交流濺鍍機氧化鋅薄膜電晶體

Abstract

我們調整交流濺鍍機的沉積參數和熱退火條件來最佳化氧化鋅薄膜(ZnO)，在此，我們調整了沉積溫度、瓦數、氬氣和氧氣的氣體比例，最好的參數是在Table. 3.5中的樣品H-50；而最好的熱退火條件是在大氣中使用300°C的高溫爐管，熱退火30分鐘，如此一來可以最佳化氧化鋅薄膜的霍爾載子遷移率。 我們使用了兩種方法去提升氧化鋅薄膜電晶體(ZnO-TFT)的元件特性，分別是降低主動層厚度、改變絕緣層材料，這兩種方法都有效的降低主動層的表面粗糙度；在第一個方法：降低ZnO主動層厚度，此方法有效地降低ZnO-TFT的平均臨界電壓，從12.9V到10.5V；而在另一個方法中，我們將元件中的SiNx絕緣層換成SiO2/SiNx雙層絕緣層，在雙層絕緣層元件中，平均臨界電壓從單層的12.9V下降到8.5V，而平均載子遷移率較單層絕緣層元件提升了3.2倍。 為了保護氧化鋅不受水氧影響，我們使用氧化鈦(TiOx)來保護氧化鋅元件，而氧化鈦是使用交流濺鍍器來沉積，此外，我們改變了在沉積保護層後的熱退火溫度，發現在大氣中以200°C熱退火30分鐘是最理想的。之後在雙層絕緣層薄膜電晶體上沉積氧化鈦保護層並熱退火，發現在上保護層前後，電流開關比從105.6提升到 106.1，臨界電壓從10.3V提高到19.2V，載子遷移率沒太大改變，在上保護層之前是1.19 cm2/V-s，上保護層之後是1.14 cm2/V-s。最後，我們持續觀察上保護層後的氧化鋅電晶體曝露在空氣中的元件特性，觀察了22天發現特性皆很穩定。

The RF-sputtered ZnO films are optimized by deposition parameters and annealing processes. The deposition temperature, RF-power and Ar/O2 ratio are changed, and the best deposition parameters are the sample H-50 in Table 3.5. The best annealing conditions for a high Hall mobility ZnO film are annealing in air at 300°C for 0.5 hour. Two methods are used to improve the performance of ZnO-TFT by reducing the surface roughness of the ZnO layer, decreasing the ZnO active layer thickness and changing gate insulator. The result of decreasing the thickness of ZnO layer in TFT indicates the threshold voltage is improved from 12.9 V to 10.5 V. In the other method, the single SiNx gate insulator of ZnO-TFT is change to the SiO2/SiNx bi-layer gate insulator. The average threshold voltage is improved from 12.9 V to 8.5 V and the average mobility of bi-layer ZnO-TFT is 3.2 times better than that of single SiNx ZnO-TFT. In order to protect the ZnO layer from moisture degradation, the RF-sputtered TiOx is used to passivate the device. It has been demonstrated that the TFTs annealed in air at 200°C for 30 minutes are the best post-passivation conditions for a TiOx passivated device. After the SiO2/SiNx bi-layer insulator ZnO-TFTs is passivated with 40 nm thick TiOx, the result indicate that the on/off ratio before and after passivation increases from 105.6 to 106.1, the threshold voltage increases from 10.3 V to 19.2 V, and the mobility are almost the same, i.e., 1.19 cm2/V-s and 1.14 cm2/V-s. Finally, the electrical properties of passivated ZnO-TFTs are stable as the devices are exposed to atmosphere for 22 days.