鰭式結構之雙通道氮化鋁鎵/氮化鎵高電子遷移率電晶體射頻功率元件製作與分析

Abstract

由於氮化鎵擁有傑出的材料特性，在射頻元件與功率元件應用上迅速發展，預期於未來的市場上將佔有一席之地。以氮化鋁鎵/氮化鎵高電子遷移率電晶體作為高頻元件的發展主流，此種異質結構會於接面處生成二維電子氣，進而提高元件載子遷移率與電子濃度。然而，隨著電子濃度的提升，載子遷移率將會有所下降，使元件特性不如預期。因此雙層的氮化鋁鎵/氮化鎵異質結構被提出，此種結構可以形成兩層二維電子氣，以彌補載子濃度不足的問題，但此種磊晶結構會使元件閾值電壓有很大的負偏移，透過鰭式結構可以改善此現象，閘極環繞鰭式通道結構以增加閘極控制力，除了能使元件較易關閉之外，更預期能夠有效抑制因高頻元件微縮線寬而產生的短通道效應。 本論文分做四部分，第一部分介紹了氮化鎵的材料特性與操作原理，並說明本論文研究動機，為論文概述; 第二部分首先針對單通道氮化鎵做奈米閘極元件製程介紹與直流特性分析，接著介紹高頻量測架設與氮化鋁鎵/氮化鎵高電子遷移率小訊號模型，並對元件之最佳偏壓點進行高頻特性分析; 第三部分進行雙通道元件的磊晶結構介紹與鰭式通道的微米閘極製程開發並簡述其特性，後續針對不同的通道距離做平面電晶體與鰭式電晶體的直流特性分析; 最後第四部分將透過電子束微影對雙通道元件進行閘極線寬的微縮，同樣針對不同通道距離做平面電晶體與鰭式電晶體的直流特性分析。最後建立雙通道氮化鋁鎵/氮化鎵高電子遷移率電晶體與鰭式結構之小訊號模型，透過變偏壓的量測分析電晶體之本質參數，觀察其高頻特性。

Due to the outstanding material properties of gallium nitride, there has been rapid development in its applications for RF and power devices, and it is expected to have a significant presence in the future market. The mainstream development of high-frequency devices relies on the use of AlGaN/GaN high-electron-mobility transistors, where a two-dimensional electron gas is formed at the interface, enhancing carrier mobility and electron concentration. However, as the electron concentration increases, the carrier mobility may decrease, affecting the device characteristics. Therefore, a double channel AlGaN/GaN heterostructure is proposed to address the issue of insufficient carrier concentration by creating two layers of two-dimensional electron gas. Nevertheless, this structure may lead to a substantial negative shift in the threshold voltage. The introduction of a fin structure is suggested to mitigate this phenomenon, employing a gate-surrounding fin-shaped channel to enhance gate control. This not only facilitates easier device turn-off but is also expected to effectively suppress short-channel effects resulting from the downscaling of high-frequency devices. This thesis is divided into four parts. The first part introduces the material properties and operational principles of gallium nitride and outlines the research motivation, serving as an overview of the thesis. The second part begins with the nano gate device fabrication process and DC characteristics analysis for single channel GaN devices. It further covers the setup of high-frequency measurements, the AlGaN/GaN high-electron-mobility transistor (HEMT) small-signal model, and high-frequency characterization at the optimal bias point. The third part delves into the introduction of the double channel device''s epitaxial structure and the development of the fin-shaped channel for micrometer gate fabrication. It briefly describes the characteristics, followed by DC analysis for planar transistors and fin-shaped transistors with different channel distances. The fourth part involves electron beam lithography for gate width scaling of double-channel devices. Similar DC characteristic analyses are performed for planar and fin-shaped transistors with different channel distances. Finally, a small-signal model is established for the double channel AlGaN/GaN high-electron-mobility transistor and fin-shaped structure, and the intrinsic parameters are analyzed through bias-dependent measurements to observe their high-frequency characteristics.