A cholesteric liquid crystal display and a driving method thereof

Abstract

The present application relates to the technical field of cholesteric liquid crystal display, and particularly relates to a cholesteric liquid crystal display and a driving method thereof, which comprises a first substrate and a second substrate arranged oppositely; a cholesteric liquid crystal layer encapsulated between the first substrate and the second substrate, the reflection wavelength of the cholesteric liquid crystal layer varying with temperature within a working temperature range; a first switch electrode and a second switch electrode for applying an electric field to the cholesteric liquid crystal layer to control the cholesteric liquid crystal layer to switch between a planar state and a focal conic state; and a transparent heating electrode array comprising a plurality of heating units corresponding to a plurality of pixel regions respectively and capable of being controlled independently, the heating units being used for heating the corresponding pixel regions to change the pitch of the cholesteric liquid crystal in the pixel regions and thus change the reflection wavelength of the pixel regions. The present application decouples the brightness control and the color control of the pixel, so that a single-layer cholesteric liquid crystal structure can realize full-color display simultaneously.

Description

Technical Field

[0001] This invention relates to the field of cholesteric liquid crystal display technology, and in particular to a cholesteric liquid crystal display and its driving method. Background Technology

[0002] Cholesteric liquid crystals are liquid crystal materials with a helical structure and bistable properties. When cholesteric liquid crystals are in the planar state (P-state), their molecules are helically arranged and can selectively reflect light of a specific wavelength corresponding to the pitch, exhibiting a bright state. When cholesteric liquid crystals are in the focal conic state (FC-state), their helical structure is disrupted, and the molecules are arranged in a multi-domain disordered manner, scattering the incident light and exhibiting a dark state. Since both the planar and focal conic states can be stably maintained after the external field is removed, reflective displays based on cholesteric liquid crystals do not require backlighting and static images do not require continuous power supply, making them widely used in low-power display scenarios such as electronic tags and e-books.

[0003] Existing cholesteric liquid crystal displays are typically electric field driven, which encapsulate cholesteric liquid crystal between two opposing substrates. By applying voltage pulses of specific amplitude and width between electrodes, each pixel switches between a planar state and a focal cone state, thereby displaying brightness and darkness information. However, in a planar state, a single-layer cholesteric liquid crystal can only reflect a single color determined by its pitch. To achieve color display, existing technologies typically employ three approaches: First, the three-layer stacking method, which stacks three layers of cholesteric liquid crystal that reflect red, green, and blue light respectively and drives each layer independently. This approach has an extremely complex structure, requires multiple alignments and bondings, resulting in low yield, high cost, and increased overall device thickness, with a significant decrease in reflectivity of the lower liquid crystal layer. Second, the color filter method, which superimposes a color filter onto a single-layer cholesteric liquid crystal display. This approach suffers from a light efficiency loss of up to two-thirds, leading to a dim display and insufficient contrast under strong outdoor light. Third, the field-sequential color method, which utilizes fast-response cholesteric liquid crystals in conjunction with red, green, and blue light to illuminate in a time-division manner. This approach requires complex synchronization control and is prone to color breakage.

[0004] Another type of existing technology is the purely thermally controlled cholesteric liquid crystal display (CLC). It utilizes the temperature sensitivity of the cholesteric liquid crystal pitch to change the reflected wavelength through localized heating, enabling full-color display with a single-layer structure. However, this type of display can only control the hue of colors, not the brightness of pixels: pixels heated to a specific temperature remain in a planar state (reflective state) and cannot switch to a focal conic state (dark state), resulting in the inability to display black and extremely poor image contrast.

[0005] Therefore, how to achieve full-color display and effective control of pixel brightness and darkness simultaneously in the same cholesteric liquid crystal display with a simple single-layer structure is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to provide a cholesteric liquid crystal display and its driving method to solve the problems in the prior art where single-layer cholesteric liquid crystal displays cannot simultaneously achieve full-color display and pixel brightness and darkness control, resulting in complex color structure, low light efficiency or inability to display black, and poor contrast.

[0007] To solve the above-mentioned technical problems, the present invention provides a cholesteric liquid crystal display, comprising:

[0008] A first substrate and a second substrate arranged opposite to each other;

[0009] A cholesteric liquid crystal layer is encapsulated between the first substrate and the second substrate, and the reflection wavelength of the cholesteric liquid crystal layer varies with temperature within the operating temperature range.

[0010] The first switching electrode and the second switching electrode are used to apply an electric field to the cholesteric liquid crystal layer to control the cholesteric liquid crystal layer to switch between a planar state and a focal conic state.

[0011] A transparent heating electrode array includes multiple heating units that correspond to multiple pixel regions and can be independently controlled. The heating units are used to heat the corresponding pixel regions to change the pitch of the cholesteric liquid crystal within the pixel regions, thereby changing the reflection wavelength of the pixel regions.

