JP3091939B2 - Manufacturing method of liquid crystal element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a liquid crystal device using a ferroelectric liquid crystal (hereinafter referred to as "FLC").

[0002]

BACKGROUND OF THE INVENTION Clark and Lagerwall are Applied Physi.
cs Letters Vol. 36, No. 11, 1980
Issued on June 1, 1998) 899-901, JP-A-56-1
No. 07216, U.S. Pat. No. 4,368,924, and U.S. Pat. No. 4,563,059, etc., describe a surface-stabilized flc (FLC).
erroelectric liquid crystal
The bistable FLC device according to 1) was identified. This bistable FLC device has a pair of pairs set at a distance small enough to control the formation of a helical array structure of liquid crystal molecules in a chiral smectic C phase (SmC ^* phase), an H phase (SmH ^* ) or the like in a bulk state. This was realized by arranging liquid crystals between substrates and arranging in one direction vertical molecular layers organized by a plurality of liquid crystal molecules.

[0003] Further, as disclosed in Japanese Patent Application Laid-Open No. 61-94023 and the like, a display element using such FLC is formed on two inner surfaces while maintaining a cell gap of about 1 to 3 µm. There is known a liquid crystal cell in which FLC is injected into a liquid crystal cell formed by facing glass substrates on which a transparent electrode is formed and subjected to an alignment treatment.

The characteristics of the above-mentioned FLC element are that the FLC has spontaneous polarization, so that the coupling force between the external electric field and the spontaneous polarization can be used for switching. Since it corresponds to one-to-one, it can be switched by the polarity of the external electric field. That is, in the state of the chiral smectic phase, one of the first optically stable state and the second optically stable state is taken in response to the applied electric field, and when no electric field is applied, the state is changed. It has a property of maintaining, that is, has bistability, and has a rapid response to a change in an electric field, and is expected to be widely used in fields such as a high-speed storage type display device.

As described above, FLC generally uses chiral smectic liquid crystal (SmC ^* , SmH ^* ), and thus exhibits a twisted orientation of the long axis of the liquid crystal molecule in a bulk state. The twist of the long axis of the liquid crystal molecule can be eliminated by placing the liquid crystal in a cell (pp. 213 to 234, NA Clark et al.).
al, MCLC, 1983, vol. 94).

A liquid crystal display device having a display panel formed of such an FLC element is disclosed, for example, in US Pat.
An image can be formed on a display screen of large-capacity pixels by using the multiplexing driving method described in, for example, Japanese Patent No. 5561. The above liquid crystal display device is
It can be used for a display screen of a word processor, a personal computer, a micro printer, a television, or the like.

The FLC element has two stable states, a light transmitting state and a blocking state, and is mainly used as a binary (white / black) display element. However, a multi-level display, that is, a halftone display is also possible. One of the halftone display methods is to create an intermediate light transmission state by controlling the area ratio of a bistable state in a pixel. Hereinafter, this method (area modulation method) will be described in detail.

FIG. 5 is a diagram schematically showing the relationship between the switching pulse amplitude and the transmittance of the FLC element. A single pulse of one polarity is applied to a cell (element) that is initially in a completely light-blocked (black) state. 7 is a graph in which the amount of transmitted light I after plotting is plotted as a function of the amplitude V of a single pulse. When the pulse amplitude is equal to or less than the threshold value V _th (V <V _th ), the transmitted light amount does not change, and the transmission state after the pulse application shows the state before the application as shown in FIG. And does not change. When the pulse amplitude exceeds the threshold value (V _th <V <V _sat ), a part of the pixel transits to the other stable state, that is, the light transmitting state shown in FIG. Furthermore pulse amplitude is increased, or the saturation value V _sat (V _sat <V)
Then, as shown in FIG. 4D, all the pixels are in a light transmitting state, and the light amount reaches a constant value. That is, in the area modulation method, the voltage is controlled so that the pulse amplitude becomes V _th <V <V _sat, and halftone is displayed.

However, in such a simple driving method,
Since the relationship between the voltage and the amount of transmitted light in FIG. 5 also depends on the cell thickness and the temperature, if there is a cell thickness distribution or a temperature distribution in the display panel, different grayscale levels are displayed for applied pulses of the same voltage amplitude. There is a problem that will be done.

