Browsing by Author "Chung, Wan-Fang"

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Analysis of Electrical Characteristics and Reliability Change of Zinc-Tin-Oxide Thin-Film Transistors by Photo-Thermal Treatment
(2013)
Chen, Yu-Chun
;
Chang, Ting-Chang
;
Li, Hung-Wei
;
Chung, Wan-Fang
;
Hsieh, Tien-Yu
This study investigates the influence of a photo-thermal treatment on the electrical characteristics and bias-induced instability of amorphous Zn-Sn-O thin film transistors. Sequences of measurements made in both vacuum and oxygen ambient reveal the most pronounced threshold voltage (V-T) shift, i.e., the highest sensitivity of oxygen, occurs in a device with photo-thermal-treatment. After gate-bias stress in vacuum, the treated device shows less V-T shift than that untreated, which can be attributed to residual adsorbed gas molecules on the backchannel. Thus, the proposed photo-thermal-treatment should be conducted before depositing a passivation layer to increase the reliability of devices after stress. (c) 2013 The Electrochemical Society. All rights reserved.
Bias-induced oxygen adsorption in zinc tin oxide thin film transistors under dynamic stress
(2010-06-28)
Chen, Yu-Chun
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Chang, Ting-Chang
;
Li, Hung-Wei
;
Chen, Shih-Ching
;
Lu, Jin
This study investigates the effects of bias-induced oxygen adsorption on the electrical characteristic instability of zinc tin oxide thin film transistors in different ambient oxygen partial pressures. When oxygen pressure is largest, the threshold voltages showed the quickest increase but the slowest recovery during the stress phase and recovery phase, respectively. This finding corresponds to the charge trapping time constant and recovery time constant, which are extracted by fitting the stretched-exponential equation and which exhibit a relationship with oxygen pressure. We suggest that the gate bias reduces the activation energy of oxygen adsorption during gate bias stress. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3457996]
Characterization of environment-dependent hysteresis in indium gallium zinc oxide thin film transistors
(2013-09-01)
Chen, Yu-Chun
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Chang, Ting-Chang
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Li, Hung-Wei
;
Chung, Wan-Fang
;
Chen, Shih-Cheng
This study investigates environmentally dependent electrical performance as a function of hysteresis phenomena for amorphous indium-gallium-zinc-oxide (a-IGZO) thin film transistors (TFTs). Because ambient gas has a great influence on the electrical characteristics of zinc oxide-based TFTs during electrical measurements, the hysteresis for current-voltage and capacitance-voltage measurements are employed in different ambient gases (ambient air, vacuum, oxygen ambient and moisture ambient) to study this issue. Although the hysteresis phenomenon has been explained by the charge trapping and de-trapping model, in order to obtain stable electrical characteristics it is necessary to clarify the original principal mechanism leading to threshold voltage instability under gate bias operations in different environments. Also, the relationship between de-trapping rate and electrical hysteresis is investigated by prolonging the integration time of the semiconductor parameter analyzer. This study may be of importance in explaining the dynamic relationship between the TFT electrical characteristics and ambient gas, as well as providing a better understanding of the environment-dependent hysteresis phenomenon of the IGZO TFTs. (C) 2012 Elsevier B.V. All rights reserved.
Dependence of Light-Accelerated Instability on Bias and Environment in Amorphous Indium-Gallium-Zinc-Oxide Thin Film Transistors
(2013)
Chen, Yu-Chun
;
Chang, Ting-Chang
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Li, Hung-Wei
;
Chung, Wan-Fang
;
Hsieh, Tien-Yu
This study examines the dependence of light-accelerated instability on bias and environment in amorphous indium-gallium-zinc-oxide thin film transistors. When device is in vacuum ambient, the threshold voltage of device after negative gate bias illumination stress (NBIS) showed bias-dependent electrical degradation behavior. However, experimental results show the degradation of electrical characteristic in a-IGZO devices does not only rely on the charge trapping mechanism for NBIS. During NBIS in oxygen, moisture-simulated and atmosphere ambient, the negative shift in electrical characteristic is suppressed when compared to that in vacuum. This implies that the adsorbent gas species in the surrounding environment dominates the electrical characteristic degradation of devices during NBIS, which leading the change of dominant mechanism from photon-created carrier trapping to adsorbed/desorbed gas phenomenon. (C) 2013 The Electrochemical Society. All rights reserved.