[0012] Optionally, the cholesteric phase liquid crystal display further includes:

[0013] A temperature sensor layer, wherein each pixel region in the temperature sensor layer corresponds to at least one temperature sensor;

[0014] The temperature sensor is used to provide feedback on the temperature of the corresponding pixel area.

[0015] Optionally, in the cholesteric liquid crystal display, at least one of the first switching electrode and the second switching electrode is a patterned electrode;

[0016] The patterned electrode is used to independently control the planar state and focal cone state of each pixel region.

[0017] Optionally, in the cholesteric liquid crystal display, a thermally insulating structure is further included between the transparent heating electrode arrays;

[0018] The thermal isolation structure is disposed between adjacent heating units to reduce thermal crosstalk between adjacent heating units.

[0019] Optionally, the cholesteric liquid crystal display further includes a light-absorbing layer;

[0020] The light-absorbing layer is disposed on the side of the second substrate opposite to the cholesteric liquid crystal layer.

[0021] A driving method for a cholesteric liquid crystal display, the driving method for driving a cholesteric liquid crystal display as described above, comprising:

[0022] The electric field control step involves applying an electric field to the cholesteric liquid crystal layer to switch each pixel region between a planar state and a focal cone state, thereby controlling the brightness of each pixel region.

[0023] The thermal control step involves independently heating the pixel region in a planar state to change the pitch of the cholesteric liquid crystal within the pixel region, thereby changing its reflection wavelength and controlling the color of the pixel region.

[0024] Optionally, in the driving method of the cholesteric liquid crystal display, the electric field control step and the thermal control step are performed separately in time.

[0025] First, the electric field control step is executed. After each pixel region completes the switching between planar state and focal cone state, the thermal control step is executed.

[0026] Optionally, in the driving method of the cholesteric liquid crystal display, the thermal control step includes:

[0027] The target reflection wavelength of the pixel region is determined based on the target color of the pixel region;

[0028] Based on the pre-stored correspondence between reflection wavelength and temperature, determine the target temperature corresponding to the target reflection wavelength;

[0029] The pixel region is heated to the target temperature.

[0030] Optionally, in the driving method of the cholesteric liquid crystal display, heating the pixel region to the target temperature includes:

[0031] The current temperature of the pixel area is detected, and the heating power of the pixel area is adjusted through closed-loop feedback control based on the deviation between the current temperature and the target temperature until the deviation is less than a preset threshold.

[0032] And / or, detect the ambient temperature and compensate the heating power according to the ambient temperature.

[0033] Optionally, the driving method for the cholesteric liquid crystal display further includes:

[0034] In the static holding step, the electric field is stopped and heating is stopped during static display, and the brightness and darkness of each pixel area are maintained by utilizing the bistable characteristics of the planar state and the focal cone state.

[0035] The cholesteric liquid crystal display provided by this invention comprises a first substrate and a second substrate disposed opposite to each other; a cholesteric liquid crystal layer encapsulated between the first substrate and the second substrate, wherein the reflection wavelength of the cholesteric liquid crystal layer varies with temperature within an operating temperature range; a first switching electrode and a second switching electrode for applying an electric field to the cholesteric liquid crystal layer to control the switching of the cholesteric liquid crystal layer between a planar state and a focal conic state; and a transparent heating electrode array comprising multiple heating units corresponding to multiple pixel regions and capable of independent control of each other, wherein the heating units are used to heat the corresponding pixel regions to change the pitch of the cholesteric liquid crystal within the pixel regions, thereby changing the reflection wavelength of the pixel regions.

[0036] This invention decouples pixel brightness control from color control. The electric field controls the switching of brightness, while thermal control adjusts the color. These two functions work independently yet collaboratively, enabling a single-layer cholesteric liquid crystal structure to simultaneously achieve full-color display without the need for three-layer stacking or color filters. This avoids the structural complexity, high cost, and reduced reflectivity associated with multi-layer stacking, as well as the light efficiency loss caused by color filters. A simple single-layer structure achieves full-color, high-contrast, and high-reflectivity display effects. This invention also provides a driving method for a cholesteric liquid crystal display with the aforementioned beneficial effects. Attached Figure Description

[0037] To more clearly illustrate the technical solutions of the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 A schematic diagram of the stacked structure of a specific embodiment of the cholesteric liquid crystal display provided by the present invention;

[0039] Figure 2 A schematic diagram of the planar layout of the transparent heating electrode array in a specific embodiment of the cholesteric liquid crystal display provided by the present invention;

[0040] Figure 3 A flowchart illustrating a specific embodiment of the driving method for a cholesteric liquid crystal display provided by the present invention;

[0041] Figure 4 This is a schematic diagram showing the relationship between the reflection wavelength and temperature of cholesteric liquid crystal materials.

