Patent Application
20100309098
1. Field of the Invention
The present invention relates to an image display apparatus in which an organic EL device is disposed at each pixel, and more particularly, to an image display apparatus using an organic EL device having a resonator structure for reinforcing a specific wavelength in each pixel.
2. Description of the Related Art
An organic EL device is a self-emission device utilizing a principle of an emission layer made of an organic material that emits light by recombination energy between holes injected from an anode and electrons injected from a cathode when an electric field is applied. Since the low voltage drive organic EL device as a stack-type device was reported by C. W. Tang et al., studies about the organic EL device made of an organic material have been performed actively.
In addition, the organic EL device has a wide viewing angle and sufficient moving picture response because of its self-emission property, and hence has ideal characteristics as a display device. In particular, because of its thin shape, light weight, and high impact resistance, the organic EL device has been developed as a display device for mobile applications in recent years.
The conventional organic EL device controls light generated in the emission layer by utilizing the resonator structure so as to improve color purity of an emission color and to enhance light extraction efficiency (see WO01/39554A). However, if the resonator structure is provided to the organic EL device, very high accuracy of an optical path length, i.e., a film thickness is required so that resonator performance is exerted without an unevenness. Here, a conventional basic resonator structure is described.
As illustrated in
It is needless to say that it is important and necessary to reduce the film thickness unevenness in the film forming process as a countermeasure against these technical problems. However, even if emission luminance is affected by the film thickness unevenness, the emission luminance may be corrected by a drive method. However, it is necessary to read luminance information of each pixel with respect to input power, and to store a corrected data table in a prepared memory. This may cause increases in number of new steps and members resulting in high cost as a demerit.
To solve these technical problems, there is proposed a structure in which one pixel has regions having different resonator lengths or a structure in which the resonator length is different between neighboring pixels (see Japanese Patent Application Laid-Open No. 2007-234581).
L1=Lave+ΔL (1)
L2=Lave−ΔL (2)
(2−Lave)/λ+Φ/(2π)=m (3)
In the expressions, Lave denotes an average optical length between the optical length L1 and the optical length L2, Φ denotes a sum of a phase shift Φ1 of reflection light generated in the reflective electrode and a phase shift Φ2 of reflection light generated in the second electrode (Φ=Φ1+Φ2) (radians), λ denotes a peak wavelength of a spectrum of light to be extracted from the second electrode, and m is an integer in which Lave becomes positive.
In this way, two peaks shifted before and after the interference peak wavelength by the same degree are used as average peaks, and hence a peak variation with respect to the film thickness unevenness may be reduced. As a result, even if some film thickness unevenness occurs, robustness may be secured for a part of light-emitting characteristics.
As described above, in the image display apparatus using the organic EL device having the resonator structure as a pixel, a film thickness unevenness in the film forming process cannot be ignored so that an unevenness of display characteristics occurs.
For instance, in the image display apparatus using the organic EL device having the resonator structure disclosed in WO01/39554A as a pixel, it is predicted that film thickness unevenness in the film forming process becomes display characteristic unevenness in the image display region.
In order to solve this problem, Japanese Patent Application Laid-Open No. 2007-234581 describes the method in which two types of light-emitting devices having different device film thicknesses shifted from the device film thickness L satisfying the interference condition by ±ΔL are combined and used. Thus, the interference characteristic with respect to the film thickness unevenness may be averaged, and hence the display characteristic unevenness may be suppressed. However, luminance variation is large before and after an extreme value satisfying the interference condition, and chromaticity variation also increases along with the interference characteristic. In this way, if only the interference condition is noted, there is a case where the display unevenness with respect to the chromaticity variation cannot be suppressed.
In view of the above-mentioned problems, an object of the present invention is to provide a structure in which display characteristics (luminance and chromaticity) with respect to a film thickness unevenness becomes robust, and to provide an image display apparatus using the structure.