FIG. 7 is a diagram for explaining this, and is a graph showing the relationship between the voltage amplitude V and the amount of transmitted light I as in FIG. 5, but showing the relationship at different temperatures, that is, at high and low temperatures, respectively. H and curve L. That is, it is not unusual for a display (display element) having a large display size to generate a temperature distribution in the same panel (display unit). Therefore, even if an attempt is made to display a halftone at a certain voltage _Vap , it is shown in FIG. would be gray levels is varied over a range from I ₁ to I ₂ as is not uniform display can be obtained.

What has been devised there is the "4-pulse method" proposed by the present inventor in Japanese Patent Application Laid-Open No. Hei 4-218022. In this driving method, as shown in FIGS. 8 and 9, a plurality of pulses (A, B, C, and D in FIG. 9) are applied to a low threshold portion and a high threshold portion on the same scanning line in the panel. Thus, the same inversion area is finally obtained ((D) in FIG. 8).

The present inventor has further disclosed in Japanese Patent Application No. 3-320542.
No. 3 proposes a “pixel shift method” in which the writing time is shorter than the “4 pulse method”.

The pixel shift method is a method of forming a distribution of electric field intensity over a plurality of scanning signal lines by simultaneously inputting and selecting different scanning signals to a plurality of scanning signal lines, and performing gradation display.

The outline of the pixel shift method will be described below.

As shown in FIG. 10, an example of a usable liquid crystal cell is one in which the threshold value in one pixel has a distribution. In the cell shown in FIG. 10, the FLC layer 55 between the electrodes
, The threshold of FLC switching also has a distribution. When the voltage applied to such a pixel is increased, switching is performed sequentially from a portion having a smaller cell thickness.

FIG. 11A shows this state. FIG.
In (a), T ₁ , T ₂ , and T ₃ indicate the temperature of the observed portion in the panel. Although the switching threshold voltage of the FLC decreases as the temperature increases, the relationship between the applied voltage and the light transmittance at the above three temperatures is shown by three curves.

The threshold value variation may be caused by other factors besides the temperature change. For convenience of explanation, the mode will be described mainly using the temperature change.

[0018] As can be seen from FIG. 11 (a), first, upon application of a voltage V _i at temperatures T ₁ after resetting the entire pixel to a dark state in a pixel can obtain a X% transmittance, temperature When but it rises to T ₂ or T _3, the same V _i
Is applied to the pixel, the transmittance becomes 100%, and the gradation display cannot be performed correctly. FIG.
(C) shows the inverted state of the pixel after writing at each temperature. Under such conditions, the written gradation information is lost due to the temperature fluctuation, so that the application range as a display element is extremely limited.

Therefore, as shown in FIG.
By displaying the pixel information over the two scanning signal lines S ₁ and S ₂ , it is possible to perform gradation display stably with respect to temperature fluctuation.

Hereinafter, this driving method will be described in detail.

FLC with continuous threshold distribution in pixel
1. Preparing a cell: A liquid crystal cell having a structure in which the cell thickness in a pixel is continuously distributed as shown in FIG. 10 can be used. Further, the present applicant has disclosed Japanese Patent Application Laid-Open No. 62-12533.
A configuration having a potential gradient in a pixel, or a configuration having a capacitance gradient, as proposed in Japanese Patent Application Publication No. 0-086. In any case, by continuously distributing the threshold value in the pixel, a region (domain) corresponding to the bright state and a region (domain) corresponding to the dark state can be mixed in the pixel. The gray scale display is enabled by the area ratio of.

This method can be used even when the light amount is modulated stepwise (for example, 16 gradations), but a continuous light amount change is necessary for analog gradation display.

Selecting Two Scanning Signal Lines Simultaneously: This operation will be described with reference to FIG. FIG. 12 (a)
Shows transmittance-applied voltage characteristics when pixels on two scanning signal lines are grouped together. In FIG. 12A, a transmittance of 0% to 100% is shown as a display area of the pixel B on the scanning signal line 2, and a transmittance of 100% to 200% is shown as a display area of the pixel A on the scanning signal line 1. ing. That is, since one pixel is configured for one scanning signal line, when two pixels are simultaneously scanned, the transmittance when both the pixel A and the pixel B are all in the light transmitting state is set to 200%. here,
Although two scanning signal lines are simultaneously selected for one piece of gradation information, a region having an area of one pixel is allocated to display one piece of gradation information. This will be described with reference to FIG.

