FR2480952A1 - PASSIVE ELECTRO-OPTICAL DISPLAY CELL - Google Patents

Abstract

A passive electro-optic display cell comprises a layer of passive electro- optic material, e.g. liquid crystal (4), between two parallel plates (1, 2), on the inner face of each of which is a set of control electrodes (7, 11) and a screen-electrode (9, 13) separated by an insulating layer (8, 12). The screen-electrodes (9, 13) and the insulating layers (8, 12) are apertured (10, 14) opposite the corresponding control electrodes (7, 11), allowing alternative or simultaneous display of two sets of information contained in the control electrode-screen combination on the respective plates, the display being either positive or negative.

Description

Electro-optically passive display cell.

  The subject of the present invention is a passive electro-optical display cell comprising a layer

  of a passive electro-optical material.

  US Pat. No. 4,137,524 discloses such a cell.

  lule which further comprises control electrodes and a counterelectrode arranged on either side of the layer

  of electro-optical material. A screen electrode is available

  between the control electrodes and the electro-

  optical. This screen electrode is pierced with an opening in

  look at each of the control electrodes.

  If the electro-optical material used is a crystal

  Nematic liquid, polarizers are arranged on either side of the cell, their polarization directions at an angle of 90 with each other. Alignment layers are additionally deposited-on the inner faces

  two plates to induce, in the absence of an elec-

  the well-known helical arrangement of molecules

liquid crystal.

  In such a cell, the shape and dimensions of the apertures in the screen determine the shape and dimensions of the display elements. These are

  constituted by the areas of the cell that can be

  individually visible or invisible vis-à-vis the

  the background of the display and which form, through their various

  bins, different signs such as numbers, letters

  or other symbols that you want to display.

  In the area of the bottom of the display, that is to say outside the areas corresponding to these openings, the appearance of the cell depends only on the voltage applied between the screen and the counter-electrode. If this voltage is zero

  or weak enough, the bottom of the cell appears clear.

  If this voltage is enough for that field it

  creates in the liquid crystal causes the alignment of

  -2- cules of the latter in a direction perpendicular to

  plates, the bottom of the cell appears dark.

  At the location of the display elements, it is the voltage applied between the control electrodes and the counter-electrode that determines the appearance of the cell. The cell is clear in these areas if this voltage is zero

  or weak enough, and dark if it is of sufficient value

  cient. The presence of the screen makes it possible to realize a

  display information in dark on a light background, that is

  to say in positive, or in light on a dark background, that is to say

in negative.

  In other embodiments, a dye

  dichroic acid is added to the liquid crystal, as well as, if

  a chiral compound. One of the polarizers at

  less can then be deleted. Unlike the previous case

  tooth, the cell appears dark in the absence of an elec-

  clever and clear in the presence of such a field. The functioning

  the cell is exactly the opposite of the one

  described above, but the cell also has

  the property of allowing positive or negative display

  tif. In any case, the presence of the screen further prevents the trace of the conductive tracks that connect the electrodes to the terminals of the cell -ne becomes visible,

  despite the fact that the counter-electrode covers the whole

  than posterior. The problems posed by the design of the counter-electrode of a conventional cell and the reciprocal alignment of its electrodes and its counter-electrode are

thus deleted.

  It is desired to be able to display more information

  tions that can not be displayed in a normal cell. When the cell is intended to be used in an electronic watch equipped with a large number of hourly or non-hourly functions, it is for example desirable for it to display information in the form of hour digits or letters indicating the day of the week or the name of the month. This problem can be solved by using cal lines of a number of segments, but at the same time,

  It is sometimes also desirable that this

  lule can display information of a very different nature

  such as a map of the world for locating the time zones whose time is indicated. This

  problem can be solved by superimposing two

  separate display units, but to the detriment of the price of

  returns and the thickness of the device.

  Depending on the manner in which it is performed, this superposition also has the disadvantage that the zones o display elements belonging to the first

  cell are superimposed on display elements belonging to

  in the second cell merge with the bottom of the

  display device. For example, when the merits of the

  is clear and a cross is displayed by darkening two rectilinear segments each belonging to one of

  cells, the center of this cross is clear.

  The purpose of the present invention is to propose

  a display cell that allows to increase considerably

  the number of digital, alphabetic or other information that can be displayed, without the inconveniences associated with the superposition of two cells, with in addition all the advantages of the cell described by the US Pat.

4137524

  This goal is achieved through the means claimed.

  The single figure of the drawing represents, as

  for example, an embodiment of the object of the invention.

  The display cell represented in this

  gure comprises two transparent glass plates, one anterior 1 and the other posterior 2, separated by an assembly frame 3, sintered glass for example, sparing between

  they a space 4 filled with nematic liquid crystal. The in-

  thus seems formed is interposed between two polarizers 5 and 6, crossed, that is to say whose directions of polarization of the light are seriviquement perpendicular to one to

the other.

  Anterior glass plate 1 carries, on its face - 4-

  turned inward, a set of control electrodes 7.

