered with Pd colloids using micromachined DNA tweezers that has a pair of opposing probes for retrieving DNA molecules. The molecules were retrieved from a solution containing lambda DNA by applying RF power between the probes in the solution. The retrieved molecules were then soaked in a colloidal solution containing cationic Pd particles,
which results in a DNA-Pd wire bridged between the tweezer probes. Current-voltage curves for the DNA-Pd wire can be measured between the DNA tweezers probes, and the resistivity of the DNA-Pd wire was approximately 74 Ωcm. We found through an observation by a scanning transmission electron microscope (STEM) that the surface of the wire was covered by Pd particles closely. We also measured the piezoresistance through a change in the distance between Pd
particles on a DNA-Pd wire using the DNA tweezers.
We have succeeded in retrieval of λ-DNA molecules (DNAs) with micromachined DNA tweezers and reported the retrieved DNAs are insulating. Two kinds of fabrication methods of narrow gap DNA tweezers are demonstrated. In order to form a pair of opposing sharp probes with nano meter size gap, an etch stop mechanism was examined for etching process by monitoring current between the probes. In a wet etching method, a free-standing Si bridge structure having a small cross-sectional portion is firstly formed and dipped into a small drop of KOH solution which was cooled using a peltiert device. Then an AC voltage is applied through the structure, which heats the portion of the bridge dominantly as well as the surrounding KOH solution. As the result, the local Si etching by the KOH solution lasts as long as the structure is bridged. Using this method, we could fabricate 50nm-gap DNA tweezers. In a dry etching, we also succeeded in narrow gap fabrication by etching a free-standing Si bridge structure in the probes tip of DNA tweezers using fluorine radical. The tweezers fabricated by dry etching have a pair of opposing probes with 120nm-gap.
The future CMOS generations for microelectronics will require advanced doping techniques capable to realize ultra-shallow, highly-doped junctions with abrupt profiles. Recent experiments have shown the potential capabilities of laser processing of Ultra Shallow Junctions (USJ). According to the International Technology Roadmap for Semiconductors, two laser processes are able to reach ultimate predictions: laser thermal processing or annealing (LTP or LTA) and Gas Immersion Laser Doping (GILD). Both processes are based on rapid melting/solidification of the substrate. During solidification, the liquid silicon, which contains the dopants, is formed epitaxially from the underlying crystalline silicon. In the case of laser thermal annealing dopants are implanted before laser processing. GILD skips the ion-implantation step: in this case dopants are chemisorbed on the Si surface before the laser shot. The dopants are then incorporated and activated during the laser process. Activation is limited to the liquid layer and this chemisorption/laser shot cycle can be repeated until the desired concentration is reached. In this paper, we investigate the possibilities and limitations of the GILD technique for two different substrates: silicon bulk and SOI. We also show some laser doping applications for the fabrication of micro and nanoresonators, widely used in the MEMS Industry.
This paper deals with the latest development of micromachining technology to fabricated nanoscopic structures and applications to nano- and bio- technologies. We have realized well-defined nano structures by using the combination of conventional photo-lithography, LOCOS, and wet anisotropic etching of silicon. The technology has been applied to develop micromachined field emitters that operated in the TEM (transmission electoron microscope) chamber, and the degradation process of the silicon tips was in-situ observed. In addition to this nanoelectromechanical research topics, we have recently expanded our research field into bio- and molecular engineering: silicon nanofabricated twin probes were used to directly manipulate DNA molecules, for instance. Futhermore, bio-molecular linear motors were tested as a mechanical power source for mechanically transferring micro/nano particles.