Birefringent Filter-Based Color Generation Scheme for a Passive Matrix Display Device

KSU.213

Abstract: This invention provides a full color liquid crystal display of passive matrix design.  The retardation and orientation of each of the first retarder stack, second retarder stack, and passive matrix- addressed optical element are optimized so as to provide a color generation stage that places desired wavelengths of light substantially along the transmission axis of the analyzer.  We found that light transmissions of 30% were able to be achieved.  The device consists of a stack of 12 bifringent layers and 3 STN devices.  We found that STN devices of the variety known as DSTNs provided the best performance.

Applications:

Applications of this invention are primarily in the area of low power, color, flat panel displays, especially as currently used in personal digital assistants like palm pilots.  We also believe that the concept envisioned of a low cost electronic paper that has full color capabilities and that is produced in an all-plastic semi-flexible design is also made possible by this invention.

Advantages:

The advantage of this technology is the large improvement in light transmission that is achieved, while at the same time maintaining high color purity.  The improvement could allow for a factor of 5 reduction in battery power consumed by the display device that could permit for batteries of 1/5 the weight and volume.  The method of manufacturing the device also has significant advantages.  In a typical conventional color display, each picture element (pixel) is divided into 3 subpixels where each one has a color filter (red, green or blue) placed over it.  This high-resolution placement of color filters is one of the most expensive aspects of producing a color display.  With the display considered here, the color is generated by sheets of plastic film that are laminated, without high resolution patterning, over the entire area of the cell.  Also, because of the subpixels that are used in a conventional display, the patterning of the electrodes and the interconnect density is very high.  In the case of the display considered here, the total number of electrodes is the same, but they are allowed to be spread over 3 times the area, making the display manufacturing of high-resolution displays more practical.

Inventors:  Dr. Salman Saeed and Dr. Philip Bos (Kent State U. LCI)