[0042] Figure label:

[0043] 100-First substrate; 200-Second substrate; 300-Cholesteric liquid crystal layer; 410-First switching electrode; 420-Second switching electrode; 500-Transparent heating electrode array; 501-Heating unit; 502-Thermal isolation structure; 600-Temperature sensor layer; 700-Light absorption layer; 800-Control circuit; 810-Electric field driving module; 820-Image processing module; 830-State mapping module; 840-Thermal control driving module; 850-Environmental compensation module; 860-Timing control module. Detailed Implementation

[0044] To enable those skilled in the art to better understand the present invention, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] The core of this invention is to provide a cholesteric liquid crystal display, the specific embodiment of which is shown in the schematic diagram of its stacked structure as follows. Figure 1 As shown, this is referred to as Specific Implementation Method One, which includes:

[0046] The first substrate 100 and the second substrate 200 are disposed opposite to each other;

[0047] A cholesteric liquid crystal layer 300 is encapsulated between the first substrate 100 and the second substrate 200, and the reflection wavelength of the cholesteric liquid crystal layer 300 changes with temperature within the operating temperature range.

[0048] The first switching electrode 410 and the second switching electrode 420 are used to apply an electric field to the cholesteric liquid crystal layer 300 to control the cholesteric liquid crystal layer 300 to switch between a planar state and a focal conic state.

[0049] The transparent heating electrode array 500 includes multiple heating units 501 that correspond to multiple pixel regions and can be independently controlled. The heating units 501 are used to heat the corresponding pixel regions to change the pitch of the cholesteric liquid crystal in the pixel region, thereby changing the reflection wavelength of the pixel region.

[0050] The first substrate 100 and the second substrate 200 can be glass substrates or flexible transparent substrates such as polyethylene terephthalate; this invention is not limited thereto. The first switching electrode 410 is disposed on the side of the first substrate 100 facing the cholesteric liquid crystal layer 300, and the second switching electrode 420 is disposed on the side of the second substrate 200 facing the cholesteric liquid crystal layer 300. The transparent heating electrode array 500 can be disposed on the side of the first switching electrode 410 facing the cholesteric liquid crystal layer 300, or it can be integrated with the first switching electrode 410 in the same layer and electrically insulated from each other; this invention is not limited thereto. Furthermore, the surfaces of the first switching electrode 410 and the second switching electrode 420 can also be covered with an alignment layer to induce liquid crystal molecules to form a uniform planar arrangement.

[0051] It should be noted that the pitch of cholesteric liquid crystals is temperature-sensitive, and typically exhibits a negative correlation. That is, as temperature increases, the thermal motion of the molecules constituting the liquid crystal intensifies, the orderliness of the molecular arrangement decreases, and the torsional elasticity maintaining the helical structure is weakened, thus shortening the pitch; conversely, as temperature decreases, the pitch lengthens. Since the reflection wavelength of cholesteric liquid crystals in a planar state is proportional to the pitch, this effect manifests optically as a reversible change in reflected color with temperature, i.e., thermochromic effect. The relationship between the reflection wavelength and temperature of cholesteric liquid crystal materials can be found by referring to... Figure 4 Accordingly, the cholesteric liquid crystal layer 300 may comprise one or more mixed thermochromic cholesteric liquid crystal materials whose reflected wavelength continuously blue-shifts with increasing temperature within the operating temperature range. By heating the pixel area to different temperatures, the pixel area can reflect different colors of light such as red, orange, yellow, green, and blue. Some highly sensitive materials can exhibit colors across the entire visible spectrum within a temperature difference of less than 1°C. Of course, the specific liquid crystal material can be selected according to the target operating temperature range and target color gamut, and this invention does not limit it.

[0052] It should also be noted that in this invention, the brightness of a pixel is controlled by an electric field, while the color of the pixel is controlled by temperature. These two controls are independent of each other. When an electric field is applied to a pixel region, switching it to a focal conic state, the pixel region scatters incident light and appears dark. When a pixel region is in a planar state, the pixel region reflects light of a wavelength corresponding to its current temperature and appears bright in the corresponding color. Therefore, this specific embodiment decouples the brightness control and color control of pixels, achieving both full-color display and true black display simultaneously with a single-layer cholesteric liquid crystal structure, without the need for three-layer stacking or color filters. Theoretical simulations have verified that in a traditional three-layer stacking scheme, the red display module is stacked at the bottom of the three-layer display module, with a maximum reflectivity of approximately 23.1%. However, using the single-layer structure of this invention, the maximum reflectivity of red is approximately 32.2%, an increase of about 40%. Simultaneously, utilizing the narrow-band Bragg reflection principle of cholesteric liquid crystal itself, the half-width at half-maximum (FWHM) of the reflection spectrum is typically 50nm to 100nm, allowing the single-layer structure to cover more than 40% of the NTSC color gamut. Furthermore, since electric field driving only requires switching between planar and focal conical states, without relying on electric fields to control grayscale and color, the requirements for the dielectric properties of liquid crystal materials are relaxed, and the selection of materials can focus on their thermochromic properties, thus expanding the optimization space for materials.

