FR2594580A1 - Method of manufacturing a dot matrix liquid crystal display and display thus manufactured - Google Patents

Abstract

A liquid crystal cell comprises a liquid crystal 14 confined between two transparent substrates 12, 13 which face each other. A multiplicity of semiconductor driving elements 15 are distributed approximately uniformly over the inner surface of the substrate 12. These elements comprise output electrodes linked to respective matrix element electrodes formed on the inner surface of the substrate 12. A drive circuit is produced in the form of a semiconductor integrated circuit on an extension of the inner surface of the substrate 12 in order selectively to drive the semiconductor drive elements.

Description

 The present invention relates to a dot matrix liquid crystal display comprising a liquid crystal cell which contains a multiplicity of matrix elements which can be selectively driven to display various patterns such as characters, graphic images or the like.

 Dot matrix liquid crystal displays have already been proposed comprising thin film transistors incorporated as driving elements in a small liquid crystal cell for selectively driving matrix elements. To excite these transistors, a multiplicity of terminals is brought out of the liquid crystal cell. Connecting these terminals to a pilot circuit is very tedious and time consuming. More specifically, a dot matrix liquid crystal color display comprises matrix elements each composed of three points of red, blue and green which must be controlled selectively. The number of terminals connected to such a color liquid crystal display is much greater than for a monochrome or black and white liquid crystal display. In case the number of matrix elements is, for example, 100 x - 100 = 10,000, the number of terminals emerging from a monochrome liquid crystal cell is 100 + 100 = 200, while the number of terminals emerging from a color liquid crystal cell is 100 + (3 x 100) = 400 since the number of points required is 100 x 100 x 3 = 30,000. The process of connecting these terminals to the pilot circuit then becomes very complex.

 The method of assembling thin film transistors in common liquid crystal cells is as follows; grid and matrix element electrodes are directly shaped on the interior surface of the substrate of the liquid crystal cell, and a grid isolation film is deposited over the entire interior surface of the substrate comprising these electrodes. A semiconductor layer is formed on the gate insulation film, facing the gates. Drain and source electrodes are deposited on the semiconductor layer at locations partially overlapping opposite sides of the gate electrodes, with interposition of the semiconductor layer and the gate insulating film. from the drain electrodes to the matrix element electrodes, it is necessary to make holes through the grid insulation film to allow contact between the electrodes. It is also necessary to deposit a protective film on the thin film transistors to avoid that they are exposed to the atmosphere, which would degrade the surface semiconductor layer before the thin film transistors are sealed in the cell. liquid crystal. Consequently, the process of manufacturing the thin film transistors of the previous liquid crystal cells required an increased number of operations by the need to make contact holes and to deposit a protective film.For large area liquid crystal cells display, many transistors must be made in the liquid crystal cell.

The greater the number of manufacturing operations, the more difficult it is to manufacture thin film transistors with uniform characteristics as well as to make all the manufactured transistors free from defects.

The object of the present invention is to provide a dot matrix liquid crystal display
- which has a smaller number of external connection terminals;
- which can be produced in a reduced number of operations and with increased yield, and which can have a large display area
- which has a small number of external connection terminals, can be manufactured in a reduced number of operations and can have a large display area.

 According to the present invention, a multiplicity of thin film transistors are closely distributed over a surface of a liquid crystal cell substrate, the transistors being part of dot matrix display elements and having output electrodes or drains related to these matrix elements. In a color liquid crystal display, colored filters are formed on the matrix elements or on another substrate located opposite these elements. These color filters have at least two colors and a set of neighboring color filters constitutes a single matrix element. A pilot circuit for the selective control of thin film transistors has at least one part made as a semiconductor integrated circuit on the substrate on which the thin film transistors are mounted. The dot matrix liquid crystal display is connected to external terminals through terminals of the pilot circuit, which results in the possibility of reducing the number of external connection terminals to facilitate this external connection. The colored filters are. preferably formed of colored ink and can be produced by printing technique. In addition, according to the present invention, the thin film transistors of the liquid crystal cell have drain and source electrodes formed on the interior surface of the substrate.

A semiconductor layer is formed between the drain and source electrodes, and covered by a gate insulating film. Grid electrodes are formed on the grid insulation film. Because of which drain electrodes are formed on the inner surface of the substrate, these electrodes and the matrix element electrodes can be made simultaneously in the pre-connected state. It is not necessary to provide a manufacturing operation to provide contact holes for the connection of these electrodes. As the semiconductor layer is completely covered by the gate insulation film, it is not necessary to form a protective film on the semiconductor layer.

