GB2204980A - Active matrix addressed liquid crystal display devices - Google Patents

Abstract

An active matrix addressed liquid crystal display device has an opaque semiconductor substrate (14) which is spaced from a transparent substrate (16) with liquid crystal (20) material therebetween, and which carries a planar array of picture element electrodes (22) together with associated switching elements (24) e.g. transistors or diodes, formed thereon. To allow transmission mode operation, the semiconductor substrate has a cellular structure, being provided with etched openings (30) aligned with the picture element electrodes (22) and closed at their ends by transparent end walls (32) upon whose surfaces remote from the openings the display electrodes are deposited and adjacent which the switching elements are located. The semiconductor substrate (14) is a single oriented slice, e.g. of silicon, providing a comparatively large display area and enabling integration of the associated picture element drive circuitry thereon. The end walls may be of the semiconductor material or of an insulative film. A further transparent sheet of plastics or glass may be secured over the lower surface of substrate 14. The switching devices as well as the row, column electrodes are disposed on the lattice structure of the semiconductor substrate defined by walls 34. <IMAGE>

Description

DESCRIPTION ACTIVE MATRIX ADDRESSED LIQUID CRYSTAL DISPLAY DEVICES AND METHODS OF MAKING SUCH DEVICES This invention relates to an active matrix addressed liquid crystal display device comprising a semiconductor substrate, a transparent substrate substantially parallel to, and spaced from, the semiconductor substrate with liquid crystal material therebetween, and a matrix of picture elements each of which comprises a picture element electrode and an associated switching element formed on the semiconductor substrate via which signals are supplied to the picture element electrode. The invention relates also to methods for making such a display device.

In known devices of this kind, the switching elements may be in the form of MOS field effect transistors or diode structures.

The picture elements are usually arranged in rows and columns. In the case, for example, of MOS transistors being used, the drain electrodes of the transistors are connected to a respective picture element electrode and the gate and source electrodes of each row and column of picture elements of the matrix array connected to respective row and column conductors formed on the semiconductor substrate. A counter electrode common to all picture elements is carried on the facing surface of the transparent substrate. The row conductors are energised one row at a time by sequential scanning with a gating signal which switches the transistors of that row on. Simultaneously with this row energisation, data signals, for example, video information, are supplied to the column conductors and appear via the "on"transistors, on the picture element electrodes to produce a display effect.The gating signal supplied to the row conductor is then removed and the row conductor for the next row of picture elements energised, the display information of the previously addressed row being maintained due to the natural capacitance of the picture elements. By supplying data signals for the picture elements of each row in turn in synchronism with row energisation, a display picture is built up.

In the case where the switching elements comprise diode structures, picture element electrodes of each row of the display device are connected via respective diode elements to one of a set of parallel row conductors carried on the semiconductor substrate. The other, transparent substrate carries a further set of parallel conductors, the column conductors, at right angles to the first set with the picture elements being defined at the intersections of the two set of conductors. As before, the row conductors are energised one at a time sequentially and data signals applied to the columns as appropriate to produce a display effect from the picture elements of the addressed row, the diode structures serving substantially to maintain this display effect until the next time the row is addressed.

The use of a semiconductor substrate leads to simplicity in the fabrication of the switching elements. It is usual for this substrate to be formed from single crystal silicon. Such a high mobility substrate offers easy addressing capabilities whilst also allowing switching elements with good operational and reliability characteristics to be formed conveniently and cheaply. However, silicon has the disadvantage that it is substantially opaque to visible light and for this reason it has been customary for liquid crystal display devices employing a silicon semiconductor substrate to be operated in reflection mode by using a light-reflective picture element electrodes on the semiconductor substrate.

It is considered preferable to use transmission mode operation if possible, for example, for high display brightness, but this requires both substrates to be substantially transparent to visible light. Whilst this has been achieved in other kinds of active matrix addressed liquid crystal display devices using for example, arrays of amorphous or poly-silicon thin film transistors (TFTs) deposited on a glass substrate, those other kinds of devices have their attendant disadvantages mainly in obtaining satisfactory switching performance and operational reliability for all the very large number of TFTs required in the arrays.

