JPH0749509A - Liquid crystal display device and liquid crystal element - Google Patents

Abstract

PURPOSE:To provide the liquid crystal display device which can be driven with a low voltage and has a wide visual angle characteristic. CONSTITUTION:This liquid crystal display device has a nematic liquid crystal layer 12 disposed between oriented layers 10 and 11. These oriented layers 10 and 11 are so arranged that the pretilt angles of liquid crystal molecules on the respective surfaces of the oriented layers 10 and 11 are paralleled. The liquid crystal layer 12 has a phase difference equal to (M+1)lambda/2 with the first operating voltage and to Mlambda/2 with the second operating voltage if M is defined as an integer larger than zero or smaller than minus 1 and lambda as the wavelength of visible light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device,
In particular, it relates to an active matrix drive type display device. Further, the present invention relates to a liquid crystal device that can be used in a display device or other application using visible light or other light.

[0002]

Twisted nematic liquid crystal displays are widely used as numeric display segment type displays for watches and pocket calculators. In a display device with a large amount of information, an active element such as a thin film transistor is formed on a transparent substrate of a liquid crystal display element and functions as a switching element for selectively driving a pixel electrode that applies a voltage to liquid crystal. With the red, green and blue color filter layers a color display is obtained.

The following are well known as high information content liquid crystal display systems.

(A) Active drive type twisted nematic (hereinafter referred to as TN) liquid crystal display system. This system features a 90 ° twist orientation of nematic liquid crystal molecules.

(B) A multiplex drive type super twisted nematic (hereinafter referred to as STN) liquid crystal display system. This system uses the steepness in the voltage-transmittance characteristic obtained by setting the twist angle of the nematic liquid crystal molecules to 180 ° or more.

Since the multiplex drive type STN liquid crystal display system causes a peculiar coloring, an optical compensator is provided for displaying black and white. This type of liquid crystal display was twisted in two subgroups, namely (b-1) a display liquid crystal cell and a liquid crystal cell in the display liquid crystal cell, in a direction opposite to the twist direction of the liquid crystal display depending on the type of optical compensator applied. Double super twisted nematic liquid crystal display system using liquid crystal cell, and (b
-2) It is roughly classified into a film compensation type liquid crystal display system using an optically anisotropic film. The film-compensated liquid crystal display system (b-2) is preferable for weight saving and cost reduction.

The active drive type T described in (a) above
The N liquid crystal display system has two groups, namely,
(A-1) Normally black system and (a-2) Normally white system. In the normally black system, a pair of polarizing plates are arranged such that their polarization directions are parallel to each other, and black display is performed without applying a voltage to the liquid crystal layer (off state). In the normally white system, polarizing plates are arranged so that their polarization directions are orthogonal to each other, and white display is performed in the off state.
The normally white display system is considered to have excellent display contrast, color reproducibility, and viewing angle dependence of a displayed image.

In the currently used TN liquid crystal type display device, since the liquid crystal molecules have a refractive index anisotropy and are oriented with a tilt with respect to the upper and lower electrode substrates, display can be performed especially by an applied voltage. When switched, the contrast of the display image changes according to the viewing angle of the user, and the viewing contrast greatly depends on the viewing angle. The display contrast increases as the viewing angle gradually increases from the direction perpendicular to the screen, and the contrast is reversed when the viewing angle exceeds a certain angle (hereinafter, this phenomenon is referred to as inversion).

In order to reduce the viewing angle dependence, the retardation plate or the retardation film is so arranged that the direction of one main refractive index of the retardation plate or the retardation film is parallel to the plane perpendicular to the liquid crystal layer and the polarizing plate. Attempts have been made to compensate for the phase difference between the ordinary and extraordinary light components by providing them. Nevertheless, even with such retarders, the above contrast reversal is only slightly improved.

As used herein, the term "parallel" means arranged in the same direction at a constant distance. Thus, "parallel" is different from "anti-parallel" which means arranged in opposite directions at a distance.

US Pat. No. 4,385,806 discloses a liquid crystal display device in which a nematic liquid crystal is arranged between glass plates coated with a transparent conductive material to form electrodes.

The electrode surface is treated by a rubbing method so as to act as an alignment film for liquid crystal molecules in contact with the surface. In particular, the alignment film is aligned such that the pretilt angles of the liquid crystal molecules on the alignment film surface are antiparallel to each other. In order to widen the viewing angle of such a display device, at least 2
One retarder device is provided.

Boss & Koehler / Beran (Mol.Cryst.Liq., 1
13,329 (1984)), in order to increase the switching speed and reduce the viewing angle dependence, pi or π.
A liquid crystal display element using a cell (hereinafter referred to as a pi cell) is disclosed. In the pi cell shown in FIG. 4, the surfaces of the substrates are processed so that the pretilt angles of the liquid crystal molecules on the upper and lower substrates are parallel to each other. Therefore, the tilt directions of the liquid crystal molecules in the upper and lower halves of the liquid crystal layer are opposite to each other even in the presence of the applied voltage. Thereby, the phase difference between the ordinary light component and the extraordinary light component in the nematic liquid crystal layer is partially compensated, so that the viewing angle dependency is reduced. But Bo
The pi cell proposed by ss is a high voltage driving type liquid crystal display device that requires a voltage of 20 to 30V. Therefore, it cannot be applied to the current active matrix drive type liquid crystal element in which the drive voltage is limited to about 5 V or less because a thin film transistor (hereinafter referred to as a TFT) formed by using, for example, amorphous silicon is used.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to enable active matrix driving with a driving voltage of about 5 V or less and to achieve a wide viewing angle characteristic. It is another object of the present invention to provide a liquid crystal display device that has the viewing angle dependency of contrast change, coloring, and reversal while having or having.