At the temperature T ₁ , the input gradation information is written in a range corresponding to 0% when the applied voltage is V ₀ and ₁₀₀ % when the applied voltage is V ₁₀₀ . As apparent from the figure, the temperature T _1, the range (pixel region) is on all the scanning signal line 2 (in FIG. 12 (b), the reference hatched portion). However, if the temperature is T
Since the lowered threshold voltage of the liquid crystal when increases from ₁ to T _2, the same voltage in a pixel when applied to the pixel, larger area than in the temperatures T ₁ is inverted.

In order to correct this, a pixel area at the temperature T ₂ is set across the scanning signal line 1 and the scanning signal line 2 (the hatched portion in FIG. 12B showing the case of the temperature T ₂ ). ).

Next, when the temperature further rises to T ₃ , the applied voltage is changed from V _{0 to} V ₁₀₀ to set the pixel area to be drawn only on the scanning signal line 1 (FIG. 12).
(B) the hatched portion shows the case of a temperature T ₃ of).

[0027] The pixel area for the gradation display by the temperature as described above, by setting staggered in two scanning signal lines, so that it is possible to maintain the correct gradation display in the temperature range of T ₃ from T ₁ become.

It is assumed that the scanning signals applied to the two scanning signal lines selected at the same time are different from each other.
To compensate by selecting two scan signal lines simultaneously, the scan signals applied to the two selected scan signal lines must be different from each other. This will be described with reference to FIG.

The scanning signals applied to the scanning signal lines 1 and 2 are set so that the threshold values of the pixel B on the scanning signal line 2 and the pixel A on the scanning signal line 1 change continuously. In FIG. 11 (b), the transmittance at a temperature T ₁ - voltage curve, until 100% transmittance indicates that appear in the region on the scanning signal line 2, until further 200% scanning signal lines 1 is displayed in the upper area. As described above, the transmittance-voltage curve needs to be set continuously and with the same gradient from the pixel B to the pixel A.

Therefore, as shown in FIG. 13, the cell shapes of the pixel A on the scanning signal line 1 and the pixel B on the scanning signal line 2 (FIG.
Even if (b) is set to be equal, substantially the same display as the case where pixels A and B are given continuous threshold characteristics (cells in FIG. 11B) can be realized.

[0031]

SUMMARY OF THE INVENTION However, FLC
In the case of performing a gray scale display by using, the propagation delay of an electric signal in a liquid crystal panel becomes a problem. In the liquid crystal panel (input I
The propagation delay of the voltage waveform (including the resistance component within C to 1 kΩ / line) is determined by the capacitance of the liquid crystal layer, the amount of current accompanying the reversal of spontaneous polarization, the wiring resistance of the electrodes, the internal resistance of the IC, and the like. .

If the spontaneous polarization of the FLC is about 6 nc / cm ² , the effect on the rising edge of the pulse can be neglected. Therefore, the bluntness of the voltage waveform (the delay of the rising edge of the applied voltage pulse) depends on the capacitance of the liquid crystal and the capacitance. In a display having a display area of 280 mm × 220 mm determined by the wiring resistance, one signal line has a capacity of about 1314 pF, the wiring resistance is about 4.1 kΩ, and the internal resistance of the IC is about 1 kΩ. About 5.1kΩ
(Common side), and the rounding of the waveform is about 15.4 μs at the rise from 0% to 90%. In the same cell, the segment side (information signal input side) has a wiring resistance of 6.4 kΩ and I
With a C internal resistance of 1.0 kΩ, the rounding is about 22.0 μs at the rise from 0% to 90%.

The rounding inside the panel ranges from about 2.7 μs to about 22.0 μs. As shown in FIG. 10, when gradation display is performed by changing the electric field strength by changing the thickness of the liquid crystal layer (cell thickness), the rounding and the following relationship are obtained.

