Display device

Abstract

A display device for displaying patterns is disclosed. In one arrangement, pixel elements having a layered structure are provided. The layered structure includes at least one phase change material layer that is thermally switchable between at least a stable high extinction coefficient state and a stable low extinction coefficient state. The ratio of the average value of the extinction coefficient of the phase change material layer in the high extinction coefficient state to the average value of the extinction coefficient of the phase change material layer in the low extinction coefficient state in the visible spectrum is greater than 3.0. The average value of the extinction coefficient in the high extinction state in the visible spectrum is less than 1.0.

Description

Technical Field

[0001] This invention relates to display devices using phase change materials (PCM). Background Technology

[0002] In WO2017134506A1 and related publications (Garcia Castillo, S. et al., “57-4: Solid State Reflective Display”) with LTPS Diode Backplane," SID Digest, 50, 1, pp 807-810 (2019), and Broughton, B. et al., "38-4: Solid-State Reflective Displays A PCM-based reflective display device is disclosed in “Utilizing Ultrathin Phase-Change Materials”, SID Digest, 48, 1, pp546-549 (2017), where the light switching effect is thermally modulated.

[0003] Color displays can be provided by combining a layered structure with a PCM (Polymer Carbon Mold) and a shutter mechanism. The PCM can switch between white and color, while the shutter mechanism can switch between transparent and opaque. Combining the PCM and shutter optics in tandem provides control over color and brightness. However, there is a desire to improve the optical performance of PCM-based displays and / or simplify their structure. Summary of the Invention

[0004] The purpose of this invention is to improve the optical performance of PCM-based displays and / or simplify their structure.

[0005] According to one aspect, the present invention provides a display device for displaying patterns, comprising: pixel elements having a layered structure, the layered structure including at least one phase change material layer, the phase change material layer being thermally switchable between at least a stable high extinction coefficient state and a stable low extinction coefficient state, wherein, for each phase change material layer: the ratio of the mean average of the extinction coefficient of the phase change material layer in the high extinction coefficient state to the mean average of the extinction coefficient of the phase change material layer in the low extinction coefficient state in the visible spectrum is greater than 3.0; the mean average of the extinction coefficient in the high extinction state in the visible spectrum is less than 1.0.

[0006] Therefore, a display device is provided that uses a PCM with a very low extinction coefficient in one of its stable states (low extinction coefficient state). Having a very low extinction coefficient means that the PCM is highly transparent in this stable state, and the PCM layer does not need to be undesirably thin. When in this stable state, the PCM has minimal impact on the brightness (reflectivity) of the pixel elements. Conversely, when the PCM is in at least one other stable state (high extinction coefficient state), the extinction coefficient is significantly higher (at least three times higher). This allows the same PCM to provide near-opaque behavior (optionally in combination with other PCMs in a layered structure). Therefore, the PCM is capable of achieving high black / white contrast without sacrificing the white-state reflectivity of the pixel elements (when configured to operate in reflective mode) or the color gamut.

[0007] In one embodiment, the layered structure of the pixel element further includes one or more additional PCM layers, each of which can switch between at least a high extinction coefficient state and a low extinction coefficient state. For each additional PCM layer, the ratio of the average extinction coefficient of the PCM layer in the high extinction coefficient state to the average extinction coefficient of the additional PCM layer in the low extinction coefficient state in the visible spectrum is greater than 3. Making one or two of the PCM layers highly transparent allows multiple PCM layers to be optically stacked in series without loss of color vibrancy and / or brightness. Therefore, a range of visual effects (e.g., colors such as red, blue, or green; white; and black) similar to those achievable using a combination of PCM and shutter can be provided without a shutter.

[0008] In one embodiment, a switching device is provided capable of applying heat to a pixel element according to each of a plurality of different heating profiles. A heating profile can be provided that causes switching of a first PCM layer in the PCM layers of the pixel element without switching at least a second PCM layer. Different heating profiles can be provided that cause switching of a second PCM layer in the pixel element without switching of the first PCM layer. Therefore, different PCM layers can be controlled independently simply by changing the heating profile. Thus, the same switching element (e.g., a heating element) can be used to switch two PCM layers. Therefore, each pixel element can be manufactured efficiently, and can be made compact and reliable.

[0009] In one embodiment, two or more of the PCM layers differ from each other only in terms of doping (e.g., doping composition and / or level). Therefore, different phase change materials can be provided using similar deposition techniques (and under similar conditions) and by providing layers with similar structures and thermal properties (including similar coefficients of thermal expansion), thereby improving device reliability and lifespan. For example, doping can be performed during deposition only when needed (e.g., adding nitrogen to the process gas). This avoids the need for different target materials.

[0010] In one embodiment, the layered structure comprises two identical PCM layers and a distinct PCM layer between them. This device has been found to offer particularly optimized performance. Furthermore, the device can be configured to operate without additional passive spacer layers (e.g., between any PCM layers), thereby facilitating fabrication (e.g., fewer deposition steps).

