Role of H<sub>2</sub>O Molecules in Passivation Layer of a-InGaZnO Thin Film Transistors

Chien, Yu‐Chieh; Chang, Ting‐Chang; Chiang, Hsiao‐Cheng; Chen, Hua-Mao; Tsao, Yu‐Ching; Shih, Chih‐Cheng; Chen, Bo-Wei; Liao, Po‐Yung; Chu, Ting-Yang; Yang, Yi-Chieh; Hung, Yu-Ju; Tsai, Tsung‐Ming; Chang, Kuan‐Chang

doi:10.1109/led.2017.2666198

Cited by 24 publications

(14 citation statements)

References 19 publications

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“…Previous studies have indicated that, under ambient moisture, water molecules are arranged by polarization because of the electric field. The overall energy barrier is decreased and the threshold voltage (V TH ) is shifted in the negative direction. , Moreover, some reports discuss the coupling of water molecules to the back-channel of the TFT under negative bias stress (NBS). , Different mechanisms such as hydrogen and metal bonding can cause the transistor to turn on early.…”

Section: Introductionmentioning

confidence: 99%

Investigation of the Capacitance–Voltage Electrical Characteristics of Thin-Film Transistors Caused by Hydrogen Diffusion under Negative Bias Stress in a Moist Environment

Chen

Kuo

Chang

et al. 2019

ACS Appl. Mater. Interfaces

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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 (VTH) 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 VTH shifts in a short-channel device. However, under negative bias stress (NBS) in ambient moisture, the negative VTH 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.

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Section: Introductionmentioning

confidence: 99%

Investigation of the Capacitance–Voltage Electrical Characteristics of Thin-Film Transistors Caused by Hydrogen Diffusion under Negative Bias Stress in a Moist Environment

Chen

Kuo

Chang

et al. 2019

ACS Appl. Mater. Interfaces

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“…In contrast, the off currents of the IZO TFTs with a passivation layer varied within approximately 10 %. This is because the passivation layer physically limits deterioration by limiting the adsorption of oxygen and moisture on the back of the IZO active layer [18], [34]. Hence, it blocks the leakage current caused by interfacial defects.…”

Section: Resultsmentioning

confidence: 99%

Improved Electrical and Temporal Stability of In-Zn Oxide Semiconductor Thin-Film Transistors With Organic Passivation Layer

Heo

Tarsoly

Lee

et al. 2022

IEEE J. Electron Devices Soc.

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Solution-processed In-Zn oxide (IZO) semiconductor thin-film transistors (TFTs) were fabricated with passivation layers of either poly(methyl methacrylate) (PMMA) or cyclic transparent optical polymer (CYTOP). According to the transfer curves obtained on the day of fabrication and after 200 days, the drain-source current of the IZO TFT without a passivation layer decreased by approximately 37 %. For the PMMA-passivated IZO TFT, it decreased by approximately 31 %. The current for the CYTOPpassivated IZO TFT showed significantly lower, only 7 % deterioration. Hence, the CYTOP-passivated IZO TFT exhibited improved electrical stability under long term ambient storage. This was attributed to the difference in the chemical composition of the two polymers, as CYTOP is a fluoropolymer, while PMMA is an ester group containing organic polymer. We show, passivation of the active layer with the proper organic film improves the stability of the high-performance solution-processed IZO TFTs.

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“…Alternatively, it is noteworthy that both VTFTs showed larger Δ V TH during the NBS than the PBS, which is inconsistent with typical behaviors of the conventional IGZO TFTs, because there are few holes to be trapped owing to n-type behaviors of the IGZO semiconductor. Thus, the origin of the negative V TH shift under NBS conditions for the fabricated VTFTs was suggested to be due to the preadsorptions of H + ions and/or H 2 O molecules on the surface of the organic Zeocoat spacer exposed to the atmosphere prior to the deposition of active channel layer. − In other words, positively charged species were trapped in the back-channel region during the device fabrication process, accelerating NBS instability. Nevertheless, the PBS and NBS stabilities of the fabricated flexible VTFTs using an ALD-grown IGZO channel layer were sufficiently comparable to those obtained from the well-fabricated conventional planar-channel IGZO TFTs, which suggests that the robust operational stability could be obtained by properly designed process conditions for the VTFTs.…”