[0034]

[Table 1]

Accordingly, the transmittance (difference) of 18% or more occurs inside the panel, so that the display quality is remarkably deteriorated.

[0036]

SUMMARY OF THE INVENTION The present invention has been achieved in view of the above-mentioned problems, and has been achieved by providing a thick metal wiring buried in an organic resin layer on an electrode substrate constituting a liquid crystal cell. This is one in which the wiring resistance in the liquid crystal panel is reduced to reduce the rounding of the input waveform to the pixel. That is, the present invention relates to a method of manufacturing a liquid crystal element in which a ferroelectric liquid crystal is sandwiched between a pair of electrode substrates arranged opposite to each other, and an intersection between a scanning electrode group and an information electrode group provided on each electrode substrate is a pixel. A UV curable resin is placed on a metal wiring formed on a substrate, and a metal mold having a predetermined shape is pressed against the UV curable resin to fill the space between the metal wirings, and is exposed to light to expose the UV curable resin. After curing, a transparent electrode is formed on the
An electric connection between a wiring and the transparent electrode is provided.

As described above, the unevenness of the halftone display in the liquid crystal cell can be reduced by reducing the rounding of the voltage waveform.

[0038]

【Example】

Example 1 As a first example of the present invention, a liquid crystal substrate as shown in FIG. 1C was manufactured. In FIG. 1, 11 is a metal mold having a grounded KN surface, 12 is a thick film (2 μm) wiring metal, 13 is a UV curing resin, 14 is a glass substrate, and 15 is I
The TO electrode 16 is an alignment film.

FIG. 1C shows an electrode substrate for providing a distribution of the interval between the upper and lower electrodes in the pixel. The surface of the ITO film 15 has an angle with respect to the surface of the glass substrate 14.

FIGS. 1 (a) and 1 (b) show a manufacturing process of the present embodiment, in which a die 11 having a KN surface ground with a diamond tool is used, and the dimensions are A = 200 μm, B = 40.
μm, C = 0.5 μm, D = 20 μm, E = 2.0 μm
And

As a manufacturing procedure, a metal wiring 12 is formed on a glass substrate 14, a UV curable resin is dropped, and a metal mold 1 is formed.
1 is brought into contact with the metal wiring 12 and pressure is applied.
It is desirable that the resin layer on the metal wiring 12 be eliminated or be sufficiently thin (about 2000 ° or less). The strength of the pressure required for this depends on the viscosity of the UV curable resin,
By applying a pressure of about gf / cm ² , the resin on the metal wiring 12 could be made sufficiently thin.

[0042] Thus, the metal wire 12 as a spacer, the mold 11 and the glass substrate 14 is bonded across the UV curable resin 13, the direction of the surface not forming a metal wiring 12 of the glass substrate 14 By irradiating ultraviolet rays,
V-curing resin 13 is cured (UV intensity is about 500 mJ
/ Cm ² ). Thereafter , the mold 11 was peeled off from the glass substrate 14 to form an electrode substrate in which the metal wiring 12 was embedded in the UV curing resin 13 . In this step, the glass substrate 1
The silane coupling treatment was performed on the 4th side to improve the adhesiveness with the UV- curable resin 13 .

As the UV curing resin, an acrylic resin manufactured by Nippon Kayaku Co., Ltd. was used. As the silane coupling material, A-174 manufactured by Nippon Unica Co., Ltd. was diluted to 5% with methanol.

An ITO film is formed by sputtering and patterning on the metal wiring buried substrate thus manufactured.
Further thereon, as an alignment film 16, an alignment film L manufactured by Hitachi Chemical Co., Ltd.
Q-1802 was formed at about 300 ° to form the electrode substrate shown in FIG.

The electrode substrate on the opposite side has the same alignment film formed on the stripe electrode, and has no unevenness.

The rubbing directions of the upper and lower substrates were parallel to each other, and the rubbing direction of the lower substrate was shifted by about 6 ° clockwise with respect to the rubbing direction of the upper substrate.
The control of the cell thickness is as follows.
The thick portion was set to 1.64 μm. In addition, the stripe electrode on the lower substrate was patterned along the ridge so that one side of the saw shape became one pixel.

