U.S. patent application number 15/088174 was filed with the patent office on 2016-07-28 for light-emitting element unit and display device.
The applicant listed for this patent is SEMICONDUCTOR ENERGY LABORATORY CO., LTD.. Invention is credited to Yoshiharu HIRAKATA, Shunpei YAMAZAKI.
Application Number | 20160218258 15/088174 |
Document ID | / |
Family ID | 45972748 |
Filed Date | 2016-07-28 |
United States Patent
Application |
20160218258 |
Kind Code |
A1 |
YAMAZAKI; Shunpei ; et
al. |
July 28, 2016 |
LIGHT-EMITTING ELEMENT UNIT AND DISPLAY DEVICE
Abstract
A light-emitting element unit which can improve color purity of
light emitted from a color filter is provided. A display device
with high color purity and high color reproducibility is provided.
The light-emitting element unit includes a wiring board, a
light-emitting element chip provided over the wiring board, a micro
optical resonator provided over the wiring board and at the
periphery of the light-emitting element chip, and a phosphor layer
covering the light-emitting element chip and the micro optical
resonator. The display device includes a display panel having a
coloring layer and a backlight module having the light-emitting
element unit. Examples of the display panel include: a liquid
crystal panel; and a display panel including an opening portion
provided over a first substrate, MEMS moving over the opening
portion in the lateral direction, and a second substrate provided
with a coloring layer in a portion corresponding to the opening
portion.
Inventors: |
YAMAZAKI; Shunpei; (Tokyo,
JP) ; HIRAKATA; Yoshiharu; (Ebina, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SEMICONDUCTOR ENERGY LABORATORY CO., LTD. |
Atsugi-shi |
|
JP |
|
|
Family ID: |
45972748 |
Appl. No.: |
15/088174 |
Filed: |
April 1, 2016 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
13277417 |
Oct 20, 2011 |
9306129 |
|
|
15088174 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 25/0753 20130101;
H01L 2924/3025 20130101; H01L 33/54 20130101; H01L 33/486 20130101;
H01L 2924/07811 20130101; G02F 1/133603 20130101; H01L 2924/1461
20130101; H01L 2224/48227 20130101; H01L 33/62 20130101; H01L
2224/48465 20130101; H01L 33/465 20130101; H01L 2224/48227
20130101; H01L 33/56 20130101; H01L 2924/00 20130101; H01L 2924/00
20130101; H01L 2924/00 20130101; H01L 2924/00 20130101; H01L
2924/07811 20130101; G02F 1/133514 20130101; H01L 2924/1461
20130101; G02F 1/133621 20130101; H01L 2924/3025 20130101; H01L
33/50 20130101; H01L 2224/48465 20130101; H01L 33/505 20130101 |
International
Class: |
H01L 33/50 20060101
H01L033/50; H01L 33/46 20060101 H01L033/46; G02F 1/1335 20060101
G02F001/1335; H01L 33/54 20060101 H01L033/54; H01L 25/075 20060101
H01L025/075; H01L 33/62 20060101 H01L033/62; H01L 33/56 20060101
H01L033/56 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 25, 2010 |
JP |
2010-238723 |
Claims
1. A display device comprising: a first substrate; a second
substrate opposite to the first substrate; a first reflective layer
provided over the first substrate, the first reflective layer
including an opening portion; a microstructure provided over the
first reflective layer corresponding to the opening portion, the
microstructure including a shutter; a transistor connected to the
microstructure; a coloring layer provided on the second substrate
facing to the opening portion; and a backlight module, wherein the
backlight module comprises a light-emitting element unit, the
light-emitting element unit comprising: a wiring board; a
light-emitting element chip provided over the wiring board; a micro
optical resonator provided at a periphery of the light-emitting
element chip; and a phosphor layer at least covering the
light-emitting element chip, and wherein the microstructure is a
movable structure.
2. The display device according to claim 1, wherein the
microstructure comprises a first movable electrode connected to one
side of the shutter, a second movable electrode provided near the
first movable electrode, and a spring connected to the other side
of the shutter.
3. The display device according to claim 2, wherein the first
movable electrode and the spring are electrically connected to a
common electrode or a ground electrode, and wherein the second
movable electrode is electrically connected to the transistor.
4. The display device according to claim 1, wherein the
microstructure moves in a direction parallel to a surface of the
first substrate.
5. The display device according to claim 1, wherein the micro
optical resonator comprises a second reflective layer, a
semi-transmissive semi-reflective layer facing the second
reflective layer, and a light-transmitting layer provided between
the second reflective layer and the semi-transmissive
semi-reflective layer.
6. The display device according to claim 5, wherein a light path
length L between the second reflective layer and the
semi-transmissive semi-reflective layer is represented by a
formula, L=(2m+1).lamda./4n, and wherein in the formula, the m
indicates an integer, the .lamda. indicates a wavelength, and the n
indicates a refractive index of the light-transmitting layer.
7. The display device according to claim 6, wherein the .lamda. is
430 nm to 490 nm.
8. The display device according to claim 6, wherein the .lamda. is
490 nm to 550 nm.
9. The display device according to claim 6, wherein the .lamda. is
550 nm to 590 nm.
10. The display device according to claim 6, wherein the .lamda. is
640 nm to 770 nm.
11. The display device according to claim 5, wherein the
light-transmitting layer comprises a plurality of layers which are
stacked.
12. The display device according to claim 1, wherein the phosphor
layer covers the micro optical resonator.
13. The display device according to claim 1, further comprising an
organic resin layer covering the phosphor layer, wherein the
organic resin layer transmits a light, and wherein a shape of the
organic resin layer is a convex shape.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a light-emitting element
unit, a backlight including a plurality of the light-emitting
element units, and a display device including the backlight.
[0003] 2. Description of the Related Art
[0004] As a backlight of a liquid crystal display device, a cold
cathode fluorescent lamp has been used. However, in recent years, a
light-emitting diode (LED) unit with less power consumption has
come into use instead of the cold cathode fluorescent lamp, because
the cold cathode fluorescent lamp requires more power consumption
in comparison to the light-emitting diode (see Patent Document
1).
[0005] The light-emitting diode which has been recently used has a
structure in which a phosphor is provided over an LED chip emitting
blue light, the phosphor is excited by the blue light to provide
yellow light, and then white light is emitted by mixing the yellow
light and the blue light.
[0006] Further, there is a backlight which emits white light by
mixing light emitted from a red-light-emitting diode, light emitted
from a blue-light-emitting diode, and light emitted from a
green-light-emitting diode.
REFERENCE
[0007] [Patent Document 1] Japanese Published Patent Application
No. 2004-240412
SUMMARY OF THE INVENTION
[0008] An emission spectrum of light from the light-emitting diode
in which a phosphor is provided over an LED chip emitting blue
light has high emission intensity at a wavelength of 450 nm
exhibiting blue and has a peak at a wavelength of 550 nm exhibiting
green. However, the intensity of the peak at the wavelength of 550
nm exhibiting green is lower than that of the peak at the
wavelength of 450 nm exhibiting blue. In addition, at a wavelength
of 700 nm exhibiting red, there is no peak and the intensity is
low.
[0009] Thus, when white light emitted from the light-emitting diode
in which a phosphor is provided over an LED chip emitting blue
light is transmitted through a color filter, the light transmitted
through the color filter has low color purity of green light and
red light. Therefore, color purity of light emitted from a display
device is reduced, which causes a problem of low color
reproducibility.
[0010] In the case where white light is emitted by using a
red-light-emitting diode, a blue-light-emitting diode, and a
green-light-emitting diode as backlights, the number of components
is increased, and it is a factor contributing to increase in
cost.
[0011] Thus, an object of one embodiment of the present invention
is to provide a light-emitting element unit which enables increase
in color purity of light emitted through a color filter, and a
backlight in which the light-emitting element unit is incorporated.
Further, an object of one embodiment of the present invention is to
provide a display device with high color purity and high color
reproducibility.
[0012] One embodiment of the present invention is a light-emitting
element unit including a wiring board, a light-emitting element
chip provided over the wiring board, a micro optical resonator
provided over the wiring board and at the periphery of the
light-emitting element chip, and a phosphor layer covering the
light-emitting element chip and the micro optical resonator. Note
that in the light-emitting element unit, an organic resin layer
which has a convex shape and a light-transmitting property
(hereinafter referred to as a light-transmitting convex organic
resin layer) may be provided to cover the phosphor layer.
[0013] The micro optical resonator includes, over a substrate, a
reflective layer, a layer having semi-transmissive and
semi-reflective properties (hereinafter referred to as a
semi-transmissive reflective layer), and a light-transmitting layer
provided between the reflective layer and the semi-transmissive
semi-reflective layer. The reflective layer and the
semi-transmissive semi-reflective layer are provided at a distance
from one another so that light at a predetermined wavelength is
reflected and interferes between the two layers to increase the
peak intensity. That is, light emitted from the light-emitting
element chip is reflected at the phosphor layer to become white
light, and then the white light is reflected and interferes in the
micro optical resonator, and thereby is emitted as light at a
predetermined wavelength. Thus, the light-emitting element unit
according to one embodiment of the present invention can emit white
light with increased peak intensity at a predetermined wavelength.
When the white light passes through a coloring layer of a color to
which the above peak corresponds, light of a color with high color
purity is produced.
