CH615282A5 - Method and device for influencing the orientation of liquid-crystal molecules - Google Patents

Description

615 282

2nd

PATENT CLAIMS

1. A method for producing a transparent orientation layer made of at least one predetermined material on a substrate of a liquid crystal cell, characterized in that at least a part of the surface of the substrate is arranged such that the surface normal forms at least two predetermined angles with the directions of particle beams of the predetermined material , wherein the rays are generated by at least one particle source and that the particles on the part of the surface form the transparent orientation layer simultaneously or alternately in succession.

2. The method according to claim 1, characterized in that the first of these predetermined angles is in a range from 0 to 30 degrees and the second in a range from 75 to 90 degrees, whereby the molecules of a liquid crystal material in the liquid crystal cell at an angle of Align almost 0 degrees with respect to the substrate surface if no voltage is applied to the electrodes of the liquid crystal cell.

3. The method according to claim 1, characterized in that the predetermined angles in a range of 70 to 90 degrees, whereby the molecules of a liquid crystal material in the liquid crystal cell align at a predetermined angle between 90 and 50 degrees with respect to the substrate surface, if no electrical Voltage is applied to the electrodes of the liquid crystal cell.

4. The method according to claim 3, characterized in that the projections of the particle beam directions on the substrate surface form an angle with one another of approximately 0 to 180 degrees.

5. The method according to any one of claims 1 to 4, characterized in that the ratio of the amounts of the material deposited at the predetermined different angles on the substrate is changed in order to influence the orientation of the liquid crystal molecules with respect to the substrate surface.

6. The method according to any one of claims 1 to 3, characterized in that the ratio of the evaporation rates at which the material is deposited on the substrate from the predetermined angles is changed in order to influence the orientation of the liquid crystal molecules with respect to the substrate surface.

7. The method according to claim 5 or claim 6, characterized in that the final thickness of the transparent orientation layer is changed in order to influence the orientation of the liquid crystal molecules with respect to the substrate surface.

8. The method according to any one of claims 1 to 3, characterized in that the projections of the particle beam directions on the substrate surface are shifted against each other in order to influence the orientation of the liquid crystal molecules with respect to the substrate surface.

9. The method according to any one of claims 1 to 4, characterized in that the substrate is moved during the vapor deposition phase.

10. The method according to claim 9, characterized in that the substrate performs a rotation at a predetermined speed during the vapor deposition phase.

11. The method according to any one of claims 1 to 4, characterized in that two predetermined materials are used, the first being deposited on the substrate by means of the first particle beam and the second by means of the second particle beam.

12. The device for carrying out the method according to claim 1, characterized by at least one device for generating particle beams from at least one material, the particle beams having at least two different directions and by elements for holding and rotating the substrate, so that the particle beams are repeated at least a part of the substrate surface impinge at least two different directions, which form predetermined angles to the substrate surface, the particles thereby forming the transparent orientation layer on this part of the substrate surface.

13. The apparatus according to claim 12, characterized in that the device for generating particle jets has a steam source for generating a steam jet and a m baffle plate with at least two openings and the baffle plate is arranged with respect to the steam source so that the steam jet is split into at least two jets and that the elements for holding and rotating the substrate have a rotary element, to the periphery of which several substrates can be attached, the rotary element being arranged with respect to the baffle plate in such a way that the two beams are repeated onto the substrates at the two predetermined angles hit when the rotating element rotates.

: 14. Device according to claim 12, characterized in that the device for generating particle jets has several steam sources for generating steam jets, and a baffle plate with several pairs of openings which split the steam jets into several pairs of jets: s and that the elements for holding the Substrate have a rotary element, on the periphery of which a plurality of substrates can be attached, the rotary element being arranged with respect to the baffle plate in such a way that each pair of rays is repeated at the two predetermined angles on the subii! strate occurs when the rotary element rotates and that the device further comprises at least one shielding plate which keeps the steam jets within a certain directional range.

15. The apparatus according to claim 12, characterized in that the device for generating particle beams has at least two steam sources which are arranged such that they generate steam jets in mutually perpendicular directions, and a baffle plate of rectangular cross section with at least two openings, the baffle plate and the steam sources being arranged in such a way that at least some of the steam jets pass through these openings and that the elements for holding and rotating the substrate also have a rotating element, on the periphery of which several substrates can be attached, wherein this rotating element is arranged with respect to the baffle plate in such a way that the parts of the steam jets repeatedly hit the substrates at two predetermined angles when the rotating element rotates.