The width of the stripe electrode was set to 300 μm, and the pixel size was set to a rectangle of 300 μm × 200 μm.

As the material of the metal wiring in this embodiment, Al has a ρ of about 3.5 × 10 ⁻⁶ Ωcm, and Mo has a ρ of about 1.2 × 10 ⁻⁵ Ωcm. When the metal wiring is made of Al, the rounding amount (0-90% voltage rising amount) is improved to about 2 μm.

Table 1 shows the liquid crystal materials used.

[0050]

[Table 2]

FIG. 2 is a block diagram of a display device according to the present embodiment, and FIG. 3 is a communication timing chart of image information.

The operation will be described below with reference to the drawings. The graphics controller 102 transmits the scanning line address information for specifying the scanning electrodes and the image information (PD0 to PD3) on the scanning line specified by the address information to the display driving circuit (the scanning line driving circuit 104 and the information line (Composed by the drive circuit 105). In this embodiment, since the image information having the scanning line address information and the display information is transferred through the same transmission line, the two types of information must be distinguished. The signal for this identification is AH / DL, and this AH / DL signal is H
At the time of level, it indicates that it is scanning line address information,
The L level indicates display information.

The scanning line address information is stored in the liquid crystal display device 10.
1, the image information PD0 to PD
After being extracted from the image information transferred as 3,
The data is output to the scanning line driving circuit 104 at the timing of driving the designated scanning line. The scanning line address information is input to the decoder 106 in the scanning line driving circuit 104, and the designated scanning electrode of the display panel 103 is driven by the scanning signal generation circuit 107 via the decoder 106. On the other hand, the display information is guided to the shift register 108 in the information line driving circuit 105, and is shifted in units of four pixels by the transfer clock. When the shift register 108 completes the shift for one scanning line in the horizontal direction, the display information for 1280 pixels is transferred to the associated line memory 109 and stored for one horizontal scanning period, and the information signal generation circuit 110 Is output to each information electrode as a display information signal.

Further, in this embodiment, the driving of the display panel 103 in the liquid crystal display device 101 and the generation of the scanning line address information and the display information in the graphics controller 102 are performed asynchronously. It is necessary to synchronize (101/102). The signal that governs this synchronization is SYNC, which is generated by the drive control circuit 111 in the liquid crystal display device 101 every horizontal scanning period. The graphics controller 102 always monitors the SYNC signal. When the SYNC signal is at the L level, the image information is transferred. When the SYNC signal is at the H level, the transfer is performed after the transfer of the image information for one horizontal scanning line is completed. Do not do. That is, in FIG. 2, upon detecting that the SYNC signal has become L level, the graphics controller 102 immediately sets the AH / DL signal to H level and starts transferring image information for one horizontal scanning line. The drive control circuit 111 in the liquid crystal display device 101 sets the SYNC signal to the H level during the image information transfer period. After the writing to the display panel 103 is completed after a predetermined horizontal scanning period, the drive control circuit (FLCD controller) 111
The NC signal is returned to the L level again, and image information of the next scanning line can be received.

(Embodiment 2) FIG. 4 shows a second embodiment of the present invention.

When the size of the liquid crystal cell is increased, the bonding area between the UV-curable resin and the mold increases, and it becomes extremely difficult to remove the mold after curing the resin, which causes a reduction in the yield in the process.

This embodiment is an example in which this problem is solved by providing a release layer (41 in FIG. 4) on the surface of the mold. As the resin used for the release layer, it is preferable that the adhesive strength to the UV curable resin is weak and the strength of the resin itself is low. For example, a water-soluble PVA (polyvinyl alcohol) resin or a positive resist is suitable.

In the present embodiment, a PVA resin layer is provided as described below, but it is considered that a liquid surface incompatible with a Langmuir film or a UV-curable resin may be subjected to a vapor treatment on the mold surface. Alternatively, the first layer may be formed of an alkyl fluoride-based thin film, and a peeling resin layer may be formed thereon.

In this example, the PVA resin was 3 ° at 80 °.
What was baked for 0 minutes was used.

In this embodiment, the rounding of the voltage waveform is reduced by the metal wiring, and the yield in the manufacturing process is improved.