Effects of Post-Deposition Annealing Atmosphere and Duration on Sol-Gel Derived Amorphous Indium-Zinc-Oxide Thin Film Transistors
(2011)
Chung, Wan-Fang
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Chang, Ting-Chang
;
Li, Hung-Wei
;
Tseng, Tseung-Yuen
;
Tai, Ya-Hsiang
This work shows the effects of post-deposition annealing atmosphere and duration on the properties of sol-gel derived amorphous indium zinc oxide thin film transistors (a-IZO TFTs). Two different post-deposition annealing atmospheres, nitrogen and oxygen, were used in this study. Experimental results showed that the O-2-annealed devices showed better electrical characteristics than the N-2-annealed samples. Under O-2-annealing, field effect mobility was enhanced to 1.47 cm(2)/V s, the threshold voltage increased to -4.61 V and the subthreshold swing improved to 0.86 V/dec. Also, the transfer characteristics of a-IZO TFTs improve with annealing time. X-ray photoelectron spectroscopy (XPS) analysis indicated that the chemical composition of the IZO film was modified by the oxygen annealing.
Environment-dependent thermal instability of sol-gel derived amorphous indium-gallium-zinc-oxide thin film transistors
(2011-04-11)
Chung, Wan-Fang
;
Chang, Ting-Chang
;
Li, Hung-Wei
;
Chen, Shih-Ching
;
Chen, Yu-Chun
The environment-dependent electrical performances as a function of temperature for sol-gel derived amorphous indium-gallium-zinc-oxide (a-IGZO) thin film transistors are investigated in this letter. In the ambients without oxygen, thermal activation dominates and enhances device performance. In oxygen-containing environments, mobility and drain current degrades and the threshold slightly increase as temperature increases. We develop a porous model for a-IGZO film relating to the drain current and mobility lowering due to film porosity and oxygen adsorption/penetration. It also relates to the threshold voltage recovery at high temperature owing to the varying form of adsorbed oxygen and the combination of oxygen and vacancies. (C) 2011 American Institute of Physics. [doi:10.1063/1.3580614]
H(2)O-Assisted O(2) Adsorption in Sol-Gel Derived Amorphous Indium Gallium Zinc Oxide Thin Film Transistors
(2011-01-01)
Chung, Wan-Fang
;
Chang, Ting-Chang
;
Li, Hung-Wei
;
Chen, Shih-Ching
;
Chen, Yu-Chun
This paper investigates the environmental effects and related adsorbent species reactions on sol-gel derived amorphous indium gallium zinc oxide thin film transistors (a-IGZO TFTs). The discrepancy between device characteristics measured in atmospheric and vacuum conditions was clarified through experiments with thermal annealing and different gas partial pressures. The measurement of a-IGZO TFTs in simulated water vapor environment was also utilized. We verified that the adsorbed water originating from the surrounding atmosphere can cause an increase in off-current and also enhance more oxygen molecule adsorption on the exposed back-channel surface, leading to more serious degradation in on-current. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3568831] All rights reserved.