Section: Results and Discussionmentioning

confidence: 99%

Highly Robust Flexible Vertical-Channel Thin-Film Transistors Using Atomic-Layer-Deposited Oxide Channels and Zeocoat Spacers on Ultrathin Polyimide Substrates

Kim

Furuta

Yoon

2019

ACS Appl. Electron. Mater.

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Mechanically flexible vertical-channel-structured thin-film transistors (VTFTs) with a channel length of 200 nm were fabricated on 1.2 μm thick colorless polyimide (CPI) substrates. All layers composing the gate stacks were prepared by atomic-layer deposition (ALD) with a good step coverage, and the process thermal budget was designed below 180 °C. Zeocoat was introduced as a spacer material to improve the device characteristics by properly determining the process conditions for clearly forming the vertical sidewalls. The transfer characteristics of the fabricated flexible ZnO and IGZO VTFTs showed the field-effect mobility of 3.31 and 6.57 cm2 V–1 s–1, the threshold voltages of 2.34 and 1.52 V, the subthreshold swings of 1.42 and 0.34 V/dec, and I ON/I OFF of 1.13 × 104 and 5.16 × 105, respectively, after the postannealing at 150 °C. The threshold voltage shifts (ΔV TH) under positive and negative bias stresses (PBS and NBS) were estimated to be +1.0, +1.8 V and −1.8, −3.8 V for 104 s for ZnO and IGZO VTFTs, respectively. The flexible IGZO VTFTs delaminated by means of a laser lift-off process did not show any marked degradation in device characteristics under mechanically strained conditions at various radii of curvature (R c). The ΔV TH values were also estimated to be +1.2 and −2.1 V under PBS and NBS at R c of 1 mm, respectively, demonstrating stable bending reliability. Appropriate choices of spacer materials, optimization of patterning process for spacer patterns, and ALD process of IGZO active channel can be proposed as key process parameters for guaranteeing excellent device performance of the oxide-channel VTFTs in this work.

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Role of H₂O Molecules in Passivation Layer of a-InGaZnO Thin Film Transistors

Cited by 24 publications

References 19 publications

Investigation of the Capacitance–Voltage Electrical Characteristics of Thin-Film Transistors Caused by Hydrogen Diffusion under Negative Bias Stress in a Moist Environment

Investigation of the Capacitance–Voltage Electrical Characteristics of Thin-Film Transistors Caused by Hydrogen Diffusion under Negative Bias Stress in a Moist Environment

Improved Electrical and Temporal Stability of In-Zn Oxide Semiconductor Thin-Film Transistors With Organic Passivation Layer

Highly Robust Flexible Vertical-Channel Thin-Film Transistors Using Atomic-Layer-Deposited Oxide Channels and Zeocoat Spacers on Ultrathin Polyimide Substrates

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Role of H2O Molecules in Passivation Layer of a-InGaZnO Thin Film Transistors

Cited by 24 publications

References 19 publications

Investigation of the Capacitance–Voltage Electrical Characteristics of Thin-Film Transistors Caused by Hydrogen Diffusion under Negative Bias Stress in a Moist Environment

Investigation of the Capacitance–Voltage Electrical Characteristics of Thin-Film Transistors Caused by Hydrogen Diffusion under Negative Bias Stress in a Moist Environment

Improved Electrical and Temporal Stability of In-Zn Oxide Semiconductor Thin-Film Transistors With Organic Passivation Layer

Highly Robust Flexible Vertical-Channel Thin-Film Transistors Using Atomic-Layer-Deposited Oxide Channels and Zeocoat Spacers on Ultrathin Polyimide Substrates

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Role of H₂O Molecules in Passivation Layer of a-InGaZnO Thin Film Transistors