GB1603905A - Alignment control of liquid crystal molecules - Google Patents

Abstract

In order to influence the orientation of liquid-crystal molecules in a liquid-crystal display when no voltage is applied to the electrodes, an orientation layer is vapour-deposited onto the substrates which bound liquid-crystal cells. In order to achieve the orientation at a desired angle relative to the substrate surfaces, a plurality of vapour depositions are undertaken simultaneously and successively from two or more angles relative to the substrate. A device for undertaking such vapour depositions has a rotation element (72) on whose circumference substrates (74) are mounted. The rotation element (72) moves the substrates (74) past a vapour source (84). The vapour jet produced by this vapour source is split up by an impact plate (76) into two parts which successively impinge onto the substrates alternately at different angles when the element (72) rotates. <IMAGE>

Description

(54) ALIGNMENT CONTROL OF LIQUID CRYSTAL MOLECULES (71) We, CITIZEN WATCH COMPANY LIMITED, a corporation organized under the laws of Japan, of No.

1-1, 2-chome, Nishishinjuku, Shinjuku-ku, Tokyo, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to controlling the alignment of molecules in a liquid crystal display device, and more particularly, to controlling said alignment by means of slant evaporation of an alignment control material onto the substrates of liquid crystal display cells.

Liquid crystal display devices have come into wide use in recent years due to several advantages. These include low levels of power dissipation, and a capability for operating with low voltages applied to the cell electrodes. Due to these advantages, liquid crystal display devices are utilized in electronic wristwatches, portable electronic calculators, etc. The most widely used liquid crystal display devices are of the twisted nematic type (referred to herein as TN type) display devices. Such devices provide a black and white type of pattern contrast. There is a strong demand for other types of liquid crystal display devices, for example with a capability for displaying data by means of contrasting colors.Such devices include guest-host type (referred to herein as GH type) displays, in which a twocolor, or pleochroic, dye is incorporated within a nematic liquid crystal material, the dye being referred to as the "guest" material and the liquid crystal as the "host" material. Other types of color display include ECB effect liquid crystal devices, in which the angle of inclination of the liquid crystal molecules is varied in accordance with voltages applied to the cell electrodes, the color of light reflected from the cell being determined by this angle of inclination. Another type of display device utilizes the principal of dynamic scattering, whereby the liquid crystal molecules to which an electric field is applied by the cell electrodes are set into a state of disorder.

The liquid crystal material of such devices can have either a positive dielectric anistropy or a negative dielectric anistropy.

In the former case, when a voltage is applied to the electrodes of the liquid crystal cell, causing an electric field to appear between the electrodes, the liquid crystal molecules tend to become aligned in the direction of the electric field. In the case of negative dielectric anistropy, when a voltage is applied, the liquid crystal molecules tend to become aligned in a perpendicular direction with respect to the electric field. In the case of a dielectric material with a positive dielectric anistropy, it is usually desirable for the liquid crystal molecules to be aligned almost parallel to the plane of the cell substrates in the absence of an applied voltage. In the case of a material with negative dielectric anistropy, the liquid crystal molecules should be aligned almost perpendicular to the plane of the cell substrate in the absence of an applied voltage.

If the liquid crystal molecules are arranged to be exactly parallel to the substrate plane in the absence of an applied voltage, then when a voltage is applied thereby causing the liquid crystal molecules to be rotated through a certain angle, some of the molecules will be rotated through equal but opposite angles with respect to other molecules. This phenomenon is referred to as reverse tilt, and results in a loss of contrast in the case of TN type devices and in unevenness of coloration in the case of a color type of display. It is known that if the liquid crystal molecules are aligned such that they have a small inclination relative to the substrate plane, then reverse tilt is eliminated. In the case of a material in which the liquid crystal molecules are arranged perpendicular to the substrate surface in the absence of an applied voltage, a similar effect occurs.In this case, to prevent reverse tilt, it is necessary to set the molecules at a slight angle with respect to the normal to the substrate plane. In this case, therefore, a tilt bias of the order of almost 90" is required, since tilt bias is normally measured relative to the substrate plane.

It is well known that the liquid crystal molecules can be aligned in a desired direction parallel the cell substrate by slant evaporative deposition of a material such as SiO or other inorganic substance upon the inner surfaces of the substrates. This is described in US Patent 3,834,792. A method is also known whereby the tilt bias of the liquid crystal molecules can be reduced to the order of 60. This is done by performing two successive evaporations, the first evaporation being performed at an incident angle of approximately 800, while an extremely thin second layer is deposited on top of the first layer at an incident angle of approximately 60". An identical effect can be obtained by reversing the order of the first and second evaporations.However if this method is utilized, then if the two evaporations layers are deposited in two separate processes, manufacturing costs are high. If both evaporations are performed by a single evaporation process, on the other hand, then the evaporation equipment becomes complex and manufacture is difficult. Also, since the second evaporation layer must be extremely thin, e.g. of the order of 20A to 60 , deposition requires extremely precise control, and so such a process is not suited to mass production techniques.