[0011] In one embodiment, the first PCM layer and / or the second PCM layer comprises any combination of one or more of the following, substantially consists of any combination of one or more of the following, or consists of any combination of one or more of the following: Sb₂S₃, Ge₂Sb₂Se₄Te, GeSbTeO, GeSnTeO, GeSnSbTeO, TeBiSnN, TeBiSnS, TeBiSnO, SeSnBi, SeSnBiO, SeSnGeO. The inventors have discovered that these materials provide a remarkably good combination of performance characteristics.

[0012] In one embodiment, the device includes a switching mechanism capable of applying heat to a pixel element from the same heating element according to each of a plurality of different heating profiles; and the plurality of heating profiles includes at least two heating profiles that cause switching of different proportions of PCM in one of the PCM layers of the pixel element. Therefore, the inventors have discovered that heating profiles can be controlled to selectively switch different proportions of the PCM layer, thereby providing further degrees of freedom for providing optical effects within a desired range. In one embodiment, for example, controlling the proportion of the PCM layer switched to a state with a high extinction coefficient (e.g., a substantially optically opaque state) to change the gray level (overall brightness) of the pixel unit.

[0013] According to one aspect, a display device for displaying patterns is provided, comprising: a pixel element having a layered structure, the layered structure including a phase change material layer switchable between at least a stable high extinction coefficient state and a stable low extinction coefficient state, wherein the average value of the extinction coefficient in the high extinction coefficient state is higher than the average value of the extinction coefficient in the low extinction coefficient state in the visible spectrum; and a switching device capable of applying heating to the pixel element from one and the same heating element according to each of a plurality of different heating profiles, wherein at least two of the heating profiles cause switching of different proportions of the phase change material layer. Attached Figure Description

[0014] The invention will now be further described by way of example with reference to the accompanying drawings, in which:

[0015] Figure 1 This is a schematic side sectional view of a portion of a display device, which includes four exemplary pixel elements, each pixel element having a layered structure;

[0016] Figure 2 It is a graph depicting the simulation results of the optical performance of the pixel element, including curves showing how reflectance and contrast change with the ratio of the extinction coefficient in each of the two different states of the PCM.

[0017] Figure 3 This is a schematic side cross-sectional view showing an example pixel element layered structure with a single PCM layer and a composite spacer layer;

[0018] Figure 4 It is a description of when Figure 3 The simulated reflectance versus wavelength curve of the device when the PCM layer is in a low extinction coefficient state;

[0019] Figure 5 It is a description of when Figure 3 The simulated reflectance versus wavelength curve of the device when the PCM layer is in a high extinction coefficient state;

[0020] Figure 6 and Figure 7 They correspond to respectively Figure 4 and Figure 5 The graph represents the scenario where standard PCM-based pixel elements are optimized as much as possible to achieve similar functionality.

[0021] Figure 8 This is a schematic side sectional view illustrating an example pixel element layered structure with multiple PCM layers;

[0022] Figure 9 Describing for Figure 8The device in its pale state, showing the simulated change in reflectivity relative to wavelength;

[0023] Figure 10 Describing for Figure 8 The red state of the device, the simulated change in reflectivity relative to wavelength;

[0024] Figure 11 Describing for Figure 8 The simulated change in reflectivity relative to wavelength in the black state of the device;

[0025] Figure 12-14 They correspond to respectively Figure 9-11 The graph represents the curve for optimizing as many stacks of standard PCM layers as possible to achieve similar functionality;

[0026] Figures 15A-15D This is a schematic top view of a pixel element, showing the progressive switching of the PCM layer in the direction towards the peripheral region of the pixel element; and

[0027] Figures 16A-16C Three example sets of group switching states are depicted, which allow switching a group of pixel elements to achieve different overall reflectivities without changing the color displayed by the group. Detailed Implementation

[0028] Figure 1 This is a schematic side sectional view of a portion of the display device 2, illustrating the function of this disclosure. The device 2 is configured to display a pattern via a plurality of pixel elements 4. Each pixel element 4 can individually switch between states with different refractive indices to define the pattern. The pattern can be a visible pattern (e.g., visible to the naked eye or through a microscope) or a machine-readable pattern (e.g., containing elements too small for the human eye or requiring wavelengths of light invisible to the human eye to observe). The pattern can define pictures, text, or other visual information.

