Forming a conductive connection between a common electrode of an optical front plane and an electrical contact part of an opposite back plane

A technique for creating a conductive connection between a contact part (24) of a display back plane (34) and a common electrode (20) of a display front plane (32), comprising the step of compressing a compressible conductive component (30) between the display front plane (32) and the display back plane (34), wherein the method further comprises the step of interposing one or more layers (10, 36) having a low modulus of elasticity not larger than 5 GPa between the contact part (24) and the compressible conductive component (30) prior to the compressing step.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/EP2013/067313 filed Aug. 20, 2013, claiming priority based on British Patent Application No. 1214812.8 filed Aug. 20, 2012, the contents of all of which are incorporated herein by reference in their entirety.

Some display devices comprise a control component laminated to an optical media component, and include an electrical contact between a common electrode of the optical media component and electrical circuitry of the control component.

The control component typically comprises an array of electronic switching devices that control respective portions of the optical media component. The array of electronic switching devices typically includes one or more blanket layers of insulating material formed over the electronic switching devices, and one conventional technique for achieving said conductive connection between the control component and the optical media component involves deliberately avoiding the deposition of insulating material on the part of the electrical circuitry (contact part) used for the conductive connection to the common electrode on the optical media component.

The inventors have identified the challenge of developing an improved technique for creating the conductive connection between the control component and the optical media component.

There is hereby provided a method of creating a conductive connection between a contact element of a control component and a common electrode of an optical media component comprising compressing a compressable conductive component between the control component and the optical media component; wherein the method further comprises interposing one or more layers having a low modulus of elasticity between said contact element and said compressable component prior to said compressing.

According to one embodiment, said one or more layers having a low modulus of elasticity comprise one or more insulating layers, and said method further comprises providing a conductive connection through said one or more organic layers between said contact element and said compressable conductive component.

According to one embodiment, said compressable conductive component is a pad comprising a conductive adhesive embedded with conductive structures.

According to one embodiment, said compressable conductive component comprises a conductive paste.

According to one embodiment, said control component comprises an array of pixel electrodes and an array of electronic switching devices for controlling the electric potential at said array of pixel electrodes; and said one or more organic layers also serve to insulate said pixel electrodes from one or more underlying conductive elements.

According to one embodiment, the method further comprises forming through the one or more insulating layers both via-holes (a) for electrically conductive connections between the electronic switching devices and the respective pixel electrodes of the pixel electrode array, and one or more via-holes (b) for an electrically conductive connection between said contact element and said common electrode of said optical media component.

According to one embodiment, the method further comprises: forming on said upper surface of said one or more insulating layers an upper conductive layer electrically connected to said array of electronic switching devices and said contact element via said via-holes (a) and said one or more via-holes (b), respectively; and patterning said upper conductive layer to both define said array of pixel electrodes, and define an electrically conductive element conductively connected to said contact element and electrically isolated from said array of pixel electrodes.

According to one embodiment, said one or more layers having a low modulus of elasticity have a Young's modulus of less than about 5 GPa.

There is also hereby provided a method of producing a control component for lamination to an optical media component, the control component comprising an array of pixel electrodes and an array of electronic switching devices for controlling the electric potential at said array of pixel electrodes, and a contact element for an electrically conductive connection to a common electrode of said optical media component; said method comprising: depositing one or more insulating layers over said array of electronic switching devices and said contact element; and forming through the one or more insulating layers both via-holes (a) for electrically conductive connections between the electronic switching devices and the respective pixel electrodes of the pixel electrode array, and one or more via-holes (b) for an electrically conductive connection between said contact element and said common electrode of said optical media component.

According to one embodiment, the method comprises: forming on said upper surface of said one or more insulating layers an upper conductive layer electrically connected to said array of electronic switching devices and said contact element via said via-holes (a) and said one or more via-holes (b), respectively; and patterning said upper conductive layer to both define said array of pixel electrodes, and define an electrically conductive element conductively connected to said contact element and electrically isolated from said array of pixel electrodes.

