氮化鎵封裝元件之暫態熱分析與可靠度測試研究

Abstract

AlGaN/GaN功率晶體，相較於傳統以矽為主體的功率元件，具有高的電子移動率、高崩潰電壓的特徵，適合操作在高功率、高頻率下，但因其熱傳導特性較差，功率晶體內二維電子氣層的通道溫度也隨元件操作下產生的自發性熱效應攀升，進而降低元件的效能及可靠度。為了達到有效的AlGaN/GaN功率晶體的熱管理，必須要掌握AlGaN/GaN功率晶體通道溫度。本研究使用電性參數估測法，建立元件電性參數量測資料曲線，推估元件之通道溫度，有別於傳統侵入式的量測手法，電性參數法有易於量測、重現性高、不受到元件結構影響與不會破壞元件結構等等優點，且可以準確量測元件通道溫度而非晶片表面溫度，並利用電性參數法推估定電流下AlGaN/GaN功率晶體通道溫度變化，計算暫態熱阻，利用結構函數理論分析元件熱傳路徑上結構熱阻熱容，此分析法不會破壞元件結構，圖像式的表達方式更易於分析結構熱阻的退化。本研究結合氮化鎵電晶體元件的高速開關速度特性，利用Low Voltage MOSFET元件穩定閘極開關之串疊電路形成常閉型(normally-off)開關，可直接取代現行MOSFET功率元件，此結構可保護氮化鎵電晶體元件避免其損壞與增加元件之穩定性，使氮化鎵電晶體元件利用更加廣泛。為了改善以冷卻曲線量測暫態熱阻需耗費較長時間的缺點，本研究發展以加熱曲線快速暫態熱阻量測方法，並將此方法應用在功率循環的可靠度實驗與封裝產線上的結構熱阻檢測上，可以得到準確結構熱阻資料，在可靠度分析結果中，可以確實觀測到元件黏晶層至黏著層之熱傳導退化趨勢，預測元件損壞週期。

The high power dissipation for AlGaN/GaN HEMT power device can result in a substantial self-heating effect on topside surface due to the lateral topologies, which will reduce the performance reliability. This paper proposes the fast static and transient thermal method which evaluates the thermal resistance constitution in the heat flow path. The method is based on the transient heating curve by the thermo-sensitive electrical parameters measurement for the cascode AlGaN/GaN HEMTs. The method is simple, non-invasive and not restricts by the device layout, package and geometry. With the help of structure function, the proposed process extracts the chip-level and junction to case thermal resistances. Furthermore, the thermal property of each package layer including contact thermal resistance is clearly shown in the graphical representation. This study also develops the short time transient measurement process which will tremendously reduce the measurement time comparing to the standard cooling curve method. Finally, the power cycle capability of Cascode GaN is investigated and use the structure function to reveal changes or failure in the thermal interface.