• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
• /
• pp.217-217
• /
• 2016

The amorphous InGaZnO (a-IGZO) is widely accepted as a promising channel material for thin-film transistor (TFT) applications owing to their outstanding electrical properties [1, 2]. However, a-IGZO TFTs have still suffered from their bias instability with illumination [1-4]. Up to now, many researchers have studied the sub-gap density of states (DOS) as the root cause of instability. It is well known that defect states can influence on the performances and stabilities of a-IGZO TFTs. The defects states should be closely related with the deposition condition, including sputtering power, and pressure. Nevertheless, it has not been reported how these defects are created during conventional RF magnetron sputtering. In general, during conventional RF magnetron sputtering process, negative oxygen ions (NOIs) can be generated by electron attachment in oxygen atom near target surface and then accelerated up to few hundreds eV by a self-bias; at this time, the high energy bombardment of NOIs induce defects in oxide thin films. Recently, we have reported that the properties of IGZO thin films are strongly related with effects of NOIs which are generated during the sputtering process [5]. From our previous results, the electrical characteristics and the chemical bonding states of a-IGZO thin films were depended with the bombardment energy of NOIs. And also, we suggest that the deep sub-gap states in a-IGZO as well as thin film properties would be influenced by the bombardment of high energetic NOIs during the sputtering process.In this study, we will introduce our novel technology named as Magnetic Field Shielded Sputtering (MFSS) process to prevent the NOIs bombardment effects and present how much to be improved the properties of a-IGZO thin film by this new deposition method. We deposited a-IGZO thin films by MFSS on SiO2/p-Si and glass substrate at various process conditions, after which we investigated the morphology, optical and electrical properties of the a-IGZO thin films.

• ETRI Journal
• /
• 제34권6호
• /
• pp.966-969
• /
• 2012

From a practical viewpoint, the topic of electrical stability in oxide thin-film transistors (TFTs) has attracted strong interest from researchers. Positive bias stress and constant current stress tests on indium-gallium-zinc-oxide (IGZO)-TFTs have revealed that an IGZO-TFT with a larger Ga portion has stronger stability, which is closely related with the strong binding of O atoms, as determined from an X-ray photoelectron spectroscopy analysis.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
• /
• pp.215.2-215.2
• /
• 2015

We fabricated dual active layer (DAL) thin film transistors (TFTs) with indium tin zinc oxide (ITZO) and indium gallium zinc oxide (IGZO) thin film layers using solution process. The ITZO and IGZO layer were used as the front and back channel, respectively. In order to investigate the bias stress stability of ITZO SAL (single active layer) and ITZO/IGZO DAL TFT, a gate bias stress of 10 V was applied for 1500 s under the dark condition. The SAL TFT composed of ITZO layer shows a poor positive bias stability of ${\delta}VTH$ of 13.7 V, whereas ${\delta}VTH$ of ITZO/IGZO DAL TFT was very small as 2.6 V. In order to find out the evidence of improved bias stress stability, we calculated the total trap density NT near the channel/gate insulator interface. The calculated NT of DAL and SAL TFT were $4.59{\times}10^{11}$ and $2.03{\times}10^{11}cm^{-2}$, respectively. The reason for improved bias stress stability is due to the reduction of defect sites such as pin-hole and pores in the active layer.

• 센서학회지
• /
• 제28권5호
• /
• pp.329-333
• /
• 2019

Solution-processed oxide thin-film transistors (TFTs) have garnered great attention, owing to their many advantages, such as low-cost, large area available for fabrication, mechanical flexibility, and optical transparency. Negative bias stress (NBS)-induced instability of sol-gel IGZO TFTs is one of the biggest concerns arising in practical applications. Thus, understanding the bias stress effect on the electrical properties of sol-gel IGZO TFTs and proposing an effective recovery method for negative bias stressed TFTs is required. In this study, we investigated the variation of transfer characteristics and the corresponding electrical parameters of sol-gel IGZO TFTs caused by NBS and positive bias recovery (PBR). Furthermore, we proposed an effective PBR method for the recovery of negative bias stressed sol-gel IGZO TFTs. The threshold voltage and field-effect mobility were affected by NBS and PBR, while current on/off ratio and sub-threshold swing were not significantly affected. The transfer characteristic of negative bias stressed IGZO TFTs increased in the positive direction after applying PBR with a negative drain voltage, compared to PBR with a positive drain voltage or a drain voltage of 0 V. These results are expected to contribute to the reduction of recovery time of negative bias stressed sol-gel IGZO TFTs.

