微米穿隧接點之微分電導與溫度關係之研究

Abstract

電子通過奈米尺度的接點之穿隧機制是一項不可或缺的研究課題。在本篇論文中， 我們製作了一系列 Al/AlOx/Y (鋁/氧化鋁/釔)與 Cr/Au/AlOx/Cr/Au (鉻/金/氧化鋁/鉻 /金)的穿隧接點(接點面積為微米尺寸)，藉由量測室溫到液氦溫度範圍的電阻隨溫度 變化的關係，以及外加大偏壓下電流與電壓的關係，來探討穿隧接點(接點面積為微 米尺寸)的穿隧機制。我們發現接點電阻率(specific contact resistivity)較小的樣品與較 大的樣品，其兩者電阻隨溫度變化的趨勢不同且微分電導對電壓的關係也不同。接點 電阻率較小的樣品，其電阻隨溫度變化的關係和大偏壓下的電流和電壓關係可以成功 用 Fluctuation-induced tunneling conduction (FIT)分析; 接點電阻率較大的樣品，其電 阻隨溫度變化的關係可以成功用 Simmons model 分析。其導致差別的原因我們猜測是 氧化層的厚度所影響，氧化層若太薄(接點電阻率較小)，電子會在電極間最靠近的區 域穿隧，則兩電極間容易形成較小的等效穿隧結(意即穿隧面積遠小於接點面積)，因 為穿隧面積很小，導致為 FIT Model 的穿隧機制; 氧化層若夠厚(接點電阻率較大)， 則有層薄絕緣層隔絕著兩電極(意即穿隧面積約等於接點面積)，導致為一般的穿隧效 應。

The electric conduction mechanism through the nano-contacts is an important study. Motivated by our previous work on metal nanowire contact, in this thesis, we fabricated a series of Al/AlOx/Y and Cr/Au/AlOx/Cr/Au micron planar tunnel junctions to address this issue. The temperature behavior of resistance and the current-voltage (I-V) characteristics in the high-bias non-ohmic regime have been measured from room temperature down to liquid-helium temperatures. We found that the tunneling behaviors in these junctions can be described in terms of two mechanisms. For samples of smaller specific contact resistivity, the temperature dependent zero-bias resistance and the high-bias non-linear I-V curves follow the fluctuation-induced tunneling (FIT) mechanism proposed by Sheng. For samples of larger specific contact resistivity, the corresponding behaviors follow the conventional elastic tunneling model proposed by Simmons. The thickness of the oxide layer is suggested to account for this difference. For the junction having a thinner oxide layer, the effective tunneling area leads to the FIT mechanism. On the other hand, for the junction having a thicker oxide layer, the effective tunneling area is close to the designed area and thus the conventional elastic tunneling results.