GB2351834A

GB2351834A - Liquid crystal display

Info

Publication number: GB2351834A
Application number: GB0016451A
Authority: GB
Inventors: Eiichi Fukiharu
Original assignee: NEC Corp
Current assignee: NEC Corp
Priority date: 1999-07-06
Filing date: 2000-07-04
Publication date: 2001-01-10
Anticipated expiration: 2020-07-04
Also published as: GB0016451D0; JP2001021883A; GB2351834B

Abstract

A reflection type liquid-crystal display has two opposed substrates 1,2, a liquid-crystal layer between the two opposed substrates, and lighting means at its front face. A first substrate 1 nearer to an observer of the reflection type liquid-crystal display than the other of the two opposed substrates has an uneven surface 12 on the observer's side that provides light-guiding means for the front light, the front light incorporating the first substrate and a light source 10 that is placed at the side of the first substrate. A portable telephone having the above reflection type liquid-crystal display is also described.

Description

2351834 LIQUID-CRYSTAL DISPLAY AND ELECTRONIC DEVICE INCORPORATING THE

DISPLAY This invention relates to a reflection type liquid-crystal display and an electronic device employing the reflection type liquid-crystal display.

Previously proposed liquid-crystal displays can be classified into a type having a transmission type liquid-crystal display and a type having a reflection type liquid-crystal display.

In the transmission liquid-crystal display, a back light is placed at the rear of a liquid-crystal cell.

On the other hand, the reflection type liquid-crystal display uses ambient light in creating a display. Therefore, it has advantages that no back light is necessary and that its electric power consumption is therefore small.

Because of this, in considering the type of liquid-crystal display to be employed in an electrical device, such as a portable telephone, a reflection type liquid-crystal display with small electric power consumption is preferable However, the reflection type liquid-crystal display may give a display to its user which is unrecognizable especially in darkness and at night, since it uses ambient light and its visibility is highly dependent on the surrounding environment. Especially in a reflection type liquid-crystal display using a colour filter for colourization, the above problem is serious. So, in order to cope in the case in which the ambient light is not sufficient, an electronic device, such as a portable telephone, needs to have a reflection type liquidcrystal display to the front side of which there is a front light.

Referring to the accompanying drawings, there is shown in FIG. 1 a diagrammatic cross sectional view of a previously proposed reflection type liquid-crystal display, and in FIG. 2 a diagrammatic cross sectional view of a portable telephone.

The reflection type liquid-crystal display shown in FIG.1 includes a glass substrate 21, a glass substrate 22, a polarizing plate 23 that transmits a specific polarized component of light from a front light, a phase-contrast plate 24 for conducting optical compensation, a diffusion plate 25 that diffuses light from the front light, a colour filter 26 of three primary colours, a transparent electrode 27 that has a light-transmitting characteristic, a liquidcrystal layer 28, and a reflecting electrode 29 that reflects light transmitted through the liquid-crystal layer 28. Further, the reflection type liquid-crystal display has a light source 30, a reflecting member 31 and a light-guiding plate 32 which form the front light.

Light emitted from the light source 30 is either supplied directly to the light-guiding plate 32, or it is reflected by the reflecting member 31 and then supplied to the light-guiding plate 32. A part of the light supplied to the side from the light source 30 is reflected by the light-guiding plate 32, and supplied to the polarizing plate 23.

Thus, the previously proposed reflection type liquid-Mstal display has a structure in which the light-guiding plate 32 of the front light is placed on the front face of a liquid-crystal display. Therefore, there is the problem that 3 the reflection type liquid-crystal display becomes thick and heavy.

Referring to the cross sectional view shown in Fig. 2 of a previously proposed portable telephone having a reflection type liquid-crystal display as shown in FIG.1, it may be seen that the telephone has a front cover 34 placed on the front face of the reflection type liquid-crystal display, and that there is the problem that the portable telephone becomes thick and heavy.

