3M Optical Systems Division

LED Backlights Made Simple—3M™ OneFilm Integrated Optics for LCDby: John Wheatley, 3M Optical Systems Division

the WorldPower that Changes

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Contents

Executive Summary ..........................................................................................................4

Architecture Overview —A Comparison ...........................................................................4

How OneFilm Works .........................................................................................................5

Key Feature Comparison ..................................................................................................6

OneFilm Eliminates Prisms and the Problems They Create ...............................................7

OneFilm Eliminates Prisms and the Problems They Create ...............................................9

Quantifying the Value of Integration —Factory Floor Simulation ........................................10

A Major Improvement in Environmental Impact of Backlights ...........................................11

Conclusion ........................................................................................................................11

Recap: 3M OneFilm Advantages .....................................................................................13

Our Vision—Integrated Optics for All Displays ..................................................................13

About 3M .........................................................................................................................14

References .......................................................................................................................15

4

Architecture Overview —A Comparison

Executive Summary

LED Backlights Made SimpleLED backlights are now used in all sizes of LCDs. They are thin and sleek, and the industry has an installed manufacturing base that allows them to be made by the millions for a host of applications, from smart phones, tablets, and laptops to monitors, televisions and signs. Their key drawbacks are that they are much more complex and costly than they need to be, and they needlessly generate many millions of pounds of plastic waste every year, compared to the alternative.

This paper discusses that alternative: 3M™ OneFilm is a radically simple approach for LED backlights based on a recent advance from 3M. Unlike today’s backlights—which require multiple films to diffuse, collimate, and polarize light—OneFilm combines all functions in a single film. The film is also very compatible with the industry’s installed manufacturing base; it is placed in the backlight as a free-floating film during assembly, in the same way that current films are applied.

Since conventional backlights use 3–4 separate films, the use of 3M OneFilm greatly reduces the number of components, assembly time, thickness, weight, and waste. It also simplifies and shortens the supply chain and reduces inventory and the labor required for assembly.

As a result, OneFilm provides multiple opportunities for cost reduction, from material costs to the simplification of design, inspection, and assembly.

From a performance standpoint, OneFilm is comparable to conventional systems (as measured by Nits/W) and exceeds conventional systems in wide-angle luminance—a benefit of particular importance in TVs and LCD signage, and devices where a shared viewing experience is key.

OneFilm also allows manufacturers to eliminate one or more prism films; this enhances the viewing experience by allowing a monotonic (i.e., a smoothly and gradually decreasing) change of luminance as the viewing angle changes. This effect is difficult to achieve with prism films, which tend to cause abrupt changes in luminance.

Our experience is that viewers prefer displays with OneFilm over conventional displays. We attribute this preference to the improved wide-angle luminance and the monotonic change in luminance.

In addition to these cost and performance advantages, OneFilm allows display manufacturers to make a notable—indeed, remarkable—improvement in the environmental profile of their products. It allows manufacturers to eliminate some 70 million pounds of plastic from the industry waste stream annually.

Traditional Display Architecture Display with OneFilm

Prism/microlens

LCD Panel

Light Guide

Reflector/Chassis

Reflective Polarizer Diffuser

LEDs OneFilm

Illustration 1Traditional Multi-film and New Single Film Backlight

A conventional LCD backlight architecture is shown on the left of Illustration 1. It consists of a back reflector mounted on the chassis, followed by a solid light guide, one or more diffuser and prism films, and a reflective polarizer. The final element is the LCD panel.

The OneFilm architecture is on the right. It consists of a single film, a light guide and conventional white back reflector mounted on the chassis. All other films—the diffuser film(s), prism film(s), and the reflective polarizer—are eliminated.

5

How OneFilm Works

5

OneFilm

Light Guide

Illustration 23M OneFilm’s angle-selective optics provide collimated polarized light.

OneFilm is based on 3M’s new Collimating Multilayer Optical Film (CMOF) technology, which enables a new class of optical film that provides the functionality of a diffuser, a prism/microlens film, and a reflective polarizer1-3. As a result, for the first time, LCDs with highly integrated optics are possible with a single free-floating film.

Rather than refracting, OneFilm collimates light by preferentially reflecting higher angle light back to the recycling cavity, while providing higher transmission for light closer to normal incidence. Wide-angle luminance and system level efficiencies are comparable to or exceed those of conventional multi-film backlights as shown in later examples.

