Enhancement of Mechanical Bending Stress Endurance Using an Organic Trench Structure in Foldable Polycrystalline Silicon TFTs

Zheng, Yu‐Zhe; Huang, Shin-Ping; Chen, Po-Hsun; Chang, Ting‐Chang; Tsai, Tsung‐Ming; Chu, Ann-Kuo; Hung, Yang‐Hao; Shih, Yu‐Shan; Wang, Yu-Xuan; Wu, Chia‐Ching; Tu, Yu‐Fa; Yuan, Chen; Sun, Pei-Jun; Chung, Yu-Hua; Chen, Wei-Han; Wang, Tai-Jui

doi:10.1109/led.2020.2980123

Cited by 8 publications

(4 citation statements)

References 21 publications

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“…The effects of mechanical strain and electrical reliability of LTPS TFTs have been previously reported (show in Table 1 ) with the conclusion that the mechanical stability is inferior to oxide TFTs. [ 15–30 ] Therefore, finding a solution to overcome the performance degradation during mechanical stress is important for more flexible and foldable AMOLED displays.…”

Section: Introductionmentioning

confidence: 99%

Poly‐Si Thin‐Film Transistors on Polyimide Substrate for 1 mm Diameter Rollable Active‐Matrix Organic Light‐Emitting Diode Display

et al. 2021

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Recently, flexible displays based on active-matrix organic lightemitting diode (AMOLED) on polyimide (PI) substrate are of increasing interest for use in foldable displays. PI substrates are not only thin and light, [1,2] but also could be processed at relatively high temperature (≥450 C). To achieve a flexible AMOLED display, thin-film transistor (TFT) array should be manufactured on a plastic substrate. [3][4][5][6][7][8][9][10][11] Popular semiconductor materials used for TFTs are amorphous silicon (a-Si), amorphous indium-gallium-zinc-oxide (a-IGZO), and polycrystalline Si (poly-Si) on PI substrate. Due to its low-temperature process on large glass substrates such as 10.5G (2.2 m Â 2.5 m), the a-Si:H has been used as a TFT switching element. However, it cannot be used for AMOLED TFT backplanes because of its threshold voltage (V TH ) shift during OLED operation. [12,13] Note that a-IGZO TFT has at least one order of magnitude higher mobility compared to a-Si:H TFT even though the TFT process temperature is similar. The a-IGZO TFT can be manufactured by using G10.5 glass so that manufacturing cost of oxide TFT backplanes for OLED can be much lower than that of low-temperature poly-Si (LTPS) TFT. Therefore, intensive studies on amorphous oxide semiconductors are being carried out for TFT backplanes of OLED displays. However, all smartphone OLED displays are still based on LTPS TFT backplanes because of its high mobility and excellent stability. The LTPS TFTs on PI substrate with high mobility and high stability are very suitable for mobile application. [14] The effects of mechanical strain and electrical reliability of LTPS TFTs have been previously reported (show in Table 1) with the conclusion that the mechanical stability is inferior to oxide TFTs. [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] Therefore, finding a solution to overcome the performance degradation during mechanical stress is important for more flexible and foldable AMOLED displays.In this article, to improve the reliability under mechanical stress, flexible LTPS TFTs were fabricated using three kinds of interlayers (ITLs): inorganic (SiO 2 /SiN x ), hybrid (SiN x /PI), and organic (PI) layers. Reliability test of the LTPS TFTs is performed using bending and rolling machines until 10 000 cycles. Using low Young's modulus organic material (PI) ITL, the change in electrical performance under mechanical strain could be reduced significantly. Especially, rolling test with rolling radius of 1 mm was examined until 10 000 cycles. The LTPS TFT with inorganic ITL shows the crack generation after rolling with 1 mm radius. However, the performance of the LTPS TFTs with hybrid ITL

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Section: Introductionmentioning

confidence: 99%

Poly‐Si Thin‐Film Transistors on Polyimide Substrate for 1 mm Diameter Rollable Active‐Matrix Organic Light‐Emitting Diode Display

et al. 2021

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“…In terms of inorganic flexible LTPS TFTs, the degradation caused by mechanical stress will vary according to the bending conditions. − , To clarify the degradation mechanism of organic flexible TFTs after mechanical stress with different conditions and directions, the tendencies of V T during fixed curve bending in a vacuum are extracted for 10 identical devices in the statistical distributions, as shown in Figure .…”