Arrangements to be described below by way of example in illustration of the invention are a significantly thinned and lightened reflection type liquid-crystal display, and an electronic device having a reflection type liquid- crystal display that is significantly thinned and lightened.

In a particular arrangement to be described below, by way of example in illustration of the invention, a reflection type liquid-crystal display has two opposed substrates, a liquid-crystal layer between the two opposed substrates, and a front light as a lighting means at the front face of the reflection type liquid-crystal display, wherein a first substrate nearer to an observer of the reflection type liquid-crystal display than the other of the two opposed substrates has an uneven surface on the observer side that functions as a light-guiding means for the front light, the front light including the first substrate and a light source that is placed at the side of the first substrate.

An electronic device to be described below by way of example in illustration of the invention includes a reflection type liquid-crystal display having two opposed substrates, a liquid-crystal layer formed between the two opposed substrates, and a front light as a lighting means at the front 4 face of the reflection type liquid-crystal display, wherein a first substrate nearer to an observer of the reflection type liquid-crystal display than the other of the two opposed substrates has an uneven surface on the observer side that functions as a light-guiding means for the front light, the front light including the first substrate and a light source that is placed at the side of the first substrate, and the reflection type liquid-crystal display being attached to the housing of the electronic device so that the first substrate is exposed.

Arrangements illustrative of the invention will now be described by way of example with reference to Figs. 3 to 7 of the accompanying drawings, in which:

Fig. 3 is a cross sectional view showing a reflection type liquid-crystal display in a first preferred arrangement, FIG. 4 is a cross sectional view showing an enlarged portion A of the reflection type liquid-crystal display shown in FIG.3, FIG. 5 is a cross sectional view showing a reflection type liquid-crystal display in a second preferred arrangement, FIG. 6 is a schematic diagram showing a portable telephone having a reflection type liquid-crystal display in a third preferred arrangement, and FIG. 7 is a cross sectional view showing an enlarged part B of FIG. 6 taken along the line C-C' in FIG.6.

Referring to Fig. 3, there is shown a reflection type liquid-crystal display having a polarizing plate 3 that transmits a specific polarized component of light from a front light, a phase-contrast plate 4 for optical compensation, a diffusing plate 5 that diffuses light from the front light, a colour filter 6 of three primary colours, a transparent electrode 7 that has a light-transmitting characteristic, a liquidcrystal layer 8, and a reflecting electrode 9 that reflects light transmitted through the liquid-crystal layer 8, which are arranged sequentially from the display-observing side (from the top in FIG. 3) between a glass substrate 1 and a glass substrate 2.

Further, the reflection type liquid-crystal display has a light source 10 that is placed along the side of the glass substrate 1, and a reflecting member 11 that converges light from the light source 10 only on the side of the glass substrate 1. The glass substrate 1, the light source 10 and the reflecting member 11 constitute the front light.

As the light source 10, a cold-cathode tube is generally used. However, when the reflection type liquid-crystal display is mounted in an electronic device, such as a portable telephone, where compactness and lightness are important, a light-emitting diode that needs no inverter circuit is suitable.

The reflecting member 11 is arranged so that the side of the light source 10 and the glass substrate 1 are completely covered. The sectional form is a quadratic curve, at the focal point of which the light source 10 is placed.

One method of making the reflection type liquid-crystal display shown in FIG. 3 will now be described. Referring to FIG. 4, the polarizing plate 3, the phase-contrast plate 4, the diffusing plate 5, the colour filter 6, the transparent electrode 7, the liquid-Mstal layer 8 and the reflecting electrode 6 9 are omitted.

In a first step, the polarizing plate 3, the phase-contrast plate 4 and the diffusing plate 5 that are of light-transmitting resin are laminated in sequence on the transparent glass substrate 1, and further the colour filter 6 that is of coloured resin dyes or pigments with three primary colours R (red), C (green) and B (blue) and the transparent electrode 7 of ITO (indium tin oxide) etc. are laminated in sequence on the diffusing plate 5.