16. The apparatus according to claim 12, characterized in that the device for generating particle jets several steam sources for generating first steam jets, at least one shielding plate between the steam sources, which keeps the steam jets within a certain directional range, and at least one steam source ss for Generating a second steam jet perpendicular to the first steam jets, and that the elements for holding and rotating the substrate have a rotary element, on the periphery of which a plurality of substrates can be attached, the rotary element being arranged with respect to the baffle plate such that the first and second Vapor jets repeatedly hit the substrates at two predetermined angles as the rotating element rotates.

17. The apparatus according to claim 12, characterized in that the device for generating particle beams

(, 5 has a steam source for generating a steam jet and an impact plate, which are arranged relative to one another such that the impact plate splits the steam jet into a first and a second jet and that the elements for holding

3rd

615 282

and to rotate the substrate, a rotating element on a field like to see almost parallel to the plane of the cell sub-surface, on the inner circumference of which several substrates in one strate. For a material with a negative dielectric

Angles to its inner surface are attachable, the anisotropy should be the liquid crystal molecules on the other hand

Orient the steam source within the inner circumference of the rotation, almost perpendicular to the plane of the cell substrate, and the device is further arranged if the liquid crystal molecules in the absence of an evacuated container, which is arranged to receive the electric field exactly parallel to the plane of the substrate rotating element with the attached substrates, which are net, they rotate when applying an electric field to the steam source and the baffle plate is intended. through a certain angle, but with single molecules

18. The apparatus according to claim 12, characterized in that the angle opposite to the other molecules is rotated so that the device for generating a particle beam is rotated len. This phenomenon is referred to as a backward tip - a steam source for generating a steam jet and a pen and has a reduction in the Contrastwir baffle plate with openings, the steam source kung in TN types and an uneven color distribution in the baffle plate being arranged such that the Steam trap resulting in color displays. It is known that this jet is prevented when it passes through the openings in a first and backward tilt when the liquid crystals are split into a second jet, and that the | s are arranged so that they have a slight inclination towards the

Identify elements for holding and rotating the substrate on one substrate level. In the case of material in which the liquid-crystal-disk-shaped rotating element, on the outer-side molecules of which are arranged perpendicular to the substrate plane, the surface of which a plurality of substrates can be attached, and this, if no voltage is applied, a similar effect occurs ben-shaped rotating element with respect to the baffle plate - on. In this case, it is necessary to arrange the molecules in a small order that the first and second steam jets are repeatedly arranged at 2i> angles to the normal of the substrate plane, around which the substrates impinges when the rotating element rotates. Avoid tipping backwards. As a result, a pre-tilt of the order of almost 90 ° is required

this inclination is usually measured from the substrate level.

js It is known that the liquid crystal molecules by means of The invention relates to a method and a device for oblique vapor deposition of SiO or other non-organic to influence the orientation of molecules in a chemical materials on the inner surfaces of substrates in one

Liquid crystal display and in particular a method and a desired direction oriented parallel to the cell substrate can be used to influence this orientation.

oblique evaporation of a material onto the substrate of .'o This is described in US Pat. No. 3,834,792. It is also liquid crystal display cells. known a method whereby the pre-inclination of the liquid

Thanks to their different pre-crystal molecules, liquid crystal displays have been reduced considerably in the order of 6 ° in the past few years. These advantages can. It consists in that two successive steps, such as low energy consumption and the possibility of vapor deposition, are carried out, the first taking place when using low voltages at the line electrodes, is at an angle of incidence of approximately 80 ° and treading on the first. Therefore, liquid crystal displays with electronic layer a very thin second layer is deposited under an imaginative wristwatches, electronic pocket calculators etc. of approximately 60 °. The same effect can be achieved. By far the most common type of be used when the order of the two evaporation processes

Liquid crystal displays is the one with twisted nematic swaps. The use of this method and the vapor deposition layers (hereinafter referred to as TN type). Such a provision of the two layers in separate processes results in directions providing a pattern with black and white contrast. It has high manufacturing costs. If, on the other hand, the two damagers have a strong need for other types of liquid crystal applications to be carried out in one operation, there are presently available which e.g. have the ability to require data pleated vapor deposition devices, and manufacturing is indicated using contrasting colors. Such a guy difficult. Furthermore, a very precise control is required, since the "guest-host" type (hereinafter referred to as GH-45, the two layers is extremely thin, ie of the order of magnitude), in which a dichroic or pleochroic from 20 to 60 Â, which is why the process for dye is embedded in nematic liquid crystal material is unsuitable for mass production.

