JP2004095545A - Electroluminescent element and luminescent device using electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an EL element having a thicker film than the conventional one and operating at low voltages without the addition of an acceptor or a donor. <P>SOLUTION: The EL element is manufactured by successively laminating an electroluminescent film 103 containing an organic compound performing electroluminescence, a floating electrode 104, an electron transmitting auxiliary layer 105, and a cathode 102 on an anode 101. The electroluminescent film 103 has thickness similar to the conventional one (an order of about 100 nm), and the electron transmit auxiliary layer 105 may have similar thickness to the electroluminescent film 103. By introducing a hole blocking material in the electron transmit auxiliary layer, the EL element operating at lower voltage than the conventional one can be realized. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to an electroluminescent element (hereinafter simply referred to as an “EL element”) having an anode, a cathode, and a film containing an organic compound that can emit light by applying an electric field (hereinafter simply referred to as “electroluminescent film”). "). In particular, the present invention relates to an EL element having a high yield and excellent reliability and driving voltage, and a light emitting device using the EL element. Note that the light-emitting device in this specification includes an image display device using an EL element. In addition, a connector, for example, a flexible printed circuit board (FPC: Flexible Printed Circuit) or a TAB (Tape Automated Bonding) tape or TCP (Tape Carrier Package) is attached to the EL element, and a printed wiring board is attached to the end of the TAB tape or TCP. It is assumed that the light emitting device also includes all the modules provided or IC modules directly mounted on an EL element by a COG (Chip On Glass) method.

An EL element using an organic compound as a light emitter is an element that emits light when an electric field is applied and a current flows. The light emission mechanism is such that by applying a voltage with an electroluminescent film sandwiched between electrodes, electrons injected from the cathode and holes injected from the anode recombine in the electroluminescent film, and excited molecules ( Hereinafter, it is said that when the molecular excitons return to the ground state, they emit energy and emit light.

In addition, as a kind of molecular exciton which an organic compound forms, it is thought that a singlet excited state and a triplet excited state are possible, However, In this specification, the case where either excited state contributes to light emission is also included. I will do it.

In such an EL element, the electroluminescent film is usually formed with a thin film of about 100 nm. Further, since the EL element is a self-luminous element in which the electroluminescent film itself emits light, a backlight as used in a conventional liquid crystal display is not necessary. Therefore, it is a great advantage that it can be made extremely thin and light.

For example, in an electroluminescent film of about 100 nm, the time from carrier injection to recombination is about several tens of nanoseconds considering carrier mobility, and the process from carrier recombination to light emission is Even if included, light emission occurs on the order of microseconds or less. Therefore, one of the features is that the response speed is very fast.

Furthermore, since an EL element using an organic compound as a light emitter is a carrier injection type element, it can be driven by a DC voltage and noise is hardly generated. Regarding the driving voltage, first, the thickness of the electroluminescent film is made to be a uniform ultra-thin film of about 100 nm, and an electrode material is selected so as to reduce the carrier injection barrier with respect to the electroluminescent film. As a result, a sufficient luminance of 100 cd / m ² was achieved at 5.5 V (see Non-Patent Document 1, for example).
C. W. C. W. Tang et al., Applied Physics Letters, 1987, Vol. 51, no. 12, 913-915

Thus, an EL element using an organic compound as a light emitter has characteristics such as thin and light weight, high-speed response, and direct current low voltage driving, and is attracting attention as a next-generation flat panel display element. Further, since it is a self-luminous type and has a wide viewing angle, the visibility is relatively good, and it is considered to be particularly effective as an element used for an in-vehicle display screen or a display screen of a portable device. In fact, some in-car audio systems use EL elements for area color display screens.

By the way, the EL element in Non-Patent Document 1 is an idea of functional separation, in which hole transport is performed by a hole transport layer, and electron transport and light emission are performed by an electron transporting light emitting layer. This concept of functional separation has further developed into a double heterostructure (three-layer structure) concept in which a light emitting layer is sandwiched between a hole transport layer and an electron transport layer (see, for example, Non-Patent Document 2).
Chihaya Adachi, 3 others, Japanese Journal of Applied Physics, Vol. 27, no. 2, L269-L271 (1988).

The advantage of such functional separation is that it is no longer necessary to have various functions (such as light-emitting properties, carrier transportability, and carrier injection properties from electrodes) at the same time due to the functional separation. Etc. (for example, it becomes unnecessary to search for a bipolar material forcibly). That is, a high light emission efficiency can be easily achieved by combining materials having good light emission characteristics and materials having excellent carrier transportability.

Among the functional separations, the concept of an anode buffer layer and a cathode buffer layer has been proposed as the introduction of the function of injecting carriers, and driving at a lower voltage is possible. For example, at the interface with the cathode, there is a report that a material that relaxes the energy barrier is inserted to improve the carrier injectability and reduce the driving voltage (see, for example, Non-Patent Document 3). In Non-Patent Document 3, the use of Li ₂ O as the cathode buffer layer succeeds in reducing the drive voltage.
Takeo Wakimoto, 5 others, IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 44, NO.8, 1245-1248 (1997).

Further, in particular, in recent years, a buffer layer using a polymer (hereinafter referred to as “polymer buffer layer”) has attracted attention (see, for example, Non-Patent Document 4). Non-Patent Document 4 reports that the use of a polymer anode buffer layer is effective in reducing the voltage, extending the life, and improving the heat resistance.
This is said to be effective in reducing short circuits.
Yoshiharu Sato, “Problems for practical use: From the viewpoint of material development”, Journal of the Japan Society of Applied Physics, Organic Molecules and Bioelectronics, vol.11, No.1, 86-99 (2000).

Furthermore, since the conductivity of the polymer buffer layer is improved by introducing an appropriate acceptor or donor, an EL element that normally cannot emit light unless the film thickness is about 100 nm can be made thicker by introducing the polymer buffer layer. The point is characteristic. It has been reported in Non-Patent Document 4 that, by this, the influence of dust and protrusions on the electrode can be reduced and the surface can be flattened. Therefore, in the conventional film thickness of about 100 nm, there is a risk of short circuit due to dust and protrusions on the electrode, but the polymer buffer layer has an effect of reducing the risk. For this reason, the improvement of the yield is also a great merit.

Therefore, the polymer buffer layer described above can simultaneously solve the theme that can be a dilemma for the EL element, that is, the drive voltage can be reduced while the film thickness is increased.

However, when aiming to increase the thickness of the polymer buffer layer, water is often used as a solvent, which is not preferable for an EL device using an organic compound that is easily affected by moisture. According to Non-Patent Document 4, it is possible to use an organic solvent depending on the material, but in any case, it is inferior in purity as compared with a process that is produced in a vacuum, and affects the deterioration of the EL element. .

Further, when an EL element using these materials as a buffer layer is applied to a display device formed by disposing each element in a matrix shape, a problem of crosstalk occurs. That is, most of the polymer buffer layers have conductivity as described above, but these polymers are usually applied to the entire surface by spin coating or the like. Between the pixel and the pixel).