H2O-Assisted O-2 Adsorption in Sol-Gel Derived Amorphous Indium Gallium Zinc Oxide Thin Film Transistors
(2011-01-01)
Chung, Wan-Fang
;
Chang, Ting-Chang
;
Li, Hung-Wei
;
Chen, Shih-Ching
;
Chen, Yu-Chun
This paper investigates the environmental effects and related adsorbent species reactions on sol-gel derived amorphous indium gallium zinc oxide thin film transistors (a-IGZO TFTs). The discrepancy between device characteristics measured in atmospheric and vacuum conditions was clarified through experiments with thermal annealing and different gas partial pressures. The measurement of a-IGZO TFTs in simulated water vapor environment was also utilized. We verified that the adsorbed water originating from the surrounding atmosphere can cause an increase in off-current and also enhance more oxygen molecule adsorption on the exposed back-channel surface, leading to more serious degradation in on-current. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3568831] All rights reserved.
High-stability oxygen sensor based on amorphous zinc tin oxide thin film transistor
(2012-06-25)
Chen, Yu-Chun
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Chang, Ting-Chang
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Li, Hung-Wei
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Chung, Wan-Fang
;
Wu, Chang-Pei
This research presents a sol-gel derived zinc tin oxide thin film transistor (TFT) as a high-stability oxygen sensor. Due to its high sensitivity, oxygen has been traditionally regarded as having a negative influence on the electrical characteristics of zinc-based TFTs; however, TFTs can also act as an oxygen sensor. After illumination with visible light in oxygen-rich ambient, a significant increase in drain current of nearly 10 4 times occurs with fixed gate and drain voltages. It is expected that an optimized method of illumination can help to reset the electrical characteristics or distinguish the on/off state of this reliable oxygen sensor. (C) 2012 American Institute of Physics. [ http://dx.doi.org/10.1063/1.4731773]
Influence of H(2)O Dipole on Subthreshold Swing of Amorphous Indium-Gallium-Zinc-Oxide Thin Film Transistors
(2011-01-01)
Chung, Wan-Fang
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Chang, Ting-Chang
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Li, Hung-Wei
;
Chen, Chi-Wen
;
Chen, Yu-Chun
The original influence of water on the back-channel of sol-gel derived amorphous indium-gallium-zinc-oxide thin film transistors was studied in various relative humidity environments. As humidity increased from 0 to 80%, the mobility increased from 0.22 to 0.24 cm(2)/(V s), threshold voltage decreased from 6.6 to 4.4 V, and subthreshold swing changed from 0.77 to 1.27 V/dec. The conflicting phenomenon among the three parameters was suggested to be due to a division of the gate voltage by the water molecules which adsorbed on the thin film transistor back-channel and acted as dipoles. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3526097] All rights reserved.
Influence of H2O Dipole on Subthreshold Swing of Amorphous Indium-Gallium-Zinc-Oxide Thin Film Transistors
(2011-01-01)
Chung, Wan-Fang
;
Chang, Ting-Chang
;
Li, Hung-Wei
;
Chen, Chi-Wen
;
Chen, Yu-Chun
The original influence of water on the back-channel of sol-gel derived amorphous indium-gallium-zinc-oxide thin film transistors was studied in various relative humidity environments. As humidity increased from 0 to 80%, the mobility increased from 0.22 to 0.24 cm(2)/(V s), threshold voltage decreased from 6.6 to 4.4 V, and subthreshold swing changed from 0.77 to 1.27 V/dec. The conflicting phenomenon among the three parameters was suggested to be due to a division of the gate voltage by the water molecules which adsorbed on the thin film transistor back-channel and acted as dipoles. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3526097] All rights reserved.