In another method which is known in the literature, a first alignment control layer is evaporated onto the substrate at an incident angle of about 800, as in the method just described, and a second layer is then evaporated on top of the first layer at an incident angle of the order of 00. The alignment mechanism in this case is not yet clearly understood. With this method too, however, the minimum tilt bias which can be controlled is in the order of 6". Since this method also presents the same disadvantages of difficulty of control and complexity as were described for the previous method, it too is unsuited to mass production techniques.

With the method of the present invention, it is possible to align the liquid crystal molecules with a small tilt bias of the order of one or two degrees, or with larger tilt bias angles of up to 90 . Deposition of an inorganic material such as Si is deposited upon the substrate surface by two evaporations. However, in contrast to the known methods described above, the two evaporations can either be performed simultaneously or can be performed in repeated alternation, and the amount of material contributed by each evaporation to the final thickness of the alignment control layer is not critical. The use of simultaneous evaporation does not form part of the present invention. In addition, the incident angles at which the evaporants reach the substrate surface can be within very wide ranges.Due to these features, it is possible to design a simple apparatus whereby a large number of substrate can be rapidly treated by this two-evaporation process almost simultaneously. Since the method of the present invention enables tilt bias angles of between 0 and 90" to be obtained, it is applicable to a wide variety of liquid crystal display devices, and is particularly suited to new types of color display device.

According to one aspect of the present invention, there is provided a method of manufacturing a liquid crystal cell comprising forming a transparent alignment film of at least one selected material on a substrate of a liquid crystal cell, comprising: positioning at least a portion of a surface of said substrate so that the normal to said substrate makes at least two predetermined different angles with respect to directions of flow of streams of particles of said selected material from at least one source of said particles; and depositing said particles of said selected material on said portion of said surface in respective alternation from said two predetermined different angles so that said transparent alignment is formed, the thickness of the transparent alignment film being of the order of more than 60A.

According to another aspect of the present invention, there is provided a liquid crystal cell having a substrate on which a transparent alignment film of at least one selected material is formed, said transparent alignment film being formed by positioning at least a portion of a surface of a substrate so that the normal to the substrate makes at least two predetermined different angles with respect to directions of flow of streams of particles of the selected material from at least one source of said particles; and depositing the particles of the selected material on the portion of the surface in respective alternation from said two predetermined different angles so that the transparent alignment film is formed.

In the accompanying drawings: Figure 1 is a diagram illustrating the general principle of slant evaporation; Figure 2 is a cross-sectional side view of a liquid crystal cell employing the principle of dynamic scattering, with no voltage applied; Figure 3 is a cross-sectional side view of a liquid crystal cell employing the principle of dynamic scattering, with a voltage applied; Figure 4 is a cross-sectional side view of a liquid crystal cell employing the guest-host principle, with no voltage applied; Figure 5 is a cross-sectional side view of a liquid crystal cell employing the guest-host principle, with a voltage applied; Figure 6 is a cross-sectional side view of a liquid crystal cell employing the ECB effect, with no voltage applied; Figure 7 is a cross-sectional side view of a liquid crystal cell employing the ECB effect with a voltage applied;; Figure 8 is a diagram illustrating the angles of incidence of evaporations in accordance with the present invention; Figure 9 is a plan view of a cell substrate illustrating the projections of the two evaporation directions upon the substrate; Figures 10 and 11 are diagrams illustrating the angles of incidence of evaporations with the present invention when it is desired to obtain a high value of tilt bias; Figure 12 is a graph showing the effect of varying the ratio of the quantities of evaporants deposited in two evaporations, when a high value of tilt bias is produced; Figure 13 is a graph showing the effect of varying the final thickness of the alignment control film, when a high value of tilt bias is produced; Figure 14 is a graph showing the effect of varying the ratio of the evaporation rates of the two evaporations, when a high value of tilt bias is produced;; Figure 15 is a plan view of a substrate showing evaporations performed from three different directions; Figure 16 is a cross-sectional view of an apparatus for performing repetitive alternating slant deposition on a plurality of substrates; Figure 17 is another view of the apparatus of Figure 16, at right angles to the view of Figure 16; Figure 18 is a cross-sectional view of a second embodiment of apparatus for performing repetitive alternate slant deposition on a plurality of substrates; Figure 19 is a general diagram illustrating a third embodiment of an apparatus for performing repetitive alternate slant deposition on a plurality of substrates; Figures 20 and 21 are fourth and fifth embodiments of apparatus for performing repetitive alternate slant deposition on a plurality of substrates.

Referring now to the diagrams, Figure 1 illustrates the process of slant deposition by a single evaporation according to a prior art method. A stream of particles of a material such as SiO, emitted from an evaporation source 4, meets a liquid crystal cell substrate 10 at an incident angle 0 with respect to the substrate normal, 2. Alignment layer 8 is thereby formed. The action of alignment layer 8 (when the substrate is incorporated into a liquid crystal cell) causes liquid crystal molecules 6 to become aligned unidirectionally at an angle a with respect to the plane of substrate 10, in the absence of a voltage being applied to the electrodes of the liquid crystal cell. The incident angle o is referred to hereinafter as the evaporation angle, while angle a is referred to hereinafter as the tilt bias.With this single slant evaporation method, if the evaporation angle is made greater than about 750, the tilt bias becomes in the order of 20 to 300 It is possible to produce a static drive type of liquid crystal display cell using such a value of tilt bias, however the viewing angle and the display contrast are severely restricted.

