JP2820163B2 - Cell thickness measurement device for liquid crystal cells - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to an apparatus for measuring a cell thickness of a liquid crystal cell, which aims to easily and accurately measure a cell thickness in a fine region, and to optically measure a liquid crystal cell to be measured. A compensating liquid crystal cell for compensating for the functional action is disposed facing the liquid crystal cell to be measured, these are sandwiched between a polarizer and an analyzer having orthogonal polarization directions, and a power supply for applying a voltage to the compensating liquid crystal cell; A light source provided on the polarizer side; and a transmitted light amount detecting unit provided on the analyzer side, wherein the transmitted light amount is detected by the transmitted light amount detecting unit while changing the voltage applied to the compensation liquid crystal cell, and the transmitted light amount is detected. The configuration is such that the cell thickness of the liquid crystal cell to be measured is measured by determining the voltage at which the light quantity becomes minimum.

[Industrial applications]

 The present invention relates to a cell thickness measuring device for a liquid crystal cell.

2. Description of the Related Art A liquid crystal display panel is composed of a liquid crystal cell in which liquid crystal is sealed between a pair of substrates, and performs image formation by applying a voltage to electrodes provided on opposing surfaces of these substrates. In a liquid crystal display panel, display characteristics such as display color and viewing angle characteristics greatly depend on the cell thickness (the thickness of the enclosed liquid crystal), and it is necessary to measure the cell thickness accurately in order to improve quality. It is.

[Conventional technology]

Conventionally, the measurement of the cell thickness of a liquid crystal cell has been performed by an apparatus as shown in FIG. In FIG. 8, a compensating liquid crystal cell 2 for compensating an optical effect on the liquid crystal cell 1 is provided. The liquid crystal cell 1 to be measured includes a pair of parallel substrates 1a and 1b.
The liquid crystal 1c is enclosed between the two. The compensating liquid crystal cell 2 is similarly formed by enclosing a liquid crystal 2c between the substrates 2a and 2b. The compensating liquid crystal cell 2 is formed so that the pair of substrates 2a and 2b are not parallel and form a wedge at a small angle. Things. The liquid crystal encapsulated therein is of the same type, but the arrangement is changed to compensate for the optical effect. For example, in the case of a liquid crystal cell including a twisted nematic (TN) type liquid crystal, the twist direction of the liquid crystal of the compensation liquid crystal cell 2 is formed in a direction opposite to the twist direction of the liquid crystal of the liquid crystal cell 1.

Such a liquid crystal cell 1 and a compensating liquid crystal cell 2 are arranged to face each other, and a polarizer 3 and an analyzer 4 whose polarization directions are orthogonal to each other are arranged on both sides of the compensating liquid crystal cell 2 and the liquid crystal cell 1 to be measured. A light source is provided below the polarizer 3, the polarized light passing through the polarizer 3 is transmitted through the liquid crystal cell 1 to be measured and the compensation liquid crystal cell 2, and the transmitted light is observed from above the analyzer 4.

In the apparatus of Figure 8, the light passing through the polarizer 3 is polarized P ₁ constant towards the line, as for example P ₂ according twist direction of the liquid crystal when the polarization P ₁ is passing through the liquid crystal cell 1 to be measured At 90
Rotate by degrees. The polarized light P ₂ that exits the liquid crystal cell 1 to be measured and enters the compensation liquid crystal cell 2 rotates as P _{3 in} a twist direction opposite to that when passing through the liquid crystal cell 1 to be measured. As described above, the compensating liquid crystal cell 2 acts to cancel the optical rotation of the liquid crystal cell 1 to be measured, and the degree of the cancellation of the optical rotation depends on the relationship between the thickness of the liquid crystal cell 1 to be measured and the thickness of the compensating liquid crystal cell 2. . If the measured liquid crystal cell 1 and the compensating liquid crystal cell 2 have the same cell thickness, the amount of polarization rotation when passing through the compensation liquid crystal cell 2 is larger than the amount of polarization rotation when passing through the measured liquid crystal cell 1. But the directions are the same but the compensating liquid crystal cell 23
The polarized light P ₃ that exits through the polarizer 3 passes through the liquid crystal cell 1 to be measured.
The same as the polarization P ₁ before entering the. The analyzer 4 transmits only polarized light orthogonal to the polarizer 3 and does not transmit polarized light P ₄ (P ₁ ) traveling from the compensating liquid crystal cell 2 to the analyzer 4. Since the compensating liquid crystal cell 2 is formed in a wedge shape, there is a point along the slope having the same thickness as the thickness of the liquid crystal cell 1 to be measured. It becomes bigger or smaller than it is. Therefore, as shown in FIG. 9, when the analyzer 4 is viewed from above, a black streak B occurs at the point of the compensating liquid crystal cell 2 where the thickness of the liquid crystal cell 1 to be measured is the same. Therefore, if the thickness of the reference point of the compensating liquid crystal cell 2 is measured in advance, the cell pressure can be easily measured simply by overlapping the liquid crystal cell 1 to be measured on the compensating liquid crystal cell 2.