There is also provided a method of producing an optical device comprising: laminating an optical media component to a control component produced as described above, wherein said laminating includes interposing an electrically conductive pad and/or conductive adhesive between said electrically conductive element and a common electrode of said optical media component.

There is also provided a method of producing an optical device comprising: forming on the upper surface of the insulating layer of a control component produced as described above an electrically conductive adhesive layer electrically connected to said contact element via said one or more via-holes (b); and laminating an optical media component to the control component, wherein said laminating includes interposing an electrically conductive pad between said electrically conductive adhesive layer and a common electrode of said optical media component, or directly contacting said electrically conductive adhesive layer with said common electrode of said optical media component.

There is also hereby provided a control component for laminating to an optical media component, wherein the control component comprises an array of pixel electrodes and an array of electronic switching devices for controlling the electric potential at said array of pixel electrodes, and a contact element for an electrically conductive connection to a common electrode of said optical media component; wherein said control component further comprises one or more insulating layers formed over both said array of electronic switching devices and said contact element; and conductive connections through said one or more insulating layers to provide both electrically conductive interconnects (a) between the electronic switching devices and respective pixel electrodes of the pixel electrode array, and one or more electrically conductive interconnects (b) between said contact element and said common electrode of said optical media component.

According to one embodiment, the control component comprises: a patterned upper layer of conductor material over the one or more insulating layers, wherein said upper layer of conductor material provides: said array of pixel electrodes; said electrically conductive interconnects (a); said one or more electrically conductive interconnects (b); and an electrically conductive element co-planar with said array of pixel electrodes, but electrically isolated from said array of pixel electrodes.

There is also hereby provided a display device comprising a control component as described above, and an optical media component laminated to said control component; and an electrically conductive pad and/or conductive adhesive interposed between said electrically conductive element and a common electrode of said optical media component.

According to one embodiment, the control component comprises an upper layer of electrically conductive adhesive material over the one or more insulating layers, wherein said upper layer of electrically conductive adhesive material provides: said one or more electrically conductive interconnects (b); and an electrically conductive element co-planar with said array of pixel electrodes, but electrically isolated from said array of pixel electrodes.

There is also provided a display device comprising a control component as described above, and an optical media component laminated to said control component; and an electrically conductive pad interposed between said electrically conductive element and a common electrode of said optical media component.

With reference toFIGS. 1 and 2, an embodiment according to the present invention involves the production of a display device comprising a control backplane34and an optical media frontplane32. The control backplane34comprises an array of TFTs for controlling the electric potential at respective pixel electrodes16. The optical media component includes for example an optical active layer18whose optical properties can be switched between at least two states by switching the electric potential at the pixel electrodes16. For example, the optical active layer could be a liquid crystal layer, or an electronic ink layer. For simplicity,FIG. 1shows only three TFTs and pixel electrodes in one dimension, but a display device will typically comprise millions of TFTs and pixel electrodes to provide a high resolution display.

The production process involves depositing a layer of conductor material such as gold on a substrate2and patterning the layer of conductor material by e.g. photolithography or laser ablation, to form: pairs of interdigitated source and drain electrodes4,6; addressing lines (not shown) connecting the source electrodes of respective rows of TFTs; and a contact part24for making an electrical contact (ECON) to a common electrode20of the optical media front plane32, as discussed below. A layer of semiconductor channel material is then deposited over the patterned conductive layer and patterned by e.g. laser ablation to form islands8of semiconductor material providing the semiconductor channel for each source/drain electrode pair. A layer10of one or more organic polymeric dielectric materials having a low Young's modulus of preferably less than about 5 GPa (further preferably no greater than about 3.2 GPa) is then deposited over the whole of the conductive layer (including the contact part24) and the semiconductor islands8. A second layer of conductive material such as gold is deposited over the dielectric layer10and patterned to form gate lines12, each of which forms the gate electrodes for a respective column of TFTs. An upper layer of organic polymeric insulating material36also having a low Young's modulus of preferably less than about 5 GPa is then deposited over the dielectric layer10and the gate lines12. The Young's modulus for a material is defined as the ratio of the stress along an axis over the strain along that axis in the range in which Hooke's law holds. It can be experimentally determined from the slope of a stress-strain curve created during tensile tests conducted on a sample of the material.