The present invention relates in particular to a method of manufacturing a dot matrix liquid crystal display comprising a first transparent substrate made of an insulating material, a second transparent substrate made of an insulating material placed next to and in parallel with the first substrate and having a watertight peripheral edge in contact against it, a liquid crystal sealingly disposed between said first and second substrates, a common electrode deposited on substantially all of an interior surface of the second substrate to thereby define a display area of said crystal display liquids, transparent matrix element electrodes formed in rows and columns directly on the first substrate to define display elements in the display area, row electrode conductors formed on the first substrate so as to follow the respective rows of said matrix element electrodes, and film transistors thin element control arranged in rows and columns and each comprising a metal source electrode connected to a corresponding one of the row electrode conductors, a metal drain electrode connected to a corresponding one of the electrodes of- matrix element and a grid electrode connected to column electrode conductors extending perpendicular to said row electrode conductors, this method comprising the steps consisting in forming said metal source and drain electrodes directly on the first substrate, forming semiconductor layers on the first substrate so that they extend astride corresponding metal electrodes of source and drain, adjacent to each other, to form insulating films of gate grid so that they cover the respective semiconductor layers, and to form said grid electrodes on corresponding grid insulation films e n look at the above respective semiconductor layers, characterized in that
said grid isolation films are produced in the form of a continuous film extending substantially entirely over the display area to cover said semiconductor layers and said matrix element electrodes1 and in that it further comprises the steps consisting at ::
- forming transparent grid electrode zones on said grid insulation film so that they cover said semiconductor layers;
forming on said transparent grid electrode zones a layer of continuous photosensitive resin capable of hardening by exposure to light;
exposing said layer of photosensitive resin to light through the first substrate, said metal source and drain electrodes acting as masks;
- Developing said layers of photosensitive resin to eliminate the parts which have not been exposed to light; and
- Etching said transparent grid electrode areas with the other parts of the photosensitive resin layer acting as masks, to thereby form said grid electrodes.

 The present invention also relates to a dot matrix liquid crystal display produced according to the method mentioned above.

To better understand the invention, we will now describe in detail, simply by way of examples, two preferred embodiments with reference to the accompanying drawings, in which
- Figure 1 is a sectional view of one. current dot matrix liquid crystal display
- Figure 2 is a circuit diagram of an electrical circuit of transistors for controlling the matrix elements of a liquid crystal display in dot matrix
- Figure 3 is a detailed plan view of a thin film transistor of an earlier liquid crystal display
- Figure 4 is a sectional view along line 100-100 of Figure 3
- Figure 5 is a perspective view of a dot matrix liquid crystal display according to the present invention
- Figure 6 is a diagram showing an arrangement of the color display elements of the dot matrix liquid crystal display shown by way of example in Figure 5;
- Figure 7 is, in plan, an enlarged detail view of part of the arrangement of Figure 6
- Figure 8 is a sectional view along line 101101 of Figure 7;
- Figure 9 is a detailed perspective view, with parts broken away, of the dot matrix liquid crystal display according to the present invention;
- Figure 10 is a symbolic diagram of a pilot circuit associated with the liquid crystal display;
- Figures 11A to 11G constitute a synchronization diagram illustrating the operation of the pilot circuit of Figure 10 ;;
- Figure 12 is a detailed plan view of a thin film transistor of the liquid crystal display according to the present invention
- Figure 13 is a sectional view along line 102102 of Figure 12
- Figures 14 to 19 are sectional views illustrating a process for manufacturing a thin film transistor according to the present invention; and
- Figure 20 is a detailed sectional view of a liquid crystal display according to another embodiment of the present invention.

 Before describing embodiments of the present invention, a description will be given, with reference to FIGS. 1 and 2, of a liquid crystal display in a current dot matrix.

 As shown in FIG. 1, a liquid crystal cell 11 comprises two transparent substrates 12, 13 placed face to face with a small spacing, and a liquid crystal 14 interposed and sealed between the transparent substrates 12, 13. A matrix 15 of transistors with a thin film is formed on the interior surface of one of the transparent substrates, 12, and a common transparent electrode 16 is deposited on almost the entire interior surface of the other transparent substrate, 13.A processing layer d orientation 17 is deposited on the matrix 15 of film transistors 20, and another orientation treatment layer 21 is deposited on the common electrode 16 with the interposition of an insulation film 19.

