高壓及高速矽基氮化鎵元件設計、製造及分析

Design, Fabrication, and Analysis of High Power and High Speed GaN-based Devices on The Si Substrate

連羿韋(Yi-Wei Lien)

指導教授 ： 徐碩鴻

國立清華大學/電機資訊學院/電子工程研究所/博士(2014年)

https://doi.org/10.6843/NTHU.2014.00553

摘要

本論文主要研究矽基氮化鋁鎵/氮化鎵異質接面元件在高功率及微波上的應用。在功率元件方面，我們藉由歐姆接面工程來提升矽基氮化鎵元件的崩潰電壓。
其一，在氮化鋁鎵/氮化鎵蕭特基二極體上提出了選擇性矽摻雜的方法。其二，在氮化鋁鎵/氮化鎵電晶體提出了混合性汲極的結構。兩種結構皆是改善毆姆接觸附近的電場，用來減緩歐姆合金造成的尖端電場。其中，選擇性矽摻雜層可以同時降低蕭特基二極體的導通電壓及提升元件逆向崩潰電壓。當矽摻雜層被採用於陽極正下方時，可以降低導通電壓，但會犧牲少許的崩潰電壓。當矽摻雜層被採用於陰極正下方時，主要功能是用來屏蔽掉歐姆合金附近的峰值電場，進而有效提升元件崩潰電壓大約20%。此外，矽摻雜層也可以幫助將接觸電阻降低。另一方面，採用混合式汲極結構的電晶體特性，可以得到一個趨近於零的汲極導通電壓。同時，與傳統歐姆汲極元件相較之下其汲極漏電流也可以被有效降低一個數量級。我們也針對混合式汲極結構中的蕭特基金屬延伸長度Lext對於元件特性的影響進行探討。當元件中蕭特基金屬延伸長度Lext被優化後，元件的最大崩潰電壓可以被提升60%並且沒有造成導通電阻劣化。在高頻元件方面，我們提出一個可以直接萃取電晶體小訊號模型中的基板寄生電容及基板寄生電阻。一個0.2微米的T型閘級電晶體被用以建立小訊號模型。另外，我們也藉由元件模擬來觀察矽基板效應於高頻特性的影響。

關鍵字

蕭特基二極體 ； 電晶體 ； 高電子遷移率電晶體 ； 氮化鎵 ； 氮化鋁鎵/氮化鎵 ； 高壓 ； 矽基板效應 ； 高頻 ； 高速

並列摘要

This thesis focuses on high performance AlGaN/GaN heterojunction devices on Si substrate for high power and high frequency applications. For high voltage applications, the contact engineering was investigated to improve device off-state characteristics in GaN on Si devices by using two different approaches, including a selective Si diffusion structure for AlGaN/GaN SBDs and a hybrid Schottky-Ohmic drain electrode structure for AlGaN/GaN HEMTs. Both two approaches are proposed to alleviate the E-field peaks at the alloy spikes and further enhance the breakdown voltage by manipulating the E-field around Ohmic contact.
First, a selective Si diffusion approach is proposed to reduce Schottky onset voltage from 1.3 V to 1.0 V and enhance the reverse blocking capability up to 20%simultaneously. With Si diffused layer underneath cathode, a low and stable contact resistance and relatively smooth ohmic metal morphology can be obtained. Second, a hybrid drain device shows nearly zero drain onset voltage and reduces drain leakage current by one order of magnitude, comparing with that of traditional ohmic drain devices. Both the gate-drain and buffer breakdown can be improved. We also investigated the impact of Schottky extension length Lext on device characteristics. After optimizing Lext, the breakdown voltage can be enhanced up to 60% without clear on-resistance RON degradation. For high frequency applications, we proposed a method to directly extract the more convergent results for parasitic substrate resistance and capacitance in small signal model of GaN-on-Si HEMTs by using derivative method. The model is verified by in-house 200-nm T-gate AlGaN/GaN HEMTs. Also, the simulation is performed to analyze the impact of substrate effect on device high frequency characteristics.

並列關鍵字

Schottky barrier diode ； transistor ； HEMT ； GaN ； AlGaN/GaN ； high voltage ； high frequency ； substrate effect

參考文獻

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