氮化鎵（GaN）功率元件之電熱模擬研究與封裝散熱分析

Abstract

氮化鋁鎵/氮化鎵高電子遷移率電晶體（AlGaN/GaN HEMT）具有寬能隙（約3.4 eV）、高崩潰電壓、高臨界崩潰電場以及高電子飽和漂移速率、高峰值電子速率、高電子飽和速率等優點，因此適用於功率電子方面及高頻通訊方面的應用。 為了滿足高功率電晶體元件之散熱需求，本篇文章提出一封裝方式，利用V型凹槽之銅座設計以提升矽基板的散熱能力，其相關之結構設計與封裝過程皆詳述其後。由於功率元件在電性操作下必定會有功率的損失，尤其是閘極開關瞬間的切換耗損，而其損失的能量大部份會轉化為熱能的形式，經熱傳導由元件到封裝再以熱對流傳熱至外部環境，為了研究與改善待測元件之熱管理，必須先了解元件操作下主動區（active region）之溫度分佈和熱點位置。 本研究先藉由電熱模擬（Silvaco）與熱分析模擬（Ansys Icepak）分析元件之電場強度分佈以及熱點溫度與位置，再由紅外線熱顯影（IR）實驗來實際量測元件主動區在操作下的溫度分佈趨勢和熱點位置，另外，利用拉曼光譜（Raman）實驗的縱向溫度量測確認二維電子氣層（2DEG）的位置，再作橫向面積的區域溫度量測，最後將實驗之結果與模擬作比較與驗證。

AlGaN/GaN high electron mobility transistors（HEMTs）are one of the prospective candidates for high switching frequency power electronics applications thanks to its wide band gap（3.4eV）, high breakdown voltage, large critical electric field, high carrier mobility, and the inherent high speed characteristics. With the high power densities that AlGaN/GaN HEMTs are capable of reaching, heat dissipation is a crucial issue. This research presents an in depth thermal study of packaged GaN on Si power devices. The device is attached in a V-groove copper base, to enhance Si substrate thermal dissipation. The effects of structure design and fabrication processes on the device performance were studied. To improve the reliability and the performance of GaN power-HEMT devices, thermal management is one of the most critical aspects. Micro-Raman spectroscopy and Infrared（IR）thermography were used to identify temperature profiles and the hot spots of the devices. For the purpose of more precise temperature measurements, temperature vs. Raman shift curve fitting of experimental data of our device is illustrated. The measurements of longitudinal temperature have been acquired, so that the position of the hottest layer（2DEG）is realized. Then, Raman area temperature map measured over the lateral hottest layer depicted in this study. The comparison between Raman/IR experiment results and finite-element electro and thermal simulation has been shown.