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A memory-type colour reflective display device is proposed. Introducing smectic liquid crystal to holographic polymer dispersed liquid crystal (HPDLC) successfully produced a memory function while keeping the advantages of HPDLC. This device is electrically writable and thermally erasable. It was able to maintain the memory state for more than 4 months. The mechanism of the memory function was analysed by comparing three HPDLC devices which were made with three different cyano-biphenyl compounds. The compounds had similar molecular structures but different phase transition temperatures. Small passive matrix devices for three primary colour devices were successfully demonstrated and colour mixing was confirmed to occur on stacking.

The memory-mode operation of a polymer dispersed liquid crystal (PDLC), which depends on the stiffness of the layer structure in the smectic-A phase, has been analysed by comparing ordinary PDLC and holographic PDLC (HPDLC). Although both PDLC films were fabricated from the same material, the temperature range of the memory-mode operation was lower in the HPDLC than in the ordinary PDLC. In calorimetric analysis, the differential scanning calorimeter curves of the ordinary and holographic PDLC films were the same. Therefore, the liquid-crystal phase does not depend on the structural difference. This suggests that the force exerted against the layer structure of the smectic phase is greater in HPDLC because the droplet size is smaller and the ratio of the surface to volume is higher.

Abstract— A method of controlling the color of a holographic polymer‐dispersed liquid‐crystal (HPDLC) reflective display device has been achieved. By merely controlling the optical setup during fabrication, without changing the materials or laser light source, three primary‐color devices were fabricated. Since the color of the device can be controlled continuously, a large color‐reproducible area on the chromaticity diagram can be obtained. The resulting device was adequately transparent at other wavelengths to enable multiple devices to be stacked to obtain a mixture of colors. There was no significant change in color when applying an electric field. The three devices had similar reflectances and electro‐optical characteristics. Therefore, this device has good potential for full‐color display applications.

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