Transflective liquid crystal display with particular first and second adjusted thickness and method of fabricating the same

• US 6,917,404 B2
• Filed: 10/28/2003
• Issued: 07/12/2005
• Est. Priority Date: 05/08/2000
• Status: Expired due to Term

• Current Assignee: LG Display Co., Ltd.
• Original Assignee: LG Philips LCD Company Limited (LG Display Co., Ltd.)
• Inventors: Baek, Heum-ll
• Primary Examiner(s): Font, Frank G.
• Assistant Examiner(s): Rude, Timothy L.
• Application Number:
  US10/694,217
• Publication Number:
  US 20040085499A1
• Time in Patent Office: 623 Days
• Field of Search: 349/114, 349/113, 349/119
• US Class Current: 349/114
• CPC Class Codes: G02F 1/133371 Cells with varying thickness of the liquid crystal layer
• CPC Class Codes: G02F 1/13363 Birefringent elements, e.g. for optical compensation
• CPC Class Codes: G02F 1/133638 Waveplates, i.e. plates with a retardation value of lambda/n
• CPC Class Codes: G02F 1/1393 the birefringence of the liquid crystal being electrically controlled, e.g. ECB-, DAP-, HAN-, PI-LC cells G02F1/1396, G02F1/141 take precedence
• CPC Class Codes: G02F 2202/40 Materials having a particular birefringence, retardation
• CPC Class Codes: G02F 2203/09 transflective
• CPC Class Codes: G02F 2413/04 Number of plates greater than or equal to 4
• CPC Class Codes: G02F 2413/08 with a particular optical axis orientation

Abstract

The invention relates to a transflective liquid crystal display device that has a high contrast ratio. The transflective liquid crystal panel includes a homogeneous liquid crystal such that the transflective liquid crystal display device will have an optical retardation when the voltage is applied. Therefore, in order to compensate the optical retardation caused by this liquid crystal, a thickness of the liquid crystal layer is adjusted. Moreover, a thickness of the retardation film is also adjusted. Accordingly, the complete dark state and the high contrast ratio are achieved in the liquid crystal display.

Claims

1. A transflective liquid crystal display, comprising:

upper and lower substrates facing into and spaced apart from each other, wherein the upper and lower substrates include a plurality of pixel regions that display images;

a liquid crystal layer interposed between the upper and lower substrates, wherein the liquid crystal layer has a first adjusted thickness to compensate a residual optical retardation of incident light caused by anchored liquid crystals near an alignment layer when a maximum operation voltage is applied;

an upper quarter wave plate (QWP) on the upper substrate, wherein the upper quarter wave plate has a second adjusted thickness to compensate the residual optical retardation caused by the liquid crystal layer when the maximum operation voltage is applied;

an upper polarizer on the upper quarter wave plate;

a transparent common electrode on a surface of the upper substrate facing into the lower substrate;

a pixel electrode over a first surface of the lower substrate, wherein the pixel electrode corresponds to each pixel region, and the pixel electrode is divided into transparent and reflective portions;

a lower quarter wave plate (QWP) on a second surface of the lower substrate;

a lower polarizer below the lower quarter wave plate; and

a backlight device arranged to be adjacent to the lower polarizer, wherein the first adjusted thickness is d+d₁, where d is a normal thickness of the liquid crystal layer and d₁ is calculated using the following equation. $T={\mathrm{Sin}}^2<br><br>2<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\varphi <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{Sin}}^2<br><br>\left[\frac{\mathrm{\pi <br><br>}·<br><br>\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>n·<br><br>d_1}{\mathrm{\lambda <br><br>}}\right],$

where T is a value of transmittance when a maximum operation voltage is applied, φ

is an angle between an optical axis of the liquid crystal layer and a transmissive axis of the polarizer, Δ

n is a birefringence of the liquid crystal layer.

2. The transflective liquid crystal display according to 1, wherein the transparent portion of the pixel electrode includes a transparent electrode being disposed on a surface of the lower substrate facing into the upper substrate.

3. The transflective liquid crystal display according to claim 2, further comprising a passivation layer on the transparent electrode.

4. The transflective liquid crystal display according to claim 3, wherein the reflective portion of the pixel electrode includes a reflective electrode.

5. The transflective liquid crystal display according to claim 4, wherein the reflective electrode is disposed on the passivation layer and has a transmitting hole in a central portion.

6. The transflective liquid crystal display according to claim 1, wherein φ

is about 45 degrees.

