High-resolution Active Matrix Research Articles

Fabrication of high-resolution active matrix driven GaN-based Micro-LED chips

Fabrication of high-resolution active matrix driven GaN-based Micro-LED chips

4‐3: Distinguished Paper: 10 µm Pixel, Quantum‐dots Color Conversion Layer for High Resolution and Full Color Active Matrix Micro‐LED Display

A fine patternable quantum‐dots (QDs) color conversion layer (CCL) for high resolution and full color active matrix (AM) micro‐LED display is demonstrated. QDs CCL could be patterned until 10 µm using photolithography process. It is found that multi‐coatings with R‐ and G‐QD CCLs on LED array can provide full color AM display.

Ten micrometer pixel, quantum dots color conversion layer for high resolution and full color active matrix micro‐LED display

AbstractA fine patternable quantum dots (QDs) color conversion layer (CCL) for high resolution and full color active matrix (AM) micro‐LED (μ‐LED) display is demonstrated. QDs CCL could be patterned until 10 μm using photolithography process. It is found that multicoatings with red and green QDs (R‐ and G‐QDs) CCLs on LED array can provide full color AM display.

Employing Drain-Bias Dependent Electrical Characteristics of Poly-Si TFTs to Improve Gray Level Control in Low Power AMOLED Displays

With development of high efficiency organic light emitting diodes (OLEDs), and high mobility polycrystalline silicon (poly-Si) thin-film transistors (TFTs), low power and high resolution active matrix OLED (AMOLED) displays are becoming popular for mobile applications. However, they suffer from poor control of lower gray levels, with the driving TFT being operated in the subthreshold regime. In this paper, with help of non-ideal drain-bias dependent electrical characteristics of poly-Si TFTs, operation of the driving TFT can be moved out from the subthreshold regime to allow better control of the gray levels. As a result, a dynamic voltage scaling (DVS) method is developed, and shown to be able to improve the luminous uniformity for better image quality, while effectively reducing the static power consumption.

61‐2: Weakening Micro‐Cavity Effects in White Top‐Emitting WOLEDs with Semitransparent Metal Top Electrode

Top emitting white organic light emitting diodes (WOLEDs) hold great promise for high brightness and high resolution active matrix OLED displays. One key challenge of high‐performance top emitting WOLEDs is the availability of top electrodes with superior optical, electrical properties. Herein, we demonstrate the improvement of both electrical and optical properties of widely used metal electrode, which is achieved by co‐depositing a proper amount of magnesium (Mg) with silver (Ag) deposition with optimized deposition rate of both Mg and Ag. Corresponding WOLEDs are fabricated using this optimized 80Å thick Mg:Ag electrode, which show a 14.73% enhanced current efficiency at 10mA/cm2 compared to their 120Å thick Mg:Ag electrode counterparts. Also, the 80Å thick Mg:Ag based WOLEDs show close‐to‐identical emission spectra at different view angles and color shift.

Development of high-resolution active matrix spatial light modulator

We developed a high-resolution active matrix spatial light modulator on a glass substrate. To integrate a switching device on the glass substrate, we designed a high-performance oxide thin-film transistor with a minimum channel length of 1 μm and a maximum processing temperature of 380°C. To drive a large number of data lines, we used multiple source drivers and data drivers as well. For an optical modulation, we optimized a liquid crystal of a high anisotropic refractive index of 0.25 with a cell gap of 2.5 μm, which was effectively operated until pixel pitch is 1.6 μm. Hologram was successfully reconstructed by fabricated SLM with 7-μm pixel pitch. For the other approach for a high-resolution spatial light modulator, we tested a phase change material of Ge2Sb2Te5 [GST]. The variation of refractive index between a polycrystalline phase and an amorphous phase of the GST film is used for a hologram reconstruction. By optimizing the underlying oxide thickness, we can show a color hologram without color filters.

A Pixel Structure Using Block Emission Driving Method for High Image Quality in Active Matrix Organic Light-Emitting Diode Displays

In this paper, we propose a pixel structure and timing diagram using the block emission (BE) driving method to improve the image quality of high-resolution active matrix organic light-emitting diode (AMOLED) displays. The proposed pixel structure reduces the boundary error pattern between blocks by adjusting the timing of the compensation ( comp ) signal for the threshold voltage variation. The test patterns, which include a pixel array and unit pixels, are designed for a 10-inch quadruple high-definition resolution format and are fabricated to verify the image quality of the AMOLED displays. The measurement results show that the emission current error at the boundary between blocks is reduced from +11% to less than ±1% by adjusting the timing of the comp signal. Also, the emission current error caused by the threshold voltage variation of the driving thin film transistors is reduced from ±8.36% to ±2.77% at a gray level of 175 by using the BE driving method. Therefore, the proposed pixel structure improves image quality in high-resolution AMOLED displays.