It is an object of the present invention to provide an active matrix addressed liquid crystal display device of the kind referred to in the opening paragraph which is capable of being operated in transmission mode.

According to one aspect of the present invention, an active matrix addressed liquid crystal display device of the kind mentioned in the opening paragraph is characterised in that the semiconductor substrate is provided with an array of openings therein which are closed at one end by respective, substantially transparent, end walls and in that the picture element electrodes are provided on the surface of the end walls remote from the openings.

The openings in the semiconductor substrate with the picture element electrodes overlying the end walls thereof act as windows through which visible light can pass from one side of the substrate to the other. Naturally, the material of the electrodes is chosen to be transparent for this purpose and may comprise indium tin oxide (ITO). The display device according to the invention can therefore operate in transmission mode even though a semiconductor substrate is employed. The invention offers therefore the advantages of a transmission mode liquid crystal display device with the addressing capabilities of a high mobility substrate.

Such a display device is particularly suited for use in an LCD projection system.

The semiconductor substrate preferably comprises silicon, although gallium arsenide may also be used.

The transparency of the end walls of the openings is determined by the material used and its physical thickness. In the case of a silicon substrate the end walls could for example be formed of a thin, integral layer of the silicon material which is left after providing the openings in the silicon substrate by etching through a predetermined part of the thickness of the silicon substrate to leave a silicon layer which is sufficiently thin to exhibit adquate transparency.

Alternatively, the end walls may be of insulative material, in the form of a membrane. This insulative material, for example silicon oxide, silicon nitride or polyimide, may be deposited on the semiconductor substrate. The insulative material may on the other hand be formed, at least in part, by treating a surface portion of the semiconductor substrate. For example, in the case of a silicon substrate, a silicon oxide or silicon nitride surface portion could be grown. Such formation of the insulative material may be carried out prior to forming the aforementioned openings by etching so that the insulative portion acts as a barrier in the etching process. The membrane forming the end walls and comprising this converted surface portion may be increased in thickness by deposition on the insulative surface portion of further insulative material.

The insulative material constituting the end walls may extend as a continuous layer over the area of the picture elements to provide a continuous surface substantially parallel to the opposing surface of the transparent substrate. Portions of this continuous layer between the end walls may be used in the fabrication of the switching elements.

The switching elements, for example in the form of transistors or diodes, may be formed on the semiconductor substrate adjacent their associated picture element electrodes with a terminal of the switching elements connected to the picture element electrodes disposed on the end wall of the openings.

Whilst more than one picture element could share a common opening formed in the semiconductor substrate, or more than one opening could be associated with a single picture element, for structural integrity preferably each picture element has associated therewith a respective and discrete opening, this opening being bounded completety around it sides by a wall of semiconductor material. The semiconductor substrate thus has a cellular structure having inherent strength and rigidity. The width of the openings may be substantially constant through the thickness of the semiconductor substrate. Alternatively, the walls of the semiconductor substrate defining the openings may taper such that the width of the openings increases towards the side of the substrate remote from the picture element electrodes.This has the advantage that a greater light collection area is obtained for each picture element with incoming light being reflected from the tapered walls towards the picture element electrode.

A further disadvantage of known active matrix addressed liquid crystal display devices using a semiconductor substrate is that the dimensions of the device are limited by the dimensions of the semiconductor slice or wafer employed. Typically, display areas have been restricted to around 80 cms across where a generally circular wafer of monocrystalline (100) oriented silicon is used as the substrate.

In accordance with a further feature of the present invention, the semiconductor substrate may comprise cm 10) oriented monocrystalline semiconductor material, such as silicon or gallium arsenide. Such a (110) oriented slice is elliptical, having a major axis of greater dimension than the diameter of the (100) oriented slice, and allows a rectangular display area within the elliptical boundary of the slice to be utilised which has a greater width than possible with a slice taken through (100) planes of a (100) oriented ingot. Using current semiconductor technology, (100) oriented silicon ingots of around 100 to 200 cms diameters can be grown enabling silicon semiconductor substrates having a width of approximately 120 to 240 cms to be achieved.