[0015]

According to one aspect of the present invention, a first substrate on which a plurality of switching elements and display pixel electrodes are formed, and at least one counter electrode facing the display pixel electrodes. A second substrate formed on the upper surface, first and second alignment films respectively provided on the facing surfaces of the first and second substrates, and the first and second alignment films.
And a nematic liquid crystal layer having a positive dielectric anisotropy provided between the first and second alignment films, and the liquid crystal molecule pretilt angles on the respective surfaces of the first and second alignment films are substantially parallel to each other. There is provided an active matrix liquid crystal display device in which the first and second alignment films are arranged so that

According to one embodiment of the invention, M is an integer greater than zero or less than minus one, λ
Is the wavelength of visible light, the liquid crystal layer is substantially equal to (M + 1) λ / 2 at the first operating voltage of the display device and substantially equal to Mλ / 2 at the second operating voltage of the display device. Have the same phase difference.

According to another embodiment of the present invention, the display device further includes a reflection member that reflects the light passing through the liquid crystal layer through the liquid crystal layer.

According to yet another embodiment of the present invention, M
Is an integer and λ is the wavelength of visible light, the liquid crystal layer is substantially equal to (M + 1) λ / 4 at the first operating voltage of the display device and Mλ at the second operating voltage of the display device. /
4 has a phase difference substantially equal to 4.

According to another embodiment of the present invention, the M is an integer greater than zero or less than minus one.

According to yet another embodiment of the present invention, the liquid crystal layer has a thickness d, the nematic liquid crystal has a refractive index anisotropy Δn, and their product d × Δn is substantially 1. Between 0.1 μm and substantially 2.75 μm.

According to another embodiment of the present invention, the display device further includes at least one retardation plate.

According to yet another embodiment of the present invention, M
Is an integer and λ is a wavelength of visible light, the above-mentioned at least 1
The total phase difference of all the two phase difference plates and the liquid crystal layer is (M + 1) λ / at the first operating voltage of the display device.
Is substantially equal to 2 and is substantially equal to Mλ / 2 at the second operating voltage of the display device.

According to still another embodiment of the present invention, the display device transmits light passing through the at least one retardation plate and the liquid crystal layer through the at least one retardation plate and the liquid crystal layer. The reflective member which reflects is further provided.

According to yet another embodiment of the present invention, M
Is an integer and λ is a wavelength of visible light, the above-mentioned at least 1
The total phase difference of all the two phase difference plates and the liquid crystal layer is (M + 1) λ / at the first operating voltage of the display device.
4 and substantially equal to Mλ / 4 at the second operating voltage of the display device.

According to yet another embodiment of the present invention said M is equal to zero and said second operating voltage is greater than said first operating voltage.

According to another embodiment of the present invention, the display device further includes a negative retardation retardation plate having a negative retardation in the light passage direction.

According to still another embodiment of the present invention, the negative phase difference of the negative phase difference plate is larger than the positive phase difference of the remaining portion of the display device in the light passage direction. Has a size substantially equal to

According to yet another embodiment of the present invention, the display device has at least one polarization direction oriented substantially at 45 ° with respect to the liquid crystal molecule pretilt angle.
It also has two polarizing plates.

According to another aspect of the present invention, the first and second
Alignment film and a nematic liquid crystal layer having a positive dielectric anisotropy provided between the first and second alignment films, and each surface of the first and second alignment films is Provided is a liquid crystal device, wherein the first and second alignment layers are arranged so as to provide substantially parallel first and second liquid crystal molecule pretilt angles, respectively, and further comprising at least one retardation plate. It

According to one embodiment of the present invention, where M is an integer and λ is a wavelength of a light beam, a phase difference obtained by combining all of the at least one retardation plate and the liquid crystal layer is the first of the elements. Is substantially equal to (M + 1) λ / 2 at an operating voltage of 1 and is substantially equal to Mλ / 2 at a second operating voltage of the device.

[0031] According to another embodiment of the present invention, the element reflects the light rays passing through the at least one retardation plate and the liquid crystal layer through the at least one retardation plate and the liquid crystal layer. Is further equipped.

According to yet another embodiment of the present invention, M
Is an integer and λ is the wavelength of the light beam, the phase difference of all the at least one retardation plate and the liquid crystal layer is substantially (M + 1) λ / 4 at the first operating voltage of the device. Equal and substantially equal to Mλ / 4 at the second operating voltage of the device.

According to yet another embodiment of the present invention, said M is equal to zero and said second operating voltage is greater than said first operating voltage.

According to yet another embodiment of the present invention, the liquid crystal layer has a thickness d, the nematic liquid crystal has a refractive index anisotropy Δn, and their product d × Δn is substantially zero. Between 0.4 μm and substantially 2.4 μm.

According to another embodiment of the present invention, the product d × Δn is substantially 0.8 μm and substantially 1.6 μm.
It is between m.

