鈀奈米裂縫製作及其在表面傳導電子發射顯示技術的應用

Abstract

表面傳導電子發射顯示器(surface conduction electron emitter display, SED)為新世代的場發射顯示器技術。本實驗主要是研究SED之電子發射元件，稱作表面傳導電子發射源(surface conduction electron emitters ,SCE)。SCE元件最關鍵的技術是如何製作奈米尺寸的裂縫，以得到低的驅動電壓及穩定場發射元件的功能。本實驗以聚焦離子束(focus ion beam, FIB)和鈀氫化原理兩種方法製作SCE元件的奈米裂縫。 改變FIB的離子束能量可以在條狀鈀薄膜上蝕刻出不同寬度的奈米裂縫，裂縫寬度越小的SCE元件其驅動電壓越低。將上述SCE元件作氫電漿表面改質處理，發現隨著氫電漿處理時間的增加，驅動電壓有降低的趨勢。場發射特性的改善是由於表面幾何結構變化造成局部的電場集中，以及鈀電子發射源與氫離子反應生成功函數較低的氫化鈀。 鈀氫化法製作奈米尺寸的裂縫，其裂縫的生成主要是因為鈀吸附氫氣後相變化的體積膨脹在鈀薄膜內產生很大的應力所致。奈米裂縫的寬度可以藉由氫氣壓力和鈀薄膜的溫度來控制。本實驗導入ANSYS有限元素分析，模擬鈀氫化後的靜態應力分佈。模擬的結果可以解釋鈀原子遷移的方向，並說明了裂縫生成的機制為應力誘發原子移動，而成長動力學則是孔洞的成核與成長機制。

Surface conduction electron emitter display (SED) is the latest developed field emission display technology. The study is focused on the fabrication of the emitting device called surface conduction electron emitters (SCE). The most critical process to fabricate the SCE device is how to produce gaps in nanometer scale with a low turn-on voltage. The study used focused ion beam (FIB) and palladium hydrogenation methods to fabricate the nanogap for SCE device.

Nanogaps of different width in the Pd strip electrode were formed by FIB sputter etching using various beam width energy. The turn-on voltage decreased with decreasing of the nanogap width. After being subjected to hydrogen plasma treatment, the turn-on voltage of the SCE device decreased with increasing the hydrogen plasma treatment time. The improvement of field emission characteristics is attributed to the change in surface geometric structure and the formation of palladium hydride (PdHx), which has a lower work function than Pd.

The nanogap formation by palladium hydrogenation is based on that a large stress develops in the metal due to phase transformation leading to volume expansion. The width of nanogap could be controlled by adjusting the hydrogen pressure and the Pd film temperature. Finite element analysis was performed to study the hydrostatic stress distribution developing in the SCE structure after the palladium hydrogenation process. The simulation result suggested that the nanogap formation was a result of stress-induced atom migration. The kinetics of developing nanogap could be considered as a process of void nucleation and growth.