Patent Application
20230176440
The specification relates generally to display panel technologies, and more particularly to microspheres for electrophoretic displays and methods of manufacture thereof.
Various technologies are employed in the manufacture of display panels. Some, e.g. liquid crystal and electrowetting displays, suffer from optical losses, leading to inefficient use of backlight. Others, such as electrochromic displays, suffer from slow response times and increased voltage requirements to drive pixels compared to LCD and electrowetting displays.
According to an aspect of the present specification, a display device including microspheres is provided. The display device includes: an outer substrate; an inner substrate; a first electrode and a second electrode disposed between the inner substrate and the outer substrate in a spaced apart relationship; and a plurality of microspheres between the first and second electrodes, each microsphere comprising a spherical shell enclosing an electrophoretic media, wherein the electrophoretic media comprises a charged particle comprising one or more first chemical entities and an oppositely charged particle comprising one or more second chemical entities, wherein the first and second chemical entities are to be induced to reversibly interact to switch between a separated state and an optically active state in response to a change in an electromagnetic field applied to the electrophoretic media by the first and second electrodes to change an optical property of the electrophoretic media.
According to another aspect of the present specification, a method of fabricating microspheres for an electrophoretic display is provided. The method includes: obtaining an emulsion of aqueous droplets dispersed in an oil phase, the aqueous droplets including an electrophoretic media, the electrophoretic media comprising a charged particle comprising one or more first chemical entities and an oppositely charged particle comprising one or more second chemical entities, wherein the first and second chemical entities are to be induced to reversibly interact to switch between a separated state and an optically active state in response to a change in an electromagnetic field applied to the electrophoretic media to change an optical property of the electrophoretic media; adding precursors to the emulsion; and forming shells at respective surfaces of each aqueous droplet, wherein the shells are formed via reactions of the precursors at the respective surfaces of each aqueous droplet.
According to another aspect of the present specification, a method of fabricating an electrophoretic display device is provided. The method includes: providing a substrate layer; obtaining an emulsion of aqueous droplets dispersed in an oil phase, the aqueous droplets including an electrophoretic media, the electrophoretic media comprising a charged particle comprising one or more first chemical entities and an oppositely charged particle comprising one or more second chemical entities, wherein the first and second chemical entities are to be induced to reversibly interact to switch between a separated state and an optically active state in response to a change in an electromagnetic field applied to the electrophoretic media to change an optical property of the electrophoretic media; adding precursors to the emulsion; forming shells at respective surfaces of each aqueous droplet, wherein the shells are formed via reactions of the precursors at the respective surfaces of each aqueous droplet to form microspheres; collecting the microspheres via settling or centrifugation; and arranging a plurality of the microspheres into a lattice on the substrate.
Implementations are described with reference to the following figures, in which:
The description below sets out certain structures and methods of manufacture for display assemblies employing electrophoretic media to control the color, contrast, and other visual attributes of the display assembly. A detailed discussion of the electrophoretic media is provided in PCT application no. PCT/IB 62019/058306 filed Sep. 30, 2019, the contents of which is incorporated herein by reference.
In brief, in some embodiments, the electrophoretic media includes two sets of nanoparticles. The particles in the first set include a negatively charged core and a polymeric corona functionalized with an optically active component. The particles in the second set include a positively charged core and a polymeric corona functionalized with a stabilizing component. The charge of the particles can be switched without loss of generality. The two component entities are selected to interact with one another when a positively charged nanoparticle is sufficiently close to a negatively charged nanoparticle and their polymeric coronae interact. When the component entities interact, they form a complex with different absorption characteristics than the separated components. For example, when separated the nanoparticles may be substantially transparent, and when physically close enough for the component entities to interact the nanoparticles may transmit certain wavelengths of light (e.g. red) and absorb others.
Thus, by controlling electric fields applied to a fluid containing nanoparticles from both of the above-mentioned sets, the separation distance between the nanoparticles can be controlled, which affects how many of the nanoparticles interact and therefore the degree to which the optical characteristics of the fluid are altered. A variety of materials, as well as additional discussion on the behavior of such materials, are provided in the above-mentioned co-pending PCT application.