OneFilm is based on 3M’s Multilayer Optical Film technology, which brought products such as 3M DBEF and 3M APF to the LCD industry.

Illustration 33M’s Multilayer Optical Film

technology, featured in the journal Science4

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Key Feature Comparison

Category Conventional( BD/Crossed Prism)

OneFilm

Number of free floating components 3–4 1

Assembly steps 3–4 1

Labor X 0.3X

On-axis brightness Similar Similar

Total light output X 1.55X

Table1Key feature comparison, conventional vs. OneFilm backlights

8.0

25 30 35 40 45 50

7.5

7.0

6.5

6.0

Horizontal Half Luminance Angle (degrees)

OneFilm

Beaded Diffuser/Crossed Prism

Microlens/Prism/Cover Sheet

Disp

lay

Effic

acy

(Nits

/W)

Illustration 4. Efficacy vs. Half Luminance angle for OneFilm and traditional multi-film stacks,

showing OneFilm has both a broad viewing angle and a display efficacy that compares favorably to conventional systems.

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OneFilm Eliminates Prisms and the Problems They Create

Prism films have been used for years in displays but cause many compromises in system design and cost. They also affect certain performance characteristics, including wide-angle luminance. Specifically, prisms typically cause abrupt changes in brightness as a function of viewing angle, as shown in Illustration 5.

3 Film Stack Beaded Diffuser/xPrism OneFilm

Illustration 5Luminance conoscopic plot comparison of 3-film stack and OneFilm

showing that OneFilm provides a much broader viewing angle with similar on-axis brightness.

Illustration 6Angular luminance detail showing monotonic characteristics of

3M OneFilm vs. crossed prism films, which is abrupt and has inversion.

Note in Illustration 6 how smooth and monotonic the OneFilm viewing angle is compared to the crossed prism films. OneFilm provides a superior viewing experience and 55% more total light output. Recent scientific studies have shown a significant consumer preference for broad viewing angle displays.5

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In addition to luminance fall-off, prisms cause many other issues affecting display quality and cost (Table 2). For example, prisms can be damaged or cause damage to other optical components (including the LCD panel) in assembly, transit, or use. Also, their periodic structure and geometry can create spatial interference patterns (moiré) and color mura, imposing constraints on the choice of panel type or other backlight films. This can introduce costly complications such as the need to introduce a bias (in-plane rotation) of the film in order to minimize these effects. Particularly in mobile devices, the need to pair appropriate panel pixel pitch to prism pitch severely limits design flexibility, development speed, and part yield. It also causes a substantial proliferation of parts (SKUs). Table 2 below summarizes these and other issues.6

Table 2Prism Related Issues

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3M OneFilm creates significant opportunities for improving the efficiency of LCD manufacturing. The top schematic of Illustration 7 shows the current LCD supply chain with a focus on the backlight materials. Today, three to four different components are supplied to the OEM. For each there are multiple steps including raw material manufacture, yielded material losses in article fabrication, packaging, and energy used for transportation by land, sea, and air. In contrast, OneFilm greatly streamlines the overall process; it reduces steps, costs and waste.

Panel Makers Integrators Brands Retailers Consumers

Cover Sheet Converting

Prism/mLens Converting

Microlens Converting

Cover Sheet Fabrication

Prism/mLensFabrication

Microlens Fabrication

Cover Sheet Materials

Prism/mLens Materials

Microlens Materials

Panel Makers Integrators Brands Retailers Consumers

OneFilm Converting

OneFilmFabrication

OneFilm Materials

Supply Chain Today

Multiple materials, inspections, assembly steps, waste sources

New Supply Chain

Streamlined, minimal materials, minimal steps

Illustration 7Supply chain efficiencies, conventional vs. OneFilm backlights

Material Suppliers

A Radical Simplification of the LCD Supply Chain

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A process simulation of a OneFilm display factory compared to a conventional three-film factory is shown in Illustration 8.7 We chose what we felt were a reasonable set of assumptions for operators, assembly steps and times, scrap and reject rates. Though each factory is unique, the results clearly indicate that large improvements in throughput, scrap, and labor efficiency are possible. This represents many opportunities for cost reduction. 3M works with customers to apply this type of analysis to specific situations and metrics of interest.

