Vertically aligned nematic mode liquid crystal display having large tilt angles and high contrast

A reflective liquid crystal display, comprising:

• a first substrate that is substantially transparent;
• a second substrate that is substantially reflective and substantially parallel with said first substrate;
• and
• a liquid crystal fluid having a birefringence (Δn) and a negative dielectric anisotropy, wherein said liquid crystal fluid is between said first and second substrates;
• said first substrate having a first liquid crystal alignment layer proximate to said liquid crystal fluid, wherein molecules of said liquid crystal fluid that are proximate to the first liquid crystal alignment layer have a first pretilt angle from about 2 degrees to about 15 degrees and a first azimuthal direction;
• said second substrate having a second liquid crystal alignment layer proximate to said liquid crystal fluid, wherein molecules of said liquid crystal fluid that are proximate to the second liquid crystal alignment layer have a second pretilt angle from about 2 degrees to about 15 degrees and a second azimuthal direction, the second azimuthal direction being substantially perpendicular to the first azimuthal direction;
• wherein:
• when an electric field is applied between said first and second substrates, a substantial number of the molecules of said liquid crystal fluid increase their tilt angles, and
• when substantially no electric field is applied between said first and second substrates, a substantial number of the molecules of said liquid crystal fluid have their azimuthal direction substantially perpendicular to said first and second substrates;
• whereby when the electric field is applied between said first and second substrates, said liquid crystal fluid changes linear polarized incident light at said first substrate to approximately circularly polarized incident light when at said second substrate, wherein said second substrate reflects back the approximately circularly polarized incident light as approximately circularly polarized light of opposite handedness, wherein said liquid crystal fluid changes the approximately circularly polarized reflected light to approximately linear polarized reflected light when at said first substrate such that the polarization directions of the linearly polarized incident light and the linearly polarized reflected light at said first substrate are approximately perpendicular, and
• whereby when substantially no electric field is applied between said first and second substrates, said liquid crystal fluid does not substantially change the polarization of light passing through the liquid crystal fluid and the polarization directions of the linearly polarized incident light and the linearly polarized reflected light at said first substrate are approximately parallel.

A method for a reflective liquid crystal display, said method comprising the steps of:

• providing a first substrate that is substantially transparent;
• providing a second substrate that is substantially reflective and substantially parallel with said first substrate;
• and
• providing a liquid crystal fluid having a birefringence (Δn) and a negative dielectric anisotropy between said first and second substrates;
• providing a first liquid crystal alignment layer on said first substrate, said first liquid crystal alignment layer being proximate to said liquid crystal fluid, wherein molecules of said liquid crystal fluid that are proximate to the first liquid crystal alignment layer have a first pretilt angle from about 2 degrees to about 15 degrees and a first azimuthal direction;
• providing a second liquid crystal alignment layer on said second substrate, said second liquid crystal alignment layer being proximate to said liquid crystal fluid, wherein molecules of said liquid crystal fluid that are proximate to the second liquid crystal alignment layer have a second pretilt angle from about 2 degrees to about 15 degrees and a second azimuthal direction, the second azimuthal direction being substantially perpendicular to the first azimuthal direction;
• such that
• when substantially no electric field is applied between said first and second substrates, said liquid crystal fluid does not change the polarization state of light passing therethrough and the polarization directions of the linearly polarized incident light and the linearly polarized reflected light at said first substrate are substantially parallel,
• when applying an electric field of an optimum value between said first and second substrates, said liquid crystal fluid changes linear polarized incident light at said first substrate to approximately circularly polarized incident light when at said second substrate, wherein said second substrate reflects back the approximately circularly polarized incident light as approximately circularly polarized light of opposite handedness, wherein said liquid crystal fluid changes the approximately circularly polarized reflected light to approximately linear polarized reflected light when at said first substrate such that the polarization directions of the linearly polarized incident light and the linearly polarized reflected light at said first substrate are approximately perpendicular, and
• when applying an electric field less than the optimum value between said first and second substrates, said liquid crystal fluid changes the polarization state of the incident linearly polarized light to elliptically polarized light upon passing through said liquid crystal fluid and being reflected back from said second substrate.

A method for a reflective liquid crystal display, said method comprising the steps of:

• providing a first substrate that is substantially transparent;
• providing a second substrate that is substantially reflective and substantially parallel with said first substrate;
• and
• providing a liquid crystal fluid having a birefringence (Δn) and a negative dielectric anisotropy, wherein said liquid crystal fluid is between said first and second substrates;
• providing a first liquid crystal alignment layer on said first substrate, said first liquid crystal alignment layer being proximate to said liquid crystal fluid, wherein molecules of said liquid crystal fluid that are proximate to the first liquid crystal alignment layer have a first pretilt angle from about 2 degrees to about 15 degrees and a first azimuthal direction;
• providing a second liquid crystal alignment layer on said second substrate, said second liquid crystal alignment layer being proximate to said liquid crystal fluid, wherein molecules of said liquid crystal fluid that are proximate to the second liquid crystal alignment layer have a second pretilt angle from about 2 degrees to about 15 degrees and a second azimuthal direction, the second azimuthal direction being substantially perpendicular to the first azimuthal direction;
• wherein:
• when applying substantially no electric field between said first and second substrates, a substantial number of the molecules of said liquid crystal fluid have their azimuthal direction substantially perpendicular to said first and second substrates;
• and
• when applying an electric field between said first and second substrates, a substantial number of the molecules of said liquid crystal fluid increase their tilt angles;
• whereby when applying the electric field between said first and second substrates, said liquid crystal fluid changes linear polarized incident light at said first substrate to approximately circularly polarized incident light when at said second substrate, wherein said second substrate reflects back the approximately circularly polarized incident light as approximately circularly polarized light of opposite handedness, wherein said liquid crystal fluid changes the approximately circularly polarized reflected light to approximately linear polarized reflected light when at said first substrate such that the polarization directions of the linearly polarized incident light and the linearly polarized reflected light at said first substrate are approximately perpendicular, and
• whereby when applying substantially no electric field between said first and second substrates, said liquid crystal fluid does not substantially change the polarization state of light passing through said liquid crystal fluid such that the polarization directions of the linearly polarized incident light and the linearly polarized reflected light at said first substrate are approximately parallel.

A reflective liquid crystal display assembly comprising:

• a first substantially transparent substrate;
• a second substantially reflective substrate located substantially parallel to said first substrate;
• a liquid crystal fluid having a birefringence (Δn) and a negative dielectric anisotropy, wherein said liquid crystal fluid is between said first and second substrates;
• first and second liquid crystal alignment layers on said first and second substrates, respectively, wherein molecules of said fluid proximate the first and second liquid crystal alignment layers have finite pretilt angles and are oriented in first and second azimuthal directions, respectively;
• wherein the assembly is configured such that (i) when substantially no electric field is applied between the substrates, a substantial number of fluid molecules are oriented substantially perpendicular to said substrates, (ii) when an electrical field of optimum value is applied between the substrates, tilt angles of a substantial number of fluid molecules increase, and (iii) when a less than optimum electric field is applied between said substrates, a substantial number of fluid molecules are oriented at intermediate tilt angles.