Browsing by Author "Chien, Yu-Chieh"

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A Dual-Gate InGaZnO4-Based Thin-Film Transistor for High-Sensitivity UV Detection
(2019-08-01)
Chen, Po-Hsun
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Tsao, Yu-Ching
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Chien, Yu-Chieh
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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 hump in capacitance-voltage measurements induced by ultraviolet light in a-IGZO thin-film transistors
(2017-01-09)
Tsao, Yu-Ching
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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.
Improving Reliability of High-Performance Ultraviolet Sensor in a-InGaZnO Thin-Film Transistors
(2019-09-01)
Tsai, Yu-Lin
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Chien, Yu-Chieh
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Chang, Ting-Chang
;
Tsao, Yu-Ching
;
Tai, Mao-Chou
High-performance ultraviolet (UV) sensors using amorphous indium gallium zinc oxide thin-film transistors (a-IGZO TFTs) can detect I-ON/I-OFF ratio up to 10(6) and match the a-IGZO panel process. However, it has a reliability issue under long-term detection. When the top gate length of the dual gate TFT is small, it is twice as reliable as a TFT where the top gate fully covers the device. The electrical properties of the device correspond to the a-IGZO energy band, such that the top gate length was positively related to the underlying energy band diagram. The integrated systems engineering technology computer aided design (ISE-TCAD) electric field simulations show that the etch stop layer (ESL) electric field is weak in the small top gate device. This means that it is difficult for the holes to either be trapped in the ESL or to generate ionized oxygen vacancies.
Investigating degradation behaviors induced by mobile Cu ions under high temperature negative bias stress in a-InGaZnO thin film transistors
(2017-09-25)
Chiang, Hsiao-Cheng
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Chang, Ting-Chang
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Liao, Po-Yung
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Chen, Bo-Wei
;
Tsao, Yu-Ching
This letter investigates the effect of negative bias temperature stress (NBTS) on amorphous InGaZnO4 thin film transistors with copper electrodes. After 2000 s of NBTS, an abnormal subthreshold swing and on-current (I-on) degradation is observed. The recovery of the Id-Vg curve after either annealing or positive bias temperature stress suggests that there are some native mobile copper ions in the active layer. Both the existence of copper and the degradation mechanism can be confirmed by AC stress with different frequencies and by transmission electron microscope energy-dispersive X-ray spectroscopy analysis. Published by AIP Publishing.
Role of H2O Molecules in Passivation Layer of a-InGaZnO Thin Film Transistors
(2017-04-01)
Chien, Yu-Chieh
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Chang, Ting-Chang
;
Chiang, Hsiao-Cheng
;
Chen, Hua-Mao
;
Tsao, Yu-Ching
This letter analyzes performance and reliability of inverted staggered type amorphous indium-gallium-zinc oxide devices in a moist environment with H2O molecules in the passivation layer. There is a negative threshold voltage shift (Delta Vth) in the saturation region (V-D = 10 V), which increases with decreasing channel length. We propose that this is explained by the drain-induced barrier lowering that is due to the H2O molecules. Moreover, a hydrogen bonding model under bias stress is also proposed, in contrast to the conventional H2O doping model. Recovery behavior after bias stress and ac operation were utilized to distinguish the difference between these models.