非晶矽薄膜電晶體可靠度分析及自我加熱效應研究

Abstract

此論文研究在博士班學長高士欽帶領下，我們探討自我加熱效應(self-heating effect)對於非晶矽薄膜電晶體的特性及可靠度上的影響。當電流引起的焦耳熱來不及從通道中被排出時，元件溫度會有明顯的上升造成self-heating effect的發生。因此藉由比較不同結構、通道寬度、環境溫度及layout形狀研究self-heating effect發生的機制。在實驗中觀察到當元件操作在大電流下(ex. 加大元件通道寬度和施加大的操作電壓 )，self-heating effect的發生會使元件有異常的大電流而且使可靠度模型(Reliability Model)失效。在不同layout形狀的元件中，可以發現在相同Stress條件下臨界電壓的飄移量是不一樣的。因此利用焦耳熱的大小並不能預測self-heating effect的發生，因為元件的散熱能力也是影響的因素之一。 最後，利用熱電阻模型來討論元件的散熱途徑。在模擬的過程中發現，所推算出的元件溫度很難與實際量測的數據做連結。因此我們利用可靠度模型去反推元件在長時間操作時的溫度，而不需知道太多複雜的材料熱特性。

In this paper, self-heating effect (SHE) on the transfer characteristic and the reliability of amorphous silicon thin film transistors (a-Si TFTs) are discussed. When the current-induced Joule heat can not be quickly dissipated, the increasing device temperature causes self-heating effect. Therefore, varying different structures, channel width, ambient temperature and the layout shape studies the mechanism of self-heating effect.In the experiment, when the device has high operation current (ex. the large channel width and the high operating voltage), self-heating effect cause the abnormal high-current and the reliability model is failed. When varying layout shapes, these devices have different stress threshold voltage shifts even under the same stress conditions. Therefore, using the Joule heat to predict self-heating effect is difficult due to heat dissipation ability of the device. Finally, the heat flow simulation is discussed. The predicted temperature is difficult to explain the actual measurements. Therefore, we use the reliability model to simulate the operation temperature without considering complex material thermal characteristics.