LTPS TFT Research Articles

P‐170: Structure Optimization of Stretchable AMOLED based on LTPS TFT

Structure optimization of stretchable AMOLED for high stretchability and high reliability was studied. High stretchability (>10%) was achieved. To improve the key reliability performance of stretchable OLED, pixel‐size hybrid encapsulation was developed, with which the panel can pass 60o C/90% 360h reliability test. A dynamic stretchable AMOLED module was fabricated.

10‐2: Temperature‐Dependent Electrical and Emissive Behavior of UV‐Excited Cd‐Free QD MicroLED Display

A 1.37” smart‐watch size active‐matrix microLED display prototype was fabricated by Cd‐free R/G/B quantum dots pumped by UV microLEDs in an innovative 4‐sub‐pixel architecture. The temperature‐dependent emission properties from such quantum dot display have been studied based on the competing processes between LTPS TFT output current and UV microLED radiance. Our studies show that with proper thermal treatment, the photo brightening of QDs can be stabilized within 5%. This presents a promising route to develop microLED displays with brightness insensitive to operation temperature up to 90ºC.

P‐138: Color Demura for LTPS TFT MicroLED Displays

In this study, a loop iterative approach is employed to gradually get closer to the actual red, green, and blue color coordinates and brightness ratio under a given grayscale to realize the brightness and chromaticity compensation (Color Demura) for LTPS TFT MicroLED display. This approach is applied to a 9.38‐inch 480 × 960 resolution MicroLED display, achieving brightness uniformity more than 95% and chromaticity non‐uniformity less than 1JNCD, respectively.

단기 전압-온도 스트레스에 의한 LTPS TFT의 Subthreshold Swing 변화

단기 전압-온도 스트레스에 의한 LTPS TFT의 Subthreshold Swing 변화

The fabrication and characterization of direct conversion flat panel X-ray imager with TlBr film

The novel direct conversion flat panel detectors (FPDs) utilizing thallium bromide (TlBr) films are developed and characterized in this study. Thin TlBr films, deposited using an evaporation technique, achieved thicknesses of 10 μm and 50 μm. A pixel sensor array, with a pixel size of 235 × 235 μm2 and a sensitive area of 29.61 × 39.48 mm2, was developed using low-temperature polysilicon thin-film transistor (LTPS TFT) technology as the initial study to explore performance characteristics of developed imaging system. The TlBr film was characterized based on the current-voltage (I–V) profile, showing a resistivity of 2.78 × 1010 Ω·cm. The LTPS TFT showed a leakage current of about 10−13 A, while the noise of TlBr FPD system was around 104 e− rms, primarily limited by the readout system. The detector system was characterized using radiation from an X-ray tube with a voltage in the range of 30 kV–100 kV and a current of 2 mA, involving an X-ray test chart as the object with the processing time of 18.15–18.30 ms per frame. Based on the contrast and contrast-to-noise ratio (CNR) values, the 10 μm and 50 μm TlBr FPD clearly captured the image in operation between 30 kV and 100 kV. The 50 μm TlBr FPD demonstrated improved sensitivity, showing pixel values with 10 times higher intensity and enhanced line pair detail at 30 kV X-ray operation. The 10 μm TlBr achieved spatial resolution of 267 μm full width at half maximum (FWHM), while the 50 μm TlBr achieved 250 μm FWHM. In the X-ray imaging demonstration, the shape and structure of anchovy was clearly distinguished. The TlBr film FPD presents promising potential for a room temperature X-ray imager.

Effect of Barrier Layer Properties of LTPS TFT Devices on AMOLED Short-term Image Sticking Performance

Effect of Barrier Layer Properties of LTPS TFT Devices on AMOLED Short-term Image Sticking Performance

11‐4: 3.55‐Watt Output Power LTPS TFT DCDC Converter for Actuators on Wearable Devices on Flexible Substrate

In this work, a high‐power LTPS DCDC converter on flexible polyimide substrate is demonstrated. The diode‐based boost‐ converter upconverts its output voltage to 9V from a 3.3V source and can reliably supply a load range of 100mA to 400mA. The efficiency of the design is reaching 54.9%. The design contains 400.000 25μm/4.5μm TFTs, resulting in a complete footprint of 10.02cm2. The DCDC converter is suitable for driving high‐power actuators on flexible wearables devices. Moreover, this work reports 3.24 ampere current through the LTPS TFT in the DCDC converter resulting in sub‐Ω ON‐resistance.