According to another aspect of the present invention, the first and second
First nematic liquid crystal layer having a positive dielectric anisotropy provided between the first and second alignment films, the first and second liquid crystals being substantially parallel to each other on each surface of the first and second alignment films. A liquid crystal device in which the first and second alignment films are arranged so as to respectively provide a molecular pretilt angle, wherein M is an integer larger than zero or smaller than minus 1, and λ is a wavelength of a light ray. A liquid crystal element in which the liquid crystal layer has a phase difference substantially equal to (M + 1) λ / 2 at a first operating voltage of the element and substantially equal to Mλ / 2 at a second operating voltage of the element Will be provided.

According to one embodiment of the present invention, the liquid crystal layer has a thickness d and a refractive index anisotropy Δn, and a product d × Δn thereof is substantially 1.1 μm, which is substantially 2. 75 μm
Between.

According to another aspect of the present invention, the first and second
First nematic liquid crystal layer having a positive dielectric anisotropy provided between the first and second alignment films, the first and second liquid crystals being substantially parallel to each other on each surface of the first and second alignment films. A liquid crystal element in which the first and second alignment films are arranged so as to respectively provide a molecular pretilt angle, wherein M is an integer and λ is a wavelength of a light beam, the liquid crystal layer is the first element of the element. There is provided a liquid crystal element having a phase difference substantially equal to (M + 1) λ / 4 at an operating voltage of λ and a substantially equal Mλ / 4 at a second operating voltage of the element.

According to one embodiment of the present invention, said M
Is greater than zero or less than minus one.

According to another embodiment of the present invention, the liquid crystal layer has a substantially constant thickness.

According to still another embodiment of the present invention, the device further comprises at least one polarizing plate having a polarization direction aligned substantially at 45 ° with respect to the liquid crystal molecule pretilt angle.

[0042]

In the liquid crystal element of the present invention, the liquid crystal molecule pretilt angles on the upper and lower substrates are substantially parallel. Therefore, the tilt directions (tilt directions) of the liquid crystal molecules in the upper and lower halves of the liquid crystal layer are opposite to each other. As a result, the phase difference between the ordinary component and the extraordinary component of the light incident on the liquid crystal layer is compensated by the upper half and the lower half of the liquid crystal layer. Therefore, the viewing angle dependence of the display characteristics of the liquid crystal device of the present invention is reduced as compared with the conventional TN type display device. Further, by forming a liquid crystal layer having an appropriate thickness using a liquid crystal having an appropriate refractive index anisotropy and optimizing the change in the phase difference with respect to the drive voltage, a liquid crystal element capable of low voltage drive is obtained. Can be provided. Furthermore, since the thickness of the liquid crystal layer can be reduced by using the retardation plate,
The switching speed of the liquid crystal element can be increased.
Further, when the reflective element is configured, the thickness of the liquid crystal layer can be reduced, so that the switching speed can be increased.

[0043]

The present invention will now be described in more detail with reference to the drawings.

The liquid crystal display device 2 shown in FIG.
The liquid crystal display element 5 is arranged between the four. The liquid crystal display element 5 has a glass substrate 6, on which a transparent electrode 8 and an alignment film 10 are formed. The alignment film 10 has a space provided between the alignment film 10 and another alignment film 11 by the spacer 13 and the liquid crystal layer 12. A transparent electrode 9 and an alignment film 11 are formed on the other glass substrate 7. Electrode 8,
9 is connected to the drive circuit 3. Liquid crystal molecules are liquid crystal layer 1
Alignment films 10 and 11 are provided so as to form a pi cell which is arranged as indicated by a short line in 2 and operates as shown in FIGS. 4 and 5. In particular, the alignment film 1
The pretilt angles of the liquid crystal molecules on the surface of 0 and 11 are parallel to each other.

Other materials may be used for this liquid crystal display device. For example, the substrates 6, 7 can be formed of transparent plastic. In another embodiment, one of the substrates is
It is reflective and may be formed of silicon.

The polarization directions of the polarizing plates 1 and 4 are the alignment film 1
The pretilt angles of the liquid crystal molecules at 0 and 11 are arranged to be substantially 45 °. The polarization directions of the polarizing plates 1 and 4 are parallel or perpendicular to each other.

In the first embodiment of the liquid crystal display device of the type shown in FIG. 1, the liquid crystal material of the liquid crystal layer 12 is E7 (refractive index anisotropy Δn = 0.22) manufactured by Merck.

The value of the product d × Δn of the liquid crystal cell is determined by the liquid crystal layer 12
By setting the thickness d of 10 μm to 2.2 μm. For the alignment films 10 and 11, a polyimide resin manufactured by Japan Synthetic Rubber Co., Ltd. is used. As the orientation treatment, a polyimide resin is rubbed with a nylon cloth. By this rubbing treatment, the pretilt angles of the liquid crystal molecules on the surfaces of the upper and lower alignment films 10 and 11 become, for example, 10 °, and the pretilt angles of the liquid crystal molecules on the surfaces of the upper and lower alignment films 10 and 11 are parallel to each other. A liquid crystal cell was prepared so that

FIG. 3 shows the results of measuring the voltage-light transmittance characteristics along the direction perpendicular to the liquid crystal cell thus manufactured. As is clear from this data, the off voltage is set to 1.5 V (first maximum value), and the on voltage is set to 3.
By adjusting the drive circuit so that it becomes 1 V (first minimum value), high-contrast display is possible.
Therefore, since such a cell can be driven by a voltage of substantially 5 V or less, active matrix driving can be applied.

