Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-01-27
2002-03-12
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S117000, C349S123000, C349S128000, C349S132000
Reexamination Certificate
active
06356329
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an in-plane switching liquid crystal display apparatus obtained by adhering two substrates, at least one of which comprise electrodes of comb-like shape, together and enclosing liquid crystal therebetween. More particularly, the present invention relates to a liquid crystal display apparatus which can restrict variations in display property such as color changes or the like depending on visual angles.
Liquid crystal display apparatuses are being widely used in watches or electronic desk calculators due to their properties of being, for instance, thin-sized, light-weighted and of consuming low electricity. Especially TN (twisted nematic) liquid crystal display apparatuses which perform active driving through, for instance, TFTs (thin film transistors) are gradually replacing CRTs which are display apparatuses of word processors or personal computers. However, such a TN liquid crystal display apparatus presents a drawback in view of display quality in that reversals of tones are generated with respect to certain visual angles arid contrast values thus change. For the aim of improving the reliability of display quality on visual angles, it has been tried in Japanese Unexamined Patent Publication 76125/1996 to expand the visual angle by dividing display pixels into multiple regions. However, the region of visual angles in which reversals of tunes did not occur was only as large as ±40° to lateral directions and −20° to +10° in vertical directions, and thus insufficient for actual use.
There are recently being suggested in-plane switching liquid crystal display apparatuses which completely differ from TN type liquid crystal display apparatuses in their driving methods, examples of which are disclosed in “Nikkei Micro Devices” by Nikkei BP, December 1995 edition, P.130 to 135, or in “Collection of Preliminary Drafts of the Semicom Kansai 96 FPD Technical Seminar” by SEMI Japan, May 30, 1996, P. 3 to 23, 3 to 27 and P. 4 to 19, 4 to 21. Since liquid crystal molecules are to be switched to an electric field in a plane parallel with respect to the substrate, there are fewer variations in display property depending on visual angles than compared to TN liquid crystal display apparatuses and thus are of favorable display property.
FIG. 13
is a partial explanatory view of a conventional in-plane switching liquid crystal display apparatus which is formed by using liquid crystal which are of positive dielectric anisotropy. In
FIG. 13
, there are shown, from among components of the liquid crystal display apparatus, an electrodes substrate, two types of comb-like shaped electrodes (hereinafter referred to as “comb-like electrodes”) formed on the electrodes substrate, and liquid crystal molecules (only four of those are shown in the drawings) which are included in the counter substrate and a liquid crystal layer, which together constitute a liquid crystal panel. As shown in
FIG. 13
, the electrodes substrate
2
with the comb-like electrodes
1
is disposed parallel to counter substrate
3
, and between the electrodes substrate
2
and the counter substrate
3
, there exists a liquid crystal layer including liquid crystal molecules
4
which are oriented substantially in parallel directions with respect to a longitudinal direction of the comb-like portions of the comb-like electrodes
1
.
Next, the display theory of the liquid crystal display apparatus will be explained based on FIG.
14
.
FIG. 14
is a partial explanatory view showing the in-plane switching liquid crystal display apparatus. In
FIG. 14
, there are only shown a liquid crystal panel and two polarizers from among components of the liquid crystal display apparatus, and of the liquid crystal panel, there are only shown an electrodes substrate, respective comb-teeth portions of two types of comb-like electrodes (one each of each comb-teeth portion), a counter substrate, and liquid crystal molecules (only seven of these are shown in the drawings) included in the liquid crystal layer. In
FIG. 14
, numeral la denotes a first comb-like electrode,
1
b
a second comb-like electrode, numeral
2
an electrodes substrate, numeral
3
a counter substrate, numeral
4
liquid crystal molecules in the liquid crystal layer, numeral
5
a first polarizer, arid numeral
6
a second polarizer. As shown in the drawings, the first polarizer
5
is disposed such that a longitudinal direction of the liquid crystal molecules
4
(a direction indicated by “N” in the drawings) is parallel to a transmission axis O of the first polarizer
5
, and the second polarizer
6
is disposed such that a transmission axis P of the second polarizer
6
is orthogonal with respect to the transmission axis O of the first polarizer
5
. It should be noted that the aligning direction (a direction indicated by “Q” in the drawings) of alignment layers (not shown) formed on surfaces of the electrodes substrate
2
and the counter, substrate
3
are parallel with respect to transmission axes O, P of the first polarizer
5
and the second polarizer. The thickness of the liquid crystal layer is defined as d. Further, the transmission axes are parallel with respect to an oscillating direction of light that has passed through the polarizer.
In case the electric field is OFF (that is, no electric field is generated between the first comb-like electrode
1
a
and the second comb-like electrode
1
b
), the oscillating direction of an incident linear polarized light, that has passed through the first polarizer
5
, is parallel to the aligning direction of the liquid crystal molecules, and since it is not affected by birefringence at the time of passing through the liquid crystal layer, the oscillating direction R
1
of light passing through the counter substrate
3
is made orthogonal to the transmission axis P of the second polarizer
6
, and light that has passed through the counter substrate
3
being impossible of passing through the polarizer
6
, a dark condition is obtained. It should be noted that since no outgoing transmission light exists in dark conditions, arrow I
1
is indicated as a broken line in the drawings.
In case the electric field is ON (that is, an electric field
1
c
is generated between the first comb-like electrode la and the second comb-like electrode
1
b
), the liquid crystal molecules
4
rotate in a direction of the electric field (note that the degree of rotation depends on the size of the electric field) while maintaining a parallel orientation (or alignment) with respect to the electrodes substrate
2
and the counter substrate
3
. Therefore, the incident linear polarized light is affected by birefringence, changes into an elliptical polarization R
2
, and a predetermined amount of light passes through the second polarizer
6
. It should be noted that the amount of light passing through the second polarizer
6
is dependent on inclinations of liquid crystal molecules in a longitudinal direction (a direction indicated by “T” in the drawings). Here, the rotating angle &thgr; is expressed by applied voltage (V). In this manner, display is performed by performing ON/OFF operations of applied voltage to the first comb-like electrode and the second comb-like electrode.
The strength of transmission light I is given by equation (1).
I=I
0
sin
2
(&pgr;R/&lgr;)sin
2
2&thgr;(V) (1)
where I
0
represents the strength of incident light to the first polarizer
5
, &lgr; a wavelength of incident light, and R retardation which is expressed by optical-path difference of ordinary light and extraordinary light (&Dgr;n) ·d, where &Dgr;n is an absolute value (|no-ne|) of a difference between a refractive index of ordinary light no and refractive index of extraordinary light ne of liquid crystal.
As it is evident from equation (1), intensity of the transmission light becomes maximum when &thgr;=&pgr;/4. Further, intensity of the transmission light outgoing from the second polarizer
6
is expressed by a function of a wavelength of incident light &lg
Fujii Masayuki
Fujita Yasuo
Matsukawa Fumio
Mizunuma Masaya
Morii Yasuhiro
Chowdhury Tarifur R.
Sikes William L.
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