Low-Temperature Deposition of Hydrogenated Amorphous Silicon in an Electron Cyclotron Resonance Reactor for Flexible Displays (original) (raw)
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2020
Hot Wire Chemical Vapor Deposition (HWCVD) is an emerging technology in semiconductor materials thin film deposition due to the high growth rates and reasonable electronic properties attainable using this method. To improve the electronic characteristics of material grown by the HWCVD method, neutral ion bombardment during growth was introduced as it is shown to be beneficial in Plasma Enhanced Chemical Vapor Deposition (PECVD). Neutral ion bombardment was accomplished by using remote Electron Cyclotron Resonance (ECR) plasma and the entire deposition technique is termed ECR-HWCVD. The ECR-HWCVD films were compared to HWCVD materials deposited without ion bombardment grown at similar conditions in the same reactor using a 10.5 cm filament to substrate distance to minimize substrate heating by radiation during deposition. The growth rate is halved when ion bombardment is added to HWCVD, however it remains four times greater than the highest quality ECR-PECVD films. Also, ECR-HWCVD material exhibited better electronic properties as shown by Urbach energy, photosensitivity, hydrogen content, microstructure parameters, and space charge limited current defect measurements. In addition, the effect of substrate temperature on hydrogen content and material microstructure was investigated. Both hydrogen content and the microstructure parameter R decreased as substrate temperature increased; and when ion bombardment was added to the deposition conditions, the microstructure parameter decreased regardless of substrate temperature.
IEEE/OSA Journal of Display Technology, 2007
The transition of thin-film transistor (TFT) backplanes from rigid plate glass to flexible substrates requires the development of a generic TFT backplane technology on a clear plastic substrate. To be sufficiently stable under bias stress, amorphous-silicon (a-Si:H) TFTs must be deposited at elevated temperatures, therefore the substrate must withstand high temperatures. We fabricated a-Si:H TFT backplanes on a clear plastic substrate at 200 C. The measured stability of the TFTs under gate bias stress was superior to TFTs fabricated at 150 C. The substrate was dimensionally stable within the measurement resolution of 1 m, allowing for well-aligned 8 8 and 32 32 arrays of 500 m 500 m pixels. The operation of the backplane is demonstrated with an electrophoretic display. This result is a step toward the drop-in replacement of glass substrates by plastic foil. Index Terms-Amorphous silicon thin-film transistor (a-Si:H TFT), clear plastic, electrophoretic display, flexible, stability.
Journal of Display Technology, 2007
The transition of thin-film transistor (TFT) backplanes from rigid plate glass to flexible substrates requires the development of a generic TFT backplane technology on a clear plastic substrate. To be sufficiently stable under bias stress, amorphous-silicon (a-Si:H) TFTs must be deposited at elevated temperatures, therefore the substrate must withstand high temperatures. We fabricated a-Si:H TFT backplanes on a clear plastic substrate at 200 C. The measured stability of the TFTs under gate bias stress was superior to TFTs fabricated at 150 C. The substrate was dimensionally stable within the measurement resolution of 1 m, allowing for well-aligned 8 8 and 32 32 arrays of 500 m 500 m pixels. The operation of the backplane is demonstrated with an electrophoretic display. This result is a step toward the drop-in replacement of glass substrates by plastic foil.
Highly stable amorphous-silicon thin-film transistors on clear plastic
Applied Physics Letters, 2008
Hydrogenated amorphous-silicon ͑a-Si: H͒ thin-film transistors ͑TFTs͒ have been fabricated on clear plastic with highly stable threshold voltages. When operated at a gate field of 2.5 ϫ 10 5 V / cm, the threshold voltage shift extrapolated to only ϳ1.2 V after ten years. This stability is achieved by a high deposition temperature for the gate silicon nitride insulator which reduces charge trapping and high hydrogen dilution during a-Si: H growth to reduce defect creation in a-Si: H. This gate field of 2.5ϫ 10 5 V / cm is sufficient to drive phosphorescent organic light emitting diodes ͑OLEDs͒ at a brightness of 1000 Cd/ m 2. The half-life of the TFT current is over ten years, slightly longer than the luminescence half-life of high quality green OLEDs.
2013
The crystallization of hydrogenated amorphous silicon layers (a-Si:H) [1,2] deposited by plasma enhanced chemical vapor deposition (PECVD) is of great interest. Generally, laser or metals are used to induce crystallization in aSi:H films. We have found that films deposited at high rf power (> 0.2 W/cm2) by PECVD technique shows some crystallites embedded in a-Si:H matrix and their after its vacuum thermal annealing at 250 and 300 C helps to further enhancement of crystallite size. These films were characterized using , UV-VIS spectrometry, Raman Spectra, of these films were measured as a function of temperature in the range of 300 C to 250 C. Keyword: Amorphous silicon, Thin Films, Growth PECVD.
IEEE Transactions on Electron Devices, 2017
Hydrogenated amorphous silicon (a-Si:H) thin-film transistor (TFT) compensation pixel circuits were fabricated on polyethylene naphthalate substrates at a maximum temperature of 170°C. The typical a-Si:H TFTs showed a field-effect mobility (μ FE) of 0.8-1.1 cm 2 /Vs, a threshold voltage (V T) of 2-3.3 V, a subthreshold swing (SS) of ∼0.65 V/decade, and an ON/OFF current ratio of 10 7-10 8. Under DC gate-bias stress without compensation, the TFT drive current decreased by ∼50% without mechanical strain and ∼60% with applied tensile strain. The TFT circuits effectively compensated for the change in the TFT drive current to within 10% of the original drive current value under mechanically strained and unstrained states. The orientation of the TFT within the circuit was found to affect the circuit compensation; TFTs having a channel length perpendicular to the mechanical strain were found to have a 50% higher threshold voltage shift (V T) compared to devices parallel to the applied strain. Index Terms-Compensation circuits, hydrogenated amorphous silicon (a-Si:H), organic light-emitting diode (OLED) display, thin-film transistors (TFTs). I. INTRODUCTION H YDROGENATED amorphous silicon (a-Si:H) thin-film transistors (TFTs) are a mature technology with applications in flat-panel electronics such as active-matrix (AM) liquid crystal displays and AM imagers [1], [2]. The technological advantages of a-Si:H are related to its capacity for synthesis and processing with low thermal budget, large-area Manuscript
Hydrogenated amorphous silicon technology for chemically sensitive thin-film transistors
Sensors and Actuators B-chemical, 1992
Top-gate hydrogenated amorphous silicon thin-film transistors have been fabricated which show electrical characteristics suitable for application in the field of chemical sensors. These devices have been specialized to two different types of sensors: (a) Pd-gate hydrogen sensors; (b) K+ ion sensors. The obtained results show that the present technology can be successfully applied to the fabrication of gas-sensitive and ion-sensitive field-effect transistors.
Materials Science and Engineering: B, 1993
Highly photoconductive hydrogenated amorphous silicon films (a-Si:H) have been deposited by a new cyclic deposition method involving thermal chemical vapour deposition at substrate temperatures of around 500 °C and intermittent hydrogen plasma treatment steps. The main features of the films are the low hydrogen content of less than 5at.% and the high photoconductivity-to-dark conductivity ratio of around 105. By simply varying either the plasma power or the duration of the hydrogenation time a transition from amorphous to microcrystalline films is observed. The electronic quality and stability under illumination of the best amorphous films obtained so far by the cyclic method were comparable with those of films deposited by conventional glow discharge.