METHOD FOR MANUFACTURING A SEMI-TRANSPARENT DISPLAY AND A SEMI-TRANSPARENT DISPLAY

Description

[0001] The invention relates to a method for manufacturing a semi-transparent display. A semi-transparent display, as defined by the invention, is a display comprising a plurality of first surface areas within which light detectable by the human eye can shine through the display from both sides. Furthermore, a semi-transparent display comprises a plurality of second surface areas within which light detectable by the human eye cannot shine through the display.

[0002] Displays are becoming increasingly important for presenting information. Transparent or semi-transparent displays are advantageous if such information needs to be projected into a person's field of vision, for example, when wearing glasses or using binoculars.

[0003] From US 2015 / 0250038 A1 and US 2015 / 0309637 A1, methods for manufacturing a display are known in which a first substrate is temporarily used at the beginning of the layer deposition process. This substrate provides the necessary mechanical stability during the initial layer deposition processes. Thin-film transistors, electrodes, and wiring layers are applied and structured onto this substrate. During the display build-up, the first substrate is removed from the layer stack and replaced by a second, usually more flexible, substrate. Because of the re-adding of a substrate, the display pixels can only be controlled via the thin-film transistors above the substrate. Therefore, miniaturization of the display pixels is also limited by the thin-film transistors. Such methods are not suitable for manufacturing microdisplays, which typically require pixel sizes in the range of 1–10 µm.Replacing the substrate also requires additional effort, which increases manufacturing costs.

[0004] OLED displays and methods for manufacturing OLED displays, in which the switching elements for controlling the display pixels are based on so-called TFT technology, are described, for example, in US 2010 / 0045919 A1 and EP 1 480 272 A2. The active layer of TFT transistors is formed above a substrate of amorphous or polycrystalline semiconductors. Such semiconductors exhibit low charge carrier mobility, and typically either an electron-conducting transistor (NMOS) or a hole-conducting transistor (PMOS) is available in the TFT process. This severely limits the realization of complex circuits. Furthermore, the structuring methods for TFT transistors are limited and generally allow minimum channel lengths in the range of 3–5 µm. Therefore, it is not possible to create microdisplays with pixel sizes in the range of 1–10 µm using TFT technology.

[0005] WO 2013 / 062707 A1 also discloses OLED displays and methods for manufacturing OLED displays in which the display is embedded in a rigid housing, which limits the application of such displays. In this case, the display is assembled from different sub-components into a complete system. The composite structure and the necessary assembly and interconnection technology limit the miniaturization of such a display, and pixel sizes in the range of 1–10 µm required for microdisplays are also not achievable.

[0006] A wafer, a well-established technology, is often used as the basis for manufacturing a display. This wafer consists of a layer of electrically non-conductive material deposited on a silicon substrate. The silicon substrate provides the wafer with its mechanical stability and, for the following illustrative descriptions, represents the back side of such a wafer. The layer of electrically non-conductive material, in turn, features numerous adjacent silicon-based active areas, within which transistors or other electrical circuits are formed. These transistors or circuits can be used to control the individual pixels of the display. Due to the arrangement of silicon-based active areas on or within an insulating layer, this technology and such a wafer are also associated with the English technical term "silicon-on-insulator" or, in short, "SOI".A SOl wafer also has at least one layer located above the active areas, which usually consists of a transparent oxide. Electrically conductive connections between the terminals of the electrical circuits in the silicon-based active areas are formed within this layer. Often, several such oxide layers are deposited on top of each other in an SOI wafer, within which several wiring levels are then formed.

[0007] With regard to the surface of a SOI wafer used to manufacture a display, it is usually divided into at least one pixel area and at least one contact area. The image-displaying component is then located within the pixel area, and electrically conductive connections to external components are formed within the contact area. Due to the silicon substrate, SOI wafers are typically opaque to light that can be perceived by the human eye.

[0008] US 005317236 A describes methods for manufacturing a semi-transparent LCD display in which SOI wafers are used as the base for the display structure, onto which an electroluminescent layer and a counter-electrode layer are deposited. To achieve transparency of the display, it is proposed to remove the silicon substrate of the SOI wafer and replace it with a transparent substrate such as glass. A disadvantage of this approach is that electrically conductive connections from the contact area of ​​the SOI wafer to other components, such as a wiring carrier, can only be made from the front side of the SOI wafer, which limits their potential applications.

[0009] The invention is therefore based on the technical problem of creating a method for manufacturing a semi-transparent display that overcomes the disadvantages of the prior art. In particular, the method according to the invention should also make it possible to create rear-side contact options to other components.

[0010] The solution to the technical problem is achieved through objects having the features of claim 1. Further advantageous embodiments of the invention are set out in the dependent claims.

