Thin-film Transistor Substrate Research Articles

Double-Sided Bonding Process Enables X-ray Flat Panel Detectors.

Metal halide perovskites have demonstrated superior sensitivity, lower detection limits, stability, and exceptional photoelectric properties in comparison to existing commercially available X-ray detector materials, showing their potential for shaping the next generation of X-ray detectors. Nevertheless, significant challenges persist in the seamless integration of these materials into pixelated array sensors for large-area X-ray direct detection imaging. In this article, we propose a strategy for fabricating large-scale array devices using a double-sided bonding process. The approach involves depositing a wet film on the surface of a thin-film transistor substrate to establish a robust bond between the substrate and δ-CsPbI3 wafer via van der Waals force, thereby facilitating area-array imaging. Additionally, the freestanding polycrystalline δ-CsPbI3 wafer demonstrated a competitive ultralow detection limit of 3.46 nGyair s-1 under 50 kVP X-ray irradiation, and the δ-CsPbI3 wafer still maintains a stable signal output (signal current drift is 3.5 × 10-5 pA cm-1 s-1 V-1) under the accumulated radiation dose of 234.9 mGyair. This strategy provides a novel perspective for the industrial production of large-area X-ray flat panel detectors utilizing perovskites and their derivatives.

Journal of the Society for Information Display

Jiun-Haw Lee Editor in Chief The November 2020 issue of the Journal of the Society for InformationDisplay(JSID) contains five regular papers and one letter. In the December issue, there are two invited papers, four regular papers,and two letters. Along with hardware research in devices and systems of displays, the issue also publishes several papers about software progress in displays and visions in algorithm and human-machine interaction (HMI). It also relates to the study in psychophysics, such as visual comfort, and perception. We are excited to see the broadened spectrum of display-related research published in JSID. Amid the COVID-19 pandemic, in-person communication has diminished. To compensate, there has been a substantial uptick in online meetings that require additional displays and better user experiences. As our field responds to the increased demands on display technologies, we welcome any advances in display-related research that elevates human interactions to a better new “normal.” We hope innovators will submit such advancements to JSID. Two invited papers were published in the December 2020 issue of JSID. In the first paper, the authors thoroughly discussed a display system's optical films for application in vehicles. This technology must consider all the safety and convenience issues that occur under harsh environments, such as high temperatures and a wide range of ambient lighting conditions. In the second invited paper, an 8-inch transparent and flexible display was demonstrated with miniLED technology and an indium-gallium-zinc-oxide, thin-film transistor (IGZO-TFT) backplane on the flexible substrate. JSID is published monthly by Wiley. Subscription fees apply, but SID members and student members have free online access via sid.org/Publications.aspx. Many universities also have an institutional subscription. JSID is indexed in the Web of Science. Submit your original manuscript online via mc.manuscriptcentral.com/sid. Author guidelines can be found on the Journal's homepage: tinyurl.com/jsidhome. Editorial board: tinyurl.com/jsideb. Please direct any questions about JSID to its editor in chief at editor@sid.org. EarlyView: accepted papers about to be published can be accessed online via tinyurl.com/jsidev. Image quality equivalence between peak luminance and chromaticity gamut | Yongmin Park and Michael J. Murdoch | doi: 10.1002/jsid.906 In this article, psychophysical research was conducted to demonstrate the tradeoff between the image quality's lightness (L) and chroma (C). Essentially, peak luminance should decrease to obtain the same image quality when the color gamut increases. In addition, the regions of interest (ROI) for various kinds of images also differ, which leads to slight alterations in the tradeoff relations. Although the experiment was conducted in a standard dynamic range (SDR) display, this line of research may be extend the concept to a high dynamic range (SDR) display in the future. Highly transparent, ultra-thin flexible, full-color mini-LED display with indium–gallium–zinc oxide thin-film transistor substrate| Yang Sun et al.| doi: 10.1002/jsid.970 As the title of this paper indicates, the authors demonstrated a full-color, transparent, and flexible display by integrating several technologies, including miniLED as the emitter, IGZO as the TFT backbone, and colorless polyimide (CPI) as the transparent and flexible substrate. The display size is 8 inches with a resolution of 46 pixels per inch (ppi) and thickness of 0.2 millimeters (mm). Optical transmittance is 60 percent. Full-width-at half-maximum (FWHM) of LED emission spectra vary from 12 to 27 nanometers (nm), resulting the color gamut of 80 percent in the color-range standard BT 2020. It successfully proves the process integration for miniLED and microLED, which also can be applied to large-size displays. The Journal is soliciting review papers on any display-related topic. If you have a great idea for a review paper, please contact the editor at editor@sid.org. Page charges for invited review papers will be waived.

