Corning Lotus NXT Glass addresses today’s LTPS-OLED manufacturing process challenges
Corning LotusTM NXT Glass, through its advantaged and balanced glass attributes, was designed to address the challenges of today’s LTPS-OLED manufacturing processes.
Display Glass Requirements for Oxide TFT Technology
An industry need has arisen for oxide TFTs, an advanced, scalable high-performance TFT display technology that meets consumer demand for brighter, faster, more lifelike images. To meet these cost and performance expectations, oxide TFT panel makers need an advanced, thermally and dimensionally stable glass to improve yields while achieving the desired resolution.
Springer Handbook of Glass: Display Glass
Corning Contributed Publication
J. David Musgraves, Juejun Hu, Laurent Calvez, "Springer Handbook of Glass", Springer International Publishing, 10.1107/978-3-319-93728-1 (2019) https://www.springer.com/us/book/9783319937267?gclid=Cj0KCQjw4cOEBhDMARIsAA3XDRj2aARcIr0bfMMTMgkz0nzk7ifQ68i3Txly8MG-pa0VdyDLRcMxSnEaAk-XEALw_wcB
Tunability of Reconfigurable Intelligent Surface (RIS) using Liquid Crystal according to various bias voltage levels
This paper introduces a proof-of-concept of RIS consisting of Merck GT7-29001 Liquid Crystal (LC) and Corning glass with metallic circle patterns for controlling redirection at Ka-band. Since this structure and fabrication process is compatible with conventional LCD manufacturing technology, significant cost reduction and large size capability can be expected compared to incumbent diode & PCB substrate fabrication process. The prototype of RIS had LC layer of a 200um thickness and its frequency tunability was over 14% when inducing bias voltages up to 25V at metal patterns. Simulation results using dielectric properties of GT7-29001 show a good agreement with the frequency tunability at measurements. Also, 23° beam steering was realized by separately inducing 0V or 10V at each metal pattern on glass.
Glass-embedded electromagnetic surface for energy saving future wireless communication
In this paper, the concept of optically transparent glass-embedded frequency selective surface (FSS), functionalities of FSS, application scenarios, design methodology, materials/processes for transparency implementation, and performance verficiation using both simultation and real samples are described. Value propositions of optically transparent FSS and display integration potentials are also discussed.
Wrap-around electrodes for Micro LED tiled displays
The authors have developed a process to create wrap-around electrodes(WAEs) on glass for use in tiled microLED display applications. The electrodeshave small size and spacing, low resistance, and good reliability. In addition,an opaque overcoat protects the edges of the tiles and reduces seam visibility.These electrodes allow bezel-free tiled operation for high-resolution displays.
Glass Panel Strength and Reliability
Ball Impact Testing of Glass: Regarding Assessment of Glass Strength
Ball impact testing was originally developed and continues to be deployed with human safety in mind. As such, the existing standards, specifications and test methods for ball impact testing are written with the objective to reduce or eliminate the risk of injury to the consumer. The issue arises when these safety driven test standards are used to assess glass strength. The current ball impact test standards are not inherently designed for determining specific strength values as they often over strss the specimens well beyond the normal point of end use failure to ensure that glass breakage occurs safely. Ball drop test should be used in scenarios where it is replicating a relevant failure mode. For this reason, the ball drop test should be used in conjunction with other relevant tests to effectively understand material strength or underlying issues in the material.
Behavior of LCD Panel During Bending
When an LCD panel is subjected to pure bending, for example during strength measurement or proof testing, the question arises “does it behave as a monolith of twice the substrate thickness?" or "does it behave as two independent substrates?”. Both theory and experiment suggest that the panel behavior depends on how its edges are held together (i.e. well bonded or loosely held together). Indeed, the former renders the panel nearly twice as strong and four fold as stiff as the latter. This paper will provide the analysis of the bending behavior of a two-layer laminate using St. Venant flexure theory. Experimental data, using strain gages, will demonstrate that an LCD panel can behave either as a monolith of twice the substrate thickness or two independent substrates depending on how its four edges are held together in the support structure including the bezel. The paper derives appropriate equations for computing panel strength when it is bent to constant curvature or when its specimens are flexed in 4-point bending for bothi) well bonded edges and ii) loosely held edges.