[0014] Further, another embodiment of the present invention is a
display device which includes a display panel having a coloring
layer, and the above-described light-emitting element unit provided
in a backlight module. Examples of the display panel having a
coloring layer includes: a liquid crystal panel; and a display
panel which includes an opening portion provided over a first
substrate, MEMS moving over the opening portion in the lateral
direction, and a second substrate provided with a coloring layer in
a portion corresponding to the opening portion.
[0015] The backlight module including the light-emitting element
unit emits white light having a peak of a wavelength corresponding
to a color of the coloring layer; thus, light transmitted through
the coloring layer in the display panel has high color purity.
Therefore, the color reproducibility of the display device can be
improved.
[0016] According to one embodiment of the present invention, a
micro optical resonator is provided at the periphery of an LED
chip, whereby a light-emitting element unit which enables an
increase in color purity of light transmitted through a color
filter, and a backlight can be provided. Furthermore, according to
one embodiment of the present invention, a display device with high
color purity and high color reproducibility can be provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIGS. 1A and 1B are a cross-sectional view and a top view
illustrating a light-emitting element unit according to the present
invention.
[0018] FIGS. 2A-1, 2A-2, 2B, and 2C illustrate a light-emitting
element unit according to the present invention.
[0019] FIG. 3 is a perspective view illustrating a backlight module
according to the present invention.
[0020] FIG. 4 is a cross-sectional view illustrating a backlight
module according to the present invention.
[0021] FIG. 5 is a cross-sectional view illustrating a backlight
module according to the present invention.
[0022] FIGS. 6A and 6B are a block diagram and a circuit diagram
illustrating a display device according to the present
invention.
[0023] FIGS. 7A and 7B are cross-sectional views each illustrating
a display device according to the present invention.
[0024] FIG. 8 is a cross-sectional view illustrating a display
device according to the present invention.
[0025] FIGS. 9A and 9B are top views each illustrating a backlight
module according to the present invention.
[0026] FIGS. 10A and 10B are a top view and a cross-sectional view
illustrating a display device according to the present
invention.
[0027] FIGS. 11A and 11B are a top view and a cross-sectional view
illustrating a display device according to the present
invention.
[0028] FIG. 12 is a cross-sectional view illustrating a display
device according to the present invention.
[0029] FIG. 13 is a perspective view illustrating a MEMS switch of
a display device according to the present invention.
[0030] FIG. 14 is a circuit diagram illustrating a display device
according to the present invention.
[0031] FIGS. 15A and 15B illustrate an example of a television
device and an example of digital signage, respectively.
DETAILED DESCRIPTION OF THE INVENTION
[0032] Hereinafter, embodiments of the present invention will be
described with reference to drawings. However, the present
invention is not limited to the following description. It is easily
understood by those skilled in the art that the mode and detail can
be variously changed unless departing from the scope and spirit of
the present invention. Therefore, the present invention should not
be interpreted as being limited to the description of the
embodiments to be given below. Note that reference numerals
denoting the same portions are commonly used in different
drawings.
Embodiment 1
[0033] In this embodiment, an LED unit and a backlight which
consume less power will be described with reference to FIGS. 1A and
1B and FIGS. 2A-1, 2A-2, 2B, and 2C.
[0034] FIG. 1A is a cross-sectional view of an LED unit 30.
[0035] The LED unit 30 includes a light-emitting element chip
(hereinafter, referred to as an LED chip 33) provided over a wiring
board 31, a phosphor layer 35 provided over the LED chip 33, and a
light-transmitting convex organic resin layer 37 provided to cover
the wiring board 31 and the phosphor layer 35. An electrode of the
LED chip 33 is electrically connected to terminals 41a and 41b
provided on side walls of the wiring board 31 through wirings 39a
and 39b.
[0036] FIG. 1B is a top view of the LED chip 33 illustrated in FIG.
1A from which the light-transmitting convex organic resin layer 37
is excluded. As illustrated in FIG. 1B, there is a feature in that
a micro optical resonator 43 is provided around the LED chip 33.
The micro optical resonator 43 is an element which can make white
light change into colored light at a predetermined wavelength.
[0037] For the wiring board 31, a glass epoxy resin substrate, a
polyimide substrate, a ceramic substrate, an alumina substrate, an
aluminum nitride substrate, or the like is used.
[0038] For the LED chip 33, a light-emitting diode which can emit
blue light is used. As the typical light-emitting diode which can
emit blue light, a diode formed using a nitride(Group III)-based
compound semiconductor is used, and examples thereof include a
diode including a GaN-based material which is represented by a
formula, In.sub.xAl.sub.yGa.sub.1-x-yN (x is greater than or equal
to 0 and less than or equal to 1, y is greater than or equal to 0
and less than or equal to 1, and "x+y" is greater than or equal to
0 and less than or equal to 1).
[0039] Typical examples of the phosphor layer 35 include an organic
resin layer having a surface on which a phosphor is printed, an
organic resin layer whose surface is coated with a phosphor, and an
organic resin layer mixed with a phosphor. As a typical example of
a yellow phosphor, YAG (yttrium aluminum garnet)-based phosphor, a
silicate-based phosphor, or the like can be given.
[0040] Note that an example in which an LED chip which can emit
blue light is used as the LED chip 33 and a phosphor layer
including a phosphor of yellow which is a complementary color of
blue is used as the phosphor layer 35 is described here.
Alternatively, an LED chip which can emit green light may be used
as the LED chip 33, and a phosphor layer including a phosphor of a
complementary color of green (red or magenta) may be used as the
phosphor layer 35.
[0041] Note that blue light has a maximum peak at a wavelength
range of 430 to 490 nm in an emission spectrum. Green light has a
maximum peak at a wavelength range of 490 to 550 nm in the emission
spectrum. Yellow light has a maximum peak at a wavelength range of
550 to 590 nm in the emission spectrum. Red light has a maximum
peak at a wavelength range of 640 to 770 nm in the emission
spectrum.
[0042] The light-transmitting convex organic resin layer 37 is
formed using a light-transmitting organic resin. There is no
particular limitation on the kind of organic resin, and typically,
an ultraviolet curable resin such as an epoxy resin or a silicone
resin, a visible light curable resin, or the like can be used as
appropriate. The above light-transmitting organic resin is formed
to have a predetermined height, a predetermined width, and a
predetermined curvature radius so that light with a desired shape
can be emitted. The above light-transmitting organic resin may be
formed by a droplet discharge method, a coating method, an
imprinting method, or the like. Alternatively, an organic resin may
be shaped to be convexed in advance, and may be compressed while
being heated. The light-transmitting convex organic resin layer 37
has a function of diffusing light emitted from the LED chip 33.
[0043] An end portion of the phosphor layer 35 is positioned on an
outer side of an end portion of the micro optical resonator 43 and
the phosphor layer 35 covers the whole of the micro optical
resonator 43, whereby light which is fully reflected between a
reflective electrode and a semi-transmissive semi-reflective
electrode in the micro optical resonator 43 is reflected or
refracted at an interface between the phosphor layer 35 and the
light-transmitting convex organic resin layer 37. Thus, light
incident on the micro optical resonator 43 can be utilized
efficiently.
[0044] The wirings 39a and 39b are thin wires formed using gold, an
alloy including gold, copper, or an alloy including copper.
[0045] The terminals 41a and 41b are conductive layers connected to
the electrode of the LED chip 33, which are formed using one
element selected from nickel, copper, silver, platinum, or gold or
an alloy material including any of the elements at 50% or more. The
terminals 41a and 41b and the electrode of the LED chip 33 are
connected by a wire bonding method using a thermo-compression
bonding method or an ultrasonic bonding method.
[0046] The micro optical resonator 43 is described below with
reference to FIGS. 2A-1, 2A-2, 2B, and 2C.
[0047] FIGS. 2A-1 and 2A-2 are enlarged cross-sectional views of
the micro optical resonator 43.
[0048] As illustrated in FIG. 2A-1, the micro optical resonator 43
includes a reflective layer 49 provided over a substrate 47, a
light-transmitting layer 51 provided over the reflective layer 49,
and a semi-transmissive semi-reflective layer 53 provided over the
light-transmitting layer 51. Further, a protective layer 55 may be
provided over the reflective layer 49, the light-transmitting layer
51, and a surface of the semi-transmissive semi-reflective layer
53.
[0049] Alternatively, as illustrated in FIG. 2A-2, the micro
optical resonator 43 may include the reflective layer 49 provided
over the substrate 47, the light-transmitting layer 51 provided
over the reflective layer 49, and a semi-transmissive
semi-reflective layer 54 provided over the reflective layer 49 and
the light-transmitting layer 51. The semi-transmissive
semi-reflective layer 54 is provided on side walls of the
light-transmitting layer 51 as illustrated in FIG. 2A-2, whereby
light which is fully reflected on an upper side and a lower side of
the light-transmitting layer 51 is also fully reflected on the side
walls of the light-transmitting layer 51. Thus, light entering the
micro optical resonator 43 can be utilized efficiently.
[0050] The reflective layer 49 is formed using a metal material
with high reflectivity. The reflectivity of the reflective layer 49
is 50% or higher, preferably 80% or higher. As the metal material
with high reflectivity, aluminum, silver, molybdenum, tungsten,
nickel, chromium, an alloy of any of these elements, an AgPdCu
alloy, or the like can be given. Further, the reflective layer 49
may have a dielectric multilayer structure in which two kinds of
transmissive insulating layers with different refractive indices
are alternately stacked. Here, as the refractive indices of the two
kinds of transmissive insulating layers are high, or as the number
of the layers is large, the reflection efficiency is high. For
example, as a stacked structure of a dielectric multilayer
structure, a stacked structure of titanium dioxide and silicon
dioxide, a stacked structure of zinc sulfide and magnesium
fluoride, a stacked structure of amorphous silicon and silicon
nitride, or the like can be employed.