For example, when a passive matrix display device using a polyethylenedioxythiophene / polystyrene sulfonic acid (hereinafter referred to as “PEDOT / PSS”), which is a conductive polymer to which an acceptor is added, is used as an anode buffer layer, crosstalk occurs. It has been reported that this occurs (for example, see Non-Patent Document 5). In Non-Patent Document 5, as a solution, crosstalk is prevented by intentionally increasing the resistivity of PEDOT / PSS. However, if the resistivity is increased, the thickness of the polymer buffer layer is now increased. The thickness cannot be increased (that is, it becomes difficult for current to flow through the EL element). Therefore, the feature of flattening the electrode surface by thickening and preventing a short circuit is lost. Further, if the resistivity is increased, the drive voltage naturally increases, and the feature of low drive voltage is lost.
A. Erschner, three others, Asia Display / IDW '01, 1427-1430 (2001).

On the other hand, there has also been proposed a method of forming a thick film EL element by co-evaporation of an organic compound and an acceptor (or donor) (for example, see Non-Patent Document 6). In Non-Patent Document 6, a thick film EL element with a low driving voltage is achieved by co-evaporating VoPc, which is a hole transporting material, and F4-TCNQ, which is an acceptor.
J. et al. Blochwitz, 3 others, Applied Physics Letters, vol. 73, 729-731 (1998))

With this method, good results can be obtained in terms of purity, and there is no problem of crosstalk because it is possible to perform painting with a shadow mask. However, there is a problem in the chemical stability of the added acceptor and donor, which affects the lifetime of the device. The problem of acceptor and donor chemical stability is also the same for the polymer buffer layer.

There is a completely different concept from the above, and a novel element structure is proposed in which the current efficiency is rather improved by increasing the film thickness (see, for example, Non-Patent Document 7). In the method of Non-Patent Document 7, more voltage must be applied compared to the conventional EL element, but there is an advantage that current efficiency can be improved.
Junji Kido, Jun Endo, Satoshi Nakata, Koichi Mori, Kei Yokoi, Toshio Matsumoto The 49th JSAP-Related Physics Conference Lecture Proceedings (2002.2.3), p. 1308, 27p-YL-3

If the element structure of Non-Patent Document 7 is used, the current efficiency can theoretically be improved as much as possible. However, as the current efficiency is doubled or tripled, the driving voltage is also doubled or tripled. End up. Therefore, it is effective as an application such as lighting, but is not suitable for an application where a low driving voltage is desired such as a portable device.

From the above, there is a demand for an EL element that has a higher yield by increasing the thickness compared to the conventional film, and that is excellent in reliability and driving voltage.

Therefore, an object of the present invention is to provide an EL element that is thicker than the conventional element and that operates at a low voltage without adding an acceptor or a donor. That is, it is an object of the present invention to provide an EL element that has a high yield and has an excellent element life and driving voltage. It is another object of the present invention to provide a light-emitting device which has a good yield and can be kept long by using such an EL element.

As a result of intensive studies, the present inventor has devised means that can solve the above problems by forming a novel element structure. The basic configuration is shown in FIG. 1, FIG. 2 and FIG.

FIG. 1 shows an EL element in which an electroluminescent film 103 containing an organic compound capable of electroluminescence, a floating electrode 104, an electron transport auxiliary layer 105, and a cathode 102 are sequentially stacked on an anode 101. The electroluminescent film 103 is about the conventional film thickness (on the order of about 100 nm), and the electron transport auxiliary layer 105 may have the same film thickness as the electroluminescent film 103.

By adopting such an element structure, the element operates at a driving voltage almost the same as that of a conventional EL element (that is, a structure in which the electroluminescent film 103 is sandwiched between the anode 101 and the cathode 102) or is driven more. The inventor has found that it is even possible to lower the voltage. This means that even if a thick EL element is manufactured without adding an acceptor or a donor, the device operates at a low voltage. That is, it leads to an EL element having a good yield and excellent element life and driving voltage.

Therefore, the EL element of the present invention is characterized in that an anode, an electroluminescent film containing an organic compound capable of electroluminescence, a floating electrode, an electron transport auxiliary layer, and a cathode are sequentially laminated.

Incidentally, in recent years, a method for forming a film on the cathode by sputtering has been studied. However, there is a concern about damage to the organic compound during sputtering, particularly damage to the light emitting region (in order to prevent damage, a method of performing sputtering after forming CuPc is the mainstream). However, in the present invention shown in FIG. 1, since the electron transport auxiliary layer 105 can be made relatively thick, the electroluminescent film 103 is hardly damaged. Therefore, the present invention is very effective when the cathode 102 is formed by sputtering.

Therefore, the present invention is characterized in that, in the structure of FIG. 1, the cathode includes a conductive film formed by a sputtering method. Moreover, it is suitable also about the method of taking out light from a cathode side by sputtering a transparent electrode as a cathode. Therefore, the present invention is characterized in that in the structure of FIG. 1, the cathode has a light-transmitting property and includes a conductive film formed by a sputtering method.

Furthermore, the effect of the present invention can also be obtained by a structure (FIG. 2) in which the same structure as FIG. 1 is laminated in the opposite direction. That is, an EL element in which an electron transport auxiliary layer 205, a floating electrode 204, an electroluminescent film 203, and an anode 201 are sequentially stacked on the cathode 202. Also in this case, the electroluminescent film 203 is about the conventional film thickness (on the order of about 100 nm), and the electron transport auxiliary layer 205 may be about the same film thickness as the electroluminescent film 203.

Therefore, the EL device of the present invention is characterized in that a cathode, an electron transport auxiliary layer, a floating electrode, an electroluminescent film containing an organic compound capable of electroluminescence, and an anode are sequentially laminated.

In FIG. 12, an electroluminescent film 603 containing an organic compound capable of electroluminescence, an electron transport layer 606, a floating electrode 604, an electron transport auxiliary layer 605, and a cathode 602 are sequentially stacked on the anode 601. It is an EL element. Thus, a structure in which the floating electrode 604 is sandwiched between the electron transport layer 606 and the electron transport auxiliary layer 605 may be employed. Thus, by separating the floating electrode 604 and the electroluminescent film 603 by the electron transport layer 606, quenching (quenching) by the floating electrode 604 can be effectively prevented. Of course, the effect of the present invention can be obtained even in a structure in which the same structure as in FIG. 12 is laminated in the opposite direction.

There are various variations in the structure of the electroluminescent film, such as a stacked structure of a hole transport layer and an electron transport layer, a single layer structure using a polymer compound, and a high-efficiency device using light emission from a triplet excited state. Over. Further, the electron transport layer and the electron transport auxiliary layer can be either a single layer structure or a laminated structure.

In addition, as a kind of molecular exciton which an organic compound forms, it is thought that a singlet excited state and a triplet excited state are possible, However, In this specification, the case where either excited state contributes to light emission is also included. I will do it.