According to the present invention, there is provided an image display apparatus using an organic EL device in which an organic compound layer are sandwiched between a reflective electrode and a transparent electrode so that emitted light interferes between the reflective electrode and the transparent electrode. Further, an arbitrary one of emission pixels includes pixel groups (A and B) which have two characteristics and have a combination of film thicknesses in which: one of the film thicknesses is smaller and another one of the film thicknesses is larger than a film thickness at a peak of a curve in a protruding shape given by an intensity variation of emission luminance with respect to a film thickness variation of the emission pixel; and the one of the film thicknesses is smaller and the another one of the film thicknesses is larger than a film thickness at a peak of a curve in a protruding shape given by a chromaticity variation of at least one component of chromaticity (CIE x, CIE y) with respect to the film thickness variation of the emission pixel.
With the image display apparatus using the organic EL device of the present invention, a complementary effect is obtained between neighboring pixels of the same color, and hence the influence of the film thickness unevenness on the display characteristic in the film forming process may be reduced. Therefore, yields of the image display apparatus using the organic EL device are improved so as to significantly contribute to reduction in cost.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
An image display apparatus using an organic EL device according to an embodiment of the present invention includes emission pixels. The emission pixel refers to a pixel in which an organic compound layer are sandwiched between a reflective film (reflective electrode) and a translucent reflective film (transparent electrode) so that emitted light interferes between the reflective film and the translucent reflective film (see
Here, the film thickness at the peak of the curve in the protruding shape given by the intensity variation of the emission luminance may be one type of film thickness satisfying an interference condition or may be two types of different film thicknesses satisfying the interference condition. In addition, the pixel groups having the two characteristics may be arranged alternately in one of a checkered pattern and a pattern similar to the checkered pattern in each emission pixel in plan view. In addition, the chromaticity variation of the at least one component of the chromaticity (CIE x, CIE y) may be a variation in CIE y of a green color pixel. The detail is described later. Note that the interference condition means the above-mentioned equation (3).
In order to display characters and graphics by using an organic EL device, it is necessary to arrange devices in matrix to form a display apparatus. The method of arranging the organic EL devices in matrix commonly include a so-called XY passive matrix time-division duty drive method and active drive method in which an active device such as a thin film transistor (TFT) is arranged in each pixel. The passive matrix method is disadvantageous in durability because it is necessary to cause a large quantity of current to flow through the devices so as to obtain sufficient luminance. At present, it is considered that the active drive type is the most practical in use, but the present invention is not limited to the active drive type.
Hereinafter, the embodiment of the image display apparatus using the organic EL device according to the present invention is described with reference to the drawings. Note that the pixel and the pixel group may be denoted by the same reference numeral in the following description.
This pixel circuit 501 includes a selection device portion 507 for selecting a pixel, a sustaining capacitor portion 510 for sustaining a gate voltage of a drive device portion 508, and the drive device portion 508 for driving an organic EL device 509. Note that a unit of the selection device portion 507 and the drive device portion 508 is integrally referred to as a pixel transistor. Then, luminance data is supplied as a voltage from the signal line 503, and hence current according to the data voltage flows in the organic EL device 509.
As a specific connection relationship, an anode of the organic EL device 509 is connected to a power supply line 504 (power supply voltage Vdd). The drive device portion 508 is connected between a cathode of the organic EL device 509 and a ground line 505. The sustaining capacitor portion 510 is connected between a gate of the drive device portion 508 and the ground line 505. The selection device portion 507 is connected between the signal line 503 and the gate of the drive device portion 508, and a gate thereof is connected to the scanning line 502. The selection device portion 507 and the drive device portion 508 are constituted of a thin film transistor (TFT), and an amorphous silicon semiconductor, a polysilicon semiconductor, a low temperature polysilicon semiconductor, or a transparent oxide semiconductor may be selected according to necessary current quantity and a sub pixel size.
Hereinafter, a target pixel (a target pixel group) is defined as a pixel (a pixel group) A, and a pixel (a pixel group) of the same color adjacent to the pixel (the pixel group) A is defined as a pixel (a pixel group) B. In addition, in the following description, any one of the expressions of “pixel” and “pixel group” is used according to contents appropriately. In addition, the pixel film thickness means a pixel film thickness 607 between interfaces necessary for multiple interference and reflection within the organic EL device with respect to light generated in the organic EL device as illustrated in
This organic EL device has two pixel film thicknesses 607 (pixel film thickness 1 for n-th order resonance and pixel film thickness 2 for (n+1)th order resonance), but it is supposed that there is one pixel film thickness in the following description of a principle. Incidentally, the present invention includes a case where one organic EL device in each pixel comprises two regions having different pixel film thicknesses in the in-plane direction. In this case, one region corresponds to pixel (pixel group) A, and the other region corresponds to pixel (pixel group) B. And, the pixel A and the pixel B are driven by a common pixel circuit.