[0011] In the method according to the invention, at least one electromagnetic radiation-emitting layer is deposited on the front side of a SOI wafer known from the prior art. This at least one electromagnetic radiation-emitting layer is preferably designed as an organic layer, but can alternatively also be an inorganic layer. For the electromagnetic radiation-emitting layer to actually emit electromagnetic radiation in a display, pixel electrodes and pixel gene electrodes adjacent to the layer are required.

[0012] In one embodiment of the invention, the pixel electrodes and pixel counter-electrodes for the at least one electromagnetic radiation-emitting layer are arranged within a plane and formed as part of the SOI wafer.

[0013] Alternatively, only the pixel electrodes can be formed as part of the SOI wafer, in which case an electrically conductive layer is additionally deposited above and adjacent to the at least one electromagnetic radiation-emitting layer, which then acts as a counter electrode. This electrically conductive layer can alternatively also be formed as a sublayer and be the upper component of the at least one electromagnetic radiation-emitting layer. In a further embodiment, the electrically conductive layer or electrically conductive sublayer is structured so that at least one pixel counter electrode can be assigned to each pixel.

[0014] It is known that organic electromagnetic radiation-emitting layers often consist of a multitude of sublayers, which can also be deposited as organic layers in the process according to the invention. By way of example only, some of these sublayers that such a layer may comprise are listed below with their English technical terms and associated abbreviations in parentheses, without claiming to be exhaustive: Hole injection layer (HIL), Hole transport layer (HTL), Electron blocking layer (EBL), Emission layer (EML), Hole blocking layer (HBL), Electron transport layer (ETL).

[0015] Subsequently, at least one transparent top layer is applied over the at least one electromagnetic radiation-emitting layer. This transparent top layer can be, for example, a glass or plastic film. The resulting intermediate product is a composite comprising at least the SOI wafer, the electromagnetic radiation-emitting layer, and the transparent top layer. Additional layers, such as barrier layers or adhesion promoter layers, can also be deposited between the SOI wafer, the electromagnetic radiation-emitting layer, and the transparent top layer.

[0016] According to the invention, the silicon substrate of the SOI wafer is removed from the composite, resulting in a residual composite. The silicon substrate can, for example, be ground off the composite mechanically and / or removed from the composite using chemical substances. The silicon substrate, which was present on the SOI wafer primarily for its mechanical stability, is not required for the mechanical stability of the residual composite of a display according to the invention, because the top layer, which can be, for example, glass or a plastic film, ensures sufficient mechanical stability of the residual composite without the silicon substrate.

[0017] Removing the silicon substrate from the composite also renders the remaining composite semi-transparent. This means that, at least in those areas of the remaining composite where no transistors, electrical circuits, or electrically conductive connections are present, light perceptible to the human eye can pass through the composite from both sides, which was prevented by the silicon substrate before its removal.

[0018] After removing the silicon substrate from the SOI wafer, in one embodiment a non-transparent layer can be deposited and structured on the back side of the remaining SOI wafer to, for example, shield the pixel circuit from interfering electromagnetic radiation arriving from the back. Transparency is maintained in areas outside the pixel circuit.

[0019] After the silicon substrate has been removed from the composite, a wiring carrier is attached to the front or back of the remaining composite according to the invention. A wiring carrier can, for example, be designed as a printed circuit board.

[0020] If the wiring carrier is attached to the front of the remaining assembly, from which electromagnetic radiation is emitted in the pixel area, the wiring carrier has a recess at least in the pixel area.

[0021] According to the invention, electrically conductive connections are formed between the contact area of ​​the former SOl wafer, which is now only partially part of the remaining composite, and the wiring carrier from the back side of the SOI wafer. This is now possible because the silicon substrate has been removed beforehand, allowing contact elements or electrically conductive elements, primarily from the lowest wiring level, to be exposed from the back side within the contact area using known process steps. If the wiring carrier is attached to the front side of the remaining composite, electrically conductive connections between the contact area and the wiring carrier can be formed, for example, as wire bonds.If the wiring carrier is attached to the back of the remaining assembly, electrically conductive connections between the contact area and the wiring carrier can be formed, for example, as a bump bond or anisotropically conductive adhesive joint.

[0022] The invention is described in more detail below using exemplary embodiments. The figures show: Fig. 1 a schematic sectional view of an SOI wafer suitable for a display assembly, Fig. 2 a schematic sectional view of an SOI wafer on which an electrically radiating layer is deposited and a cover layer is applied, Fig. 3 a schematic sectional view of the composite made of Fig. 2 , from which the silicon substrate has been removed, Fig. 4 a schematic sectional view of the remaining composite made of Fig. 3 , where electrically conductive elements are exposed, Fig. 5 a schematic sectional view of the remaining composite made of Fig. 4 , to which a wiring carrier is attached on the front, Fig. 6 a schematic sectional view of the remaining assembly made of Fig. 4 , to which a wiring carrier is attached on the back, Fig. 7 a schematic representation of the rear of a residual assembly, to which a wiring carrier is attached on the front.