Low-cost and low-topography fabrication of multilayer interconnections for microfluidic devices

Multilayer interconnections are needed for microdevices with a large number of independent electrodes. A multi-level photolithographic process is commonly employed to provide multilayer interconnections in integrated circuit devices, but it is often too expensive for large-area or disposable devices frequently needed for microfluidics. The printed circuit board (PCB) can provide multilayer interconnection at low cost, but its rough topography poses a challenge for small droplets to slide over. Here we report a low-cost fabrication of low-topography multilayer interconnects by selective and controlled anodization of thin-film metal layers. The process utilizes anodization of metal (tantalum in this paper) or, more specifically, repetitions of a partial anodization to form insulation layers between conductive layers and a full anodization to form isolating regions between electrodes, replacing the usual process of depositing, planarizing, and etching insulation layers. After verifying the electric connections and insulations as intended, the developed method is applied to electrowetting-on-dielectric (EWOD), whose complex microfluidic products are currently built on PCB or thin-film transistor substrates. To demonstrate the utility, we fabricate a three metal-layer EWOD device with steps (surface topography) less than 1 micrometer (vs. > 10 micrometers of PCB EWOD devices) and confirm basic digital microfluidic operations.

Electrical Stimulation, Recording and Impedance-Based Real-Time Position Detection of Cultured Neurons Using Thin-Film-Transistor Array

A novel thin-film-transistor (TFT)-based microsystem array derived from flat panel technology has been developed for functional extracellular neural stimulation and recording. These arrays are microfabricated to meet the needs of optical transparency and extremely high density of electrodes with a large sensor area over 25 mm $\times$ 27 mm. Indium tin oxide has been used for surface electrode fabrication with the pitches of 50 and 100 $\mu \text{m}$ and an optical transparency of ~95%. Each individual electrode is controlled through transistor drain voltage. The array consists of 30000 transistors over 243.75 mm2 chip area. The device has an extra extra high dot per inch (extra extra high density) resolution of 359.2 PPI (pixels per inch) or $7.07\times 10^{-4}$ mm dot pitch. The durability of the stimulated electrodes is extremely high, lasting more than one billion pulses without failure in dry as well as wet environments. Primary neuron cell cultures were established inside the polydimethylsiloxane chamber on the TFT substrate. Extracellular electrical signals were successfully recorded for both the current- and voltage-type stimulations. The binary presence of cells in a given region was achieved by means of impedance measurement. [2017-0266]

Printable organometallic perovskite enables large-area, low-dose X-ray imaging.

Medical X-ray imaging procedures require digital flat detectors operating at low doses to reduce radiation health risks. Solution-processed organic-inorganic hybrid perovskites have characteristics that make them good candidates for the photoconductive layer of such sensitive detectors. However, such detectors have not yet been built on thin-film transistor arrays because it has been difficult to prepare thick perovskite films (more than a few hundred micrometres) over large areas (a detector is typically 50 centimetres by 50 centimetres). We report here an all-solution-based (in contrast to conventional vacuum processing) synthetic route to producing printable polycrystalline perovskites with sharply faceted large grains having morphologies and optoelectronic properties comparable to those of single crystals. High sensitivities of up to 11 microcoulombs per air KERMA of milligray per square centimetre (μC mGyair-1 cm-2) are achieved under irradiation with a 100-kilovolt bremsstrahlung source, which are at least one order of magnitude higher than the sensitivities achieved with currently used amorphous selenium or thallium-doped cesium iodide detectors. We demonstrate X-ray imaging in a conventional thin-film transistor substrate by embedding an 830-micrometre-thick perovskite film and an additional two interlayers of polymer/perovskite composites to provide conformal interfaces between perovskite films and electrodes that control dark currents and temporal charge carrier transportation. Such an all-solution-based perovskite detector could enable low-dose X-ray imaging, and could also be used in photoconductive devices for radiation imaging, sensing and energy harvesting.