In addition, as an index for comparing emission efficiency of light-emitting devices with different colors, “luminance/CIE y” is defined. CIE y is a y value in an xy chromaticity diagram that is defined by the CIE 1931 standard colorimetric system. If the luminance is the same as a stimulus value Y, the “luminance/CIE y” becomes a sum of tristimulus values based on y=Y/(X+Y+Z). If the CIE y is different between light-emitting devices with the same luminance, the “luminance/CIE y” means that the drive power is different by the difference thereof. In other words, if the “luminance/CIE y” value is higher, the emission efficiency becomes relatively higher, and hence the drive power for emitting light of the same luminance becomes relatively low. When the device is controlled actually, the power is controlled. Therefore, it is convenient to consider by the “luminance/CIE y”. Hereinafter, any one of “luminance” and “luminance/CIE y” is used according to description. Although the xy chromaticity diagram of CIE-XYZ colorimetric system is often used as the chromaticity expression, the CIELUV space or the CIELAB space may be used according to purpose.
In order to form a film of an organic compound layer on the substrate, it is common to adopt the method of preparing an organic material as a raw material in a metal melting pot, heating the melting pot in a vacuum chamber, and sublimating or evaporating the organic material. This film forming method has a tendency that the film thickness becomes larger as the distance between the evaporation source and the substrate is smaller while the film thickness becomes smaller as the distance is larger. This tendency depends on directivity of the evaporation and a diffusion distance of the evaporation material, and reproducibility thereof is relatively high. Therefore, if the evaporation source is located at the center of the substrate, the film thickness unevenness is apt to occur as illustrated in
In addition, the electrode layer or the like made of an inorganic film is usually formed by sputtering film forming. For instance, in the case of face target RF sputtering film forming, there is a strong correlation between a plasma density distribution and a film forming unevenness. The plasma density distribution depends on an apparatus structure, and reproducibility thereof is also relatively high. The film thickness unevenness in the sputtering film forming is smaller than that in vacuum heat evaporation, but is generally in the range from ±3 to ±5% in the entire region.
As being clear from
First, if the luminance is to be made robust, the pixel film thicknesses of the pixel groups A 801 and B 802 are constituted so that the luminance varies in a complementary manner with respect to the film thickness variation. Here, to vary the luminance in a complementary manner means that when the pixel film thickness increases (or decreases), for example, the luminance of the pixel A 801 increases (or decreases) so that the characteristic varies to be the pixel A′ 803 (A″ 806). In addition, it means that the luminance of the pixel B 802 decrease (increases) so that the characteristic varies to be the pixel B′ 804 (B″ 807). Even if the pixel film thickness increases or decreases, if the pixel A 801 and the pixel B 802 maintain the relationship in the variation, the average luminance characteristics of the pixel A 801 and the pixel B 802 have a small variation with respect to the film thickness variation, which means that the luminance is made robust. In other words, in order that the luminance values of the pixel group A 801 and the pixel group B 802 have a complementary characteristic, it is necessary that in one of the pixel groups A 801 and B 802, the luminance increases while in the other, the luminance decreases when the pixel film thickness varies.
In order to realize the relationship between the pixel group A and the pixel group B, two combinations having the pixel film thickness variations as illustrated in
In order to make the film thickness unevennesses (907 and 908) of the pixel A 901 and the pixel B 902 substantially similar to each other, the film forming quantity only needs to be adjusted to be different in the same film forming step. The film thickness unevennesses (907 and 908) are substantially similar to each other, and hence even if a position of the target pixel (pixel A 901) in the display region is moved, a difference in pixel film thickness between the pixel group A 901 and the pixel group B 902 becomes substantially constant. Then, the pixel film thicknesses thereof are determined so that the maximum value of luminance is sandwiched between the pixel A 901 and the pixel B 902. Thus, a combination of the pixel A 901 and the pixel B 902 having the complementary function may be realized.