Between the inner and outer substrates 108 and 104, the device 100 includes an outer electrode layer 112 and an inner electrode layer 116 (also referred to herein as simply electrodes 112 and 116). The electrodes 112 and 116 may be formed of indium tin oxide (ITO) film. Other materials, such as silver nanowires, may also be employed in addition to or instead of ITO. The outer electrode 112 is translucent or transparent, to allow the passage of ambient light into the assembly 1700 for absorption, transmission, or reflection.
The electrodes 112 and 116 are disposed in a spaced-apart relationship relative to each other. In particular, the outer electrode 112 may be adjacent to the outer substrate 104, and in the present example is directly affixed to the inner side of the outer substrate 104. In other examples, additional materials (e.g., adhesives) may be placed between the outer substrate 104 and the outer electrode 112. Similarly, the inner substrate 116 may be adjacent to the inner substrate 108 and may be affixed to the inner substrate 108. The inner electrode 116 may be translucent or transparent (e.g., an ITO film or an array of silver nanowires), or, in other examples, may provide a reflective surface. In other examples, the electrodes 112 and 116 may be arranged in a spaced-apart relationship laterally on the display, each extending from the inner substrate 108 to the outer substrate 104. In such examples, the electrodes may be made of doped silicon, metal, or other conductive material including a transparent conductive material.
One of the electrodes 112 and 116 is driven by a controller 118 (e.g., connected to the internal electronics of a computing device such as a smartphone or the like), while the other of the electrodes 112 and 116 is a reference electrode.
Between the electrodes 112 and 116, the device 100 includes a plurality of microspheres 120 (referred to generically as a microsphere 120 and collectively as microspheres 120). Preferably, the microspheres 120 are of about the same size, for example, having a dispersity index of between about 1 and 1.2. The microspheres 120 are generally arranged in a lattice between the first and second electrodes. For example, the lattice may be a face-centered cubic packing arrangement, or a hexagonal close packing arrangement, or a combination of the two (i.e., the lattice may be imperfect), or other lattices. The microspheres 120 may be suspended, in some examples, in a suspension fluid 122.
In some examples, the device 100 may further include inner and outer dielectric layers (not shown) between the electrodes 112 and the microspheres 120 to prevent the hydrolysis of the suspension fluid 122 by the electrodes 112 and 116. The device 100 may further include one or more spacer beads (not shown) between the electrodes 112 and 116 to promote uniform spacing of the substrates 104 and 108 as well as the electrodes 112 and 116.
Referring to
Specifically, the charged nanoparticles 132 and 136 have opposite charges and comprise complementary chemical entities which may be induced to reversibly interact to switch between a separated state and an optically active state in response to a change in an applied electromagnetic field. More particularly, the first and second electrodes 112 and 116 may be controlled to apply an electromagnetic field to the microspheres 120 to change an optical property of the electrophoretic media 128 contained in the microspheres 120.
Each microsphere 120 has a diameter of between about 100 nm to about 20 μm, and preferably between about 300 nm to about 1 μm. In other examples, the diameter of the microspheres 120 may be smaller than 100 nm or larger than 20 μm. The shell 124 of each microsphere has a thickness of between about 5 nm and about 80 nm. The shell 124 may be made of a solid material which is relatively rigid and has a high dielectric constant at low frequency to reduce the voltage drop across the shell material. In particular, the shell 124 is of sufficient width to be substantially nonporous and resistant to mechanical stresses imposed during manufacture and use of the device 100. For example, the shells 124 may be formed of a ceramic or glass material, such as a silica-titania blend. Other suitable materials for forming the shells, such as urea-formaldehyde, may also occur to those skilled in the art.