According to visual observation, such a pi cell has reduced contrast inversion when a voltage is applied and has a wide viewing angle characteristic.

In the second and third embodiments of the liquid crystal display device of the type shown in FIG. 1, which differ from the first embodiment, the liquid crystal layer thickness d is 5 μm and 12.5 μm, respectively, and the product d
XΔn is 1.1 μm and 2.75 μm, respectively. As a result of evaluating these liquid crystal cells, it was found that the liquid crystal cells having d × Δn of 1.1 μm or 2.75 μm gave almost the same results as those obtained in the first example. In particular, the contrast inversion is reduced and the viewing angle characteristics are significantly widened.

With respect to the liquid crystal display device shown in FIG. 1, the driving voltage drop, response characteristics and viewing angle characteristics were evaluated. From this evaluation, it was found that it is desirable to set the optimum value d × Δn of the pi cell in the range of about 1.1 to 2.75 μm in practical use. If the value of d × Δn is smaller than 1.1 μm, the required driving voltage exceeds 5V. If the value of d × Δn is larger than 2.75 μm, the viewing angle characteristics are impaired.

FIG. 2 shows an active matrix drive liquid crystal panel using a pi cell of the type shown in FIG. This liquid crystal panel has a first substrate 20, on which a switching transistor 21 and a display pixel electrode 22 are formed near each intersection of a signal electrode 23 and a scanning electrode 24. The counter electrode 25 is formed on the second substrate 26. A pi cell mode liquid crystal layer 27 is provided between the first substrate 20 and the second substrate 26. As the switching transistor 21, an a-Si or p-Si thin film transistor (TFT) was formed.

Using the same liquid crystal material and the same liquid crystal layer thickness d as in the first embodiment of the liquid crystal display device shown in FIG. 1, one embodiment of the active matrix driven liquid crystal panel of the type shown in FIG. 2 was produced. . With this liquid crystal panel,
Substantially improved viewing angle characteristics and reduced contrast inversion.

FIG. 6 shows a liquid crystal display device similar to that shown in FIG. The same reference numerals mean corresponding parts, and the description thereof is omitted here. In the liquid crystal display device shown in FIG. 6, the thickness of the liquid crystal layer 12 is reduced, and a retardation film or a retardation film 30 is provided on the opposite side of the liquid crystal display element 5 between the liquid crystal display element and the polarizing plates 1 and 4. , 31 are different from the liquid crystal display device of FIG.

In the liquid crystal device of the type shown in FIG. 6, the thickness d of the liquid crystal layer 12 is 6.5 μm, and the value of d × Δn is 1.4.
The difference from the liquid crystal display device shown in FIG. One retardation plate having a retardation of 0.14 μm is provided. Such a liquid crystal display device has substantially the same characteristics as the first embodiment of the liquid crystal display device shown in FIG.
In particular, the viewing angle is substantially widened and the contrast reversal is substantially reduced.

With reference to FIGS. 1, 2 and 6, when a voltage is applied to the liquid crystal layer, the tilt directions of the liquid crystal molecules in the upper and lower halves of the liquid crystal layer are opposite to each other as shown in FIG. For example,
When light enters the liquid crystal layer “off-axis” from the direction of the viewing angle θ with respect to the normal line in FIG. 5, the phase difference between the ordinary and extraordinary light components in the upper and lower halves of the liquid crystal layer (hereinafter referred to as the retardation value). Called) are different from each other. For example, in FIG. 5 where θ> 0, the retardation value of the lower half of the liquid crystal layer (Rlow = Δ
n′low × d / 2) is low, but the retardation value (Rup = Δn′up × d / 2) of the upper half of the liquid crystal layer is high. As a result, the retardation value (Rlow + Rup) of all liquid crystal layers
Does not depend much on the viewing angle θ, and the direction of the normal line in FIG. 5 (θ = 0
Since the value is substantially the same as the value (Δn′o × d) in (°), the contrast of the liquid crystal display device does not depend much on the viewing angle. Therefore, since the optical phase difference is compensated in the upper and lower layers of the liquid crystal, the viewing angle dependency is improved. Parameter Δ
n ′ represents the apparent refractive index anisotropy seen by light passing through the layer at a viewing angle θ. In the TN cell, a phase difference is forcedly generated, resulting in a narrow viewing angle. In contrast to this, in the Pi cell, the phase difference is compensated in the upper and lower halves of the liquid crystal layer to realize a wide viewing angle.

The viewing angle dependence of the light transmittance of the pi cell is reduced not only in the on / off state but also in the intermediate state corresponding to the gray scale of the liquid crystal display device. Also, incorporating one or more retarders or films allows the use of thin cells and reduces switching times.

The display devices shown in FIGS. 1, 2 and 6 are transmissive, whereas the liquid crystal display device shown in FIG. 7 is reflective. The display device shown in FIG. 7 is different from the display device of FIG. 6 in that the polarizing plate 4 and the phase difference generating member 31 of FIG. 6 are omitted and a mirror or another reflecting member 40 is provided. Instead of providing a reflective member, for example,
A reflective substrate made of silicon may be used. Therefore, light incident on the display device from above in FIG. 7 is transmitted through the polarizing plate 1 and the liquid crystal element 5, and is reflected by the mirror 40,
The light is transmitted through the display element 5 and the polarizing plate 1. In this way, the display element 5, especially the liquid crystal layer 12, can be thinned, and the switching speed of the display device is increased.