 As shown in FIG. 2, the matrix 15 of thin film transistors is composed of colon conductors 81,82,831 ... substantially parallel to one another and transversely equidistant, and row conductors 91t92t93t --- substantially parallel to each other, transversely equidistant and perpendicular to the column conductors. Thin film transistors 6 are provided at respective points of intersection of the column and row conductors. Each of the transistors 6 comprises a grid connected to the row conductor 9 and a source connected to the column conductor 8. Each of the rectangular frames or spaces defined by the row and column conductors is substantially filled by an electrode of matrix element (of drain) 2 to which the drain of a corresponding transistor 6 is connected.

 A voltage is applied between a column conductor 81,82,83, ". Selected and a row conductor 91,92,93, ... selected to energize transistor 6 located at the intersection of the column and row conductors Voltage is then applied between the matrix element electrode 9 of the energized transistor 6 and the common electrode 16 to thereby give the matrix element electrode 2 a different appearance from that of the rest of the cell. The display can be selectively caused in this way in all the matrix elements of the liquid crystal cell 11.

 In the arrangement according to the prior art, a circuit 26 for controlling the column conductors 81, 82, 83, ...

and a circuit (not shown) for driving the row conductors 91 92 ′ 93 ... are mounted on a wiring base 18 on which the liquid crystal cell 11 is supported. The column conductors 81, 82, 83 ,. .. and the row conductors 91 ′ 92 ′ 93 / have respective terminals connected to corresponding terminals of the column control circuits 26 and of row control circuits. When the number of matrix elements is 100 x 100 = 10,000, the number of terminals to be connected to the control circuits reaches 100 + 100 = 200, and it is a tedious task to connect the terminals of the crystal cell liquid to the pilot circuits. In particular for a color display liquid crystal cell, each matrix element is generally composed of three points of red, green and blue which can be controlled independently. In the case of matrix elements planned in number reaching 100 x 100 = 10 000, the total number of points is 100 x 100 x 3 = 30 000 and the number of necessary terminals reaches 100 + (3 x 100) = 400. This increased number of terminals makes it more complex and longer to couple the color display liquid crystal cell with the control circuits.

 The anterior thin film transistor 6 has a structure as shown in FIGS. 3 and 4. Grid electrodes 5 (with row conductors 9) are shaped on a substrate 12 by first depositing a layer of metal such as chromium over the entire substrate 12, then by etching the metal layer according to a prescribed pattern. Then, the matrix element (drain) electrodes 2 are likewise shaped in the form of transparent metallic films on the substrate 12 by deposition on the latter of a metallic layer, then selective etching of the metallic layer. Next, a grid insulation film 22, made of silicon nitride, is deposited over the entire surface of the substrate 12, and holes 23 are formed in the grid insulation film 22 to allow contact with the electrodes. of matrix element 2. A semiconductor layer 24, made of amorphous silicon, is deposited on each gate electrode 5, with the interposition of the gate isolation film 22.

Subsequently, drain electrodes 25 and source electrodes 3 (to which a column conductor 8 is coupled) are shaped, made of aluminum on each semiconductor layer 24, at locations partially overlapping opposite sides of the gate electrode 5, with the interposition of the semiconductor layer 24 and the gate insulating film 22.

The drain electrode 25 is connected to the matrix element electrode 2 through the contact hole 23.

 The manufacture of the current thin film transistor 6 required a relatively large number of operations. It was therefore difficult to manufacture a multiplicity of thin film twisted transistors 6 with uniform characteristics and free from defects covering a large display area. Whereas the semiconductor layer 24 has an exposed part between the drain 25 and source 3 electrodes, the exposed part can come into contact with air humidity, which degrades the characteristics of transistor 6 after manufacture of the matrix of transistors 15 on the substrate 12 and before putting the assembly in the form of a liquid crystal cell 11.To avoid this risk, it is necessary to cover the semiconductor layer 24 with a protective film after depositing the electrodes 25 and 3, which increases the number of manufacturing operations.

 We will now describe a dot matrix liquid crystal color display according to the present invention. Figure 5 shows the appearance of such a color liquid crystal display. The color liquid crystal display comprises a liquid crystal cell 11 composed of two transparent substrates 12, 13 arranged facing each other and a liquid crystal 14 sealed between the substrates 12, 13.

A multiplicity of color display elements are formed on a surface of one of the substrates in the liquid crystal cell 11.

 As shown in FIG. 6, these color display elements are brought together by groups of elements of three types: display in red 1R, display in green 1G and display in blue 1B distributed almost uniformly over the substrate.

In the embodiment chosen by way of example, the color display elements are oblong and parallel to each other and each group of three matrix display elements in different colors constitutes a substantially square region 10 which serves as matrix element. The matrix elements 10 are arranged in columns and in rows. To simplify the process of controlling these matrix elements 10, the display elements are arranged in red1 in green and in blue lR, 1G, 1V in a straight line in longitudinal directions parallel to each other.