[0053] In a preferred embodiment, the cholesteric liquid crystal display further includes a temperature sensor layer 600, wherein each pixel region in the temperature sensor layer 600 corresponds to at least one temperature sensor;

[0054] The temperature sensor is used to provide feedback on the temperature of the corresponding pixel area.

[0055] In this preferred embodiment, the temperature sensor layer 600 is positioned close to the cholesteric liquid crystal layer 300 to reflect the actual temperature of the liquid crystal in each pixel region as accurately as possible. Since the reflection wavelength of cholesteric liquid crystal is highly sensitive to temperature, a temperature deviation on the order of 0.5°C can cause a noticeable color shift. By configuring a temperature sensor for each pixel region, real-time feedback can be provided for the closed-loop temperature control described later, enabling the temperature of each pixel region to be quickly and accurately controlled near the target value, thereby ensuring the accuracy and stability of color display.

[0056] In a preferred embodiment, at least one of the first switching electrode 410 and the second switching electrode 420 is a patterned electrode;

[0057] The patterned electrode is used to independently control the planar state and focal cone state of each pixel region.

[0058] In this preferred embodiment, both the first switching electrode 410 and the second switching electrode 420 can be patterned electrodes, or one can be a patterned electrode and the other a common electrode covering the entire surface. When a patterned electrode is used, voltage pulses can be applied independently to each pixel area, thereby achieving independent control of the planar state and focal cone state at the pixel level. This allows any pixel to individually present a bright or dark state, improving the flexibility and accuracy of the displayed content. Of course, in situations where high display accuracy is not required, both the first switching electrode 410 and the second switching electrode 420 can be whole-surface electrodes, only achieving a unified state switching across the entire screen. This invention does not limit this.

[0059] In a preferred embodiment, the transparent heating electrode array 500 further includes a thermal insulation structure 502 between them;

[0060] The thermal isolation structure 502 is disposed between adjacent heating units 501 to reduce thermal crosstalk between adjacent heating units 501.

[0061] The planar layout of the transparent heating electrode array 500 can be referenced. Figure 2 The multiple heating units 501 are arranged in pixels, electrically isolated from each other, and can be independently controlled. A thermal isolation structure 502 is provided between adjacent heating units 501. It should be noted that in this invention, the target temperatures of adjacent pixels may differ. If significant heat conduction occurs between adjacent heating units, the heat from the heated pixel will diffuse to adjacent pixels, causing the actual temperature of adjacent pixels to deviate from their target temperature, thus causing color crosstalk. This preferred embodiment blocks the lateral heat conduction path between adjacent pixels by providing a thermal isolation structure 502 with a low thermal conductivity between adjacent heating units 501, reducing thermal crosstalk and ensuring the independence and accuracy of the color of each pixel. The thermal isolation structure 502 can be made of a dielectric material with low thermal conductivity or can be in the form of a hollow isolation groove; this invention is not limited thereto.

[0062] In one specific implementation, the thermal isolation structure 502 is disposed on the same layer as the heating unit 501 and surrounds each heating unit 501 in a grid pattern. That is, the thermal isolation structure 502 fills the gaps between adjacent heating units 501, and its height is flush with that of the heating unit 501. The thermal isolation structure 502 is made of a transparent dielectric material with a thermal conductivity of less than 0.5 W / (m·K), such as polyimide, SU-8 photoresist, porous silica, or aerogel material. Its thermal conductivity is significantly lower than that of transparent conductive materials such as indium tin oxide and glass substrates, which can effectively suppress the lateral diffusion of heat along the heating layer. The width of the thermal isolation structure 502 can be 5% to 20% of the pixel pitch, for example, 2 μm to 50 μm. The larger the width, the better the heat insulation effect, but the effective aperture ratio of the pixel decreases accordingly. A trade-off can be made based on the pixel size and color crosstalk tolerance. Furthermore, since the dielectric material is an electrically insulating material, the thermal isolation structure 502 can also simultaneously achieve electrical isolation between adjacent heating units 501 without the need for additional insulation spacing.

