本論文以top-gate為模型，比較雙層絕緣層(SiO2/HfO2)與單層絕緣層(PECVD-SiO2)結構之IGZO薄膜電晶體特性。透過實驗發現，雙層絕緣層結構之IGZO薄膜電晶體能保護元件，有效避免電漿製程對IGZO薄膜特性的影響。因IGZO薄膜表層極易受環境影響，像是氧氣、水氣、光與溫度都會改變IGZO薄膜的表現，且在沉積PECVD-SiO2時，含有氫元素之電漿也會對IGZO薄膜進行佈植，使得薄膜中之電子濃度提升，讓單層絕緣層結構之IGZO薄膜呈現高導電的電性，元件也因此無法關閉。反觀本研究提出的雙層絕緣層IGZO薄膜電晶體，因為有電子束蒸鍍的HfO2做保護層降低電將對薄膜的影響，所以元件才具備正常的開關特性曲線。
為了近一步提升雙層絕緣層IGZO薄膜電晶體之特性，我們在沉積閘極氧化層之前，將元件放置在PECVD產生的氧電漿環境下，進而修補IGZO薄膜的表層缺陷，提升IGZO薄膜的品質，讓電子在通道層中傳輸時得以更加順利。從不同溫度下的電性表現可以看出，經過氧電漿處理的元件相較於未經處理的，因通道缺陷濃度較低，而具有相對較穩定的臨限電壓(VTH)，這是因為在溫度上升後，能響應的缺陷能態減少，使得元件呈現相對較穩定的特性。因此，氧電漿處理法有應用於改善IGZO通道層薄膜之潛力。

We proposed a bi-layer dielectric SiO2/HfO2 structure and compared its performance to that of single-layer dielectric SiO2 structure for the fabrication of amorphous In-Ga-Zn-O thin-film transistors (IGZO-TFTs). Bi-layer dielectric structure has been demonstrated to be a good protection layer during plasma process for the deposition of PECVD-SiO¬2. The IGZO film has a weak top surface which is sensitive to the environment conditions, such like gas, moisture, light and temperature. In addition, hydrogen specie itself was found to act as a carrier of donors in the IGZO thin-film during depositing the SiO2 dielectric by plasma-enhanced chemical vapor deposition (PECVD) system. In this paper, top-gate structure of amorphous IGZO-TFT with single-layer PECVD-SiO2 gate dielectric shows high conductivity, indicating that top surface of IGZO thin-film has poor quality. In contrast, when bi-layer PECVD-SiO2/HfO2 gate dielectric is applied to fabricate IGZO-TFT, a normal transfer characteristics is achieved. This behavior can be attributed to the protection effect of HfO2 dielectric deposited by electron-beam evaporation system.
Furthermore, O2 plasma surface treatment on IGZO active layer prior to depositing the gate dielectric is also executed. The O2 plasma treatment effectively improve the device performance of top-gate IGZO-TFT with bi-layer gate dielectric. The results suggest that the density of trap states for IGZO-TFT with O2 plasma treatment is much lower than that in as-fabricated devices. Consequently, the temperature effect of instable transfer characteristics of IGZO-TFT has significantly suppressed due to repairing the trap defects by O2 plasma surface treatment.

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