Pixel structures to compensate nonuniform threshold voltage and mobility of polycrystalline silicon thin-film transistors using subthreshold current for large-size active matrix organic light-emitting diode displays

We propose pixel structures for large-size and high-resolution active matrix organic light-emitting diode (AMOLED) displays using a polycrystalline silicon (poly-Si) thin-film transistor (TFT) backplane. The proposed pixel structures compensate the variations of the threshold voltage and mobility of the driving TFT using the subthreshold current. The simulated results show that the emission current error of the proposed pixel structure B ranges from −2.25 to 2.02 least significant bit (LSB) when the variations of the threshold voltage and mobility of the driving TFT are ±0.5 V and ±10%, respectively.

35.4: Programmable Pulse Width LTPS TFT Shift Register for High Resolution and High Frame Rate Active Matrix Flat Panel Displays

AbstractThis paper proposes a programmable pulse width LTPS TFT shift register where an output pulse width is programmed only by adjusting a start pulse width without any additional clock signals and reconfiguration. Since an overlap interval of the output pulses is easily controlled in the shift register which operates with precharging scheme, the proposed shift register can be applied to high resolution and high frame rate display without the problem of insufficient line time. The performance of this circuit is verified by SMART SPICE at low‐temperature poly silicon (LTPS) thin film transistor (TFT) process. The pulse width is changed by the step size of two line time with only two input clock signals which leads to small area for circuit implementation and simulated power consumption is similar to that of the conventional shift register.

56.5L: Late‐News Paper: All‐Printed Oxide Thin Film Transistor Arrays for High Resolution Active Matrix

AbstractWe have demonstrated all‐printed oxide TFT arrays for 100 ppi RGB active matrix fabricated by inkjet printing and spin coating without photolithography and mask process. The average mobility of TFTs was 7.49 ± 1.67 cm2/Vs on a thermally oxidized SiO2 /Si substrate. Moreover, in the case of using of a printed oxide high‐k gate insulator and an n‐type doped active layer on a glass substrate, the average mobility of all‐printed oxide TFTs was 2.54 ± 0.32 cm2/Vs.

Effect of gate dielectric scaling in nanometer scale vertical thin film transistors

A short channel vertical thin film transistor (VTFT) with 30 nm SiNx gate dielectric is reported for low voltage, high-resolution active matrix applications. The device demonstrates an ON/OFF current ratio as high as 109, leakage current in the fA range, and a sub-threshold slope steeper than 0.23 V/dec exhibiting a marked improvement with scaling of the gate dielectric thickness.

Review paper: Transparent amorphous oxide semiconductor thin film transistor

Thin film transistors (TFTs) with oxide semiconductors have drawn great attention in the last few years, especially for large area electronic applications, such as high resolution active matrix liquid crystal displays (AMLCDs) and active matrix organic light-emitting diodes (AMOLEDs), because of their high electron mobility and spatial uniform property. This paper reviews and summarizes recent emerging reports that include potential applications, oxide semiconductor materials, and the impact of the fabrication process on electrical performance. We also address the stability behavior of such devices under bias/illumination stress and critical factors related to reliability, such as the gate insulator, the ambient and the device structure.

A luminance adjusting algorithm for high resolution and high image quality AMOLED displays of mobile phone applications

A luminance adjusting algorithm using light sensing scanner is proposed for small-sized high resolution and high image quality active matrix organic light emitting diode (AMOLED) displays such as smartphone applications. By using simple pixel structure with the proposed algorithm, high aperture ratio in high resolution display can be achieved. Experimental results show that the standard deviation of luminance improves from 7.07 to 1.81 LSB when the proposed adjusting method is used to 3.5-inch AMOLED display with 8-bit gray scale.

Vertical Transistor with Ultrathin Silicon Nitride Gate Dielectric

Nanoscale vertical thin-film transistors (VTFTs) are fabricated employing a new ultrathin silicon nitride (SiNx) gate dielectric for applications in high-resolution active matrix flat panel electronics. Illustrated are the cross-section schematic and SEM image of a 500 nm channel length VTFT with a 50 nm thick SiNx gate dielectric. The device demonstrates excellent gate control with gate leakage as low as 0.1 nA cm−2.

