Browsing by Author "Chen, Guan-Fu"

Now showing 1 - 7 of 7

A Dual-Gate InGaZnO4-Based Thin-Film Transistor for High-Sensitivity UV Detection
(2019-08-01)
Chen, Po-Hsun
;
Tsao, Yu-Ching
;
Chien, Yu-Chieh
;
Chiang, Hsiao-Cheng
;
Chen, Hua-Mao
UV-sensing devices have received significant recent attention for applications in areas such as human health, fire detection, and optical communication. One key factor for product commercialization is determining the optimal materials that allow for integration of excellent UV-sensing properties with compatibility with industrial fabrication processes. However, current UV sensors often fail to achieve this due to either mismatched materials or a device that must be excessively large in order to produce enough photocurrent for UV detection. The UV-light-sensing properties of an amorphous InGaZnO4 (IGZO) thin-film transistor with a dual-gate structure and relatively small device size (width/length = 50 mu m/10 mu m) that achieves high sensitivity through a threshold-voltage-(V-th)-adjustment method is proposed. Comparing the drain currents under UV exposure to those under darkened conditions indicates that the ratio between the photoinduced and dark current reaches 10(6). Furthermore, the UV sensitivity of the dual-gate transistors can be adjusted by varying the bottom gate voltage, with each pixel of the sensor then being read out separately via scan line pulses. This allows the dual-gate a-IGZO transistor to be used for high-performance UV sensing while being effectively integrated in display applications.
Abnormal Dual Channel Formation Induced by Hydrogen Diffusion From SiNx Interlayer Dielectric in Top Gate a-InGaZnO Transistors
(2017-03-01)
Chen, Guan-Fu
;
Chang, Ting-Chang
;
Chen, Hua-Mao
;
Chen, Bo-Wei
;
Chen, Hong-Chih
This letter investigates effects of different channel dimensions in top-gate a-InGaZnO4 thin-film transistors with SiNx interlayer dielectric. In narrow channel devices, hydrogen atoms in the SiNx layer diffuse into the entire active layer, inducing a single channel. However, in wider channel devices, the diffusion distance for hydrogen atoms is insufficient to affect the whole channel, instead inducing a double channel. In addition, under hot carrier stress, narrow and wide channels exhibit different degradation behaviors, with simulations showing a strong electrical field at IGZO near the drain terminal of the main channel, which is unaffected by hydrogen.
Abnormal hump in capacitance-voltage measurements induced by ultraviolet light in a-IGZO thin-film transistors
(2017-01-09)
Tsao, Yu-Ching
;
Chang, Ting-Chang
;
Chen, Hua-Mao
;
Chen, Bo-Wei
;
Chiang, Hsiao-Cheng
This work demonstrates the generation of abnormal capacitance for amorphous indium-gallium-zinc oxide (a-InGaZnO4) thin-film transistors after being subjected to negative bias stress under ultraviolet light illumination stress (NBIS). At various operation frequencies, there are two-step tendencies in their capacitance-voltage curves. When gate bias is smaller than threshold voltage, the measured capacitance is dominated by interface defects. Conversely, the measured capacitance is dominated by oxygen vacancies when gate bias is larger than threshold voltage. The impact of these interface defects and oxygen vacancies on capacitance-voltage curves is verified by TCAD simulation software. Published by AIP Publishing.
An Energy-Band Model for Dual-Gate-Voltage Sweeping in Hydrogenated Amorphous Silicon Thin-Film Transistors
(2019-06-01)
Chen, Guan-Fu
;
Chen, Hong-Chih
;
Chang, Ting-Chang
;
Huang, Shin-Ping
;
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
;
Chang, Ting-Chang
;
Liao, Po-Yung
;
Chen, Bo-Wei
;
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.
;
Chang, Ting-Chang
;
Liao, Po-Yung
;
Chen, Li-Hui
;
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.
Investigation of the Capacitance-Voltage Electrical Characteristics of Thin-Film Transistors Caused by Hydrogen Diffusion under Negative Bias Stress in a Moist Environment
(2019-10-30)
Chen, Hong-Chih
;
Kuo, Chuan-Wei
;
Chang, Ting-Chang
;
Lai, Wei-Chih
;
Chen, Po-Hsun
In this study, the impact of moisture on the electrical characteristics of an amorphous In-Ga-Zn-O thin-film transistor (a-IGZO TFT) was investigated. In commercial applications of such TFTs, high stability and quality performance in humid environments are essential. During TFT operation under ambient moisture, the electrolysis of water molecules occurs via the tip electric field effect. Hydrogen diffuses from the etch-stop layer or back-channel into the main channel under a negative electric field. The hydrogen atoms act as shallow donors (which causes the carrier concentration in the channel to rise), causing the threshold voltage (V-TH) to shift in the negative direction. Hydrogen diffusion from the overlap of the source/drain and gate electrodes to the channel center caused by the tip electric field induces a significant barrier lowering and V-TH shifts in a short-channel device. However, under negative bias stress (NBS) in ambient moisture, the negative V-TH shift is more obvious in short- than in long-channel devices, indicating suppressed hydrogen diffusion in long-channel devices. This is attributed to the electrolysis of water by the tip electric field at the source, drain, and gate electrodes, which causes hydrogen to diffuse to the center of the channel. Here, a novel physical model of the capacitance-voltage (C-V) electrical property changes under ambient moisture is proposed, based on the early appearance of abnormalities in the C-V measurements. The electrolysis of water caused by the tip electric field and electrical abnormalities caused by hydrogen diffusion into the a-IGZO active layer are explained by this model. A secondary-ion mass spectrometry analysis shows that hydrogen content in the channel generally increases under NBS in ambient moisture. The degradation behavior due to moisture in a-IGZO is clarified. Thus, inhibiting the tip electric field may benefit future flexible-display and gas-sensing applications.