However, not only robustness of luminance but also robustness of chromaticity needs to be actually considered. The case where luminance and chromaticity are made robust with respect to the film thickness unevenness is described with reference to
For instance, it is supposed that the target chromaticity 1006 has a sharp maximum shape when a graph of the chromaticity coordinates with respect to the pixel film thickness is plotted. In this case, using a region in which the luminance varies gradually, the pixel (group) A 1001 and the pixel (group) B 1002 are set so as to sandwich the maximum value of the target chromaticity 1006. In order to select the region in which the luminance varies gradually, the film thickness of the structure that gives the maximum interference luminance and its vicinity needs to be avoided.
Then, even if the pixel film thickness increases or decreases, an average luminance of the pixel A 1001 and the pixel B 1002 is substantially constant so that any one of the pixel A 1001 and the pixel B 1002 becomes close to the target chromaticity 1006. By setting the pixel A 1001 and the pixel B 1002 in this way, a chromaticity unevenness with respect to the film thickness unevenness may be reduced. In this case, in order that chromaticity of the pixel group A 1001 and chromaticity of the pixel group B 1002 have a complementary characteristic, it is necessary that a chromaticity coordinate variation with respect to the pixel film thickness variation increases in one of the pixel group A 1001 and the pixel group B 1002 while it decreases in the other.
The description shows the case of one pixel film thickness, but actually, most device structures include two or more pixel film thicknesses (resonator structure). In this case, the pixel film thicknesses are assigned to two axes, for example, so as to consider a combination of the pixel groups satisfying the complementary characteristic by creating a contour graph concerning the luminance and the chromaticity as illustrated in
The pixel A 1101 and the pixel B 1102 sandwich the target chromaticity 1104 giving the maximum shape, and are set so as to have a film thickness structure in which the luminance varies gradually in a complementary manner with respect to the film thickness variation. It is not always necessary to sandwich the peak 1103 giving the maximum luminance, but it is necessary to set the pixel A and the pixel B on both ends on which the variation in luminance becomes a protruding shape. Thus, the luminance variation with respect to the film thickness unevenness may be suppressed while correcting the chromaticity variation.
In addition, the pixel A 1101 and the pixel B 1102 may be set with respect to each of two different maximum values (peaks of the protruding shapes). Here, the case where two protruding shapes are given in the contour graph 1105 of the luminance is considered as two interference conditions. As individual interference order numbers of “pixel film thickness 1, pixel film thickness 2”, two conditions such as “a, b” and “a, b+1” or “a, b” and “a+1, b” are considered. Note that the interference condition means the above-mentioned equation (3), and the interference order number corresponds to m in the equation (3).
For instance,
The individual interference order numbers of “pixel film thickness 1, pixel film thickness 2” correspond to two of “a, b” and “a, b+1”. In this case, the pixel A 1201 is set to a thinner side than the film thickness structure at the interference order number (a, b) peak, and the pixel B 1202 is set to a thicker side than the film thickness structure of the interference order number (a, b+1) peak. As a reason for selecting this structure, it is considered that the pixel film thickness 2 (except for the pixel film thickness 1) includes the cathode and a wiring resistance may be reduced by increasing the thickness of the cathode. Similarly to the above description, it is not always necessary that the pixel A and the pixel B sandwich the peak 1203 giving the maximum luminance, but it is necessary to set the pixel A and the pixel B on both ends on which the luminance variation becomes a protruding shape.
As to the arrangement of the pixel group A and the pixel group B in the image display apparatus according to the present invention, the pixel group A and the pixel group B may be arranged so as to be adjacent to each other for one pixel in plan view. If the pixel group A and the pixel group B are arranged to be adjacent to each other alternately, characteristics of the pixel group A and the pixel group B may be averaged effectively. For instance, in the case where the pixel arrangement is a stripe arrangement, if the pixel group A and the pixel group B are arranged in a checkered pattern as illustrated in
In addition, there are currently considered various pixel arrangements other than the stripe arrangement, and there is no problem if the pixel group A and the pixel group B are arranged to be adjacent to each other substantially alternately in the same manner as in the checkered pattern. For instance,
The image display apparatus of the present invention may be embodied in a high resolution pixel form that is equal to or higher than human visual recognition. Then, the state in which the pixel group A and the pixel group B vary in a complementary manner cannot be distinguished and recognized, and hence averaged light-emitting characteristics between the pixel group A and the pixel group B may be recognized substantially. What extent of resolution is actually adopted is determined based on an application specification, but 100 to 150 pixels per inch or higher resolution may be adopted in the case of a diagonal panel size of 3 inches, for example.