Referring now to
The inclusion of the microspheres 120 in the display device 100 increases the display quality of the display device 100. For example, if the microspheres 120 are provided in substantial quantities to provide multiple layers of the nanoparticles, the contrast of the device 100 is increased as compared to a single layer of nanoparticles. Specifically, by having multiple layers of particles the number of color absorbing groups through which an incident light ray would pass on its way through the display 100 is increased. The thickness of the display device 100, as defined by the distance between the substrates 104 and 108 may be varied to increase or decrease the contrast provided by the microspheres 120. Specifically, incident light will traverse a larger volume of the electrophoretic media when the thickness of the device 100 increases. The increased thickness and traversal of a larger volume of the electrophoretic media provides for better color absorption, and hence better reflection of the desired colors.
The microspheres 120 also improve the uniformity of the display device 100. For example, the microspheres contain oppositely charged particles 132 and 136 which move in response to the applied electric field 200 and would move along the electric potential gradient, which in some instances may be laterally towards adjacent electrodes, changing the concentration of oppositely charged particles 132 and 136 in different regions of the display device 100. The microspheres 120 restrict this lateral movement, maintaining a substantially uniform distribution across the display device 100. In other words, the microspheres reduce the migration of the electrophoretic media and accumulation of the electrophoretic media in one region of the display device 100 and a lack or depletion of the electrophoretic media in a different region. Accordingly, by employing the microspheres containing the electrophoretic media, each section of the display device 100 will include substantially the same amount of electrophoretic media, dispersed evenly within the microspheres 120.
In some examples, the first and second electrodes 112 and 116, and the microspheres 320 contained therein may form a sub-pixel assembly. That is, the display device 100 may include multiple of such assemblies, for example arranged in a rectangular array, wherein each sub-pixel assembly represents one pixel or part of one pixel of the display device 100. In other examples, the sub-pixel assemblies may be arranged in other suitable arrangements. Thus, a complete display may include a plurality of the sub-pixel assemblies, with each assembly including a pair of spaced apart electrodes to control the electrophoretic media in the microspheres of each pixel (or sub-pixel) independently to allow for regular display capabilities. In some examples, each assembly may include a respective controller 118 and each controller 118 may be connected to a central display processor of the display device 100. That is, the central display processor may communicate with the controllers 118 to apply appropriate voltages to the electrodes 112 and 116 of each assembly according to the image to be displayed on the device 100. In other examples, the central display processor may control the sub-pixel assemblies directly (i.e., the central display processor may act as the controller 118 for each sub-pixel assembly).
In some examples, the microspheres 120 may be contained in multiple layer structures, and multiple layer structures may be included in the display 100 to allow for different colors to be provided in each layer structure. For example, referring to
Turning now to
The method 400 begins at block 405, at which a water-in-oil emulsion is obtained. In particular, the aqueous phase of the emulsion includes aqueous droplets containing water and electrophoretic nanoparticles. For example, the electrophoretic particles may be synthesized in water, and additives may be added to make up the aqueous phase. The electrophoretic particles, being electrically charged, will typically approximately uniformly disperse in the aqueous phase, allowing for an approximately uniform distribution of the electrophoretic particles in the droplets of the resulting water-in-oil emulsion. In some examples, the aqueous phase may further include one or more polar cosolvents, catalysts, thickening agents and non-ionic surfactants. The oil phase may comprise a solvent such as cyclohexane, polyoxyethylene sorbitan monooleate, polyisoprene, combinations of the above, or the like, as well as non-ionic surfactants and thickening agents contained therein. Preferably, the aqueous droplets have a dispersity index of between about 1 and about 1.2. That is, the aqueous droplets are preferably around the same size.
