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Transflective LCD with more flexible filter design

IP.com Disclosure Number: IPCOM000030855D
Publication Date: 2004-Aug-30
Document File: 5 page(s) / 472K

Publishing Venue

The IP.com Prior Art Database

Abstract

ID698080

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Transflective LCD with more flexible color filter design

Summary

The use of transflective color displays is gaining huge momentum in the mobile phone industry and market. In such displays a good balance between color performance and brightness in both reflective (low power standby mode) and transmissive mode is very important for the end-user. In order to reduce the time-to-market, lower the development and production cost of color filters that are needed to create display solutions for mobile phone makers in accordance to their color-performance requirements, the use of a modified multi-thickness color filter design is proposed. The modified color filter design creates much more flexibility to develop a required color performance and does not add any costs.

Most of the color displays in today's mobile phones are transflective, which makes them well readable under all ambient light conditions. However, the transflective type LCD has a problem of different color purity between reflective and transmissive mode. In a conventionally designed transflective display with the same color filter thickness for the reflective and transmissive areas of the pixels, the color purity in reflective mode is higher than in transmissive mode. The reason is that in reflective mode the light passes the color filter twice; in transmissive mode only once (fig.1a).

Transmissive mode

Glass

ITO

Liquid crystal ITO

Colour filter Internal reflector Glass

Reflective mode

Figure 1a conventional transflective design with the same color filter thickness in the reflective and transmissive area.

Several types of color filters have been developed and described to match the color reproduction area between reflective and transmissive mode. The multi-thickness color filter type (MT-CF type) has a different color filter resin thickness in reflective (trefl) and transmissive mode(ttransm); see Figure 1b.

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Glass

ITO

Liquid crystal ITO

Colour filter Internal reflector Glass

Reflective mode

Figure 1b example of a MultiThickness (MT) color filter. In the reflective area the color filter thickness is the summation of the thickness of a colorless transparent resist and the color filter resist. The transparent colorless resist covers the whole reflective area.

The MT-technology is based on having a constant resin height 'ttotal' for the reflective and transmissive part per color dot. In case of the reflective part, the total resin height can be split into a part consisting of actual color filter resin (as is used in the transmissive part) and a part consisting of colorless transparent resist, hence: 'ttotal = trefl + tcolorless resin = ttransm

By adapting the thickness in transmissive and reflective mode the color purity, the transmittance and reflectance can be optimized to give the desired performance. The difference in thickness is achieved by positioning an island of colorless transparent resin within a do...