[0051] The reflective layer 49 can be formed by a sputtering
method, an evaporation method, or the like.
[0052] The semi-transmissive semi-reflective layer 53 has
reflectivity which is higher than or equal to 30% and lower than or
equal to 70%, preferably higher than or equal to 40% and lower than
or equal to 60%. The semi-transmissive semi-reflective layer 53 can
be formed using silver, aluminum, an aluminum alloy, a
magnesium-silver alloy, or the like. In order to achieve the above
reflectivity, the thickness of the semi-transmissive
semi-reflective layer 53 is greater than or equal to 5 nm and less
than or equal to 20 nm, preferably greater than or equal to 7 nm
and less than or equal to 15 nm.
[0053] The semi-transmissive semi-reflective layer 53 can be formed
by a sputtering method, an evaporation method, or the like.
[0054] As the light-transmitting layer 51, a light-transmitting
insulating layer or a light-transmitting conductive layer can be
used. Typical examples of the light-transmitting insulating layer
include silicon oxide, silicon oxynitride, alumina, aluminum
nitride, and an epoxy resin. Typical examples of the
light-transmitting conductive layer include indium oxide including
tungsten oxide, indium zinc oxide including tungsten oxide, indium
oxide including titanium oxide, indium tin oxide including titanium
oxide, indium tin oxide, indium zinc oxide, and indium tin oxide to
which silicon oxide is added. Note that the light-transmitting
layer 51 may have a stacked structure of a plurality of layers.
[0055] A structure of a light-emitting element unit which can make
white light change into colored light at a predetermined wavelength
is described below with reference to FIG. 2B. FIG. 2B is an
enlarged view of the phosphor layer 35 covering the LED chip 33 and
the micro optical resonator 43 of FIG. 1A.
[0056] When light is repeatedly reflected between the reflective
layer 49 and the semi-transmissive semi-reflective layer 53 and
interferes, the intensity of light at a predetermined wavelength is
increased, and an emission spectrum having a sharp peak is
obtained. Such a structure is called a micro optical resonator
structure (a microcavity structure). Light emitted from the LED
chip 33 is reflected at a specific position of the phosphor layer
35, an interface between the phosphor layer 35 and the
light-transmitting convex organic resin layer 37, an interface
between the light-transmitting convex organic resin layer 37 and
the air, or the like to be white light W. Then, the white light W
enters the micro optical resonator 43. The entering light is
reflected and interferes between the reflective layer 49 and the
semi-transmissive semi-reflective layer 53, and after that, light G
at a predetermined wavelength is emitted from the micro optical
resonator 43. Thus, from the LED unit 30, white light having a
sharp peak at a predetermined wavelength in an emission spectrum is
emitted.
[0057] In order to increase the intensity of light at the
predetermined wavelength, in the micro optical resonator 43, a
light path length L between the reflective layer 49 and the
semi-transmissive semi-reflective layer 53 may be determined in
accordance with the wavelength. The light path length L in this
case is described below.
[0058] An interference between light (.theta.) at a wavelength
.lamda. passing from the semi-transmissive semi-reflective layer 53
to the reflective layer 49 and light returned from the reflective
layer 49 to the semi-transmissive semi-reflective layer 53 is
represented by Formula 1.
sin(.theta.)+sin(.theta.+2.pi..times.2nL/.lamda.+.pi.) (Formula
1)
[0059] By modifying Formula 1, Formula 2 can be obtained.
-2 cos(.theta.+2.pi.nL/.lamda.).times.sin(2.pi.nL/.lamda.) (Formula
2)
[0060] Formula 2 has the maximum value when the value
"sin(2.pi.nL/.lamda.)" satisfies Formula 3.
2.pi.nL/.lamda.=.pi.(2m+1)/2(m is an integer) (Formula 3)
[0061] From the above, when the light path length L between the
reflective layer 49 and the semi-transmissive semi-reflective layer
53 is obtained from Formula 4, light whose wavelength .lamda. has
the increased intensity can be emitted from the micro optical
resonator 43.
L=(2m+1).lamda./4n (Formula 4)
Note that n represents the refractive index of the
light-transmitting layer 51.
[0062] Further, in the case where the light-transmitting layer 51
has a stacked structure of a plurality layers (n layers), assuming
that the refractive indices of the layers are n.sub.1, n.sub.2, . .
. n.sub.n and the light path lengths of the layers obtained by
Formula 4 are l.sub.1, l.sub.2, . . . l.sub.n, the light path
length L is the sum of l.sub.1 to l.sub.n.
[0063] FIG. 2C is a schematic diagram of the emission intensity of
light emitted from the LED unit. A curve 56 indicates an emission
spectrum of light emitted from an LED unit which does not include
the micro optical resonator 43. The curve 56 has a steep peak at a
wavelength in the vicinity of 450 nm exhibiting blue, but the
spectrum intensity in the vicinity of 550 nm exhibiting green and
the spectrum intensity in the vicinity of 700 nm exhibiting red are
low. Thus, even when the white light passes through a red coloring
layer or a green coloring layer, the color purity is low in either
case.
[0064] A curve 56r indicates an emission spectrum of light emitted
from an LED unit including the micro optical resonator 43 which has
the light path length L enhancing the intensity of red light. A
curve 56g indicates an emission spectrum of an LED unit including
the micro optical resonator 43 which has the light path length L
enhancing the intensity of green light. A curve 56b indicates an
emission spectrum of an LED unit including the micro optical
resonator 43 which has the light path length L enhancing the
intensity of blue light.
[0065] The curve 56r has a steep peak in the vicinity of 700 nm
exhibiting red in addition to a peak in the vicinity of 450 nm
exhibiting blue.
[0066] The curve 56g has a steep peak in the vicinity of 550 nm
exhibiting green in addition to a peak in the vicinity of 450 nm
exhibiting blue.
[0067] The curve 56b has a higher peak than the curve 56 in the
vicinity of 450 nm exhibiting blue.
[0068] As described above, a micro optical resonator having a light
path length which enhances the intensity of light at the
predetermined wavelength is provided in the LED unit 30, whereby
the intensity of light at the predetermined wavelength emitted from
the LED unit 30 can be increased as compared to that emitted from a
conventional LED unit in which the micro optical resonator is not
provided. Therefore, when the light passes through a coloring layer
which transmits light with the increased intensity of light at the
predetermined wavelength, the color purity of the transmitted light
is increased as compared to the conventional case. For example,
when white light having the high intensity of red light passes
through a red coloring layer, the red color purity is increased as
compared to the conventional case.
[0069] Note that in this embodiment, the LED chip 33 emits blue
light. Thus, white light emitted from the LED unit has the
sufficiently high peak intensity exhibiting blue, and accordingly,
the micro optical resonator which makes the intensity of the light
at wavelength exhibiting blue increase is not necessarily provided.
Similarly, in the case where the LED chip emits red light or green
light, the micro optical resonator which makes the intensity of the
light at wavelength exhibiting red or green increase is not
necessarily provided.
[0070] Next, a backlight module including the LED unit illustrated
in FIGS. 1A and 1B and FIGS. 2A-1, 2A-2, 2B, and 2C will be
described with reference to FIG. 3, FIG. 4, and FIG. 5.
[0071] FIG. 3 is a perspective view of a direct-below-type
backlight module 40. The LED units 30 are arranged over a substrate
58 so as to be connected in series. A reflective sheet 61 is
provided around the LED units 30. Although not illustrated, the LED
units 30 are electrically connected to a control circuit board via
a connector and a wiring. In this case, the control circuit board
is provided on the back side of the backlight module 40.
[0072] Next, details of the backlight module are described with
reference to FIG. 4. Here, the LED units surrounded by a dashed
line 50 in FIG. 3 are used for description.
[0073] Over the substrate 58 provided with a wiring 57, an LED unit
60r emitting white light having at least a peak of red wavelength,
an LED unit 60g emitting white light having at least a peak of
green wavelength, and an LED unit 60b emitting white light having
at least a peak of blue wavelength are provided. Each of the LED
units 60r, 60g, and 60b is connected to the wiring 57 with a
conductive paste 59. The reflective sheet 61 is provided over a
portion where the substrate 58 and the wiring 57 are exposed.
[0074] There is no particular limitation on a substrate used as the
substrate 58 as long as it can withstand heat generation in the
manufacturing process or practical use. Typical examples of the
substrate 58 includes a glass substrate, a plastic substrate, a
glass epoxy resin substrate, a polyimide substrate, a ceramic
substrate, an alumina substrate, an aluminum nitride substrate, and
a printed board. In the case where a printed board where a wiring
is formed in advance by a printing method or the like is prepared
for the backlight module 40, the wiring 57 described later need not
be formed by an evaporation method, a sputtering method, a droplet
discharge method (such as an inkjet method, screen printing, or
offset printing), a coating method, or the like; thus,
manufacturing with high yield can be conducted. Here, a glass epoxy
resin substrate is used as the substrate 58.
[0075] The wiring 57 is formed using one element selected from
aluminum, nickel, copper, silver, platinum, or gold, or an alloy
material including any of the elements at 50% or more. The wiring
57 is formed by an evaporation method, an inkjet method, a printing
method, or the like.
[0076] The conductive paste 59 is formed using an alloy including
plural elements selected from tin, silver, bismuth, copper, indium,
nickel, antimony, zinc, and the like.