Since the above-described electron transport auxiliary layer is a layer that conceptually allows only electrons to pass, it is preferable to have an electron transport material having a higher electron mobility than a hole mobility.

Also, a more preferable configuration of the present invention is that a hole blocking material is contained in at least one of the electroluminescent film and the electron transport auxiliary layer. By adopting such a configuration, a driving voltage lower than or equal to that of a conventional EL element (that is, a structure in which the electroluminescent film 103 is simply sandwiched between the anode 101 and the cathode 102) can be achieved. . In this case, a configuration in which a hole blocking material is contained in the electron transport auxiliary layer is more preferable.

Note that these hole blocking materials preferably have an ionization potential of 5.8 eV or more. As a suitable material group, an organic compound including a phenanthroline skeleton and a pentacoordinate metal complex having a group 13 element as a central metal can be given.

By the way, normally, the cathode must use a material having a small work function, that is, an easily oxidizable and unstable material. When the cathode is sequentially stacked from the anode to the cathode, the unstable cathode is exposed to the outermost surface. (For example, FIG. 1). However, the EL element of the present invention has an advantage that it operates sufficiently even when a cathode is formed using a conductor having a work function of 3.5 eV or more when a hole blocking material is applied to the electron transport auxiliary layer. . Therefore, in the present invention, when a hole blocking material is applied to the electron transport auxiliary layer, the cathode is made of a conductor having a work function of 3.5 eV or more.

The floating electrode is preferably made of a conductor having a work function of 3.5 eV or less because electrons need to be injected into the electroluminescent film. When the work function is 3.5 eV or less, it is an unstable conductor that is easily oxidized, but in the invention, it is floating, that is, the surrounding area is covered with another material, so that deterioration can be suppressed. .

Further, as another configuration of the floating electrode, a configuration including an insulating film provided on the side in contact with the electroluminescent film and a conductive film provided on the side in contact with the electron transport layer may be employed. In this case, lithium fluoride or calcium fluoride is effective as the insulating film.

In the EL element of the present invention described above, the electron transport auxiliary layer can be formed with a thickness of 10 nm to 1 μm. Therefore, an effect sufficient for increasing the thickness of the EL element itself can be obtained.

Since the EL element of the present invention described above operates at a low voltage even when a thick EL element is manufactured without adding an acceptor or a donor, the yield is high and the element lifetime and It is an EL element that is excellent in driving voltage. Therefore, a light-emitting device using the EL element of the present invention and an electric appliance using the light-emitting device have an advantage of good yield and keeping it long.

Therefore, the present invention includes a light-emitting device using the above-described EL element of the present invention and an electric appliance using the light-emitting device.

Note that the light emitting device in this specification includes an image display device using an EL element. In addition, a connector, for example, a flexible printed circuit board (FPC: Flexible Printed Circuit) or a TAB (Tape Automated Bonding) tape or TCP (Tape Carrier Package) is attached to the EL element, and a printed wiring board is attached to the end of the TAB tape or TCP. It is assumed that the light emitting device also includes all the modules provided or IC modules directly mounted on an EL element by a COG (Chip On Glass) method.

By implementing the present invention as described above, it is possible to provide an EL element that is thicker than the conventional film and that operates at a low voltage without adding an acceptor or a donor. it can. That is, it is possible to provide an EL element that has a good yield and excellent element life and driving voltage. Further, by using such an EL element, it is possible to provide a light-emitting device which has a good yield and can be kept long.

Hereinafter, an embodiment of the present invention will be described in detail with reference to an operation principle and a specific configuration example. Note that in the EL element, one of the electrodes may be transparent in order to extract emitted light. Therefore, not only the conventional device structure in which a transparent electrode is formed on the substrate and the light is extracted from the substrate side, but also the structure in which the light is extracted from the opposite side of the substrate and the structure in which the light is extracted from both sides of the electrode are applied. Is possible.

First, the operation principle of the EL element of the present invention will be described with reference to FIGS. FIG. 3A shows an organic compound layer 303 sandwiched between electrodes 301 and 302, where 303 is a layer made of an electron transporting material. The electrodes 301 and 302 are designed so that only an electronic current flows as shown in the figure. Further, it is assumed that the current density J1 flows when the voltage V is applied with the film thickness 303 as d.

At this time, J1 is a current called a space charge limited current (SCLC). SCLC is a current that flows by injecting and moving a space charge from the outside, and its current density is expressed by the child rule, that is, the following formula (1). ε is a relative dielectric constant, ε ₀ is a vacuum dielectric constant, and μ is a carrier mobility.

Generalizing this equation, it can be expressed as the following equation (2). α is a material-specific constant.

Here, it is assumed that exactly the same material is doubled, that is, a 2d film is formed and a voltage of V is applied (FIG. 3B). The current density J2 at this time is represented by the following formula (3).

From the formulas (2) and (3), J1 = 8 · J2. In other words, it can be seen that the current does not flow abruptly as the film thickness is increased by simply applying it to the SCLC equation.

Here, as shown in FIG. 3C, it is assumed that the floating electrode 304 is sandwiched between the first organic compound layer 303a and the second organic compound layer 303b in the middle of FIG. 3B. At this time, if the floating electrode 304 has almost no electron injection barrier to the first organic compound layer 303a and the hole injection barrier to the second organic compound layer 303b is extremely high, the floating electrode 304 is It is a layer that only allows electrons to pass through.

Since the first organic compound layer 303a and the second organic compound layer 303b are made of the same material, the current density J3 in this case can be expressed by the following formula (4).

Thus, even when the simplest model is taken into consideration, a current twice as large as that in FIG. 3B can be passed only by sandwiching the floating electrode 304. That is, in the structures of FIGS. 3A to 3C, if the same voltage V is applied, J1> J3> J2 from the equations (2) to (4).

Based on this concept, FIG. 4 shows a comparison between a conventional EL element, a conventional double-thickness EL element, and the EL element of the present invention. FIG. 4A shows a conventional EL device in which a hole transport layer 403, an electron transport layer 404, and a cathode 402 are stacked on an anode 401. Either the hole transport layer 403 or the electron transport layer 404 may emit light.

On the other hand, FIG. 4B shows an EL element having a film thickness twice that of FIG. 4A. For comparison with FIG. 4C, only the electron transport layer 404 is further formed by 100 nm. It is a film. In FIG. 4 (b), almost no current flows and only weak light emission can be obtained due to the film thickness (only the electron transport layer becomes thick, so that the carrier balance is lost or the light path is changed to weaken the light emission). This phenomenon naturally exists, but is not taken into consideration here, and it is considered that the fact that current does not flow has a more serious effect on light emission.)

Here, FIG. 4C shows the EL element of the present invention (the structure of FIG. 1). A floating electrode 405 is inserted into the electron transport layer 404 of FIG. This is divided into a layer 404-1 and a second electron transport layer 404-2. In other words, the second electron transport layer and the cathode may be further laminated on the element shown in FIG.