[Problems to be solved by the invention]

However, in the above-described device, the liquid crystal cell 1 to be measured is
The point where black streaks B are formed changes when the thickness of
There is a problem that the relationship between the point where the black streak B is formed and the reference point of the compensating liquid crystal cell 2 deviates, making it difficult to measure the cell thickness accurately. Further, the above-described apparatus is not suitable for measuring the thickness of the liquid crystal cell 1 to be measured at each minute point corresponding to a pixel.

SUMMARY OF THE INVENTION An object of the present invention is to provide a cell thickness measuring device for a liquid crystal display cell which can easily and accurately measure even a cell thickness in a fine region.

[Means for solving the problem]

According to the cell thickness measuring apparatus for a liquid crystal cell of the present invention, a compensating liquid crystal cell for compensating an optical effect on a liquid crystal cell to be measured is arranged opposite to the liquid crystal cell to be measured, A polarizer and an analyzer whose polarization directions are orthogonal to each other are arranged on both sides of the liquid crystal cell, a power supply for applying a voltage to the compensating liquid crystal cell, a light source provided on the polarizer side, and a transmission provided on the analyzer side. A light quantity detecting means, wherein the transmitted light quantity is detected by the transmitted light quantity detecting means while changing the voltage applied to the compensation liquid crystal cell, and a voltage at which the transmitted light quantity becomes the minimum is obtained, thereby to reduce the cell thickness of the liquid crystal cell to be measured. It is characterized in that it is measured.

(Operation)

In the above configuration, changing the voltage applied to the compensation liquid crystal cell changes the light transmission characteristics of the compensation liquid crystal cell.
Therefore, when the amount of transmitted light passing through the liquid crystal cell to be measured and the compensating liquid crystal cell is detected, the amount of transmitted light also changes according to the applied voltage. The transmitted light amount shows a downwardly convex pattern according to the configuration of the liquid crystal cell to be measured and the compensation liquid crystal cell, and has a minimum value.
Therefore, the cell thickness of the liquid crystal cell to be measured is measured by finding the voltage at which the amount of transmitted light is minimum. The relationship between the applied voltage and the cell thickness of the liquid crystal cell to be measured can be prepared in advance.

〔Example〕

1 to 3, a liquid crystal cell thickness measuring apparatus according to an embodiment of the present invention uses a twisted nematic (TN) liquid crystal cell 10 including a twisted nematic (TN) type liquid crystal. Liquid crystal cell containing liquid crystal
12 is provided. The cell thickness of the compensation liquid crystal cell 12 is the liquid crystal cell to be measured.
It is approximately equal to the cell thickness of 10, but does not have to be exactly equal. As shown in FIG. 2, the liquid crystal cell 10 to be measured is, for example, a pair of parallel transparent substrates 10a and 10b.
And a liquid crystal 10c sealed between the substrates 10a and 10b. Electrodes 10d and 10e for image formation are formed on opposing surfaces of the two substrates 10a and 10b, that is, inner surfaces, respectively, and the electrodes 10d of the lower substrate 10a are provided by the number of pixels,
The electrode 10e of the upper substrate 10b is a solid ITO electrode film common to these electrodes 10d. The lower substrate 10a can be configured as an active matrix substrate incorporating a thin film transistor (TFT), and in this case, each electrode 10d is connected to each transistor. When a color liquid crystal display panel is formed, a color filter is provided on an upper substrate 10b, and an electrode 10e is provided thereon. Further, the waste film 10f and 10g are arranged on the respective substrates 10a and 10b so as to be in contact with the liquid crystal 10c. On the other hand, as shown in FIG. 3, the compensating liquid crystal cell 12 similarly has a pair of parallel transparent substrates 12a and 12b.
And a liquid crystal 12c sealed between the substrates 12a and 12b. However, the electrodes 12d and 12e are both solid electrode films of ITO. Alignment films 12f and 12g have liquid crystal 12c on respective substrates 12a and 12b.
It is arranged so that it may contact.