[0077] In this embodiment, the LED units 60r, 60g, and 60b are
mounted over the substrate 58 by a reflow process using the
conductive paste. Typically, a surface of the wiring 57 formed over
the substrate 58 is coated with a conductive paste by screen
printing or a dispenser method, and the LED units 60r, 60g, and 60b
are mounted thereover with a mounter. Then, the conductive paste is
heated at 250.degree. C. to 350.degree. C. to be melted, so that
terminals of the LED units 60r, 60g, and 60b and the wiring 57 are
electrically and mechanically connected.
[0078] Instead of the mounting method by a reflow process using a
conductive paste, local pressure bonding may be performed with use
of an anisotropic conductive adhesive, so that the LED units 60r,
60g, and 60b may be mounted over the substrate 58.
[0079] As the reflective sheet 61, a substrate provided with white
pigment which is light reflective coating is used. Typical examples
of the reflective sheet 61 include plastic with a surface on which
a white coating is printed or applied, and plastic mixed with the
white coating. The white coating includes organic pigment or
inorganic pigment such as zinc oxide, titanium oxide, calcium
carbonate, silicon oxide, or boron nitride. As the plastic, PET,
polyester, polyolefin, or the like can be given. Further, foamable
PET including a phosphor material can be used. Alternatively,
instead of using the reflective sheet 61, the substrate 58 and the
wiring 57 may be coated with a white solder resist. With the
reflective sheet 61 or the white solder resist, light emitted from
the LED chip to the substrate side can be reflected.
[0080] As the LED units 60r, 60g, and 60b, LED units which are
similar to the LED unit 30 illustrated in FIG. 1A can be used.
[0081] The LED units 60r, 60g, and 60b include micro optical
resonators 43r, 43g, and 43b, respectively. The micro optical
resonators 43r, 43g, and 43b emit light of high intensity with
respect to red, light of high intensity with respect to green, and
light of high intensity with respect to blue by causing
interference of light emitted from the LED chips. Light path
lengths of the micro optical resonators 43r, 43g, and 43b are
determined so as to increase the intensities of light at
wavelengths exhibiting red, green, and blue respectively. This is
not limited to these three specific colors, the light path lengths
of the micro optical resonators 43r, 43g, and 43b can be determined
to increase the intensities of light at any wavelength. Thus, the
thicknesses of the micro optical resonators 43r, 43g, and 43b are
different from each other.
[0082] Furthermore, as illustrated in FIG. 5, an organic resin
layer 63 having a light-transmitting property (a light-transmitting
organic resin layer 63) may be provided over the LED units 60r,
60g, and 60b and the reflective sheet 61. For the organic resin
layer 63, any of the organic resin that can be used for the
light-transmitting convex organic resin layer 37 can be used as
appropriate. Note that the light-transmitting organic resin layer
63 is formed so as not to contain air at an interface between the
light-transmitting convex organic resin layer 37 and the
light-transmitting organic resin layer 63. Further, it is
preferable to select a material so that the light-transmitting
organic resin layer 63 can have an optical refractive index which
uniforms luminance of light emitted from the light-transmitting
convex organic resin layer 37 and which is close to an optical
refractive index of the light-transmitting convex organic resin
layer 37. The light-transmitting organic resin layer 63 is formed
by a droplet discharge method, a coating method, a spin coating
method, a dipping method, or the like, or may be formed with a tool
such as a doctor knife, a roll coater, a curtain coater, or a knife
coater.
[0083] With use of the above-described LED unit and backlight
module, the color purity of light transmitted through the coloring
layer can be increased.
Embodiment 2
[0084] In this embodiment, a liquid crystal display device
including the backlight module described in Embodiment 1 will be
described.
[0085] The liquid crystal display device in this embodiment can be
implemented for both passive matrix type and active matrix type.
FIG. 6A is a block diagram illustrating a structure of an
active-matrix liquid crystal display device 200.
[0086] In FIG. 6A, the liquid crystal display device 200 includes a
pixel portion 210 which displays an image, a signal line driver
circuit 214, a scan line driver circuit 211, a backlight module 40
which emits light to the pixel portion 210, and an LED control
circuit 212 which controls a signal sent to an LED unit included in
the backlight module 40. In addition, a circuit which is necessary
for operating the liquid crystal display device, such as an image
processing circuit (an image engine or the like) is included. All
of them are provided for the control circuit board described in
Embodiment 1. Note that the driver circuits, the processing
circuit, and the image processing circuit are each roughly divided
into a logical circuit portion and a switch portion or a buffer
portion, and details of the structures of the circuits are omitted.
Further, part of or entire of the above circuit may be mounted
using a semiconductor device such as an IC.
[0087] The pixel portion 210 includes a plurality of pixels 215
provided on a liquid crystal panel. The scan line driver circuit
211 is a circuit which drives the pixels 215 and has a function of
outputting a plurality of display selection signals which are pulse
signals. The signal line driver circuit 214 has a function of
generating a display data signal on the basis of an inputted image
signal and outputting the generated display data signal. Further,
the outputted display data signal is inputted to the corresponding
pixel.
[0088] FIG. 6B is a circuit diagram of the pixel 215. In the pixel
215, a transistor (mainly, a thin film transistor: TFT) is provided
as a switching element for controlling potential of a pixel
electrode. The pixel 215 includes: a thin film transistor 221 in
which a gate is electrically connected to a scan line 219 and a
first electrode is electrically connected to a signal line 217; a
capacitor 223 in which a first electrode is electrically connected
to a second electrode of the thin film transistor 221 and a second
electrode is electrically connected to a wiring for supplying a
fixed potential (also referred to as a capacitor line); and a
liquid crystal element 225 in which one of electrodes (also
referred to as a pixel electrode) is electrically connected to the
second electrode of the thin film transistor 221 and the first
electrode of the capacitor 223 and the other electrode (also
referred to as a counter electrode) is electrically connected to a
wiring for supplying a counter potential.
[0089] In this specification, a liquid crystal panel displays an
image by controlling light transmission or non-transmission by the
optical modulation action of a liquid crystal. The optical
modulation action of a liquid crystal is controlled by an electric
field applied to the liquid crystal (including a horizontal
electric field, a vertical electric field, and an oblique electric
field).
[0090] Next, an embodiment of the liquid crystal display device 200
is described with reference to a cross-sectional view of the liquid
crystal display device 200 illustrated in FIGS. 7A and 7B. The
liquid crystal display device illustrated in FIG. 7A includes: the
backlight module 40 described in Embodiment 1; a diffusion plate
301 overlapping with the backlight module 40; a first polarizing
plate 303 overlapping with the backlight module 40 and the
diffusion plate 301; a liquid crystal panel 305 overlapping with
the backlight module 40, the diffusion plate 301, and the first
polarizing plate 303; and a second polarizing plate 307 overlapping
with the backlight module 40, the diffusion plate 301, the first
polarizing plate 303, and the liquid crystal panel 305. Note that
although not illustrated, a reflective plate may be provided on an
outer side of the backlight module 40, so that light leaking
through the backlight module 40 is reflected and incident on the
liquid crystal panel 305.
[0091] A circuit necessary for operating the liquid crystal display
device 200 is connected to the liquid crystal panel 305 and the
backlight module 40. Note that the scan line driver circuit 211 and
the signal line driver circuit 214 may be provided in the liquid
crystal panel 305.
[0092] Next, details of components included in the liquid crystal
display device 200 are described.
[0093] As the backlight module 40, the backlight module described
in Embodiment 1 is used. The backlight module described in
Embodiment 1 includes the micro optical resonator having a light
path length which enhances the intensity of light at the
predetermined wavelength; thus, light emitted from the LED unit can
have higher intensity of light at the predetermined wavelength than
white light emitted from the conventional LED unit. Therefore, when
the light passes through a coloring layer which transmits a color
of high intensity at the predetermined wavelength, the color purity
of the transmitted light is increased more than the convention
case. As a result, color reproducibly of the display device in this
embodiment can be increased.
[0094] There is no particular limitation on the first polarizing
plate 303 which polarizes light emitted from the diffusion plate
301 as long as it can make the light emitted from the diffusion
plate 301 polarize. A commercial product may be used, and one which
is conventionally used can be employed. For example, a polarizing
plate including a high molecule such as polyvinyl alcohol can be
used. The first polarizing plate 303 may have a plate shape or a
sheet shape (a film shape). In addition, it is preferable to use a
polarizing plate which has the optical refractive index as
equivalent as possible to that of another component included in the
liquid crystal display device 200.
[0095] The liquid crystal panel 305 includes a layer including a
switching element (hereinafter, referred to as an element layer
317) over a substrate 315, a pixel electrode 319 formed over the
element layer 317, a counter substrate 321 provided with a
light-blocking layer 335, a coloring layer 337, a protective layer
339, and a common electrode 323, a sealant 325, and a liquid
crystal 327 which transmits or blocks incident light. Although not
illustrated in FIGS. 7A and 7B, a spacer is provided so that a
distance (a cell gap) between the pixel electrode 319 and the
common electrode 323 is controlled to be constant. As the spacer, a
bead spacer or a spacer obtained by selective etching of an
insulating layer (a post spacer) can be used.