[0029] Each pixel element 4 includes a layered structure. The layered structure comprises multiple layers, one layer on top of another. The layered structure may include a stack of thin films. The layered structure includes at least one phase change material (PCM) layer 6. The PCM layer 6 is switchable between a stable high extinction coefficient state and a stable low extinction coefficient state. The high extinction coefficient state and the low extinction coefficient state are stable in the sense that no energy is required to maintain the PCM in the switched state. The high extinction coefficient state may be substantially crystalline, and the low extinction coefficient state may be substantially amorphous. The switching is achieved thermally. Thermal energy for the switching can be provided in various ways. Typically, an electric heater is used to provide the thermal energy. Figure 1In the example, the heating element 8 is positioned in thermal contact with the layered structure of each pixel element 4. The heating element 8 may include a resistance heater. Each heating element 8 can be controlled independently of each other. Therefore, each heating element 8 can be individually addressable. Individual addressability can be provided by any of a variety of known techniques for driving individual pixels in a pixel array. Each heating element 8 may, for example, include an electronic unit (e.g., a thin-film electronic selector element, such as a thin-film transistor or diode typically formed of, for example, doped amorphous silicon, polycrystalline silicon, or crystalline silicon) that drives the heating element 8 when addressed by signals from row and column lines where the electronic unit intersects. The signals may be generated by external control electronics. Switching of the pixel elements 4 can be performed sequentially and / or simultaneously in a controlled manner to define a desired pattern to be written into the display device. Multiple heating elements 8 can be considered as examples of switching devices capable of applying heat to the pixel elements 4.

[0030] The layered structure of each pixel element 4 may include layers other than the PCM layer 6, which, for example, affect the optical effects achieved by the PCM through interference effects. In one embodiment, all layers in the layered structure of each pixel element 4 are solid-state and configured such that their thicknesses, refractive indices, and absorption properties combine to produce different, distinct, and / or significantly different reflection spectra in different states of the PCM. In one embodiment, the display device 2 is a reflective display. Therefore, the display device 2 may include a reflective layer 10. In the case of multiple PCM layers 6, the reflective layer 10 is located on the same side of each PCM layer 6. A passive (i.e., non-switchable) spacer layer 12 may be disposed between the reflective layer 10 and at least one PCM layer 6. A capping layer 14 may be disposed on the side of each PCM layer 6 opposite to the reflective layer 10. Both the spacer layer 12 and the capping layer 14 are light-transmitting and ideally as transparent as possible.

[0031] Each of the capping layer 14 and the spacer layer 12 may consist of a single layer or comprise multiple layers having refractive indices different from each other (i.e., in the case where the capping layer 14 or the spacer layer 12 consists of multiple layers, at least two of these layers have refractive indices different from each other). The thickness and refractive index of one or more materials forming the capping layer 14 and / or the spacer layer 12 are selected to produce a desired spectral response (through interference and / or absorption). Materials that can be used to form the capping layer 14 and / or the spacer layer 12 may include (but are not limited to) ZnO, TiO2, SiO2, Si3N4, TaO, ITO, and ZnS-SiO2.

[0032] Each of one or more layers in the layered structure of each pixel element 4 may optionally span multiple pixel elements 4 for ease of fabrication. Therefore, one or more layers may be shared by different pixel elements 4. Figure 1 In the example, all layers in the layered structure of the pixel element 4 shown are shared among all the pixel elements 4 shown. In other embodiments, each pixel element 4 may be provided with a layered structure that is discontinuous with the layered structure of each other pixel element 4 (e.g., each pixel element 4 may include a layer stack separated from the layer stacks of each other pixel element 4 by a filler material).

[0033] In one embodiment, for most or all wavelengths in the visible light range, the extinction coefficient in the high extinction coefficient state is at least three times higher (optionally at least four times higher, optionally at least five times higher, optionally at least ten times higher) than that in the low extinction coefficient state. In one embodiment, the ratio of the average value of the extinction coefficient of PCM layer 6 in the high extinction coefficient state to the average value of the extinction coefficient of PCM layer 6 in the low extinction coefficient state in the visible spectrum is greater than 3.0 (optionally greater than 4.0, optionally greater than 5.0, optionally greater than 7.5, optionally greater than 10.0). The extinction coefficient is understood herein to refer to the imaginary part of the refractive index. Apart from having a large difference between the extinction coefficients in the two stable states, the composition of PCM layer 6 is chosen such that the extinction coefficient in the high extinction coefficient state is limited to an average value not greater than 1.0. For example, in the high extinction state, the average value of the extinction coefficient in the visible spectrum is less than 1.0. The inventors have discovered that this combination of properties of the PCM layer 6 allows for high black / white contrast without sacrificing white reflectivity or color gamut and without requiring the PCM layer 6 to be undesirably thin.

[0034] The above effects are Figure 2 As shown in the figure, Figure 2 The results of simulating the optical performance of a pixel element 4 having this PCM layer 6 are depicted. The graphs depict the simulated changes in reflectance (left y-axis; curve 101) and contrast (right y-axis; curve 102) as the ratio of the extinction coefficient in a high extinction coefficient state (in this case, the crystalline state) to the extinction coefficient in a low extinction coefficient state (in this case, the amorphous state). Horizontal dashed arrows indicate the performance of the inventor's best prior art device. Shaded areas indicate the regions in which the embodiments of this disclosure operate. Both reflectance and contrast are improved compared to the inventor's best prior art device.