Before forming this laminated structure, an uneven surface 12 is formed, in advance, on the opposite face to the face of the glass substrate 1 on which the lamination structure is formed. The uneven surface 12 is composed of 1 to 100 gm deep grooves 12a that are arranged at certain intervals, and slope sections 12b that form the wall of the groove 12a. Of the uneven surface 12, part (including the bottom of the groove 12a) except the slope section 12b forms a flat section 12c. The uneven surface 12 thus shaped may be formed by etching, or in any other suitable way.

On the other hand, the reflecting electrode 9 of Al etc. is formed on the transparent glass substrate 2 with a light-transmitting characteristic.

Then, the glass substrate 1 and the glass substrate 2 are caused to adhere to each other while making the transparent electrode 7 opposite to the reflecting electrode 9. In this case, a clearance with a given height is formed by a spacer between the transparent electrode 7 and the reflecting electrode 9. The liquid-crystal layer 8 is formed by injecting liquid crystal into the clearance.

Finally, the light source 10 and the reflecting member 11 covering the 7 light source 10 are attached at the side of the glass substrate 1. Thus, the reflection type liquid-crystal display is made.

The operation of the reflection type liquid-crystal display thus made will now be described.

Part of the light emitted from the light source 10 in all directions is applied to the side of the glass substrate 1 and the remainder is applied to the reflecting plate 11. Light applied to the reflecting plate 11, whose sectional form is a quadratic curve, reflects in the parallel direction to the centre line of the quadratic curve, and is applied to the side of the glass substrate 1.

Then, a part of the light applied to the glass substrate 1 is applied to the interface of the glass substrate 1 and its peripheral media. The interface includes an upper interface formed by the sloping section 12b, a flat section 12c, and a lower interface 12d.

Light applied to the sloping section 12b that forms a reflecting face is reflected from the sloping section 12b, as shown in FIG. 4, and is applied to the polarizing plate 3, while leaving the glass substrate 1 at a nearly perpendicular angle.

On the other hand, light applied to the upper flat section 12c or the lower interface 12d at an angle bigger than an incident angle determined by the refractive indices of the glass substrate I and the peripheral medium is subject to total reflection.

Therefore, the light applied to the upper flat section 12c or the lower interface 12d is repeatedly subject to total reflection while being propagated 8 between the flat section 12c and interface 12d until it enters the sloping section 12b.

Then, the polarizing plate 3 transmits only a specific polarized component of the light applied to it from the glass substrate 1.

The phase-contrast plate 4 provides an optical compensation of the incident light according to the arrangement of liquid-crystal molecules in the liquid-crystal layer 8, so as to enhance the contrast ratio.

The diffusing plate 5 diffuses light so that light transmitted through the phase-contrast plate 4 is uniformly applied to the liquid-crystal layer 8.

A voltage according to information to be displayed is applied to the transparent electrode 7 and the reflecting electrode 9, whereby the level of the light-transmitting characteristic of the liquid-crystal layer 8 is controlled, and light transmitted through the transparent electrode 7 and applied to the liquid-crystal layer 8 is subject to optical modulation. Light transmitted through the liquid-crystal layer 8 is applied to the reflecting electrode 9.

Light reflected by the reflecting electrode 9 reaches the glass substrate 1 tracking through the reverse route to that of incident light. Part of the light reaching the glass substrate 1 is transmitted through the glass substrate 1, reaching the eyes of an observer. Thus, the observer recognizes the information displayed.

Accordingly, in this arrangement, the glass substrate 1 near to the observer of the two opposed glass substrates 1, 2 functions as a light guiding plate for the front light. Therefore, as compared with previously proposed arrangements, the reflection type liquid-crystal display in the 9 above described arrangement is thinner and lighter by one sheet of the lightguiding plate.

A second arrangement will now be described with reference to Fig. 5.