• 마이크로전자및패키징학회지
• /
• 제30권3호
• /
• pp.56-63
• /
• 2023

본 연구에서는 졸-겔 IGZO(Indium-Gallium-Zinc Oxide) 박막을 만들고 이에 전자빔을 조사 한 후 박막 트랜지스터로 제작하여 전자빔 조사가 박막 트랜지스터의 전기적 특성에 미치는 영향을 비교 분석하였다. 특히 전자빔이 조사되는 환경을 대기 중과 질소 분위기(<200 ppm O₂)로 두고 전자빔 조사 선량 세기를 100kGy와 200kGy로 각각 조사한 후 350℃ 온도에서의 열처리만 진행한 비교군과 비교 분석을 진행하였다. 전자빔 조사에 따른 졸-겔 IGZO 박막의 물성 변화를 분석하기 위해 UV-Visible spectroscopy, X-ray diffraction(XRD)와 X-ray photoelectron spectroscopy(XPS)를 분석 결과, 전자빔 조사 전·후의 모든 조건 하에서 가시광 영역에서의 80% 이상의 높은 투과도를 보여줌을 확인할 수 있었고, XRD 분석 결과를 통해 전자빔 조사와 관계없이 비정질 특성을 유지함을 확인하였다. 특히 전자빔 조사에 따라 졸-겔 IGZO 박막에 화학적 조성 변화가 있음을 확인하였는데, 질소 분위기에서 전자빔을 조사하게 되면 M-O결합과 관련된 peak이 차지하는 비율이 높아짐을 확인할 수 있었다. 질소 분위기에서 전자빔이 조사된 TFT들은 on/off 비율, 전자 이동도에서 향상된 특성을 보여주었으며, 시간에 따라 트랜지스터의 특성들(on/off 비율, 문턱전압, 전자이동도, 하위임계값 스윙)의 수치 또한 큰 변화 없이 유지됨이 확인되어, 졸-겔 공정 TFT 제작에 있어서 질소 분위기에서의 전자빔 조사공정이 IGZO기반 박막 트랜지스터의 전기적특성의 개선에 기여할 수 있을 것으로 기대된다.

• Transactions on Electrical and Electronic Materials
• /
• 제17권3호
• /
• pp.143-145
• /
• 2016

In order to find suitable source and drain (S/D) electrodes for amorphous InGaZnO thin film transistors (a-IGZO TFTs), the specific contact resistance of interface between the channel layers and various S/D electrodes, such as Ti/Au, a-IZO and multilayer of a-IGZO/Ag/a-IGZO, was investigated using the transmission line model. The a-IGZO TFTs with a-IGZO/Ag/a-IGZO of S/D electrodes had good performance and low contact resistance due to the homo-junction with channel layer. The stability was measured with different electrodes by a positive bias stress test. The result shows the a-IGZO TFTs with a-IGZO/Ag/a-IGZO electrodes were more stable than other devices.

• 한국표면공학회지
• /
• 제48권6호
• /
• pp.322-328
• /
• 2015

We investigated the diffusion behaviors, electrical properties, microstructures, and composition of In-Ga-Zn-O (IGZO) oxide thin films deposited by radio frequency reactive magnetron sputtering with increasing annealing temperatures. The samples were deposited at room temperature and then annealed at 300, 400, 500, 600 and $700^{\circ}C$ in air ambient for 2 h. According to the results of time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy, no diffusion of In, Ga, and Zn components were observed at 300, 400, 500, $600^{\circ}C$, but there was a diffusion at $700^{\circ}C$. However, for the sample annealed at $700^{\circ}C$, considerable diffusion occurred. Especially, the concentration of In and Ga components were similar at the IGZO thin film but were decreased near the interface between the IGZO and glass substrate, while the concentration of Zn was decreased at the IGZO thin film and some Zn were partially diffused into the glass substrate. The high-resolution transmission electron microscopy results showed that a phase change at the interface between IGZO film and glass substrate began to occur at $500^{\circ}C$ and an unidentified crystalline phase was observed at the interface between IGZO film and glass substrate due to a rapid change in composition of In, Ga and Zn at $700^{\circ}C$. The best values of electron mobility of $15.5cm^2/V{\cdot}s$ and resistivity of $0.21{\Omega}cm$ were obtained from the sample annealed at $600^{\circ}C$.

