以Ni-DNA製作憶阻性元件

Abstract

DNA是一種長度可調的一維奈米材料，直徑為2奈米，長度則可達數微米的天然奈米線。為了增加DNA導電性，將Ni離子螯合於DNA奈米線中。本實驗中，以電子束微影與熱蒸鍍技術製成間距約為100奈米的空電極，再利用DNA硫金鍵自組裝或電泳的方式，將Ni-DNA置於電極中間製成元件，即可兩點量測Ni-DNA奈米線的電性傳輸。 由於Ni-DNA中Ni離子的氧化還原反應，在電壓掃描過程中會有負微分電阻(NDR)以及遲滯現象的發生，且氧化還原峰值大小及電壓與掃描速率有關。因為負微分電阻的特性，可讓Ni-DNA奈米線設計成為憶阻性元件。 將Ni-DNA奈米線當作記憶體材料使用時，可透過輸入電壓讀取不同Ni2+與Ni3+濃度比例下輸出電流的非對稱性，判別Ni-DNA中氧化還原狀態。並在交流與直流讀取方式比較下，發現直流讀取方式可讓狀態維持更久。另外，還可以控制不同的偏壓寫入時間，用直流讀取方式觀察出多種可分辨狀態，利用這些機制便可將元件設計成多重狀態的記憶體使用。

DNA is one of the most promising quasi-one-dimensional nanomaterials because of its adjustable length and self-assembly properties. In order to increase the intrinsic conductivity of DNA, DNA is chelated with Ni ions. In this work, the Ti/Au electrodes were deposited and patterned on the substrate by standard electron-beam lithography and thermal evaporation. Moreover, we immobilize Ni-DNA on the gold electrode surface of device by using DNA self-assembled monolayer (SAM) or electrophoretic placement. In these measurements, current flowing through the Ni-DNA was measured when the bias voltage was supplied on the two gold electrodes. I-V curves show obviously a hysteretic loop and a feature of negative differential resistance (NDR) that indicates the emergence of a memristive system. In our previous studies, we verified that the NDR effect is attributed to the redox reaction between Ni2+ and Ni3+ within the DNA base pairs. Ni-DNA nanowires are further used to demonstrate the application of memory devices. The memory device can be set by either positive or negative writing, and it can be read by current at a constant bias voltage across the pair electrodes. In addition, the polarized states remain longer in time under the DC reading in comparison with the AC reading. The multiple state of the Ni-DNA device is possibly attributed to a different ratio between Ni3+ and Ni2+ ions in Ni-DNA nanowires for different writing time. If the writing time and the writing process are precisely controlled, the Ni-DNA memory device can be operated at multiple states.