Although in the arrangement described above glass substrates 1, 2 are used, it is possible to use transparent resin substrates such as those shown at la, 2a with a light-transmitting characteristic. Also, as shown in FIG. 5, the order of the phase-contrast plate 4 and diffusion plate 5 may be changed.

Although in the first arrangement described above, the formation of the uneven surface 12 on the glass substrate 1 is defined by the sloping section 12b and the flat section 12c, the uneven surface formed on glass substrate 1 or the resin substrate la may be saw-tooth shaped.

In FIG. 6 there is shown a portable telephone having a reflection type liquid-crystal display, while the-cross sectional view of FIG. 7 shows an enlarged part B of FIG. 6 taken along the line C-C' in FIG. 6. In FIG. 6, there are shown a housing 13 of the portable telephone, an antenna 14, a receiver 15, and a keypad 16.

As shown in FIG. 7, a reflection type liquid-crystal display of either the first or second arrangement described above may be incorporated in the housing 13 of the portable telephone without any additional front cover. Thus, since the front cover is omitted, the portable telephone is thinner and lighter than it would otherwise be.

It will be understood that the portable telephone is simply an example of an electronic device in which the display arrangements described may be incorporated. The application of the display arrangements is not limited to portable telephones and can also be used with any electronic devices.

It will be appreciated that in the illustrative arrangements described, the one glass substrate which is the nearer to an observer than the other of the two opposed glass substrates functions as a light-guiding plate for a front light. Therefore, as compared with previously proposed arrangements, a reflection type liquid-crystal display can be made thinner and lighter as a result of the omission of one sheet of the light-guiding plate.

There has also been described a reflection type liquid-crystal display attached to a housing in such a way that a first substrate is exposed.

Therefore, the generally used front cover of a device can be omitted since the first substrate of a display described above is able to function as the front cover. Thus, an electronic device employing the reflection type liquidcrystal display described above can be thinner and lighter by one sheet as a result of the omission of the front cover of the device.

Although particular arrangements illustrative of the invention have been described, by way of example, it will be understood that variations and modifications thereof, as well as other arrangements may be conceived within the scope of the appended claims.

Claims

11 CLAIMS

1 A reflection type liquid-crystal display, including two opposed substrates, a liquid-crystal layer between the two opposed substrates, and a front light acting as a lighting means at the front face of the reflection type liquid-crystal display, wherein a first one of the substrates nearer to an observer of the reflection type liquid-crystal display than the other of the two opposed substrates has an uneven surface on the observer side that functions as a light-guiding means for the front light, and wherein the front light includes the first one of the substrates and a light source that is placed at the side of the first substrate.

2. A reflection type liquid-crystal display, as claimed in claim 1, further including a polarizing plate for transmitting a specific polarized component of light emitted from the front light, a phase-contrast plate for optical compensation, a diffusion plate for diffusing light, a colour filter of three primary colours, a transparent electrode with a light-transmitting characteristic, and a reflecting electrode for reflecting light transmitted through the liquid-crystal layer arranged between the two opposed substrates.

3. An electronic device, including a reflection type liquid-crystal display having two opposed substrates, a liquid-crystal layer between the two 12 opposed substrates, and a front light acting as a lighting means at the front face of the reflection type liquid-crystal display, wherein a first substrate nearer to an observer of the reflection type liquidcrystal display than the other of the two opposed substrates has an uneven surface on the observer side that functions as a light-guiding means for the front light, the front light including the first substrate and a light source that is placed at the side of the first substrate, and the reflection type liquid- crystal display being incorporated in the housing of the electronic device so that the first substrate is exposed. 10

4. A reflection type liquid crystal display as claimed in claim 1 substantially as described herein with reference to FIGS. 3 and 4, or FIG. 5 of the accompanying drawings.

5. An electronic device as claimed in claim 3 including an arrangement substantially as described herein with reference to FIGS. 6 and 7 of the accompanying drawings.