• 한국전기전자재료학회논문지
• /
• 제23권12호
• /
• pp.961-965
• /
• 2010

In this study, we investigated the optical, electrical, and structural properties of the IGZO($In_2O_3:Ga_2O_3:ZnO$=1:9:90 wt.%) thin films prepared by RF-magnetron sputtering system under various substrate temperatures. All of the IGZO thin films shows an average transmittance of over the 80% in visible range. Most of all, deposited IGZO thin film at $100^{\circ}C$ substrate temperature have ZnO (002) of main growth peak and 17.02 nm of increased grains. And also IGZO thin film have low resistivity($1.35{\times}10^{-3}\;\Omega{\cdot}cm$), high carrier concentration($6.62{\times}10^{20} cm^{-3}$) and mobility($80.1 cm^2$/Vsec). IGZO thin film have 2.08 mV at surface potential of electric force microscopy(EFM). We suggest that pre-annealing at $100^{\circ}C$ can be applied for improving optical, electrical and structural properties.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
• /
• pp.466-468
• /
• 2012

Amorphous InGaZnO (${\alpha}$-IGZO) thin-film transistors (TFTs) are are very promising due to their potential use in thin film electronics and display drivers [1]. However, the stability of AOS-TFTs under the various stresses has been issued for the practical AOSs applications [2]. Up to now, many researchers have studied to understand the sub-gap density of states (DOS) as the root cause of instability [3]. Nomura et al. reported that these deep defects are located in the surface layer of the ${\alpha}$-IGZO channel [4]. Also, Kim et al. reported that the interfacial traps can be affected by different RF-power during RF magnetron sputtering process [5]. It is well known that these trap states can influence on the performances and stabilities of ${\alpha}$-IGZO TFTs. Nevertheless, it has not been reported how these defect states are created during conventional RF magnetron sputtering. In general, during conventional RF magnetron sputtering process, negative oxygen ions (NOI) can be generated by electron attachment in oxygen atom near target surface and accelerated up to few hundreds eV by self-bias of RF magnetron sputter; the high energy bombardment of NOIs generates bulk defects in oxide thin films [6-10] and can change the defect states of ${\alpha}$-IGZO thin film. In this paper, we have confirmed that the NOIs accelerated by the self-bias were one of the dominant causes of instability in ${\alpha}$-IGZO TFTs when the channel layer was deposited by conventional RF magnetron sputtering system. Finally, we will introduce our novel technology named as Magnetic Field Shielded Sputtering (MFSS) process [9-10] to eliminate the NOI bombardment effects and present how much to be improved the instability of ${\alpha}$-IGZO TFTs by this new deposition method.

• 반도체디스플레이기술학회지
• /
• 제15권4호
• /
• pp.46-50
• /
• 2016

In this study, we have investigated the effect of the substrate temperature and hydrogen flow rate on the characteristics of IGZO thin films for the TCO(transparent conducting oxide). For this purpose, IGZO thin films were deposited by RF magnetron sputtering at room temperature and $300^{\circ}C$ with various $H_2$ flow rate. In order to investigate the influences of the hydrogen, the flow rate of hydrogen in argon mixing gas has been changed from 0.1sccm to 1.0sccm. IGZO thin films deposited at room temperature show amorphous structure, whereas IGZO thin films deposited at $300^{\circ}C$ show crystalline structure having an (222) preferential orientation. The electrical resistivity of the amorphous-IGZO films deposited at R.T. was lower than that of the crystalline-IGZO thin films deposited at $300^{\circ}C$. The increase of electrical resistivity with increasing substrate temperature was interpreted in terms of the decrease of the charge carrier mobility. The transmittance of the IGZO films deposited at $300^{\circ}C$ was decreased deposited with hydrogen gas.