[0063] In another specific implementation, the thermal isolation structure 502 is a hollow isolation groove disposed between adjacent heating units 501. The hollow isolation groove can be formed by photolithography and etching on the transparent conductive layer and part of the underlying dielectric layer after film deposition. The groove is filled with air or subjected to vacuum treatment. The thermal conductivity of air is approximately 0.026 W / (m·K), far lower than that of any solid thin film material, thus the hollow form can achieve stronger thermal insulation capabilities. The depth of the hollow isolation groove can be greater than or equal to the thickness of the heating unit 501 to completely cut off the lateral heat conduction path within the heating layer. A planarization encapsulation layer can also be covered above the hollow isolation groove to avoid affecting the subsequent film layer fabrication and liquid crystal cell encapsulation.

[0064] Of course, the two forms mentioned above can also be used in combination. For example, a dielectric material with low thermal conductivity can be filled into the hollow isolation groove to balance thermal insulation performance and structural strength. By setting the thermal isolation structure 502, thermal crosstalk between adjacent pixel areas is reduced, and each pixel area can establish and maintain its target temperature more quickly. This not only improves the independence and accuracy of color display, but also reduces the additional heating power consumed to combat thermal crosstalk, which helps to reduce the overall power consumption of the display.

[0065] In a preferred embodiment, the heating unit 501 is a transparent conductive material unit; the transparent conductive material is indium tin oxide or silver nanowires;

[0066] The visible light transmittance of the heating unit 501 is not less than 80%.

[0067] It should be noted that this invention is a reflective display. Ambient light needs to pass through the transparent heating electrode array 500 to be incident on the cholesteric liquid crystal layer 300, and reflected light also needs to pass through the transparent heating electrode array 500 again to exit. Therefore, the heating unit 501 is located in the display light path. In this preferred embodiment, the heating unit 501 is made of a material that combines conductivity and transparency, such as indium tin oxide or silver nanowires, and has a visible light transmittance of not less than 80%. This allows it to heat the corresponding pixel area by generating Joule heat through electricity, while minimizing the loss of incident and reflected light, thus ensuring the overall reflectivity and brightness of the display. Of course, the heating unit 501 can also be made of other transparent conductive materials that meet the transmittance requirements; this invention is not limited to these materials.

[0068] In a preferred embodiment, the cholesteric liquid crystal display further includes a light-absorbing layer 700;

[0069] The light absorption layer 700 is disposed on the side of the second substrate 200 opposite to the cholesteric liquid crystal layer 300, and is used to absorb the scattered light when the cholesteric liquid crystal layer 300 is in the focal conic state.

[0070] In this preferred embodiment, the light-absorbing layer 700 can be a black coating or a black backplate. When the pixel area is in a focal conic state, the incident light is scattered by the liquid crystal layer and passes through the second substrate 200, where it is absorbed by the light-absorbing layer 700, making the pixel area appear pure black and further improving the contrast of the display. Combined with the light-absorbing layer 700, the display of the present invention operates in a pure reflective mode, eliminating backlight leakage problems and significantly improving display contrast. Theoretical calculations show that even in strong light environments, the contrast ratio can still reach over 10:1, making it very suitable for outdoor applications.

[0071] In a preferred embodiment, the cholesteric liquid crystal display further includes a control circuit 800, which is electrically connected to the first switching electrode 410, the second switching electrode 420, the transparent heating electrode array 500, and the temperature sensor layer 600.

[0072] Specifically, the control circuit 800 may include: an electric field driving module 810, used to generate a voltage waveform that switches the pixel region between a planar state and a focal conic state; an image processing module 820, used to decompose the input image signal into a luminance signal representing the target grayscale and a color signal representing the target reflection wavelength; a state mapping module 830, used to determine whether the target state of each pixel region is planar or focal conic based on the luminance signal, and to determine the target temperature of each pixel region based on the color signal; a thermal control driving module 840, used to drive the heating unit 501 based on temperature feedback, so that the pixel region reaches the target temperature; an environmental compensation module 850, used to detect the ambient temperature and to compensate the heating power of the transparent heating electrode array 500 in real time based on the ambient temperature; and a timing control module 860, used to coordinate the timing of the electric field driving and the thermal control driving. The specific working process of each of the above modules will be described in detail in the specific implementation of the driving method below, and will not be repeated here.

[0073] The cholesteric liquid crystal display provided by the present invention comprises a first substrate 100 and a second substrate 200 disposed opposite to each other; a cholesteric liquid crystal layer 300 encapsulated between the first substrate 100 and the second substrate 200, wherein the reflection wavelength of the cholesteric liquid crystal layer 300 varies with temperature within its operating temperature range; a first switching electrode 410 and a second switching electrode 420 for applying an electric field to the cholesteric liquid crystal layer 300 to control the cholesteric liquid crystal layer 300 to switch between a planar state and a focal conic state; and a transparent heating electrode array 500 including multiple heating units 501 corresponding to multiple pixel regions and capable of being independently controlled by each other, wherein the heating units 501 are used to heat the corresponding pixel regions to change the pitch of the cholesteric liquid crystal within the pixel region, thereby changing the reflection wavelength of the pixel region. This invention decouples pixel brightness control from color control. The electric field is responsible for switching brightness on and off, while thermal control is responsible for color adjustment. The two work independently and collaboratively, enabling a single-layer cholesteric liquid crystal structure to achieve full-color display simultaneously without the need for three-layer stacking or color filters. This avoids the structural complexity, high cost, and reduced reflectivity caused by multi-layer stacking, as well as the light efficiency loss caused by color filters. A full-color, high-contrast, and high-reflectivity display effect is achieved with a simple single-layer structure.

