FR3085763A1 - TRANSMISSION SCREEN WITH LIQUID CRYSTALS ON SILICON - Google Patents

Abstract

The present description relates to a liquid crystal display screen, comprising: - a control circuit (105) integrated in and on a silicon layer (103) and comprising a plurality of elementary control cells (107); - an insulating layer (201) coating a first face of the control circuit; - a liquid crystal layer (111) coating a first face of the insulating layer (201) opposite the control circuit; and - a plurality of first transparent electrodes (109) disposed between the first face of the insulating layer (201) and the liquid crystal layer (111), each first electrode (109) being electrically connected to a corresponding elementary cell (107) of the control circuit (105) via a via (203) passing through the insulating layer.

Description

DESCRIPTION

TITLE: Transmissive liquid crystal screen on silicon

Technical Field The present description relates generally to the field of liquid crystal display screens. It relates more particularly to a transmissive liquid crystal screen on silicon, and to a method of manufacturing such a screen.

PRIOR ART [0002] Conventionally, a liquid crystal display screen comprises a layer of liquid crystals, electrodes arranged on either side of the layer of liquid crystals making it possible to locally modulate the electric field applied to the layer. of liquid crystals and therefore the transparency of the liquid crystal layer so as to display images, and a control circuit connected to the electrodes and making it possible to control the voltage levels applied to the electrodes.

It would be desirable to be able to at least partially improve one or more aspects of known liquid crystal display screens.

Summary of the invention [0004] Thus, one embodiment provides a liquid crystal display screen, comprising:

- a control circuit integrated in and on a silicon layer and comprising a plurality of elementary control cells;

- an insulating layer covering a first face of the control circuit;

- a layer of liquid crystals coating a first face of the insulating layer opposite the control circuit; and a plurality of first transparent electrodes

B17038- DD18712CV arranged between the first face of the insulating layer and the liquid crystal layer, each first electrode being electrically connected to a corresponding elementary cell of the control circuit via a via passing through the insulating layer.

According to one embodiment, each first electrode is directly in contact with the side walls and with the bottom of the via.

According to one embodiment, each first electrode is directly in contact with the silicon layer of the control circuit at the bottom of the via.

According to one embodiment, each first electrode comprises a stack of monoatomic layers of a transparent conductive material.

According to one embodiment, the material of the first electrodes is a material of the group comprising zinc oxide doped with aluminum and tin oxide.

According to one embodiment, each first electrode comprises a stack of monoatomic layers of tin oxide interspersed with metallic monoatomic layers.

According to one embodiment, each first electrode comprises a metallic monoatomic layer directly in contact with the silicon layer of the control circuit.

According to one embodiment, the metallic monoatomic layers of the first electrodes are aluminum layers.

According to one embodiment, the screen further comprises a transparent support substrate disposed on the side of a second face of the control circuit opposite to its first

B17038- DD18712CV face, and a backlight light source disposed on the side of the support substrate opposite the control circuit.

According to one embodiment, the screen further comprises a second transparent electrode disposed on the side of the layer of liquid crystals opposite to the first electrodes. Another embodiment provides a method of manufacturing a screen. liquid crystal display, comprising the following successive steps:

a) forming a control circuit integrated in and on a silicon layer, the control circuit comprising a plurality of elementary control cells;

b) depositing an insulating layer on a first face of the control circuit;

c) forming, on a first face of the insulating layer opposite the control circuit, a plurality of first transparent electrodes, each first electrode being electrically connected to a corresponding elementary cell of the control circuit via a via passing through the insulating layer; and

d) depositing a layer of liquid crystals on the first face of the insulating layer.

According to one embodiment, each first electrode is formed by depositing a transparent conductive material in successive monoatomic layers.