and the dye as a guest, the liquid crystal material as a host. In the literature, another method is known, referred to as material. Other types are liquid crystal, on which a first layer for influencing orientation is also based, which is based on the ECB effect, the angle of incidence of about 80 ° on the substrate being the angle of application of the liquid crystal molecules corresponding to that being vaporized, as in the above Procedure and then a second

Voltage changes, which is applied to the cell electrodes. Layer with an angle of incidence of the order of magnitude 0 ° above and the color of the reflected light is evaporated from this layer onto the first layer. The orientation measurement angle depends. Another type of mechanism finally used in this case is not yet fully understood - the principle of dynamic scattering, with the order of 55 den. In this method, the minimum angle of the advance liquid crystals is destroyed by an electric field which is applied to the cell inclination, which is controllable and also in the size electrodes. 6 °. Because this method has the same disadvantages and

The liquid crystal material of such devices can cause difficulties, such as the one described above - neither a positive or a negative dielectric anisotropy method, it is also unpreferable for mass production. In the first case, the liquid crystal molecules have been suitable.

when applying a voltage to the cell electrodes and the The object of the invention is to provide a method and an occurrence of an electric field between them the Ten device, which have the above-mentioned disadvantages to align in the direction of the electric field. In the past.

In the case of negative dielectric anisotropy, the molecules have the process according to the invention

when the voltage is applied, on the other hand, there is a tendency to lower that at least part of the surface of the substrate is oriented properly to the electric field. In the case of dielek- is arranged such that the surface normal of at least trical material with positive dielectric anisotropy is two predetermined angles with the directions of particle particles, the liquid crystal molecules are formed in the absence of an electric radiation of the predetermined material, the rays

615 282

4th

are generated by at least one particle source, and that the particles on the part of the surface form the transparent orientation layer simultaneously or alternately in succession.

The device according to the invention for carrying out the method is characterized by at least one device for generating particle beams from at least one material, the particle beams having at least two different directions, and by elements for holding and rotating the substrate, so that the particle beams are repeatedly directed onto at least one Impact part of the substrate surface in at least two different directions, which form predetermined angles to the substrate surface, the particles thereby forming the transparent orientation layer on this part of the substrate surface.

With the method according to the invention, liquid crystal molecules with a small pre-tilt in the range of 1 or 2 degrees or a large pre-tilt up to almost 90 degrees can be aligned. Inorganic material such as Si is deposited on the substrate by means of two evaporation processes. However, in contrast to the known methods, the two evaporation processes can take place either simultaneously or alternately in succession, the amount of material of the final layer resulting from each evaporation not being critical. In addition, the angles of incidence at which the steam reaches the substrate surface can vary within a very wide range. Thanks to these properties, it is possible to design a simple device with which a large number of substrates can be exposed to the evaporation process almost simultaneously. Since the method according to the invention enables pre-inclinations between 0 ° and 90 °, it can be applied to a variety of different liquid crystal displays and is particularly suitable for new types of color displays.

Exemplary embodiments of the invention are described below with reference to the drawing. Show it:

Fig. 1 is a diagram explaining the general principle of oblique evaporation;

2 shows a sectional view of a liquid crystal cell based on the principle of dynamic scattering, with no voltage being applied;

3 shows a sectional view of a liquid crystal cell based on the principle of dynamic scattering, with voltage being applied;

Fig. 4 is a sectional view of a guest host type liquid crystal cell without voltage;

Fig. 5 is a sectional view of a guest host type liquid crystal cell under voltage;

6 is a sectional view of an ECB type liquid crystal cell without voltage;

Fig. 7 is a sectional view of an ECB type liquid crystal cell under voltage;

FIG. 8 is a diagram illustrating the evaporation incidence angles according to the present invention;

9 shows a plan view of a cell substrate to show the projections of the two vapor deposition directions on the substrate;

10 and 11 are diagrams showing the angles of incidence of the vapor deposition according to the invention when a large pre-tilt value is desired;

Fig. 12 is a graph showing the effect of changing the ratio of materials deposited in two evaporation processes when a large pre-tilt value is made;

Fig. 13 is a graph showing the effect of changing the thickness of the orientation affecting layer when a large pre-tilt value is made;

Fig. 14 is a graph showing the effect of changing the deposition rate of two depositions when a large pre-tilt value is made;

15 is a plan view of a substrate, depicting vapor deposition from three directions;

16 shows a sectional view of a device for successively alternating oblique vapor deposition of a plurality of substrates;

FIG. 17 shows a view of the device from FIG. 16 perpendicular to the sectional plane there;

18 shows a sectional view of a second embodiment of the device for successively alternating oblique vapor deposition on a plurality of substrates;

19 is a schematic representation of a third such device, and

20 and 21 a fourth and fifth such device.