[0096] As the substrate 315 and the counter substrate 321, a
light-transmitting substrate is preferable, for example, a glass
substrate of barium borosilicate glass, aluminoborosilicate glass,
or the like; a quartz substrate; or a plastic substrate which can
withstand a process temperature in a manufacturing process of the
liquid crystal display device 200 and the element layer 317 can be
used. Further, as the substrate 315 and the counter substrate 321,
a glass substrate having any of the following sizes can be used:
the 3rd generation (550 mm.times.650 mm), the 3.5th generation (600
mm.times.720 mm or 620 mm.times.750 mm), the 4th generation (680
mm.times.880 mm or 730 mm.times.920 mm), the 5th generation (1100
mm.times.1300 mm), the 6th generation (1500 mm.times.1850 mm), the
7th generation (1870 mm.times.2200 mm), the 8th generation (2200
mm.times.2400 mm), the 9th generation (2400 mm.times.2800 mm or
2450 mm.times.3050 mm), and the 10th generation (2950 mm.times.3400
mm).
[0097] A typical example of the switching element formed in the
element layer 317 includes a transistor. Although a transistor is
described later, the transistor preferably uses a semiconductor, in
a channel, which has characteristics needed for operation of a
liquid crystal display device in a variety of conditions (e.g.,
temperature characteristics which allows the device to operate
under high temperature and low temperature). Amorphous silicon can
be used for a channel region, but as a typical example of a
semiconductor with more improved temperature characteristics,
microcrystalline silicon having a plurality of crystalline regions,
polysilicon, or the like is preferably used. Further, an oxide
semiconductor can be used for a channel region, and an
In--Ga--Zn--O-based oxide or the like is given as an oxide
semiconductor. A transistor including the above-described
semiconductor has a small shift in the threshold voltage and high
reliability even when the temperature of the transistor becomes
increased by heat generation of the backlight module 40 or heat
from external light; thus, the transistor operates with high
performance even under an environment where the temperature largely
changes.
[0098] The pixel electrode 319 and the common pixel electrode 323
can be formed using a light-transmitting conductive material such
as indium oxide containing tungsten oxide, indium zinc oxide
containing tungsten oxide, indium oxide containing titanium oxide,
indium tin oxide containing titanium oxide, indium tin oxide,
indium zinc oxide, or indium tin oxide containing silicon
oxide.
[0099] The light-blocking layer 335 is formed using a
light-blocking material that reflects or absorbs light. The
light-blocking layer can be formed using, for example, a black
organic resin and may be formed by mixing a black resin of a
pigment material, carbon black, titanium black, or the like into a
resin material such as photosensitive or non-photosensitive
polyimide. Alternatively, a light-blocking metal layer can be used,
which is made of chromium, molybdenum, nickel, titanium, cobalt,
copper, tungsten, or aluminum, for example.
[0100] The coloring layer 337 can be formed using a
light-transmitting chromatic-color resin layer. As the
light-transmitting chromatic-color resin layer, a photosensitive or
non-photosensitive organic resin can be given as a typical example.
Use of the photosensitive organic resin layer makes it possible to
reduce the number of resist masks; thus, the steps are simplified,
which is preferable.
[0101] Chromatic colors are colors except achromatic colors such as
black, gray, or white. The coloring layer is formed of a material
which only transmits light colored chromatic color in order to
function as the color filter. As chromatic color, red, green, blue,
or the like can be used. Alternatively, cyan, magenta, yellow, or
the like may also be used. "Transmitting only the chromatic color
light" means that light transmitted through the coloring layer has
a peak at the wavelength of the chromatic color light.
[0102] An optimal thickness of the coloring layer 337 may be
adjusted as appropriate in consideration of relation between the
concentration of a coloring material included and the
transmissivity of light.
[0103] The protective layer 339 is formed of a flat insulating
layer. As a typical example of the protective layer 339, an acrylic
region, an epoxy resin, or the like can be used.
[0104] Note that the coloring layer 337 is provided on the counter
substrate 321, but a coloring layer may be formed to function as an
interlayer insulating layer included in the element layer 317. For
example, a light-transmitting chromatic-color resin layer
functioning as a color filter layer may be used for an interlayer
insulating layer.
[0105] In the case where the interlayer insulating layer is formed
directly on the element substrate side as a coloring layer, the
problem of misalignment between the coloring layer and a pixel
region does not occur, whereby the formation region can be
controlled more precisely even when a pixel has a minute pattern.
In addition, the same insulating layer serves as the interlayer
insulating layer and the coloring layer, which brings advantages of
process simplification and cost reduction.
[0106] The optical modulation action of the liquid crystal 327 is
controlled by an electric field (including a horizontal electric
field, a vertical electric field, and a diagonal electric field)
applied to the liquid crystal 327. Note that the following can be
used for the liquid crystal 327 and a driving mode of the liquid
crystal element: a nematic liquid crystal, a cholesteric liquid
crystal, a smectic liquid crystal, a discotic liquid crystal, a
thermotropic liquid crystal, a lyotropic liquid crystal, a
low-molecular liquid crystal, a high-molecular liquid crystal, a
ferroelectric liquid crystal, an anti-ferroelectric liquid crystal,
a main chain type liquid crystal, a side chain type high-molecular
liquid crystal, a plasma address liquid crystal (PALC), a
banana-shaped liquid crystal, a TN (Twisted Nematic) mode, an STN
(Super Twisted Nematic) mode, an IPS (In-Plane-Switching) mode, an
FFS (Fringe Field Switching) mode, an MVA (Multi-domain Vertical
Alignment) mode, a PVA (Patterned Vertical Alignment), an ASV
(Advanced Super View) mode, an ASM (Axially Symmetric aligned
Micro-cell) mode, an OCB (Optical Compensated Birefringence) mode,
an ECB (Electrically Controlled Birefringence) mode, an FLC
(Ferroelectric Liquid Crystal) mode, an AFLC (Anti Ferroelectric
Liquid Crystal) mode, a PDLC (Polymer Dispersed Liquid Crystal)
mode, and a guest host mode. Note that this invention is not
limited thereto, and various kinds of liquid crystal elements can
be used. The alignment of the liquid crystal 327 can be easily
performed by rubbing treatment with use of an alignment film.
[0107] Alternatively, a blue-phase liquid crystal for which an
alignment film is not necessary may be used for the liquid crystal
327. A blue phase is one of liquid crystal phases, which is
generated just before a cholesteric phase changes into an isotropic
phase while temperature of cholesteric liquid crystal is increased.
Since the blue phase is generated within an only narrow range of
temperature, liquid crystal composition containing a chiral agent
so as to improve the temperature range is used for the liquid
crystal layer. As for the liquid crystal composition which contains
a blue-phase liquid crystal and a chiral material, the response
speed is as high as 10 .mu.s to 100 .mu.s, alignment treatment is
not necessary and viewing angle dependence is low due to optical
isotropy.
[0108] The sealant 325 has a function of sealing the liquid crystal
327 between the substrate 315 and the counter substrate 321.
[0109] The sealant 325 is preferably a visible-light curing resin,
an ultraviolet curing resin, or a thermosetting resin. Typically,
an acrylic resin, an epoxy resin, an amine resin, or the like can
be used. Further, a photopolymerization initiator (typically, an
ultraviolet light polymerization initiator), a thermosetting agent,
a filler, or a coupling agent may be included in the sealant.
[0110] There is no particular limitation on the second polarizing
plate 307 as long as it can make light emitted from the liquid
crystal panel 305 polarize. The same plate as the first polarizing
plate 303 can be used. In addition, it is preferable to use a
polarizing plate which has the optical refractive index as
equivalent as possible to that of another component included in the
liquid crystal display device 200. The second polarizing plate 307
is provided so that a slit thereof is perpendicular to a slit of
the first polarizing plate 303. The second polarizing plate 307 may
have a plate shape or a sheet shape (a film-like shape).
[0111] In this manner, the liquid crystal display device 200 can be
manufactured.
[0112] Next, as another embodiment of the liquid crystal display
device 200, a liquid crystal display device 300 in which an optical
member is provided between the diffusion plate 301 and the first
polarizing plate 303 is described. The optical member improves
front luminance of light emitted from the backlight module 40 and
having uniform brightness at the diffusion plate 301.
[0113] FIG. 7B is a cross-sectional view of the liquid crystal
display device 300. As an optical member 333 improving frontal
luminance of a pixel portion in the liquid crystal display device,
a luminance improving sheet (film) such as a prism sheet or a
microlens sheet can be used, which is an optical member that makes
light enter the liquid crystal panel 305 as vertically as
possible.
[0114] The backlight module 40 and the diffusion plate 301
described in the liquid crystal display device 200 of FIG. 7A can
be used here as appropriate. The number of luminance improving
sheets (films) to be used may be one, but when a plurality of
luminance improving sheets (films) are used, frontal luminance of
the pixel portion in the liquid crystal display device can be
improved. In such a case, the luminance improving sheets (films)
may be just arranged so that air is held between the sheets.
[0115] Further, as the first polarizing plate 303, the liquid
crystal panel 305, and the second polarizing plate 307, those
described in the liquid crystal display device 200 can be used as
appropriate.
[0116] The liquid crystal panel 305 described in the liquid crystal
display device 200 is provided to overlap with the backlight module
40 to which the diffusion plate 301 and the optical member 333 are
bonded, whereby the liquid crystal display device 300 can be
manufactured.
[0117] Next, a liquid crystal display device which can uniform
brightness of light emitted from the backlight module described in
the liquid crystal display devices 200 and 300 is described with
reference to FIG. 8.
[0118] A liquid crystal display device 400 illustrated in FIG. 8
includes a backlight module 62 which is planarized and has the
light-transmitting organic resin layer 63 as illustrated in FIG. 5.
