Device and Process Design Based on Functional Oxide Thin Films for Advanced Memory Applications

고상한 경희대학교 대학원 2025 국내석사

In this work, we present an integrated approach for implementing high-performance and high- reliability memory technology by precisely controlling the material-specific electrical properties of functional oxide thin films and applying them to the structural design of memory devices. In particular, representative oxide materials such as HfO2, Al2O3, and InGaZnO (IGZO) were applied to various roles such as ferroelectric layers, insulating layers, and channel layers, respectively, and the memory performance parameters such as charge storage characteristics, bias stability, and data retention characteristics of the devices were experimentally verified by controlling the process conditions and the stacked structure, and the possibility of applying them to memory devices was verified. First, the crystallization behavior and ferroelectric characteristic changes were analyzed by introducing an Al2O3 capping layer on an undoped HfO2 thin film. The crystal phase transition and polarization switching characteristics according to the temperature conditions of the HfO2 atomic layer deposition (ALD) process were evaluated, and it was confirmed that the polarization characteristics, leakage current, and endurance of the ferroelectric capacitor with the metal- insulator-ferroelectric-metal (MIFM) structure were significantly improved through the stabilization of the ferroelectric phase, which is the orthorhombic phase (o-phase). This suggests an effective methodology that can implement excellent ferroelectric characteristics only through interface control without separate doping. Second, by designing the IGZO thin film as a double-layer (DL) structure and depositing it with different oxygen partial pressures (PO2) during the sputtering process, we attempted to improve the performance in a 2-transistor-0-capacitor (2T0C) DRAM cell. The heterogeneous interface formed between the upper and lower IGZO layers served as an additional conduction path, and the storage efficiency and retention time were increased by advantageously utilizing the parasitic capacitance through geometric optimization of the active area. Through this, we propose a performance improvement method of 2T0C DRAM cells by combining structural design and material control. Finally, we designed a HfO2/Al2O3 nanolaminate gate insulator (GI) structure to secure electrical reliability while utilizing high-K dielectrics in the thin film transistor (TFT) constituting the 2T0C DRAM cell. By periodically laminating HfO2 and Al2O3 through a 150 °C ALD process, we simultaneously achieved crystallization suppression and interface defect reduction, which led to low-voltage operation and improved bias stress stability. When applied to an actual 2T0C DRAM cell, it was successfully verified by showing excellent long-term retention behavior. These results provide guidelines for the design of insulators for low-temperature oxide transistor- based memories.

Stress instability of length-dependent characteristic variations in amorphous InGaZnO TFTs

박수혜 Graduate School, Yonsei University 2013 국내석사

8-inch wafer-scale multiple-channel a-IGZO thin-film transistors for application of NO2 gas detection

