氧化鋅變阻器電學性質之研究

Abstract

於本論文中, 吾人探討氧化鋅晶粒均勻度, 燒結溫度和外加突波次數對氧 化鋅變阻器電性之影響o 根據研究之結果, 發現氧化鋅變阻器可以利用水 樣沉澱法所製造之球形粉末, 製得均勻之微觀結構, 並且由於此一均勻之 微觀結構, 造成氧化鋅變阻器具有高非歐姆電性和漏電流之 對於氧化鋅 變阻器非歐姆電性隨不同燒結溫度而變之現象, 可由電流- 電壓和電容- 電壓之量測得知o 此一電性之變化, 乃是晶界之介面缺陷密度和氧化鋅晶 粒之施體濃度隨不同燒結溫度而變之結果o 而氧化鋅變阻器之介電性質也 會受燒結溫度之影響, 吾人利用介電損耗和複數平面等分析方法, 發現氧 化鋅變阻器內部有兩種深本體缺陷, 它們分別為正一價之氧空位離子和正 二價之鋅間隙離子, 這些離子之特性隨不同燒結溫度而變之行為, 將在本 論文中詳細討論o此外, 突波電流對氧化鋅變阻器電性之影響, 則以電 流- 電壓量測和對交流訊號之反應來研究o 經由吾人之研究發現, 氧化鋅 變阻器其參考電壓 Vo.1mA 和漏電流, 隨不同突波次數而變化之電流- 電 壓衰化現象, 源自於晶界之背對背蕭特基能障受到外加突波不對稱之損壞 o 而氧化鋅變阻器之深本體缺陷和傳導機制也會因外加突波而受到影響, 缺陷能態之鬆弛時間和鬆弛損耗數量隨著外加突波次數之增加而減少o同 時, 於本論文中發現, 當量測溫度或電場升高時, 氧化鋅變阻器之電阻將 下降o 這是因為溫度或電場之升高促使氧化鋅晶粒產生更多之傳導載子通 過晶界, 因而破壞了晶界之絕緣性o 並且當大量之帶電載子通過晶界時, 氧化鋅變阻器明顯得表現出非杜拜特性, 此一非杜拜特性 一個非杜拜電 容來模擬晶界而得到解釋o The homogeneity of ZnO particle size, sintering temperature, and the number of applied surge are demonstrated to affect therical properties of the ZnO varistors. Based on our studies, the following observations should be made. It is found that a homogeneous microstructure of the ZnO varistors can be obtained by employing the well-shaped spherical green powders produced by an aqueous precipitation method, and that the homogeneous microstructure results in the high nonohmic characteristic and low leakage current. The variation of the nonohmic behavior with sintering temperature is indicated from I-V and C-V measurements to be a result of the changes of the interface defect density at theboundaries and the donor concentration in the ZnO grains. The dielectric characteristic of the ZnO varistors is also affected by sintering temperature. With the dielectric loss analysis and the complex plane analysis, it is found that therewo intrinsic defects within the ZnO varistors. The degradation of the I-V behaviors in Vo.1mA and leakage current with varying numbers of applied surge is contributed by the asymmetrical deformation of the back-to-back Schottky barriers at the grain boundaries. As well, the characteristics of the deep bulk traps and conduction mechanism of the ZnO varistors are affected by the applied surge. Moreover, the device resistance is found to decrease as the temperature/ applied field increases. This is attributed to deter- ioration of the insulating property of the grain boundaries due to generation of conduction carriers in the ZnO grains. As aamount of these charge carriers pass through the grain boundaries, the ZnO varistors remarkably reveal a non-Debyecteristic.