[0023] A SOl wafer 100, known from the prior art and suitable for a display structure, is in Fig. 1 The SOI wafer 100 is shown schematically as a cross-section. The SOI wafer 100 comprises, in sequence, a back-side silicon substrate 101, a transparent layer 102 made of an electrically non-conductive material, and several transparent silicon oxide layers 103, on the surface of which contacts 104, functioning as pixel electrodes, are formed. Within the layer 102 made of electrically non-conductive material, a multitude of silicon-based active areas 105 are embedded, within which electrical circuits 106 for controlling pixel cells are formed. Electrically conductive elements 107 are also formed within the silicon oxide layers 103, extending, for example, between the terminals of the circuits 106 and / or from the terminals of the circuits 106 to the contacts 104.

[0024] The in Fig. 1 The illustrated SOI wafer structure is merely an example. Alternatively, a SOI wafer known from the prior art may also have a different structure. For example, active regions of an SOI wafer may be located on top of layer 102 rather than within it. It should therefore be noted that all SOI wafers known from the prior art that are suitable for constructing a display can also be used for the inventive method and for constructing a display according to the invention.

[0025] The SOI wafer 100 is divided into a pixel area 109 and a contact area 110. In the embodiment of Fig. 1 The contact area 110 completely encloses the pixel area 109. For clarity, the cross-sectional views of the Fig. 1 bis 6 Only an excerpt from the pixel area of ​​an SOI wafer 100 is shown, which comprises only two silicon-based active regions 105. In contrast, a complete pixel area can contain several thousand such silicon-based active regions 105 arranged side by side.

[0026] In Fig. 2 The schematic cross-sectional view shows that, according to the invention, a transparent, electromagnetic radiation-emitting layer 201 is first deposited onto an SOI wafer using known process steps, and then a transparent top layer 202, which in this exemplary embodiment consists of glass, is applied, resulting in a composite consisting of SOI wafer 100, layer 201, and top layer 202. In this exemplary embodiment, the electromagnetic radiation-emitting layer 201 is designed as an organic layer and consists of a plurality of known sublayers, as previously described. Furthermore, layer 201 comprises, as its upper layer, a sublayer of an electrically conductive material, wherein the sublayer of the electrically conductive material is structured according to the pixel arrangement of the resulting display and functions as a pixel counter electrode.

[0027] According to the invention, after the composite of SOI wafer 100, layer 201 and cover layer 202 has been produced, the silicon substrate 101 of the original SOI wafer 100 is removed from the composite. This creates a residual composite 301, which is Fig. 3 schematically represented as a cross-section, which is semi-transparent. This means that the remaining composite 301 is transparent from both sides with respect to light perceptible to the human eye, at least within the pixel area 109 in the sub-areas 302 where no circuit elements or electrically conductive elements are formed, as indicated by the two arrows in Fig. 3 is shown schematically. Furthermore, the remaining assembly 301 also has sub-areas, such as the contact areas 110 and the sub-areas 303 of the pixel area 109, within which circuit elements and / or electrically conductive elements are formed and which therefore have a lower transparency compared to the sub-areas 302.

[0028] In addition to the resulting semi-transparency of the remaining composite 301, removing the silicon substrate 100 from the composite offers a further advantage. It is now possible to introduce recesses 401 into the back of the remaining composite 301 using known process steps. These recesses expose electrically conductive elements 402 of the lowest wiring level within the contact area 110, as described in Fig. 4 schematically represented as a cross-section.

[0029] In Fig. 5 A schematic cross-sectional view shows how a wiring carrier 501 is attached to the front of the remaining assembly 301. The wiring carrier 501 has a recess 502 in the pixel area of ​​the remaining assembly 301, through which electromagnetic radiation 503 from the display pixels and light 508 penetrating the remaining assembly 301 can pass. Furthermore, in Fig. 5 shown that contact elements 505 of a front-mounted wiring carrier 501 can be contacted with the electrically conductive elements 402 exposed on the rear, for example by means of wire bonds 506.

[0030] An alternative display structure according to the invention is described in Fig. 6 schematically represented as a cross-section. From the Fig. 4 In an alternative approach, a wiring carrier 601 was attached to the back of the known residual assembly 301. The wiring carrier 601 also has a recess 602 in the pixel area of ​​the residual assembly 301. Alternatively, if the wiring carrier is attached to the back, there may be no recess in the pixel area if the property of semi-transparency is not required for a display. In this embodiment, the electrically conductive elements 402 of the residual assembly 301 exposed on the back are made of... Fig. 6 electrically conductively connected to contact elements 604 of the wiring carrier 601 by means of so-called bump bonds 603.

