Transparent amorphous In-Zn-O based thin film transistors for future optoelectronics

Abstract

In this dissertation, the main work focus on the fabrication of indium zinc oxide (InZnO) related materials thin films (a-IGZO, a-CIZO) by using a radio frequency (RF) magnetron sputtering system and sol-gel solution process for optical device applications. The influence of deposition parameters on the structural, electrical and optical properties of thin films was investigated. Based on thin film deposition technique, the novel post-treatment processes for the formation of InZnO related films were developed. As the demonstration, high quality InZnO related thin films as the channel layer was applied into thin film transistors (TFTs). First, we present the electrical characteristics of a-IGZO TFTs with a double-active-layer structure as a novel approach for high TFT performance. A double active a-IGZO layer with different oxygen contents is fabricated by varying the oxygen partial pressure during sputtering. The deliberately stacked top and bottom layers in a double layer matrix are designed to have oxygen-ion-rich and oxygen-ion-poor regions, respectively. The electrical properties of the TFTs based on double- and single-active layers are compared. Second, electrical and optical characteristics of amorphous cerium-gallium-zinc-oxide (a-CIZO) thin film transistors (TFTs) are systematically studied using co-sputtering method which was a combination of RF sputtered IZO with a fixed power and CeO2 with varied powers. The resistivity of a-CIZO film was increased with increasing the CeO2 sputtering power while IZO sputtering power had been fixed. It is reported that the Ce ions may play a key role in enhancing the stability of the IZO TFTs, due to their high oxygen bonding ability, hence suppressing the formation of oxygen vacancies. Finally, we also perform solution-based synthesis of Li-doped ZnO TFTs in order to implement the electrical stability of TFTs under ambient air conditions. The structural and electrical properties of Li-doped ZnO TFTs were analyzed by varying the concentrations of Li-dopants, together with those of un-doped ZnO TFTs for comparison. In particular, our experiment adopted a carbon-free synthesis method without using hydrocarbon complexes that can easily degrade electrical properties of TFTs. X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) were also performed for closer investigation of chemical binding states and structural properties of Li-doped ZnO TFTs.|본 논문에서는 미래의 광학전자기기 응용을 위한 InZnO에 바탕을 둔 관련물질(a-IGZO, a-CIZO)을 제작하는데 있어 라디오주파수 마그네트론 스퍼터링 기법과 졸겔 용액 기법을 사용하였다. 제작기법의 요인들이 박막의 구조적, 전기적, 광학적 성질에 영향을 미치는 것에 대해 조사하였다. 박막의 증착기법에 기반을 두고 새로운 후처리 과정을 통해 InZnO 관련 물질들을 제작하였다. 좋은 품질의 InZnO 관련 물질들은 채널층으로서 박막트랜지스터 소자에 적용되었다. 먼저, 박막트랜지스터의 성능 향상을 위해 a-IGZO 활성층을 2중층으로 갖는 박막트랜지스터의 전기적 특성을 연구하였다. 2중 활성층은 스퍼터링을 하는 동안 산소분압의 변화에 따른 산소함량의 차이로 구분지었다. 위, 아래의 구조로 적층된 형태로서 산소 이온이 풍부한 층과 부족한 층으로 각각 나뉘도록 했다. 둘째, InZnO 증착파워를 고정시킨채 CeO2 증착 파워를 변화시키는 코스퍼터링 방법을 이용하여 제작된 CeInZnO 박막 트랜지스터의 전기적, 광학적 특성에 대해 연구하였다. 비정질 CIZO 박막은 CeO2 의 증착 파워가 증가함에 따라 비저항도 증가하였다. Ce 이온은 높은 산소 결함 능력으로 산소가 빠져나가는 것을 막아서 IZO 박막트랜지스터의 전기적 안정성을 향상시킬 수 있다. 마지막으로, Li이 도핑된 ZnO 박막 트랜지스터를 용액 합성법으로 제작하여 대기압에서의 전기적 안정성에 대해 연구하였다. Li이 도핑된 ZnO 박막 트랜지스터의 구조적, 전기적 특성을 Li 도핑 농도에 따라 분석하였고 이를 ZnO 박막 트랜지스터와 비교하였다. 특히, 본연구에서는 박막 트랜지스터의 전기적 특성을 저하시는 탄화수소 화합물을 사용하지 않는 무탄소 기법을 적용하였다. Li이 도핑된 ZnO 박막 트랜지스터의 화학적 결합 상태와 구조적 특성 분석을 위해 XPS 와 SIMS분석을 실시하였다.; In this dissertation, the main work focus on the fabrication of indium zinc oxide (InZnO) related materials thin films (a-IGZO, a-CIZO) by using a radio frequency (RF) magnetron sputtering system and sol-gel solution process for optical device applications. The influence of deposition parameters on the structural, electrical and optical properties of thin films was investigated. Based on thin film deposition technique, the novel post-treatment processes for the formation of InZnO related films were developed. As the demonstration, high quality InZnO related thin films as the channel layer was applied into thin film transistors (TFTs). First, we present the electrical characteristics of a-IGZO TFTs with a double-active-layer structure as a novel approach for high TFT performance. A double active a-IGZO layer with different oxygen contents is fabricated by varying the oxygen partial pressure during sputtering. The deliberately stacked top and bottom layers in a double layer matrix are designed to have oxygen-ion-rich and oxygen-ion-poor regions, respectively. The electrical properties of the TFTs based on double- and single-active layers are compared. Second, electrical and optical characteristics of amorphous cerium-gallium-zinc-oxide (a-CIZO) thin film transistors (TFTs) are systematically studied using co-sputtering method which was a combination of RF sputtered IZO with a fixed power and CeO2 with varied powers. The resistivity of a-CIZO film was increased with increasing the CeO2 sputtering power while IZO sputtering power had been fixed. It is reported that the Ce ions may play a key role in enhancing the stability of the IZO TFTs, due to their high oxygen bonding ability, hence suppressing the formation of oxygen vacancies. Finally, we also perform solution-based synthesis of Li-doped ZnO TFTs in order to implement the electrical stability of TFTs under ambient air conditions. The structural and electrical properties of Li-doped ZnO TFTs were analyzed by varying the concentrations of Li-dopants, together with those of un-doped ZnO TFTs for comparison. In particular, our experiment adopted a carbon-free synthesis method without using hydrocarbon complexes that can easily degrade electrical properties of TFTs. X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) were also performed for closer investigation of chemical binding states and structural properties of Li-doped ZnO TFTs.