Best Practices in Strength Testing of LCD Glass
This paper provides general guidelines and watch outs while conducting strength testing on LCD glass. Importance of failure modes, large deflections, membrane stresses, failure locations, device design, fatigue, fractography and strain gauging are discussed in this paper. It also gives an example on why panels cannot be treated as monolithic glass when calculating the strength
Edge Strength Measurement of Free-form Displays
The Edge Strength Measurement System (ESMS) is proposed as a method for measuring the edge strength of free-form displays. Its feasibility on free-form monolithic glass samples with varying radius of curvatures is demonstrated. Finite element modeling and digital image correlation are performed to determine the load-to-stress correlation and understand the measurement sensitivity. ESMS can provide full edge testing which can help detect weak flaws and improve product reliability of free-form displays.
Edge Strength Measurement of Ultra-Thin LCD Panels
The feasibility of using Corning’s edge strength measurement system (ESMS) for ultra-thin LCD panels has been demonstrated. Panels were used to validate the load-to-stress correlation: digital image correlation, finite element analysis and mirror radius measurement all showed good agreement, supporting the robustness of the strength measurement. The edge strength of panels was measured by both static and dynamic ESMS. Test results revealed that dynamic ESMS is advantaged over static in better capturing the relevant flaw population owing to its larger test area. Accurate edge strength measurement via ESMS coupled with selective fracture analysis on the weakest flaws will assist in improving the edge strength of ultra-thin LCD panels.
Four Point Bending of AMLCD Panel
The four-point bend test is used extensively to measure the edge (and surface) strength of AMLCD displays both in panel form and single substrate. The subtleties of four-point bend test for AMLCD panel applications and how one might use additional techniques, such as strain gage, finite element modeling and failure mode analysis, to better understand the data generated, are investigated. This paper attempts to show the following: i) the standard four-point bend equation (FIgure 1) is not applicable to thin AMLCD panels, ii) the edges and surface experience dfiferent stress, iii) stresses can be quantified by knowing break location and the appropriate strain level and iv) failure mode analysis can support the strain analysis and provide valuable information to the experimenter.
Fracture Analysis, a Basic Tool to Solve Breakage Issues (Part I)
Fracture analysis can provide information on both the tensile stress and the origin of breakage. This analytical technique gives important information in determining mechanism of breakage, such as direction of crack propagation, type of the stress, direction of impact and friction, location of the origin.
High Strength, Damage Resistant Display Panels
Chemical etching can significantly increase the strength of surfaes and edges of display panels. This can be done in a selective fashion by targeting the desired region in need of increased strength. If done properly, the strength increase can be greater than ten times the original strength with values in excess of 1 GPa.
Improved Methodology for testing edge strength for ultra thin panels
Traditional testing methodologies (four point bend and three point bend) have limited effectiveness as panel thicknesses decrease due to a variety of interconnected factors. This limited effectiveness impacts the ability to make reliability predictions based on edge strength measurements. This paper provides an improved methodology for testing the edge strength of ultra-thin panels for reliability predictions through a system of rollers strategically placed only at the edge of the glass panel.
Mechanical Reliability of Glass in Curved Displays
This paper explores Corning's approach and recommendations regarding the mechanical reliability of glass for curved displays.
Strength Measurements of Thin AMLCD Panels
The biaxial strength using ring-on-ring (ROR) test and uniaxial strength using 4-point bend test (4PB) were measured for 13.3” panels with substrate thicknesses ranging from 0.25 mm to 0.5 mm. The effect of the thinning process was quantified by this data, along with identifying break sources using fractography. Strain gages were used to convert failure load to strength.
The Mechanical Reliability of Glass Displays in Bending
The mechanical reliability of glass under stress is controlled by the strength of the existing flaw population and the subcritical growth of those flaws under stress. Each glass application requires a mechanical reliability strategy that is optimized for that application. The purpose here is to establish that strategy for the case of glass in displays where the intent is to bend the display permanently. Fracture mechanics is used as a well-established framework for combining strength and fatigue effects on display glass sheets.