[0031] In Fig. 7Finally, a display assembly according to the invention is shown schematically in a rear view, in which a wiring carrier 701 is attached to the front of a residual assembly 702, with a detail section 703 of a pixel area 704 of the residual assembly 702 being shown greatly enlarged for better illustration. In addition to the pixel area 704, the residual assembly 702 also has a contact area 705. Electrically conductive elements 706 exposed on the rear side within the contact area 705 are electrically connected to contact elements 708 of the wiring carrier 701 by means of wire bonds 707.

[0032] For the sake of clarity, only four pixels 709 are schematically depicted in detail 703. Detail 703 is intended to further illustrate that, in a display according to the invention, there are a plurality of sub-areas 710 between the pixels 709, within which no circuits for controlling the pixels 709 and no electrically conductive connections 711 are formed, which is why the sub-areas 710 are transparent. Since the surface areas of a display according to the invention, within which, for example, circuits or electrodes for controlling pixels 709 or electrically conductive connections 711 are formed, have at least a lower or even significantly reduced transparency compared to the sub-areas 710, a display according to the invention is referred to as semi-transparent.

Claims

1. Method for manufacturing a semi-transparent display, comprising: a) providing an SOI wafer (100) whose surface comprises at least one pixel region (109) and at least one contact region (110) situated next to the pixel region, wherein the SOI wafer (100) includes, on its rear side, a silicon substrate (101) and above the same, viewed in this order, a transparent layer (102) made from an electrically non-conductive material as well as multiple transparent silicon oxide layers (103), wherein, at the surface of one of the transparent silicon oxide layers (103), contacts (104) serving as pixel electrodes are formed, wherein, in the layer (102) of electrically non-conductive material, a multitude of silicon-based active regions (105) are embedded in which electrical circuits (106) for controlling pixel cells are formed, and wherein, in the silicon oxide layers (103), electrically conductive elements (107) for connecting circuits (106) are formed; b) depositing at least one electromagnetic radiation emitting layer (201) on the front side of the SOI wafer (100) and on the contacts (104) serving as pixel electrodes; c) applying at least one transparent cover layer (202) above the at least one electromagnetic radiation emitting layer (201); d) attaching a wiring carrier (501; 601) to the composite including, at least, the SOI wafer (100), the electromagnetic radiation emitting layer (201) and the transparent cover layer (202), characterized in that, prior to attaching the wiring carrier (501; 601) to the composite, consisting of the SOI wafer (100), the electromagnetic radiation emitting layer (201) and the transparent cover layer (202), the silicon substrate (101) is removed from the composite, thereby creating a remaining composite (301), wherein depressions (401) are introduced on the rear side of the remaining composite, which expose electrically conductive elements (402) within the contact region (110) and wherein electrically conductive connections between the electrically conductive elements (402) that are exposed within the contact region (110) of the composite (301) and the wiring carrier (501; 601) are formed.

2. Method according to claim 1, characterized in that the wiring carrier (501) is attached to the front side of the remaining composite (301).

3. Method according to claim 2, characterized in that the electrically conductive connections between the contact region (110) of the SOI wafer (100) and the wiring carrier (501) are formed to be a wire bond (506).

4. Method according to claim 1, characterized in that the wiring carrier (601) is attached to the rear side of the remaining composite (301).

5. Method according to claim 4, characterized in that the electrically conductive connections between the contact region (110) of the SOI wafer and the wiring carrier (601) are formed to be a bump bond (603) or an anisotropically conducting bond.

6. Method according to any one of claims 1 to 5, characterized in that the at least one electromagnetic radiation emitting layer (201) is formed to be an organic layer.

7. Method according to any one of claims 1 to 5, characterized in that the at least one electromagnetic radiation emitting layer is formed to be an inorganic layer.

8. Method according to any one of claims 1 to 7, characterized in that the silicon substrate (101) is mechanically abraded from the composite and / or that the silicon substrate (101) is removed from the composite using chemical substances.

9. Method according to any one of the preceding claims, characterized in that the at least one transparent cover layer (202) is formed to be glass or a plastic film.

10. Method according to any one of claims 1 to 9, characterized in that pixel electrodes and pixel counter electrodes for the at least one electromagnetic radiation emitting layer are arranged on one level and as a component of the SOI wafer.

11. Method according to any one of claims 1 to 9, characterized in that the contacts (104) serving as pixel electrodes are formed as a component of the SOI wafer, wherein an electrically conductive layer is deposited above and adjacent the at least one electromagnetic radiation emitting layer.

12. Method according to claim 11, characterized in that the electrically conductive layer is structured.