The pixel group A and the pixel group B in the image display apparatus of the present invention have different film thicknesses of at least one layer constituting the organic EL device. The layer to be varied so as to function in a complementary manner is determined by considering a process condition, tact, cost, and other conditions.
It is not necessary to apply the present invention to every color in the display region. The present invention may be applied to only a specific color. For instance, it is very effective to apply the present invention to only the green color that has a highest visual sensitivity considering process cost.
In addition, the effect of the present invention may be exerted on the entire display region, but there may be a case where the effect cannot be exerted completely due to characteristics of “luminance and chromaticity” determined from the device structure and a relationship between the set film thicknesses of the pixel group A and the pixel group B. However, compared with the case where the present invention is not applied, it is a matter of tuning operation how the characteristic unevenness may be suppressed without decreasing characteristic efficiency of the entire display region.
Next, the image display apparatus according to the embodiment of the present invention, particularly, a display panel portion is described. Based on a difference of a light extraction direction with respect to the substrate, the device structure is classified roughly into two types (bottom emission and top emission). In the case of the bottom emission structure, the glass substrate, the transparent electrode, the organic EL device, and the reflective electrode are usually disposed in this order so as to extract light that passes through the substrate. In addition, in the case of the top emission structure, the glass substrate, the reflective electrode, the organic EL device, and the transparent electrode are usually disposed in this order so as to extract light from the side opposite to the substrate. Each of the bottom emission structure and the top emission structure has an advantage and a disadvantage, and hence an appropriate structure is selected according to the application. The reflective electrode may be selected appropriately so as to satisfy a design specification without a problem even in the case of using a metal film or a combination of a transparent electrode and a metal film. Further, the side of the organic EL device that contacts with atmosphere is provided with a glass cap in which desiccant is disposed or a sealing film having a sufficient moisture resistance function, and hence atmosphere stability of the device may be secured.
These components are described in more detail. Glass, Si wafer, ceramic such as alumina, a transparent resin, stainless steel with an insulating film, or the like is used as the substrate constituting the organic EL device. In the case of the bottom emission structure, a member having good light transparency is used. Wiring for driving the device, a transistor portion, a sustaining capacitor portion for sustaining a gate voltage of a transistor in the drive device portion, and wiring for turning on each of the electronic devices are formed and arranged on the substrate by a photolithography process. Note that the wiring for driving the device includes a power supply line, a signal line, a selection line and a ground line, while the transistor portion includes the drive device portion and the selection device portion.
As an electrode of the organic EL device, the anode has a role of injecting holes into the hole-transporting layer, and it is effective to have a work function of 4.5 eV or higher. An anode material used in the present invention is not particularly limited, but an oxide transparent electrode material such as an indium-tin oxide alloy (ITO), indium oxide, or zinc oxide may be used.
As the cathode, a material having a small work function may be used for the purpose of injection of electrons into the electron-transporting band or emission layer. The cathode material is not particularly limited. Specific examples include indium, aluminum, magnesium, a magnesium-indium alloy, a magnesium-aluminum alloy, an aluminum-lithium alloy, an aluminum-scandium-lithium alloy, and a magnesium-silver alloy, and mixtures thereof. Here, as to these electrodes, one of the anode and the cathode is transparent in the visible light region while the other electrode has a high reflectivity. In addition, the thickness of these electrodes is not particularly limited as long as the electrodes perform the natural functions as electrodes, but preferably, the thickness is within the range from 0.02 to 2 μm.
The device structure of the organic EL emission portion according to the present invention is the structure in which one or two organic compound layers or more are stacked between the above-mentioned electrodes, and this structure is not interpreted as a limitation. As examples, the following five structures may be exemplified:
(1) anode, emission layer, cathode;
(2) anode, hole-transporting layer, emission layer, electron-transporting layer, cathode;
(3) anode, hole-transporting layer, emission layer, cathode;
(4) anode, emission layer, electron-transporting layer, cathode; and
(5) anode, hole-transporting layer, emission layer, electron-transporting layer, electron injection layer, cathode.
