Development of a 10 nm gap DNA electric tester and investigation of electric elements based on DNA molecules

本研究的目的是开发一种具有10 nm间隙的DNA电测试仪，并使用DNA测试仪进行电元件的研究。为了形成具有良好再现性的小间隙，需要在探针制造过程中实现一种小间隙检测机制。为此，研制了一种新的窄间隙DNA测试仪的制作方法。为了检测在硅蚀刻期间一对探针之间的小间隙的形成，监测流过两个探针的电流。在该蚀刻中，仅探针结构的尖端浸入KOH溶液中，同时在两个探针之间施加AC功率。施加的电流在硅结构的最西部局部加热，导致硅的局部蚀刻。当形成间隙时，由于电流通路被中断，电流下降。因此，局部加热将结束，最终停止蚀刻。利用这种方法，大约50 nm的间隙DNA镊子可以制造。利用研制的DNA测试仪和更宽间隙的DNA测试仪，对DNA束的电学性能进行了测试。可再现和明确的结果是湿度依赖性。我们发现DNA束的电导率受湿度的强烈影响。这一结果与文献报道的结果一致。此外，我们还研制了一种Pd包覆的DNA丝，并测量了其电学特性。电线的电阻率约为74 ohm-cm。即使在真空和非常低的温度（高达77 K）下，也观察到DNA-Pd线的电流流动。由于在这种情况下湿度的影响将被消除，因此电流应该在涂覆的Pd层中流动。

The aim of this study is to develop a DNA electric tester having a 10 nm gap between two electric probes and investigation of electric elements using DNA testers. To form such a small gap with good reproducibility, a kind of the small-gap detection mechanism should be implemented for probe fabrication process. For this purpose, a new fabrication method of a narrow gap DNA tester has been developed. In order to detect the formation of a small gap between a pair of probes during silicon etching, current flow though the two probes was monitored. In this etching, only the tips of the probe structure are dipped into a KOH solution while AC power is applied between the two probes. The applying current heat up at the narrowest part of the silicon structure locally, resulting in silicon etching locally. When a gap is formed, the current is dropped since the current pass is broken. The local heating will hence finished, eventually stopping the etching. Using this method, approximately 50 nm gap DNA tweezers could be fabricated. Successive Al film deposition will make the gap smaller.Using the developed DNA testers and more wider gap DNA testers, electrical properties of DNA bundle were examined. The reproducible and explicit result is humidity dependency. We found that electrical conductance of DNA bundles is strongly affected by humidity. This result is consistent with literatures reported by other researchers.Furthermore, we have developed a Pd coated DNA wire and measured its electrical characteristics. The wire showed the electrical resistively of approximately 74 ohm-cm. Even in vacuum and at very low temperature (up to 77K), the current flow was observed for the DNA-Pd wire. Since the effect of humidity will be eliminated in this case, the current flow was supposed to be in the coated Pd layer.