Further, the backlight module 62, the diffusion plate 301, the
first polarizing plate 303, the liquid crystal panel 305, and the
second polarizing plate 307 are bonded to one another with
light-transmitting adhesives 311, 313, 329, and 331.
[0119] That is, in the liquid crystal display device 400, the
backlight module 62, the diffusion plate 301, the first polarizing
plate 303, the liquid crystal panel 305, and the second polarizing
plate 307 overlap with and are bonded to one another and sealed.
The liquid crystal display device 400 in which all components are
bonded is not provided with a layer containing air and having
smaller refractive index than the diffusion plate 301, the first
polarizing plate 303, the liquid crystal panel 305, and the second
polarizing plate 307. In the liquid crystal display device 400,
differences of optical refractive indices among the above
components are small, and light reflection in the liquid crystal
display device 400 is suppressed, so that light emitted from the
backlight module 62 can be efficiently utilized. As a result, power
consumption of the LED unit and display power of the display device
can be reduced.
[0120] As the light-transmitting adhesives 311, 313, 329, and 331,
it is preferable to use an adhesive which has an optical refractive
index as equivalent as possible to that of the backlight module 62
and the diffusion plate 301. For example, as the light-transmitting
adhesives 311, 313, 329, and 331, an adhesive containing an epoxy
resin, an adhesive containing a urethane resin, an adhesive
containing a silicone resin, or the like can be used. The adhesives
are formed, depending on a selected material, by a droplet
discharge method, a coating method, a spin coating method, a
dipping method, or the like. Further, the adhesives may be formed
with a tool such as a doctor knife, a roll coater, a curtain
coater, or a knife coater.
[0121] Next, a driving method of an LED unit in the liquid crystal
display device which is one embodiment of the present invention is
described.
[0122] FIGS. 9A and 9B are top views of backlight modules. In the
case where an image is displayed by lighting LED units 411
constantly in a backlight module 410 and controlling light
transmission or non-transmission with liquid crystals in the liquid
crystal panel, a complicated light-emitting element control circuit
is not needed, which is a simplified structure (see FIG. 9A).
[0123] However, consumed power of the LED unit accounts for a large
share of power consumed by the entire liquid crystal display
device. That is, it is not preferable in terms of power consumption
that the LED units are constantly lit.
[0124] As an effective driving method of an LED unit in a
direct-below type backlight module which is one embodiment of the
present invention, there is a local dimming method in which LED
units are divided into a plurality of regions and the LED units
themselves have contrast between the regions in accordance with
contrast of a displayed image.
[0125] A backlight module 420 illustrated in FIG. 9B is in a local
diming state. Luminance of LED units 421 and 422 in regions
corresponding to dark image portions is decreased, and luminance of
LED units 423 in a region corresponding to a bright image portion
is increased. By driving the LED units in this way, the contrast
ratio of an image is increased, and power consumption of the LED
units can be reduced.
[0126] Here, details of the liquid crystal panel 305 are described.
First, an active-matrix liquid crystal panel is described with
reference to FIGS. 10A and 10B.
[0127] FIG. 10A is a top view of the liquid crystal panel 305,
which illustrates two pixels.
[0128] In FIG. 10A, a plurality of signal lines 405 (including a
source electrode 405a) are arranged in parallel (is extended in the
vertical direction in the drawing) to be spaced from each other. A
plurality of scan lines 401 (including a gate electrode 401a) are
provided apart from each other and extended in a direction
generally perpendicular to the signal lines 405 (a horizontal
direction in the drawing). The plurality of signal lines are
connected to the signal line driver circuit 214 (see FIG. 6A), and
the plurality of scan lines and capacitor wirings 403 are connected
to the scan line driver circuit 211 (see FIG. 6A).
[0129] In addition, the capacitor wirings 403 are adjacent to the
plurality of scan lines 401 and extended in a direction parallel to
the scan lines 401, that is, in a direction generally perpendicular
to the signal lines 405 (in the horizontal direction in the
drawing). A storage capacitor 406 is surrounded by a dashed-dotted
line in FIG. 10A, and includes a gate insulating layer 402 serving
as a dielectric, the capacitor wiring 403, and a drain wiring 409
(including a drain electrode 409a). A pixel electrode 319 is
electrically connected to the drain wiring 409 through an opening
portion 450.
[0130] A transistor 430 which controls the potential of the pixel
electrode 319 is provided at an upper left corner of the drawing. A
plurality of pixel electrodes 319 and a plurality of transistors
430 are arranged in matrix.
[0131] Further, a pixel structure is not limited to that
illustrated in FIGS. 10A and 10B, and a capacitor may be formed
without providing a capacitor wiring. In such a structure, the
pixel electrode overlaps with a scan line of an adjacent pixel with
a gate insulating layer and another insulating layer interposed
therebetween. In this case, the capacitor wiring can be omitted,
whereby the aperture ratio of a pixel can be increased.
[0132] FIG. 10B is a cross-sectional view taken along line A-B in
FIG. 10A. Divided portions in FIG. 10B correspond to omitted
portions between the line A-B in FIG. 10A.
[0133] Hereinafter, a structure of the transistor 430 is described.
The transistor 430 is an inverted-staggered thin film transistor
(TFT) which includes, over the substrate 315 having an insulating
surface, a gate electrode 401a, the gate insulating layer 402, a
semiconductor layer 408, the source electrode 405a, and the drain
electrode 409a. The above components can be formed through the
desired deposition steps, the desired photolithography steps, and
the desired etching steps.
[0134] There is no particular limitation on a structure of a
transistor which can be applied to the liquid crystal panel 305.
For example, a staggered type or planar type transistor having a
top-gate structure or bottom-gate structure can be used. The
transistor may have a single-gate structure in which one channel
formation region is formed, a double-gate structure in which two
channel formation regions are formed, or a triple-gate structure in
which three channel formation regions are formed. Alternatively,
the transistor may have a dual-gate structure having two gate
electrodes, one of which is provided above a channel region with a
gate insulating layer interposed therebetween and the other of
which is provided below the channel formation region with another
gate insulating layer interposed therebetween. The transistor of
this embodiment has a single-gate structure.
[0135] An insulating layer 407 is provided to cover the transistor
430 and to be in contact with the semiconductor layer 408, and an
interlayer insulating layer 413 is stacked thereover.
[0136] For the semiconductor layer 408, as described above, it is
preferable to use a semiconductor having characteristics needed for
operation of the liquid crystal display device even in a variety of
conditions (e.g., temperature characteristics which allows the
device to operate under high temperature and low temperature). As a
typical example of the semiconductor having temperature
characteristics, although amorphous silicon can be used,
microcrystalline silicon which has a plurality of crystalline
regions, or polycrystalline silicon is preferable in order to
obtain more excellent temperature characteristics. Alternatively,
an oxide semiconductor can be used. Examples of an oxide
semiconductor include In--Ga--Zn--O-based oxide and the like.
Further, a transistor element including the above-described
semiconductor has a small shift in the threshold voltage and high
reliability, even when the temperature of the transistor element is
increased by heat generation of the backlight module or heat from
external light; thus, the transistor element operates with high
performance even under an environment where the temperature largely
changes.
[0137] In the capacitor 406 indicated by a dashed line, the gate
insulating layer 402 serving as a dielectric is stacked between the
capacitor wiring 403 and the drain electrode 409a as described
above. The capacitor wiring 403 is formed from the same layer as
the gate electrode 401a under the same condition; thus, it is
formed at the time of formation of the gate electrode 401a.
Therefore, there is no need for forming the capacitor 406
independently from the transistor 430. The capacitor 406 can be
formed by a desired photolithography step through a procedure for
forming the transistor 430.
[0138] The substrate 315 and the counter substrate 321 are bonded
to be fixed with the sealant 325 so that the liquid crystal 327 is
interposed therebetween (see FIGS. 7A and 7B). The above-described
materials can be used for the sealant 325 and the liquid crystal
327. The liquid crystal 327 can be formed by a dispenser method (a
dropping method), or an injection method by which liquid crystal is
injected using a capillary phenomenon or the like after the
substrate 315 is bonded to the counter substrate 321. In the case
where a photocurable resin such as an ultraviolet curable resin is
used as the sealant 325 and a liquid crystal layer is formed by a
dropping method, the sealant 325 may be cured by the light
irradiation step of the polymer stabilization treatment.
[0139] In addition, a spacer 415 is provided so that the distance
(the cell gap) between the pixel electrode 319 and the common pixel
electrode 323 is controlled to be constant. Although a bead spacer
is used here, a spacer obtained by selective etching of an
insulating layer (a post spacer) may be used. In the liquid crystal
display device including the liquid crystal 327, the cell gap is
preferably greater than or equal to 1 .mu.m and less than or equal
to 20 .mu.m. In this specification, the thickness of a cell gap
refers to the length (film thickness) of a thickest part of the
liquid crystal.
[0140] In addition, a light-blocking layer (a black matrix) is
provided in a region overlapping with the semiconductor layer and a
contact hole of the transistor 430 or between pixels. Further, a
coloring layer is provided in a region corresponding to the pixel
electrode.
[0141] Next, a passive-matrix liquid crystal panel 305 which can be
manufactured more easily than the active-matrix liquid crystal
panel 305 in which a switching element (a transistor) is provided
in the pixel, is described with reference to FIGS. 11A and 11B. In
the passive-matrix liquid crystal panel 305, it is not necessary to
provide a switching element (a transistor) in a pixel, which
enables the passive-matrix liquid crystal panel 305 to be easily
manufactured.