The elliptical shape of the semiconductor substrate thus formed offers a further advantage in that after delimitation of the generally rectangular display area occupied by the picture elements in the central region thereof, peripheral portions of the substrate are available for utilisation in forming the display devices associated addressing circuitry, for example a digital shift register for sequentially addressing rows of picture elements with a scanning signal and an analogue shift register/sampling circuit for driving column conductors with data signals derived by sampling, for example, a video signal. Thus the addressing circuitry is integrated on the same semiconductor substrate as the array of picture elements thereby simplifying fabrication, especially as regards interconnection between the driving circiuts and the row and column conductors, and increasing reliability.

According to another aspect of the present invention, a method of making an active matrix addressed liquid crystal display device in accordance with the first aspect of the present invention and in which the semiconductor substrate comprises (110) oriented monocrystalline semiconductor material, such as silicon, is characterised by the step of forming the substrate by slicing a (100) oriented ingot of the material at 45 degrees to its main axis. This method avoids the difficulties associated with growing a (110) oriented ingot.

As previously mentioned, the openings in the semiconductor substrate serving to define windows may be formed using an etching process. In a preferred embodiment, such openings are formed conveniently using an orientation dependent etching technique. In the case of the semiconductor substrate comprising (110) oriented monocrystalline silicon, or gallium arsenide, the orientation requirement for vertical etching results in parallelogram shaped openings. The surrounding walls of silicon material are masked during the etching process by a dielectric pattern disposed on the exposed surface of the substrate or by selectively doping the silicon material in a predetermined pattern with boron. The method allows some control over the size of the openings but their shape is predetermined by the nature of the slice.The parallelogram shaped openings are arranged side-by-side in a regular array of rows and columns with the bounding walls of the openings of the array interlinked in a grid arrangement forming a cellular structure.

The switching elements and the conductors for supplying signals thereto are preferably disposed on the surface of the walls adjacent to the end walls carrying the picture element electrodes.

When diodes are used, only one set of conductors need be provided on the semiconductor substrate, but when transistors are used, two, column and row, sets of conductors are required. These conductors, for addressing the switching elements may extend entirely along these surface areas of the walls in zig-zag fashion, or, in part, over the end walls.

An active matrix addressed liquid crystal display device, and methods for making such a device, in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic plan view of the display device; Figure 2 is a cross-sectional view, not to scale, through a part of the display device, and Figure 3 is a diagrammatic plan view of a portion of the device of Figure 1 on an enlarged scale, showing some of the picture elements of the device.

Referring to Figure 1, the active matrix addressed liquid crystal display device has a- rectangular display area, indicated by the boundary line 12, comprising a matrix array of individually addressable picture elements arranged in rows and columns, a few of which are indicated schematically at 10. For example, the array may have 400 columns and 200 rows providing 800,000 display elements.

The display area 12 occupies a central part of the overall area of a substrate 14 formed of semiconductor material which is generally elliptical in shape for reasons which will become apparent. The semiconductor substrate 14 has formed thereon switching elements 15 for the picture elements.

The upper substrate of the display device comprises a transparent sheet 16 of, for example, glass, which is rectangular and overlies the display area 12. Alternatively however, this upper substrate may also be formed as an ellipse corresponding in shape with the semiconductor substrate 14. TN liquid crystal material is contained in the space between the two, parallel, substrates 14 and 16 using seals (not shown) extending around the periphery of the display area 12.