 According to the present invention, each of the color display elements 1R, 1G, 1B is composed of a semiconductor driver or thin film transistor and of a color filter located on an output electrode of the latter. More precisely, as shown in FIGS. 7 and 8, one of the substrates 12 of the liquid crystal cell 11 is formed from a transparent glass plate. Rectangular (matrix element) drain electrodes 2R, 2G, 2B about as wide as the color display elements are formed on the substrate 12, and narrower source electrodes 3R, 3G, 3B are deposited on the substrate 12 near the drain electrodes 2R, 2G, 2B respectively, parallel to them. Films 4R, 4G, 4B made of amorphous silicon form semiconductor layers between the drain 2R and source 3R electrodes, between the electrodes drain 2G and source 3G and between the drain 2B and source 3B electrodes, respectively. A gate isolation film 22, made of silicon nitride, is formed over the electrodes and the substrate. Grid electrodes 5R, 5G, 5B are deposited on the grid isolation film 22 opposite the amorphous silicon films 4R, 4G, 4B respectively. It is preferable that the drain electrodes 2R, 2G and 2B from source 3R, 3G and 3B be in the form of transparent electrodes of indium oxide or tin oxide. The grid electrodes 5R, 5G, 5B can be made of aluminum.

 Source electrodes 3R, 3G, 3B, drain (matrix element) electrodes 2R, 2G, 2B, amorphous silicon films 4R, 4G, 4B, gate isolation film 22 and gate electrodes 5R, 5G, 5B together constitute thin film transistors 6R, 6G, 6B respectively. On the GR, 6G, 6B thin film transistors are formed respectively red, green and blue colored filters 7R, 7G, 7B covering the drain (output) electrodes 2R, 2G, 2B, respectively, with interposition of the film d grid isolation 22. The colored filters 7R, 7G, 7B are formed by a screen printing or offset printing process.

 As illustrated in FIG. 9, an orientation treatment layer 17, such as a layer of polyvinyl alcohol, is deposited on the color display elements thus formed on the substrate 12. The substrate 13 disposed opposite the substrate 12 is, for example, made of transparent glass. A common transparent electrode 16 is formed on the entire interior surface of the substrate 13. An insulation film 19, such as silicon nitride film, is formed on the common transparent electrode 16, and another orientation processing layer 21 is deposited on the insulation film 19. A liquid crystal 14 is sealed between the orientation processing layers 17, 21. The liquid crystal cell 11 having the above-mentioned structure constitutes a liquid crystal cell of the so-called type guest-host in black or a nematic liquid crystal twisted in black and white. A poloriser 27 is fixed to the outer surface of the substrate 13.

 As shown in Figure 6, column conductors 81, 82, 83, ... are formed on the substrate 12 along the columns of color display elements, and the source electrode 3R, 3G or 3B of an adjacent color display element is to each column conductor. Row conductors 91t 92 93t are formed on the substrate along the rows of color display elements, and the gate electrode 5R, 5G or 5B of an adjacent color display element is connected to each row conductor.

 The color display elements can be selectively controlled by a control circuit as shown in FIG. 10. The source conductors 81, 82, 83, ... and the gate conductors 91 '92' 93 have terminals brought out of the display plane 28. The terminals of the source conductors 81, 82, 83, ... are respectively connected to corresponding outputs of bit locations of a lock circuit 26 serving as column driver, the locations of bit of latch 26 being connected to bit location outputs of a shift register 29. In operation, display data comes from a data terminal 31 under binary signals of "1" or "0" indicating whether or not there should be display on the color display elements of a row. These display data are successively introduced in series into the shift register 29 in synchronism with a rhythm signal arriving from a rhythm terminal 33. Once the display data of a row thus introduced, the data stored in the shift register 29 are introduced in parallel and locked in the latch circuit 26 in response to a locking order coming from a terminal 34.

 The locking order arriving from terminal 34 is also applied to a gate conductor selection and control circuit 32, which then selectively selects gate conductors 91 92 '93 at the rate of one at a time.