[0035] Figure 3An exemplary configuration is depicted, wherein the layered structure of pixel element 4 includes layers in the following sequence: a reflective layer 10 composed of 100 nm Ag; a PCM layer 6 composed of 23.8 nm Sb2S3; a passive spacer layer 12, which includes a spacer sublayer 12A composed of 21 nm Ag, a spacer sublayer 12B composed of 78 nm ZnS-SiO2, and a spacer sublayer 12C composed of 22 nm Ag; and a capping layer 14 composed of 43 nm ZnS-SiO2. Figure 4 It is a graph depicting the simulated reflectivity as a function of wavelength when PCM layer 6 is in a low extinction coefficient state. Figure 5 This is a graph depicting the simulated reflectance as a function of wavelength when PCM layer 6 is in a high extinction coefficient state. The reflectance in the low extinction coefficient state was found to be 46. The contrast between the low and high extinction coefficient states was found to be 15.3.

[0036] Figure 6 and 7 They correspond to respectively Figure 4 and 5 The graph represents the scenario where standard PCM-based pixel elements are optimized as much as possible to achieve similar functionality. In this case, the resulting (optimized) sequence of layers is as follows: 100nm Ag; 38nm ZnS-SiO2; 9nm Ge2Sb2Te5 PCM; 37nm ZnS-SiO2 capping layer. The reflectance was found to be 29 in the low extinction coefficient state. The contrast ratio between the two states of the PCM was found to be 7.8.

[0037] The above discussion Figure 3-5 In the example, the layered structure of pixel element 4 includes only a single PCM layer 6. In other embodiments, the layered structure of pixel element 4 includes one or more additional PCM layers (i.e., such that there is one PCM layer 6 and one or more additional PCM layers 6). Each additional PCM layer 6 may switch between at least a high extinction coefficient state and a low extinction coefficient state. For each additional PCM layer 6, the ratio of the average value of the extinction coefficient of the additional PCM layer 6 in the high extinction coefficient state to the average value of the extinction coefficient of the additional PCM layer 6 in the low extinction coefficient state in the visible spectrum is greater than 3.0 (optionally greater than 4.0, optionally greater than 5.0, optionally greater than 7.5, optionally greater than 10.0).

[0038] In such an embodiment (with multiple PCM layers 6), a switching device (e.g., including a heating element 8) can be configured to apply heating to the pixel element 4 according to each of a plurality of different heating profiles. Therefore, the switching device can selectively apply each heating profile. Each heating profile can define the variation of power provided by the heating element 8 of the pixel element 4 over time. Different heating profiles can last for different time periods and / or involve different average power and / or different shapes of power versus time (square pulse, rise, fall, oscillation, etc.). Applying different heating profiles allows selective switching between different phases, such as selectively switching the PCM from an amorphous state to a crystalline state or vice versa. For example, a control signal including a current pulse with relatively low amplitude and long duration can effectively switch the PCM from an amorphous state to a crystalline state, resulting in a heating profile that allows the PCM to be heated above its crystallization temperature T. C However, it is lower than the melting temperature T of PCM. M The temperature. The temperature is set at the crystallization temperature T. C The above-mentioned time is sufficient for PCM to crystallize. A control signal including high-amplitude but short-duration current pulses can effectively switch PCM from a crystalline state to an amorphous state, resulting in a heating profile that allows PCM to be heated above the melting temperature T. M The temperature is increased to melt the PCM, but the PCM is cooled quickly enough so that recrystallization does not occur excessively and the PCM freezes into an amorphous state. After the PCM is heated, it remains in the selected stable state (e.g., amorphous or crystalline) until further heating is applied. Therefore, when based on PCM, the pixel area naturally remains in a given optical state without any signal being applied, and thus can operate with significantly less power than other display technologies. Switching can be effectively performed an unlimited number of times. The switching speed is also very fast, typically less than 300 ns, which is certainly several orders of magnitude faster than what the human eye can perceive.