A cross-section through a typical part of the display device within the display area 12 is shown in Figure 2. Here, the liquid crystal material is referenced at 20. The upper substrate 16 carries a continuous transparent electrode 21, for example of indium tin oxide, ITO, over the entire display area 12. The lower, semiconductor, substrate 14 carries a planar array of transparent picture element electrodes 22, only one of which is shown in entirety in Figure 2. Each of these picture element electrodes 22 defines, together with an opposing portion of the continuous electrode 21 and the liquid crystal material 20 therebetween, a respective picture element 10.Each picture element is controlled by an associated switching element which in the particular embodiment of Figures 1, 2 and 3 comprises an MOS transistor 24 arranged laterally of its picture element electrode and formed in a known manner on the semiconductor substrate 14. The drain electrode 25 of the transistor 24 is connected directly to the picture element electrode 22. The drain and source electrodes are connected via conductive pads through an insulative layer constituting the gate insulator layer to respective doped regions in the silicon substrate. The central gate terminal and source terminal comprise parts or integral extensions of row and column conductors carried on the substrate 14. The sources of all transistors 24 in a column of the matrix are connected electrically to a common column conductor 18, parts of which are visible in Figure 2 as the source of the transistors.The gates of all transistors 24 in a row of the matrix are connected to a common row conductor 19 (again parts of which is visible as the gate terminals in Figure 2), the two sets of column and row conductors thus provided being mutually insulated.

The display device is driven in conventional fashion. For displaying video or TV pictures therefore, the row conductors 19 are supplied with a scanning (gating) signal sequentially so as to turn each row of transistors "on" in turn. While a row is scanned in this manner, video data signals are applied to the column (source) conductors 18 and since the transistors of the row being addressed are turned "on", these signals are passed to the drains of the transistors concerned and so appear at the picture element electrodes of that row to produce the desired electro-optic effect from the picture elements of that row. Subsequently, the next row conductor is addressed to turn "on" the transistors in that next row and the transistors in the previously addressed row are turned "off".Video data signals are now applied to the column conductors 18 for this next row to produce a display effect from the picture elements of that row whilst the video data across the picture elements of the preceding row is maintained due to the natural capacitance of the picture elements and the high impedance of the transistors in their "off" state until the next time that row is addressed during the subsequent field period. Whilst not shown in Figure 1, each picture element may further include a shortage capacitor connected in known manner. All rows of the display are addressed in turn, one line at a time, thus building up a complete picture in one field period. The sign of the video data voltage is reversed in alternate fields to prevent electro-chemical degradation of the liquid crystal material.

Heretofore, it has been common for display devices employing a semiconductor substrate, for example of silicon, to be operated in reflective mode in view of the non-transparency of the semiconductor substrates at the kind of thicknesses normally necessary to provide adequate support and rigidity. The display device according to the invention, however, is intended to be operated in transmission mode and to this end the semiconductor substrate is provided with an array of openings defining windows therein through which light can pass and which are aligned with the picture element locations as determined by the picture element electrodes 22.Referring to Figures 2 and 3 in particular, the semiconductor substrate 14 comprises a slice of single crystal silicon around 250 to 700 micrometers in thickness which is etched selectively to form a regular array of openings 30 therein extending through at least most of the thickness of the slice.

These openings 30 are closed at their ends adjacent the liquid crystal material 20 by end walls 32 whose surfaces closest to the liquid crystal material form, together with laterally-adjacent surface areas of the remaining structure of the silicon slice consisting of end surfaces of walls referenced 34 in Figure 2, a substantially planar and continuous surface over the display area on which the picture element electrodes 22 and the row and column address conductors 18 and 19 are carried. In the embodiment shown, each opening is associated with one picture element and the cross-sectional area of the opening corresponds substantially to the picture element electrode area.

The end walls 32 may be obtained by forming a thin surface layer of insulative silicon oxide or silicon nitride, both of which are transparent, prior to etching of the slice to define the openings 30. This surface layer is a membranous layer which may be grown and/or deposited. The thin layer constituting the end walls 32 extends completely and continuously over the eventual display area 12 of the device, thus covering also the end surface areas of the walls 34 of the silicon slice structure surrounding the subsequently-formed openings 30 upon which the transistors, 24 are formed. The silicon oxide or nitride acts as a barrier to etching so that upon etching of the openings, the thickness of the silicon slice at the selected regions can be etched through to the thin layer which then becomes the end walls 32.Portions of this continuous insulative layer overlying the end surfaces of the walls 34 are utilised as the gate insulator layer of the transistors.

