非晶態氧化銦鋅鎵電子元件與技術之研究

Abstract

在低溫製程及軟性薄膜電子元件的科技發展上，透明金屬氧化物半導體薄膜元件備受關注。由於其物理本質特性，金屬氧化物半導體在非晶態下仍可保持高載子遷移率，使其可在低溫(甚至室溫)環境下製程。同時，其在可見光波段具有高穿透性，可應用於透明電子元件或提升顯示器的開口率。除了元件中的主動層外，找到適當的可撓曲介電材質是實現軟性電子的重要關鍵。如：TFT中需要高品質的介電層作為閘極絕緣層(gate insulator)；為了延長元件的使用壽命，所使用的阻擋水氣、氧氣的保護層(passivation layer)也是不可或缺的。另外，由於軟性可撓曲基板較無法耐高溫，因此如何在低溫下成長出高品質的介電薄膜也是軟性電子發展的重要課題。 在本論文中，我們探討在ICP-CVD系統中，以前驅物Hexamethyldisiloxane (HMDSO)與O2在低溫下(接近室溫)成長出高品質的介電有機無機複合薄膜。藉由調整HMDSO、O2氣體比例、CVD功率等參數，可控制薄膜本身特性偏向較矽氧樹脂(有機)或是較二氧化矽(無機)。此複合薄膜在可見光波段展現出高穿透性且具有高崩潰電場，可達5.1 MV/cm，並有與高溫350℃下 PECVD所成長出的SiOx同等級的低漏電流。同時，有機-無機複合薄膜具有相當不錯的水氧阻隔性，在薄膜厚度為150 nm下，其水氣穿透率便可小於 ，達到量測機台極限。最後，成功將此有機無機複合薄膜應用於非晶態氧化銦鋅鎵(a-IGZO)薄膜電晶體，並展現出不錯的元件特性。 除了薄膜電晶體外，整流二極體在顯示器電路上、大尺寸電子、軟性電子及透明電子應用上也是必備的。在本論文中，我們成功利用高功函數(~5.1 eV)、高導電、透明有機高分子導體PEDOT:PSS搭配n型非晶態氧化銦鋅鎵(a-IGZO)製造出蕭基接面而形成蕭基二極體。此蕭基二極體展現出低驅動電壓及高整流比(>105, ±1 V)特性，而理想因子為1.5到1.6間。藉由搭配不同的基板及電極，成功製造出軟性、透明及軟性透明的PEDOT:PSS/a-IGZO蕭基二極體。

In the development of low-temperature-processed and flexible thin-film transistors, transparent metal-oxide semiconductors have drawn wide attention. Because of their adequate carrier mobility in the amorphous state, metal-oxide semiconductors are compatible with low temperature processes. Besides, their high transparency can raises the display aperture ratio and could be applied in transparent electronics. In addition to active semiconducting materials, flexible and high-performance dielectric materials are also essential for fully realizing flexible electronics and displays. For instance, high-performance dielectrics are needed for gate insulators of TFTs. To prolong device reliability and lifetimes, passivation layers with low water and oxygen permeation rate are also required. Furthermore, these dielectric materials should be deposited at low temperatures (or even room temperature) to be compatible with plastic substrates often used in flexible electronics. In this thesis, we investigated the ICP-CVD growth of high-performance dielectric materials at low temperature with organosilicon precursor hexamethyldisiloxane (HMDSO) and O2. By tuning HMDSO/O2 gas ratios, and ICP-CVD powers, organic-inorganic hybrid films were obtained at (or near) room temperature with characteristics tunable from silicone-like (more organic) to silica-like (more inorganic) characteristics. The hybrid films are highly transparent in visible-light region with transmittance >90%, and the hybrid films show high breakdown fields of up to 5.1 MV/cm and low leakage currents, which are comparable to the characteristics of SiOx deposited by PECVD at the temperature of 350℃. The 150-nm hybrid films on PEN plastic substrates exhibit good barrier properties, with low water vapor transmission rate < as measured by Mocon Aquatran model 1 (indeed beyond instrument limit), making it also promising for passivation and barrier applications of flexible electronics. We also successfully applied these hybrid films to a-IGZO TFTs with decent electrical characteristics. In addition to thin-film transistors, rectified diodes are also an essential circuit element for realizing functional circuits in displays, large-area electronics, flexible electronics, and transparent electronics. In this thesis, we report the successful use of the high-work-function, high-conductivity transparent conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the Schottky contact to form the Schottky junction (and thus Schottky diode) with the n-type semiconductor a-IGZO. The Schottky didoes exhibited a low apparent turn-on voltage, a high rectification ratio of >105 at ±1 V, and a decent ideality factor of ~1.5-1.6. We also demonstrated the applications of PEDOT:PSS/a-IGZO Schottky junctions to various types of Schottky diodes, including the flexible, the transparent, and the flexible transparent PEDOT:PSS/a-IGZO Schottky diodes, by using different substrates and different counter electrodes.