For example, to obtain a monodisperse emulsion, a course emulsion may first be obtained by adding the aqueous phase to the oil phase in the presence of a surfactant. The volume fraction of the aqueous phase may be between about 50% to about 75% of the total volume of the emulsion. The coarse emulsion may then be sheared into smaller aqueous droplets of nearly uniform size by methods known in the art. For example, the coarse emulsion may be subjected to a high-shear Couette flow to fracture the aqueous phase into the aqueous droplets, or the coarse emulsion may be passed through a homogenizer, one or more porous membranes, microfluidics devices or the like. In some examples, multiple passes and/or multiple shearing methods may be applied to obtain the desired size and size dispersity. Specifically, the aqueous droplets of the emulsion form a template on which the shells 124 of the microspheres 120 are formed. Accordingly, the droplets preferably have a size of between about 300 nm and about 1 μm, and a low size dispersity (i.e., between about 1 and 1.2)
At block 410, precursors are added to the emulsion. The precursor is generally a compound configured to react with the aqueous droplets to form the shells 124 of the microspheres 120. For example, the precursors may be organometallic precursors such as a mixture of tetramethyl orthosilicate (TMOS) [3-(2-Aminoethylamino)propyl]trimethoxysilane (AEAPTMS) and titanium tetrapropoxide (TTIP). More generally the precursors are selected according to the desired shell material for the microspheres 120. The precursors may be added to the emulsion over a predefined period of time. For example, the precursors may be added dropwise to the emulsion over the course of about 2 minutes. More generally precursors may be added to the emulsion slowly to reduce concentration gradients and reduce the likelihood of the microspheres combining and growing together and promote the growth of separate capsules. Further, the emulsion and precursors may be mixed in order to better disperse the precursors in the emulsion to further promote the growth of separate capsules.
When the precursors are added to the emulsion, they reach the surface of the aqueous droplets and are hydrolyzed by the water phase and undergo condensation reactions to form the shell 124. For example, the organometallic precursors may form metal-oxygen-metal bonds, which begin to connect to form a network of glass-like material around the aqueous droplets. In other examples, the precursors may react with the aqueous droplets in a different manner to form the shells 124. For example, polymeric precursors may undergo condensation. Once the surface of a droplet is covered, the reaction becomes diffusion-limited by how quickly the water and precursors can come into contact through the newly formed barrier. Further, as the thickness of the shell 124 increases during formation, the water and/or precursor must diffuse through the existing shell 124 to continue reacting, slowing the reaction down where the shell 124 is thicker. Conversely, the reaction may occur more quickly in regions where the shell 124 is thinner or non-existent. The diffusion-limiting nature of the reaction therefore provides better uniformity in the thickness of the shell 124 around any given droplet and between droplets.
A mixture of different precursors may be added to change the properties of the shell, the reaction rate, and the surface morphology of the shell. For example, elements such as titanium may be used as an additive to increase the dielectric constant of the material, which reduces the voltage drop across the shell. Different precursors may be used to tune the refractive index of the shells so that depending on the choice of suspension fluid 122 and electrophoretic dispersion 128 the shells scatter less of the light incident upon them. For example, the refractive index of the shells 124 may be selected to match the refractive index of the suspension fluid 122, which in turn may be selected to match the refractive index of the electrophoretic dispersion 128. By matching the refractive indices of the shell 124, the suspension fluid 122, and the electrophoretic dispersion 128, each microsphere 120 will scatter less light and overall haze caused by light scattering is reduced.
In some examples, the aqueous droplets and the oil phase may include other components to promote and facilitate the formation of the shell. For example, the aqueous droplets may include a catalyst (e.g., ammonia, in the example given above) to catalyze the shell-formation reactions (e.g., hydrolysis is catalyzed by ammonia, in the example given above). The aqueous droplets and/or the oil phase may further include thickening agents to control the rate of reaction. In particular, thickening agents decrease the diffusion of the precursors to the shell interface, thus slowing down the reaction and allowing the shells 124 to form more uniformly. The oil phase may also include other components to deter the aggregation of the aqueous droplets. For example, long-chain oil soluble polymers, such as polyisoprene, or hydrophobic polymeric nanoparticles can help maintain a hydrophobic barrier between colliding particles. Polymeric surfactants such as poly isoprene-block-vinyl alcohol can be used for steric stabilization of the droplets, which absorb kinetic energy of the droplets when they collide, increasing their resistance to coalescence. After adding the precursors, the emulsion may be agitated (e.g., by stirring) and allowed to react for a predefined period of time (e.g., between about 2 minutes and about 24 hours).
