TN TFT Structure

Twisted Nematic ("TN") Thin-Film Transistor ("TFT") Displays fundamentally operate with Liquid Crystal fluid much like their monochrome counterparts. The TN fluid rotates horizontally within the planes of glass with thread-like alignment allowing light through. Linear Polarizing films on the top and bottom will control the passage of light, minimize unwanted light and improve contrast of the display.

The TFT layer adds an important function of electrically powering all pixels separately from the the logic drive. The response of traditional LC fluid is too slow for video frame rates, so the need of having each pixels in parallel operation is necessary. The majority of TFT displays are full color display designs. A color filter is used so that white backlighting can accomplish primary colors. The most common solution will be Red, Green, and Blue ("RGB") sub-pixel patterns that are independently addressable.

FV TFT Structure

Free-View ("FV") Thin-Film Transistor ("TFT") Displays have a fundamental difference in the Liquid Crystal ("LC") layer. FV TFTs use various approaches to vertical alignment. This means that the LC fluid rotates perpendicular the glass plane vertically. One of the most important advantages of this is the removal of linear polarizing films that create asymmetrical viewing angles. Other thin films will often be used for controlling reflected light and improving contrast, but these may be circular polarizers or other solutions.

Free-View technology would encompass all similar vertically-aligned technologies such as In-Plane Switching ("IPS"), Advanced Fringe Field Switching ("AFFS"), Multi-Domain Vertical Alignment ("MVA"), Patterned Vertical Alignment ("PVA"), Advanced Super View ("ASV"), Plane Line Switching ("PLS"), and other panel related technologies. OSD Displays would procure licensed TFT cell from authorized channels to incorporate into various free-view display module solutions.

Basic TFT Function

The transistor in a TFT display functionally is similar to a Metal Oxide Semiconductor Field Effect Transistor ("MOSFET"), but structurally utilizes non-metal substrates. For displays, the substrate of choice is glass with ITO similar to traditional LCD products. The TFT must utilize amorphous silicon ("a-Si") or Low-Temperature Poly-Silicon ("LTPS") for the transistor substrate. This silicon is deposited on glass in a thin layer along with dielectric material in the glass processing stage. An very basic summary of TFT function can be referencing the T + C² architecture. The transistor acts in a switchlike functionality for each pixel. The liquid crystal capacitor ("Clc") is the capacitance formed in structure by parallel plates of the display and common electrodes that drains into the common voltage ("Vcom"). Since the voltage in the LCD panel will drain, the storage capacitor ("Cst") is added to maintain the voltage across the cell during the panel refresh cycle.

Photolithography

Photolithography is a common process for optical electronics of putting transparent circuitry on glass substrate. The circuit is a fine layer of Indium Tin Oxide ("ITO") which serves as conductive circuit on the glass with minimal observability. The process is performed in a cleanroom under light-sensitive conditions. The general process includes application of photoresist to determine where ITO is allowed, controlled exposure and development baking stage, and removal of the photoresist materials. There are many cleaning stages throughout this process.

IC Bonding

LCD products may be directly driven by a customer processor, but many panel designs will have substantial quantities of pixels or segments to multiplex. For this consideration, many designs will incorporate an application-specific integrated circuit ("ASIC"), commonly just referred to as the display driver IC. These ICs must be paired to provide the correct number of segments & commons for drive of the panel and equally provide the correct power and drive techniques for avoiding accumulation of charge in the panel structure. Display drivers can support various interface protocols and standards. These semiconductors can be bonded by Chip-On-Glass ("COG"), Chip-On-Flex ("COF"), and Chip-On-Board ("COB") bonding methods. Most modern displays are migrating towards compact COG driver packages for cost efficiency.

Interconnect Bonding

Custom LCD solutions may have various interconnection options for your system. TFT Displays natively will be designed for a bonded interconnection option such as flexible printed circuit ("FPC"). Flex-to-glass bonding is accomplished with Anisotropic Conductive Film ("ACF") that is a durable conductive adhesive between the glass and film attachment area. After bonding, it is common for electrical insulation, limiting environmental exposure, and strain relief material to be applied over the bond area on the glass and FPC. Common material for securing the bond area include Room Temperature Vulcanized ("RTV") silicone which allows for improved quality in storage, handling, and subsequent module integration processes. These interconnects may be customized for specific pin assignments, consolidation with touch panel and backlighting, and designed to pair with interface boards such as HDMI, eDP DisplayPort, and other interface-to-interface conversion board solutions for system compatibility requirements.

Backlighting

TFT Displays are nearly exclusively utilizing white light emitting diode ("LED") backlight technology. LED backlights primarily use light guides to optically diffuse the light across the surface area of the LCD. Light boxes are internally reflecting, have rear reflection gradients based on LED arrangement, and have diffuser and/or brightness enhancement film ("BEF") layers for uniformity and blending purposes. Premium materials can combine these film layers for lower light attenuation. TFT Displays may frequently seek high-intensity, or sunlight readable, configurations that may exceed 800 cd/m² (a.k.a. "nits"). Backlighting can also seek increased lifecycle ratings such as 50,000 hours of operation life. OSD also may have select designs with integrated backlight enable pins for external controllers, or backlight power drivers integrated. Solutions may be customized or sourced to meet customer requirements.

Module Assembly

Liquid Crystal Modules ("LCM") for TFT panels include the TFT display with integrated driver, backlighting, frames, optional touchscreens, and driving electronics. Our factory has some industry standard configurations, but the many of our customers will encounter specific combinations of backlighting, touch, display, frames, and interconnection preference combinations. Some applications may seek additional value-added user-interface ("UI") needs including buttons, touchscreens, temperature or other sensors, cameras, and other system components adjacent to the display. Our factory is able to integrate the displays from simple modules, UI subassembly, reaching complex full box builds or enclosed monitors. OSD's value proposition sources from our ability to leverage off-the-shelf ("OTS") materials as often as possible to minimize tooling costs, unit pricing, and development time whenever possible.

Quality & Packaging

At the end of our assembly, the final stage is all about our customers. Throughout the display process, various components are tested individually and as subsystems, but the final product is also inspected. OSD Performs 100% inspection on LCD modules including cosmetic, functional, and conformance tests. We maintain a continuous-improvement quality system compatible with our ISO certifications. We additionally are able to cooperate with customers implementing specific test fixtures, or standards, agreed in specification. The completed and tested glass-based product is then focused on protective packaging and preparation for transport globally. Protective packaging can often be custom designed for LCDs and we have packaging design specialists to work with our customers to define this packaging to various levels of requirements . Many items will have customized packaging specifications that can be discussed depending on program requirements. OSD is able to accommodate customer-specified cartons, trays, resale packaging, carton labels with customized inventory management labels, and much more to integrate with the customer's supply chain.