Oxygen-Adsorption-Induced Anomalous Capacitance Degradation in Amorphous Indium-Gallium-Zinc-Oxide Thin-Film-Transistors under Hot-Carrier Stress
(2012)
Chung, Wan-Fang
;
Chang, Ting-Chang
;
Lin, Chia-Sheng
;
Tu, Kuan-Jen
;
Li, Hung-Wei
This paper investigates anomalous capacitance-voltage (C-V) degradation in amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film-transistors (TFTs) under hot carrier stress. In vacuum hot carrier stress, both the gate-to-drain capacitance (C(GD)) and the gate-to-source capacitance (C(GS)) curves exhibited positive shifts due to electron trapping in the gate dielectric. In addition, an observed increase in capacitance value at a lower gate voltage in the C(GD) measurement only can be ascribed to interface state creation. However, when the hot carrier stress was performed in an oxygen-rich environment, the C(GD)-V(G) curve showed a significantly positive shift due to the electric-field-induced oxygen adsorption near the drain terminal. The degradation in the C(GS)-V(G) curve is due not only to the positive shift, but also the anomalous two step turn-on behavior. This phenomenon can be ascribed to the electron trapping in the gate dielectric and electric-field-induced oxygen adsorption on the channel layer, especially in the area adjacent to the drain terminal. The electron trapping increased the source energy barrier, with the electric-field-induced oxygen adsorption further raising the energy-band near the drain, resulting in a two-step turn-on behavior in the C(GS)-V(G) curve. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.075203jes] All rights reserved.
Spin-on ZnO thin film transistors with oxidation treatment
(2007)
Huang, Chen-Shuo
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Chou, Yi-Teh
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Liu, Po-Tsun
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Chung, Wan-Fang
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Huang, Chien-Jui
The ZnO TFTs was fabricated by spin-on method and investigated by modulating deposition environments. It was discovered that the conductivity of ZnO TFTs can be obviously changed by modulating curing temperature and the performances can be improved by incorporating oxygen.
Study on degradation of crystallized laterally grown poly-Si TFT under Dynamic Stress
(2007)
Lu, Hau-Yan
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Chung, Wan-Fang
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Tseng, Tzu-Yi
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Chen, Yu-Cheng
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Liu, Po-Tsun
The influence of protrusion grain boundary on the degradation of crystallized laterally grown poly-Si TFT under Dynamic Stress is investigated. The degradation of TFT with protrusion grain boundary is more severe and the different damage of the source/drain junction in the TFT with grain boundary closed to source side.
Surface states related the bias stability of amorphous In-Ga-Zn-O thin film transistors under different ambient gasses
(2011-12-30)
Chen, Yu-Chun
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Chang, Ting-Chang
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Li, Hung-Wei
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Chen, Shih-Cheng
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Chung, Wan-Fang
This paper investigates the origin of the bias stability under ambient gas (oxygen, moisture and vacuum) of In-Ga-Zn-O thin film transistors with different annealing temperatures. In Zn-based TFTs, the electrical characteristic of device is a strongly function with the ambient gas, the simultaneous gas ambient and bias stresses are applied on devices annealed in atmosphere ambient to study this issue. The result shows the device which is annealed at temperature up to 330 degrees C has worst reliability. We suppose that the sensitivity of gas ambient depend the defect state, which is associated to the annealing temperature, of surface in a-IGZO. (C) 2011 Elsevier B.V. All rights reserved.
The Impact of Active Layer Pre-Treatment on Bias Stress Stability of Sol-gel Derived Amorphous Indium-Gallium-Zinc-Oxide Thin Film Transistor
(2011)
Chung, Wan-Fang
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Chang, Ting-Chang
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Li, Hung-Wei
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Chen, Yu-Chun
;
Li, Iue-Hen
We have investigated the gate bias stress-induced instability on the electrical properties with different pre-treatments for sol-gel derived amorphous indium gallium zinc oxide thin film transistors (a-IGZO TFTs). The device with illuminating and heating pre-treatments under the positive/negative gate bias stress in vacuum had the smallest threshold voltage shift as the stress duration increased, while the device with oxygen gas pre-treatment exhibited an obvious variation. These electrical instabilities were ascribed to the charge trapping in the gate insulator and the oxygen/water adsorption on the active layer. It indicates that the specific pre-treatment for the a-IGZO film can improve the device stability. It also provides the important information for the subsequent passivation process concerning the pre-treatment of the active layer.