P‐63: Simple Pixel Circuit with External Compensation for High PPI Active‐Matrix MicroLED Displays Using PWM Method

This work presents a novel pixel circuit that consists of five transistors and two capacitors for active‐matrix micro‐LED (AMμLED) displays. The proposed pixel circuit uses external compensation to compensate for variations in the low‐temperature polycrystalline‐silicon thin‐film transistor (LTPS TFT) threshold voltage and adopts pulse width modulation (PWM) to modulate the grayscale. According to the simulation results and a layout example, the proposed pixel circuit is expected to be applied in high pixels per inch (PPI) car displays in the future.

5‐5: Development of 1500PPI VR LCD display device based on LTPO process structure

In this paper, LTPO structure was used to develop 1500PPI LCD VR display device, and LTPS TFT process structure was used for peripheral driving to ensure excellent driving performance. The display area adopts oxide TFT process structure to achieve high aperture rate pixel design, and the actual aperture rate can reach 38%.In addition, the Com metal shading layer (CM) is designed above the COM electrode to block the crosstalk light of adjacent pixels and improve the crosstalk effect. The measurement is based on the perspective of 30°, Δuv<4JNCD@White，Δuv<10JNCD@RGB.

85‐2: 2117PPI VR LCD with ultra‐high aperture opening ratio

In this paper, the Pixel Design and the Process Technology of ultra‐high PPI display are investigated. For increasing the aperture open ratio in pixel design, the width of metal data line, the size of TFT and the crosstalk between metal lines are separately researched. The minimum of light shield for LTPS TFT is achieved since the mechanism between photoillumination and off‐state current is analyzed. In the meanwhile, the process of narrow metal lines and small via holes are developed. For conclusion, the aperture open ratio of backplane panel is achieved more than 55%.

45‐2: 14.6‐inch 202‐ppi Rollable Micro LED Display with Color Conversion Technology

The 14.6‐inch 202‐ppi rollable micro LED display was fabricated on flexible LTPS TFT backplanes. The tiny micro LEDs, those size are less than 30 um, were bonded on backplanes by flip‐chip soldering technologies. More than 11 million micro LEDs were transferred to achieve brightness of >1000 nits, contrast ratio of >1,000,000:1 and resolution of 2560xRGBx1440. We investigated the structure and mechanism to achieve the rollable capability for micro LED displays.

67‐2: Adoption of Blue Light Semiconductor Laser Diode (BLDA) in LTPS TFT Manufacturing

We have investigated adoption of CW blue laser diode annealing (BLDA) in manufacturing process of LTPS TFT backplane. Our experiments have shown that except crystallization annealing, BLDA can be adopted in dehydrogenation of precursor amorphous silicon film, and also can be used in the activation after ion implantation. By using BLDA dehydrogenation of H2 content as high as 20% can be implemented. In the activation, BLDA can achieve surface resistance much lower than using conventional RTA.

87‐5: AM Mini‐LED Based on LTPS TFT Backplane with over 5000 Dimming Zones and High Driving Bits

LCD with Mini‐LED backlight performs high brightness and high contrast ratio. In this paper novel Mini‐LED based on LTPS TFT backplane is proposed for LCD backlight with over 5000 dimming zones and excellent image quality. Moreover, based on special driving circuit, 12‐14 driving bits, that is 4096‐16384 gray level, is achieved, which can improve local contrast ratio of the image. Compared to PM Mini‐LED, AM Mini‐LED shows superior performance on high dimming zone design, fewer LED drivers and improvement of image quality.

6.1: Adoption of Silicon Blue Semiconductor Laser Diode in Dehydrogenation of LTPS TFT Manufacturing

We have investigated de‐hydrogenation of amorphous film using CW blue light semiconductor laser annealing (BLDA). Dehydrogenation of hydrogen content as high as 20% can be implemented by using BLDA. This technology can be applied for large substrate beyond G8. We will report related experiment results in this paper.