Depolarization effect in liquid crystal displays.

We develop a rigorous model to simulate an LCD's contrast ratio (CR) and viewing angle by considering the depolarization effect in thin-film transistor substrate, LC layer, color filter (CF) array, etc. To mitigate the depolarization effect, we propose a new device structure by adding a thin in-cell polarizer between LC layer and CF array. Based on the analysis using our new model, the maximum CR of a multi-domain vertical alignment (MVA) LCD can reach > 20,000:1, while for the fringe-field switching (FFS) mode it can reach > 3000:1. We also discuss other approaches to further enhance the CR. Our model is a powerful tool to analyze the CR degradation mechanism and to guide the future LCD device and material optimizations.

82‐1: Distinguished Paper: Glass Substrate for Micro Display Devices

Glass substrate suitable for wearable micro display devices for augmented/virtual reality was developed. This glass has highly matched thermal expansion coefficient with that of silicon and it enables to suppress amount of warpage caused by the boding between Si and glass wafers. The glass also shows lower thermal shrinkage than that of conventional non alkali glass for thin film transistor substrate. In this paper, the effect of the temperature dependence of CTE on warpage generation after bonding process was investigated using both numerical simulation and experiment. The newly developed glass showed remarkably low warpage after the bonding process.

Glass substrate for micro display devices

Glass substrate suitable for wearable micro display devices for augmented/virtual reality was developed. This glass has highly matched thermal expansion coefficient with that of silicon, and it enables to suppress the amount of warpage caused by the boding between Si and glass wafers. The glass also shows lower thermal shrinkage than that of conventional non-alkali glass for thin-film transistor substrate. In this paper, the effect of the temperature dependence of the thermal expansion coefficient on warpage generation after bonding process was investigated using both numerical simulation and experiment. The newly developed glass showed remarkably low warpage after the bonding process.

Accurate transmittance analysis of liquid crystal displays using a rational fraction approach in the time domain

Transmittance of liquid crystal display (LCD) is accurately characterized by using a rational fraction approach to extract complex multi-poles corresponding to a modified Drude–Lorentz dispersive model in the time-domain simulation. Here, the multi-pole fitting accuracy to the measured complex refractive indices of color filters and polarizers with low absorption coefficients and high noise levels is significantly improved with the suggested multi-pole fitting algorithm. Then, the transmittance and power distribution of LCD for oblique incidence are analyzed with high angle accuracy, and the color shift arising from the misalignment between the color filter and thin-film transistor substrates is effectively evaluated.

An electrostatic discharge model for thin‐film transistor fabrication

AbstractElectrostatic discharge (ESD) is a significant cause of yield loss in thin‐film transistor (TFT) array manufacturing. TFT arrays are at increased risk relative to other electronic components because the TFTs are unprotected; the array has a large inherent capacitance, and TFT processing includes many chucking and conveyance steps that result in triboelectric charge generation. To reduce or eliminate ESD‐caused fallout, an understanding must be gained of an ESD event's fundamental physics, including the mechanism of charge generation, ESD event physics, and TFT failure modes.An equivalent circuit model has been developed to address the physics of how ESD events occur. The ESD event scenarios modeled with this circuit are as follows: (1) the substrate glass is lifted from the chuck, resulting in a non‐uniform static charge; (2) this charge induces a voltage on the A‐side components; (3) the substrate is lifted, causing a voltage increases; (4) the uneven charge generated results in voltage gradients between TFTs, resulting in an ESD event. This model combines the effects of TFT substrate lifting and charge generation, with a simplified equivalent circuit representing the TFT array. The behavior of this circuit was simulated with a spice model (Electronics Research Laboratory of the University of California, Berkeley, CA, USA.) to characterize the ESD pulse.