[0074] The present invention also provides a driving method for a cholesteric liquid crystal display, wherein the driving method is used to drive any of the cholesteric liquid crystal displays described above, and a flowchart of a specific embodiment is shown below. Figure 3 As shown, it includes:

[0075] S1: Electric field control step, applying an electric field to the cholesteric liquid crystal layer 300 to switch each pixel region between a planar state and a focal cone state, so as to control the brightness of each pixel region.

[0076] S2: Thermal control step, independently heating the pixel area in the planar state to change the pitch of the cholesteric liquid crystal in the pixel area, thereby changing its reflection wavelength and controlling the color of the pixel area.

[0077] Of course, there is no strict order between steps S1 and S2, and they can be adjusted according to actual needs.

[0078] Before executing the electric field control step, an image decomposition step may be included, specifically receiving the input color image signal and decomposing each pixel into a luminance component and a color component. The luminance component can be an 8-bit target grayscale, i.e., gray levels 0 to 255, and the color component can be a target hue, such as an RGB value. Subsequently, a state decision is made: if the luminance component of a pixel is less than a luminance threshold, such as 128, then the pixel is determined to be in a dark state, with its target state being a focal cone state; if the luminance component of the pixel is greater than or equal to the luminance threshold, then the pixel is determined to be in a bright state, with its target state being a planar state. Of course, the luminance threshold can be adjusted according to actual display requirements, and this invention does not limit it.

[0079] As one specific implementation, the electric field control step includes:

[0080] First, apply a reset pulse to all pixel regions to switch all pixel regions to the planar state; then apply a focal-cone state write pulse only to pixel regions whose target state is focal-cone state to switch them to the focal-cone state; for pixel regions whose target state is planar state, do not apply a focal-cone state write pulse to keep them in the planar state.

[0081] In this specific embodiment, the reset pulse can be a high-voltage square wave with an amplitude of ±100V and a width of 10ms, and the focal cone state write pulse can be a low-frequency square wave with an amplitude of 30V and a width of 30ms. The method of full-screen reset followed by selective writing eliminates the need to design complex multi-level drive waveforms for each pixel, simplifying the control logic of the electric field drive. Of course, the amplitude, width, and waveform of the above pulses are merely examples and can be adjusted according to the characteristics of the liquid crystal material and device parameters; this invention does not limit these adjustments.

[0082] In a preferred embodiment, the electric field control step and the thermal control step are performed separately in time.

[0083] First, the electric field control step is executed. After each pixel region completes the switching between planar state and focal cone state, the thermal control step is executed.

[0084] It is important to note that parameters such as the elastic constant, viscosity, and dielectric constant of liquid crystal materials all change with temperature. If a switching electric field is applied simultaneously with heating, the temperature change will cause the threshold voltage and response characteristics required for electric field switching to drift, affecting the reliability of state switching. Conversely, the electric field switching process may also interfere with the stability of the temperature field. In this preferred embodiment, the timing of the two is coordinated by the timing control module 860. First, the planar state and focal cone state switching of all pixels are completed, and then thermal control color adjustment is performed on the pixels in the planar state. This ensures that electric field control and thermal control do not overlap in time, thereby ensuring that brightness control and color control are independent and do not interfere with each other, further guaranteeing the accuracy and stability of the display.

[0085] In a preferred embodiment, the thermal control step includes:

[0086] The target reflection wavelength of a pixel region is determined based on the target color of that pixel region.

[0087] Based on the pre-stored correspondence between reflection wavelength and temperature, the target temperature corresponding to the target reflection wavelength is determined; the pixel area is then heated to the target temperature.

[0088] In this preferred embodiment, for a pixel region in a planar state, its color components are extracted and converted into a target reflection wavelength. Then, based on a pre-calibrated and stored calibration curve of reflection wavelength and temperature, the target temperature corresponding to the target reflection wavelength is obtained, and this target temperature is used as the heating target for the pixel region. Thus, color control is transformed into an intuitive one-to-one mapping between target temperature and reflection wavelength. Compared to the existing electric field-driven displays that rely on precise pulse width modulation or pulse amplitude modulation algorithms to achieve grayscale and color, this significantly reduces the complexity of the driving algorithm and driving hardware. The calibration curve can be obtained by calibrating the liquid crystal material used before the display leaves the factory; this invention is not limited to this.

