短閘極場效電板增強型氮化鋁鎵/氮化鎵高電子遷移率電晶體製作與電流特性分析

Fabrication and Investigation of Current Behavior of Enhancement-Mode p-GaN/AlGaN/GaN High Electron Mobility Transistor with Submicron Gate Length

楊智淵(Jhih-Yuan Yang)

指導教授 ： 黃建璋

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2022年)

https://doi.org/10.6342/NTU202200208

摘要

隨著半導體技術發展，元件需要操作於更高的電壓以及頻率下，其中III-V族材料氮化鎵被視為極具潛力的新世代半導體材料。氮化鎵擁有高崩潰電壓及高電子遷移率的特性，和能夠操作於高壓及高頻條件下。而氮化鋁鎵/氮化鎵高電子遷移率電晶體中，在氮化鋁鎵/氮化鎵異質接面處形成的高濃度二維電子氣，提供了低阻抗的電流通道。本論文將探討小閘極長度之氮化鎵高電子遷移率電晶體製程方法，以及其電流特性的理論模型。
在第二章中，我們首先做出了傳統氮化鋁鎵/氮化鎵高電子遷移率電晶體並探討移除矽基板之後的特性。移除矽基板後，直流特性沒顯著的改變，但藉由移除矽基板產生的漏電流路徑及其他高頻寄生元件效應，能有效的改善元件的高頻特性。而選擇性移除矽基板時，發現移除閘極與汲極間的矽基板效果大於閘極與源極間的，原因是由於具有高電壓之汲極與基板間會產生更多感應電荷，對於元件高頻表現影響較大。此研究提供了一有效且低成本的方式提升元件在低阻值矽基板上的高頻表現。
在第三章，我們主要討論場效電板增強型氮化鋁鎵/氮化鎵高電子遷移率電晶體。我們製作了不同p型氮化鎵長度及閘極長度的元件。並探討在相同閘極長度下，p型氮化鎵長度不同時對元件產生的影響。發現元件之閾值電壓會隨著p型氮化鎵長度增加而增加。原因是當p型氮化鎵長度大於閘極時，閘極對二維電子氣控制力下降，需要施加更大的閘極電壓控制p型氮化鎵邊緣的二維電子氣。接著也做了元件切換速度的比較，並且透過閘極電容簡單估算閘極電荷大小，了解不同類型的閘極結構，對切換速度的影響。

關鍵字

高電子遷移率電晶體 ； 增強型氮化鋁鎵/氮化鎵高電子遷移率電晶體 ； 矽基板移除技術 ； 高頻訊號 ； 小訊號模型 ； 閾值電壓 ； 切換時間 ； 閘極電荷

並列摘要

With semiconductor technology development, devices are required to operate at higher voltage and frequency. The III-V group material such as Gallium Nitride is regarded as a new generation semiconductor material with great potential.
Gallium Nitride has several advantages over silicon, such as higher breakdown voltage and higher electron mobility make it able to operate under high-voltage and high-frequency conditions. In the AlGaN/GaN high electron mobility transistor (HEMT), the high-concentration of two-dimensional electron gas (2DEG) formed in the AlGaN/GaN heterojunction provides a low on-resistance. This thesis will discuss the manufacturing method of GaN high electron mobility transistor with a small gate length and the theoretical model of its current characteristics.
In chapter 2, we fabricated a traditional AlGaN/GaN high electron mobility transistor and discussed the electrical characteristics after removing the silicon substrate. After the silicon substrate is removed, the DC characteristics and the cutoff frequency(fT) are not significantly changed. However, by eliminating the leakage current path and other parasitic element effects generated by the silicon substrate, the power gain cut-off frequency (fmax) of the device can be effectively improved. And if silicon substrate is selectively removed, it is found that removing the silicon substrate under the gate and the drain region is more critical to RF performance than that under gate and source region. The reason is that the variation of the induced charge between drain electrode is larger. This result suggests a cost-effective approach to fabricate GaN HEMTs on LR Si substrate with better RF performance.
In Chapter 3, we mainly discuss enhancement-mode p-GaN/AlGaN/GaN high electron mobility transistors. We fabricated devices with different p-GaN lengths and gate lengths. Under the same gate length, the influence of different p-GaN sizes on the device is discussed. It is found that the device's threshold voltage increases with the length of the p-GaN cap layer. The reason is that when the size of the p-GaN cap layer is greater than the gate length, the controllability of the 2DEG channel decreases and a larger gate voltage is required to control the 2DEG at the edge of the p-GaN cap layer. Then, the switching speed of the components was compared, and the gate charge was simply estimated through the gate capacitance to understand the influence of different types of gate structures on the switching speed.

並列關鍵字

GaN-on-Si HEMTs ； enhancement-mode HEMT ； substrate removal ； microwave power ； small-signal model ； threshold voltage ； switching characteristics ； gate charge

參考文獻

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