  These electrodes 7 are covered with an insulating layer 8, which itself carries a screen electrode 9. The control electrodes 7, the insulating layer 8 and the screen electrode 9 are transparent. The insulating layer 8 and the screen electrode 9 are pierced with openings 10, each located opposite one of them.

electrodes 7.

  Like the plate 1, the posterior plate 2 is transparent and is provided with a set of magnetic electrodes 11, covered with an insulating layer 12 which itself carries a shield electrode 13. The control electrodes 11. the

  insulation layer 12 and screen electrode 13 are also trans-

  relatives. Always as on plate 1, the insulating coumee

  12 and the screen electrode 13 are pierced with openings 14 si-

  killed, each, in front of one of the electrodes 11.

  The shape, the dimensions and the arrangement of these openings 14 are different from those of the openings 11

  practiced in the insulating layer 8 and in the electromagnetic

screen 9. -

  Each of the plates 1 and 2 is additionally rewvLte

  internally, over all its surface, a layer of dual

  planar homogeneous liquid crystal molecules, o shown in the drawing. These alignment layers are such that, in the absence of an electric field, the liquid crystal molecules which are in contact with them are toes substantially parallel to the plates 1 and 2 and, in addition, substantially parallel to the direction of polarization of

polarizers 5, respectively 6.

  A protective layer, made of silieium oxide for example, also not shown, may, if necessary, be deposited on the entire surface of the plates 1 and 2, before the

deposition of alignment layers. -

  Finally, a reflector-diffuser 15 is arranged to

the back of the cell.

  The cell described and shown operates as follows: -5-

  In a first mode of operation, electricity

  trodes II and the screen 13 of the posterior plate 2

  to the same potential, which will be designated later by

  PI. The cell functions exactly like the cell describing

  in US Patent No. 4,137,524. Under these conditions, in fact, these electrodes 11 and the screen 13 together form a continuous counterelectrode covering the entire plate

posterior 2.

  If the screen 9 is also set to the potential P1, the bottom of the display appears in clear, and each electrode 7 causes the dark display of the corresponding display element when it is brought to a potential P2

  sufficiently different from the potential P1, or on the contrary the effect

  This form element, the dimensions and the location of each display element are determined by the shape, the dimensions and the location of the openings in the display element. 9. By their various combinations, these display elements allow the visualization of a certain number of

  selected information in a set of information de-

  completed. If, on the other hand, the screen 9 is set to the potential P2 *, the background of the display appears dark and the electrodes 7 cause the clear appearance of the display element corresponding to them when they are brought to potential. Pl, and erasing this display element when they

are brought to potential P2.

  In this first display mode, the information forming part of the information set determined by the shape, the dimensions and the arrangement of the openings 10 can therefore be displayed selectively, and, in addition, in positive

or in negative.

  In a second mode of operation, all the electrodes 7 and the screen 9 of the anterior plate 1 are put at the same potential Pl. Under these conditions,

  these electrodes 7 and the screen 9 together form a counter

  continuous electrode covering the entire anterior plate 1.

  under these conditions, the screen 13 of the posterior plate 2 is also set to the potential Pi, the bottom of the display also appears in clear, the electrodes 1i cause the dark appearance of the element display corresponding to them when they are brought to the potential P2 or its erasure when they are brought to the potential Pl. If, on the other hand, the screen 13 is set to the potential P2 the bottom of the display appears in dark. The electrodes 11

  then cause the appearance of the display element in clear

  which corresponds to them when they are put to

  pl and its erasure when put to the

P2.

  We see that, in this second mode of operation,

  information that is part of a second set of informa-

  can be displayed in positive or negative. The information of this second game is determined by the shape, the dimensions and the arrangement of the openings 14 practiced in the screen 13. It is important to note that the information of this second game is completely different and independent of those of the first game. information of one of these games may be, for example, the conventional time information, such as the hour, minute and second of the real time, displayed in digital form. Those of

  the other game may be, for example, information

  alphabetical forms, such as the name of a

  day of the week or a month, or a combination of informa-

  digital, alphabetical or other forms. They can be the same time information, but presented under

  pseudoanalogical form, that is, by elements of

  in the form of radially arranged segments

  center point so as to simulate the appearance of the

  the ones of a classic watch. Many other combinations can

Moreover, they must be imagined.

  In a third mode of operation, the

  lule according to the invention allows to display separately or if-

  simultaneously information forming part of the two sets of information defined above. To allow a positive display in this third mode, the two screens 9 and 13 - 7 - are brought to the same potential PI. The background of the display is

  so clear. The electrodes 7, respectively 11, correspond to

  The electrodes 7 corresponding to display elements which must be made visible, that is to say, are brought to this potential Pl. The electrodes 7 corresponding to display elements which must remain invisible, that is, clear. say dark, are brought to potential P2, as above. Electrodes

  It corresponds to display elements which must also

  can be made visible are instead brought to a po-

  P3 such that the potential difference P3-Pl is substantially equal, in absolute value, unlike

  potential P2-P1, but of opposite sign.

  The display elements corresponding to electri-

  trodes 7 set to this potential P2 and located entirely in front of the screen 13 or electrodes it brought to the potential Pl have exactly the same aspect as in the first mode of operation when the information of the first game are

displayed in positive.