In the case of a dynamic drive type of liquid crystal cell such a value of tilt bias results in the threshold characteristics being insufficiently sharply defined, so that practical devices cannot be produced by this method.

If deposition is performed by a single slant evaporation process at an evaporation angle of the order of 600, then the liquid crystal molecules become aligned at a tilt bias of 0 , i.e. perfectly parallel to the substrate plane. In this case, when a control voltage is applied to the cell electrodes, all of the liquid crystal molecules are rotated through a fixed angle by the action of the resultant electric field, but some are rotated in the opposite direction to others. This phenomenon is referred to as reverse tilt. It results in a reduction of contrast in the case of a TN type cell, and uneven display coloration in the case of color display cells.

Thus, this method too is not practicable.

In the case of a material having a positive dielectric anistropy, whereby the liquid crystal molecules become aligned in the direction of an applied electric field, it is desirable for the molecules to have a very small inclination with respect to the substrate plane, rather than being perfectly parallel to the plane. This is because this slight inclination, corresponding to the tilt bias defined above, prevents the occurrence of reverse tilt. For a liquid crystal material with a positive dielectric anistropy, a tilt bias of the order of 1" to 20 is desirable.

In the case of a liquid crystal material having a negative dielectric anistropy, for which the liquid crystal molecules become aligned perpendicular to the direction of an applied electric field, it is desirable for the liquid crystal molecules to have a large tilt bias, in most cases, approaching 900.

Some examples of liquid crystal display cells will now be described. In these examples, it is assumed that the liquid crystal material possesses a negative dielectric anistropy.

Referring to Figure 2, a cross-sectional side view is shown therein of a dynamic scattering type (referred to hereinafter as a DS type) liquid crystal display cell. A fluid crystal material, whose molecules are indicated by numeral 23, is enclosed between the inner surfaces of two substrates 26 and 30, forming a liquid crystal cell sealed at its periphery by a sealant material 28. Transparent conductive electrodes 22 and 24 are formed on the inner surfaces of substrates 28 and 30 respectively. Figure 2 indicates the case when no voltage is being applied to the cell electrodes, so that molecules 23 are aligned in a direction almost perpendicular to the cell substrates by the action of an alignment film on the inner surfaces of the substrates.As shown in Figure 3, when an alternating voltage is applied to the cell electrodes, the condition of parallel alignment of the liquid crystal molecules situated between the cell electrodes become disrupted, so that the molecules are set into a disordered, or scattered, condition. A contrasting pattern is thereby produced, due to a difference between the reflectance properties of the perpendicularly aligned molecules 32 and the disordered molecules situated between the cell electrodes, indicated by numeral 34.

Figure 4 illustrates a guest-host, or GH type of liquid crystal display cell. As in the case of the example shown in Figures 2 and 3 above, a liquid crystal material is held between two substrates 26 and 30 to form a liquid crystal cell which is sealed by a sealant material 28, while an electric field can be generated between two electrodes 22 and 24. A dichroic dye is combined with the liquid crystal material, so that the molecules of this dye are interspersed between the liquid crystal molecules. Here, the dye molecules are indicated by numeral 34 and the liquid crystal molecules by 36. In the absence of a voltage being applied to electrodes 22 and 24, the dichroic dye molecules are held almost perpendicular to the substrate surface due to the action of the surrounding liquid crystal molecules, which are considerably more numerous than the dye molecules.When an alternating voltage is applied to the cell electrodes 22 and 24, as shown in Figure 5, the liquid crystal molecules situated between the electrodes, indicated by numeral 37, become aligned almost parallel to the substrate plane. As a result, the molecules of the dichroic dye which are situated between the electrodes, indicated by numeral 39, also become aligned almost parallel to the substrate. The dichroic dye exhibits different color absorption properties on the incident light, depending upon whether its molecules are aligned parallel to or perpendicular to the direction of the incident light. A color contrast therefore is obtained between the dye mdecules situated between the cell electrodes, and the part of the dye which is situated outside the electrodes.In the case of this type of cell, if reverse tilt occurs so that some of the dichroic dye molecules becomes rotated through opposite angles when a voltage is applied to the cell electrodes 22 and 24, then uneven coloration is produced and the display visibility is reduced. It is therefore important for the liquid crystal molecules to be given a small degree of tilt bias, such that they are aligned almost, but not quite, perpendicular to the substrate plane in the absence of an applied voltage.