Next, the combination of the organic dielectric layer10and organic insulating layer36are patterned by e.g. laser ablation to form (a) an array of via-holes38each extending down to the drain electrode6of a respective TFT; and (b) a plurality of distinct via-holes40extending down to the electrical contact. Conductor material is then deposited over the patterned organic insulating layer36to both fill the via-holes38and40(thereby forming conductive interconnects14,26) and form a further, continuous conductor layer extending over the organic insulating layer36. This further conductor layer is then patterned by e.g. laser ablation to (i) define an array of pixel electrodes16each conductively connected to a drain electrode6of a respective TFT, and (ii) to electrically isolate the contact part24from the pixel electrodes16.

The optical media front plane32is thereafter laminated to the control backplane34. The optical media front plane32comprises the optical active layer18supported on a substrate22via a common electrode layer20. The common electrode layer extends beyond the edge of the optical active layer18. A compressable conductive pad30comprising a conductive adhesive embedded with metallised fibres and/or metallised balls is interposed between the common electrode layer20and the part28of the upper conductive layer conductively connected to the contact part24(but electrically isolated from the pixel electrodes16); and a reliable electrical connection between the contact parts24and28is created by compressing the conductive pad30between the optical media front plane32and control back plane34. Depending on the material used for the conductive pad30, it may be effective to apply an electrically conductive glue (or other bonding promoter) between the conductive pad30and said part28of the upper conductive layer. Alternatively, one or more droplets of electrically conductive compressable glue or paste could be deposited with relatively high precision on said part28of the upper conductive layer instead of the conductive pad30. During operation of the display device, the common electrode provides a common electric potential at the opposite side of the whole of the optical active layer18, against which the electrical potentials at the pixel electrodes16are independently switched.

According to one variation, the via-holes26used for the ECON are not filled with the same conductor material used for the pixel electrodes16. Instead, the area of the insulating layer36above the contact part24is masked during deposition of the conductor material used for filling the via-holes38and forming the pixel electrodes16; and one or more droplets of an electrically conductive glue are thereafter deposited with high precision to fill the via-holes40and form a layer of electrically conductive glue48over the part of the insulating layer36above the contact part24and via-holes26. The resulting deposit of electrically conductive glue48can be configured to make direct contact with the common electrode20of the optical media front plane32(as inFIG. 4), or via a conductive pad30(as inFIG. 3).

The use of organic materials having a low Young's modulus between the contact part28of the upper conductive layer and the contact part24of the lower conductive layer in the region of the conductive pad (or electrically conductive glue) is beneficial for avoiding cracks forming under the pressure at which the optical media front plane32is laminated to the control plane32.

The above-described technique also facilitates a reduction of the space required on the substrate for forming the ECON, because the formation of via-holes40through the organic dielectric layer10and organic insulating layer36, and the filling of the via-holes40with conductive material and/or the deposition of droplets of conductive glue can be readily achieved with a relatively high degree of reliable accuracy. The above-described technique also avoids (i) the difficulty of performing the deposition of the dielectric layer10and insulating layer36with the high alignment accuracy required (or the inefficiency of trimming the edges of these layers10,36after deposition) to avoid these layers10,26covering a contact part24situated close to the rest of the electric circuitry at the same level, or (ii) having to disadvantageously increase the distance between this contact part24and the remainder of the electrical circuitry at the same level (and thereby increasing the footprint of the backplane34) to an extent that the dielectric layer10and the insulating layer36can be selectively deposited other than over the contact part24without requiring high alignment accuracy.