In an alternative construction, the depth to which the openings 30 are etched may be controlled so as to leave an integral end wall of the silicon material which is sufficiently thin compared with the overall thickness of the silicon slice to be substantially transparent to light, for example around 20nm. An insulative layer is then formed by growing and/or depositing for example a thin layer of silicon nitride or silicon oxide over the exposed planar surface of the silicon slice.

In another alternative construction, the silicon slice may be etched completely through and a separately formed insulative film, for example of polyimide, disposed tautly over the surface of the remaining slice structure and secured thereto, by means of adhesive or peripheral clamping for example, to produce an integral structure. This film would appear similar to the layer, including the end walls 32, shown in Figure 2.

The sides of each of the openings 30 in the semiconductor substrate 14 defined by the walls 34 are substantially parallel and extend orthogonally to the plane of the electrodes 22. Each opening 30 allows light incident over the area of the opening at the side remote from the wall 32 to pass unimpeded through at least a major portion of the thickness of the substrate 14 and thence through the transparent end wall 32 and associated picture element electrode 22 of the picture element concerned, thereby permitting the device to be operated in transmission mode. The openings 30 in the substrate 14 are individually defined and mutually separated by the walls 34 of silicon material which surround each opening completely.

These walls are interconnected to produce a grid structure of lattice-like configuration which exhibits sufficient strength and rigidity such that, even though etched, the substrate is still capable of performing its intended supporting function satisfactorily.

The transistors 24 are fabricated on surface regions of these walls 34 using conventional techniques. The associated column (source) and row (gate) conductors are deposited using suitable conductive material either entirely on the end surfaces of these walls 34 or in part over selected regions of the end walls 34 not occupied by the picture element electrodes 22.

The semiconductor substrate 14 comprises a (110) oriented slice obtained from an ingot of monocrystalline silicon, although gallium arsenide may also be used, which slice is advantageously obtained by cutting a (100) ingot at 45 degrees to its main axis, thereby avoiding the problems usually encountered in growing a (110) ingot with the necessary high quality. The (110) slice has the advantage over circular (100) slices conventionally-used that it provides a larger surface area enabling a greater rectangular display area to be used. A (110) slice of single crystal silicon is elliptical in shape, as illustrated in Figure 1.

Besides providing a larger display area than possible a circular (100) slice, the elliptical shape of the substrate 14 has the further useful advantage in that the display device's driving circuitry can be incorporated on the regions of the slice outside the display area 12, these regions, of course, being free of etched openings which are present only in the display area. As shown diagrammatically in Figure 1, therefore, a row conductor address circuit, generally designated 40, comprising a digital shift register circuit providing scanning signals can be processed on the slice laterally of the display area 12. Similarly, a column conductor address circuit, comprising a further shift register and an analogue sample and hold circuit providing data signals, can also be processed on the slice, as shown at 41.The incorporation of such address circuitry on the same silicon slice as the picture elements with their associated switching transistors, considerable eases fabrication of the display device, particularly as regards the provision of interconnections between the driving circuitry and the row and column conductors, 18 and 19.

As a result of using a (110) oriented slice of silicon for the substrate 14, the openings provided therein for each picture element are parallelogram shape in plan view, as can be seen from Figure 3 which shows a typical portion of the substrate 14 in plan view. Referring to that Figure, the grid-like wall structure of the silicon slice remaining after etching of the openings 30 consists of first and second sets of substantially parallel walls 34 intersecting each other at an angle and, in this particular example, the row and column conductors extend respectively generally horizontally and vertically in zig-zag fashion, as shown at 45 and 40 for example, over the surface of the grid-like wall structure. These conductors are mutually insulated electrically where they cross or overlap by an intervening layer of insulative material.The switching transistors 24 may be located on this wall structure at any convenient point for interconnection with their associated row (gate) and column (source) conductors.