[0089] In a preferred embodiment, heating the pixel region to the target temperature includes:

[0090] The current temperature of the pixel area is detected, and the heating power of the pixel area is adjusted through closed-loop feedback control based on the deviation between the current temperature and the target temperature until the deviation is less than a preset threshold.

[0091] And / or, detect the ambient temperature and compensate the heating power according to the ambient temperature.

[0092] As one specific implementation, the closed-loop feedback control can be proportional-integral-derivative control, i.e., PID control, and its execution flow is as follows:

[0093] First, the temperature T of the pixel area is read in real time by the temperature sensor layer 600. current ;

[0094] Secondly, calculate the difference between the current temperature and the target temperature T. target Deviation between:

[0095] e=T target -T current ;

[0096] Then, perform PID calculation:

[0097] Proportional term P=K p ·e;

[0098] Integral term I=I previous +K i ·e·Δt;

[0099] Differential term D=K d ·(ee previous ) / Δt;

[0100] Output power P output =P+I+D;

[0101] Where K p K i K d These are the proportional coefficient, integral coefficient, and derivative coefficient, respectively; Δt is the control period; I previous With e previous The integral term and deviation of the previous control cycle are respectively used. Finally, the power signal corresponding to the output power is sent to the corresponding heating unit 501. The power signal can be a voltage signal or a current duty cycle signal. The above steps are repeated to form a closed loop. The control cycle can be in the millisecond range, for example, 10ms to 50ms. The preset threshold can be set to 0.2℃, that is, when the absolute value of the deviation is less than 0.2℃, the pixel area is considered to have reached the target temperature. Since a temperature difference on the order of 0.5℃ may cause color shift, this specific embodiment uses PID closed-loop control to automatically, continuously, and smoothly calculate the required heating power based on the deviation, so that the pixel temperature quickly and accurately reaches and stabilizes near the target value, ensuring the accuracy of color display. Of course, other feedback control algorithms can also be used for the closed-loop feedback control, which is not limited here.

[0102] Furthermore, the environmental compensation module 850 can detect the ambient temperature in real time and compensate the heating power accordingly. It is important to note that fluctuations in ambient temperature alter the heat dissipation conditions of the pixel area: at lower ambient temperatures, the pixels dissipate heat more quickly, increasing the heating power required to maintain the same target temperature; conversely, at higher ambient temperatures, the opposite occurs. This preferred embodiment incorporates ambient temperature as a controllable parameter into the control loop, rather than allowing it to become a disturbance. Experimental simulations show that within an ambient temperature range of 0°C to 50°C, through real-time correction via environmental compensation, the color error ΔE*ab of each pixel on the display can be controlled within 3, imperceptible to the naked eye. This overcomes the interference of ambient temperature changes on the display effect and ensures color consistency across a wide temperature range.

[0103] In a preferred embodiment, the driving method for the cholesteric liquid crystal display further includes:

[0104] In the static holding step, the electric field is stopped and heating is stopped during static display, and the brightness and darkness of each pixel area are maintained by utilizing the bistable characteristics of the planar state and the focal cone state.

[0105] In this preferred embodiment, both the planar state and the focal conic state are stable states of the cholesteric liquid crystal, which can be maintained without power supply after the electric field is removed. Therefore, after one frame is displayed, the electric field driving module 810 stops outputting, and the brightness and darkness of each pixel area are maintained with zero power consumption. At the same time, the thermal control driving module 840 also stops heating output. After heating stops, the temperature of the pixel area in the planar state will gradually approach the ambient temperature over time, and its reflected color will correspondingly approach the color corresponding to the ambient temperature. The electric field control step and the thermal control step are only executed again when the next image is updated. For application scenarios with long screen update intervals, such as e-book applications that refresh the screen once per hour, if the heating energy consumption for each refresh is E, the average power consumption is approximately E / 3600 per second. The total power consumption of this preferred embodiment in such typical application scenarios is expected to be 60% to 90% lower than that of the prior art. Of course, for application scenarios that require maintaining a color image between two refreshes, the thermal control drive module 840 can maintain the relevant pixel area at the target temperature with a maintenance power much lower than the refresh power consumption. The specific choice can be made based on the application scenario's requirements for power consumption and color preservation, and this invention does not limit this.