In Fig. 1, the process of oblique deposition by means of a single vapor deposition process is shown, as is already known. A particle stream of a material such as SiO, which is emitted by a steam source 4, strikes a substrate 10 of a liquid crystal cell at an angle of incidence with respect to the substrate normal 2. The orientation layer 8 is thereby formed. The effect of the orientation layer 8 causes liquid crystal molecules 6 (if the substrate is installed in a liquid crystal cell to align uniformly at an angle A with respect to the substrate plane 10, if no voltage is applied to the electrodes of the liquid crystal cell. The angle of incidence 0 is referred to below as the vapor deposition angle, while the angle a is called advance-1 (1 gung. With this single oblique evaporation, the advance inclination becomes about 20 ° to 30 ° if the evaporation angle is greater than 75 °. With such an advance inclination, statically operated liquid crystal displays can be produced, However, in the case of dynamically operated liquid crystal cells, such a value of the pretilt leads to insufficiently defined threshold characteristics, so that practically usable devices cannot be produced with this method.

40

If the deposit is made by means of individual oblique evaporation in an evaporation angle of the order of 60 °

the liquid crystal molecules align with a pre-tilt of 0 °, i.e. exactly parallel to the substrate plane. If a control voltage is now applied to the cell electrodes, all liquid crystal molecules will rotate by a certain angle due to the effect of the resulting electric field, but some will rotate in the opposite direction to the others. This phenomenon is known as backward tipping. It leads to a decrease in the contrast in TN cells and uneven display coloration in color display cells. For this reason, the method is also practically not applicable.

In the case of a material with positive dielectric anisotropy, where the liquid crystal molecules align in the direction of an applied electric field, it is desirable that the molecules have a very small inclination with respect to the substrate plane instead of being exactly parallel to the plane. This is because the small inclination, which corresponds to the pre-inclination defined above, prevents tipping backwards. For a liquid crystal material with positive dielectric anisotropy, a pre-tilt in the range of 1 to 2 degrees is desirable.

In the case of a liquid crystal material with negative dielectric anisotropy, where the liquid crystal molecules are oriented perpendicular to the direction of an applied electric field, it is desirable that the liquid crystal molecules have a large pre-tilt, usually almost 90 °.

5

615 282

Some examples of liquid crystal display cells are described below. These examples assume that the liquid crystal material has negative dielectric anisotropy.

2 shows the sectional view of a liquid crystal display type, which uses the principle of dynamic scattering (hereinafter referred to as DS type). A liquid crystal material, the molecules of which are described by reference numeral 23, is enclosed between the inner surfaces of two substrates 26 and 30 and forms a liquid crystal cell which is sealed at its outer edge with a sealing material 28. Transparent conductive electrodes 22 and 24 are attached to the inner surfaces of the substrates 28 and 30. FIG. 2 shows the case where no voltage is applied to the cell electrodes, so that the molecules 23 are oriented almost perpendicular to the cell substrates by the action of an orientation layer on the inner surfaces of the substrates. As shown in Fig. 3,

the state of parallel alignment of the liquid crystal molecules located between the cell electrodes is destroyed,

when AC voltage is applied to the cell electrodes, 2II so that the molecules are placed in a disordered or scattered state. As a result of the different reflection properties of the vertically ordered molecules 23 and the disordered molecules 34 located between the electrodes, no contrast pattern is achieved. ^

FIG. 4 shows a guest-host (or GH) type of liquid crystal display. As in the example of FIGS. 2 and 3, a liquid crystal material is contained between two substrates 26 and 30 and forms a liquid crystal cell which is sealed by means of sealing material 28 , wherein an electrical field can be generated between electrodes 22 m and 24. A dichroic dye is combined with the liquid crystal material in such a way that the dye molecules are distributed between the liquid crystal molecules. The dye molecules are numbered 34 and the liquid crystal molecules are numbered k. In the absence of a voltage between the electrodes 22 and 24, the dichroic dye molecules are aligned almost perpendicular to the substrate surface by the action of the much more numerous liquid crystal molecules surrounding them. 40