Figure 6 illustrates an ECB effect color liquid crystal display cell, with the same general configuration as described for the examples of Figures 2 to 5 above. As shown in Figure 6 in the absence of an applied voltage on cell electrodes 22 and 24, the liquid crystal molecules are aligned almost perpendicular to the substrate plane. When an alternating voltage is applied to the cell electrodes 22 and 24, as shown in Figure 7, then the liquid crystal molecules situated between the electrodes, indicated by numeral 42, become tilted away from the normal to the substrate plane. In this case, the wavelength of the light absorbed by the part of the liquid crystal situated between the electrodes is dependent upon the inclination of the liquid crystal molecules. It is therefore possible to produce a continuously variable multicolor display.In addition, it is not necessary that the liquid crystal molecules be aligned almost perpendicular to the substrate plane as shown in Figure 6 in the absence of an applied voltage. Instead, the molecules can be given a tilt bias significantly smaller than 90 , depending upon the type of color display effect which is desired. It is a feature of the present invention that such values of tilt bias can easily be produced, with a high degree of consistency and repeatability.

A method of the present invention whereby liquid crystal molecules may be aligned almost parallel to the substrate plane will now be described. Referring to Figure 8, a first evaporation is performed in direction 52, making an incident angle Oi with respect to the normal to the plane of substrate 10. The incident angle at which evaporation is performed will be referred to hereinafter as the evaporation angle. A second evaporation is performed in direction 50 at an evaporation angle 02.

These two evaporations are performed in repetitive alternation. The materials deposited by these first and second evaporations comprise an alignment control layer, 8, which is also called an alignment film. It is a feature of the present invention that 02 may be substantially within a range of 0 +30 while Oi can be substantially within the range 75" to 900 The evaporants used for the first and second evaporations can be the same, i.e. SiO, or can be different. If the amount of evaporant deposited by the first evaporation is very large by comparison with that of the second evaporation, then the alignment properties of the alignment layer become similar to those of a layer produced by the single evaporation process.If the amount of material deposited by the second evaporation is much greater than that of the first evaporation, then, the degree of alignment control provided by the alignment layer is weakened. It is found that if the amounts of evaporant deposited in the first and second evaporations respectively have a ratio that is within the range 10:1 to 1:20, a tilt bias of less than about 2 degrees is obtained. If a tilt bias of the order of 10 is permissible, then the above range can be extended to from 20:1 to 1:20. The maximum tilt bias which is allowable will depend upon the particular type of liquid crystal cell.It has been found by experiment that if SiO alone is used as the evaporant material in both the first and second evaporations, then if the final thickness of the alignment layer is less than 60A, the alignment properties are insufficient and cell contrast is uneven and unsatisfactory.

The alignment film should therefore have a thickness of more than 60A. If the thickness is made considerably greater, say in the order of 2000A, good alignment properties are obtained, but the alignment layer causes coloration of the display to appear, thereby affecting the display visibility. However, from the viewpoint of ease of manufacture, a thickness of the order of 2000A is preferable to a thinner alignment layer. It has been found that if the material deposited by the second evaporation is SiO2, or a mixture of SiO and SiO2, then the coloration effect just described can be considerably reduced. Experiments have also been performed in which evaporation angle 8, was varied during the deposition process in a periodic manner.It was found that if this is done, the ranges of evaporation angles given above, e.g. 75" to 90" for angle 81 and 00+30" for H2, can be exceeded during a part of each deposition period, in the case of repetitive alternating of the first and second evaporations. This is possible so long as the proportion of evaporant which is deposited at an evaporation angle outside the limits given above does not reach 50% of the total evaporant deposited.The range in which evaporation angle 02 can be varied during the evaporation process depends upon the angle OI between the projection on the substrate plane of the direction of the first evaporation and the projection on the substrate plane of the direction of the second evaporation. This angle is referred to hereinafter as the evaporation intersection angle.

The concept of the evaporation intersection angle may be more clearly understood by referring to Figure 9.

Numerals 56 and 54 indicate the projections on the plane of substrate 10 of the first and second evaporations respectively. The evaporation intersection angle is shown as p. It has been found that if the evaporation intersection angle is either or or 1800, then satisfactory values of tilt bias are obtained for periodic variation of evaporation angle 82 within the range 0 +30 . If evaporation intersection angle is 900, then satisfactory results are obtained for periodic variation of evaporation angle 82 within the range 0 +60 . It was also found that with an evaporation intersection angle of 90 , the evaporation angle 02 can vary periodically within the range 00j900, provided the proportion of evaporant deposited in the second evaporation within the evaporation angle 0Of300 is 50% or more of the total evaporant deposited by the second evaporation. It is therefore clear that the permissible range of variation for the evaporation angles of the first and second evaporations can be extremely large. Precise control of the evaporation angle is completely unnecessary. It has also been found that the final thickness of the alignment layer is not critical.Thus, the method of the present invention enables a high degree of design and operating freedom with regard to the equipment used to manufacture liquid crystal substrates having an alignment control film.

