環境阻抗對點接觸單一金屬接面元件的庫倫阻塞之影響

Environment impedance dependence of the Coulomb blockade behavior in point-contact single junctions

仲崇道(Chung-Dau Chung)

指導教授 ： 齊正中 ； 陳啟東

國立清華大學/理學院/物理學系/博士(2009年)

https://doi.org/10.6843/NTHU.2009.00442

摘要

本論文以單一金屬結點接觸實驗探討環境對庫倫阻塞現象的影響。本元件的製作是以鉛作為點接觸的上電極，以鈷做為點接觸的下電極中間以氮化矽薄膜(厚度約三十奈米)作為絕緣層。在此點接觸結構下的元件有不同的接觸面積，我們在溫度範圍(300K~2K)研究這些元件的電子傳輸行為。在室溫之下，所有的元件均表現線性的電流偏壓特徵曲線。由此我們定義出漸進線電阻Ra。我們發現在室溫下元件具有高阻值時 (Ra > RK≡h/e2) 當我們將之下低溫量測時有趨向絕緣體的傳輸特性。它們的零偏壓電阻隨溫度下降而上升，而它們的電流偏壓特徵曲線顯示出在零偏壓附近其傳輸電流減小。另一方面，我們發現在室溫下元件具有低阻值時 (Ra < RK) ，它們的零偏壓電阻隨溫度下降而下降，有趨向導體的傳輸特性。而它們的電流偏壓特徵曲線在零偏壓附近呈現線性。我們引進簡單電路模型的應用來解釋我們在實驗上看到的現象。該電路模型由一單一金屬節(金屬節電容並聯穿遂電阻) 再串聯環境阻抗。金屬點接觸元件便由單一金屬節所感受到的附近環境任意金屬結晶堆砌形成不同的環境電阻所描述。電流偏壓特徵曲線與零偏壓下的微分電導對溫度的變化皆由P(E)理論模擬出結果。P(E)理論是描述穿遂電子在具有能量E之下，與環境交換能量的機率。在元件製程的過程中我們發現奈米孔隙附近出現煙囪狀的金屬結構。這些煙囪結構的成核過程發生在Si3N4薄膜上的奈米孔隙附近並可藉由液態氮冷卻的過程中觀察此成核過程 而此過程可以藉由熱蒸鍍、濺鍍等不同的方式形成。

關鍵字

庫倫阻塞 ； 單一金屬接面 ； 環境 ； 漲落 ； 耗散

並列摘要

In this thesis work, the effects of environment on Coulomb blockade behavior in point-contact single junctions are studied experimentally. The devices consist of a lead top-electrode and a cobalt bottom-electrode which are separated by a thin Si3N4 membrane with a nanopore within which the two electrodes form a junction. The transport behaviors of the point-contacts with different contact areas were investigated for temperatures ranging between 2K and 300K. At room temperature, all devices exhibited linear current-voltage (IV) characteristics with a well defined asymptotic resistance Ra. The devices showing high resistance (Ra >RK≡h/e2) at room temperature exhibited insulating behavior with the zero-bias resistance Ro increases with decreasing temperature, and the IV curves showed a suppression in current at low-bias voltage region. On the contrary, the devices showing low resistance (Ra < RK) at room temperature exhibited metallic behavior with Ro decreases with decreasing temperature, and the IV curves were linear in the voltage region of interest. A model circuit was proposed to explain the observed behaviors. This model consists of a single tunnel junction (a capacitor shunted with a tunnel resistor) connecting in series with environment of variable impedance. The single junction represents the point contact, which sees an environment comprising randomly stacked metal grains.
The IV and Ro(T) characteristics of this model circuit were calculated based on P(E) theory which describes the probability for energy exchange between tunneling electrons with energy E and the environment of various impedance, and a good agreement was obtained.During the course of device fabrication, we noticed the presence of chimney metal structures surrounding the nanopores. The chimneys are considered to be formed by nucleation process at the edge of the Si3N4 pores because this process can be observed by cooling the substrates with LN2. The nucleation process has been tested using different evaporation methods, evaporation rates with various metals and is found to be very robust.

並列關鍵字

Coulomb Blockade ； single junction ； environment ； fluctuation ； dissipation

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