• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1453-1454
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• 2011

We have investigated the effect of silicon contents (0~0.4 molar ratios) on the performance of solution processed silicon-indium-zinc oxide (SIZO) thin-film transistors (TFTs). Despites its solution processed channel layer, low annealed temperature below $200^{\circ}C$ in air has been used for SIZO-TFTs. The $V_{th}$ is shifted from -4.04 to 5.15 V as increasing Si ratio in the SIZO-TFTs. The positive shift of $V_{th}$ as increasing Si contents in SIZO system indicates that Si suppresses the carrier generation in the active channel layer since $V_{th}$ is defined as the voltage required accumulating sufficient charge carriers to form a conductive channel path.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.3-3
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• 2010

We investigated the influence of the indium content on the threshold voltage ($V_{th}$) shift of sol-gel-derived indium-gallium-zinc oxide (IGZO) thin film transistors (TFTs). Surplus indium composition ratio into IGZO decreases the value of $V_{th}$ of IGZO TFTs showed huge $V_{th}$ shift in the negative direction. $V_{th}$ shift decreases from 10 to -28.2V as Indium composition ratio is increased. Because the free electron density is increased according to variation of the Indium composition ratio.

• ETRI Journal
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• v.31 no.6
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• pp.653-659
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• 2009

We have investigated the channel protection layer (PL) effect on the performance of an oxide thin film transistor (TFT) with a staggered top gate ZnO TFT and Al-doped zinc tin oxide (AZTO) TFT. Deposition of an ultra-thin PL on oxide semiconductor films enables TFTs to behave well by protecting the channel from a photo-resist (PR) stripper which removes the depleted surface of the active layer and increases the carrier amount in the channel. In addition, adopting a PL prevents channel contamination from the organic PR and results in high mobility and small subthreshold swings. The PL process plays a critical role in the performance of oxide TFTs. When a plasma process is introduced on the surface of an active layer during the PL process, and as the plasma power is increased, the TFT characteristics degrade, resulting in lower mobility and higher threshold voltage. Therefore, it is very important to form an interface using a minimized plasma process.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2013.10a
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• pp.390-392
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• 2013

The research was observed the characteristic of ZnO based oxide semiconductors for the transparent conducting display. The optical-physical properties of ZnO based oxide semiconductors) grown on p-Si wafer were presented. ZnO based oxide semiconductors was prepared by the RF magnetron sputtering system. The characteristic of ZnO based oxide semiconductorswas strongly influenced by the amount of localized electron state by the defects. The PL spectra moved to long wave number with increasing the defects in the film. The mobility of a-IGZO film was increased with increasing the oxygen gas flow rate. The resistivity of ZnO based oxide semiconductors was also related to the mobility of ZnO based oxide semiconductors, and the mobility increased at the sample with low resistivity. The electric characteristic of a-IGZO TFTs showed that it is an n-type semiconductor.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.160-160
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• 2015

InGaZnO (IGZO) thin-film transistors (TFTs) are very promising due to their potential use in high performance display backplane [1]. However, the stability of IGZO TFTs under the various stresses has been issued for the practical IGZO 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 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 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 IGZO thin film. In this study, we have confirmed that the NOIs accelerated by the self-bias were one of the dominant causes of instability in 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 IGZO TFTs by this new deposition method.

• Transactions on Electrical and Electronic Materials
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• v.18 no.1
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• pp.55-57
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• 2017