Quantifying the Value of Integration —Factory Floor Simulation

Illustration 8Factory Floor Model of OneFilm vs. Traditional Factory

1111

The resulting material reduction can be dramatic. We estimate that changing from a multi-film system to OneFilm could reduce waste by approximately 70%. For the industry as a whole, this means approximately 70 million pounds (32 million kg) of plastic could be eliminated (Illustration 9).

It is now possible to make LCD backlights using only one free-floating film. This enables multiple cost-down, best-in-class system value propositions including: fewest parts, thinnest, lightest weight, and lowest amount of material (Illustration 10). Integration, as shown here with OneFilm, provides simplification in all aspects from product design to supply chain to the factory floor. This presents a rare opportunity to provide new value propositions to consumers and to make non-incremental advancements in the environmental profile of LCD display technology.

A Major Improvement in Environmental Impact of Backlights

Conclusion

Illustration 9Industry-wide material reduction potential with OneFilm8-9

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Illustration 103M OneFilm simplifies all aspects of product development and manufacturing, from product design to supply chain to the factory floor.

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Illustration 11The 3M Portfolio of Solutions for LCD Integrated Optics

Cost reduction Fewer components, fewer inspection steps, streamlined factory floor and supply chain operations.

Waste stream reduction Cuts the amount of plastic used for optical films by up to 70%.

Robustness Prism-related issues such as moiré and rainbow mura are eliminated.

Energy efficiency ENERGY STAR compatible.

Broad luminance angle Suitable for monitor, TV, signage, or mobile devices.

Monotonic luminance angle A noticeably superior viewing experience.

Scalable For all size displays.

Manufacturing flexibility OneFilm can be used on multiple types and sizes of displays. Assembly time is reduced.

No change in backlight assembly method

OneFilm backlight assembly is done in the traditional way.

Number of SKUs The inspection, handling, waste, and assembly of multiple films is reduced by as much as 75%.

Thickness reduction Display thickness can be reduced due to elimination of several films and their respective “z-gaps.”

Weight reduction Removal of several free-floating films reduces weight by about one pound (454 g) in a 52" TV.

Recap: 3M OneFilm Advantages

Our Vision—Integrated Optics for All Displays

New Integrated Optics Architectures

On-Panel for Edge-Lit

OneFilm

On-Panel for Direct-lit

Conventional Backlight Architecture

Prism/microlens

LCD Panel

Light Guide

Box/Chassis

Reflective Polarizer

Diffuser Reflector

OneFilm

3M has a portfolio of solutions to enable the industry to realize the benefits of integrated optics. These include the free-floating OneFilm, as well as on-panel integration for direct and edge-lit systems (Illustration 11). For more information please contact 3M Optical Systems Division.

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About 3M

3M is a member of the Sustainability Consortium Electronics Sector Working Group. The Sustainability Consortium is an independent organization of diverse global participants who work collaboratively to build a scientific foundation that drives innovation to improve consumer product sustainability through all stages of a product’s life cycle. The Sustainability Consortium develops transparent methodologies, tools and strategies to drive a new generation of products and supply networks that address environmental, social and economic imperatives.10

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References

1. T. Liu et. al., SID ’09 Digest, 55.1, Edge-lit Hollow Backlight Using Tunable Reflective Polarizer for LCD Displays.2. J. Wheatley et. al., Optics Express, Vol. 17, 2009, Efficient LED Light Distribution Cavities using Low Loss, Angle-Selective

Interference Transflectors.3. J. Wheatley et. al, SID ’11 Digest, 60.1, LCD Integrated Optics.4. M. Weber, et. al., Science, March 2000: Vol. 287 no. 5462 pp. 2451-2456.5. 3M White Paper on Broad Viewing Angle, 2012.6. J. Wheatley et. al., SID ’12 Digest, Invited Paper, Greener Displays through Integrated Optics: Display Backlights using

OneFilm.7. Lanner Witness software, Forward House, 17 High Street, Henley-in-Arden, Warwickshire, B95 %AA, UK.8. Seung-Jin Lee and Joyce Cooper, Estimating Regional Material Flows for LCDs, Proceedings of the IEEE International

Symposium on Electronics and the Environment ISEE (May 2008).9. 3M White Papers on Sustainability, 2011-2012.10. The Sustainability Consortium, www.sustainabilityconsortium.org.

John Wheatley, Division Scientist, 3M Optical Systems Division, jwheatley1@mmm.com.

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