[0142] FIG. 11A is a top view of the passive-matrix liquid crystal
panel 305. FIG. 11B is a cross-sectional view taken along line C-D
in FIG. 11A. The liquid crystal 327, the light-blocking layer 335,
the coloring layer 337, the protective layer 339, and the counter
substrate 321 are provided as illustrated in FIG. 11B though they
are not illustrated in FIG. 11A.
[0143] Common electrodes 1706a, 1706b, and 1706c, an insulating
layer 1707, and pixel electrodes 1701a, 1701b, and 1701c are
provided between the counter substrate 321 and the substrate 315.
The pixel electrodes 1701a, 1701b, and 1701c correspond to the
pixel electrode 319 for active matrix type (see FIGS. 7A and 7B),
and the common electrodes 1706a, 1706b, and 1706c correspond to the
common electrode 323 for active matrix type (see FIGS. 7A and 7B).
Further, the pixel electrodes 1701a, 1701b, and 1701c are
controlled by a common driver corresponding to a scan line driver
circuit for active matrix type, and the common electrodes 1706a,
1706b, and 1706c are controlled by a segment driver corresponding
to a signal line driver circuit for active matrix type.
[0144] The pixel electrodes 1701a, 1701b, and 1701c and the common
electrodes 1706a, 1706b, and 1706c each have a shape with an
opening pattern which includes a rectangular opening (slit) in a
pixel region of a liquid crystal element.
[0145] With an electric field formed between the pixel electrodes
1701a, 1701b, and 1701c and the common electrodes 1706a, 1706b, and
1706c, the liquid crystal 327 is controlled. An electric field in a
lateral direction is formed for the liquid crystal, so that liquid
crystal molecules can be controlled using the electric field. The
liquid crystal molecules can be controlled in the direction
parallel to the substrate, whereby a wide viewing angle is
obtained.
[0146] The counter substrate 321 is provided with the
light-blocking layer 335, the coloring layer 337, and the
protective layer 339.
[0147] Although not illustrated, the spacer can be used for keeping
the cell gap, and the above-described sealant can be used for
sealing the liquid crystal 327 in the same manner as the liquid
crystal display device of the active matrix type.
[0148] Note that this embodiment can be implemented in free
combination with any of the other embodiments.
Embodiment 3
[0149] In this embodiment, a display device which controls the
amount of light, in each pixel, transmitted from a backlight with
use of micro electro mechanical systems (MEMS) will be described
with reference to FIG. 12, FIG. 13, and FIG. 14.
[0150] FIG. 12 is a cross-sectional view of a display device 500
which controls the amount of light, in each pixel, transmitted from
a backlight with use of MEMS having a three-dimensional structure
and a microstructure part of which can be moved.
[0151] A reflective layer 503 is formed over a first substrate 501.
A light-transmitting insulating layer 505 is provided over the
reflective layer 503. MEMS switches 507r, 507g, and 507b are formed
over the light-transmitting insulating layer 505. Note that
although not illustrated, the light-transmitting insulating layer
505 includes a plurality of insulating layers, and transistors
connected to the MEMS switches 507r, 507g, and 507b are formed
between the insulating layers. As the transistors, the transistor
described in Embodiment 2 can be used as appropriate. On a second
substrate 511 facing the first substrate 501, a light-blocking
layer 513 is formed in a portion facing the reflective layer 503,
and coloring layers 514r, 514g, and 514b are formed in portions
facing opening portions 503r, 503g, and 503b surrounded by the
reflective layer 503. Note that the coloring layer 514r transmits
red light, the coloring layer 514g transmits green light, and the
coloring layer 514b transmits blue light.
[0152] Further, a diffusion plate 515, a luminance improvement
sheet 517, and a backlight 519 are provided on the first substrate
501 side in this order. The first substrate 501 and the diffusion
plate 515, the diffusion plate 515 and the luminance improvement
sheet 517, and the luminance improvement sheet 517 and the
backlight 519 are bonded with light-transmitting adhesives 521,
523, and 525.
[0153] A chassis 527 formed using a metal sheet or molded plastic
is provided to be extended from the second substrate 511 side so as
to cover the backlight 519.
[0154] In the display device 500 described in this embodiment, for
example, the opening portions 503g and 503b surrounded by the
reflective layer 503 are covered by a non-opening portion in a
shutter 508g of the MEMS switch 507g and a non-opening portion in a
shutter 508b of the MEMS switch 507b, whereby light from the
backlight 519 is reflected at the non-opening portions in the
shutters 508g and 508b and is not transmitted. A shutter 508r of
the MEMS switch 507r does not cover the opening portion 503r
surrounded by the reflective layer 503 but moves to an upper
portion of the reflective layer 503. Therefore, light from the
backlight 519 passes through the opening portion 503r, and light of
a color of a coloring layer (in this case, red) is emitted.
[0155] Further, luminance of each pixel or gradation can be
controlled with the number of opening and closing times of the MEMS
switch 507 or the duty ratio.
[0156] As the first substrate 501 and the second substrate 511,
substrates similar to those of the liquid crystal display device
described in Embodiment 2 can be used as appropriate.
[0157] The reflective layer 503 is formed using aluminum, silver,
molybdenum, tungsten, nickel, chromium, an alloy containing any of
these, an AgPdCu alloy, or the like. The thickness of the
reflective layer 503 is greater than or equal to 30 nm and less
than or equal to 1000 nm. The opening portion may have a
rectangular shape, a circular shape, an elliptical shape, a
polygonal shape, or the like. Through the opening portions 503r,
503g, and 503b, light emitted from the backlight 519 is transmitted
to the outside of the display device. Note that light which is
emitted from the backlight 519 and does not pass through the
opening portion is reflected at the reflective layer 503 and
reflected again at a backlight module, so that the reflected light
can be reused.
[0158] The reflective layer 503 can be formed as follows: a film is
formed by a sputtering method, an evaporation method, or the like;
and the film is partly etched by a photolithography step.
Alternatively, the reflective layer 503 can be formed by a printing
method, an inkjet method, or the like.
[0159] The light-transmitting insulating layer 505 is formed using
silicon oxide, silicon nitride, silicon oxynitride, silicon nitride
oxide, or the like by a sputtering method, a CVD method, an
evaporation method, or the like.
[0160] The MEMS switches 507r, 507g, and 507b have the same
structure. Here, with use of the MEMS switch 507r as a typical
example, the structure of the MEMS switch is described with
reference to FIG. 12 and FIG. 13.
[0161] FIG. 13 is a perspective view of the MEMS switch 507r. The
MEMS switch 507r includes a shutter 543 connected to an actuator
541. The shutter 543 has opening portions. The actuator 541 has two
flexible actuators 545. One of sides of the shutter 543 is
connected to the actuators 545. The actuators 545 have a function
of moving the shutter 543 in the lateral direction which is a
direction parallel to a surface of the insulating layer 505.
[0162] Each actuator 545 includes a movable electrode 551 connected
to the shutter 543 and a structure body 549 and a movable electrode
555 connected to a structure body 553. The movable electrode 555 is
adjacent to the movable electrode 551, and one end of the movable
electrode 555 is connected to the structure body 553, and the other
end can be freely moved. The end portion of the movable electrode
555, which can be freely moved, is bent so as to be closest to the
connection portion of the movable electrode 551 and the structure
body 549.
[0163] The other side of the shutter 543 is connected to a spring
547 which has restoring force opposing force applied by the
actuator 541. The spring 547 is connected to a structure body
557.
[0164] The structure bodies 549, 553, and 557 function as
mechanical supports which lifts the shutter 543, the actuators 545,
and the spring 547 in the vicinity of the surface of the insulating
layer 505.
[0165] An opening portion 559 surrounded by the reflective layer is
provided below the shutter 543. The opening portion 559 corresponds
to the opening portion 503r in FIG. 12.
[0166] The structure body 553 included in the MEMS switch 507r is
connected to the transistor which is not illustrated. Thus, a given
voltage can be applied to the movable electrode 555 connected to
the structure body 553 through the transistor. The structure bodies
549 and 557 are each connected to a ground electrode (GND) with the
reflective layer 503 illustrated in FIG. 12. Therefore, a potential
of the movable electrode 551 connected to the structure body 549
and a potential of the spring 547 connected to the structure body
557 are GND. Note that the structure bodies 549 and 557 may be
electrically connected to a common electrode to which a given
voltage can be applied.
[0167] When the voltage is applied to the movable electrode 555,
the movable electrode 551 and the movable electrode 555 are
electrically drawn to each other due to a potential difference
between the movable electrode 555 and the movable electrode 551. As
a result, the shutter 543 connected to the movable electrode 551 is
drawn toward the structure body 553 and moves to the structure body
553 in the lateral direction. Since the movable electrode 551 has a
function of a spring, when the voltage between the potential of the
movable electrode 551 and the potential of the movable electrode
555 is removed, the movable electrode 551 releases the stress
stored in the movable electrode 551 and pushes the shutter 543 back
to the original position.
[0168] The manufacturing method of the MEMS switch 507r is
described below. A sacrificial layer with a predetermined shape is
formed by a photolithography step over the insulating layer 505.
The sacrificial layer can be formed using an organic resin such as
polyimide or acrylic, an inorganic insulating layer such as a
silicon oxide layer, a silicon nitride layer, a silicon oxynitride
layer, or a silicon nitride oxide layer, or the like.
