WO-2026092762-A1 - DEVICE USING FERROELECTRIC LIQUID CRYSTAL CELL AND METHOD FOR MANUFACTURING THE SAME

Abstract

A FLC cell includes upper substrate and lower substrates, upper and lower transparent conductive layers, upper and lower alignment layers, and a FLC layer. The upper and lower substrates are arranged to define an enclosed region. The upper transparent conductive layer is disposed on the upper substrate. The lower transparent conductive layer is disposed on the lower substrate. The upper alignment layer is disposed on the upper transparent conductive layer. The lower alignment layer is disposed on the lower transparent conductive layer. The FLC layer is positioned between the upper alignment layer and the lower alignment layer. The upper alignment layer and the lower alignment layer are configured to provide an anchoring energy to FLC molecules of the FLC layer. The anchoring energy is balanced with the helical elastic energy of ferroelectric liquid crystal of the FLC layer to achieve stable molecular alignment and high-contrast electro-optical performance.

Inventors

• SWAMINATHAN, Vigneshwaran
• Chen, Zhaoyi
• MATHEW, Chris
• VASHCHENKO, Valerii
• SRIVASTAVA, ABHISHEK KUMAR

Assignees

• THE HONG KONG UNIVERSITY OF SCIENCE AND TECHNOLOGY

Dates

Publication Date

20260507

Application Date

20251104

Priority Date

20241104

Claims (16)

1. A ferroelectric liquid crystal (FLC) cell, comprising: an upper substrate and a lower substrate which are arranged in parallel and spaced apart to define an enclosed region; an upper transparent conductive layer disposed on an inner surface of the upper substrate; a lower transparent conductive layer disposed on an inner surface of the lower substrate; an upper alignment layer disposed on the upper transparent conductive layer; a lower alignment layer disposed on the lower transparent conductive layer; and a ferroelectric liquid crystal layer (FLC layer) positioned between the upper alignment layer and the lower alignment layer, wherein the upper alignment layer and the lower alignment layer are configured to provide an anchoring energy to ferroelectric liquid crystal molecules of the FLC layer, and wherein the anchoring energy is balanced with the helical elastic energy of ferroelectric liquid crystal of the FLC layer to achieve stable molecular alignment and high-contrast electro-optical performance.
2. The FLC cell of claim 1, wherein the upper alignment layer and the lower alignment layer provide planar alignment for the ferroelectric liquid crystal molecules of the FLC layer which is configured to guide the ferroelectric liquid crystal molecules to adopt a uniform orientation parallel to alignment surfaces of the upper alignment layer and the lower alignment layer.
3. The FLC cell of claim 1, wherein the upper and lower alignment layers are formed from polyimide-based thin films implemented in a polymerized state and aligned using a uniaxial rubbing process.
4. The FLC cell of claim 1, further comprising: spacers positioned between the upper substrate and the lower substrate to maintain the fixed cell gap and to make uniform cell thickness for the FLC layer.
5. The FLC cell of claim 1, wherein the anchoring energy applied to the ferroelectric liquid crystal molecules of the FLC layer by the first and second alignment layers ranges between W Q 10 -4 to 10 -3 J/m 2 .
6. The FLC cell of claim 5, wherein elastic constant K within the ferroelectric liquid crystal layer of the FLC layer ranges between 10 -11 to 10 -10 N.
7. The FLC cell of claim 1, wherein a relation between the anchoring energy and the helical elastic energy of the ferroelectric liquid crystal is calculated accordingly to the following formula: where K is the elastic constant, q 0 =2π/p 0 is the wave vector of the helix defined by the helix pitch, is the cell gap, and W Q is the anchoring energy coefficient associated with the alignment layer, thereby providing optimal contrast ratio and suppressing residual diffraction effects.
8. A method for manufacturing a ferroelectric liquid crystal (FLC) cell, comprising: providing an upper substrate and a lower substrate; depositing an upper transparent conductive layer on an inner surface of the upper substrate; depositing a lower transparent conductive layer on an inner surface of the lower substrate; depositing an upper alignment layer on the upper transparent conductive layer; depositing a lower alignment layer on the lower transparent conductive layer; subjecting the upper alignment layer and the lower alignment layer to a uniaxial rubbing treatment, such that the upper alignment layer has a first alignment axis and the lower alignment layer has a second alignment axis for defining a molecular orientation direction, thereby establishing an antiparallel alignment axis; aligning and positioning the upper and lower substrates and maintaining a fixed cell gap using spacers to create an enclosed region between the upper and lower alignment layers; and introducing a ferroelectric liquid crystal layer (FLC layer) into the enclosed region between the upper and lower alignment layers.
9. The method of claim 8, wherein the upper alignment layer and the lower alignment layer provide planar alignment for ferroelectric liquid crystal molecules of the FLC layer which is configured to guide the ferroelectric liquid crystal molecules to adopt a uniform orientation parallel to alignment surfaces of the upper alignment layer and the lower alignment layer.
10. The method of claim 8, further comprising: performing a uniaxial rubbing treatment to control the anchoring energy for the FLC layer by: adjusting a roller height to regulate contact pressure, a roller speed to control rubbing intensity, a rotational torque to modify a rubbing force applied to the upper and lower alignment layers, or combinations thereof.
11. The method of claim 10, further comprising adjusting the anchoring energy by: either performing a thermal annealing process, or performing a post-rubbing solvent treatment process, or performing both processes in combinations thereof.
12. The method of claim 8, wherein the upper and lower alignment layers are formed from polyamic acid-based thin films and subsequently subjected to thermal or chemical imidization.
13. The method of claim 12, wherein the upper and lower alignment layers are prepared from the solution of polyimide precursor in a solvent mixture and depositing onto the substrates using a spin-coating technique to achieve a uniform thin film.
14. The method of claim 13, wherein the poly-amic acid is dissolved in NMP (N-Methyl-2-pyrrolidone) and BC (Ethylene Glycol Monobutyl Ether) in a 7: 3 ratio.
15. The method of claim 14, further comprising: adjusting the anchoring energy to be slightly less than the helical elastic energy of the ferroelectric liquid crystal accordingly to the following equation: where K is the elastic constant, q 0 =2π/p 0 is the wave vector of the helix defined by the helix pitch, is the cell gap, and W Q is the anchoring energy coefficient associated with the alignment layer, thereby providing optimal contrast ratio and suppressing residual diffraction effects.
16. The method of claim 8, wherein the FLC layer is introduced into the enclosed region by injecting a ferroelectric liquid crystal material and applying a controlled capillary filling process to promote uniform molecular alignment.