Organic compounds to be used in the hole-transporting layer, the emission layer, the electron-transporting layer, the hole injection layer, and the electron injection layer are not particularly limited and may be formed of low molecular materials, high molecular materials, or a combination thereof. Further, inorganic compounds may be used when required.
Examples of the compounds include the following.
A hole-transporting material may have excellent mobility for facilitating injection of a hole from an anode and for transporting the injected hole to an emission layer. Examples of low molecular weight materials and high molecular weight materials having hole-injection transporting property include, but are of course not limited to, a triarylamine derivative, a phenylenediamine derivative, a triazole derivative, an oxadiazole derivative, an imidazole derivative, a pyrazoline derivative, a pyrazolone derivative, an oxazole derivative, a fluorenone derivative, a hydrazone derivative, a stilbene derivative, a phthalocyanine derivative, a porphyrin derivative, poly(vinylcarbazole), poly(silylene), poly(thiophene), and other conductive polymers.
As the light-emitting material, fluorescent materials and phosphorescent materials having high emission efficiency are used. The light-emitting material of the present invention is not particularly limited and any compound generally used as a light-emitting material may be used. Examples include a tris(8-quinolinol)aluminum complex (Alq3), bis diphenyl vinyl biphenyl (BDPVBi), 1,3-bis(p-t-butylphenyl-1,3,4-oxadizolyl)phenylene (OXD-7), N,N′-bis(2,5-di-t-butylphenyl) perylene tetracarboxylic diimide (BPPC), and 1,4-bis(p-tolyl-p-methylstyrylphenylamino)naphthalene.
The electron-transporting material may be arbitrarily selected from materials which have a function of transporting the injected electron into the emission layer. The material is selected in consideration of, for example, the balance with the mobility of a carrier of the hole-transporting material. Examples of the material having electron-injection/transporting property include, but are of course not limited to, an oxadiazole derivative, an oxazole derivative, a thiazole derivative, a thiadiazole derivative, a pyrazine derivative, a triazole derivative, a triazine derivative, a perylene derivative, a quinoline derivative, a quinoxaline derivative, a fluorenone derivative, an anthrone derivative, a phenanthroline derivative, and an organometallic complex.
Examples of the hole injection material include transition metal oxide such as MoO3, WO3, and V2O5, and copper phthalocyanine (Cupc).
In addition, examples of the electron injection material include an alkali metal, an alkali-earth metal, a compound thereof, and the like. The electron injection material is contained in the above-mentioned electron-transporting material by a ratio within the range from 0.1 to several tens percent, and hence the electron injectability may be given. The electron injection layer is not necessarily an essential layer, but considering a damage that may be caused afterward in the film forming process for the transparent cathode, the electron injection layer of a thickness within the range from 10 to 100 nm may be inserted so that good electron injectability may be secured.
Further, as production methods for the anode, the hole-transporting layer, the emission layer, the electron-transporting layer, the hole injection layer, the electron injection layer, and the cathode, a vacuum evaporation method, an ionization-assisted evaporation method, sputtering, plasma, or a known coating method are generally used. Further, the anode, the hole-transporting layer, the emission layer, the electron-transporting layer, the hole injection layer, the electron injection layer, and the cathode may be formed using any known coating method (such as a spin coating, dipping, casting, LB, or inkjet method) in which a compound is dissolved in an appropriate solvent. However, for application of the present invention, it is required that the film thickness unevenness generated in the display region and the film thickness itself be accurately determined. In addition, only in the case where reproducibility of the film thickness unevenness and the value of the film thickness is obtained, the film forming method may be freely selected.
After the film forming of the anode, the hole-transporting layer, the emission layer, the electron-transporting layer, the hole injection layer, the electron injection layer, and the cathode, a protective layer is provided for the purpose of preventing contact with, for example, oxygen or moisture. Examples of the protective layer include a metal nitride film made of, for example, silicon nitride or silicon oxynitride, a metal oxide film made of, for example, tantalum oxide, and a diamond thin film. In addition, the examples include a polymer film made of, for example, a fluorine resin, poly(p-xylene), polyethylene, a silicone resin, or a polystyrene resin, and a photocurable resin. In the case of the top emission structure, the protective layer is formed on the light extraction side of the transparent cathode, and therefore there is a need to satisfy the required specifications of moisture permeability and transparency.