BRIEF DESCRIPTION OF THE DRAWINGS These characteristics and advantages, as well as others, will be explained in detail in the following description of particular embodiments made without implied limitation in relation to the attached figures among which:

[Fig. 1] Figure 1 is a sectional view schematically showing an example of a liquid crystal display screen according to one embodiment;

B17038- DD18712CV [0018] [Fig. 2] Figure 2 is a sectional view showing in more detail an embodiment of the screen of Figure 1;

[Fig. 3] Figure 3 is a sectional view showing in more detail another embodiment of the screen of Figure 1;

[Fig. 4] Figure 4 is a sectional view showing a step of an example of a method of manufacturing the screen of Figure 3;

[Fig. 5] Figure 5 is a sectional view showing another step of an example of a method of manufacturing the screen of Figure 3;

[Fig. 6] Figure 6 is a sectional view showing another step of an example of a method of manufacturing the screen of Figure 3;

[Fig. 7] Figure 7 is a sectional view showing another step of an example of a method of manufacturing the screen of Figure 3;

[Fig. 8] Figure 8 is a sectional view showing another step of an example of a method of manufacturing the screen of Figure 3; and [Fig. 25] 9] FIG. 9 is a sectional view showing another step of an example of a method for manufacturing the screen of FIG. 3.

Description of the embodiments The same elements have been designated by the same references in the different figures. In particular, the structural and / or functional elements common to the various embodiments may have the same references and may have identical structural, dimensional and material properties.

B17038- DD18712CV For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been shown and are detailed. We are particularly interested here in the production of the polarization electrodes for the liquid crystal layer and in the connection of these electrodes to the control circuit of a liquid crystal display screen. The realization of the various other elements that a liquid crystal display screen may include, such as the liquid crystal layer itself, the control circuit, possible polarization filters, possible color filtering elements, a source of backlighting, etc., has not been detailed, the production of these elements being within the reach of those skilled in the art from the indications of this description.

Unless otherwise specified, when reference is made to two elements electrically connected to each other, this means directly connected without intermediate elements other than conductors, and when reference is made to two elements connected or coupled together, this means that these two elements can be connected or be linked or coupled via one or more other elements.

In the following description, when reference is made to qualifiers for absolute position, such as the terms front, rear, top, bottom, left, right, etc., or relative, such as the terms above, below, upper, lower, etc., or to orientation qualifiers, such as the terms horizontal, vertical, etc., reference is made unless otherwise specified in the orientation of the figures, it being understood that, in practice, the described devices can be oriented differently.

B17038- DD18712CV Unless otherwise specified, the expressions approximately, approximately, substantially, and of the order of mean to the nearest 10%, preferably to the nearest 5%.

Figure 1 is a sectional view schematically showing an example of a liquid crystal display screen according to one embodiment.

The display screen of Figure 1 comprises a transparent support substrate 101, for example glass, on an upper face of which is disposed a layer of silicon 103, for example monocrystalline silicon, in and on which is integrated a control circuit 105. The silicon layer 103 extends for example continuously over substantially the entire surface of the substrate 101. The control circuit 105 comprises a plurality of elementary control cells 107, for example identical or similar ( to manufacturing dispersions). The elementary control cells 107 are for example arranged in a matrix according to rows and columns.

Each elementary cell 107 of the control circuit

105 is surmounted by a transparent conductive electrode 109, disposed on the upper face of the control circuit 105 and electrically connected to the cell 107. In this example, the electrodes 109 connected to the various elementary control cells 107 are separated. Each elementary cell 107 can be individually controlled to apply a specific bias potential to the electrode 109 to which it is connected. Each elementary cell 107 comprises for example one or more MOS transistors. By way of example, each elementary cell 107 comprises a single MOS transistor. The integrated control circuit 105 is for example produced in technology

CMOS.

B17038- DD18712CV The display screen of FIG. 1 further comprises a layer of liquid crystals 111 arranged on the side of the upper face of the electrodes 109. In this example, the layer of liquid crystals 111 extends from continuously over substantially the entire upper face of the semiconductor layer 103.

The display screen of Figure 1 further comprises a transparent conductive electrode 113 coating the upper face of the liquid crystal layer 111. The electrode 113 extends for example continuously over substantially the entire face upper part of the liquid crystal layer 111. The upper electrode 113 can be connected to the control circuit 105 in a peripheral part (not shown) of the display screen, or via one or more vias ( not shown) passing through the liquid crystal layer 111. The upper electrode 113 is for example connected to a node for supplying a fixed reference potential of the control circuit 105.

The display screen of Figure 1 thus comprises a plurality of pixels, defined respectively by the elementary cells 107 and by the lower electrodes 109 of the stack. More particularly, each pixel comprises an elementary control cell 107, the electrode 109 connected to this cell, a portion of the layer of liquid crystals 109 disposed opposite (vertically) from the electrode 109, and a portion of the electrode 113 arranged opposite the electrode 109.