The liquid crystal cell 10 to be measured and the compensation liquid crystal cell 12 are arranged to face each other. In this case, the liquid crystal cell 10 to be measured and the compensation liquid crystal cell 12 can be arranged so as to be in contact with each other,
Alternatively, they may be arranged with a gap so as not to contact. Further, a polarizer 14 is provided below the liquid crystal cell 10 to be measured.
Are arranged, and an analyzer 16 is arranged above the compensation liquid crystal cell 12. The analyzer 16 is arranged in a crossed Nicols relationship with the polarizer 14, that is, so that the transmitted polarization directions are orthogonal to each other. A light source 18 is provided below the polarizer 14, and a transmitted light amount detecting means 20 is provided above the analyzer 16. The transmitted light amount detecting means 20 is constituted by, for example, a photodiode or a photomultiplier.

Further, a power supply 22 for applying a voltage to the compensation liquid crystal cell 12 is provided, and the power supply 22 is connected to upper and lower electrodes 12 d,
Connected to 12e. When measuring the cell thickness, no voltage is applied to the electrodes 10d and 10e of the liquid crystal cell 10 to be measured.

In such a configuration, the light passing through the polarizer 14 from the light source 18 is a polarized light P ₁ constant towards the line, P ₂ according twist direction of the liquid crystal when the polarization P ₁ is passing through the liquid crystal cell 10 to be measured
Rotate 90 degrees like. Furthermore, the polarized light P ₂ that exits the liquid crystal cell 10 to be measured and enters the compensation liquid crystal cell 12
Than when passing through the 10 to optical rotation as P ₃ according to the reverse twist direction. like this. The compensating liquid crystal cell 12 acts to cancel the optical rotation of the liquid crystal cell 1 to be measured. The degree of canceling the optical rotation depends on the relationship between the thickness of the liquid crystal cell 10 to be measured and the thickness of the compensating liquid crystal cell 12. In the measurement of the cell thickness of the prior art, the cell thickness of the liquid crystal cell 10 to be measured is determined by the reference thickness of the compensation liquid crystal cell 12, but in the present invention, the transmission is performed while changing the voltage applied to the compensation liquid crystal cell 12 pressure. The transmitted light quantity is detected by the light quantity detecting means 20, and the cell thickness of the liquid crystal cell 10 to be measured is measured by obtaining a voltage at which the transmitted light quantity becomes the minimum.

For this purpose, as shown in FIG. 6, it is preferable to provide a computer controller 24 which receives the output of the transmitted light amount detecting means 20 and sends a control output to the power supply 22. The sixth
FIG. 1 is a view showing an embodiment in which the present invention is carried out using a microscope 26. The liquid crystal cell 10 to be measured and the compensation liquid crystal cell 1 shown in FIG.
2. The polarizer 14, and the analyzer 16 are supported by a holder 28 as an assembly 100, and the holder 28
It can be attached to 30. The stage 30 is movable vertically and horizontally. Light source 18 is a microscope
The transmitted light amount detecting means 20 is attached to the eyepiece 32 of the microscope 26. The power supply applies a voltage to the upper and lower electrodes 12d and 12e of the compensation liquid crystal cell 12. In this manner, the cell thickness can be measured even in a minute area of the liquid crystal cell 10 to be measured.