[0039] In one embodiment, within each pixel element 4, each PCM layer 6 is in thermal contact with every other PCM layer 6 (of the same pixel element 4). This thermal contact causes the heating provided by the switching device to result in substantially the same temperature change during heating of each PCM layer 6 in the pixel element 4. However, different PCM layers 6 are configured such that each heating profile can have different effects on different PCM layers 6 (e.g., switching or not switching each PCM layer 6). For example, in some embodiments, the plurality of heating profiles includes a heating profile that causes a first PCM layer 6 in the pixel element 4 to switch without causing at least a second PCM layer 6 in the PCM layer 4 to switch. In some embodiments, the plurality of heating profiles includes a heating profile that causes a second PCM layer 6 to switch without causing a first PCM layer 6 to switch. Similarly, the plurality of heating profiles can be configured such that there are heating profiles capable of simultaneously causing two or more PCM layers 6 to switch from a high extinction coefficient state to a low extinction coefficient state and heating profiles capable of simultaneously causing two or more PCM layers to switch from a low extinction coefficient state to a high extinction coefficient state. The ability to selectively switch different combinations of PCM layers 6 can be achieved, for example, by arranging different PCM layers 6 with appropriately different transition temperatures (e.g., different melting points, crystallization temperatures, etc.). This allows for a wide range of combinations of switching states for the PCM layers 6 without any corresponding increase in the complexity of the switching device. The switching device can, for example, still include a single heating element 8 for each pixel element 8, and different switching functions can be achieved simply by changing the heating profile provided by the heating element 8 (e.g., by changing the average heating power and / or duration).

[0040] The wide range of combinations of switching states in multiple PCM layers 6 allows for a corresponding wide range of optical effects. In particular, in addition to black / white level control, color control can also be provided.

[0041] Figure 8 An exemplary construction is depicted, in which three PCM layers 6 are provided. In this particular example, the layered structure comprises the following sequence of layers: a reflective layer 10 composed of 100 nm Ag; a first PCM layer 6A composed of 18 nm Sb₂S₃; a second PCM layer 6B composed of 40 nm Sb₂S₃ (with different doping than the first PCM layer 6A); a third PCM layer 6C composed of 14 nm Sb₂S₃ (with the same doping as the first PCM layer 6A); and a capping layer 14 composed of 49 nm ZnS-SiO₂. This construction provides pixel elements 4 that can switch between grayscale, red, and black states. Figure 9 The simulated variation of reflectivity with respect to wavelength is depicted for the gray-white state (where all three PCM layers 6A-6C are switched to the amorphous state). Figure 10The simulated variation of reflectivity with respect to wavelength for the red state is depicted (where PCM layers 6A and 6C are in a crystalline state and PCM layer 6B is in an amorphous state). Figure 11 The simulated variation of reflectance with wavelength for the black state is depicted (where all three PCM layers 6A-6C are switched to the crystalline state). The three different curves in each plot correspond to different reflection angles (0 degrees, 45 degrees, and 60 degrees). The reflectance in the gray-white state was found to be... Figure 9 The black / white contrast ratio is 61.5. Figure 9 and 11 The value is 16.6.

[0042] Figure 8 The device example illustrates the case where the layered structure comprises two identical PCM layers and a different PCM layer located between them.

[0043] Figure 8 The device further illustrates the case where two or more PCM layers 6 in pixel element 4 differ from each other only in terms of doping (e.g., by means of differences in doping amount or doping composition). Those skilled in the art will appreciate the various studies demonstrating how doping alters the properties of a PCM related to PCM switching, and thus will be able to select appropriate doping for the specific PCM used. As an illustrative example, refer to Kojima et al. (Rie Kojima et al., 1998 Jpn. J. Appl. Phys. 37 2098), which showed the crystallization temperature of GeSbTe films as a function of N doping. Further refer to G Betti Beneventi et al. (“Carbon-doped GeTe Phase-Change Memory featuring remarkable RESET current reduction”, Solid-State Device Research Conference (ESSDERC), 2010 Proceedings of the European; 313-316; 2010 / 9 / 14), which showed the properties of GeTe PCM as a function of C doping.

[0044] Each of one or more PCM layers 6 may include any combination of one or more of the following, substantially constitute any combination of one or more of the following, or constitute any combination of one or more of the following: Sb2S3; Ge2Sb2Se4Te; GeSbTeO; GeSnTeO; GeSnSbTeO; TeBiSnN; TeBiSnS; TeBiSnO; SeSnBi; SeSnBiO; SeSnGeO.

[0045] In some embodiments, each of one or more PCM layers 6 may comprise AgSbSe2, be substantially composed of AgSbSe2, or be composed of AgSbSe2. AgSbTe2 is one of the best PCM alloys for high-speed PC optical discs, exhibiting extremely fast crystallization rate, good cycling performance, and a low melting temperature (552°C). The large light absorption of the composition at blue-violet wavelengths is not optimal for use as PCM layer 6. On the other hand, AgSbSe2 is a p-type semiconductor with high transmittance and a low crystallization rate, exhibiting good cycling performance (although its melting temperature of 610°C is slightly higher than that of AgSbTe2), thus making it suitable for use as PCM layer 6. Related compositions that may have lower melting points, such as (Ag2Se), may also be used. 1-x (Sb2Se3) x Preferably, 0.5 ≤ x or 0.5 ≤ x < 0.7.

[0046] Furthermore, AgSbSe2 and AgSbTe2 have similar rock-salt-type crystal structures and can be easily mixed. The mixture of the two alloys provides further options for PCM layer 6. For example, AgSbTe2 can be used... 2-y Se y Preferably, 2≥y≥0.5.