  The same applies to the display elements corresponding to electrodes 11 set at potential P3 and situated entirely in front of screen 9 or electrodes 7 set at potential P1. These elements also have exactly the same value.

  same aspect as in the second mode of operation,

  that the information of the second game is displayed in positive.

  The display elements, or the parts of elements corresponding to electrodes 7 set at the potential P2 and situated opposite or partially opposite, of electrodes h1 set at the potential P3 also have the same aspect although the potential difference P2-P3 applied to these electrodes

  substantially equal to twice the difference in potential

P2-Pl.

  The characteristics of the liquid crystal are indeed such that the appearance of a display element does not change

  when the voltage applied to his electri-

  command trodes exceeds a specified value, called

saturation voltage.

  To simultaneously display in negative information

  the first and second sets of information

  tions, the screen must be set to potential P1 and the screen

  13 potential P2, as in the second mode of operation.

  above. In this third mode, however,

  P1 and P2 must be chosen in such a way as to fulfill the following two conditions: P2-P l>, U; and P P2-Pl [J-sat m 2 2 threshold where U is the saturation voltage above which The dark aspect of the cell is practically no longer modified, and where U s is the voltage below which the clear threshold aspect of the cell no longer changes. It obviously takes

  that the liquid crystal used is such that these two

  U sat and Useuil are defined. But this constraint is easy to respect, such liquid crystals being well known. The electrodes 7, respectively 11, corresponding to display elements which must remain invisible are set to the potential P1, respectively P2, as in FIG.

  second mode of operation above, in ne-

  NEGATIVE. The electrodes 7, respectively 11, corresponding to display elements which must be made visible

are put at the potential Pm.

  The display elements corresponding to electri-

  trodes 7 set to this potential Pm and located entirely in front of the screen 13 or electrodes it put to potential P2

  appear clearly because the difference between these

  P2 and Pm is equal to or lower than the threshold voltage., It is the same for the display elements corresponding to electrodes it put at this potential Pm and located entirely in front of the screen 9 or electrodes 7

  brought to potential P1, since the difference between these

  P and Pm are also lower than the threshold voltage. The display elements, or the element parts, corresponding to electrodes 7, respectively 11, placed at the potential Pm and located opposite, or partially opposite

  electrodes 11 and 7, respectively,

  tential Pm, obviously also appear in clear since

  the potential difference between these electrodes is zero.

  It can therefore be seen that, in this third mode of operation, 1-a cell according to the invention makes it possible to display

  simultaneously in positive or negative information

  part of the first and second sets of information. The

  zones where display elements of the first game are super-

  pose to elements of the second game have an identical appearance

  to that of the zones where these elements are separated.

  The table below summarizes the operation of the cell in this third mode. It indicates the clear appearance

  or dark background of the display and two display elements

  chage E1 and E2 each corresponding to an electrode 7,

  11, for the various combinations of potentials

  applied to these electrodes and to the screens 9 and 13.

  9 13 7 Background El E2 -Pl Pl Pl Pl Clear Light Z Pl Pl P2 Pl Clear Dark Pl Pl Pl Pl P3 Clear Clear Dark Pl Pi P2 P3 Clear Dark Dark Pl P2 Pl P2 Dark Dark Dark Pl P2 Pm P2 Dark Light Dark Pl P2 Pl Pm dark dark light Pl P2 Pm Pm dark light clear It is obvious that the potentials applied to

  screens and electrodes in the three modes of operation

  described above have been given by way of example only.

  Other combinations of potentials could give the same results. These potentials could notably be alternative. In this case, it would no longer be the values

  absolute differences that would cause the visualization

  erating or erasing the display elements, but the

  effective values of these differences.

  The cell described above, which is of the type

- 10 -

  called "nematic twist", works in reflection because of the presence of the reflector-diffuser 15. It is obvious

  it can operate in transmission if that broadcaster

reflector 15 is removed.

  In addition, the same arrangement of screen electrodes - pierced openings can be applied with the same

  advantages to so-called "Heilmeyer" cells, in the

  which dichroic molecules are mixed with the crystal

  liquid, as well as so-called "White-Taylor" cells, -

  which additionally contain a chiral compound.

  It should also be noted that insulating layers 8

  and 12 could be continuous and not open

  tures. The manufacture of the cell would be a little sim-

  folded, but the contrast would be slightly diminished. This decrease could however be offset by a slight

  increased control voltages of the cell.

  Finally, other electro-optical materials can

  to be used, in particular a liquid crystal with a diffusion

  namic or dipolar suspension.

- he -

Claims (1)

Claim   Passive electro-optical display cell   carrying a layer of a passive electro-optical material having first and second faces, characterized by the   it includes a first and a second elec-   control trodes arranged respectively opposite   said first and second faces, a first elec-   trode-screen disposed between said first face and said first set of electrodes and pierced with apertures each arranged opposite one of the electrodes of said first set, and a second shield electrode disposed between said second face and said second set of electrodes and breakthrough openings   each facing one of the electrodes of said cond game