FIG. 4 is a diagram showing the relationship between the voltage applied to the compensation liquid crystal cell 12 and the amount of transmitted light detected by the transmitted light amount detecting means 20. As is apparent from FIG. 4, as the applied voltage increases, the amount of transmitted light decreases, reaches a minimum at a predetermined voltage value _VL , and then increases rapidly. The predetermined voltage value _VL is determined according to the thickness of the liquid crystal cell 10 to be measured, and will be described in detail below.

Here, [Delta] n the (Δn = n _e -n _o) the refractive index anisotropy of the liquid crystal and the thickness of the liquid crystal and d and (cell thickness). The subscript 1 is given to the liquid crystal cell 19 to be measured, and the subscript 2 is given to the one representing the compensating liquid crystal cell 12. When a voltage is applied to the compensating liquid crystal cell 12, the liquid crystal molecules gradually rise, but the elevation angle of each liquid crystal molecule differs between the vicinity of the substrate and the central portion between the substrates. cos ² θ> is used. The substantial birefringence when a voltage is applied to the compensation liquid crystal cell 12 is Δn ₂ · d ₂ · <cos ² θ>.

When Δn ₁ · d ₁ = Δn ₂ · d ₂ · <cos ² θ> holds, the optical rotations of the measured liquid crystal cell 10 and the compensating liquid crystal cell 12 cancel each other out, and the amount of transmitted light becomes a specific minimum value V _L. Therefore, if the amount of transmitted light shows a specific minimum value _VL , it is not known whether or not the cell thicknesses of the measured liquid crystal cell 10 and the compensating liquid crystal cell 12 are the same, but it means that the optical rotation of each cell is the same.
In the above equation, Δn ₁ , Δn ₂ , d ₂ are known, and d ₁ , <c
os ² θ> is unknown. Therefore, if <cos ² θ> is known, d ₁ can be known. The principle of the present invention is that <cos ² θ
> Is determined corresponding to the applied voltage of the compensation liquid crystal cell 12, and the relationship between <cos ² θ> and the applied voltage is prepared in advance.

One example representative of this relationship is shown in FIG. <
Instead of using cos ² θ directly, Δn ₂ · d ₂ <cos ² θ> obtained by multiplying <cos ² θ> by a constant Δn ₂ · d ₂ can be used, and Δn ₂ · d ₂ · <cos ² θ> is equal to Δn ₁ · d ₁ . Here, first, data that indicates the relationship between <cos ² θ> and the applied voltage is prepared from Δn ₁ · d ₁ . First, Δn ₁
the Known reference liquid crystal cell was prepared several points to d _1, each reference crystal cell overlapping the compensating liquid crystal cell 12 in place of the measured liquid crystal cell 10 of FIG. 1, the amount of transmitted light was measured while applying a voltage , A predetermined voltage value _{VL at} which the amount of transmitted light is minimized. Each circle in FIG. 5 indicates a predetermined voltage value of each reference liquid crystal cell.
_VL is plotted on a graph and these predetermined voltage values _VL are plotted to obtain a generally applicable straight line or curve.

Therefore, for the unknown d ₁ liquid crystal cell 10 to be measured, the liquid crystal cell 10 to be measured is superimposed on the compensating liquid crystal cell 12, and the amount of transmitted light is measured while applying a voltage. I asked _L, and the can be determined unknown [Delta] n · d ₁ of the predetermined voltage value V _L is applied to the relationship of FIG. 5. For example, if the predetermined voltage value _VL is 3.6 V as shown in FIG. 4, Δn ₁ · d ₁ where the predetermined voltage value _{VL in} FIG. 5 becomes 3.6 V
Is 0.505 μm. It is known that Δn ₁ is 0.09, and d ₁ is 0.505 ÷ 0.09 to 5.6 μm. In this way, the cell thickness of the measurement liquid crystal cell 10 can be accurately measured.