The display screen of Figure 1 further comprises a backlight light source 115, for example a white light source, disposed on the side of the underside of the support substrate 101. The light source 115 is arranged to illuminate the underside of the support substrate 101. For example, the light source 115

B17038- DD18712CV is an extended source adapted to uniformly illuminate the entire underside of the support substrate 101. In the example shown, the light source 115 is located at a non-zero distance from the rear face of the support substrate 101. As a variant, the light source 115 can be attached to the rear face of the support substrate 101.

The display screen of FIG. 1 is a so-called transmissive screen, that is to say that, in operation, the light emitted by the light source 115 passes through the control circuit 105, the electrodes 109, the liquid crystal layer 111 and the electrode 113. The control circuit 105 is controlled to apply, in each pixel, a specific bias voltage between the electrode 109 (specific to the pixel) and the electrode 113 (common to all screen pixels), so as to locally control, pixel by pixel, the transparency of the liquid crystal layer. Thus, the light emitted by the light source 115 is intensity-modulated by the liquid crystal layer 111 as a function of the control signals applied to the electrodes 109 by the control circuit 105, which makes it possible to generate a visible image from the side of the upper face of the liquid crystal layer 111.

To allow the passage of light through the control circuit 105, the silicon layer 103 in and on which the circuit 105 is integrated is preferably relatively thin. For example, the thickness of the silicon layer 103 is less than 50 nm.

In the example of Figure 1, the display screen is a color screen, that is to say that it comprises different pixels adapted to emit light in ranges of different lengths. For this, each pixel includes a filter element 117, for example a resin pellet

B17038- DD18712CV colored, placed on the side of the upper face of the liquid crystal layer. Each filter element 117 is adapted to transmit only part of the emission spectrum of the light source 115, and to absorb the light emitted by the light source 115 outside of its transmission band. Different pixels of the display screen include filter elements 117 having different transmission bands, which enables color images to be displayed. By way of example, the display screen comprises pixels of a first type, comprising filter elements 117B suitable for transmitting mainly blue light, for example in a range of wavelengths between 410 and 480 nm, pixels of a second type, comprising 117G filter elements suitable for transmitting predominantly green light, for example in a wavelength range between 490 and 550 nm, and pixels of a third type , comprising filter elements 117R suitable for transmitting mainly red light, for example in a range of wavelengths between 590 and 670 nm. The pixels of the first, second and third types are for example regularly distributed alternately over the entire surface of the screen. In the example of FIG. 1, the filtering elements 117 are arranged on the upper face of the upper electrode 113.

The display screen may further comprise a stack 119 of one or more compensation and / or anti-reflective layers, arranged on the side of the upper face of the screen. In the example of FIG. 1, the stack 119 covers the upper face of the filter elements 117. The stack 119 extends for example continuously over the entire surface of the sensor.

B17038- DD18712CV [0042] Figure 2 is a sectional view showing in more detail an embodiment of a liquid crystal display screen of the type described in connection with Figure 1. Figure 2 shows more particularly an enlargement of a portion of the screen of FIG. 1, comprising an elementary cell 107 of the control circuit and the corresponding transparent electrode 109. FIG. 2 also shows a corresponding portion of the support substrate 101 and a corresponding portion of the liquid crystal layer 111. For the sake of simplification, the light source 115, the upper electrode 113, the filter element corresponding 117 and stack 119 have however not been shown.

In the example of Figure 2, the screen comprises an intermediate layer 201 of an electrically insulating material, interfacing between the upper face of the control circuit 105 and the lower face of the electrode 109. The layer 201 is for example a layer of silicon oxide. By way of example, the thickness of the layer 201 is between 0.1 and 1 μm, for example of the order of 0.5 μm. The lower face of the insulating layer 201 is for example in contact with the upper face of the silicon layer 103 of the control circuit 105. The upper face of the insulating layer 201 is for example in contact with the lower face of the electrodes 109. By way of example, the lower face of the liquid crystal layer 111 is in contact with the upper face of the electrodes 109 and with the upper face of the insulating layer 201 in the areas of the layer 201 not coated by the electrodes 109. In each pixel, the transparent electrode 109 of the pixel preferably extends, when viewed from above, over the major part of the surface of the pixel.