A method will now be described for depositing an alignment film upon the liquid crystal substrate surfaces whereby a tilt bias of any desired angle broadly within the range 900 to 500 or so, can be obtained. This method is particularly applicable to certain recently developed types of color liquid crystal display cells. Referring to Figure 10, it can be seen that two evaporations are performed in directions 58 and 60, at evaporation angles O and 02 respectively.

The evaporation at direction 60 will be referred to here as the first evaporation, and the evaporation in direction 58 will be referred to as the second evaporation. An evaporant is deposited in these directions upon substrate 10, forming an alignment film, the molecules of which are indicated by numeral 42. As in the case of the evaporation method described above, the first and second evaporations is performed in repetitive alternation. It is a feature of this method of the present invention that at least one of the first and second evaporations must be performed at an evaporation angle of 700 or more.In general, with this method, both the first and second evaporations should be performed at an evaporation angle of more than 70"; It is thought that this causes certain molecules of the alignment control layer to become oriented perpendicular to the substrate while others are oriented at an angle to the surface. This has been reduced both from electron microscope examination, and from measurement of the density of the alignment layer. It is thought that this results in the appearance of gaps, or cavities, in the alignment film, which provide the particular alignment properties obtained by this method. If both of the first and second evaporations are performed at an angle of less than 70 , then this effect is not obtained.

It has been found that, by this method, the tilt bias of the liquid crystal molecules can be controlled at a desired value by varying certain evaporation parameters.

These parameters are the ratio of the amounts of evaporant deposited by the first and second evaporations, the thickness of the final alignment the ratio of the layer, evaporation angles, the ratio of the evaporation rates of the first and second evaporations, the types of evaporant used for each evaporation, and the angular differences between the evaporation directions.

If the evaporation angles, evaporation rate, amounts of evaporant deposited, and the types of evaporant material are identical for each evaporation, and the evaporation directions are symmetrically arranged (such that the evaporation angles are 1800 in the case of a two-evaporation process, and are 1200 in the case of a three-evaporation process as described below), and if the thickness of the final layer of the evaporant film to be deposited is extremely thin by comparison with 20A, then a tilt bias of almost 90" can be produced. B suitably varying the above parameters, a bias tilt of less than 90" can be obtained as required.In addition, if one of the above parameters changed from an identical or symmetrical condltion, it is still possible to obtain a tilt angle of almost 900 if required, by suitably varying one or more of the other parameters to compensate.

Figure 11 illustrates the case in which evaporations are performed from two directions, 62 and 64, at evaporation angles 062 and 064 respectively. It is assumed that the same evaporant material is used and that the rates of evaporation in directions 62 and 64 are V62 and V64 respectively. These result in an alignment film being formed which causes liquid crystal molecules 68 to become inclined at a tilt bias angle a. If the quantity of evaporant deposited from direction 64, which we can designate as T64, is greater than the quantity of evaporant deposited from direction 62, referred to as T62, then a tilt bias of less than 90" is obtained, as shown in Figure 11.

The way in which the tilt bias of the liquid crystal molecules changes in accordance with changes in the ratio of the evaporant quantities of the first and second evaporations is shown in Figure 12. The graph of Figure 12 applies to the case of evaporation angles 056 and 057 being both 85 , and the evaporant material being SiO.

If the relative proportions of evaporant deposited are fixed, and if a difference is established between the evaporation angles, then the tilt bias is decreased in accordance with increase of the difference between the evaporation angles.

It has also been found that if the first and second evaporations are performed in repetitive alternation, the thickness of the layer deposited in the final evaporation step has a significant effect upon the tilt bias control properties of the alignment film.

This factor can also be used to control the value of tilt bias of the liquid crystal molecules. This is illustrated by the graph of Figure 13. It is apparent that the tilt bias angle can be controlled to be close to 900 by varying the thickness of the layer deposited in the final stage of the evaporation process.

Figure 14 shows the effect of differences in the evaporation rates of the first and second evaporations. It can be seen that, as the difference between the rates of evaporation (shown in the graph of Figure 14 as a ratio) increases, the tilt bias of the liquid crystal molecules is decreased.

Figure 15 is a plan view of evaporation from three different directions, 91, 92, and 93, upon a substrate 94, the evaporation intersection angles being 091, 092 and 093 respectively. If all other parameters are equalized and evaporation intersection angles 091, 092 and 093 are made equal to 1200 each, then an alignment film is deposited which causes the liquid crystal molecules to be aligned with a tilt bias of 90 . If, on the other hand, 891 is greater than 092, and 892 equals 093, the resultant alignment film causes the liquid crystal molecules to be aligned at a tilt bias inclined in direction 91. Thus, it is possible to control the degree of tilt bias by variation of the evaporation intersection angles. This is also possible in the case of evaporation from two directions, or from four or more directions.

It is also possible to control the degree of tilt bias of the liquid crystal molecules by varying the types of evaporant material deposited from different directions.

Referring again to Figure 10, let us assume that a material having relatively strong properties of aligning liquid crystal molecules parallel to the substrate plane is deposited from direction 60, while a material having relatively weak alignment properties is deposited from direction 58, with all other parameters such as evaporation angles Oi and O2 being equalized. This will result in an alignment layer being formed which will cause the liquid crystal molecules to become tilted in the direction of evaporation 60. The material with the strongest alignment properties for liquid crystal known at present is SiO.