FIG. 8 shows a schematic of a basic pi cell.
In particular, this figure shows the "rubbing direction" indicated by arrow 42.
Indicate parallel alignment films 10 and 11. The contrast changes depending on the viewing angle. To evaluate this, the viewing angle is
It shall be on two planes perpendicular to each other. First (AB)
The surface is perpendicular to the alignment films 10 and 11, but parallel to the rubbing direction 42, whereas the second (CD) surface is perpendicular to the alignment films 10 and 11 and is parallel to the rubbing direction 42. It is also vertical.

FIGS. 9 and 10 show standard light transmittances for various viewing angles in the CD plane and the AB plane, respectively, for a known TN display device. As shown in FIG. 9, the curve representing the light transmittance for each drive voltage shown adjacent to each other does not relatively change even if the viewing angle on the CD surface changes. On the other hand, as shown in FIG.
When the viewing angle on the B surface changes, the light transmittance changes significantly. As described above, the conventional TN display device has a problem in that the viewing angle is narrow and relatively asymmetric on the AB plane, and contrast inversion occurs.

FIGS. 11 and 12 are graphs for a known pi cell of the type (discussed above) disclosed by Boss shown in FIG. 8 and correspond to FIGS. 10 and 9, respectively.
In such a pi cell, a driving voltage of over 20 volts is required to achieve a sufficient contrast between the on and off states. The pit cell has an itching speed of about 2 milliseconds, which is an order of magnitude faster than the switching speed of a conventional TN display device, but a display device based on the pi cell of the type shown in FIG. 8 has a limited viewing angle on the CD surface. To be done. As shown in FIG. 12, in such a display device, contrast inversion occurs when the viewing angle on the CD surface deviates from ± 20 °.

FIG. 13 shows the phase difference of the pi cell of the type shown in FIG. 8 with respect to the drive voltage at zero viewing angle. When the driving voltage is increased, the phase difference asymptotically decreases to zero, but it does not reach zero at the allowable driving voltage. As the drive voltage decreases, the pi-cell approaches an unstable state. In this state, the liquid crystal molecules in the central region of the liquid crystal cell are
It no longer stably aligns vertically with respect to the alignment film. In order for the liquid crystal display device to achieve the zeroth minimum light transmittance that substantially blocks the transmission of light, the phase difference must be equal to zero at the allowable driving voltage, which is the same as the conventional p
It is not possible with i-cells. In such cells, the first maximum light transmission can be achieved with a drive voltage of about 1.5 volts, which drive voltage is high enough to avoid the above instability. These maximum and minimum transmittances are achieved with polarizing plates that are orthogonal to each other. With parallel polarizers, the first maximum light transmission is achieved with a drive voltage of about 1.5 volts, but the zeroth maximum light transmission is not achieved because it requires zero phase difference.

As described above, by selecting a liquid crystal having an appropriate positive dielectric anisotropy and forming a liquid crystal layer having an appropriate thickness, the liquid crystal layer is higher than the unstable region of operation and is finite. Thus, it is possible to achieve the first maximum light transmittance and the first minimum light transmittance with a driving voltage low enough to drive such a liquid crystal display device. This is shown in Figure 3 as described above.

FIG. 14 shows an outline of the pi cell type shown in FIG. In this case, the pi cell has the fixed phase difference generating member or the phase difference plate 30. Fixed phase difference generating member 30
By using, the thickness of the liquid crystal layer can be reduced, and as a result, the display device switching speed is improved. However, the phase difference generating member adjusts the total phase difference of the display device so that the zeroth minimum (or maximum) light transmittance can be achieved with a limited driving voltage.

This effect is shown in FIG. FIG. 15 shows FIG.
The same "uncompensated" phase difference as the curve shown in FIG.
It shows with. Fixed phase difference generating member 30 having different phase difference
The effect of is shown by curves 51 to 53. The curve 51 is
The combination of the phase difference between the liquid crystal layer and the λ / 8 phase difference generating member 30 is shown, and the curves 52 and 53 are λ / 4 and λ.
The effect of the / 2 phase difference generating member is shown. The fixed phase difference generating member 30 provides a negative phase difference. This negative phase difference causes the phase difference of the liquid crystal layer to be zero so that the phase difference of the display device can be zero with a limited drive voltage, that is, each of the curves 51 to 53 crosses the axis of zero phase difference. Is subtracted from.
Therefore, these curves differ from the curve 50 which does not intersect the zero phase difference axis and approaches the zero phase difference axis in a close manner. Thus, in curves 51 to 53, at drive voltages of about 6 volts, about 4 volts and about 2.5 volts, respectively,
A zeroth minimum (or maximum) light transmission is achieved.

FIG. 15 shown at + λ / 2 and −λ / 2.
The horizontal lines correspond to the positive and negative first maximum light transmittances, and in order for the liquid crystal device to function properly, the corresponding retardation curves must intersect with one of these lines. Curve 51
And 52 are driving voltages at which the liquid crystal display device becomes stable +
It intersects the λ / 2 line, but the curve 53 does not. Therefore, the fixed phase difference generating member 30 can be a λ / 8 or λ / 4 phase difference generating member, and the liquid crystal display device has the first maximum light transmittance and the zeroth minimum light value at an allowable driving voltage. It can work with transmittance. In the embodiment, the use of the λ / 2 phase difference generating member results in no acceptable movement.