When an alternating voltage is applied to the cell electrodes 22 and 24, as shown in FIG. 5, the liquid crystal molecules between the electrodes, which are designated by the number 37, align almost parallel to the substrate surface. As a result, the dichroic dye molecules 39, which are located between the electrodes, are also aligned almost parallel to the substrate. Depending on the alignment of its molecules parallel or perpendicular to the direction of light incidence, the dichroic dye has different color absorption of the incident light. Therefore, a color contrast is created between the dye molecules between the electrodes and the part of the dye that is outside the electrodes. In this type of cell there is uneven coloring and poor visibility of the display if the tilting back occurs, in which process some dichroic color molecules rotate through opposite angles when a voltage is applied to the cell electrodes 22 and 24. It is therefore important to give the liquid crystal molecules a slight pre-tilt so that they are aligned almost but not completely perpendicular to the substrate plane, if no voltage is applied.

FIG. 6 shows an ECB-type liquid crystal color display with the same general arrangement as has already been described with reference to FIGS. 2 to 5. In the absence of a voltage between the cell electrodes 22 and 24, the liquid crystal stall molecules are aligned almost perpendicular to the substrate plane. If an alternating voltage is connected to the cell electrodes 22 and 24, as shown in FIG. 7, the liquid crystal molecules 42 between the electrodes are rotated away from the normal direction to the substrate plane. The wavelength of the light absorbed by the liquid crystals, which are located between the electrodes, depends on the inclination of the liquid crystal molecules. It is therefore possible to generate a continuously changeable multicolor display.

In addition, it is not necessary for the liquid crystal molecules to be arranged almost perpendicular to the substrate plane in the absence of a voltage, as shown in FIG. 6. Rather, the molecules can be given a pre-tilt of significantly less than 90 °, depending on the desired color display effect. It is the purpose of the invention that such pre-tilt values can be set reliably and reproducibly.

A method according to the invention is described below, by means of which liquid crystal molecules can be aligned almost parallel to the substrate plane. 8, a first evaporation is carried out in the direction 52 with an angle of incidence 0h with respect to the normal to the substrate 10. The angle of incidence at which the vapor deposition takes place is called the vapor deposition angle. A second evaporation is carried out in the direction 50 at an evaporation angle 02. These two evaporations can be carried out together or alternately in succession. The material deposited by means of these evaporations forms a layer 8 for influencing the orientation, which is also called the orientation layer.

It is a feature of the present invention that © 2 is substantially in the range of 0 ° ± 30 °, while 0, is substantially between 75 ° and 90 °. The same material, e.g. SiO, or different materials can be used. If the deposited amount of material of the first deposition is very large compared to that of the second deposition, the orientation properties of the orientation layer become similar to those which are generated by a single deposition. If, on the other hand, the amount of material deposited by means of the second vapor deposition is significantly larger than that of the first vapor deposition, the degree of influence on the orientation is weakened by the orientation layer. It has been found that a pre-tilt of less than about 2 ° is achieved if the amounts of the materials deposited during the first or second vapor deposition have a ratio in the size range from 10: 1 to 1:20. If a 10 ° advance inclination is permissible, the above ratio can be extended to the range 20: 1 to 1:20. The maximum allowable pre-tilt depends on the specific type of liquid crystal cell. It was found experimentally that the orientation properties are insufficient and the cell contrast is uneven and unsatisfactory if SiO alone is used in both vapor depositions and the final layer thickness of the orientation layer is less than 60 Â. Therefore the orientation layer should be thicker than 60 Â. If its thickness is increased significantly, for example in the order of 2000 Â, good orientation properties are obtained, but the orientation layer produces a coloration of the display, which affects the visibility of the display. However, from the standpoint of ease of manufacture, a thickness of 2000 Â is preferable to a thinner orientation layer. It was found that the color effect just described can be significantly reduced if SiO 2 or a mixture of SiO and SiO 2 is used as the second vapor deposition material. Experiments were also carried out in which the evaporation angle © was periodically changed during the evaporation process. It was found that in the event of successive alternate depositions of the first and second depositions, the area of the above

615 282

6

indicated evaporation angle, e.g. 75 ° to 90 ° for Â, and 0 ° ± 30 ° for Ä2 can be increased during part of each evaporation period. This is possible to the extent that the fraction of the material deposited at an evaporation angle, which lies outside the limits mentioned, does not reach 50% of the total amount deposited. The range in which the deposition angle 02 can be changed during the deposition process depends on the angle between the projection of the first deposition direction onto the substrate plane and the projection of the second deposition direction onto the substrate plane. This angle is referred to below as the intermediate vapor deposition angle.

