蕭特基阻障多晶矽薄膜電晶體之研製

Abstract

在本篇論文中，我們提出、並且成功驗證一種新結構的蕭特基阻障多晶矽薄膜電晶體(SB-TFT)。此一結構，結合了金屬矽化源/汲極(silicided soucre/drain)和電場誘導汲極(field induced drain)兩個概念。因此，在適當的偏壓條件下，同一顆電晶體除了可以展現出n型通道和p型通道的操作特性，還能達到良好的開/關電流比例特性(on/off current ratio超過106)，並能有效抑制閘極誘導汲極漏電流(gate-induced drain leakage)的發生 其次，我們也對元件的漏電流特性加以探討。我們發現，在常溫之下，傳統結構的蕭特基阻障多晶矽薄膜電晶體其漏電機制是由場發射(field emission)和熱激發放射(thermionic emission)所主導，在高電場操作條件下，場發射則會主導漏電流。而對於具電場誘導汲極結構的蕭特基阻障多晶矽薄膜電晶體，其漏電流和電場沒有明顯相依關係，熱激發放射是其主要的漏電機制。 除了良好的電性外，我們提出的新結構薄膜電晶體在製程上也較為簡單且便宜。因此，此一結構有潛力運用在未來的金氧半場效電晶體(CMOS)製程，以及大尺寸顯示器應用上。

In this thesis, we have proposed and demonstrated a novel poly-Si Schottky barrier thin-film transistor (SB-TFT) with field induced drain (FID). The FID SB-TFT features Co-silicided source/drain and a metal field-plate (i.e., sub-gate) lying over the passivation oxide. It depicts superior ambipolar operation capability by simply switching the bias polarity on the main-gate and the sub-gate. So depending on the polarity of the field-plate bias, the device can be set for n- and p-channel operations with positive and negative field-plate biases, respectively. Excellent on/off current ratios over 106 have been achieved for both n- and p-channel operations if proper bias conditions are chosen. In addition, the GIDL (gate-induced drain leakage)-like off-state leakage current encountered in devices with conventional SB-TFT could be completely suppressed. In this work, we also carried out further study on characterizing the off-state leakage of the devices at different temperatures. For the device with conventional structure, the field emission and thermionic emission from the drain are presumably the primary conduction mechanisms of off-state leakage Under the condition when the field strength is weak, the thermionic emission would dominate the conduction. When the field strength increases, the field emission will become significant. On the other hand, when FID scheme is implemented, the FID would drag the high-field region in the channel away from the drain side. As a result, thermionic emission would be the major conduction mechanism in the off state. In addition to superior electrical characteristics, the FID SB-TFT also features simpler and cheaper fabrication processing, making it very promising for CMOS integration and future large-area electronic applications.