When selecting the grid conductor 91 for example, there is display or non-display of the color display elements placed at the junctions between the grid conductor 91 and those of the source conductors 81, 82, 83 ,. .. to which locked output bits are applied in the latch circuit 26. While the gate conductor 91 is the subject of the selection for display, data intended for a next disturbed conductor are introduced into the register at offset 29, and the stored data are then locked in the lock circuit 26 during a new lock order coming from the terminal 34. In response to this lock order, the gate conductor selection and control circuit 32 chooses the gate conductor 92 for selective display on the color display elements connected to the gate conductor 92 A detailed structure of the control circuit comprising components such as the damper shift 29, circuit lock 26, and gate conductor selector 32 is described, for example, in a brief communication entitled "Progress Toward Flat-Panel TV" by A.G. Fischer in "onemissive Electrooptics Displays" A.R. metz and F.K. von Willisen, 1976, Plenum Press, New York.

 As illustrated in FIG. 11A, control pulses with successive phase shifts are applied repeatedly to the. gate conductors 91 to 9120 When a thin film transistor 61l located, for example, at the intersection of the source conductor 81 and the zorilla conductor 91 is selected, a voltage V applies to the source conductor 81, as indicated in FIG. 11B, when the gate conductor 91 is selected in a first cycle and, consequently, the drain electrode of the thin film transistor 61l charges up to the voltage V, as indicated in 6 11D in FIG. 11C, and remains at this voltage. At this time, a constant voltage V / 2 applies to the source conductor of any element not then selected, for example to the thin film transistor 621 located at the intersection of the source 81 and gate 9 conductors. Consequently, the voltage present on the drain of the thin film transistor 621 is maintained at V / 2 as indicated at 621D in FIG. 11D. A voltage V / 2 is permanently applied to the common electrode 16 as shown in FIG. 11E.

 Consequently, the voltage V / 2 applies as voltage 611DC between the drain of the selected transistor 61l and the common electrode 16, as shown in FIG. 11F, and the voltage 621DC applied between the drain of the unselected transistor and the common electrode is zero, as shown in Figure llG. When the gate conductor 91 is selected during a next cycle, the selected source conductor 81 is kept at zero voltage, and the drain voltage 611D of the selected transistor 611 is also zero. The drain voltage 621D of the non-selected transistor remains V / 2. So, during this cycle, the voltage 611DC applied between the drain of the selected transistor and the common electrode becomes -v / 2. The voltage between the drain of the selected transistor and the common electrode changes alternately between V / 2 and -V / 2, so that the part of the liquid crystal cell facing the transparent drain electrode of the selected transistor appears through the color of the color filter fixed to the transistor concerned.

 If there is a total number of grid conductors of 120, comprising the grid conductors 91 to 9 the total number of source conductors required is three times the number of grid conductors, ie 360. It would be tedious and long remove all these conductors from the liquid crystal display and connect them to external pilots.

 According to the present invention, the peripheral circuits for driving the semiconductor pilot elements are formed on the surface of the substrate on which the thin film transistors 6R, 6G, 6B for driving the liquid crystals are produced. More specifically, the latch circuit 26 serving as a column driver and the shift register 29 are produced in the form of integrated circuits on the substrate 12, and the gate conductor selection and control circuit 32 is produced in the form of a circuit. integrated on the substrate, as illustrated in FIG. 5. The gate and source conductors starting from the liquid crystal cell 11 are connected to these circuits 26, -29, 32 on the substrate 12, and other necessary conductors are wired to the substrate 12. When the latch circuit 26, the shift register 27 and the gate conductor selection and control circuit 32 are to be placed in the form of integrated circuits on the substrate 12, they are preferably produced under form of thin film transistors like the thin film transistors constituting the color display elements. In this way, the peripheral circuits 26, 29, 32 can be formed at the same time as the thin film transistors 6R, 6G, 6B on the substrate 12 without having to increase the number of manufacturing operations required.

 Whereas the operating speed of the thin film transistors is relatively slow, it is necessary to subject the amorphous silicon films 4R, 4G, 4B to an annealing treatment with the electron beam or with the laser ensuring great mobility to increase the operating speed of the circuits 26, 29, 32. This treatment conferring great mobility can be carried out in a relatively short time since the thin film transistors constituting the color display elements do not require such treatment to increase mobility. It is not necessary to mount all the circuits 26, 29, 32 on the substrate 12: one can only place on the substrate 12 some of them, for example the circuits 26, 29 or the only circuit 32. The circuits 26, 29 32 mounted on the substrate 12 can be formed between ordinary bipolar or mono-clear integrated circuits. Amorphous silicon thin film transistors can be replaced by polycrystalline thin film transistors.

 With the above-mentioned arrangement, the peripheral circuits such as selection and control circuits of the semiconductor elements intended to control the display elements or matrix element of the liquid crystal cell are mounted on the substrate 12 of the latter. ci, so that the external connection terminals can be half as numerous as those of the previous structures, this to simplify the connection to the external terminals.