The term intermediate vapor deposition angle can be explained with reference to FIG. 9. Reference numerals 56 and 54 denote the projections of the first and the second vapor deposition direction onto the substrate 10. The intermediate vapor deposition angle is denoted by β. It has been found that satisfactory pre-tilt angle values are obtained with a periodic change in the vapor deposition angle © 2 within the range 0 ° ± 30 ° if the intermediate vapor deposition angle is either 0 ° or 180 °. If the intermediate vapor deposition angle is 90 °, satisfactory results are obtained when the vapor deposition angle 02 is changed periodically in the range of 0 ° ± 60 °. It was also found that with the intermediate vapor deposition angle of 90 °, the vapor deposition angle 02 can vary periodically in a range of 0 ° ± 90 °, provided that the proportion of the material deposited in the second vapor deposition within a vapor deposition angle in the range 0 ° ± 30 ° 50% or more of the total amount deposited in the second vapor deposition. It can be seen from this that the permissible variation range of the evaporation angles of the first and second evaporation is extremely large. Precise control of the evaporation angle is therefore completely unnecessary. It has also been found that the final thickness of the orientation layer is not critical. Accordingly, the method according to the invention enables a relatively free configuration of a device for producing liquid crystal substrates with an orientation layer.

A method for depositing an orientation layer on liquid crystal substrate surfaces will now be described below, with which any pre-inclination angle in the range from 90 ° to 50 ° can be obtained. This method is particularly suitable for use on certain liquid crystal cells for color display that were only recently developed. 10 shows two vapor depositions which are carried out in directions 58 and 60 at vapor deposition angles of 0 and 0, respectively. The evaporation in direction 60 is referred to here as the first, that in direction 58 as the second evaporation. In these directions, a material is deposited on the substrate 10 and forms an orientation layer, the molecules of which are identified by the reference number 42.

As with the aforementioned vapor deposition method, the first and the second vapor deposition can be carried out either simultaneously or alternately in succession. It is a feature of this method of the invention that at least one of the two evaporation takes place at an evaporation angle of 70 ° or more. Normally, both evaporation processes should take place at an evaporation angle of more than 70 °. It is believed that this causes certain molecules of the orientation layer to align perpendicular to the substrate, while others orient themselves at certain angles to the surface. This could be concluded from electron microscopic examinations as well as density measurements of the orientation layer. One imagines that this creates gaps or hollows in the orientation layer, which cause the special orientation properties which are obtained by means of this method. This effect does not occur if both the first and the second vapor deposition are carried out at an angle of less than 70 °.

It has been found that by changing certain vapor deposition parameters using this method, the pre-tilt of the liquid crystal molecules can be adjusted to a desired value. These parameters are the ratio of the amounts of material deposited by means of the first and the second vapor deposition, the final thickness of the orientation layer, the vapor deposition angle, the ratio of the vapor deposition rates of the first and the second vapor deposition, the type of the vapor deposition material used in each vapor deposition.

If the evaporation angles, the evaporation rate, the amounts of the deposited material and the deposited materials are the same for each deposition, the deposition directions are arranged symmetrically (so that the deposition angles are 180 ° in a two-stage process and 120 ° in a three-stage process, as described below ) and if the thickness of the final layer of the orientation layer is very thin compared to 20 Â, then a pre-tilt of almost 90 ° can be generated. A suitable inclination of less than 90 ° can be achieved, if desired, by changing the above parameters. Furthermore, even if one of the parameters mentioned changes from the state of identity or symmetry, it is possible to achieve a pre-inclination angle of almost 90 ° by suitably changing one or more other parameters for compensation.

FIG. 11 shows the case in which the evaporation takes place from two directions, 52 and 64, at evaporation angles 0 62 and © 64. It is assumed that the same evaporation material is used and that the evaporation rates are in directions 62 and 64, V62 and V64, respectively. This results in an orientation layer, which causes the liquid crystal molecules 68 to assume a pre-inclination a. If the amount of material deposited from direction 64 and designated T64 is greater than the amount of material deposited from direction 62 and designated T62, a pre-tilt of less than 90 ° is obtained, as shown in Fig. 11 shown.

The relationship between the change in the pretilt of the liquid crystal molecules and the ratio of the amounts of material from the first and second evaporation is shown in FIG. 12.

The graph in FIG. 12 applies to the case where both evaporation angles are © 56 and 0 57, 85 ° and the evaporation material is SiO. If the ratio of the amount of material deposited is fixed and a different evaporation angle is selected, the pre-inclination decreases in accordance with the increase in the difference between the evaporation angles.