A method of fabricating the substrate 14 of the display device will now be described, it being understood that fabrication of the opposing substrate, with its continuous electrode, is accomplished in conventional manner. This method relates to the kind of semiconductor substrate 14 previously described in which the end walls 32 comprise silicon oxide or nitride.

Starting with a (100) ingot of single crystal silicon, the ingot is cut at 45 degrees to its main axis to produce an elliptical (110) slice which is then polished on one side using a known process. It is necessary also to polish the other side of the slice, either mechanically or chemically, although the stage at which this is done is not critical. The active matrix of switching transistors and the drive circuitry is then fabricated using appropriate silicon device technology. The picture element electrodes 22 and row and column conductors are deposited in a conventional manner with appropriate interconnections to the transistors and driving circuitry.

In fabricating the transistors, the silicon oxide or nitride layer, produced as described previously by growing and/or deposition, is utilised.

The surface of the slice on which the switching transistors are formed is then protected and the desired window pattern, corresponding to the desired display element array, is defined on the opposite surface of the slice, following polishing of this opposite surface. The pattern is defined in boron doped silicon or a dielectric to act as an etching mask. Alignment of the window pattern with the transistor array on the surface of the slice does not have to be very accurate. Alignment to around tens of microns is sufficient.

The slice is then etched in an orientation dependent etch such as KOH or a catechol etch such as ethylenediamine pyrocatechol etch to etch through the silicon forming the openings 30. The orientation requirement for vertical etching of (110) oriented material results in parallelogram shaped openings whose four sides are substantially equal in length. The openings formed in this manner can be as small as approximately O.lmm across but more typically would have sides of approximately O.5mm.

The display device is then completed using conventional LCD technology by assembly of the two substrates 16 and 14 and introduction of liquid crystal material therebetween. The opposing surfaces of the two substrates are covered by a liquid crystal orientation layer of, for example, polyimide material, and the outer surfaces of the substrates are covered with, respectively, polariser and analyser films (not shown) in conventional manner.

The display device thus formed has the advantages normally associated with devices employing high mobility stable semiconductor substrates and also fewer necessary connection leads with on-board multiplex drive capability as a result of the incorporation on the substrate of the driving circuitry. Although the use of a (110) oriented slice for the semiconductor substrate can lead to comparatively large display areas being obtained, the device its construction also lends itself to the production of compact display devices allowing easier redundancy and suitable for use in LCD projection systems. As the technology utilised is largely proven and well developed, high yields are possible as well as the advantages pertaining to transmissive type liquid crystal display devices.

It is envisaged that the openings 30 formed in the semiconductor substrate 14 need not have substantially constant width through the thickness of the substrate. Instead, by using known etching techniques the walls 34 of the grid-like structure may taper outwardly towards the side of the substrate 14 remote from the end walls 32. In this way, the area of light collection for each display element is increased. Incoming light is reflected from the sides of the openings towards the display elements.

Moreover, in order to provide additional support and protection to the semiconductor substrate 14 if considered desirable, a further transparent sheet, of plastics or glass may be secured over the lower surface of the substrate 14 in contact with the end surfaces of the walls 34 and secured to the substrate 14 by any suitable means, such as adhesive.

Whilst the particular embodiment of display device described above utilises transistors as switching elements for the picture elements, diode structures such as MIMs (Metal-Insulator-Metal structures) may be used instead, these being fabricated on the semiconductor substrate 14 in similar manner to, and at the same locations as, the transistors 24. Of course with this alternative kind of active matrix display device, only one set of address conductors need be carried on the substrate 14, for example in the row conductors, with the electrode carried on the opposing substrate 12 being sub-divided into a set of separate and parallel column conductors extending generally at right angles to the row conductors on the substrate 14, and defining at their intersections with the row conductors the location of the picture elements. The column conductor driving circiut 41 may still be formed on the semiconductor substrate and interconnected with the column conductors carried on the other substrate 16.