7. The transflective liquid crystal display according to claim 1, wherein a slow axis of the lower QWP is perpendicular to that of the upper QWP.

8. The transflective liquid crystal display according to claim 1, wherein the liquid crystal layer includes a homogeneous liquid crystal that is arranged in a vertical direction when a voltage is applied.

9. The transflective liquid crystal display according to claim 1, wherein the optical axis of the liquid crystal layer is parallel to the slow axis of the lower QWP.

10. A transflective liquid crystal display, comprising:

upper and lower substrates facing into and spaced apart from each other, wherein the upper and lower substrates include a plurality of pixel regions that display images;

a liquid crystal layer interposed between the upper and lower substrates, wherein the liquid crystal layer has a first adjusted thickness to compensate a residual optical retardation of incident light caused by anchored liquid crystals near an alignment layer when a maximum operation voltage is applied;

an upper quarter wave plate (QWP) on the upper substrate, wherein the upper quarter wave plate has a second adjusted thickness to compensate the residual optical retardation caused by the liquid crystal layer when the maximum operation voltage is applied;

an upper polarizer on the upper quarter wave plate;

a transparent common electrode on a surface of the upper substrate facing into the lower substrate;

a pixel electrode over a first surface of the lower substrate, wherein the pixel electrode corresponds to each pixel region, and the pixel electrode is divided into transparent and reflective portions;

a lower quarter wave plate (QWP) on a second surface of the lower substrate;

a lower polarizer below the lower quarter wave plate; and

a backlight device arranged to be adjacent to the lower polarizer, wherein the second adjusted thickness of the upper QWP is d+d₂, where a normal thickness of the upper QWP is d and d₂ is calculated from the following equation, $T={\mathrm{Sin}}^2<br><br>2<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\varphi <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{Sin}}^2<br><br>\left[\frac{\mathrm{\pi <br><br>}·<br><br>\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>n·<br><br>d_2}{\mathrm{\lambda <br><br>}}\right],$

where T is a value of transmittance, φ

is an angle between a slow axis of the upper QWP and a transmissive axis of the polarizer, Δ

n is a birefringence of the upper QWP.

11. The transflective liquid crystal display according to claim 10, wherein φ

is about 45 degrees.

12. A transflective liquid crystal display, comprising:

upper and lower substrates facing into and spaced apart from each other, wherein the upper and lower substrates include a plurality of pixel regions that display images;

an upper quarter wave plate (QWP) on the upper substrate;

an upper polarizer on the upper quarter wave plate;

a lower quarter wave plate (QWP) below the lower substrate;

a lower polarizer below the lower quarter wave plate;

a backlight device arranged to be adjacent to the lower polarizer;

a liquid crystal layer interposed between the upper and lower substrates;

a transparent common electrode on a surface of the upper substrate facing into the lower substrate;

an upper alignment layer between the transparent common electrode and the liquid crystal layer;

a pixel electrode over the lower substrate, wherein the pixel electrode corresponds to each pixel region, and the pixel electrode is divided into transparent and reflective portions; and

a lower alignment layer between the pixel electrode and the liquid crystal layer;

wherein a transmissive axis of the upper polarizer is perpendicular to a transmissive axis of the lower polarizer, a slow axis of the upper QWP is perpendicular to a slow axis of the lower QWP, the slow axis of the upper QWP forms an angle of 45°

with the transmissive axis of the upper polarizer, an optical retardation of the upper QWP is λ

d/4+α

, α

a ranges from zero to 100 nm, and the slow axis of the lower QWP is parallel to an orientation direction of the liquid crystal display layer, and wherein the first adjusted thickness is d+d₁, where d is a normal thickness of the liquid crystal layer and d₁ is calculated using the following equation. $T={\mathrm{Sin}}^2<br><br>2<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\varphi <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{Sin}}^2<br><br>\left[\frac{\mathrm{\pi <br><br>}·<br><br>\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>n·<br><br>d_1}{\mathrm{\lambda <br><br>}}\right],$

where T is a value of transmittance when a maximum operation voltage is applied, φ

is an angle between an optical axis of the liquid crystal layer and a transmissive axis of the polarizer, Δ

n is a birefringence of the liquid crystal layer.

13. The transflective liquid crystal display according to claim 12, wherein an optical retardation of the liquid crystal layer is λ

/4+α

.

14. The transflective liquid crystal display according to claim 12, wherein an optimum value of α

for adjusting the optical retardation ranges from zero to 50 nm.