It has also been found that the thickness of the layer which is deposited in the final vapor deposition step has a marked effect on the orientation properties of the orientation layer if the first and the second vapor deposition are carried out alternately in succession. This factor can also be used to set the pre-tilt value of the liquid crystal molecules. This is explained using the graph in FIG. 13. It can be seen that the pre-inclination angle can be adjusted up to close to 90 ° by changing the thickness of the layer deposited in the final phase of the vapor deposition process.

Fig. 14 shows the effect of the difference between the deposition rates of the first and the second deposition. As can be seen, the pretilt angle of the liquid crystal molecules decreases as the deposition rate difference increases (which is shown as a ratio in Fig. 14).

15 is a plan view of one of three different directions 91, 92 and 93 deposition to be carried out on a substrate, the intermediate deposition angles © 91,

S

OK

1 ^

20th

25th

30th

15

40

45

50

55

huh

fi5

7

615 282

0 92 and 0 93 are. If all other parameters are equal to one another and the intermediate vapor deposition angles 0 91, 0 92, 0 93 are all 120 °, the orientation layer deposited in this way has the effect that the liquid crystal molecules arrange themselves with a pretilt of 90 °. If, on the other hand, 0 91 is greater than 0 92 and 0 92 is equal to 0 93, the orientation layer causes the liquid crystal molecules to arrange in the direction 91 with a pretilt. It is thus possible to vary the degree of pre-inclination by changing the intermediate vapor deposition angle. This can also be carried out in the case of vapor deposition from two, four or more directions. Furthermore, the degree of pre-tilt of the liquid crystal molecules can also be influenced by using different vapor deposition materials from different directions. For this purpose, reference is again made to FIG. 10 and it is assumed that a material with relatively good properties for orienting the liquid crystal molecules is deposited parallel to the substrate plane from direction 60, whereas one with relatively poor orientation properties is deposited from direction 58 and all other parameters how evaporation angles 01 and 02 are the same. This leads to an orientation layer which causes the liquid crystal molecules to rotate in the direction of vapor deposition 60. The material with the best orientation properties for liquid crystal molecules is currently SiO.

Some general embodiments of simple devices will now be described, by means of which substrates for liquid crystal cells according to the present invention can be provided with orientation layers. It is emphasized that in the exemplary embodiments shown here, the evaporation angles are aligned to those cases where the orientation layer produces a small pre-tilt value of the liquid crystal molecules, i.e. a degree or two. However, it is easy to see that the device can be modified in any case in which orientation layers which produce larger pre-tilt values are to be produced according to the method of the invention.

16, a rotating element 72 is mounted on a rotatable shaft 70, by means of which it can be rotated. A number of substrates 74 for liquid crystal cells are attached to the outer periphery of the rotary element 72. These substrates are arranged with the surfaces on which the orientation layer is to be deposited on the outside. A baffle plate 76 is attached between the rotating element 72 and the steam source 84, which generates a jet 82 of evaporated material. The openings 82 and 80 in the baffle 76 split the beam 82 into two separate beams, and it is apparent that the location of these openings determines the angles at which the portions of the beam 82 strike the substrates 74. As the rotating member 72 rotates, the deposition angle at which the deposition occurs on each substrate varies within a certain range, which is determined by factors such as the size of the openings 78 and 80.

However, as has been explained above, the method according to the invention allows such a periodic variation of the vapor deposition angle. Accordingly, when the rotating member 72 rotates, first and second evaporations are carried out alternately in succession. It is clear that the first and the second vapor deposition take place almost simultaneously if the rotational speed of the rotary member is sufficiently high and that a large number of substrates can then be treated quickly. The exemplary embodiment shown in FIG. 16 can be used for an intermediate vapor deposition angle of 0 °, the same vapor source 84 being able to be used for both the first and the second vapor deposition. It can be seen that the deposition angle and the relative

The amount of material deposited in the first and second vapor deposition can be easily changed by varying the position of the baffle plate 76 and the positions and sizes of the openings 78 and 80. Since these positions are defined afterwards, a high degree of constancy and reproducibility of the orientation influence is achieved. The evaporation angle and the ratio of the evaporation amounts can also be changed by changing the distance between the steam source 84, the baffle plate 76 and the rotating element 72 or by varying the diameter of the rotating element 72. Furthermore, the evaporation angles can be influenced by moving the steam source 84 to the right or left from the position shown in FIG. 16.

