High mobility nanocrystalline silicon transistors on clear plastic substrates (original) (raw)
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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.
IEEE Journal of Solid-state Circuits, 2004
This paper presents design considerations along with measurement results pertinent to hydrogenated amorphous silicon (a-Si:H) thin film transistor (TFT) drive circuits for active matrix organic light emitting diode (AMOLED) displays. We describe both pixel architectures and TFT circuit topologies that are amenable for vertically integrated, high aperture ratio pixels. Here, the OLED layer is integrated directly above the TFT circuit layer, to provide an active pixel area that is at least 90% of the total pixel area with an aperture ratio that remains virtually independent of scaling. Both voltage-programmed and current-programmed drive circuits are considered. The latter provides compensation for shifts in device characteristics due to metastable shifts in the threshold voltage of the TFT. Various drive circuits on glass and plastic were fabricated and tested. Integration of on-panel gate drivers is also discussed where we present the architecture of an a-Si:H based gate de-multiplexer that is threshold voltage shift invariant. In addition, a programmable current mirror with good linearity and stability is presented. Programmable current sources are an essential requirement in the design of source driver output stages.
IEEE Electron Device Letters, 2000
We have fabricated active-matrix organic light emit-7 ting diode (AMOLED) test arrays on an optically clear high-8 temperature flexible plastic substrate at process temperatures as 9 high as 285 • C using amorphous silicon thin-film transistors (a-Si 10 TFTs). The substrate transparency allows for the operation of 11 AMOLED pixels as bottom-emission devices, and the improved 12 stability of the a-Si TFTs processed at higher temperatures sig-13 nificantly improves the reliability of light emission over time. 14 Index Terms-Active matrix, active-matrix organic light-15 emitting-diode (AMOLED) display, amorphous silicon, clear 16 plastic, stability, thin-film transistor. 17 I. INTRODUCTION 18 A CTIVE-MATRIX organic light-emitting-diode 19 (AMOLED) displays have all the necessary features 20 to become the dominant technology for the next generation of 21 flat-panel and flexible displays. Compared to liquid crystals 22 displays (LCDs), OLEDs offer superior properties such as high-23 speed response, wide viewing angle, simple structure and low 24 fabrication cost. In addition, OLEDs are emissive devices and 25 do not need backlight illumination and color filters, resulting in 26 low power consumption [1], [2]. Integrating OLEDs with TFTs 27 in the form of active matrices is required for achieving very 28 low power consumptions in mid-sized and large-sized displays 29 [3], [4]. Since the introduction of AMOLED displays, low-30 temperature poly-Si has been the material of choice for making 31 the TFT backplanes due to the relatively high mobility and sta-32 bility of poly-Si TFTs [4], [5]. However, with the improvement 33 of OLED efficiency and especially the introduction of phos-34
IEEE Electron Device Letters, 1997
We report the integration of organic light emitting devices (OLED's) and amorphous Si (a-Si) thin-film transistors (TFT's) on both glass, and unbreakable and lightweight thin stainless steel foil substrates. The doped-polymer OLED's were built following fabrication of driver TFT's in a stacked structure. Due to the opacity of the steel substrate, top-emitting OLED structures were developed. It is shown that the a-Si TFT's provide adequate current levels to drive the OLED's at video brightness (100 cd/m 2 ). This work demonstrates that lightweight and rugged TFT backplanes with integrated OLED's are essential elements for robust and highly portable active-matrix emissive flat-panel displays.
2015
We have developed a fabrication process for amorphous-silicon thin-film transistors (a-Si:H TFTs) on free-standing clear plastic substrates at temperatures up to 300oC. The 300oC fabrication process is made possible by using a unique clear plastic substrate that has a very low coefficient of thermal expansion (CTE < 10ppm/oC) and a glass transition temperature higher than 300oC. Our TFTs have a conventional inverted-staggered gate back-channel passivated geometry, which we designed to achieve two goals: accurate overlay alignment and a high effective mobility. A requirement that becomes particularly difficult to meet in the making of TFT backplanes on plastic foil at 300oC is minimizing overlay misalignment. Even though we use a substrate that has a relatively low CTE, accurately aligning the TFTs on the free-standing, 70-micrometer thick substrate is challenging. To deal with this immediate challenge, and to continue developing processes for free-standing web substrates, we are ...
