Narrow-gap DNA tweezers for short DNA molecules

Abstract

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.