[0047] Furthermore, AgBiTe2 and AgBiSe2 are known to possess rock salt structures similar to AgSbSe2. Therefore, Ag(Sb) can also be used. 1-z Bi z Te 2-y Se y Preferably, 2≥y≥0.5 and / or 1≥z≥0.

[0048] In view of the foregoing, each of one or more PCM layers 6 may therefore comprise any combination of one or more of the following, substantially consist of any combination of one or more of the following, or consist of any combination of one or more of the following:

[0049] (Ag2Se) 1-x (Sb2Se3) x Preferably, 0.5 ≤ x;

[0050] (Ag2Se) 1-x (Sb2Se3) x Preferably, 0.5 ≤ x < 0.7;

[0051] AgSbSe2;

[0052] AgSbTe 2-y Sey Preferably, 2 ≥ y ≥ 0.5; and

[0053] Ag(Sb 1-z Bi z Te 2-y Se y Preferably, 2≥y≥0.5 and / or 1≥z≥0.

[0054] Other materials that can be used in PCM layer 6 include any combination of the following:

[0055] (Te 80 Sn 15 Ge5) 1-x S x Preferably, 0 ≤ x ≤ 0.2;

[0056] (Te 80 Sn 15 Ge5) 1-x Se x Preferably, 0 ≤ x ≤ 0.4;

[0057] (Te 80 Sn 15 Bi5) 1-x S x Preferably, 0 ≤ x ≤ 0.2; and

[0058] (Te 80 Sn 15 Bi5) 1-x Se x Preferably, 0 ≤ x ≤ 0.4.

[0059] Figure 12-14 They correspond to respectively Figure 9-11 The graph represents the curve for optimizing a stack including as many standard PCM layers as possible to achieve similar functionality. In this case, the resulting (optimized) sequence of layers is as follows: 100nm Ag; 166nm ZnS-SiO2; 12nm PCM1; 29nm PCM2; 20nm Ag; 53nm ZnS-SiO2; 15nm PCM1; 44nm ZnS-SiO2. Reflectivity in gray-white state ( Figure 12 The reflectance of the red state (where PCM1 and PCM2 are both in an amorphous state) is 23.4. Figure 13 (where PCM1 is crystalline and PCM2 is amorphous) has a black / white contrast ratio of 3.5. Figure 12 and 14 The value is 7.

[0060] In some other embodiments, three different PCM layers 6 are provided in pixel element 4. The three different PCM layers 6 can be switched independently to allow for full color control (e.g., providing not only different hues of a single color such as red, as referenced above). Figure 8-14 The discussion also includes different shades of different colors such as red, green and blue, as well as total reflectance control independent of total color control.

[0061] In one embodiment, a shutter-like effect is achieved by arranging multiple heating profiles, including at least two heating profiles, which cause switching of different proportions of the PCM in one of the PCM layers 6 of the pixel element 4 by heating from the same heating element 8 (dedicated to a given pixel element 4). Switching of different proportions of the PCM layer 6 can result in the pixel element 4 having different corresponding reflectivities. For example, switching different proportions can include switching different proportions of the PCM layer 6 from an amorphous state to a crystalline state (a higher proportion of the crystalline state typically corresponds to a lower reflectivity), or vice versa. Different heating profiles can, for example, have different durations. Heating profiles with longer durations can be used to switch larger proportions of the PCM layer 6 between different available states of the PCM layer 6. Heating profiles with shorter durations can be used to switch smaller proportions of the PCM layer 6. Heating using electrical pulses can be considered equivalent to charging a "thermal capacitor." Short, large pulses and long, small pulses can be used to achieve the same temperature.

[0062] In some embodiments, heating from the heating element 8 of a given pixel element 4 is applied substantially uniformly to the PCM layer 6 of that pixel element 4, and different proportions of the PCM layer 6 are switched by arranging different portions of the PCM layer 6 to lose heat at different rates. In some embodiments, this is achieved by arranging the regions of the PCM layer 6 that are peripheral when viewed from a plane perpendicular to the PCM layer 6 of the pixel element 8 to lose heat faster than other regions, such that during the application of the heating profile, the switching of the PCM layer proceeds outward toward the peripheral regions. Figures 15A-15D An example device of this type is illustrated. Figure 15A The PCM layer 6 of a single pixel element 4 is shown before any heating profile is applied. Figure 15B The diagram shows the profile after the first heating is applied. Figure 15A The PCM layer 6. The first heating profile applies heat to the PCM layer 6 substantially uniformly, but because the peripheral regions lose heat more quickly (e.g., through cooler regions closer to the outside of pixel element 4), only the central region experiences a sufficiently high temperature rise to switch between the different states of the PCM. The shaded areas represent the PCM switched by the heating profile. Figure 15C The second heating profile is shown after it is applied. Figure 15A The PCM layer 6. Similar to the first heating profile, the second heating profile applies heat to the PCM layer 6 substantially uniformly, with the peripheral regions losing heat faster than other regions. However, because the second heating profile involves a longer duration (and / or higher power) of heating application, it allows for a greater proportion of switching of the PCM layer 6. Figure 15D It shows the application to Figure 15A The heating profile of the PCM layer 6 is sufficient to allow complete switching of all PCM in the PCM layer 6 of the pixel element 4. The design of the heating element determines which pulse switches which region. A heating element can be designed to switch 50% of the region for a given pulse and 100% of the region for a longer or higher amplitude pulse. In some embodiments, a heat sink structure can be disposed around the periphery of the pixel element 4 to aid in peripheral cooling and / or prevent heat leakage from one pixel element 4 to adjacent pixel elements 4.