At this time, by providing the floating electrode 405 with the same function as the floating electrode 304 described in FIG. 3, the second electron transport layer 404-2 only transports electrons and does not contribute to light emission. And by the analogy of the content demonstrated in FIG. 3, compared with FIG.4 (b), many electric currents can be sent. Therefore, even if the film thickness is increased, a certain amount of current can be passed to ensure light emission. The second electron transport layer 404-2 at this time corresponds to the electron transport auxiliary layer of the present invention.

Of course, when this simplest model is considered, the amount of current flowing through the element of the present invention of FIG. 4 (c) is still smaller than the amount of current flowing through the conventional element of FIG. 4 (a). Accordingly, the light emission is weakened accordingly. However, in practice, as shown in an example described later, it is known that FIG. 4C is much closer to the characteristics of FIG. 4A than FIG. 4B. This is because the current flowing in the actual EL element does not follow a simple child rule (Equation (1)), but a more complex current (specifically, a TCLC (Trap Charge Limited Current) limited by carrier trapping). )).

Of course, such a concept can also be applied to the hole transport layer side. That is, the structure is "anode \ hole transport auxiliary layer \ floating electrode \ electroluminescent film \ cathode". However, in general, since an organic compound is less easily transported by an electron, the concept of embedding a floating electrode in an electron transport layer as shown in FIG. 4C of the present invention is more effective.

By making further improvements based on the principle described above, it is easier for the element of FIG. 4C to flow than the element of FIG. That is, it was discovered that a reversal phenomenon can occur, that is, it can operate at a low voltage). This phenomenon is achieved by introducing a hole-blocking material anywhere between the anode 401 and the cathode 402 in the element structure of FIG. The driving voltage decreases most when the hole blocking material is introduced into the second electron transport layer 404-2 (that is, the electron transport auxiliary layer in the present invention).

Although it is difficult to explain this phenomenon easily, we think as follows. By introducing a hole blocking material, hole carriers are effectively blocked and accumulated locally. In particular, when a hole blocking material is introduced into the electron transport auxiliary layer, a large amount of hole carriers are locally accumulated because the floating electrode 405 is a conductor. Electrons are effectively transported or injected into the electroluminescent film by the internal electric field generated by the accumulated hole carriers. As a result, it is considered that the drive voltage could be further reduced as compared with the conventional FIG. 4A even with the element of FIG.

The basic operation principle of the present invention has been described above. In the following, the preferred configuration of the electron transport auxiliary layer used in the present invention, the preferred configuration of the floating electrode, the preferred configuration material of the electroluminescent film, and the like are listed. However, the present invention is not limited to these.

First, as described above, an electron transporting material is preferable as a constituent material of the electron transport auxiliary layer. However, a metal complex is often used as the electron transporting material, and tris (8-quinolinolato) aluminum (abbreviation: Alq). ), Tris (4-methyl-8-quinolinolato) aluminum (abbreviation: Almq), bis (10-hydroxybenzo [h] -quinolinato) beryllium (abbreviation: Bebq), and other metal complexes having a quinoline skeleton or a benzoquinoline skeleton, And bis (2-methyl-8-quinolinolato)-(4-hydroxy-biphenylyl) -aluminum (abbreviated as BAlq) which is a mixed ligand complex. In addition, bis [2- (2-hydroxyphenyl) -benzoxazolate] zinc (abbreviation: Zn (BOX) ₂ ), bis [2- (2-hydroxyphenyl) -benzothiazolate] zinc (abbreviation: Zn (BTZ)) There are also metal complexes having an oxazole or thiazole ligand such as ₂ ). In addition to metal complexes, 2- (4-biphenylyl) -5- (4-tert-butylphenyl) -1,3,4-oxadiazole (abbreviation: PBD), 1,3-bis [5- Oxadiazole derivatives such as (p-tert-butylphenyl) -1,3,4-oxadiazol-2-yl] benzene (abbreviation: OXD-7), 3- (4-tert-butylphenyl) -4 -Phenyl-5- (4-biphenylyl) -1,2,4-triazole (abbreviation: TAZ), 3- (4-tert-butylphenyl) -4- (4-ethylphenyl) -5- (4-biphenylyl) ) -1,2,4-triazole (abbreviation: p-EtTAZ) and other triazole derivatives, bathophenanthroline (abbreviation: BPhen), phenanthrori such as bathocuproin (abbreviation: BCP) Derivative has an electron transporting property.

Also, the constituent material of the electron transport auxiliary layer is preferably a hole blocking material, such as PBD, OXD-7, TAZ, p-EtTAZ, BPhen, BCP, and the like. In particular, organic compounds having a phenanthroline skeleton such as BPhen and BCP have high hole blocking properties. Further, a pentacoordinate metal complex having a group 13 element typified by BAlq as described above as a central metal is preferable from the viewpoint of film quality stability.

As the floating electrode, a metal thin film, a metal oxide thin film, an organic conductor thin film, or a combination thereof can be used. In particular, since it is necessary to inject electrons into the electroluminescent film, the work function is preferably made of a conductor having a work function of 3.5 eV or less, an alkali metal, an alkaline earth metal, a rare earth metal, or an alloy containing these metal elements Etc. are available. For example, Mg: Ag alloy, Al: Li alloy, Ba, Ca, Yb, Er, etc. can be used. Alternatively, a structure including an inorganic dielectric thin film such as LiF, a metal oxide thin film such as Li oxide, an organic thin film containing alkali metal or alkaline earth metal ions, and a metal film such as Al may be used. Furthermore, the floating electrode may be formed in a cluster shape instead of a film shape.

As a configuration of the electroluminescent film, a structure and a constituent material of a generally used EL element may be used. Specifically, as described in Non-Patent Document 1, a stacked structure of a hole transport layer and an electron transport layer, a single layer structure using a polymer compound, and a high light emission using triplet excited state are used. There are many variations such as efficiency elements.

As the anode material, transparent conductive inorganic compounds such as ITO (indium tin oxide) and IZO (indium zinc oxide) are often used as long as light is extracted from the anode. Ultra-thin films such as gold are also possible. When non-transparent may be used (when light is extracted from the cathode side), a metal / alloy or conductor having a certain work function that does not transmit light may be used, and examples thereof include W, Ti, and TiN. If the material has a high melting point, it is better to form it by sputtering.

The cathode material is preferably made of a conductor having a work function of 3.5 eV or less, and an alkali metal, an alkaline earth metal, a rare earth metal, or an alloy containing these metal elements can be used. For example, Mg: Ag alloy, Al: Li alloy, Ba, Ca, Yb, Er, etc. can be used. Alternatively, a structure including an inorganic dielectric thin film such as LiF, a metal oxide thin film such as Li oxide, an organic thin film containing alkali metal or alkaline earth metal ions, and a metal film such as Al may be used. In addition, when a hole blocking material is applied to the electron transport auxiliary layer, a general-purpose metal such as Al may be used. Further, these cathodes may be formed by a sputtering method.