Some general descriptions of embodiments of simple apparatus whereby liquid crystal cell substrates may be processed to form alignment films in accordance with the methods of the present invention will now be described. It should be noted that for the embodiments shown here, the evaporation angles shown are applicable to the case of alignment films which cause the liquid crystal molecules to have a low value of tilt bias, i.e. one or two degrees. It will however be apparent that the apparatus may easily modified in each case to produce alignment layers which provide larger degrees of tilt bias, in accordance with the methods of the present invention.

Referring to Figure 16, a rotary member, 72 is mounted on a rotatable shaft 70, by which 72 can be rotated. A number of liquid crystal cell substrates 74 are mounted on the outer periphery of rotary member 72. These substrates are mounted with the surfaces upon which an alignment film is to be deposited facing outwards. A baffle plate 76 is equipped between rotary member 72 and an evaporation source 84, which produces an evaporant beam 82. Evaporant beam 82 is split into two separate beams by means of openings 78 and 80 in mask plate 76, and it is apparent that the positions of these openings will determine the angles at which the portions of the evaporant beam 82 will impinge upon substrates 74.As rotary member 72 rotates, the evaporation angle at which deposition is performed upon each substrate will vary within a certain range, which is determined by such factors as the sizes of openings 78 and 80. However as explained above, such a periodic variation of the evaporation angle is made permissible by the methods of the present invention. Thus, as rotary member 72 rotates, the first and second evaporations are alternately and repetitively performed. lt is apparent that if the speed of rotation of member 72 is made sufficiently great, the first and second evaporations will be performed almost concurrently in effect, and that a number of substrates can be processed rapidly.The embodiment shown in Figure 18 is applicable to an evaporation intersection angle of 0 , so that the same evaporation source, 84, can be used for both the first and second evaporations. It is apparent that the evaporation angles, and the relative proportions of evaporant deposited in the first and second evaporations can be easily changed by altering the positions of mask plate 76 and the positions and sizes of openings 78 and 80. Since these positions can then be fixed, a high degree of consistency and repeatability of alignment control can be obtained. The evaporation angles and relative proportions of evaporant deposited can also be varied by changing the distance between evaporation source 84, mask plate 76, and rotary member 72, or by varying the diameter of rotary member 72.The evaporation angles can also be varied by moving evaporation source 84 to the right or to the left of the position shown in Figure 16.

Referring now to Figure 17, an apparatus is shown whereby a plurality of substrates are mounted both around the periphery and along the axis of rotary member 72. The operation of this apparatus may be understood by treating the arrangement shown in Figure 16 as a cross-sectional view of the apparatus of Figure 17, at right angles to the axis of shaft 70. Screen plates 86 are equipped in order to prevent unwanted deposition by evaporant beams from adjacent evaporation sources.

Referring now to Figure 18, an embodiment is shown therein of an apparatus whereby separate evaporation sources 101 and 96 are provided for the first and second evaporations. Evaporation angles are controlled by openings 100 and 104 in mask plate 94. These openings also serve to determine the relative proportions of evaporant deposited from eva orant sources 96 and 101. As of the embodiment shown in Figure 16 above, the evaporation angle and relative proportions of evaporants can also be varied by altering the position of mask plate 94. Since separate evaporation sources are provided for the first and second evaporations in this case, it is possible to use different types of evaporant material for these evaporations, and also to select suitable evaporation methods for evaporation sources 101 and 96, in accordance with the types of evaporant used.It is possible to use SiO for the first evaporant, for example, because of its strong alignment properties while SiO2 can be used as the second evaporant, due to its high degree of transparency. Other materials can also be used as evaporants.

The use of separate sources also enables various methods such as electron beam evaporation, ion plating, etc. to provide particular desired alignment properties for the substrates. The evaporation control equipment required for an embodiment of the type shown in Figure 18 is more complex than the arrangement shown in Figure 16, for example. However, with the methods of the present invention, the permissible range of evaporant quantity ratios is extremely wide, and the final thickness of the alignment film can be greater than 100A. Thus, even for the embodiment shown in Figure 18, the control required for the deposition process is much simple at every stage than that of previously shown methods of substrate deposition by two-evaporation methods.

With the embodiment shown in Figure 19, whereby a plurality of substrates are mounted axially and circumferentially on a rotatable member 108, the evaporation intersection angles vary along the axis of member 108. This is due to the fact that a single evaporation source 112 for the second evaporation is used together with a number of evaporation sources 116 for the first evaporation. It is apparent that the evaporation angle for the second evaporation also changes depending upon the location of substrates along the axis of member 108. However, all of the evaporation angles can be held within the range 75" to 90" by suitably positioning evaporation source 112.With this arrangement, the evaporation intersection angles is of the order of 90 , so that the permissible limits for the evaporation angle of the second evaporation are very broad, as explained previously. Because of this fact, it is unnecessary to provide a mask plate to control the evaporation angle of the second evaporation.