Section: Resultsmentioning

confidence: 99%

“…However, apart from the high process cost, the endurance of LTPS TFTs has challenges with repeated bending at a small radius ( R ) of curvature. The main reason is that the LTPS TFT devices have the intrinsic issue of insufficient mechanical bending endurance, such as the threshold voltage ( V T ) shift and the I – V “hump” after repeated bending stress; these degradation behaviors will seriously affect the screen update of the display. − The poor mechanical endurance of LTPS TFTs is mainly caused by a factor of the difference between Young’s moduli of the deposited layers. ,− To mitigate the weakness of mechanical properties from LTPS TFTs during long-term bending, additional costs and a difficult production process have been conducted on the panel module, such as organic trench and wing-shape LTPS. − However, compared to LTPS TFTs, organic TFTs have a relatively simple process and similar Young’s moduli between deposited layers. According to the above advantages, it can be shown that organic TFTs have great superiority in flexible display applications.…”

Section: Introductionmentioning

confidence: 99%

Physical Mechanism of the Mechanical Bending of High-Performance Organic TFTs and the Effect of Atmospheric Factors

Zheng

Chen

et al. 2022

ACS Appl. Electron. Mater.

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In this paper, we investigate the electrical characteristics of organic thin-film transistors (OTFTs) after mechanical bending stress conducted in a range of different atmospheres. After 100,000 cycles of channel-width-axis compressive bending and a long-term fixed curve at a bending radius of R = 5 mm in an atmospheric environment, the threshold voltage (V T ) is seen to shift in the positive direction. Following annealing after bending, the V T recovers to a value more negative than the initial V T for both dynamic and static bending tests. Performing bending tests in a vacuum, which eliminates the influence of the ambient atmosphere on the OTFTs, shows that the degradation of the device under atmospheric bending is dominated by two mechanisms. Gasses present in the ambient environment (humidity, N 2 , CO 2 , and O 2 ) are introduced sequentially to understand their effect on the OTFTs. By studying the effects in the vacuum and atmosphere, we are able to separate the physical effects of mechanical bending on the OTFTs from the changes induced by exposure to environmental factors. Due to different mechanical bending conditions, the small molecules at the surface of the active layer cause different electrical characteristics. Finally, a physical model of mechanical bending and atmospheric factors for organic TFTs is proposed.

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“…The carrier mobility (µ) of OTFTs has now surpassed 2 cm 2 V −1 s −1 , above that of amorphous silicon transistors (1 cm 2 V −1 s −1 ) [ 33 , 34 , 35 , 36 ]. However, considering the need of high-resolution displays, it is still lower than inorganic semiconductor materials like LTPS TFTs and oxide semiconductors like IGZO TFTs [ 37 , 38 , 39 ]. As a result, effectively boosting output current and improving reliability are critical concerns for OTFT commercialization.…”

Section: Introductionmentioning

confidence: 99%

Dual-Gate Organic Thin-Film Transistor and Multiplexer Chips for the Next Generation of Flexible EG-ISFET Sensor Chips

Rezaee

Carrabina

2023

Sensors

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Ion-sensitive field-effect transistors (ISFETs) are used as elementary devices to build many types of chemical sensors and biosensors. Organic thin-film transistor (OTFT) ISFETs use either small molecules or polymers as semiconductors together with an additive manufacturing process of much lower cost than standard silicon sensors and have the additional advantage of being environmentally friendly. OTFT ISFETs’ drawbacks include limited sensitivity and higher variability. In this paper, we propose a novel design technique for integrating extended-gate OTFT ISFETs (OTFT EG-ISFETs) together with dual-gate OTFT multiplexers (MUXs) made in the same process. The achieved results show that our OTFT ISFET sensors are of the state of the art of the literature. Our microsystem architecture enables switching between the different ISFETs implemented in the chip. In the case of sensors with the same gain, we have a fault-tolerant architecture since we are able to replace the faulty sensor with a fault-free one on the chip. For a chip including sensors with different gains, an external processor can select the sensor with the required sensitivity.

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Enhancement of Mechanical Bending Stress Endurance Using an Organic Trench Structure in Foldable Polycrystalline Silicon TFTs

Cited by 8 publications

References 21 publications

Poly‐Si Thin‐Film Transistors on Polyimide Substrate for 1 mm Diameter Rollable Active‐Matrix Organic Light‐Emitting Diode Display

Poly‐Si Thin‐Film Transistors on Polyimide Substrate for 1 mm Diameter Rollable Active‐Matrix Organic Light‐Emitting Diode Display

Physical Mechanism of the Mechanical Bending of High-Performance Organic TFTs and the Effect of Atmospheric Factors

Dual-Gate Organic Thin-Film Transistor and Multiplexer Chips for the Next Generation of Flexible EG-ISFET Sensor Chips

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