Journal of the Society for Information Display, 2007
A process temperature of ~300°C produces amorphous-silicon (a-Si) thin-film transistors (TFTs) with the best performance and long-term stability. Clear organic polymers (plastics) are the most versatile substrate materials for flexible displays. However, clear plastics with a glass-transition temperature (T g) in excess of 300°C can have coefficients of thermal expansion (CTE) much larger than that of the silicon nitride (SiN x) and a-Si in TFTs deposited by plasma-enhanced chemical vapor deposition (PECVD). The difference in the CTE that may lead to cracking of the device films can limit the process temperature to well below that of the T g of the plastic. A model of the mechanical interaction of the TFT stack and the plastic substrate, which provides design guidelines for avoid cracking during TFT fabrication, is presented. The fracture point is determined by a critical interfacial stress. The model was used to successfully fabricate a-Si TFTs on novel clear-plastic substrates with a maximum process temperature of up to 280°C. The TFTs made at high temperatures have higher mobility, lower leakage current, and higher stability than TFTs made on conventional low-T g clear-plastic substrates.
P-102: Amorphous Silicon Thin-Film Transistors-based Active-Matrix Organic Light-Emitting Displays
SID Symposium Digest of Technical Papers, 2002
In this paper, we describe hydrogenated amorphous silicon (a-Si:H) thin-film transistor (TFT)-based active-matrix arrays for active-matrix organic light-emitting displays (AM-OLEDs). The proposed pixel electrode circuits based on three a-Si:H TFTs can supply a continuous output current for AM-OLEDs. Each pixel circuit has compensation circuits that can adjust for the OLED and a-Si:H TFTs electrical characteristics shifts.
IEEE Transactions on Electron Devices, 2011
The influences of metal-induced laterally crystallized silicon channel corners on the performance and reliability of thin-film transistors (TFTs) were investigated. It was found that the TFT with the channel width, mostly applied to active matrix organic light-emitting diodes, had weak immunity to electrical stresses because of the heaviest weight of silicide-rich channel corner on the channel width by the geometric effect. The proposed TFT fabrication, which is composed of two consecutive adjacent step switches, makes TFTs practically channel-corner-free, resulting in high reliability. Moreover, it enables TFTs to have more current flow paths that maintain a high performance.
IEICE Transactions on Electronics, 2010
Hydrogenated polymorphous Silicon allows to fabricate TFTs with very interesting characteristics including better threshold voltage stability than a-Si TFTs, lower leakage current than μc-Si:H TFTs and excellent uniformity. Investigation of threshold voltage shift mechanisms of pm-Si:H TFTs has shown a specific semiconductor material degradation with different activation energies compared to a-Si:H TFTs. TEM analysis has evidenced for the first time a significant structural difference between pm-Si:H and a-Si:H materials, in the TFT device configuration. Pm-Si:H appears to be very suitable for low cost and high performance AM-OLED fabrication.
Advanced Amorphous Silicon Thin-Film Transistors for AM-OLEDs: Electrical Performance and Stability
IEEE Transactions on Electron Devices, 2000
We fabricated and characterized the advanced amorphous silicon thin-film transistors with a bilayer structure for both the active and gate dielectric films. The electrical field across the gate insulator has a significant influence on the device threshold voltage electrical stability. We show that high thin-film transistor stability can be achieved even under the presence of a high channel current. Its electrical and high-temperature stability improves up to a factor of five when the TFT biasing condition changes from the linear to the saturation region of operation.