B17038- DD18712CV In each pixel of the screen, the transparent electrode 109 of the pixel is connected to the elementary control cell 107 of the pixel by means of an opening or a via 203 passing vertically through the layer insulating 201. More particularly, in the example of FIG. 2, in each pixel of the screen, an opaque conductive layer 205, for example a metallic layer, for example a layer of titanium, covers the side walls and the bottom of the via 203 accordingly. The conductive layer 205 is for example in contact with the insulating layer 201 at the side walls of via 203. In the example shown, the conductive layer 205 further extends over part of the upper face of the layer 201, for example in contact with the upper face of the layer 205, on the periphery of via 203. When viewed from above, the opaque conductive layer 205 preferably extends over less than 10 percent of the pixel surface.

The transparent electrode 109 of the pixel is in contact with the conductive layer 205 of the pixel. More particularly in the example shown, part of the electrode 109 is disposed on and in contact with the upper face of the conductive layer 205 at at least part of the portion of the conductive layer 205 covering the upper face. layer 201. At the bottom of via 203, the conductive layer 205 is in contact with the upper face of the control circuit, and more particularly with a connection area of the elementary pixel control cell 107, forming a contact ohmic with this connection area. Thus, the transparent electrode 109 of the pixel is connected to the elementary control cell 107 of the pixel by means of the conductive layer 205 in order to allow the control of the pixel. For example, at the bottom of via 203, the conductive layer 205 is directly in contact, mechanically and electrically, with the upper face of

B17038- DD18712CV

layer silicon 103 in which is carried out the circuit of order from pixel • 0046] In the example of achievement of Figure 2, the electrodes lower 109 of pixels of sensor are through example in indium tin oxide (ITO). at l example title, the electrodes lower 109 of pixels of sensor have a

thickness between 20 and 100 nm. The thickness of the conductive layer 205 is for example between 20 and 100 nm.

A limitation of the structure of FIG. 2 is that the opaque conductive layer 205, connecting the transparent electrode 109 of the pixel to the elementary pixel control cell 107, limits the aperture factor of the pixel, ie -to say the ratio between the transmissive surface of the pixel and the opaque surface of the pixel, and this especially for pixels of small dimensions, for example in screens in which the inter-pixel pitch is less than 20 μm.

Furthermore, the production of a screen of the type described in relation to FIG. 2 requires two successive sequences of deposition steps, photolithography and etching, in order to respectively produce the conductive layers 205 and the transparent electrodes 109.

Figure 3 is a sectional view showing another embodiment of a liquid crystal display screen of the type described in connection with Figure 1. As in Figure 2, Figure 3 shows more particularly an enlargement of a portion of the screen in FIG. 1, comprising an elementary cell 107 of the control circuit and the corresponding transparent electrode 109.

As in the example of Figure 2, the screen of Figure 3 comprises an intermediate layer 201 of an electrically insulating material, interfacing between the face

B17038- DD18712CV upper of the control circuit 105 and the lower face of the electrode 109. In addition, as in the example in FIG. 2, in each pixel of the screen, the transparent electrode 109 of the pixel is connected to the elementary pixel control cell 107 via a via 203 passing through the insulating layer 201.

The screen of Figure 3 differs from the screen of Figure 2 mainly in that, in the example of Figure 3, there is no provision for an opaque conductive layer intermediate between the transparent electrode 109 and the upper face of the integrated control circuit 105.

In the example of Figure 3, in each pixel of the screen, the transparent electrode 109 extends not only on the upper face of the insulating layer 201, but also covers the side walls and the bottom of the via 203. The transparent electrode 109 is for example directly in contact with the insulating layer 201 at the side walls of via 203. At the bottom of via 203, the transparent electrode 109 comes directly into contact with the upper face of the control circuit 105, and more particularly with a connection zone of the elementary pixel control cell 107, forming an ohmic contact with this connection zone. By way of example, at the bottom of via 203, the transparent electrode 109 is directly in contact, mechanically and electrically, with the upper face of the silicon layer 103.

Compared to the screen of Figure 2, an advantage of the screen of Figure 3 is that the pixel opening factor is increased due to the removal of the opaque conductive layer 205 in each pixel. In addition, the production of the screen is simplified insofar as the steps for forming localized conductive layers 205 can be omitted.