In addition, each device itself may be covered with, for example, glass, a gas impermeable film, or a metal, and packaged with a proper sealing resin. In addition, a desiccant may be incorporated into the protective layer for improving the moisture resistance.
Hereinafter, examples of the present invention are described, but the present invention is not limited to the examples. In addition, the pixel region of the image display apparatus is exemplified in the detailed description, but the same is true for other pixel region portions.
The structure film thickness of the same color pixels in the organic EL device is fixed to one design value so as to form a film, and the formed film is regarded as a reference (hereinafter, referred to as Ref.). Further, two pixels that are complementary to the Ref. are regarded as the pixel A and the pixel B.
In Example 1, the luminance and the chromaticity were made robust with respect to the film thickness unevenness in the image display apparatus using the light-emitting device of only the green color.
As the pixel arrangement, the display apparatus was manufactured as illustrated in
As illustrated in
The above-mentioned organic EL display apparatus was manufactured by the following method. First, TFT drive circuits made of low temperature polysilicon were formed on the glass substrate as the support member. Wiring was laid so that current and signals corresponding to one pixel positional coordinates [X(i), Y(i)] may be supplied and controlled. Specifically, a ground line, a signal line, and a common power supply line were arranged along the long side of the pixel, and a scanning line was arranged along the short side of the pixel. A leveling film made of an acrylic resin was formed thereon so as to form a TFT substrate 103.
Further, Ag alloy (AgPdCu) as a reflective metal was formed thereon by the sputtering method to have a thickness of approximately 100 nm, and a reflective electrode 104 was patterned. A transparent conductive film ITO was formed by the sputtering method to have a thickness of 77 nm, and an anode layer 105 was patterned. Further, a device separation film was formed with an acrylic resin so as to prepare a substrate with an anode. This was cleaned by ultrasonic cleaning with isopropyl alcohol (IPA), and then dried after boil washing. After that, it was cleaned by UV/ozone cleaning, and film forming of the organic compound was performed by the vacuum evaporation.
A film of FLO3 was formed as the hole-transporting layer 106 on the cleaned anode layer 105. A shadow mask was used for separating film thicknesses of the pixel A and the pixel B. The film of 110 nm was formed as the hole-transporting layer of the pixel group A, and the film of 130 nm was formed as the hole-transporting layer of the pixel group B. A vacuum degree in this case was 1×10-4 Pa, and an evaporation rate was 0.2 nm/sec.
Next, a film of a green emission layer was formed as an organic emission layer 107 by using a shadow mask. As the green emission layer, Alq3 as host and light-emitting compound coumarin 6 were evaporated together so as to form the emission layer having a thickness of 40 nm. The film forming was performed in the condition of a vacuum degree of 1×10-4 Pa in the evaporation, and a film forming rate of 0.2 nm/sec.
Further, as a common electron-transporting layer 108, a film of bathophenanthroline (Bphen) was formed to have a film thickness of 10 nm by the vacuum evaporation method. The vacuum degree in the evaporation was 1×10-4 Pa, the film forming rate was 0.2 nm/sec. Next, Bphen and Cs2CO3 were evaporated together (at a weight ratio of 90:10) as a common electron injection layer 109, so as to have a film thickness of 20 nm. Vacuum degree in the evaporation was 3×10-4 Pa, and the film forming rate was 0.2 nm/sec.
The substrate on which film forming had been performed up to the electron injection layer 109 was moved to the sputtering device without breaking the vacuum, and an IZO film was formed as the cathode layer (transparent cathode) 110. The IZO film of the pixel A was formed to have a thickness of 60 nm, and the IZO film of the pixel B was formed to have a thickness of 70 nm. Further, a sealing glass substrate 111 having desiccant provided to the inside thereof was bonded to seal with sealing adhesive, and hence the organic EL display apparatus was obtained.
The film thickness values of the Ref. are shown in Table 1 below, in which the film thickness of the hole-transporting layer is 120 nm, the IZO film thickness of the cathode is 65 nm, and other film thicknesses are the same as those of the pixel A and the pixel B.