In addition, when extracting light from the cathode side, an ultra-thin film of the above-mentioned cathode material may be used. However, in the structure in which the cathode is finally formed as shown in FIG. 1, there is a method using an ITO sputtered film. At this time, it is preferable to sputter ITO after forming the CuPc film, but even if there is no CuPc, the electron transport auxiliary layer is thick and therefore the damage to the light emitting region is small.

The structure of the material used for the EL element of the present invention has been described above. Next, a multi-chamber system manufacturing in which the EL element or a light emitting device using the EL element is fully automated from deposition to sealing. A specific example of manufacturing with an apparatus is illustrated. A diagram of the manufacturing apparatus is shown in FIG.

FIG. 5 illustrates gates 500a to 500y, transfer chambers 502, 504a, 508, 514, and 518, delivery chambers 505, 507, and 511, a preparation chamber 501, a first film formation chamber 506H, and a second film formation chamber. 506B, a third film formation chamber 506G, a fourth film formation chamber 506R, a fifth film formation chamber 506E, other film formation chambers 509, 510, 512, 513, 532, and an installation chamber 526R in which a vapor deposition source is installed. 526G, 526B, 526E, 526H, pretreatment chambers 503a, 503b, sealing chamber 516, mask stock chamber 524, sealing substrate stock chamber 530, cassette chambers 520a, 520b, tray mounting stage 521, , And a take-out chamber 519. Note that a transfer mechanism 504b for transferring the substrate 504c is provided in the transfer chamber 504a, and each of the other transfer chambers is also provided with a transfer mechanism.

Hereinafter, a procedure in which a substrate on which an anode and an insulator (partition) covering the end of the anode are provided in advance is carried into the manufacturing apparatus shown in FIG. 5 and an EL element or a light emitting device using the EL element is manufactured. Illustrate. As an example of manufacturing a light-emitting device using an EL element, for example, a plurality of thin film transistors (current control TFTs) connected to an anode in advance on a substrate and other thin film transistors (such as switching TFTs) are provided. A substrate for an active matrix light-emitting device which is provided with a driver circuit including a thin film transistor may be used.

First, the substrate is set in the cassette chamber 520a or the cassette chamber 520b. When the substrate is a large substrate (for example, 300 mm × 360 mm), it is set in the cassette chamber 520b. In the case of a normal substrate (for example, 127 mm × 127 mm), after being set in the cassette chamber 520a, it is transported to the tray mounting stage 521, and a plurality of substrates are set on the tray (for example, 300 mm × 360 mm).

The set substrate (substrate provided with an anode and an insulator covering the end of the anode) is transferred to the transfer chamber 518.

Before setting in the cassette chamber, a porous sponge (typically made of PVA (polyvinyl alcohol)) containing a surface active agent (weak alkaline) to the anode surface to reduce point defects. It is preferable to remove the dust on the surface by washing with nylon or the like. As a cleaning mechanism, a cleaning device having a roll brush (manufactured by PVA) that rotates around an axis parallel to the surface of the substrate and contacts the surface of the substrate may be used, or may rotate around an axis perpendicular to the surface of the substrate. You may use the washing | cleaning apparatus which has a disk brush (product made from PVA) which contacts the surface of a board | substrate while moving. In order to remove moisture and other gases contained in the substrate before forming a film containing an organic compound, annealing for deaeration is preferably performed in a vacuum, and is connected to the transfer chamber 518. Then, it may be transferred to the baking chamber 523 and annealed there. Further, a UV irradiation mechanism may be provided in the baking chamber 523 so that ultraviolet irradiation can be performed as the anode surface treatment.

In the film formation chamber 512, a hole injection layer made of a polymer material may be formed by an inkjet method, a spin coating method, or the like. Alternatively, the film may be formed by an inkjet method in a vacuum with the substrate placed vertically. Poly (ethylenedioxythiophene) / poly (styrenesulfonic acid) aqueous solution (PEDOT / PSS), polyaniline / camphorsulfonic acid aqueous solution (PANI / CSA), PTPDES acting as a hole injection layer (anode buffer layer) on the anode Et-PTPDK, PPBA, or the like may be applied to the entire surface and fired. When firing, it is preferably performed in the baking chamber 523. When a hole injection layer made of a polymer material is formed by a coating method using spin coating or the like, flatness is improved, and coverage and film thickness uniformity of a film formed thereon are improved. be able to. In particular, since the thickness of the light emitting layer becomes uniform, uniform light emission can be obtained. In this case, it is preferable to perform vacuum heating (100 to 200 ° C.) immediately after forming the hole injection layer by a coating method and immediately before film formation by the vapor deposition method. What is necessary is just to perform in the pre-processing chamber 503b when heating in a vacuum. For example, after cleaning the surface of the anode with a sponge, it is carried into a cassette chamber, conveyed to a film forming chamber 512, and a poly (ethylenedioxythiophene) / poly (styrenesulfonic acid) aqueous solution (PEDOT / PSS) is formed by spin coating. After coating with a film thickness of 60 nm on the entire surface, it is transported to a baking chamber 523 and pre-baked at 80 ° C. for 10 minutes, main-baked at 200 ° C. for 1 hour, and further transported to the pretreatment chamber 503b to be heated immediately before vapor deposition. (170 ° C., heating for 30 minutes, cooling for 30 minutes), the light-emitting layer may be formed by a vapor deposition method without being exposed to the atmosphere by being transferred to the film formation chambers 506R, 506G, and 506B. In particular, when an ITO film is used as an anode material and there are irregularities and fine particles on the surface, these effects can be reduced by setting the PEDOT / PSS film thickness to 30 nm or more.

In addition, PEDOT / PSS does not have good wettability when applied on an ITO film, so the wettability is improved by first applying the PEDOT / PSS solution by spin coating and then washing with pure water. It is preferable to apply the PEDOT / PSS solution again by a spin coating method and perform baking to form a film with good uniformity. After the first application, the surface is modified by once washing with pure water, and the effect of removing fine particles is obtained.

Next, the substrate is transferred from the transfer chamber 518 provided with the substrate transfer mechanism to the preparation chamber 501. In the manufacturing apparatus of this embodiment, the preparation chamber 501 is provided with a substrate reversing mechanism, and the substrate can be reversed appropriately.

Then, it is transferred to a transfer chamber 502 connected to the preparation chamber 501. The preparation chamber 501 is connected to a vacuum evacuation treatment chamber, and it is preferable to introduce an inert gas to atmospheric pressure after evacuating and transporting the substrate to the transport chamber 502. It is preferable to evacuate and maintain the vacuum in advance so that moisture and oxygen do not exist in the transfer chamber 502 as much as possible.

The vacuum evacuation chamber is provided with a magnetic levitation turbo molecular pump, a cryopump, or a dry pump. As a result, the ultimate vacuum of the transfer chamber 502 connected to the charging chamber can be 10 ⁻⁵ to 10 ⁻⁶ Pa, and the back diffusion of impurities from the pump side and the exhaust system can be controlled. . In order to prevent impurities from being introduced into the apparatus, an inert gas such as nitrogen or a rare gas is used as the introduced gas. These gases introduced into the apparatus are those purified by a gas purifier before being introduced into the apparatus. Therefore, it is necessary to provide a gas purifier so that the gas is introduced into the vapor deposition apparatus after being highly purified. Thereby, since oxygen, water, and other impurities contained in the gas can be removed in advance, these impurities can be prevented from being introduced into the apparatus.