20.4: Activation of Doped Silicon Film Using Semiconductor Blue Light Diode Laser Annealing

We have investigated activation annealing of the doped poly silicon film of LTPS TFT by using CW semiconductor blue light diode laser. It has been found that by full melting and re‐crystallization, the sheet resistance can be reduced significantly to 1/3 of which can be realized by using conventional RTA treatment. We will report the experiment results in the paper.

46.2: Invited Paper: 4.82‐inch LTPS TFT Micro‐LED Display for Tiled Display Modules

Micro‐LED, as one of the most promising advanced display technologies, has attracted increasing research interest from academia and display industry. With the outstanding performance in brightness, lifetime, and contrast, Micro‐LED display shows tremendous potential for applications in various electronic terminals. Moreover, due to the advantages of high reliability and isolated encapsulation, Micro‐LED can achieve bezel‐less splicing. Therefore, compared with traditional display, Micro‐LED large‐size display panels can be realized by stitching multiple bezel‐less display modules in accordance with customer requirements, such as 110 inch luxury TV. In this paper, we introduce the 4.82 inch Micro‐LED panel, which is a building block of large tiled displays, can be realized with mass transfer and LTPS TFT technology. This may pave the way for future seamless‐tiled TV products.

P‐29: Influence of the Static Bending Stress on LTPS TFT

We investigated the degradation behavior of p‐channel LTPS TFTs on PI substrate under the static bending stress. In order to evaluate the bending durability of flexible LTPS TFTs, device‐bending tests under different bending strains and directions have been performed. The performance of TFT under tensile bending stress degraded (ΔVth≈ 0.38V) worse than compressive bending stress (ΔVth ≈0.07V), which might be originated from both the generation of interface trap states (ΔNit) and channel boundary trap density (ΔNtrap) under tensile bending stress much higher than compression‐bent. In the meanwhile, the stress distribution has also been simulated. According to the results of test and simulation, we speculated the mechanical stress near the source and drain electrodes caused the traps in gate insulator, which in turn cause electron trapping.

76‐1: Invited Paper: MicroLED Display with Tiling Technology

A 27″ tiling display by using LTPS TFT active matrix structure is demonstrated. With a novel pixel design and tiling technology, the seamless feature is realized by 4 pieces 13.5″ panels with 625um pixel pitch. In this article, we will discuss the challenges and solutions of different seamless tiling technologies from process point of view.

Ultra‐highTgand ultra‐low coefficient of thermal expansion polyimide films based on hydrogen bond interaction

AbstractTo tolerate high processing temperature during the fabrication of low‐temperature polycrystalline silicon thin‐film transistors (LTPS–TFT) in flexible OLED devices, the polyimide (PI) films, which are used as substrate, should have ultra‐high glass transition temperature (Tg > 450°C) and ultra‐low coefficient of thermal expansion (CTE at 0–5 ppm K−1). In this paper, two novel heterocyclic monomers, namely, N,N'‐(xanthone‐2,7‐diyl)bis(4‐aminobenzamide) (p‐DAXBA) and N,N'‐(xanthone‐2,7‐diyl)bis(3‐aminobenzamide) (m‐DAXBA), which contain a xanthone moiety, are prepared and polycondensed with pyromellitic dianhydride (PMDA), respectively. PI films (PIa and PIb) with intrinsic highTgand low CTE are designed from the perspective of rigid conjugate xanthone structure and hydrogen bonding interaction. It is found that the PIa films prepared byp‐DAXBA have better linear structure of molecular chains and show relatively higherTgand lower CTE. TheTgof PIa‐40 is greater than 450°C, and CTE can reach as low as 2.7 ppm K−1, tensile strength of 179 MPa, modulus of 5.67 GPa, indicating potential application prospect as a flexible OLED substrate.

Foldable OLED Display with 620 Degree Celsius LTPS TFT Manufactured by Weak Bonding Method

Foldable OLED Display with 620 Degree Celsius LTPS TFT Manufactured by Weak Bonding Method