• Journal of the Microelectronics and Packaging Society
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• v.26 no.3
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• pp.59-62
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• 2019

In this study, we have developed solution-processed, F-doped In-Ga-Zn-O semiconductors and investigated their applications to thin-film transistors. In order for forming the appropriate channel layer, precursor solutions were formulated by dissolving the metal salts in the designated solvent and an additive, ammonium fluoride, was incorporated additionally as a chemical modifier. We have studied thermal and chemical contributions by a thermal annealing and an incorporation of chemical modifier, from which it was revealed that electrical performances of the thin-film transistors comprising the channel layer annealed at a low temperature can be improved significantly along with an addition of ammonium fluoride. As a result, when the 20 mol% fluorine was incorporated into the semiconductor layer, electrical characteristics were accomplished with a field-effect mobility of $1.2cm^2/V{\cdot}sec$ and an $I_{on}/_{off}$ of $7{\times}10^6$.

• Journal of the Korean Society of Radiology
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• v.17 no.4
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• pp.625-631
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• 2023

The important requirement of industrial dynamic X-ray detector operating under high tube voltage up to 450 kVp for 24 hours and 7 days is to obtain significantly high radiation resistance. This study presents the radiation resistance characteristics of various thin film transistors (TFTs) with a-Si, poly-Si and IGZO semiconducting layers. IGZO TFT offering dozens of times higher field effect mobility than a-Si TFT was processed with highly hydrogenated plasma in between IGZO semiconducting layer and inter-layered dielectric. The hydrogenated IGZO TFT showed most sustainable radiation resistance up to 10,000Gy accumulated, thus, concluded that it is a sole switching device in X-ray imaging sensor offering dynamic X-ray imaging at high frame rate under extremely severe radiation environment such as automated X-ray inspection.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.204.2-204.2
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• 2015

산화물 반도체는 비정질임에도 불구하고 높은 이동도를 나타내며, 적은 누설 전류, 낮은 소비전력, 저온 공정 가능, 가시광선 영역에서 투명한 성질을 가지고 있다. 이와 같은 다양한 장점들로 인해 산화물 반도체를 이용한 트랜지스터는 차세대 플랫 패널 디스플레이 적용에 있어서 핵심 기술로 각광받고 있다. 한편, 소자의 크기가 점점 더 작아짐에 따라 고집적화에 따른 scaling down은 항상 언급되는 이슈이다. 이와 관련하여 소자의 높은 on current는 트랜지스터를 더 작게 구현할 수 있다는 가능성을 보여준다. 따라서 현재 소자의 on current를 높이기 위해서 소자의 구조를 변형하는 연구가 활발히 진행되고 있다. 본 연구에서는 소자의 on current를 높이기 위한 방법으로 ITO buried layer를 이용한 산화물 반도체 pseudo 트랜지스터를 제작하였다. 먼저 채널을 형성하기 전에 ITO buried layer를 형성시켜준 후, 채널 영역으로서 InGaZnO (2:1:1)를 용액 공정을 이용하여 형성시켰다. 이어서 소자의 전기적 특성 향상을 위해 마이크로웨이브 열처리를 1800 W에서 2분간 실시하였다. 또한 대조군으로 ITO buried layer를 갖지 않는 소자를 같은 방법으로 제작하여 평가하였다. 그 결과 ITO buried later를 갖는 소자에서 대조군과 비교하여 높은 on current를 나타냄을 확인하였다. 이와 같은 결과는 낮은 저항의 ITO buried layer가 current path를 제공함과 동시에 더 두꺼운 채널 층을 형성시켜 높은 on current에 기여하기 때문이다. 결과적으로 ITO buried layer를 갖는 소자 구조를 이용함으로써 고성능 트랜지스터를 제작하여 소자를 집적화 함에 있어서 유망한 소자가 될 것으로 예상된다.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.163-163
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• 2015

The effect of nematic liquid crystal(5CB-4-Cyano-4'-pentylbiphenyl) on the amorphous indium gallium zinc oxide thin film transistors(a-IGZO TFTs) was investigated. Through dropping the 5CB on the a-IGZO TFT's channel layer which is deposited by RF-magnetron sputtering, properties of a-IGZO TFTs was dramatically improved. When drain bias was induced, 5CB molecules were oriented by Freedericksz transition generating positive charges to one side of dipoles. From increment of the capacitance by orientation of liquid crystals, the drain current was increased, and we analyzed these phenomena mathematically by using MOSFET model. Transfer characteristic showed improvement such as decreasing of subthreshold slope(SS) value 0.4 to 0.2 and 0.45 to 0.25 at linear region and saturation region, respectively. Furthermore, in positive bias system(PBS), prevention effect for electron trapping by 5CB liquid crystal dipoles was observed, which showing decrease of threshold voltage shift [(${\delta}V$]_TH) when induced +20V for 1~1000sec at the gate electrode.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.351-351
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• 2013