B17038- DD18712CV In the example of FIG. 3, the lower electrodes 109 of the sensor pixels are preferably made of a transparent conductive material deposited by deposition in successive monoatomic layers or ALD (from the English Atomic Layer Deposition), for example zinc oxide doped with aluminum (AZO), or tin oxide (SnO _x , for example SnCL), or any other transparent conductive oxide (TCO) depositable by ALD. In a preferred embodiment, the lower electrodes 109 consist of a stack of monoatomic layers of tin oxide into which are inserted monoatomic layers of aluminum, for example less than 20% of aluminum layers, this which increases the electrical conductivity of the electrode without significantly degrading its transparency. Preferably, the electrodes 109 comprise at least one monoatomic layer of aluminum directly in contact, mechanically and electrically, with the upper face of the layer of silicon 103, which makes it possible to significantly reduce the resistance to resumption of contact on silicon. The thickness of the electrodes 109 is preferably relatively small, for example less than 25 nm and preferably less than 15 nm. This is made possible by the use of an ALD type deposit, which makes it possible to obtain very thin and very conformal layers, without risk of electrical discontinuity. This advantageously makes it possible to improve the transparency of the electrodes 109.

Figures 4 to 9 are sectional views illustrating successive steps of an example of a method of manufacturing a liquid crystal display screen of the type described in connection with Figure 3. Figures 4 to 9 show more particularly the production of transparent electrodes 109 of the screen. In Figures 4 to 9, only two screen pixels have been (partially) shown.

B17038- DD18712CV FIG. 4 represents a starting structure comprising the transparent support substrate 101, and the control circuit 105 coating the upper face of the substrate 101. The construction of the control circuit 105 on the upper face of the substrate support 101 comprises for example a step of transferring a relatively thick layer of silicon, for example of thickness greater than 100 μm, onto the upper face of the substrate 101, then a step of thinning the silicon layer, for example by mechanical and / or chemical consumption, from the upper face of the silicon layer, until the desired silicon thickness is obtained for the layer 103. As a variant, it is possible to use an SOI substrate comprising in stacking a base substrate, an insulating layer and a surface layer of silicon. The SOI substrate is bonded to the support substrate 101 at its silicon surface layer, then the base substrate and the insulating layer are eliminated by mechanical and / or chemical consumption. The silicon surface layer integral with the support substrate 101 forms the layer 103 and can optionally be thinned.

The control circuit 105 can then be formed in and on the layer 103, by conventional methods of producing integrated circuits, for example in CMOS technology.

FIG. 4 more particularly illustrates a step of depositing the insulating layer 201 on the upper face of the control circuit 105, then producing, in each pixel, from the upper face of the layer 201, a opening or via 203 passing through the layer 201 and opening onto the upper face of the control circuit 105. The insulating layer is for example deposited continuously over substantially the entire upper surface of the control circuit

B17038- DD18712CV control 105. The vias 203 are for example formed by photolithography and etching. By way of example, the vias 203 have, when viewed from above, a maximum dimension of less than 1 μm and preferably of the order of 0.5 μm. In top view, the vias 203 have for example a circular shape.

FIG. 5 illustrates a step of depositing a transparent conductive layer 301 intended to form the future transparent electrodes 109 of the screen. In this example, layer 301 is deposited by deposition in successive monoatomic layers (ALD). Layer 301 consists of a stack of monoatomic layers of a transparent conductive material, possibly interposed with metallic monoatomic layers (not detailed in the figure). Advantageously, a metallic monoatomic layer will be positioned directly in contact with the layer 103 in order to obtain better electrical contact. The layer 301 is deposited continuously and in conformity over the entire upper surface of the structure of FIG. 4. Thus, the layer 301 is deposited, with a substantially uniform thickness, not only on the upper face of the layer 201, but also on the side walls and at the bottom of the vias 203.

FIG. 6 illustrates a step of depositing a layer of protective resin 303 on the upper face of the layer 301, with a view to a subsequent step of localized etching of the layer 301 to define the electrodes 109 of the 'screen. The layer 303 is for example made of a photosensitive resin. At this stage, the layer 303 extends continuously over substantially the entire surface of the screen.