 When the colored filters carried by the controlled semiconductor elements are produced by printing, they can be produced using simple equipment without the use of an expensive vapor deposition or ion doping apparatus, and they can also be produced in the atmosphere so that they cover a relatively large area. The color filters allow good color reproduction, can be made inexpensively, are sufficiently thin compared to the liquid crystal 14 and have a sufficient color density. It is easy to attach in an alternating pattern color filters such as red, green and blue. Ink cannot infiltrate colored filters into the liquid crystal 14 because the treatment layer orientation 17 in polyvinyl alcohol is stable with respect to the liquid crystal 14. Consequently, the operation of the liquid crystal display is made stable. Even in the presence of the colored filters, the orientation processing layer is capable of easily determining the orientation of the molecules of the liquid crystal 14. Instead of being produced by screen printing, the colored filters can be done by offset printing to meet more stringent precision requirements. When the substrates can be given a reduced thickness, any selected matrix elements can be clearly visible when viewed obliquely, so it is possible not to attach a color filter to the thin film transistors, but to mount colored filters on the substrate 13 (as shown in FIG. 5) opposite the drain electrodes. The substrates 12, 13 can be formed from high polymers such as polyamide or fluorinated plastics. Although, as shown, the color display elements are arranged in columns and rows assigned to the different colors, they can be arranged in circles so that a group of three adjacent display elements has display elements in red, green and blue. Instead of additive primary colors, subtractive primary colors can be used for the color display.

 The thin film transistors 6R, 6G, 6B of Figures 5 and 6 may have the structure shown in Figures 3 and t. The present invention is applicable to liquid crystal displays not only in color, but also in black and white.

 We will describe such a liquid crystal display in black and white with reference to Figures 12 and 13. The matrix elements 2, drain electrodes 25 and source electrodes (source conductors 8) 3 are formed on a substrate 12. Each square-shaped matrix elements 2 have a side that is split in part to form one of the drain electrodes 25. These matrix elements 2, the drain electrodes 25, the source electrodes 3 and the source conductors 8 can be shaped simultaneously. selectively etching a transparent metal sheet deposited on the entire surface of the substrate 12. The source electrodes 3 can be made of an opaque metal.

 A semiconductor layer 24 such as amorphous silicon is formed on the substrate 12 between the drain electrode 25 and the source electrode 3. The semiconductor layer 24 can be made of polycrystalline silicon, monocrystalline silicon, tellurium, sulfide of cadmium or cadmium selenide.

A gate isolation film 22 is formed over the entire surface comprising the semiconductor layers 24. The gate isolation film 22 may be made of silicon nitride or silicon dioxide. It can be formed only on the semiconductor layers 24. Grid electrodes (grid conductors 9) 5 are formed on the grid insulation film 22. The grid electrodes are arranged opposite the drain electrodes 25 and from source 3, with the interposition of the semiconductor layer 24 and the gate insulation film 22.

The grid electrodes 5 and grid conductors 9 can be made of aluminum or polycrystalline silicon and can be in the form of a transparent electrically conductive film.

 A method of manufacturing a thin film transistor will be described by way of example with reference to FIGS. 14 to 19. As shown in FIG. 14, an opaque layer of a metal such as Nichrome, chromium or molybdenum is exposed in a layer of the order of 1000 to 2000 A on a transparent insulated substrate 12, which may be a wart, by vapor deposition or sputtering, and the matrix elements, drain electrodes 25 (2) and source electrodes 3 are shaped by photoengraving.

 A semiconductor layer, made of amorphous or polycrystalline silicon, is formed over a thickness of 3000 A, for example, on the transparent substrate 12 over the drain 25 and source 3 electrodes by DVC (vapor deposition) process. chemical) to plasma. The semiconductor layer is then treated by photoetching to form a semiconductor silicon layer 24, or channel region, which extends between the drain and source 3 electrodes 3 and is deposited on their edges, as illustrated in the figure. 15.

 Next, a gate insulation film 22 is deposited on the transparent substrate 12 over the entire semiconductor silicon layer 24, as shown in FIG. 16. The gate insulation film 22 can be made of nitride of silicon or silicon dioxide and have a thickness of between 2,000 and 3,000 A. The gate isolation film 22 can be formed by DVC plasma process.

 As shown in FIG. 17, a transparent electrode 5 ′ made of ITO (mixture of In 2 O 3 and SnO 2) or of tin oxide is formed on the isolation film Ae grids 22 by vapor deposition or sputtering, the transparent electrode 5 'having a thickness of 1000 A or less, for example between 400 and 500 A. Next, a layer of photosensitive resin for negatives 37 is formed on the trans-arent electrodes 5'. the photoscrsirlc resin bends 37 are exposed to an ultraviolet beam 39 radiating through the transparent substrate 12.

