Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-07-30
2003-07-01
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S143000
Reexamination Certificate
active
06587173
ABSTRACT:
The present invention claims the benefit of Korean Patent Application No. P 2000-45924 filed in Korea on Aug. 8, 2000, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device (hereinafter, referred to as LCD), and relates more particularly to a multidomain LCD having a simplified manufacturing process, an improved viewing angle and increased transmissivity.
2. Description of Related Art
When manufacturing LCD devices, the aim is to provide a vivid viewing screen that does not fatigue a user's eyes.
A LCD is comprised of two substrates that face each other with liquid crystal injected between the two substrates. A LCD generally uses a liquid crystal having a twisted nematic (hereinafter, referred to as TN) mode. The liquid crystal has different refractive anisotropy between the light propagating in a direction of the longitudinal axes of liquid crystal molecules (n
11
) and the light propagating in a direction perpendicular to the direction of the longitudinal axes (n
⊥
). This difference results in a viewing angle that is substantially narrow.
Many solutions for addressing the problem of a narrow viewing angle in a LCD have been proposed, examples of which are as follows: a film compensated mode in which a compensating film is provided to compensate for the viewing angle; a multidomain mode in which a pixel is divided into a plurality of domains, so that the main viewing angle on the respective domains is different from each other, thereby increasing the effective viewing angle; a vertical alignment mode in which the alignment of the liquid crystal is in a vertical direction when a voltage is not applied; and an in-plane switching mode in which the liquid crystal molecules are rotated horizontally by using a parallel electric field formed by the two electrodes arranged on a single substrate.
The liquid crystal cells in which the multidomain mode is applied are a domain divided twisted nematic (DDTN) liquid crystal cell, a two-domain twisted nematic (TDTN) liquid crystal cell, a complementary twisted nematic (CTN) liquid crystal cell and a four-domain twisted nematic (FDTN) liquid crystal cell. In the case of a FDTN, the four domains are divided on the unit pixel such that the gray inversion in four directions compensate for each other, thereby providing a broader viewing angle than that of a two-domain liquid crystal cell.
The above-mentioned multidomain modes are achieved by mechanical rubbing or irradiating light on the alignment layers of the two substrates, respectively, to control both a pretilt angle and a pretilt direction so as to control the direction of the liquid crystal. In the case of mechanical rubbing, a photolithography is carried out several times. Whereas in the case of irradiating the light, the light irradiating process has to be carried out several times for each domain using a mask. Both of these process require a complicated manufacturing process.
However, the alignment treatment has not been widely used in recent years. Another method has been developed in which a slit in the electrode formed on the substrate distorts the electric field applied to the liquid crystal layer, such that the direction of the liquid crystal molecules are positioned in a desired direction. Examples of the above method are patterned vertical alignment (hereinafter, referred to as PVA) and lateral field induced vertical alignment (hereinafter, referred to as LFIVA).
The PVA is carried out with a plurality of slits formed by etching the transparent electrodes on both the upper and lower substrates, and thus, the azimuth angle of the alignment of the liquid crystal is determined by a lateral electric field generated at the time when a voltage is applied to pixels. The LFIVA is carried out with a plurality of slits formed in the pixel electrode and with the common electrode rubbed in the longitudinal directions of the slits, such that the electric field formed has horizontal components as well as vertical components.
The formation of the slits requires a patterning process comprising the steps of: forming an electrode film on the whole surface of the substrate; forming a photoresist film on the electrode film; exposing the photoresist film using a mask; etching the exposed photoresist film to form a pattern; and patterning the electrode film by using the patterned photoresist as a mask.
Vertical alignment is made in the LIFVA so that the directions of the longitudinal axes of the liquid crystal molecules are aligned vertically to the substrate surface. In more detail, the liquid crystal having a negative dielectric anisotropy is injected, so that the longitudinal axes of the liquid crystal molecules are disposed vertically on the plane of the alignment layer when no voltage is applied. On the other hand, the liquid crystal molecules move from being vertically disposed on the plane of the alignment layer to being horizontally disposed on the plane of the alignment layer when a voltage over a threshold voltage is applied.
FIG. 1
is a sectional view of related art PVA, and
FIG. 2
is a sectional view of related art LFIVA.
As shown in
FIG. 1
, the conventional PVA comprises first and second substrates
11
and
15
facing each other with a liquid crystal layer
10
formed between the first substrate
11
and second substrate
15
. The first substrate
11
has a black matrix (not shown) for preventing light-leakage, a color filter layer
13
between the black matrixes and a common electrode
14
having a plurality of slits on the color filter layer
13
. The second substrate
15
has a plurality of data lines and gate lines (not shown) arranged perpendicularly to one another that define a plurality of pixel areas. Each of the pixel areas has a thin film transistor (not shown) with a gate electrode, a gate insulation film
16
, a semiconductor layer, a source electrode and a drain electrode. At the cross point of the data lines and gate lines, a protective film
17
is formed on the whole surface of the thin film transistor, and a pixel electrode
18
is connected to the drain electrode of the thin film transistor on the protective film
17
. The pixel electrode
18
has a plurality of slits
19
.
Specifically, the plurality of slits in the common electrode
14
and the pixel electrode
18
, each respectively require a patterning process.
In more detail, the first substrate
11
and second substrate
15
are first prepared. The gate lines and the gate electrode (not shown) are formed on the second substrate
15
. Then, the gate insulation film
16
is formed on the gate electrode of the second substrate
15
. Thereafter, a semiconductor layer (not shown) is formed on the gate insulation film
16
and subsequently the data lines are formed perpendicularly to the gate lines. At the same time, the source/drain electrodes (not shown) are formed on the semiconductor layer.
The gate lines, gate electrode, data lines and source/drain electrodes are formed of a metal having a low resistance, such as Cu, Al and Mo or an Al alloy, by sputtering and patterning. The gate insulation film
16
is formed of an inorganic material having an excellent adhesion with the above metal and a high insulation internal pressure, such as SiNx, SiOx, etc., by plasma enhanced chemical vapor deposition (PECVD).
Next, the protective film
17
of SiNx, SiOx or Benzocyclobutene (BCB) having a low dielectric constant is formed on the whole surface of the laminated layer. Then, the protective film
17
is selectively removed to expose a predetermined portion of the drain electrode to form a contact hole. Subsequently, the pixel electrode
18
made of a transparent conductive material, is formed on the protective film
17
and is electrically connected to the drain electrode through the contact hole.
Thereafter, the photoresist (not shown) is applied on the pixel electrode
18
and is patterned using photolithography. Then, the pixel electrode
18
is selectively etched using the photoresist pattern as a
Yoo Jang Jin
Yoon Ki Hyuk
Di Grazio Jeanne
G. Philips LCD Co., Ltd.
Kim Robert H.
Morgan & Lewis & Bockius, LLP
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