FIG. 17 shows a device in which a plurality of substrates are attached both along the periphery and along the axis of the rotary element 72. The functioning of this device can be understood by understanding the arrangement shown in FIG. 16 as a section perpendicular to the shaft 70 of the device of FIG. 17. 20 In order to prevent unwanted deposits by steam jets from neighboring steam sources, shielding plates 86 are arranged between these sources.

18 shows an embodiment of a device in which separate steam sources 101 and 96 are provided for the first and the second evaporation. The evaporation angles are determined by openings 100 and 104 in a baffle 94. These openings also serve to determine the ratio of the amounts of material deposited by the steam sources 96 and 101. As already in the device from FIG. N> 16, the evaporation angle and the ratio of the deposited amounts of material can also be varied here by changing the position of the baffle plate 94. Since different steam sources are provided for the first and the second vapor deposition, different vapor deposition materials can be used for the two .15 vapor depositions and steam generation methods adapted to these can be used for the steam sources 101 and 96, depending on the type of material used. For example, it is possible to use SiO 2 for the first vapor deposition because of its good orientation properties and SiO 2 as the second vapor deposition material because of its good transparency. Of course, other materials can also be used in steam sources. The use of separate sources makes it possible, for example, to use various methods for producing particularly desired orientation properties of the 45 substrates, such as steam generation by means of electron beam, ion plating etc. The device for controlling the vapor deposition, which is necessary for an exemplary embodiment according to FIG. 18, is more complicated as e.g. the device in Fig. 16. According to the method of this invention, however, the range of the ratio of the deposited materials thus permissible is very large and the final thickness of the orientation layer can exceed 100 Â. Therefore, even for the exemplary embodiment in FIG. 18, the necessary control of the evaporation process in each phase is much simpler than in the previously known method 55 with two evaporation processes.

In the device shown in FIG. 19, in which a plurality of substrates are attached along the circumference and the axis of a rotary element 108, the evaporation angles vary along the axis of the element 108. (This is because a single steam source 112 for the second vapor deposition is used for the first vapor deposition together with a plurality of vapor sources 116. It is obvious that the vapor deposition angle for the second vapor deposition also changes in accordance with the position of the substrates along (, 5) the axis of the element 108. All these vapor deposition angles move however, in the range of 75 ° to 90 ° if the steam source 112 is appropriately attached. With this arrangement, the intermediate vapor deposition angle becomes approximately 90 ° so that the

615 282

8th

permissible bounds of the deposition angle for the second deposition become very large, as explained above. For this reason, it is not necessary to attach a baffle plate to control the evaporation angle of the second evaporation.

In the device shown in Fig. 20, substrates 120 for liquid crystal cells are attached to the inner periphery of a rotating member 118 at an angle to the inner surface of that member with the substrate surfaces on which the orientation layer is to be deposited facing inward. The element 118 is rotated by means of a shaft 124 and is contained in an evacuated vessel 122. The steam source 128, which is located within the periphery of the rotary member 118, generates a steam jet which is split into two parts by the baffle plate 126. It is possible to use a series of steam sources arranged parallel to the shaft 104 so that a series of substrates which are attached to the periphery of the element are treated simultaneously, as in the examples of FIGS. 17 and 19 can. Furthermore, separate steam sources can be used for the first and second evaporation, whereby the same advantages as described in connection with FIG. 18 can be achieved. In this case, the second steam source can be located near the center of the rotating element 118. When arranging

20, the evaporation device can be accommodated in a simple and convenient manner within an evacuated vessel.

In the arrangement shown in FIG. 21, the cell substrates 134 are fastened on a disk-shaped rotating element 132, which rotates about a shaft 130. A steam jet from a steam source 136 is split into two parts through openings 138 and 140 in a baffle plate 142. Accordingly, when the element 132 rotates, first and second depositions are alternately performed on the substrates 134 one after another. As with the examples described above, the evaporation angles and the relative amounts of the material deposited in the two evaporation processes can be changed by changing the location and size of the 15 openings 138 and 140, the position of the steam source 136 and the distances between the steam source 136, baffle plate 142 and Rotating element 132 can be varied.

It can be seen from the above description that, according to the 2i) invention, a transparent orientation layer is deposited on the substrate of a liquid crystal display under at least two predetermined vapor deposition angles. The expression “predetermined vapor deposition angles” encompasses both fixed vapor deposition angles and variable vapor deposition angles.

C.

3 sheets of drawings