Third Embodiment FIG. 14 shows a third embodiment of the present invention. First, a metal wiring 12 of about 1 μm is formed on a glass substrate 14 (a). Next, a color filter layer (R, G, B) 14 is formed on the substrate.
1a to 141c are formed (b). A metal wiring having the same pattern as the metal wiring 12 formed in (a) is formed on the already formed metal wiring 12 (about 5000 °) (c). A UV curable resin 13 is dropped on the substrate (d), and a metal wiring is formed.
A light-shielding metal layer at the time of exposure was provided on the surface in the same shape as No. 12 . A transparent substrate having a smooth surface is placed on the mold 11
(E). After pressing the glass substrate 14 and the mold 11 with sufficient force, the mold 11 is irradiated with UV light from the mold 11 side for exposure (700 mJ / cm ₂ for 1 min).
After the UV curing resin 13 is cured, the press-contacted mold 11 is separated from the glass substrate 14 (f).

The remaining amount of the resin on the metal wiring 12 is determined by the smoothness of the mold and the pressure at the time of pressure bonding.
When a force of / cm ² was applied, a resin layer of about 3000 ° was partially left. However, since the resin layer remaining on the metal wiring is not cured, it can be removed by washing. Therefore, after cleaning, an ITO film is formed and patterned, so that electrical contact with the metal wiring can be obtained.

Depending on the thickness of the remaining resin layer on the metal wiring, the ITO layer and the metal wiring may be electrically insulated.
Can be conducted by vapor deposition and patterning with a thickness of about 1000 ° (h).

In this embodiment, the width of the metal wiring is about 20 μm.
m. The same UV curing resin as in Example 1 was used, and the silane coupling treatment was performed on the glass substrate side.

[0065]

As described above, according to the present invention,
It is possible to manufacture a liquid crystal element having excellent display characteristics by reducing propagation delay of a voltage waveform without adding a complicated step.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a block diagram of a liquid crystal display device to which the liquid crystal element obtained in Example 1 is applied.

3 is a communication timing chart of image information of the liquid crystal display device shown in FIG.

FIG. 4 is an explanatory view of a second embodiment of the present invention.

FIG. 5 is a diagram schematically showing the relationship between voltage and transmittance in a conventional area modulation method.

FIG. 6 is a diagram showing a voltage and a light transmission state of a pixel in a conventional area modulation method.

FIG. 7 is a diagram showing a change in voltage-transmittance shown in FIG. 5 with temperature.

FIG. 8 is an explanatory diagram of a driving method of a conventional four-pulse method.

FIG. 9 is an explanatory diagram of a driving method using a conventional four-pulse method.

FIG. 10 is a sectional view of a liquid crystal cell having a cell thickness gradient used for gradation display of an FLC element.

FIG. 11 is an explanatory diagram of a conventional pixel shift method.

FIG. 12 is an explanatory diagram of a conventional pixel shift method.

FIG. 13 is an explanatory diagram of a conventional pixel shift method.

FIG. 14 is an explanatory view of a third embodiment of the present invention.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hideaki Takao 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-5-313149 (JP, A) JP-A-63 -133121 (JP, A) JP-A-4-218022 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/1343 G02F 1/141 G02F 1/13 101 G02F 1 / 133 G09F 9/30

Claims (3)

(57) [Claims] 1. A method of manufacturing a liquid crystal element in which a ferroelectric liquid crystal is sandwiched between a pair of electrode substrates disposed opposite to each other, and an intersection between a scanning electrode group and an information electrode group provided on each electrode substrate is a pixel. By placing a UV curable resin on a metal wiring formed on a substrate and pressing a mold having a predetermined shape,
A UV curable resin is filled between the metal wirings and exposed to light,
After curing the V-cured resin, a transparent electrode is formed on top of it
And electrically connecting the metal wiring and the transparent electrode . 2. The method according to claim 1, wherein the resin pressing surface of the mold is a plane parallel to the substrate. 3. The liquid crystal device according to claim 1, wherein periodic irregularities are formed on the resin pressing surface of the mold so that the thickness of the UV curing resin has a distribution within one pixel. Manufacturing method.