In addition, when the hole injection layer is formed by spin coating, the film is formed on the entire surface, and therefore, the end surface and peripheral edge of the substrate, the terminal portion, the connection region between the cathode and the lower wiring, and the like are selectively removed. It is preferable to remove by using O ₂ ashing or laser in the pretreatment chamber 503a.

In order to eliminate the phenomenon (shrink) that the non-light-emitting region expands from the peripheral portion of the pixel, it is preferable to perform vacuum heating immediately before the deposition of the electroluminescent film, which is transferred to the pretreatment chamber 503b and included in the substrate. In order to thoroughly remove moisture and other gases, annealing for deaeration is performed in a vacuum (5 × 10 ⁻³ Torr (0.665 Pa) or less, preferably 10 ⁻⁴ to 10 ⁻⁶ Pa). In the pretreatment chamber 503b, a plurality of substrates are uniformly heated using a flat plate heater (typically a sheath heater). In particular, when an organic resin film is used as a material for the interlayer insulating film and the partition wall, depending on the organic resin material, moisture may be easily adsorbed and further degassing may occur. It is effective to perform vacuum heating to remove adsorbed moisture by performing natural cooling for 30 minutes after heating for ˜250 ° C., preferably 150 ° C. to 200 ° C., for example, 30 minutes or more.

After the above vacuum heating, the substrate may be transferred to the film formation chamber 506H to form a hole injection layer or a hole transport layer.

Next, the substrate is transferred from the transfer chamber 502 to the delivery chamber 505, and further, the substrate is transferred from the transfer chamber 505 to the transfer chamber 504a without being exposed to the atmosphere.

Thereafter, the substrate is appropriately transferred to the film formation chambers 506R, 506G, 506B, and 506E connected to the transfer chamber 504a, and an electroluminescent film including a light emitting layer, an electron transport layer, an electron injection layer, or the like is appropriately formed.

Here, the film formation chambers 506R, 506G, 506B, 506E, and 506H will be described.

In each of the film forming chambers 506R, 506G, 506B, 506E, and 506H, a movable evaporation source holder is installed. A plurality of vapor deposition source holders are prepared, and a plurality of containers (crucibles) filled with EL materials are appropriately provided, and are installed in the film forming chamber in this state. A film can be selectively formed by setting the substrate by a face-down method, aligning the position of a vapor deposition mask with a CCD or the like, and performing vapor deposition by a resistance heating method. Note that the vapor deposition mask is stocked in the mask stock chamber 524 and is appropriately transported to the film formation chamber when vapor deposition is performed.

The EL system is preferably installed in these film forming chambers by using the following manufacturing system. That is, it is preferable to form a film using a container (typically a crucible) in which an EL material is stored in advance by a material manufacturer. Further, it is preferable that the installation is performed without touching the atmosphere. When the material is transferred from the material manufacturer, the crucible is preferably introduced into the film formation chamber while being sealed in the second container. Desirably, the installation chambers 526R, 526G, 526B, 526H, and 526E having vacuum exhaust means connected to the respective film formation chambers 506R, 506G, 506B, 506H, and 506E are set to a vacuum or an inert gas atmosphere. Remove the crucible from the container and place the crucible in the film formation chamber. By doing so, the crucible and the EL material accommodated in the crucible can be prevented from being contaminated. Note that a metal mask can be stocked in the installation chambers 526R, 526G, 526B, 526H, and 526E.

By appropriately selecting an EL material to be installed in the film formation chambers 506R, 506G, 506B, 506H, and 506E, the entire EL element can be a single color (specifically, white) or full color (specifically, red, green, and blue). EL element exhibiting light emission) can be formed. For example, in the case of forming a green EL element, a hole transport layer or a hole injection layer is formed in the film formation chamber 506H, a light emitting layer (G) is formed in the film formation chamber 506G, and an electron transport layer or electron injection layer is formed in the film formation chamber 506E. A green EL element can be obtained by sequentially forming the cathode and then forming the cathode. For example, when forming a full-color EL element, a hole transport layer or a hole injection layer, a light emitting layer (R), an electron transport layer or an electron injection layer are sequentially stacked in the film formation chamber 506R using an R vapor deposition mask. Then, using a deposition mask for G in the film formation chamber 506G, a hole transport layer or a hole injection layer, a light emitting layer (G), an electron transport layer or an electron injection layer are sequentially stacked, and the film for the B is formed in the film formation chamber 506B. A full color EL device can be obtained by forming a cathode after sequentially stacking a hole transport layer or hole injection layer, a light emitting layer (B), an electron transport layer or an electron injection layer using the above evaporation mask.

Note that the electroluminescent layer that emits white light is a three-wavelength type containing three primary colors of red, green, and blue, and blue / yellow, or blue-green / orange when light-emitting layers having different emission colors are stacked. The two-wavelength type using a complementary color relationship such as It is also possible to form a white EL element in one film formation chamber. For example, when obtaining a white EL element using a three-wavelength type, a plurality of vapor deposition source holders are prepared in one film forming chamber, and aromatic diamine (TPD) and second vapor deposition source are used as the first vapor deposition source holder. The holder is p-EtTAZ, the third evaporation source holder is Alq ₃ , the fourth evaporation source holder is an EL material obtained by adding NileRed as a red luminescent dye to Alq ₃ , and the fifth evaporation source holder is Alq ₃ is enclosed and installed in each film forming chamber in this state. Then, the first to fifth vapor deposition source holders start moving in order to perform vapor deposition on the substrate and stack them. Specifically, TPD is sublimated from the first vapor deposition source holder by heating and vapor deposited on the entire surface of the substrate. Thereafter, p-EtTAZ is sublimated from the second deposition source holder, Alq ₃ is sublimated from the _third deposition source holder, Alq ₃ : NileRed is sublimated from the fourth deposition source holder, and the fifth deposition source holder. Then, Alq ₃ is sublimated and deposited on the entire surface of the substrate. Thereafter, a white EL element can be obtained by forming a cathode.

After appropriately laminating the electroluminescent film by the above steps, the substrate is transferred from the transfer chamber 504a to the delivery chamber 507, and further transferred from the delivery chamber 507 to the transfer chamber 508 without being exposed to the atmosphere.

Next, the substrate is transferred to the film formation chamber 510 by a transfer mechanism installed in the transfer chamber 508 to form a floating electrode. This floating electrode is made of a metal film (an alloy such as MgAg, MgIn, CaF ₂ , LiF, Ca ₃ N ₂ , or an element belonging to Group 1 or 2 of the periodic table and aluminum formed by vapor deposition using resistance heating. Is a film formed by a co-evaporation method, or a laminated film thereof.