Glass Processing - Mechanical
Analytical Approach to Evaluate Maximum Gravitational Sag and its Variations of Glass Substrate for LCD
We present analytical formulas to evaluate the gravitational sag of glass substrate for Flat Panel Displays (FPD). The formulas are derived for the parallel line supports (knife-edges). Past studies and comparison with finite element analysis in this paper show that a continuous line support is a very close approximation to collinear point supports with the kind of support spacing typical in todays cassette designs. Two, three and four supporting lines are considered. A new concept of initial shapes of the glass substrate is introduced to enable evaluation of sag variations caused by various process factors analytically and numerically. We show that both the sag magnitude of the glass substrate and its variations due to various process factors may be drastically decreased with increased number of horizontal supports. The analytical results are verified numerically with the finite-element method.
Optics / Mura
Patterned Glass Diffuser for Luminance Increase and with Glass Circuit Board in a MiniLED Backlight
This paper reports progress on monitor-sized, dimensionally and thermally stable MiniLED backlights enabled by a patterned glass diffuser (PGD). One PGD based backlight, while being thinner, shows a higher luminance than a reference MiniLED backlight. Another all-in-one PGD enhances a glass circuit board based MiniLED backlight.
Integrated ultra-thin direct-lit LCD backlight using glass components
In this paper, we present the results of development of a backlight in which a single glass plate serves as both a light guide and a core of the printed circuit delivering current to the MiniLED light sources. The backlight integrates a patterned glass diffuser (PGD) and a glass printed circuit board (GCB). The integrated backlight has the advantages of exceptional thinness, reduced component count and weight, very low thermal expansion, fixed registration, and improved heat dissipation, making it uniquely suitable for portable displays such as those in tablet or laptop computers. An early prototype had a total thickness of 2.5 mm and demonstrated luminance uniformity better than 98.5%. In the future versions, we project that the thickness can be further reduced to 1.5 mm, while keeping all the advantages of direct-lit backlights including high luminance and local dimming capability.
Electroluminescent Quantum Dots (ELQD) Performance Modeling
An optimized top emitting (TE) electroluminescent quantum dot (ELQD) LED device design is achieved using Finite Difference Time Domain (FDTD) simulation by allowing the thicknesses for QD Emission layer (EML) and an adjacent hole transmission layer (HTL) to differ for R, G, and B subpixels. Optical extraction efficiencies for R, G, and B subpixels reach ~15, ~23, and ~24 % resp., while small angular color shift is sustained. Angular characteristics of the device are very sensitive to the thickness variation of the individual material layers in the design, indicating the importance of thickness control in device fabrication process.
Panel Stress Determines Light Leakage in Curved LCD
Substrate stress state determines the light leakage (LL) from dark state VA and IPS liquid crystal (LC) curved panels. Membrane stress creates VA but not IPS LL. Shear and bending stress create IPS but not VA LL. This result enables mitigation, design, and possibly new processes/components to enable non-traditional form factor LCDs.
Patterned Glass Diffuser (PGD) for Mini-LED Backlights
A report on a monitor-sized, thin, dimensionally and thermally stable mini-LED backlight enabled by a patterned glass diffuser (PGD). Our backlight has a luminance between 0.9× and 1.05× compared to a reference mini-LED backlight using a thick diffuser plate, while providing a better local dimming control, comparable zone, panel luminance uniformity and color uniformity. The PGD technology can reduce the number of LEDs.
Ultra-slim Direct-lit LCD Backlight Using Glass Light Guide Plate
A report on the design and performance of a direct-lit LCD backlight prototype which is only 5 mm thick and capable of full array 2D local dimming. Equipped with a 15.6” LC display panel, the prototype reaches peak brightness of 2000 nits. The measured contrast numbers meet VESA Display HDR 600 specification.
Surface Science / Substrate Cleaning
Effective Cleaning of Glass Substrates
Surface contamination is one of the major causes of yield loss, with a unique set of challenges for large display glass sheets that support the industry. Here, we review the use of different cleaning approaches applied to display glasses during manufacturing, discussing the advantages of some choices over others.