FIG. 16 shows the drive voltage dependence of the transmittance in the display device corresponding to the curves 50 to 53 in FIG. A curve 60 in FIG. 16 shows the light transmittance of the pi cell having no fixed phase difference generating member, and corresponds to the curve 50 in FIG. As can be seen from the curve 60 in FIG. 16, the first maximum light transmission is achieved at about 1.5 volts, while the zeroth minimum light transmission is obtained in close proximity. Curve 63
Corresponds to the λ / 2 phase difference generating member, and shows that the zeroth minimum light transmittance is achieved, but the negative first maximum light transmittance is obtained in a close manner. The curves 61 and 62 correspond to the curves 51 and 52 in FIG. 15, and the zeroth minimum light transmittance and the first maximum light transmittance are λ /
8 and λ / 4 phase difference generating member 30 are shown to be achieved.

Theoretically, the fixed phase difference generating member 30 is
Although it can take any value other than an integral multiple of λ / 2, in practice, the phase difference of the phase difference generating member 30 is a usable or appropriate driving voltage, and the maximum transmittance and the next minimum transmittance are Chosen to be accomplished. This means that in the pi cell that does not use the fixed phase difference generating member, the phase difference of the liquid crystal layer is (M + 1) λ / 2 and Mλ / 2 at the allowable driving voltage, where
This is accomplished by ensuring that M is an integer greater than zero or less than -1. For pi cells with fixed retarder, the same formula applies, but M can be any integer including zero or -1, where retard is the retarder and liquid crystal layer. Is the sum of the phase differences of.

FIGS. 17 and 18 show A of a pi cell having no fixed phase difference generating member, that is, a pi cell operating between the first maximum light transmittance and the first minimum light transmittance.
The viewing-angle dependence of the transmittance in B surface and CD surface is shown.
In particular, these curves are 8.8 micrometers thick and
E7 relates to a liquid crystal layer containing a liquid crystal. In FIG. 17, FIG.
And "normal" and "inverted" corresponding to the pi cell type whose performance is shown by curves 50 and 60 in FIG.
The areas are shown for comparison.

19 and 20 show the performance of a liquid crystal display device of the type shown in FIG. In this type of liquid crystal display device, a layer having a thickness of 5 micrometers made of an E7 liquid crystal material has a phase difference generating member 30 fixed to 52 nanometers.
Used in combination with. The viewing angle tolerance is substantially wider when compared to known types of pi cells. In particular, the "inverted" region occurs at ± 20 ° in the AB plane in the conventional pi cell, whereas it does not occur up to ± 30 ° in this type of liquid crystal display device.

FIGS. 21 and 22 correspond to FIGS. 19 and 20, respectively, in the same device, but with a fixed negative phase difference generating member of 441 nanometers that provides a negative phase difference in the direction of zero viewing angle. is doing. By partially compensating for the retardation of the liquid crystal layer in this direction, the performance of the display in terms of contrast and viewing angle is substantially improved. 23 and 24 correspond to FIGS. 21 and 22, and show the operation of the display device in which the negative phase difference generating member provides the negative phase difference fixed at 882 nanometers in the direction of the viewing angle of zero. Also in these figures, the contrast and viewing angle performance of the display device are substantially improved. Therefore,
It is possible to maintain acceptable contrast performance, generate no contrast reversals, and provide a substantially symmetrical viewing angle up to ± 40 °.

In order to evaluate the switching performance, the switching speeds of the three examples of the display device constituting the embodiment of the present invention were measured. In the display device of the type shown in FIG. 6 which has a liquid crystal layer made of E7 liquid crystal material and having a thickness of 5 μm, together with one 72 nm fixed phase difference generating member, switching from the maximum light transmittance to the minimum light transmittance is performed. The time was 0.3 milliseconds, while the switching time from the minimum light transmittance to the maximum light transmittance was 1.8 milliseconds. 17
In the reflection mode display device of the type shown in FIG. 7 which has a positive phase difference generating member fixed at 4 nanometers and a liquid crystal layer made of E7 liquid crystal material and having a thickness of 5 micrometers, the switching time from the maximum transmittance to the minimum transmittance is Is 0.22
In contrast to the millisecond, the switching time from the minimum transmittance to the maximum transmittance was 0.77 milliseconds. In a reflection-mode display device having a liquid crystal layer made of E7 liquid crystal material and having a thickness of 2 micrometers, together with a positive phase difference generating member fixed at 152 nanometers, the switching time from the maximum transmittance to the minimum transmittance is 0.07 mm. In contrast to the second, the switching time from the minimum transmittance to the maximum transmittance was 0.55 milliseconds.

As described above, it becomes possible to provide a liquid crystal element for display and other purposes, which has substantially improved performance as compared with the known TN and pi cell types. Switching speed can be substantially improved in both transmissive and reflective modes. In the reflection mode, the switching speed is remarkably improved as compared with the known pi cell. The contrast properties are substantially improved compared to known pi cells. Furthermore, since the liquid crystal element of the present invention can be operated with a sufficiently low drive voltage, for example, active matrix drive can be applied using a thin film transistor. Further, the viewing angle range of the liquid crystal device of the present invention is substantially wider than that of known TN and known pi cell devices.