[0169] Next, a conductive layer is formed over the sacrificial
layer by a printing method, a sputtering method, an evaporation
method, or the like, and then, is selectively etched, so that the
MEMS switch 507 is formed. Alternatively, the MEMS switch 507 is
formed by an inkjet method.
[0170] Next, the sacrificial layer is removed, whereby the MEMS
switch 507r which can be moved in a space can be formed. After
that, the surface of the MEMS switch 507r is preferably oxidized by
oxygen plasma, thermal oxidation treatment, or the like, so that an
oxide film is formed. Alternatively, an insulating film including
alumina, silicon oxide, silicon nitride, silicon oxynitride,
silicon nitride oxide, DLC (diamond-like carbon), or the like is
preferably formed on the surface of the MEMS switch 507r by an
atomic layer deposition method or a CVD method. By providing the
insulating film for the MEMS switch 507, deterioration in
characteristics of the MEMS switch 507 over time can be
reduced.
[0171] The MEMS switch 507r can be formed using metal such as
aluminum, copper, nickel, chromium, titanium, molybdenum, tantalum,
or neodymium or an alloy containing any of these. The MEMS switch
507 is formed to have a thickness greater than or equal to 100 nm
and less than or equal to 5 .mu.m.
[0172] The light-blocking layer 513 provided for the second
substrate 511 is provided to cover the reflective layer 503.
[0173] The coloring layers 514r, 514g, and 514b provided for the
second substrate 511 can be formed in a manner similar to that of
the coloring layer 337 described in Embodiment 2. Note that as the
coloring layer, a coloring layer which transmits another color can
be provided as appropriate.
[0174] Note that although not illustrated, the first substrate 501
and the second substrate 511 are fixed with a sealant to hold a
certain space therebetween.
[0175] As the diffusion plate 515 and the luminance improvement
sheet 517 illustrated in FIG. 12, the diffusion plate 301 and the
luminance improvement sheet described in Embodiment 2 can be used
as appropriate.
[0176] As the backlight 519, the backlight described in Embodiment
1 can be used.
[0177] With use of the backlight described in Embodiment 1, the
color purity of light emitted from the second substrate 511 is
increased. Therefore, color reproducibility of the display device
can be increased. Since the display device including the MEMS
switch has high use efficiency of light which is emitted from the
backlight 519, high contrast can be sufficiently obtained even when
luminance of the backlight is decreased; thus, power consumption of
the display device can be reduced.
[0178] Next, a circuit diagram and an operation method of the
display device described in this embodiment are described with
reference to FIG. 13 and FIG. 14.
[0179] FIG. 14 is a circuit diagram of a display device described
in this embodiment. A display device 600 includes a scan line
driver circuit 601, a signal line driver circuit 603, and a pixel
portion 605. The pixel portion 605 is provided with scan lines 609
connected to the scan line driver circuit 601 and signal lines 611
connected to the signal line driver circuit 603. In the pixel
portion 605, pixels 607 are arranged in matrix. The scan line
driver circuit 601 is a circuit which makes the pixels 607 drive
and has a function of outputting a plurality of display selection
signals that are pulse signals. Further, the signal line driver
circuit 603 has a function of generating a data voltage Vd in
accordance with an inputted image signal and applying the generated
data voltage Vd to the signal lines 611. Each pixel 607 is provided
with a transistor 613 in which a gate is connected to the scan line
609 and a first electrode is connected to the signal line 611, a
MEMS switch 615 in which a first terminal is connected to a second
electrode of the transistor 613, and a capacitor 617 in which a
first electrode is connected to the second electrode of the
transistor 613 and the first terminal of the MEMS switch 615. A
second terminal of the MEMS switch 615 and a second electrode of
the capacitor 617 are connected to a ground electrode.
[0180] The transistor 613 controls the voltage applied to the MEMS
switch 615. The transistor described in Embodiment 2 can be used
for the transistor 613. Instead of the transistor, a diode or a
metal insulator metal (MIM) may be used.
[0181] The MEMS switch 615 corresponds to the MEMS switch 507r
illustrated in FIG. 13.
[0182] The MEMS switch 615 includes an actuator having two movable
electrodes and a shutter. The two movable electrodes have
capacitance different from each other.
[0183] The transistor 613 is connected to the movable electrode 555
having lower capacitance with the structure body 553 in the MEMS
switch 615. The movable electrode 551 in the MEMS switch 507 is
connected to the shutter 543 with a large area and thus has high
capacitance and is connected to a common electrode or a ground
electrode with the structure body 549. The spring 547 is connected
to the common electrode or the ground electrode with the structure
body 557.
[0184] A writing voltage Vwe is sequentially applied to the scan
lines 609, so that the transistors 613 are turned on in sequence.
The data voltage Vd is applied to the selected signal line 611. The
data voltage Vd is written to the MEMS switch 615 and the capacitor
617 which are connected to the transistor 613 that is on. Thus, a
potential difference is generated between the movable electrode 555
and the shutter 543. Due to generation of the potential difference,
the shutter is electrically drawn toward the movable electrode 555,
moves, and does not overlap with an opening portion of the pixel
portion; thus, light from the backlight passes through the opening
portion.
[0185] In a display device of an analog driving method, the data
voltage Vd is applied to the signal lines 611 in accordance with
desired luminance of the pixels 607. The moving distance of the
shutter in the MEMS switch 615 depends on the data voltage Vd. In
accordance with the moving distance of the shutter, an area where
the opening portion of the pixel portion overlaps with the opening
portion of the shutter varies or the opening portion of the pixel
portion does not overlap with the opening portion of the shutter;
thus, the amount of light, which passes through the opening
portion, from the backlight varies.
[0186] In the display device of a digital driving method, as the
data voltage Vd, a voltage that is lower than the voltage at which
the actuator of the MEMS switch 615 operates (the operation
threshold voltage) or higher than the operation threshold voltage
is applied. With application of the data voltage Vd that is higher
than the operation threshold voltage, the shutter of the MEMS
switch 615 moves, and light from the backlight is transmitted
through the opening portion of the pixel portion.
[0187] The voltage applied to the signal line 611 is held in the
capacitor 617 of the pixel 607 even after the application of the
wiring voltage Vwe is stopped. The voltage of the capacitor 617 is
substantially stored until the whole video frame has been written
or new data is written to the signal line 611. Thus, the number of
times of writing can be minimized, and power consumption of the
display device can be reduced.
[0188] Note that in this embodiment, the circuit diagram in which
one transistor is connected to the MEMS switch 615 is illustrated,
but the circuit configuration is not limited to this, and
transistors can be provided as appropriate.
[0189] The display device including the MEMS switch has high use
efficiency of light emitted from the backlight; thus, sufficiently
high contrast can be obtained even when luminance of the backlight
is decreased. As a result, power consumption of the display device
can be reduced.
Embodiment 4
[0190] A display device of one embodiment of the present invention
can be applied to a variety of electronic devices. Examples of
electronic devices include a television device (also referred to as
a TV or a television receiver). In addition, a display device of
one embodiment of the present invention can be applied to indoor
digital signage, public information display (PID), advertisements
in vehicles such as a train, or the like. In particular, since the
display device of one embodiment of the present invention can
improve color purity, the use of the display device as the above
electronic devices is effective in obtaining color reproducibility.
Examples of electronic devices in which the display device of one
embodiment of the present invention is used are illustrated in
FIGS. 15A and 15B.
[0191] FIG. 15A illustrates an example of a television device. In a
television device 1000, a display portion 1002 is incorporated in a
housing 1001. Images can be displayed on the display portion 1002.
Here, the housing 1001 is supported by a housing 1004. In addition,
the television device 1000 is provided with a speaker 1003,
operation keys 1005 (including a power switch or an operation
switch), a connection terminal 1006, a sensor 1007 (having a
function of measuring force, displacement, position, speed,
distance, light, temperature, sound, time, electric field, current,
voltage, electric power, or infrared ray), a microphone 1008, and
the like.
[0192] The television device 1000 can be operated with the
operation switch or a separate remote controller 1010. With
operation keys 1009 provided in the remote controller 1010,
channels or volume can be controlled, whereby an image displayed on
the display portion 1002 can be controlled. The remote controller
1010 may include a display portion 1011 for displaying data output
from the remote controller 1010.
[0193] Note that the television device 1000 is provided with a
receiver, a modem, and the like. A general television broadcast can
be received with the receiver. Moreover, when the display device is
connected to a communication network with or without wires via the
modem, one-way (from a sender to a receiver) or two-way (between a
sender and a receiver or between receivers) information
communication can be performed.
[0194] FIG. 15B illustrates an example of digital signage. For
example, digital signage 2000 includes two housings, a housing 2002
and a housing 2004. The housing 2002 includes a display portion
2006 and two speakers, a speaker 2008 and a speaker 2010. In
addition, the digital signage 2000 may be provided with a sensor so
as to operate in a following manner: an image is not displayed when
a person is not close to the digital signage or the like.
[0195] The display device of one embodiment of the present
invention can be used for the display portion 1002 in the
television device 1000 and the display portion 2006 in the digital
signage 2000 and has an advantage of improving color purity. Thus,
color reproducibility of the television device 1000 and the digital
signage 2000 can be increased.
[0196] Note that this embodiment can be implemented in free
combination with any of the other embodiments.
[0197] This application is based on Japanese Patent Application
serial no. 2010-238723 filed with Japan Patent Office on Oct. 25,
2010, the entire contents of which are hereby incorporated by
reference.
* * * * *