Description

DEVICE USING FERROELECTRIC LIQUID CRYSTAL CELL AND METHOD FOR MANUFACTURING THE SAME Inventors: Vigneshwaran SWAMINATHAN; Zhaoyi CHEN; Chris MATHEW;Valerii VASHCHENKO; Abhishek Kumar SRIVASTAVA Technical Field: The present invention relates to a ferroelectric liquid crystal (FLC) cell with an optimized alignment layer; more particularly, to FLC devices with polyimide-based alignment layers and with optimized anchoring energy for FLC. Background: In the field of liquid crystal technology, ferroelectric liquid crystals (FLCs) are distinguished by their fast electro-optical switching capabilities, enabling advancements in high-resolution and energy-efficient displays. By reducing or eliminating the need for color filters in liquid crystal display (LCD) stacks, FLCs improve display efficiency. Field sequential color (FSC) displays, which rely on fast liquid crystal response times, benefit from the sub-microsecond electro-optical switching of FLCs. Surface-stabilized ferroelectric liquid crystals (SSFLCs) , a significant development in this field, utilize surface boundary conditions to suppress the helical structure, contributing to improved electro-optical performance. Research has established the ferroelectric behavior of liquid crystalline molecules, where chiral units in tilted smectic phases exhibit spontaneous polarization. This arrangement forms a helical structure, allowing for faster reorientation compared to nematic liquid crystals, resulting in significantly improved switching speeds. The introduction of SSFLC electro-optic modes enabled sub-microsecond responses using a homogeneously aligned glass sandwich cell. However, achieving high-contrast, defect-free mono-domain alignment remained challenging. Surface anchoring often led to layer buckling, resulting in chevron and zigzag defects that degraded optical performance. Despite ongoing efforts, optical quality limitations have hindered the commercialization of FLC-based displays. Electrically suppressed helix FLC (ESHFLC) features a shorter helix pitch compared to SSFLC, enabling defect-free mono-domain textures, high contrast, and a saturated electro-optical response at 5V. ESHFLC) maintains microsecond switching speeds essential for FSC displays. Achieving high contrast requires balancing the anchoring and elastic energies of FLC molecules to suppress defects. Unlike SSFLC, which suppresses the helix at the surface, ESHFLC retains its helical structure, preventing zigzag and chevron defects. However, recently, studies on ESHFLC alignment layers highlight limitations in stability and scalability for mass production. Therefore, an industry-compatible alignment layer for ESHFLC is needed, one that can be integrated into display manufacturing processes to overcome alignment challenges and improve production feasibility. Summary of Invention: It is an objective of the present invention to provide devices and methods to address the aforementioned shortcomings and unmet needs in the state of the art. In the present invention, a device for electrically suppressed helix ferroelectric liquid crystal (ESHFLC) and deformed helix FLC (DHFLC) technology is provided, introducing a novel alignment layer and optimization techniques utilizing polyimide through a rubbing process. The concentration of this alignment layer is analyzed alongside surface roughness to address large-scale manufacturing challenges in FLC. A set of process is revealed for tuning the anchoring energy post hard baking, such as thermal annealing, solvent washing and mechanical pressing. By precisely calibrating anchoring and elastic energies, a high contrast ratio is achieved. In contrast to surface stabilized FLC (SSFLC) technology, ESHFLC and DHFLC maintain the helix pitch while balancing anchoring energy, which serves an essential factor for field sequential color displays. This optimized alignment layer solution, directly deployable in display production facilities, offers a pathway for the commercial adoption of ESHFLC and DHFLC technology, enhancing the efficiency and quality of FLC-based display technologies. In accordance with a first aspect of the present invention, a FLC cell is provided. The FLC cell includes an upper substrate, a lower substrate, an upper transparent conductive layer, a lower transparent conductive layer, an upper alignment layer, a lower alignment layer, and a ferroelectric liquid crystal layer (FLC layer) . The upper substrate and the lower substrate are arranged in parallel and spaced apart to define an enclosed region. The upper transparent conductive layer is disposed on an inner surface of the upper substrate. The lower transparent conductive layer is disposed on an inner surface of the lower substrate. The upper alignment layer is disposed on the upper transparent conductive layer. The lower alignment layer is disposed on the lower transparent conductive layer. The FLC layer is positioned between the upper alignment layer and the lower alignment layer. The up