[0075]

As described above, according to the present invention, active matrix driving can be performed with a driving voltage of about 5 V or less, wide viewing angle characteristics can be obtained, and viewing angle dependence such as contrast change, coloring, and inversion can be achieved. A liquid crystal display device that can be reduced or eliminated is obtained.

[0076]

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a pi cell type liquid crystal display device according to one embodiment of the present invention.

FIG. 2 is a diagram showing a structure of an active matrix drive type liquid crystal display device using a display element of the type shown in FIG.

3 is a graph showing applied voltage-transmittance characteristics of the pi cell display device of FIG. 1. FIG.

FIG. 4 is a schematic cross-sectional view showing the orientation of liquid crystal molecules in the on and off states in the pi cell.

FIG. 5 is a diagram showing “on-axis” and “off-axis” transmission characteristics of an off-state liquid crystal layer in a pi cell.

FIG. 6 is a schematic cross-sectional view of a pi cell type liquid crystal display device according to another embodiment of the present invention.

FIG. 7 is a cross-sectional view showing a model of a pi cell reflection mode liquid crystal display device according to still another embodiment of the present invention.

FIG. 8 is a schematic diagram of a pi cell exemplifying the definition of a viewing angle.

FIG. 9 is a graph showing the light transmittance T (%) with respect to the viewing angle of the CD surface when different drive voltages are applied to a known TN display device.

FIG. 10 is a graph showing the light transmittance T (%) with respect to the viewing angle of the AB plane when different driving voltages are applied to a known TN display device.

FIG. 11 shows the light transmittance T with respect to the viewing angle of the CD surface when different driving voltages are applied to a known pi cell display device.
It is a graph which shows (%).

FIG. 12 shows the light transmittance T with respect to the viewing angle of the AB plane when different driving voltages are applied to a known pi cell display device.
It is a graph which shows (%).

FIG. 13 is a graph showing retardation (μm) with respect to a drive voltage of a known pi cell display device.

FIG. 14 is a schematic diagram of a pi cell of the type shown in FIG.

FIG. 15: Retardation (μm) with respect to driving voltage of some pi-cell displays including embodiments of the present invention.
It is a graph which shows.

FIG. 16 is a graph showing retardation as a percentage of a driving voltage of some pi cell display devices including an embodiment of the present invention.

FIG. 17 is a diagram showing the light transmittance T with respect to the viewing angle of the CD surface when different drive voltages are applied to the display device of the type shown in FIG.
It is a graph which shows (%).

18 is a light transmittance T with respect to the viewing angle of the AB plane when different drive voltages are applied to the display device of the type shown in FIG.
It is a graph which shows (%).

FIG. 19 is a light transmittance T with respect to the viewing angle of the CD surface when different drive voltages are applied to the display device of the type shown in FIG.
It is a graph which shows (%).

20 is a graph showing the light transmittance T with respect to the viewing angle of the AB plane when different driving voltages are applied to the display device of the type shown in FIG.
It is a graph which shows (%).

21 is a graph showing the light transmittance T (%) with respect to the viewing angle of the CD surface when different drive voltages are applied to the display device of the type shown in FIG. 6 including the negative phase difference generating member.

22 is a graph showing the light transmittance T (%) with respect to the viewing angle of the AB plane when different drive voltages are applied to the display device of the type shown in FIG. 6 including the negative phase difference generating member.

FIG. 23 is a graph showing C when different driving voltages are applied to the display device of the type shown in FIG. 6 including another negative phase difference generating member.
It is a graph which shows the light transmittance T (%) with respect to the viewing angle of D surface.

FIG. 24 is a diagram showing a case where different driving voltages are applied to the display device of the type shown in FIG. 6 including another negative phase difference generating member;
It is a graph which shows the light transmittance T (%) with respect to the viewing angle of B surface.

[Explanation of symbols]

 1 Polarizing Plate 2 Liquid Crystal Display Device 3 Driving Circuit 4 Polarizing Plate 5 Liquid Crystal Display Element 6 Glass Substrate 7 Glass Substrate 8 Electrode 9 Electrode 10 Alignment Film 11 Alignment Film 12 Liquid Crystal Layer 13 Spacer

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Shuichi Kanzaki 5-9-29 Ukyo, Nara City, Nara Prefecture

Claims (27)