FIG. 7 is a diagram summarizing the procedure for measuring the cell thickness of the measurement liquid crystal cell 10. In step 51, a voltage is supplied to the compensation liquid crystal cell 12, and in step 52, the amount of light transmitted from the analyzer 16 is detected. In step 53, the relationship between the supply voltage and the amount of transmitted light is monitored to determine a predetermined voltage value _VL that minimizes the amount of transmitted light. Next, the predetermined voltage value _VL detected in step 54 is applied to the relation of the database, and Δ
Find n ₁ · d ₁ . Once Δn ₁ · d ₁ is known, it is easy to calculate d ₁ .

In this embodiment, the measured liquid crystal cell 10 and the compensation liquid crystal cell
Numeral 12 contains a twisted-nematic (TN) type liquid crystal. However, in the present invention, twisted nematic (T
The present invention can be applied to a liquid crystal cell containing a liquid crystal other than the N) type liquid crystal, for example, a homogeneous type liquid crystal.

〔The invention's effect〕

As described above, according to the present invention, a compensating liquid crystal cell for compensating an optical effect on a liquid crystal cell to be measured is disposed opposite to the liquid crystal cell to be measured, A polarizer and an analyzer whose polarization directions are orthogonal to each other are arranged on both sides of the liquid crystal cell, a power supply for applying a voltage to the compensating liquid crystal cell, a light source provided on the polarizer side, and a transmission provided on the analyzer side. A light quantity detecting means, wherein the transmitted light quantity is detected by the transmitted light quantity detecting means while changing the voltage applied to the compensation liquid crystal cell, and a voltage at which the transmitted light quantity becomes the minimum is obtained, thereby to reduce the cell thickness of the liquid crystal cell to be measured. Since the measurement is performed, the cell thickness of the liquid crystal cell can be easily and accurately measured by measuring the voltage value and the amount of transmitted light, and the cell thickness can be measured even in a minute area of the liquid crystal cell. it can.

[Brief description of the drawings]

1 is a view showing an embodiment of the present invention, FIG. 2 is a sectional view of a liquid crystal cell to be measured in FIG. 1, FIG. 3 is a sectional view of a compensating liquid crystal cell in FIG. 1, and FIG. FIG. 5 is a diagram showing the relationship between the voltage at which the transmitted light amount becomes minimum and the cell thickness alternative value, FIG. 6 is a front view showing the embodiment mounted on a microscope, and FIG. Is a diagram showing a cell thickness measurement procedure, and FIG.
FIG. 9 is a diagram showing the prior art, and FIG. 9 is a diagram showing black streaks generated in the analyzer of FIG. 10: Liquid crystal cell to be measured, 12: Compensating liquid crystal cell, 14: Polarizer, 16: Analyzer, 18: Light source, 20: Transmitted light amount detecting means, 22: Power supply.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Makoto Ohashi 1015 Uedanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited (56) References JP-A-1-97807 (JP, A) (58) Fields investigated (Int.Cl. ⁶ , DB name) G01B 11/00-11/30 G02F 1/13

Claims (3)

(57) [Claims] 1. A liquid crystal cell to be measured and a compensating liquid crystal cell for compensating an optical effect on the liquid crystal cell to be measured are arranged opposite to the liquid crystal cell to be measured. A polarizer (14) and an analyzer (16) whose polarization directions are orthogonal to each other are arranged, and a power supply (22) for applying a voltage to the compensation liquid crystal cell, and a light source (18) provided on the polarizer side And a transmitted light amount detecting means (20) provided on the analyzer side, wherein the transmitted light amount is detected by the transmitted light amount detecting means while changing the voltage applied to the compensation liquid crystal cell, and the transmitted light amount is minimized. A cell thickness measuring device for a liquid crystal cell, wherein the cell thickness of a liquid crystal cell to be measured is measured by obtaining a voltage. 2. The cell thickness measuring apparatus according to claim 1, wherein when the liquid crystal cell to be measured includes a twisted nematic liquid crystal, a compensation liquid crystal cell including a twisted nematic liquid crystal is used. 3. The cell thickness measuring apparatus for a liquid crystal cell according to claim 1, wherein when the liquid crystal cell to be measured contains a homogeneous liquid crystal, a compensating liquid crystal cell containing a homogeneous liquid crystal is used.