 The parts of the photosensitive resin layer 37 which are exposed to the ultraviolet beam harden. By development, there is obtained in the photosensitive resin layer a pattern 37p of shape defined by the drain and source electrodes 25 acting as caches.

 By using the photosensitive layer pattern 37p as a mask, the transparent electrode 5 ′ is etched into a transparent grid electrode 5 and the mask pattern 37p is eliminated as shown in FIG. 19.

 Consequently, the matrix element 2 and drain 25 electrodes are shaped simultaneously and are not coupled to each other by any contact hole. Whereas neither this contact hole, nor others are provided, no operation is to be expected to provide contact holes such as the holes 23 of the prior arrangement shown in FIG. 4. When the electrode of source 3 is to be produced in the form of a transparent electrode, it can be shaped at the same time as the matrix element electrode 2, which makes it possible to make the number of manufacturing operations less than that necessary for the manufacture of the common structure shown in FIGS. 3 and 4. Consequently, with the liquid crystal display of the present invention, the matrix of thin film transistors can be produced by a lower number of operations than according to the prior art; so that it is relatively easy to shape an array of elements with uniform characteristics and free from defects for a large display area.

 Whereas the semiconductor layer 24 is sandwiched between the substrate 12 and the gate insulation film 22, it is not likely to be exposed after shaping of the matrix of thin film transistors and before assembly thereof. ci in the liquid crystal cell 11. The semiconductor layer 24 therefore does not tend to take unstable characteristics and it is useless to cover it with a protective layer. This results in the possibility of manufacturing liquid crystal cells with a very superior rendering.

 When the liquid crystal display according to the invention is used as a transmission type liquid crystal display, an opaque film, for example of aluminum or black ink, is formed on the outer surface of the substrate. 12 opposite the semiconductor layer 24, between the drain 25 and source 3 electrodes, for the purpose of protection against any undesirable effects caused by light, such as modifications of the resistance of the semiconductor layer 24 when that -this is amorphous silicon.

It is possible to ensure the automatic positioning of the gate electrode 5 due to the fact that it is produced by exposure and development using as cover the drain 25 and source 3 electrodes. The drain 25 and source 3 electrodes and the gate electrode 5 can be permanently maintained in a constant relative arrangement. This reduces the distance, called channel length
L, which separates the drain and source electrodes 25. It is therefore easy to manufacture a thin film transistor having a short cut-off time and a large drain current. Such thin film transistors can be produced in the form of a matrix covering a large area, with a high degree of integration, while reducing the variations in the characteristics of these transistors.

 In FIG. 8, the colored filters 7R, 7G, 7B are formed on the grid isolation film 22 opposite the matrix element electrodes 2R, 2G, 2B with interposition of the grid isolation film 22. However , the colored filters 7R, 7G, 7B can be formed on the common electrode 19 carried by the substrate 13 as shown in FIG. 20. (Similar or corresponding parts are designated in FIG. 20 by the same numerical references as on the figure 8). The colored filters 7R, 7G, 7B are arranged so as to overlap the matrix element electrodes 2R, 2G, 2B respectively in a direction normal to the substrates 12, 13. The filters 7R, 7G, 7B can be easily formed, for example by printing, on the substrate 13 on which thin film transistors 6R, 6G, 6B are not made.

 It goes without saying that numerous modifications and variants can be made to the preferred embodiments described, without however departing from the scope of the invention.

Claims (10)