Monolithic LED Microdisplay on Active Matrix Substrate Using Flip-Chip Technology

A monolithic high-resolution (individual pixel size 300times300 mum2) active matrix (AM) programmed 8times8 micro-LED array was fabricated using flip-chip technology. The display was composed of an AM panel and a LED microarray. The AM panel included driving circuits composed of p-type MOS transistors for each pixel. The n-electrodes of the LED pixels in the microarray were connected together, and the p-electrodes were connected to individual outputs of the driving circuits on the AM panel. Using flip-chip technology, the LED microarray was then flipped onto the AM panel to create a microdisplay.

10-Bit Current Driver LSI for Large-Size and High-Resolution Active Matrix Organic Light Emitting Diode Displays

We present the 10-bit current driver LSI with 2-set current digital-to-analog converters (DACs) and output channel current sample and hold (S/H) circuits for large-size and high-resolution active matrix organic light emitting diode (AMOLED) display applications. This current driver LSI has 300 output channels and the output current ranges from 0 μA to 290 μA. The maximum output current level can be controlled by 2-bit control signals because the maximum output current level depends on display size and resolution. The chip was fabricated using 0.65 μm BiCMOS process and characterized. The chip size is 16.8 mm x 3.6 mm. Experimental results show that the output current DNL is less than 0.4 LSB and that INL is less than 1.5 LSB. This is good enough to apply 15.5 inch WXGA (1280 x RGB x 768) AMOLED displays.

Current-Sensing and Voltage-Feedback Driving Method for Large-Area High-Resolution Active Matrix Organic Light Emitting Diodes

There is the problem of picture quality nonuniformity due to thin film transistor (TFT) characteristic variations throughout a panel of large-area high-resolution active matrix organic light emitting diodes. The current programming method could solve this issue, but it also requires very long charging time of a data line at low gray shades. Therefore, we propose a new driving method and a pixel circuit with emission-current sensing and feedback operation in order to resolve these problems. The proposed driving method and pixel circuit successfully compensate threshold voltage and mobility variations of TFTs and overcome the data line charging problem. Simulation results show that emission current deviations of the proposed driving method are less than 1.7% with ±10.0% mobility and ±0.3 V threshold voltage variations of pixel-driving TFTs, which means the proposed driving method is applicable to large-area high-resolution applications.

5.1: Invited Paper: History and Status of Organic Light Emitting Device (OLED) Technology for Vehicular Applications

AbstractWith the drive to convey much more information in today's vehicles to both driver and passenger, organic light emitting device (OLED) technology has begun to capture the attention of automotive systems designers and engineers. OLED displays are bright, emissive devices that offer excellent color gamut, wide viewing angle and high contrast. Passive matrix (PM) monochrome and multi‐color OLEDs have been introduced in products including an automotive audio console and cellular telephone. In the near future, full‐color, high‐resolution active matrix (AM) OLEDs with excellent power efficiency, particularly through the use of new high‐efficiency phosphorescent materials, will also be available. Finally, continued progress toward meeting more rigorous requirements, for thermal stability and extended lifetimes, including those of the automotive environment, are foreseen. Moreover, recent technological advances such as display flexibility and transparency have created exciting new ways to integrate OLEDs into vehicles. In this paper, we discuss the status of OLED technology, highlighting some of the key features and performance measures that are most important to the automotive designer and engineer.

A multi-level multi-phase charge-recycling method for low-power AMLCD column drivers

This paper describes a new low-power design concept appropriate for column drivers of high-resolution active matrix liquid crystal displays with a dot inversion method. The proposed multi-level multiphase charge-recycling method reduces power consumption incurred in driving highly capacitive column lines by storing the charge into the external capacitors and reusing it in the next cycle. With the proposed method, power consumption can be reduced asymptotically to zero with the infinite number of storage capacitors. However it is also shown that total power reduction can be counterbalanced by the power consumption in driving switches used in the recycling process. Analytical equations, simulation results, and measurement results from an experimental chip are shown to validate the proposed method. Dynamic power reduction of 55%-70% is measured with a three-level five-phase charge-recycling method compared with a conventional column driver.

Electroluminescent displays

This article will review the electrical and optical properties of thin film electroluminescent (EL) displays. A simple electrical model for thin film electroluminescent (TFEL) device operation will be presented and used to describe the luminance and power consumption of TFEL devices. The basic material characteristics that are desirable for EL phosphors will be described. Progress in the development of multicolor and full color EL displays will be presented including device structures and phosphor advancements. Recent work on devices that combine EL technology with high resolution active matrix circuitry to achieve high resolution displays for head-mounted applications will be described.