[0063] By applying uneven heating to the PCM layer 6, a similar effect to the one described above can be achieved. Figures 15A-15D The effect described is that non-uniform heating is controlled so that different portions of the PCM layer 6 switch at different rates during heating by the heating element 8. Non-uniform heating can be achieved in various ways. For example, the heating element 8 can be configured to apply heating to an area significantly smaller than the PCM layer 6 in the pixel element 4. For example, when viewed from a plane perpendicular to the PCM layer 6, the heating element 8 may include a resistance heater having a surface area less than 75%, optionally less than 50%, or optionally less than 25% of the surface area of ​​the PCM layer 6 in the pixel element 4. In some embodiments, the heating element 8 in each pixel element 4 includes a plurality of parallel strips to apply a Venetian blind-like effect.

[0064] In some embodiments, grayscale is controlled by controlling groups of pixel elements 4. In these cases, the switching device can be configured to switch each group of adjacent pixel elements 4 between a predetermined set of group switching states. Each group switching state defines a different combination of pixel states of pixel elements 4 in that group. Each pixel state is defined by whether each PCM layer 4 in the pixel element 4 is in a high extinction coefficient state or a low extinction coefficient state. The set of group switching states allows the group to have multiple different reflectivities without changing the color of the group.

[0065] Figures 16A-16CThree example sets of group switching states are depicted. Each group of pixel elements 4 in these examples contains ten pixel elements 4 (each group of pixel elements has 5 rows and 2 columns). In one particular implementation, each pixel element 4 has a surface area of ​​50 micrometers × 40 micrometers, which results in a total surface area of ​​250 micrometers × 80 micrometers per group. Figure 16A The set contains eight groups of switching states, where each pixel element 4 can switch between multiple pixel states. In the example shown, three exemplary pixel states are depicted (e.g., white state, bright state, and dark state), but each pixel element 4 can be configured to switch between many more different states as described above. Figure 16B The collection contains usage and Figure 16A The same pixel element 4 has six groups switching states. Figure 16C The collection contains usage and Figure 16A and 16B The same pixel element 4 has four group switching states. By providing different numbers of group switching states, higher or lower levels of grayscale granularity can be obtained. Various algorithms can be used to define different combinations of pixel states for each grayscale level. Figures 16A-16C An exemplary arrangement for demonstrating this principle is shown, in which the gray levels gradually increase (i.e., darken) from left to right, optionally with a vibrant state in the middle. Figure 16A ).

Claims

1. A display device for displaying patterns, comprising: A pixel element having a layered structure, the layered structure including at least one phase change material layer, the phase change material layer being thermally switchable between at least a stable high extinction coefficient state and a stable low extinction coefficient state; and A switching device capable of applying heat to the pixel element from the same heating element according to each of a plurality of different heating profiles, wherein the plurality of heating profiles includes at least two heating profiles that cause switching of different proportions of phase change material in one of the phase change material layers of the pixel element. For each of the phase change material layers: The ratio of the average value of the extinction coefficient of the phase change material layer in the visible spectrum under the high extinction coefficient state to the average value of the extinction coefficient of the phase change material layer in the visible spectrum under the low extinction coefficient state is greater than 3.0; and The average extinction coefficient in the high extinction coefficient state is less than 1.0 in the visible spectrum.

2. The device according to claim 1, wherein, The layered structure of the pixel element also includes one or more additional phase change material layers, each of which can switch between at least a high extinction coefficient state and a low extinction coefficient state.

3. The device according to claim 2, wherein, For each additional phase change material layer, the ratio of the average extinction coefficient of the additional phase change material layer in the high extinction coefficient state to the average extinction coefficient of the additional phase change material layer in the low extinction coefficient state in the visible spectrum is greater than 3.

0.

4. The device according to claim 2 or 3 further includes a switching device capable of applying heating to the pixel element according to each of a plurality of different heating profiles.