In the manufactured organic EL display apparatus, the drive signal programmed to have a rate of 16.7 msec per frame was input to the drive driver, and hence each pixel circuit supplied emission current to the organic EL device. Then, light emissions of the regions that were considered to be an upper limit value, an average value, and a lower limit value in each film thickness value of the pixel group A and the pixel group B were measured.
Results of the measurement of the Ref. item and the complementary item are shown in Table 2 below. As being complementary, an unevenness range of luminance with respect to the film thickness unevenness changed from 13.9% to 13.3% (unevenness ratio to an average value of itself), the unevenness range of the chromaticity was decreased from 0.105 to 0.082 of CIE x, and from 0.026 to 0.014 of CIE y. As being clear from the results, robustness of the luminance and the chromaticity was improved with respect to the film thickness unevenness.
The method of manufacturing the light-emitting device according to Example 2 and the structure of the image display apparatus are similar to those of Example 1. However, the pixel A and the pixel B are not constituted so as to sandwich the one extreme value as illustrated in the map diagram of
In the manufactured organic EL display apparatus, the drive signal programmed to have a rate of 16.7 msec per frame was input to the drive driver, and hence each pixel circuit supplied emission current to the organic EL device. Then, light emissions of the regions that were considered to be an upper limit value, an average value, and a lower limit value in each film thickness value of the pixel group A and the pixel group B were measured.
Results of the measurement of the Ref. item and the complementary item are shown in Table 4 below. As being complementary, an unevenness range of luminance with respect to the film thickness unevenness was decreased from 13.9% to 13.2% (unevenness ratio to an average value of itself), the unevenness range width of the chromaticity was decreased from 0.105 to 0.085 of CIE x, and from 0.026 to 0.016 of CIE y. As being clear from the results, robustness of the luminance and the chromaticity was improved with respect to the film thickness unevenness. Further, in this example, reduction in power consumption was also observed due to reduction in wiring resistance of the cathode.
In Example 3, an RGB full color image display apparatus was manufactured so that the complementary pixel groups (A and B) are set only in the green color devices. A panel size is 3 inches of QVGA (150 pixels per inch), in which three color devices of 320 pixels in row and 240 pixels in column are arranged as a stripe arrangement. An emission area is set to have 40% aperture based on a device separation film between colors, a BM arrangement and the like. A method of manufacturing the light-emitting device and a fundamental structure of the image display apparatus are similar to those of Example 1. A specific film thickness structure of a red color device is shown in Table 5 below, a specific film thickness structure of a green color device is shown in Table 6 below, and a specific film thickness structure of a blue color device is shown in Table 7 below.
In the manufactured organic EL display apparatus, the drive signal programmed to have a rate of 16.7 msec per frame was input to the drive driver, and hence each pixel circuit supplied emission current to the organic EL device. Then, light emissions of the green color of the regions that were considered to be an upper limit value, an average value, and a lower limit value in each film thickness value of the pixel group A and the pixel group B were measured. Table 8 below shows measured data concerning the unevenness range of the relative luminance and the chromaticity.
Results of the measurement of the Ref. item and the complementary item were compared. As being complementary, an unevenness range of luminance with respect to the film thickness unevenness was decreased from 14.9% to 11.3% (decrease of 3.6%), the unevenness range of the chromaticity was decreased from 0.107 to 0.082 of CIE x, and from 0.055 to 0.038 of CIE y. In this way, as being complementary, robustness of the luminance and the chromaticity was improved with respect to the film thickness unevenness.
In this way, the RGB full color image display apparatus was manufactured, in which the light-emitting characteristics of the green color having high visual sensitivity were made robust.
In order to reduce cost of an image display apparatus such as a display or a monitor, it is inevitable that a mother substrate becomes large. This is true also for the organic EL display apparatus, but it is very difficult to form the thin film device such as the organic EL device uniformly in a large area. However, according to the image display apparatus of the present invention, yield may be improved without developing or introducing a new device or technique. The image display apparatus of the present invention has high potential to be developed as a technique for solving a manufacturing problem with the organic EL device.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2009-134064, filed Jun. 3, 2009, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-134064 | Jun 2009 | JP | national |