한국 전체 에너지 사용량 중약 24%의 에너지가 건축물 부분에 소비되고 있다. 건축물의 벽체나 유리창 등을 통해서 에너지 손실이 이루어지는데 유리창은 벽체에 비해 약 10배 이상 낮은 단열 특성을 가지고 있기 때문에 유리창을 통한 열손실량은 더 크다. 이러한 유리창 부분의 열손실 문제를 해결할 수 있는 방안으로 좋은 단열 특성 및 낮은 방사율을 가지고 있는 Low-e coating 방법을 사용하였다. 본 실험에서는 XG glass 기판 위에 IGZO/Ag/IGZO OMO 구조의 다층 박막을 증착하였다. RF magnetron sputtering방법을 이용하여 OMO 구조의 상부와 하부의 Oxide layer로 IGZO 박막을 증착하였다. 사용된 IGZO 타겟은 $In_2O_3$ (99.99%), $Ga_2O_3$ (99.99%), ZnO (99.99%)의 분말을 각각 1:1:1 mol% 조성비로 혼합하여 소결하여 제작하였다. Thermal Evaporator 장비를 이용하여 OMO 구조의 Metal layer로 Ag (99.999%)를 증착하였다. 실험 기판은 크기 $30{\times}30mm$의 0.7T XG glass를 사용하였다. OMO 구조의 산화층 IGZO 박막은 상/하층 동일 조건으로 기판 온도는 실온으로 고정하였으며, 초기 압력 $3.0{\times}10^{-6}$ Torr, 증착 압력 $3.0{\times}10^{-2}$ Torr, RF 파워 50W, Ar 유량 50 sccm로 고정시키고 증착 시간이 변화하면서 박막을 증착하였다. OMO 구조의 Metal layer로 Ag 증착 조건은 초기 진공도가 약 $6.0{\times}10^{-6}$ Torr 이하로 유지하고 기판을 2 Rpm의 속도로 회전시켰다. 이후 0.3 V로 Ag를 10분간 가열하여 충분히 녹인 후 Film Thickness Monitor로 두께를 확인하였다. OMO 다층 박막의 산화물층 변화에 따라 로이다층 박막의 구조적, 광학적 및 전기적 특성을 분석하였다. XRD 분석결과에 의하여 Bragg's 법칙을 만족하는 피크가 나타나지 않는 비정질 구조임을 확인할 수 있으며, AFM 분석결과에 통해서 최소 1.3 nm의 Roughness를 나타내었다. UV-Visible-NIR 분광광도계를 이용하여 다층 박막은 가시광선 영역에서 평균 80%의 광 투과성을 보여 IR 영역에서 평균 30% 투과하고 좋은 차단 특성을 나왔다. Low-e 특성을 갖는 유리창을 통해서 에너지 절약을 이룰 수 있는 것을 확인할 수 있었다.

• JSTS:Journal of Semiconductor Technology and Science
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• v.17 no.2
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• pp.239-244
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• 2017

We experimentally investigate the physical mechanism for asymmetrical degradation in amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs) under simultaneous gate and drain bias stresses. The transfer curves exhibit an asymmetrical negative shift after the application of gate-to-source ($V_{GS}$) and drain-to-source ($V_{DS}$) bias stresses of ($V_{GS}=24V$, $V_{DS}=15.9V$) and ($V_{GS}=22V$, $V_{DS}=20V$), but the asymmetrical degradation is more significant after the bias stress ($V_{GS}$, $V_{DS}$) of (22 V, 20 V) nevertheless the vertical electric field at the source is higher under the bias stress ($V_{GS}$, $V_{DS}$) of (24 V, 15.9 V) than (22 V, 20 V). By using the modified external load resistance method, we extract the source contact resistance ($R_S$) and the voltage drop at $R_S$ ($V_{S,\;drop}$) in the fabricated a-IGZO TFT under both bias stresses. A significantly higher RS and $V_{S,\;drop}$ are extracted under the bias stress ($V_{GS}$, $V_{DS}$) of (22 V, 20V) than (24 V, 15.9 V), which implies that the high horizontal electric field across the source contact due to the large voltage drop at the reverse biased Schottky junction is the dominant physical mechanism causing the asymmetrical degradation of a-IGZO TFTs under simultaneous gate and drain bias stresses.