 1. Method for manufacturing a dot matrix liquid crystal display comprising a first transparent substrate (12) made of an insulating material, a second transparent substrate (13) made of an insulating material placed next to and in parallel with the first substrate and having a sealed peripheral edge in contact against it, a liquid crystal (14) sealingly disposed between said first and second substrates, a common electrode (16) deposited on substantially all of an interior surface of the second substrate to thereby define a display area of said liquid crystal display, transparent matrix element electrodes (2) formed in rows and columns directly on the first substrate to define display elements in the display area, electrode conductors of row C8) formed on the first substrate so as to follow the respective rows of said matrix element electrodes, and of thin film transistors of element control (6) arranged in rows and columns and each comprising a metal source electrode (3) connected to one corresponding to the row electrode conductors, a metal drain electrode (25) connected to the a corresponding of the matrix element electrodes and a grid electrode (5) connected to column electrode conductors (9) extending perpendicular to said row electrode conductors, this method comprising the steps of forming said electrodes metal from source and drain directly on the first substrate, to form semiconductor layers (24) on the first substrate so that they extend astride metal electrodes of source and drain corresponding, neighboring the one from the other, forming gate insulating films (22) so that they cover the respective semiconductor layers, and forming said gate electrodes on grating isolation films the corresponding opposite said respective semiconductor layers, characterized in that  said grid isolation films are produced in the form of a continuous film extending substantially entirely over the display area to cover said semiconductor layers and said electrodes of matrix element, and in that it further comprises the steps consists in  - forming zones of transparent grid electrode (5 ′) on said grid insulation film so that they cover said semiconductor layers;  - forming on said transparent grid electrode areas a layer of continuous photosensitive resin (37) capable of hardening by exposure to light;  - Exposing said layer of photosensitive resin to light through the first substrate, said metal source and drain electrodes acting as masks;  - Developing said layers of photosensitive resin to eliminate the parts which have not been exposed to light; and  - Etching said transparent grid electrode areas with the other parts of the photosensitive resin layer acting as masks, thereby forming said grid electrodes.  2. Method according to claim 1, characterized in that the row electrode conductors are metallic and are formed in one piece and simultaneously with the respective source electrodes.  3. Method according to claim 1, characterized in that thin film transistors forming integrated control circuits (26, 29, 32) are formed for driving said thin film element driving transistors on a marginal part. from the first substrate external to said liquid crystal arranged in a sealed manner simultaneously with the formation of said thin film element driving transistors.  4. Method according to claim 3, characterized in that the semiconductor layers of all of said thin film transistors are made of amorphous silicon.  5. Method according to claim 4, characterized in that it further comprises a step during which the layers of amorphous silicon are annealed at least of said control circuits in order to enhance the mobility of these semiconductor layers.  6. dot matrix liquid crystal display produced according to the method according to claim 1, comprising a first transparent substrate (12) made of an insulating material, a second transparent substrate (13) made of an insulating material disposed near the first substrate and parallel to it and having a sealed peripheral edge in contact against it, a common electrode (16) deposited substantially entirely on an interior surface of the second substrate in order to define a display area of the liquid crystal display, electrodes of transparent matrix element (2) formed in rows and columns directly on the first substrate to define display elements within the display area, row electrode conductors (8) formed on the first substrate so as to go along the respective rows of said matrix element electrodes1 and of the thin film element driving transistors (6) arranged in rows and in column and each comprising a metal source electrode (3) formed directly on the first substrate and connected to one, corresponding, of the row electrode conductors, a metal drain electrode (25) formed directly on the first substrate and connected to one, corresponding, of the matrix element electrodes, a semiconductor layer (24) formed on the first substrate to extend between, and overlap corresponding metal electrodes of source and drain adjacent one of the other, a gate insulating film (22) formed so as to cover the corresponding semiconductor layer and a gate electrode (5) formed on the corresponding gate insulating film and connected to conductors column electrodes (9) extending perpendicular to said row electrode conductors, characterized in that said gate insulation films are in the form of continuous film extending over substantially e completely the display area for covering the semiconductor layers and the matrix element electrodes, in that each of the grid electrodes is a transparent electrode of width substantially equal to the interval separating the opposite edges of source electrodes and corresponding drain and in that the gate electrode extends above this interval in the axis thereof.  7. Dot matrix liquid crystal display according to claim 6, characterized in that each of the matrix element electrodes is composed of a set of separate color element electrodes, in that the thin film transistors element control are assigned and each connected to said color element electrodes and in that there are provided colored filters of different colors formed on said grid isolation film opposite, respectively, element electrodes of each game's color.  8. dot matrix liquid crystal display according to claim 6, characterized in that each of the matrix element electrodes is composed of a set of separate color element electrodes, in that the thin film transistors of element control are assigned and each connected to said color element electrodes and in that there are provided colored filters of different colors formed on said common electrode opposite, respectively, said color element electrodes of each set .  9. dot matrix liquid crystal display according to claim 6, 7 or 8, characterized in that an integrated pilot circuit assembly (26, 29, 32) is provided formed on a marginal part of the first substrate to the exterior of said liquid crystal arranged in a sealed manner and comprising thin film transistors having the same structure as said element driving thin film transistors and formed simultaneously with them, for selectively energizing said thin film driving transistors element.  10. Dot matrix liquid crystal display according to claim 6, 7 or 8, characterized in that said column electrode conductors connected to respective grid electrodes are formed so as to extend over said film of grid insulation.