[Claims] 1. A first substrate on which a plurality of switching elements and display pixel electrodes are formed on an upper surface, a second substrate on which at least one counter electrode facing the display pixel electrodes is formed, A first alignment film and a second alignment film, which are provided on opposite surfaces of the first and second substrates, respectively;
And a nematic liquid crystal layer having a positive dielectric anisotropy provided between the first and second alignment films, and the liquid crystal molecule pretilt angles on the respective surfaces of the first and second alignment films are substantially equal to each other. An active matrix liquid crystal display device in which the first and second alignment films are arranged so as to be parallel to. 2. M greater than zero or minus one
Is a smaller integer, λ is the wavelength of visible light, the liquid crystal layer is (M + 1) at the first operating voltage of the display device.
2. A phase difference substantially equal to .lambda. / 2 and at a second operating voltage of the display device substantially equal to M.lambda./2.
Display device according to. 3. The display device according to claim 1, further comprising a reflecting member that reflects light that has passed through the liquid crystal layer through the liquid crystal layer. 4. When M is an integer and λ is a wavelength of visible light,
At the first operating voltage of the display device, the liquid crystal layer is (M
4. A display device according to claim 3, having a phase difference substantially equal to +1) λ / 4 and substantially equal to Mλ / 4 at a second operating voltage of the display device. 5. The display device according to claim 4, wherein the M is an integer larger than zero or smaller than minus one. 6. The liquid crystal layer has a thickness d and the nematic liquid crystal has a refractive index anisotropy Δn, the product d ×
The display device according to claim 1, wherein Δn is substantially between 1.1 μm and 2.75 μm. 7. The display device according to claim 1, further comprising at least one retardation plate. 8. When M is an integer and λ is a wavelength of visible light,
The phase difference of all of the at least one retardation plate and the liquid crystal layer is substantially equal to (M + 1) λ / 2 at the first operating voltage of the display device, and
The display device according to claim 7, wherein the operating voltage is substantially equal to Mλ / 2. 9. The reflection member according to claim 7, further comprising a reflection member that reflects light that has passed through the at least one retardation plate and the liquid crystal layer through the at least one retardation plate and the liquid crystal layer. Display device. 10. When M is an integer and λ is a wavelength of visible light, a phase difference obtained by combining all of the at least one retardation plate and the liquid crystal layer is () at a first operating voltage of the display device. 10. M + 1) λ / 4, substantially equal to Mλ / 4 at the second operating voltage of the display device.
Display device according to. 11. The display device according to claim 8, wherein the M is equal to zero, and the second operating voltage is higher than the first operating voltage. 12. A negative retardation retardation plate having a negative retardation in the light passage direction is further provided.
1. The display device according to any one of 1. 13. The negative phase difference of the negative phase difference plate is substantially equal to the positive phase difference of the rest of the display device in the light passage direction. The display device according to claim 12, which has. 14. The display according to claim 1, further comprising at least one polarizing plate having a polarization direction aligned substantially at 45 ° with respect to the liquid crystal molecule pretilt angle. apparatus. 15. A first and a second alignment film, and a nematic liquid crystal layer having a positive dielectric anisotropy provided between the first and the second alignment films, and the first and the second alignment films. The first and second alignment films are arranged so as to respectively provide first and second liquid crystal molecule pretilt angles that are substantially parallel to each other on each surface of the second alignment film, and at least one retardation plate. A liquid crystal element further equipped with. 16. When M is an integer and λ is a wavelength of a light ray,
The total phase difference of all the at least one phase difference plate and the liquid crystal layer is (M +
16. The device of claim 15 wherein 1) is substantially equal to λ / 2 and is substantially equal to Mλ / 2 at a second operating voltage of the device. 17. The device according to claim 15, further comprising a reflecting member that reflects a light beam that has passed through the at least one retardation plate and the liquid crystal layer through the at least one retardation plate and the liquid crystal layer. . 18. When M is an integer and λ is a wavelength of a light ray,
The total phase difference of all the at least one phase difference plate and the liquid crystal layer is (M +
18. The device of claim 17, wherein 1) is substantially equal to λ / 4 and is substantially equal to Mλ / 4 at a second operating voltage of the device. 19. A device according to claim 16 or 18, wherein the M is equal to zero and the second operating voltage is greater than the first operating voltage. 20. The liquid crystal layer has a thickness d, and the nematic liquid crystal has a refractive index anisotropy Δn.
The device according to claim 15, wherein xΔn is substantially between 0.4 μm and substantially 2.4 μm. 21. The product d × Δn is substantially 0.8 μm.
21. The device of claim 20, which is between and substantially 1.6 μm. 22. A nematic liquid crystal layer having a positive dielectric constant anisotropy provided between the first and second alignment films, wherein the surfaces of the first and second alignment films are substantially parallel to each other. A liquid crystal device in which the first and second alignment films are arranged so as to provide first and second liquid crystal molecule pretilt angles parallel to, respectively, wherein M is greater than zero or less than minus one. The liquid crystal layer is substantially equal to (M + 1) λ / 2 at the first operating voltage of the element and Mλ / 2 at the second operating voltage of the element, where λ is the wavelength of the light ray.
A liquid crystal element having a retardation substantially equal to. 23. The liquid crystal layer has a thickness d and a refractive index anisotropy Δn, and their product d × Δn is substantially 1.1 μm.
23. The device of claim 22, which is between and substantially 2.75 μm. 24. A nematic liquid crystal layer having a positive dielectric constant anisotropy provided between the first and second alignment films, wherein each surface of the first and second alignment films is substantially parallel to each other. A liquid crystal element in which the first and second alignment films are arranged so as to respectively provide first and second liquid crystal molecule pretilt angles parallel to, where M is an integer and λ is a wavelength of a light beam,
The liquid crystal layer is (M + 1) λ at the first operating voltage of the device.
Substantially equal to / 4 and M at the second operating voltage of the device.
A liquid crystal device having a retardation substantially equal to λ / 4. 25. The device of claim 24, wherein M is greater than zero or less than minus one. 26. The device according to claim 15, wherein the liquid crystal layer has a substantially constant thickness. 27. The device according to claim 15, further comprising at least one polarizing plate having a polarization direction oriented substantially at 45 ° with respect to the liquid crystal molecule pretilt angle. .