• Journal of Information Display
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• v.12 no.4
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• pp.209-212
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• 2011

The threshold voltage shift (${\Delta}V_{th}$) under positive-voltage bias stress (PBS) of InGaZnO (IGZO) thin-film transistors (TFTs) annealed at different temperatures in air was investigated. The dramatic degradation of the electrical performance was observed at the sample that was annealed at $700^{\circ}C$. The degradation of the saturation mobility (${\mu}_{sat}$) resulted from the diffusion of indium atoms into the interface of the IGZO/gate insulator after crystallization, and the degradation of the subthreshold slope (S-factor) was due to the increase in the interfacial and bulk trap density. In spite of the degradation of the electrical performance of the sample that was annealed at $700^{\circ}C$, it showed a smaller ${\Delta}V_{th}$ under PBS conditions for $10^4$ s than the samples that were annealed at $500^{\circ}C$, which is attributed to the nanocrystal-embedded structure. The sample that was annealed at $600^{\circ}C$ showed the best performance and the smallest ${\Delta}V_{th}$ among the fabricated samples with a ${\mu}_{sat}$ of $9.38cm^2/V$ s, an S-factor of 0.46V/decade, and a ${\Delta}V_{th}$ of 0.009V, which is due to the passivation of the defects by high thermal annealing without structural change.

• JSTS:Journal of Semiconductor Technology and Science
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• v.15 no.5
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• pp.519-525
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• 2015

Positive bias stress-induced instability in amorphous indium-gallium-zinc-oxide (a-IGZO) bottom-gate thin-film transistors (TFTs) was investigated under high $V_{GS}$/low $V_{DS}$ and low $V_{GS}$/high $V_{DS}$ stress conditions through incorporating a forward/reverse $V_{GS}$ sweep and a low/high $V_{DS}$ read-out conditions. Our results showed that the electron trapping into the gate insulator dominantly occurs when high $V_{GS}$/low $V_{DS}$ stress is applied. On the other hand, when low $V_{GS}$/high $V_{DS}$ stress is applied, it was found that holes are uniformly trapped into the etch stopper and electrons are locally trapped into the gate insulator simultaneously. During a recovery after the high $V_{GS}$/low $V_{DS}$ stress, the trapped electrons were detrapped from the gate insulator. In the case of recovery after the low $V_{GS}$/high $V_{DS}$ stress, it was observed that the electrons in the gate insulator diffuse to a direction toward the source electrode and the holes were detrapped to out of the etch stopper. Also, we found that the potential profile in the a-IGZO bottom-gate TFT becomes complicatedly modulated during the positive $V_{GS}/V_{DS}$ stress and the recovery causing various threshold voltages and subthreshold swings under various read-out conditions, and this modulation needs to be fully considered in the design of oxide TFT-based active matrix organic light emitting diode display backplane.

• Journal of the Korean Society of Radiology
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• v.17 no.3
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• pp.359-365
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• 2023

In order to satisfy the requirements of dynamic X-ray imaging with high frame rate and low image lag, minimizing parasitic capacitance in photodiode and overlapped electrodes in pixels is critically required. This study presents duoPIX^TM dynamic X-ray imaging sensor composing of readout thin film transistor, reset thin film transistor and photodiode in a pixel. Furthermore, dynamic X-ray detector using duoPIX^TM imaging sensor was manufactured and evaluated its X-ray imaging performances such as frame rate, sensitivity, noise, MTF and image lag. duoPIX^TM dynamic X-ray detector has 150 × 150 mm² imaging area, 73 um pixel pitch, 2048 × 2048 matrix resolution(4.2M pixels) and maximum 50 frames per second. By means of comparison with conventional dynamic X-ray detector, duoPIX^TM dynamic X-ray detector showed overall better performances than conventional dynamic X-ray detector as shown in the previous study.

• Journal of the Korean institute of surface engineering
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• v.47 no.2
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• pp.81-85
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• 2014

Ga doped ZnO (GZO)/Al bi-layered films were deposited on the glass substrate by RF and DC magnetron sputtering and then vacuum annealed at different temperatures of 100, 200 and $300^{\circ}C$ for 30 minutes to consider the effects of annealing temperature on the structural, electrical and optical properties of the films. For all depositions, the thicknesses of the GZO and Al films were kept constant at 95 and 5 nm, respectively, by controlling the deposition time. As-deposited GZO/Al bi-layered films showed a relatively low optical transmittance of 62%, while the films annealed at $300^{\circ}C$ showed a higher transmittance of 81%, compared to the other films. In addition, the electrical resistivity of the films was influenced by annealing temperature and the lowest resistivity of $9.8{\times}10^{-4}{\Omega}cm$ was observed in the films annealed at $300^{\circ}C$. Due to the increased carrier mobility, 2.35 $cm^2V^{-1}S^{-1}$ of the films. From the experimental results, it can be concluded that increasing the annealing temperature enhanced the optical and electrical properties of the GZO/Al films.