FIG. 7 illustrates a step of forming localized openings 305 in the resin layer 303, for example by photolithography and development of the resin in the layer 303. The openings 305 pass entirely through the resin layer 303 and lead to the upper side

B17038- DD18712CV of layer 301. When viewed from above, the openings 305 define the outline of the future electrodes 109 of the screen.

For example, the width of the openings 305, defining the distance between two neighboring electrodes 109 of the screen, is less than 1 μm.

FIG. 8 illustrates a step of etching the transparent conductive layer 301 at the bottom of the openings 305 of the resin layer 303. During this step, the portions of the layer 301 arranged opposite the openings 305 are completely withdrawn. In other words, the openings 305 are extended through the layer 301 to the upper face of the insulating layer 201, so as to isolate the electrodes 109 from the different pixels of the screen from one another.

The etching of the layer 301 is for example carried out by plasma etching, for example of the IBE type (from the English Ion Beam Etching - etching by ion beam).

FIG. 9 illustrates a step of removing the protective resin layer 303 before subsequent steps, not detailed, of depositing the liquid crystal layer 111, the upper electrode 113, possible filtering elements 117 , and the stack 119 of the screen (Figure 1).

Various embodiments and variants have been described. Those skilled in the art will understand that certain features of these various embodiments and variants could be combined, and other variants will be apparent to those skilled in the art. In particular, the embodiments described are not limited to the examples of dimensions and materials mentioned in the present description.

In addition, although we have described, in relation to Figure 1, an embodiment of a color display screen, the embodiments described can be adapted to the production of a screen d '' grayscale display,

B17038- DD18712CV not including differentiated filter elements 117R

117G, 117B.

Claims (12)

1. Liquid crystal display screen, comprising: - a control circuit (105) integrated in and on a silicon layer (103) and comprising a plurality of elementary control cells (107); - an insulating layer (201) coating a first face of the control circuit; a liquid crystal layer (111) coating a first face of the insulating layer (201) opposite the control circuit; and - a plurality of first transparent electrodes (109) arranged between the first face of the insulating layer (201) and the liquid crystal layer (111), each first electrode (109) being electrically connected to a corresponding elementary cell (107) of the control circuit (105) via a via (203) passing through the insulating layer (201). 2. Screen according to claim 1, in which each first electrode (109) is directly in contact with the side walls and with the bottom of the via (203). 3. Screen according to claim 1 or 2, wherein each first electrode (109) is directly in contact with the silicon layer (103) of the control circuit (105) at the bottom of the via (203). 4. Screen according to any one of claims 1 to 3, in which each first electrode (109) comprises a stack of monoatomic layers of a transparent conductive material. 5. Screen according to claim 4, in which said material of the first electrodes (109) is a material of the group comprising zinc oxide doped with aluminum and tin oxide. B17038- DD18712CV 6. Screen according to claim 5, in which each first electrode (109) comprises a stack of monoatomic layers of tin oxide interspersed with metallic monoatomic layers. 7. Screen according to claim 6, wherein each first electrode (109) comprises a metallic monoatomic layer directly in contact with the silicon layer (103) of the control circuit (105). 8. Screen according to claim 5 or 6, wherein said metallic monoatomic layers of the first electrodes (109) are layers of aluminum. 9. Screen according to any one of claims 1 to 8, further comprising a transparent support substrate (101) disposed on the side of a second face of the control circuit (105) opposite its first face, and a light source backlight (115) disposed on the side of the support substrate (101) opposite the control circuit (105). 10. Screen according to any one of claims 1 to 9, further comprising a second transparent electrode (113) disposed on the side of the liquid crystal layer (111) opposite the first electrodes (109). 11. Method for manufacturing a liquid crystal display screen, comprising the following successive steps: a) forming a control circuit (105) integrated in and on a silicon layer (103), the control circuit (105) comprising a plurality of elementary control cells (107); b) depositing an insulating layer (201) on a first face of the control circuit (105); B17038- DD18712CV c) forming, on a first face of the insulating layer (201) opposite the control circuit (105), a plurality of first transparent electrodes (109), each first electrode being electrically connected to a corresponding elementary cell (107) of the circuit control (105) via a via passing through the insulating layer (201); and d) depositing a layer of liquid crystals (111) on the first face of the insulating layer (201). 12. The method of claim 11, wherein each first electrode (109) is formed by depositing a transparent conductive material in successive monoatomic layers.