Further, the substrate is transferred to the film formation chamber 532 to form an electron transport auxiliary layer. The material used at this time is preferably a hole blocking material such as BCP or BAlq. After the formation of the electron transport auxiliary layer, a cathode is formed. However, the cathode may be formed by vapor deposition in the above-described film formation chamber 510 or may be formed by sputtering in the film formation chamber 509. .

In the case of manufacturing a top emission type light emitting device, the cathode is preferably transparent or translucent, and the metal film thin film (1 nm to 10 nm) or the metal film thin film (1 nm to 10 nm) A laminate with a transparent conductive film is preferably used as the cathode. In this case, a film made of a transparent conductive film (ITO (indium oxide tin oxide alloy), indium oxide zinc oxide alloy (In ₂ O ₃ —ZnO), zinc oxide (ZnO), etc.) is formed in the film formation chamber 509 by sputtering. May be formed.

The EL element of the present invention is formed through the above steps.

Alternatively, the protective film may be sealed by forming a protective film made of a silicon nitride film or a silicon nitride oxide film by being transferred to the deposition chamber 513 connected to the transfer chamber 508. Here, a target made of silicon, a target made of silicon oxide, or a target made of silicon nitride is provided in the film formation chamber 513. For example, the silicon nitride film can be formed over the cathode by using a target made of silicon and setting the film formation chamber atmosphere to a nitrogen atmosphere or an atmosphere containing nitrogen and argon. Further, a thin film containing carbon as a main component (DLC film, CN film, amorphous carbon film) may be formed as a protective film, or a film formation chamber using a CVD method may be provided separately. Diamond-like carbon film (also called DLC film) is formed by plasma CVD method (typically RF plasma CVD method, microwave CVD method, electron cyclotron resonance (ECR) CVD method, hot filament CVD method, etc.), combustion flame method It can be formed by sputtering, ion beam vapor deposition, laser vapor deposition or the like. The reaction gas used for film formation was hydrogen gas and a hydrocarbon gas (for example, CH ₄ , C ₂ H ₂ , C ₆ H _6, etc.), ionized by glow discharge, and negative self-bias was applied. Films are formed by accelerated collision of ions with the cathode. The CN film may be formed using C ₂ H ₄ gas and N ₂ gas as the reaction gas. Note that the DLC film and the CN film are insulating films that are transparent or translucent to visible light. Transparent to visible light means that the visible light transmittance is 80 to 100%, and translucent to visible light means that the visible light transmittance is 50 to 80%.

Next, the substrate on which the EL element is formed is transferred from the transfer chamber 508 to the delivery chamber 511 without being exposed to the atmosphere, and further transferred from the delivery chamber 511 to the transfer chamber 514. Next, the substrate over which the EL element is formed is transferred from the transfer chamber 514 to the sealing chamber 516.

The sealing substrate is set and prepared in the load chamber 517 from the outside. Note that it is preferable to perform annealing in advance in advance in order to remove impurities such as moisture. In the case of forming a sealing material to be bonded to a substrate provided with an EL element on the sealing substrate, the sealing material is formed in the sealing chamber, and the sealing substrate on which the sealing material is formed is used as the sealing substrate stock chamber. Transport to 530. Note that a desiccant may be provided on the sealing substrate in the sealing chamber. Note that, here, an example in which the sealing material is formed over the sealing substrate is described; however, there is no particular limitation, and the sealing material may be formed over the substrate over which the EL element is formed.

Next, the substrate and the sealing substrate are bonded to each other in the sealing chamber 516, and the pair of bonded substrates is irradiated with UV light by an ultraviolet irradiation mechanism provided in the sealing chamber 516 to cure the sealing material. In addition, although ultraviolet curable resin was used here as a sealing material, if it is an adhesive material, it will not specifically limit.

Next, the pair of bonded substrates is transferred from the sealing chamber 516 to the transfer chamber 514 and then transferred from the transfer chamber 514 to the take-out chamber 519 and taken out.

As described above, by using the manufacturing apparatus shown in FIG. 5, it is not necessary to expose the EL element to the atmosphere until the EL element is completely enclosed in a sealed space, so that a highly reliable light-emitting device can be manufactured. Note that in the transfer chambers 514 and 518, vacuum and a nitrogen atmosphere at atmospheric pressure are repeated, but it is desirable that the transfer chambers 502, 504a, and 508 are always kept in vacuum.

Although not shown here, there is provided a control control device that realizes automation by controlling a path for moving the substrate to each processing chamber.

Moreover, in the manufacturing apparatus shown in FIG. 5, after carrying in the board | substrate provided with the transparent conductive film (or metal film (TiN)) as an anode and forming an electroluminescent film | membrane, a floating electrode, and an electron transport auxiliary layer, it is transparent or By forming a translucent cathode (for example, a laminate of a thin metal film (Al, Ag) and a transparent conductive film), a top emission (or double emission) EL element can be formed. Note that a top emission EL element refers to an element that extracts light emitted from an electroluminescent film through a cathode.

Further, in the manufacturing apparatus shown in FIG. 5, a substrate provided with a transparent conductive film as an anode is carried in, an electroluminescent film, a floating electrode, an electron transport auxiliary layer are formed, and then a cathode made of a metal film (Al, Ag). It is also possible to form a bottom emission type EL element. Note that a bottom emission EL element refers to an element that extracts light emitted from an electroluminescent layer from an anode, which is a transparent electrode, toward a TFT and further passes through a substrate.

In this example, the EL element of the present invention shown in FIG. 1 is specifically exemplified.

First, copper phthalocyanine (abbreviation: CuPc) 20 nm as a hole injection material and 4,4′-bis [N- (1-naphthyl) as a hole transport material are formed on a substrate on which an ITO film is formed as an anode 101 with a thickness of 110 nm. ) -N-phenyl-amino] -biphenyl (abbreviation: α-NPD) 30 nm, and Alq which is an electron transporting light-emitting material is formed 50 nm successively. The above corresponds to the electroluminescent film 103.

Next, 2 nm of calcium fluoride and 20 nm of aluminum are deposited to form the floating electrode 104. Further, as the electron transport auxiliary layer 105, Alq is deposited to a thickness of 100 nm. Finally, 2 nm of calcium fluoride and 100 nm of aluminum are deposited as the cathode 102 to obtain the EL element of the present invention. This element corresponds to the structure of FIG. 4C, but is hereinafter referred to as element C. The pixel size is 2 mm square.

FIG. 6 shows the initial characteristics of the element C (in order from the top, the luminance-current density characteristic, the luminance-voltage characteristic, and the current-voltage characteristic). Despite the thick film, it can be seen that a certain amount of current flows and light emission occurs.

[Comparative Example 1]
In order to compare with Example 1, two types of elements were produced. First, a conventional EL element, that is, an EL element having a structure of “ITO (110 nm) / CuPc (20 nm) / α-NPD (30 nm) / Alq (50 nm) / CaF ₂ (2 nm) / Al (100 nm)” Was made. This element corresponds to the structure of FIG. 4A, but is hereinafter referred to as element A. The pixel size is 2 mm square.

