ELECTRICALLY CONTROLLED INTERFERENCE COLOR FILTER AND THE USE THEREOF

Abstract

The invention relates to an electrically controlled interference colour filter comprising at least two transparent electrodes, at least one nematic liquid crystal layer and alignment layers for alignment of the liquid crystals. When an electrical field is applied the liquid crystals can be realigned and thus the transmission wavelength range of the interference colour filter can be shifted.

Claims

1-14. (canceled)

15. An electrically controllable interference colour filter, comprising at least two transparent electrodes, at least one orientation layer and a nematic liquid crystal layer, the nematic liquid crystal layer and the at least one orientation layer are in direct contact for orientation of the liquid crystals wherein, the transmission wavelength range of the interference colour filter is displaceable by applying an electrical field or by reorientation of the liquid crystals.

16. The interference colour filter according to claim 15, wherein the nematic liquid crystal layer has a layer thickness in the range of 100 nm to 1,000 nm.

17. The interference colour filter according to claim 15, wherein the nematic liquid crystal layer comprises liquid crystals selected from the group consisting of biphenyls, terphenyls, quaterphenyls, and tolanes.

18. The interference colour filter according to claim 15, wherein the nematic liquid crystal layer is in direct contact at both surfaces with respectively one orientation layer.

19. The interference colour filter according to claim 15, wherein the at least one orientation layer is selected from the group consisting of photoreactive ethene groups, coumar-, phenylacryl-, 2-(2-furyl)acryl-3-(2-thienyl)acryl- and trans-stilbene derivatives.

20. The interference colour filter according to claim 15, wherein the at least one orientation layer is monomolecular and bonded chemically covalently to the at least one dielectric reflective layer.

21. The interference colour filter according to claim 15, wherein the interface tension of the at least one orientation layer corresponds to the interface tension of the nematic liquid crystal layer, with a difference in interface tension of at most 1 mN/m.

22. The interference colour filter according to claim 15, wherein the interference colour filter has a distance layer and has at least one recess which receives the nematic liquid crystal layer.

23. The interference colour filter according to claim 15, wherein the interference colour filter has at least one dielectric reflective layer.

24. The interference colour filter according to claim 23, wherein the at least one dielectric reflective layer consists of a several pairs of layers made of a material with a refractive index<1.5 and a material with a refractive index>2.0.

25. The interference colour filter according to claim 23, wherein the dielectric reflective layers are integrated on the side of the transparent electrodes which is orientated towards the nematic liquid crystal layer, on the side of the transparent electrodes which is orientated away from the nematic liquid crystal layer or the transparent electrodes are integrated in the dielectric reflective layers.

26. The interference colour filter according to claim 15, wherein the transparent electrodes comprise a transparent electrically conductive material or consist thereof.

27. The interference colour filter according to claim 24, wherein the material with a refractive index<1.5 is SiO.sub.2 and the material with a refractive index>2.0 is Ta.sub.2O.sub.5, Nb.sub.2O.sub.5 or TiO.sub.2.

28. The interference colour filter according to claim 26, wherein the transparent electrically conductive material is selected from the group consisting of indium-tin oxide (ITO), aluminium-doped zinc oxide (AZO), fluorine-tin oxide (FTO), antimony-tin oxide (ATO), graphene, silver nanowires, and carbon nanotubes.

29. The interference colour filter according to claim 17, wherein the nematic liquid crystal layer comprises liquid crystals selected from the group consisting of substituted cyano, fluoro-, isothiocyanates of biphenylene, terphenylene, quaterphenylene or tolanes.

Description

[0019] FIG. 1 shows the schematic construction of an interference colour filter according to the invention.

[0020] FIG. 2 shows various structures for components used according to the invention for the orientation layer.

[0021] FIG. 3 shows, with reference to a diagram, the displacement of the transmission range of an interference colour filter according to the invention in a spectral range not used for light transmission.

[0022] In FIG. 1, an interference colour filter according to the invention is illustrated, which filter has two orientation layers (105) and (105′), between which a nematic liquid crystal layer (106) is disposed. The thickness of the nematic liquid crystal layer (106) is thereby defined by the surrounding distance layer (104). On the side of the orientation layers (105) and (105′) which is orientated away from the nematic liquid crystal layer (106), the dielectric reflective layers (103) and (103′) are respectively disposed. On these in turn, the transparent electrodes (102) and (102′) are deposited. In addition, the interference colour filter according to the invention also has outer carrier layers (101) and (101′).

EXAMPLE 1

[0023] Example 1 relates to an electrically controllable interference colour filter designed for green light with a wavelength of 575 nm.

[0024] For the example, commercial ITO glasses of the company Präzisions Glas & Optik GmbH (CEC050P) were used with a surface resistance of 40 Ω/□. The transmission of the ITO glass is 80% at 450 nm and 87% at 700 nm. Two of these ITO glasses are coated respectively with a dielectric reflective layer (103) which is designed for a wavelength of 575 nm. The dielectric reflective layer consists of four SiO.sub.2— and four Ta.sub.2O.sub.5 layers which are sputtered on in an alternate layer sequence starting with SiO.sub.2 (S[HL]̂4 H-575 nm).