Jeonghee Ko 국민대학교 일반대학원 2023 국내석사

Sensors that detect various types of gases that are harmful to the human body have a wide range of applications in industry and home. However, there is a lack of research on nitrogen dioxide (NO2), which causes major adverse effects on the human body such as hypertension and myocardial infarction. While sensors using metal oxide semiconductor technology with 2-terminal have been reported, they generally suffer from limited sensitivity and vulnerability to temperature changes. In comparison, 3-terminal transistor-based gas sensors show high sensitivity and are favorable for miniaturization. In particular, amorphous IGZO (a-IGZO) thin-film transistors (TFTs) are representative high-performance, high-reliability, and high-stability n-type semiconductors, and have the advantages of high carrier mobility and low-temperature processing. In addition, its amorphous structure allows it to be uniformly deposited over a large area and it is known to be an excellent material in terms of reproducibility. Therefore, for the commercialization and performance development of gas sensors, we propose an optimal channel structure with excellent performance based on a-IGZO TFTs fabricated on an industry-standard 8-inch wafer. The first chapter compares the advantages and limitations of different gas sensor types, and presents the advantages of a-IGZO TFT-based gas sensors. Furthermore, we briefly summarize the progress and limitations of previous studies and propose metrics for the evaluation of gas sensor measurement results in this work. In the second chapter, we fabricate and demonstrate a-IGZO TFTs at the scale of an industry-standard 8-inch wafer, and characterize the device depending on the geometry of the channel. Moving away from device-level studies, we move up to the wafer level and study multiple channel structures with a-IGZOs as active layers. Devices with multi-channel structures maintain excellent performance and do not require additional fabrication processes and costs because they utilize existing photolithography facilities. In the third chapter, a sensor to detect NO2 based on the fabricated device is studied. We extracted the property of the fabricated device based on the NO2 sensing mechanism using a-IGZO. Additionally, we confirmed the sensing performance in the multiple channel structure and performed NO2 gas sensing in the device after RTP. In this study, in order to mass-produce a-IGZO TFTs, we moved from device-level research to wafer-level research. Furthermore, we tried to find an amorphous IGZO thin-film transistor with an optimal channel structure and conducted experiments to detect NO2 gas in the fabricated a-IGZO TFT. This paper suggests the possibility of mass production of a-IGZO TFTs fabricated at the wafer scale and is expected to provide guidelines for the structure of a-IGZO channels to improve the performance of NO2 gas detection sensors. 인체에 유해한 다양한 종류의 가스를 검출하는 센서는 산업 및 가정 분야에서 다양하게 적용되고 있습니다. 하지만, 고혈압이나 심근경색 등 인체에 큰 부작용을 발생시키는 이산화질소에 대한 연구가 부족한 실정입니다. 다양한 종류의 가스 센서들 중, 금속 산화물 반도체 기반 2 단자 가스 센서가 보고되고 있으나, 일반적으로 민감도가 제한적이고 온도 변화에 취약하다는 단점이 있습니다. 이에 비해 3 단자 트랜지스터 기반 가스 센서는 높은 민감도를 가지고 있고 소형화에 유리해 광범위하게 연구되고 있습니다. 특히, 비정질 IGZO 박막 트랜지스터는 대표적인 고성능, 고신뢰성, 고안정성 n 형 반도체이고 높은 캐리어 이동도를 가지고 저온 공정이 가능하다는 장점이 있습니다. 또한 비정질 구조로 넓은 면적에 균일하게 증착할 수 있고 재현성 측면에서 우수한 재료로 알려져 있습니다. 따라서, 가스 센서의 상용화 및 성능 개발을 위해 산업-표준 8인치 웨이퍼 위에 제작된 비정질 IGZO 박막트랜지스를 기반으로 성능이 우수한 최적의 채널 구조를 제안합니다. 첫번째 장에서는, 가스 센서의 종류에 따른 장단점과 한계를 비교하고, 비정질 IGZO 박막트랜지스터 기반 가스 센서의 장점을 소개합니다. 더 나아가 이전 연구들의 진행사항과 한계점을 간략히 요약하고, 이를 바탕으로 본 논문이 진행한 가스 센서 측정 결과의 평가를 위한 지표들에 대해 제안합니다. 두번째 장에서는, 산업 표준 규격인 8 인치 웨이퍼 규모의 비정질 IGZO 박막 트랜지스터를 제작 및 시연하고, 채널의 기하학적 구조에 따른 소자의 특성을 분석합니다. 소자 레벨의 연구에서 벗어나 웨이퍼 수준의 상향된 연구를 진행하고, IGZO 를 기반으로 한 다중 채널 구조에 대해 연구합니다. 다중 채널 구조의 소자는 우수한 성능을 유지하며 기존 포토리소그래피 설비를 활용하기 때문에 추가적인 제조 공정 및 비용이 발생하지 않습니다. 세번째 장에서는, 제작된 소자를 기반으로 이산화 질소를 감지하는 센서에 대해 연구합니다. 비정질 IGZO 를 활용한 이산화질소 감지 메커니즘을 바탕으로 제작한 소자에서의 성능을 측정하였습니다. 또한 다중채널 구조에서의 센싱 성능을 확인하고 급속 열처리를 진행한 소자에서 이산화질소를 감지하였습니다. 본 연구에서 비정질 IGZO 박막트랜지스터의 대량생산을 위해 소자 레벨의 연구에서 벗어나 웨이퍼 수준의 상향된 연구를 진행하였습니다. 더 나아가 최적의 채널 구조를 갖는 비정질 IGZO 박막 트랜지스터를 찾고자 하였고, 제작된 비정질 IGZO 박막트랜지스터에서 이산화질소 가스를 검출하는 실험을 진행하였습니다. 본 논문은 웨이퍼 스케일로 제작된 비정질 IGZO 박막트랜지스터의 대량 생산 가능성을 시사하였고 이산화질소 가스 감지 센서의 성능 향상을 위한 비정질 IGZO 채널의 구조에 대한 가이드라인을 제공할 수 있을 것이라고 기대합니다.