Browsing by Author "Zhang, Shengdong"

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An Energy-Band Model for Dual-Gate-Voltage Sweeping in Hydrogenated Amorphous Silicon Thin-Film Transistors
(2019-06-01)
Chen, Guan-Fu
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Chen, Hong-Chih
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Chang, Ting-Chang
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Huang, Shin-Ping
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Chen, Hua-Mao
This paper clarifies the correct transmission mechanism, misattributed in the previous research, of a hydrogenated amorphous silicon thin-film transistor (a-Si:H TFT) device. Complete drain current-gate voltage (I-D-V-G) transfer characteristics including the forward and backward gate sweeps (gate voltage carried out in the OFF-state -> on-state and the ON-state -> OFF-state) are performed, and the physics models of an energy-band schematic are clearly explained. This paper reveals that the I-D-V-G curve stretch-out behavior of the subthreshold region is due to the leakage of the Poole-Frenkel region. At the Poole-Frenkel regions, electrons transfer to the drain terminal, and holes remain in the valance band of the a-Si:H bulk. The remaining holes represent the positive voltage and cause the electron barrier height lowering. This causes an increase in subthreshold current of the subthreshold region. Finally, three experiments are performed to prove the correctness of these models, and the a-Si TFTs device improvement methods will be proposed to enhance the stability and performance of product of the a-Si TFTs.
Combined Effects of Light Illumination and Various Bottom Gate Length on the Instability of Via-Contact-Type Amorphous InGaZnO Thin-Film Transistors
(2018-02-01)
Yang, Chung-I
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Chang, Ting-Chang
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Liao, Po-Yung
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Chen, Bo-Wei
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Chou, Wu-Ching
This paper utilizes electrical analyses and a study of physical mechanisms to investigate metal gate structure-dependent performance in amorphous InGaZnO (a-IGZO) thin-film transistors. The effects of different shielding areas between the IGZO layer and metal gate are investigated. In devices with shorter metal gate lengths, an abnormal rise in capacitance at the off-state in capacitance-voltage (C-V) characteristic curves can be observed. This can be attributed to the stronger electric field induced by the edge of the metal gate under bias sweep when the metal gate length is shorter than the IGZO layer length. Light illumination measurements indicate a negative shift in threshold voltage and an increase in subthreshold-leakage current regardless of relative metal gate length. Moreover, negative threshold voltage shift becomes more severe with a more obvious hump in C-V characteristic curves under back-light illumination of a shorter width device, a phenomenon which has been verified by simulation.
Drain-Induced-Barrier-Lowing-Like Effect Induced by Oxygen-Vacancy in Scaling-Down via-Contact Type Amorphous InGaZnO Thin-Film Transistors
(2018-01-01)
Yang, Chung-I.
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Chang, Ting-Chang
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Liao, Po-Yung
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Chen, Li-Hui
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Chen, Bo-Wei
This investigation considers a method to ameliorate drain induced barrier lowing behavior in amorphous-indium-gallium-zinc-oxide thin-film transistors. The Vth is found to shift negatively when increasing the ID-VG measurement condition VD from 0.1 to 15 V. The current-voltage curves show that this degradation is caused by the effective channel length (L-eff) being shorter than the mask channel length (L). Using the transmission line method to extract Leff, we discover that the degradation will be completely suppressed by an annealing treatment. As a result, the degradation mechanism of shorter channel length a-IGZO thin film transistors is due to oxygen-vacancies which are located between the channel and the source/drain junction.
Recovery of failed resistive switching random access memory devices by a low-temperature supercritical treatment
(2017-06-01)
Du, Xiaoqin
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Wu, Xiaojing
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Chang, Ting-Chang
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Chang, Kuan-Chang
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Pan, Chih-Hung
The successful recovery of resistive switching random access memory (RRAM) devices that have undergone switching failure is achieved by introducing a low-temperature supercritical-fluid process that passivates the switching layer. These failed RRAM devices, which are incapable of switching between high-and low-resistance states, were treated with supercritical carbon dioxide with pure water at 120 degrees C for 1 h. After the treatment, the devices became operational again and showed excellent current-voltage (I-V) characteristics and reliability as before. On the basis of the current conduction mechanism fitting results, we propose a model to explain the phenomenon. (C) 2017 The Japan Society of Applied Physics
Solving the Scaling Issue of Increasing Forming Voltage in Resistive Random Access Memory Using High-k Spacer Structure
(2017-09-01)
Tseng, Yi-Ting
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Chen, Po-Hsun
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Chang, Ting-Chang
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Chang, Kuan-Chang
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Tsai, Tsung-Ming
In this study, the rising forming voltage issue during device cell scale-down in resistance random access memory (RRAM) is solved by introducing new high-permittivity (high-k) material as the side-wall spacer structure, unlike the normally used low-permittivity (low-k) material. Simulated electrical fields based on COMSOL Multiphysics software results suggest a RRAM device with a high-k spacer effectively confines the electric field. The effects of this confined electric field are notable, especially when the device cell is scaled down. The device fabrication process is modified to incorporate the high-k sidewall. Cross-sectional transmission electron microscopy imaging confirms the existence of SiO2 and HfO2 as the spacer structures in two different devices. Electrical measurements of forming voltages ranging from 1 to 0.16 mu m(2) are conducted to verify the effects. Statistical measurements confirm that the forming voltages of the devices with high-k material as sidewall do not increase with a reduction in device cell size. Moreover, reliability tests, including endurance and retention for the high-k sidewall device, also exhibit very stable resistance switching characteristics. As a result, the structure that is proposed successfully solves the forming voltage issues within small device cells in RRAM without any cost to device reliability.