5. The device according to claim 4, wherein, Within the pixel element, the individual phase change material layers are in thermal contact with each other, such that the heating of each of the phase change material layers in the pixel element causes the same temperature change.

6. The device according to claim 4, wherein, The plurality of heating profiles include heating profiles that cause a first phase change material layer in the phase change material layer of the pixel element to switch, without causing at least a second phase change material layer in the phase change material layer to switch.

7. The device according to claim 6, wherein, The plurality of heating profiles include heating profiles that cause the second phase change material layer in the pixel element to switch without causing the first phase change material layer in the pixel element to switch.

8. The device according to claim 4, wherein, The plurality of heating profiles includes heating profiles that simultaneously cause two or more phase change material layers to switch from the high extinction coefficient state to the low extinction coefficient state, and heating profiles that simultaneously cause two or more phase change material layers to switch from the low extinction coefficient state to the high extinction coefficient state.

9. The device according to claim 2 or 3, wherein, Two or more of the phase change material layers are different from each other only by doping, wherein the doping includes either or both of oxygen and nitrogen as dopants.

10. The device according to claim 2 or 3, wherein, The layered structure comprises two identical phase change material layers and a different phase change material layer located between them.

11. The device according to claim 2 or 3, wherein, The layered structure comprises three different phase change material layers.

12. The device according to claim 11, wherein, The three different phase change material layers are configured to be independently switchable to allow full color control and total reflectivity control independent of the full color control.

13. The device according to any one of claims 1-3, wherein, Each of one or more of the phase change material layers includes or is composed of one or more of the following: (Ag2Se) 1-x (Sb2Se3) x Where 0.5 ≤ x; (Ag2Se) 1-x (Sb2Se3) x Where 0.5 ≤ x < 0.7; AgSbSe2; AgSbTe 2-y Se y Where 2≥y≥0.5; Ag(Sb 1-z Bi z Te 2-y Se y Where 2≥y≥0.5 and / or 1≥z≥0; (Te 80 Sn 15 Ge5) 1-x S x , where 0 ≤ x ≤ 0.2; (Te 80 Sn 15 Ge5) 1-x Se x , where 0 ≤ x ≤ 0.4; (Te 80 Sn 15 Bi5) 1-x S x , where 0 ≤ x ≤ 0.2; and (Te 80 Sn 15 Bi5) 1-x Se x , where 0≤x≤0.

4.

14. The device according to any one of claims 1-3, wherein, Each of one or more of the phase change material layers includes or is composed of one or more of the following: Sb2S3, Ge2Sb2Se4Te, GeSbTeO, GeSnTeO, GeSnSbTeO, TeBiSnN, TeBiSnS, TeBiSnO, SeSnBi, SeSnBiO, SeSnGeO.

15. The device according to any one of claims 1-3, wherein, The high extinction coefficient state is a crystalline state, while the low extinction coefficient state is an amorphous state.

16. The device according to any one of claims 1-3, wherein, The pixel element also includes a reflective layer located on the same side of each of the phase change material layers.

17. The device according to claim 16, wherein, The pixel element also includes a capping layer on the side of each of the phase change material layers opposite to the reflective layer.

18. The device according to claim 16, wherein, The pixel element also includes a passive spacer layer located on the same side of the reflective layer as each of the phase change material layers.

19. The device according to claim 1, wherein, Switching the different proportions of the phase change material layer gives the pixel elements different reflectivities.

20. The device according to claim 1, wherein, The heating profiles that cause different proportions of the phase change material layer in the pixel element to switch include heating profiles with different durations.

21. The device according to claim 1, wherein, The heating from the heating element is uniformly applied to the phase change material layer of the pixel element, and the switching of different proportions of the phase change material layer is achieved by setting different parts of the phase change material layer to lose heat at different rates.

22. The device according to claim 21, wherein, The phase change material layer is configured such that, when viewed from a plane perpendicular to the phase change material layer, the region surrounding the pixel element loses heat faster than other regions, such that during the application of a heating profile, the switching of the phase change material layer proceeds outward toward the region surrounding the pixel element.

23. The device according to claim 1, wherein, Heating from the heating element is applied unevenly to the phase change material layer so that different portions of the phase change material layer switch at different rates during heating by the heating element.

24. The device according to claim 1, wherein, A plurality of said pixel elements are provided, and the switching device is configured to switch the phase change material layer in each pixel element independently of each other pixel element.

25. The device according to claim 24, wherein: The plurality of pixel elements includes a plurality of pixel element groups; The switching device is configured to switch each group of adjacent pixel elements between a predetermined set of group switching states. and Each group switching state defines different combinations of pixel states for pixel elements in the pixel element group, and each pixel state is defined by whether each phase change material layer in the pixel element is in the high extinction coefficient state or the low extinction coefficient state.

26. The device according to claim 25, wherein, The set of group switching states allows the group to have multiple different reflectivities without changing the group's color.

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