Amorphous oxide thin film transistors (TFTs) were fabricated with 0.5 wt% silicon doped zinc tin oxide (a-0.5SZTO) thin film deposited by radio frequency (RF) magnetron sputtering. In order to investigate the effect of annealing treatment on the electrical properties of TFTs, a-0.5SZTO thin films were annealed at three different temperatures ($300^{\circ}C$, $500^{\circ}C$, and $700^{\circ}C$ for 2 hours in a air atmosphere. The structural and electrical properties of a-0.5SZTO TFTs were measured using X-ray diffraction and a semiconductor analyzer. As annealing temperature increased from $300^{\circ}C$ to $500^{\circ}C$, no peak was observed. This provided crystalline properties indicating that the amorphous phase was observed up to $500^{\circ}C$. The electrical properties of a-0.5SZTO TFTs, such as the field effect mobility (${\mu}_{FE}$) of $24.31cm^2/Vs$, on current ($I_{ON}$) of $2.38{\times}10^{-4}A$, and subthreshold swing (S.S) of 0.59 V/decade improved with the thermal annealing treatment. This improvement was mainly due to the increased carrier concentration and decreased structural defects by rearranged atoms. However, when a-0.5SZTO TFTs were annealed at $700^{\circ}C$, a crystalline peak was observed. As a result, electrical properties degraded. ${\mu}_{FE}$ was $0.06cm^2/Vs$, $I_{ON}$ was $5.27{\times}10^{-7}A$, and S.S was 2.09 V/decade. This degradation of electrical properties was mainly due to increased interfacial and bulk trap densities of forming grain boundaries caused by the annealing treatment.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.466-468
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• 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.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.540-542
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• 2009

Phosphorus doped ZnO (PZO) thin films were deposited on $SiO_2$/n-Si substrates using DC magnetron sputtering system varying oxygen partial pressures from 0 to 40 % under Ar atmosphere. The deposited films showed reduced n-type conductivity due to the compensating donor effects by phosphorus dopant. The bias-time stability shows relatively good stability over bias and time comparing to un-doped ZnO-based TFTs.

• Journal of the Korean Vacuum Society
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• v.16 no.5
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• pp.359-365
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• 2007

In this paper we present a bottom-gate type of zinc oxide (ZnO) and Gallium (Ga) doped zinc oxide (GZO) based thin film transistors (TFTs) through applying a radio frequency (RF) magnetron sputtering method at room temperature. The gate leakage current can be reduced up to several ph by applying $SiO_2$ thermally grown instead of using new gate oxide materials. The root mean square (RMS) values of the ZnO and GZO film surface were measured as 1.07 nm and 1.65 nm, respectively. Also, the transmittances of the ZnO and GZO film were more than 80% and 75%, respectively, and they were changed as their film thickness. The ZnO and GZO film had a wurtzite structure that was arranged well as a (002) orientation. The ZnO TFT had a threshold voltage of 2.5 V, a field effect mobility of $0.027\;cm^2/(V{\cdot}s)$, a on/off ratio of $10^4$, a gate voltage swing of 17 V/decade and it operated in a enhancement mode. In case of the GZO TFT, it operated in a depletion mode with a threshold voltage of -3.4 V, a field effect mobility of $0.023\;cm^2/(V{\cdot}s)$, a on/off ratio of $2{\times}10^4$ and a gate voltage swing of 3.3 V/decade. We successfully demonstrated that the TFTs with the enhancement and depletion mode type can be fabricated by using pure ZnO and 1wt% Ga-doped ZnO.

• Korean Journal of Materials Research
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• v.27 no.4
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• pp.216-220
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• 2017

The effect of electron beam (EB) irradiation on the electrical properties of Zn-Sn-O (ZTO) thin films fabricated using a sol-gel process was investigated. As the EB dose increased, the saturation mobility of ZTO thin film transistors (TFTs) was found to slightly decrease, and the subthreshold swing and on/off ratio degenerated. X-ray photoelectron spectroscopy analysis of the O 1s core level showed that the relative area of oxygen vacancies ($V_O$) increased from 10.35 to 12.56 % as the EB dose increased from 0 to $7.5{\times}10^{16}electrons/cm^2$. Also, spectroscopic ellipsometry analysis showed that the optical band gap varied from 3.53 to 3.96 eV with increasing EB dose. From the results of the electrical property and XPS analyses of the ZTO TFTs, it was found that the electrical characteristic of the ZTO thin films changed from semiconductor to conductor with increasing EB dose. It is thought that the electrical property change is due to the formation of defect sites like oxygen vacancies.