With the embodiment shown in Figure 20; liquid crystal cell substrates 120 are mounted on the inner periphery of rotary member 118, at an angle to the inner surface of member 118, and with the substrate surfaces on which an alignment layer is to be deposited facing inwards. Member 118 is rotated by a shaft 124, and is enclosed within an evacuated vessel 122. Evaporation source 128, provided within the periphery of rotary member 118, generates an evaporant beam which is split into two paths by a mask plate 126. It is possible to use a series of evaporation sources arranged parallel to shaft 124, so that a series of peripherally disposed substrates may be processed simultaneously, as for the examples shown in Figures 17 and 19 above.It is also Ssfible to use separate evaporation sources lax us first and second evaporations, to obtain the same advantages as explained for the example of Figure 18 above. In this case, the second evaporation source could be located close to the center of rotation of member 118. With the arrangement shown in Figure 20, installation of the evaporation equipment within an evacuated vessel is simple and convenient.

With the arrangement shown in Figure 21, cell substrates 134 are mounted on a disk-shaped rotary member 132 which is rotated by a shaft 130. A beam of evaporant from an evaporation source 136 is split into two paths by openings 138 and 140 in a mask plate 142. Thus, as member 132 rotates, first and second evaporation are repetitively and alternately performed on substrates 134. As with the previously described examples, the evaporation angles and the relative quantities of evaporant deposited in the first and second evaporations can be varied by altering the positions and sizes of openings 138 and 140, the position of evaporant source 136, and the distances between evaporant source 136, mask plate 142 and rotary member 132.

It will now be appreciated from the foregoing description that in accordance with the present invention a transparent alignment film is deposited on a substrate of a liquid crystal cell at least two predetermined evaporation angles. ,The terminology "predetermined angles" is intended to mean "fixed evaporation angles" as well as "variable evaporation angles".

WHAT WE CLAIM IS: 1. A method of manufacturing a liquid crystal cell comprising forming a transparent alignment film of at least one selected material on a substrate of the liquid crystal cell, comprising: positioning at least a portion of a surface of said substrate so that the normal to said substrate makes at least two predetermined different angles with respect to directions of flow of streams of particles of said selected material from at least one source of said particles; and depositing said particles of said selected material on said portion of said surface in repetitive alternation from said two predetermined different angles so that said transparent alignment film is formed, the thickness of the transparent alignment film being of the order of more than 60A.

2. A method as claimed in claim 1, in which a first one of said predetermined different angles is in the range substantially zero degrees to thirty degrees and a second one of said predetermined different angles is in the range substantially seventy five degrees to ninety degrees so that molecules

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (18)

**WARNING** start of CLMS field may overlap end of DESC **. materials can also be used as evaporants. The use of separate sources also enables various methods such as electron beam evaporation, ion plating, etc. to provide particular desired alignment properties for the substrates. The evaporation control equipment required for an embodiment of the type shown in Figure 18 is more complex than the arrangement shown in Figure 16, for example. However, with the methods of the present invention, the permissible range of evaporant quantity ratios is extremely wide, and the final thickness of the alignment film can be greater than 100A. Thus, even for the embodiment shown in Figure 18, the control required for the deposition process is much simple at every stage than that of previously shown methods of substrate deposition by two-evaporation methods. With the embodiment shown in Figure 19, whereby a plurality of substrates are mounted axially and circumferentially on a rotatable member 108, the evaporation intersection angles vary along the axis of member 108. This is due to the fact that a single evaporation source 112 for the second evaporation is used together with a number of evaporation sources 116 for the first evaporation. It is apparent that the evaporation angle for the second evaporation also changes depending upon the location of substrates along the axis of member 108. However, all of the evaporation angles can be held within the range 75" to 90" by suitably positioning evaporation source 112.With this arrangement, the evaporation intersection angles is of the order of 90 , so that the permissible limits for the evaporation angle of the second evaporation are very broad, as explained previously. Because of this fact, it is unnecessary to provide a mask plate to control the evaporation angle of the second evaporation. With the embodiment shown in Figure 20; liquid crystal cell substrates 120 are mounted on the inner periphery of rotary member 118, at an angle to the inner surface of member 118, and with the substrate surfaces on which an alignment layer is to be deposited facing inwards. Member 118 is rotated by a shaft 124, and is enclosed within an evacuated vessel 122. Evaporation source 128, provided within the periphery of rotary member 118, generates an evaporant beam which is split into two paths by a mask plate 126. It is possible to use a series of evaporation sources arranged parallel to shaft 124, so that a series of peripherally disposed substrates may be processed simultaneously, as for the examples shown in Figures 17 and 19 above.It is also Ssfible to use separate evaporation sources lax us first and second evaporations, to obtain the same advantages as explained for the example of Figure 18 above. In this case, the second evaporation source could be located close to the center of rotation of member 118. With the arrangement shown in Figure 20, installation of the evaporation equipment within an evacuated vessel is simple and convenient. With the arrangement shown in Figure 21, cell substrates 134 are mounted on a disk-shaped rotary member 132 which is rotated by a shaft 130. A beam of evaporant from an evaporation source 136 is split into two paths by openings 138 and 140 in a mask plate 142. Thus, as member 132 rotates, first and second evaporation are repetitively and alternately performed on substrates 134. As with the previously described examples, the evaporation angles and the relative quantities of evaporant deposited in the first and second evaporations can be varied by altering the positions and sizes of openings 138 and 140, the position of evaporant source 136, and the distances between evaporant source 136, mask plate 142 and rotary member 132. It will now be appreciated from the foregoing description that in accordance with the present invention a transparent alignment film is deposited on a substrate of a liquid crystal cell at least two predetermined evaporation angles. ,The terminology "predetermined angles" is intended to mean "fixed evaporation angles" as well as "variable evaporation angles". WHAT WE CLAIM IS:

1. A method of manufacturing a liquid crystal cell comprising forming a transparent alignment film of at least one selected material on a substrate of the liquid crystal cell, comprising: positioning at least a portion of a surface of said substrate so that the normal to said substrate makes at least two predetermined different angles with respect to directions of flow of streams of particles of said selected material from at least one source of said particles; and depositing said particles of said selected material on said portion of said surface in repetitive alternation from said two predetermined different angles so that said transparent alignment film is formed, the thickness of the transparent alignment film being of the order of more than 60A.

2. A method as claimed in claim 1, in which a first one of said predetermined different angles is in the range substantially zero degrees to thirty degrees and a second one of said predetermined different angles is in the range substantially seventy five degrees to ninety degrees so that molecules

of a liquid crystal material in said liquid crystal cell become aligned at a angle of close to zero degrees with respect to said surface of said substrate in the absence of a voltage being applied to electrodes of said liquid crystal cell.

3. A method as claimed in claim 1, in which said predetermined different angles are in the range substantially seventy degrees to ninety degrees so that molecules of a liquid crystal material in said liquid crystal cell become aligned at a desired angle broadly in the range ninety degrees to fifty degrees with respect to said surface of said substrate in the absence of a voltage being applied to electrodes of said liquid crystal cell.

4. A method as claimed in claim 3, in which the projections on the plane of said substrate surface of the directions of said streams of particles make an angle of about zero degrees or one hundred and eighty degrees with respect to each other.

5. A method as claimed in any one of preceding claims 1 to 4, in which the relative proportions of said selected material deposited on said substrate from said predetermined different angles are varied to control the alignment of said liquid crystal molecules with respect to said substrate surface.

6. A method as claimed in any one of preceding claims 1, 2 or 3, in which the relative rates at which said selected material is deposited on said substrate from said predetermined angles respectively are varied to control the alignment of said liquid crystal molecules with respect to said substrate surface.

7. A method as claimed in claim 5 or 6, in which the final thickness of said transparent alignment film is varied to control the alignment of said liquid crystal molecules with respect to said substrate surface.

8. A method as claimed in any one of preceding claims 1, 2, and 3, in which the projections on the plane of said substrate surface of the directions of said streams of particles are varied relative to one another to control the alignment of said liquid crystal molecules with respect to said substrate surface.

9. A method as claimed in any one of preceding claims 1 to 4, in which said substrate is moved during said deposition step.

10. A method as claimed in claim 9, in which said substrate is rotated at a predetermined speed during said deposition step.

11. A method as claimed in any one of preceding claims 1 to 4, in which said selected material comprises a first material and a second material deposited on said substrate by first and second streams of particles.

12. A liquid crystal cell having a substrate on which a transparent alignment film of at least one selected material is formed, said transparent alignment film being formed by positioning at least a portion of a surface of a substrate so that the normal to the substrate makes at least two predetermined different angles with respect to directions of flow of streams of particles of the selected material from at least one source of said particles; and depositing the particles of the selected material on the portion of the surface in repetitive alternation from said two predetermined different angles so that the transparent alignment film is formed.

13. A liquid crystal cell as claimed in claim 12, wherein the thickness of the transparent alignment film is greater than 60 .

14. A liquid crystal cell as claimed in claim 12 or 13, wherein the molecules of liquid crystal material are aligned at an angle of substantially zero degrees with respect to said surface of said substrate in the absence of a voltage being applied to electrodes of the liquid crystal cell.

15. A liquid crystal cell as claimed in claim 12 or 13, wherein the molecules of liquid crystal material are aligned at a desired angle in the range 90" to 500 with respect to said surface of said substrate in the absence of a voltage being applied to electrodes of the liquid crystal cell.

16. A liquid crystal cell as claimed in any of claims 12 to 15, wherein the selected material comprises a first material and a second material deposited on said substrate by first and second streams of particles.

17. A method of manufactunng a liquid crystal cell substantially as hereinbefore described with reference to the accompanying drawings.

18. A liquid crystal cell substantially as hereinbefore described with reference to the accompanying drawings.