Experimental Study on Indium Recovery from Discarded TFT-LCD Panels

With the rapid development of the technology of liquid crystal display, LCDs have become the main stream displays. However, if there are no appropriate ways to recycle the discarded LCDs, the environment will be polluted and the resources will be wasted. TFT-LCD panels mainly consist of the color filter (CF) substrate and the thin film transistor (TFT) substrate which both have a surface covered with indium-tin oxide (ITO). ITO layer contains the metal of indium which is rare, precious and of high value. In view of the difference of the structure and material of the CF substrate and TFT substrate, an efficient and green process has been presented for recycling the indium by means of theoretical analysis and experimental verification. Under heating condition, the sodium hydroxide solution is used to dissolve the color filter of the CF substrate and the ITO layer attached to the color filter can be eliminated quickly and the metal indium can be enriched by filtering solution. By grinding the ITO layer on the TFT substrate with the aid of water-proof sand paper and collecting ITO scraps, indium can also be enriched quickly. The experiments show that the indium content of the CF substrate and TFT substrate are both quite low. Enriching indium on the premise of not dissolving indium is beneficial to the concentrated recovery of indium and is helpful to raise the recycling efficiency and protect the environment.

High mobility organic thin film transistors based on monocrystalline rubrene films grown by low pressure hot wall deposition

Monocrystalline rubrene (5,6,11,12-tetraphenylnaphthacene) films with thickness between 1 and 10 μm and grain sizes as large as 100 μm×2 mm were deposited on thin film transistor substrates at rates ∼500 nm/min by a low pressure and hot wall deposition method. Organic thin film transistors with these high quality thin films as active channels have field effect mobility as high as 2.4 cm2/V s and ON/OFF current ratios around 106. The morphology and crystallinity of rubrene films under different deposition conditions were also studied to determine the optimal film deposition conditions.

In-line Automatic Defect Inspection and Repair Method for a High Yield TFT Array Production

We have developed an automated circuit defect inspection and repair method that can be used to improve the yield ratio of Thin Film Transistor substrates for liquid crystal displays. The method focuses on correcting resist patterns after the development process to ensure shape regularity. We built a prototype system and confirmed that the method is valid. This method can be used to produce a high yield of TFT-LCD at a low cost and eliminate defects.

P‐91: TFT Substrate Birefringence Induced Asymmetrical Viewing Angle and Compensation Methods

AbstractThin‐film transistor (TFT) processes for small pixel geometries can induce optical birefringence effects and change the viewing angle from symmetrical to asymmetrical. We experimentally identified the TFT substrate as the source of the birefringence and developed four methods to compensate the added optical birefringence effects to restore the symmetrical viewing angle. We also developed two special wide viewing angle polarizers with Fuji Film wide viewing angle film, and special compensation films to compensate the TFT substrate's birefringence.

Mechanically strained a-Si:H AMOLED driver circuits

AbstractThis paper examines the variations in performance of amorphous silicon (a-Si:H) thin-film transistor (TFT) pixel driver circuits for active-matrix organic light-emitting diode (AMOLED) displays, which are subject to compressive or tensile mechanical strain. The external strain is induced by bending of the TFT substrate, and is measured by the observed changes in resistance of in-situ strain gauges. Mechanical strain impacts the performance of the circuit in terms of its drive current, which may be attributed to mobility and Fermi energy shifts in the individual TFTs. The effect of strain-induced shifts in the TFTs as a function of strain orientation (longitudinal or transverse) with respect to direction of current flow is also examined. Our measurements show that the variation in the drain current of a longitudinally oriented TFT can be as much as ∼ 1.5% for strains as high as 10−3. Proper layout and circuit design can suppress the effect of strain-induced shifts, and should be taken into consideration when designing stable TFT driver circuits for mechanically flexible AMOLED displays.