In some examples, prior to adding the precursors to the emulsion, the emulsion may first be diluted to add additional oil phase. For example, the formation of the shell 124 by the precursors may generate alcohols which may affect the aqueous droplet stability. In particular, the alcohols may destabilize the emulsion, causing inversion to an oil-in-water emulsion if the dispersed phase (aqueous) makes up too high of a fraction of the total. Accordingly, dilution of the emulsion (e.g., by a factor of between about 4 times and more than 20 times) may assist in the stabilization of the aqueous droplets after the generation of the alcohols. Further, the emulsions may be diluted to promote uniform coating of the droplets, for example to reduce particle aggregation which may decrease diffusion of the precursors.
For example, referring to
Returning to
At block 420, the microspheres are collected. For example, the microspheres may be collected via settling or centrifugation, depending on the relative densities of the dispersed and continuous phases. In some examples, the microspheres may also be sorted by size using centrifugation, as settling velocity is highly dependent on the size of the droplet.
Referring now to
At block 605, a transparent substrate layer is provided. The substrate layer may be either of the substrate layers 104 or 108, as will be seen below. The substrate layer may be, for example, silicon dioxide, borosilicate glass or any other doped silicate. Other suitable dielectric substrates will also occur to those skilled in the art. In some embodiments, a flexible substrate may be provided. The substrate layer is preferably thin in order to decrease the thickness of the display device. However, the substrate layer is also sufficiently thick to withstand the manufacturing process. In some examples, the substrate layer has a thickness of 0.1 to 1 mm. Preferably the substrate layer has a thickness of about 0.3 mm to about 0.6 mm.
At block 610, electrophoretic microspheres are fabricated. The microspheres may be fabricated, for example, according to the method 400. That is, the microspheres may be fabricated by obtaining an emulsion of aqueous droplets dispersed in an oil phase. Specifically, the aqueous droplets include electrophoretic particles. Organometallic precursors may then be added to the emulsion to form shells at respective surfaces of each aqueous droplet to form the microspheres.
At block 615, the microspheres are collected, for example via settling or centrifugation. In some examples, the microspheres may also be sorted by size using centrifugation, as settling velocity is highly dependent on the size of the microsphere. Further, a subset of microspheres for use in the display may be selected. For example, the subset of microspheres may be selected to have a dispersity index of between about 1 and about 1.2.
At block 620, the microspheres are arranged into a lattice on the substrate. The lattice may include one or more layers of microspheres, and preferably, between 7 layers and 100 layers. The lattice may be, for example, a face-centered cubic packing arrangement or a hexagonal close packing arrangement. In other examples, the lattice may be a mixture of the above packing arrangements, or a different packing arrangement.
The lattice may be arranged, for example, via settling and centrifugation of a concentrated suspension of the microspheres. In some examples, the settling and centrifugation may be aided by small amplitude vibrations. In other examples, the microspheres may be suspended in a mixture of solvents, including at least one volatile diluent. The suspension may be spread over the substrate to produce a uniform film on the substrate. The high volatility diluent is allowed to evaporate, during which time the film is compressed to its final thickness by surface tension, forming a lattice in the process.
In some examples, for example in either of the above lattice arrangement processes, the suspension may further include a spacer material, such as uniformly sized silica spheres with a diameter equal to the desired thickness.
In other examples, other suitable processes for arranging the microspheres into a lattice are contemplated.
For example, referring to
Returning to
Advantageously, the microspheres may be deposited as a liquid in the same manner as existing liquid crystal display manufacturing processes. Further, the electrophoretic microspheres reduce the need for polarizers, color filters, and layers to align the liquid crystals in a specific direction. Rather, the microspheres may be stacked in layers to allow for richer color capabilities.
The scope of the claims should not be limited by the embodiments set forth in the above examples but should be given the broadest interpretation consistent with the description as a whole.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2021/053755 | 5/4/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63019648 | May 2020 | US |