[0106] The cholesteric liquid crystal display provided by this invention encapsulates a cholesteric liquid crystal layer 300 with a temperature-dependent reflectance wavelength between a first substrate 100 and a second substrate 200 disposed opposite to each other. On one hand, an electric field is applied to the cholesteric liquid crystal layer 300 through a first switching electrode 410 and a second switching electrode 420 to control the switching of each pixel region between a planar state and a focal conic state, thereby controlling the brightness of the pixels. On the other hand, each pixel region is independently heated by heating units 501 independently controlled in a transparent heating electrode array 500, changing the pitch of the cholesteric liquid crystal within the pixel region and thus changing its reflectance wavelength, thereby controlling the color of the pixels. Thus, this invention decouples the brightness control and color control of pixels, enabling a single-layer cholesteric liquid crystal structure to simultaneously achieve full-color display and true black display without the need for three-layer stacking or color filters. This avoids the structural complexity, high cost, and reduced reflectivity caused by multi-layer stacking, as well as the light efficiency loss caused by color filters. At the same time, it overcomes the inherent defects of pure thermal control schemes, such as the inability to display black and poor contrast. A full-color, high-contrast, and high-reflectivity display effect is achieved with a simple single-layer structure. The present invention also provides a driving method for a cholesteric liquid crystal display with the above-mentioned beneficial effects.

[0107] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the method section.

[0108] It should be noted that, in this specification, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0109] The cholesteric liquid crystal display and its driving method provided by the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the present invention.

Claims

1. A cholesteric liquid crystal display, characterized by comprising: include: A first substrate and a second substrate arranged opposite to each other; A cholesteric liquid crystal layer is encapsulated between the first substrate and the second substrate, and the reflection wavelength of the cholesteric liquid crystal layer varies with temperature within the operating temperature range. The first switching electrode and the second switching electrode are used to apply an electric field to the cholesteric liquid crystal layer to control the cholesteric liquid crystal layer to switch between a planar state and a focal conic state, thereby controlling the brightness of each pixel area. A transparent heating electrode array includes multiple heating units that correspond to multiple pixel regions and can be independently controlled by each other. The heating units are used to heat the corresponding pixel regions to change the pitch of the cholesteric liquid crystal in the pixel region, thereby changing the reflection wavelength of the pixel region to control the color of each pixel region, thus decoupling the brightness control and color control of each pixel region.

2. The cholesteric liquid crystal display of claim 1, wherein, Also includes: A temperature sensor layer, wherein each pixel region in the temperature sensor layer corresponds to at least one temperature sensor; The temperature sensor is used to provide feedback on the temperature of the corresponding pixel area.

3. The cholesteric liquid crystal display of claim 1, wherein, At least one of the first switching electrode and the second switching electrode is a patterned electrode; The patterned electrode is used to independently control the planar state and focal cone state of each pixel region.

4. The cholesteric liquid crystal display of claim 1, wherein, The transparent heating electrode array also includes a thermal isolation structure; The thermal isolation structure is disposed between adjacent heating units to reduce thermal crosstalk between adjacent heating units.

5. The cholesteric liquid crystal display of claim 1, wherein, It also includes a light-absorbing layer; The light-absorbing layer is disposed on the side of the second substrate opposite to the cholesteric liquid crystal layer.

6. A driving method of a cholesteric liquid crystal display device, characterized by comprising the steps of: The driving method for the cholesteric liquid crystal display is used to drive the cholesteric liquid crystal display as described in any one of claims 1 to 5, comprising: The electric field control step involves applying an electric field to the cholesteric liquid crystal layer to switch each pixel region between a planar state and a focal cone state, thereby controlling the brightness of each pixel region. The thermal control step involves independently heating the pixel region in a planar state to change the pitch of the cholesteric liquid crystal within the pixel region, thereby changing its reflection wavelength and controlling the color of the pixel region.

7. The driving method for a cholesteric liquid crystal display as described in claim 6, characterized in that, The electric field control step and the thermal control step are performed separately in time. First, the electric field control step is executed. After each pixel region completes the switching between planar state and focal cone state, the thermal control step is executed.

8. The driving method for a cholesteric liquid crystal display as described in claim 6, characterized in that, The thermal control steps include: The target reflection wavelength of the pixel region is determined based on the target color of the pixel region; Based on the pre-stored correspondence between reflection wavelength and temperature, determine the target temperature corresponding to the target reflection wavelength; The pixel region is heated to the target temperature.

9. The driving method for a cholesteric liquid crystal display as described in claim 8, characterized in that, Heating the pixel region to the target temperature includes: The current temperature of the pixel area is detected, and the heating power of the pixel area is adjusted through closed-loop feedback control based on the deviation between the current temperature and the target temperature until the deviation is less than a preset threshold. And / or, detect the ambient temperature and compensate the heating power according to the ambient temperature.

10. The driving method for a cholesteric liquid crystal display as described in claim 6, characterized in that, Also includes: In the static holding step, the electric field is stopped and heating is stopped during static display, and the brightness and darkness of each pixel area are maintained by utilizing the bistable characteristics of the planar state and the focal cone state.

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