[0025] On the first of the two produced ITO glasses with reflective layer, trans-3-(3-(5-chloropentyloxy)phenyl)acrylic acid phenyl ester is subsequently bonded, in the immersion process, covalently to the reflective layer surface, as a result of which a monomolecular organic layer with photoreactive ethene groups is formed. By photochemical crosslinking with linear polarised light, the structured surface of the orientation layer (105) is produced therefrom. Elipsometric measurements show that the thickness of the orientation layer, as to be expected for a monomolecular layer, is below the detection limit of 2 nm, as a condition of the process.

[0026] On the second ITO glass provided with the reflective layer, the distance layer (104) is applied in the form of two webs on opposite ends of the substrate. A recess is thereby produced in the centre of the substrate and, after assembly of the two half-cells (ITO glass+reflective layer+orientation layer/ITO glass+reflective layer+distance layer), forms the cavity into which the liquid crystal layer (106) is filled. In order to be able to adjust exactly the ultrathin distance layer (104) and hence the resulting ultrathin liquid crystal layer (106), the distance layer is produced in the sputtering process, the cavity surface being covered by a mask. For the present embodiment, SiO.sub.2 was sputtered on with a layer thickness of 753 nm. A LC layer is produced with analogously 753 nm.

[0027] Both half-cells (ITO glass+reflective layer+orientation layer/ITO glass+reflective layer+distance layer) are joined, plane-parallel, according to a conventional LCD-assembly technique, to form the interference filter.

[0028] The cavity of the interference filter is filled with a nematic liquid crystal in the last step. In the present embodiment, a eutectic liquid crystal mixture was used of this purpose, which mixture has a nematic phase with Δn=6% at room temperature and the interface tension of which is adapted to that of the orientation layer, Δγ=γOS−γLC=0.8 mN/m.

[0029] The thus produced colour filter can be connected to the ITO electrodes thereof by applying a voltage of 11 V. The switching times of the colour filter are, with t.sub.on=580 μs and, for t.sub.off=1.33 ms, in the μs/ms range. If a monochromatic or narrow-band light (LED or laser diode) with a central wavelength of 575 nm is used as backlight, the switching effect of the cell is associated with a switching effect which is clearly visible to the naked eye of green to black. In the “off” state, the colour filter is transparent for light of wavelength 575 nm, whereas, in the “on” state, the backlight is blocked practically completely. The transmission wavelength in the “on” state is in the unused spectral range. The transmission spectra of the colour filter in the “off” and “on” state for the wavelength range of 520 nm to 600 nm are shown in image 3. These spectra were measured with nonpolarised light. In the “off” state, the colour filter has, in the observed wavelength range, two transmission peaks with maxima at 545 nm and 575 nm. The range therebetween is defined as free spectral range. As a function of the applied voltage, the peak is displaced continuously from 575 nm to 545 nm.

EXAMPLE 2

[0030] Example 2 is an electrically controllable interference colour filter designed for blue light with a wavelength of 450 nm. Embodiment 2 was produced analogously to embodiment 1. For adaptation to the changed transmission wavelength, firstly the thickness of the SiO.sub.2 and Ta.sub.2O.sub.5 layers of the reflective layer (103) was changed to 76.36 nm (SiO.sub.2)/51.07 nm (Ta.sub.2O.sub.5) and secondly the thickness of the spacer layer to 558 nm. The thus produced colour filter switches at a voltage of 9.2 V at the ITO electrodes thereof. With a monochromatic backlight, the colour filter switches from blue to black. Likewise as in embodiment 1, the switching effect is clearly visible with the naked eye.

EXAMPLE 3

[0031] Example 3 is an electrically controllable interference colour filter designed for red light with a wavelength of 632 nm. Embodiment 3 was likewise produced analogously to embodiment 1 with adaptation of the thickness of the SiO.sub.2 and Ta.sub.2O.sub.5 layers to 95.53 nm (SiO.sub.2)/64.12 (Ta.sub.2O.sub.5) of the reflective layer and of the thickness of the spacer layer to 798 nm. The thus produced colour filter switches at a voltage of 11.9 V at the ITO electrodes thereof. With a monochromatic backlight, the colour filter switches from red to black. Likewise as in embodiments 1 and 2, the switching effect is clearly visible with the naked eye.

[0032] It is evident to the person skilled in the art that, by changing the selection of the nematic liquid crystal (variation of Δn, Δε, viscosity) of the reflective layer configuration and layer materials (number of pairs of reflective layers, layer thicknesses and dielectric properties of the layers), the thickness of the liquid crystal layer, chemical structure of the monomolecular orientation layer (variation in the interface properties), the switching time and threshold voltage of the electrically controllable filter can be displaced both to higher and to lower values. It is likewise evident that the maximum displacement range of the wavelength is determined by Δn and the used displacement range can be controlled variably via the voltage. The embodiments can be used as single filter or as RGB filter, also in matrix form.