Claims (23)

CLAIM(S)

1. An active matrix addressed liquid crystal display device comprising a semiconductor substrate, a transparent substrate substantially parallel to, and spaced from, the semiconductor substrate with liquid crystal material therebetween, and a matrix of picture elements each of which comprises a picture element electrode and an associated switching element formed on the semiconductor substrate via which signals are supplied to the picture element electrode, characterised in that the semiconductor substrate is provided with an array of openings therein which are closed at one end by respective, substantially transparent, end walls and in that the picture element electrodes are provided on the surface of the end walls remote from the openings.

2. An active matrix addressed liquid crystal display device according to Claim 1, characterised in that the end walls comprise a layer of the semiconductor material of the substate which is sufficiently thin as to exhibit transparency.

3. An active matrix addressed liquid crystal display device according to Claim 1, characterised in that the end walls comprise insulative material.

4. An active matrix addressed liquid crystal display device according to Claim 3, characterised in that the insulative material of the end walls comprises polyimide material.

5. An active matrix addressed liquid crystal display device according to Claim 3, characterised in that the insulative material comprises silicon oxide.

6. A active matrix addressed liquid crystal display device according to Claim 3, characterised in that the insulative material comprises silicon nitride.

7. An active matrix addressed liquid crystal display device according to Claim 5 or Claim 6, characterised in that the insulative material of the end walls is formed, at least in part, by treating a surface portion of the semiconductor substrate.

8. An active matrix addressed liquid crystal display device according to any one of Claims 3 to 7, characterised in that the insulative material constituting the end walls extends as a continuous layer over the area of the picture elements providing a continuous surface substantially parallel to the opposing surface of the transparent substrate.

9. An active matrix addressed liquid crystal display device according to any one of Claims 1 to 8, characterised in that each opening in the semiconductor substrate has associated therewith a respective one picture element electrode.

10. An active matrix addressed liquid crystal display device according to any one of Claims 1 to 9, characterised in that each opening in the semiconductor substrate is bounded completely around its sides by a wall of semiconductor material.

11. An active matrix addressed liquid crystal display device according to Claim 10, characterised in that the switching elements and electrical conductors for supplying signals thereto are formed on the surface of the walls of the semiconductor substrate between the end walls of the openings.

12. An active matrix addressed liquid crystal display device according to Claim 10 or 11, characterised in that the width of the openings is substantially constant through the thickness of the semiconductor substrate.

13. An active matrix addressed liquid crystal display device according to Claim 10 or 11, characterised in that the walls of the semiconductor substrate defining the openings taper such that the width of the openings increases towards the side of the semiconductor substrate remote from the picture element electrodes.

14. An active matrix addressed liquid crystal display device according to any one of Claims 1 to 13, characterised in that the switching elements comprise transistors.

15. An active matrix addressed liquid crystal display device according to any one of Claims 1 to 13, characterised in that the switching elements comprise diode structures.

16. An active matrix addressed liquid crystal display device according to any one of Claims 1 to 15, characterised in that the semiconductor substrate comprises (110) oriented monocrystalline semiconductor material.

17. An active matrix addressed liquid crystal display device according to Claim 16, characterised in that circuits for driving the picture elements are integrated on the semiconductor substrate outside the area occupied by the picture elements.

18. An active matrix addressed liquid crystal display device according to any one of Claim 1 to 17, characterised in that the semiconductor substrate comprises silicon.

19. A method of making an active matrix addressed liquid crystal display device as claimed in Claim 16, characterised in that the method includes the step of forming the (110) oriented monocrystalline semiconductor material by slicing a (100) oriented ingot of the material at 45 degrees to its main axis.

20. A method according to Claim 19, characterised by the step of forming the openings in the semiconductor substrate by orientation dependent etching.

21. A method according to Claim 20, characterised in that the semiconductor substrate comprise silicon.

22. A method of making an active matrix addressed liquid crystal display device substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

23. An active matrix addressed liquid crystal display device substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.