Further, compared with the element structure of Example 1, a floating electrode is not formed, that is, “ITO (110 nm) \ CuPc (20 nm) \ α-NPD (30 nm) \ Alq (150 nm) \ CaF ₂ (2 nm) \ An EL element having a structure of “Al (100 nm)” was also produced. This element corresponds to the structure of FIG. 4B, but is hereinafter referred to as element B. The pixel size is 2 mm square.

The initial characteristics of element A and element B are shown in FIG. Although the element C of the present invention does not reach the element A, the characteristics are much improved as compared with the element B. Therefore, it was found that the present invention can be driven with a certain voltage even if the film thickness is increased.

In this example, the EL element of the present invention shown in FIG. 1 is specifically exemplified. In this example, the EL element of the present invention (hereinafter referred to as element D) in which a hole blocking material is introduced into an electroluminescent film, and the EL of the present invention in which a hole blocking material is introduced into an electron transport auxiliary layer. Two examples of elements (hereinafter referred to as element E) are illustrated.

The structure of the element D is “ITO (110 nm) \ CuPc (20 nm) \ α-NPD (30 nm) \ Alq (40 nm) \ BCP (10 nm) \ CaF ₂ (2 nm) \ Al (20 nm) \ Au (20 nm) \ Alq (100 nm) \ CaF ₂ (2 nm) \ Al (100 nm) ”. The structure of the element E is “ITO (110 nm) / CuPc (20 nm) / α-NPD (30 nm) / Alq (50 nm) / CaF ₂ (2 nm) / Al (20 nm) / BCP (100 nm) / Al (100 nm). ) ”. Both of the hole blocking materials in the element D and the element E are BCP. In any element, the size of the pixel is 2 mm square.

These initial characteristics (in order from the top, luminance-current density characteristic, luminance-voltage characteristic, and current-voltage characteristic) are shown in FIG. In either case, it can be seen that a sufficient current flows and emits light at a sufficiently low driving voltage, regardless of the thickness of about 200 nm. In addition, since the element E has better characteristics than the element D, it can be seen that it is better to introduce the hole blocking material into the electron transport auxiliary layer.

[Comparative Example 2]
For comparison, the data of element A is also shown in FIG. As can be seen from this figure, by introducing a hole blocking material in the EL element of the present invention, the phenomenon that the driving voltage is lower than that of the conventional EL element, despite the film thickness being twice that of the conventional EL element. It was observed. In particular, the reduction in voltage on the high luminance side is remarkable, but as can be seen from the current-voltage characteristics, the rise of the diode characteristics is steep (the current tends to flow on the high voltage side). This seems to be the cause.

From the above, it was found that, by carrying out the present invention, it can be driven at a lower voltage than before even if the film thickness is increased.

In this example, the EL element of the present invention shown in FIG. 2 is specifically exemplified.

Basically, the device shown in FIG. 2 can be manufactured through a process reverse to that shown in FIG. First, 100 nm of BCP is formed as the electron transport auxiliary layer 205 on the substrate on which Al is formed as the cathode 202, and further 20 nm of Al: Li alloy is formed as the floating electrode 204.

Next, the electroluminescent film 203 is formed by sequentially stacking 50 nm of Alq which is an electron transporting light emitting material, 30 nm of α-NPD which is a hole transporting material, and 20 nm of CuPc which is a hole injecting material. Finally, a film of about 20 nm of Au is formed as the anode 201 to obtain the EL element of the present invention. In the case of this embodiment, light emission is taken out from the upper surface side (Au side).

In this embodiment, an example of a light emitting device having a bottom emission structure is illustrated. A schematic diagram thereof is shown in FIG.

8A is a top view illustrating the light-emitting device, and FIG. 8B is a cross-sectional view taken along line A-A ′ in FIG. 8A. Reference numeral 801 indicated by a dotted line denotes a source signal line driver circuit, reference numeral 802 denotes a pixel portion, and reference numeral 803 denotes a gate signal line driver circuit. Reference numeral 804 denotes a sealing substrate, and reference numeral 805 denotes a sealing material containing a gap material for maintaining the space between the sealed spaces. The inside surrounded by the sealing material 805 is an inert gas (typically nitrogen gas). ). A small amount of moisture is removed by the desiccant 807 in the inner space surrounded by the sealant 805, and the space is sufficiently dried.

Note that reference numeral 808 denotes wiring for transmitting signals input to the source signal line driver circuit 801 and the gate signal line driver circuit 803, and a video signal and a clock signal are received from an FPC (flexible printed circuit) 809 serving as an external input terminal. receive.

Next, the cross-sectional structure will be described with reference to FIG. A driver circuit and a pixel portion are formed over the substrate 810. Here, a source signal line driver circuit 801 and a pixel portion 802 are shown as driver circuits. Note that as the source signal line driver circuit 801, a CMOS circuit in which an n-channel TFT 823 and a p-channel TFT 824 are combined is formed.

The pixel portion 802 is formed of a plurality of pixels including a switching TFT 811, a current control TFT 812, and a first electrode (anode) 813 made of a transparent conductive film electrically connected to the drain thereof.

Here, the first electrode 813 is formed so as to partially overlap with the connection electrode, and the first electrode 813 is electrically connected to the drain region of the TFT through the connection electrode. The first electrode 813 is a transparent conductive film having a large work function (ITO (indium tin oxide alloy), indium oxide zinc oxide alloy (In ₂ O ₃ —ZnO), zinc oxide (ZnO), or the like. ) Is desirable.

In addition, insulators 814 (referred to as banks, partition walls, barriers, banks, or the like) 814 are formed at both ends of the first electrode (anode) 813. In order to improve the coverage, a curved surface having a curvature is formed at the upper end portion or the lower end portion of the insulator 814. Alternatively, the insulator 814 may be covered with a protective film made of an aluminum nitride film, an aluminum nitride oxide film, a thin film containing carbon as its main component, or a silicon nitride film.

Further, a layer 815 containing an organic compound is selectively formed over the first electrode (anode) 813 by an evaporation method using an evaporation mask or an inkjet method. Note that the layer 815 containing an organic compound in this embodiment refers to the three layers of the electroluminescent film 103, the floating electrode 104, and the electron transport auxiliary layer 105 in FIG. Specifically, a structure as shown in Embodiment 2 may be formed. However, the floating electrode is preferably applied separately for each pixel in order to prevent crosstalk.

Further, a second electrode (cathode) 816 is formed over the layer 815 containing an organic compound. As the cathode, a material having a low work function (Al, Ag, Li, Ca, or an alloy thereof, MgAg, MgIn, AlLi, CaF ₂ , or Ca ₃ N ₂ ) may be used. In this manner, the EL element 818 of the present invention including the first electrode (anode) 813, the layer 815 containing an organic compound, and the second electrode (cathode) 816 is formed. The EL element 818 emits light in the arrow direction shown in FIG. Here, the EL element 818 is one of EL elements that can obtain monochromatic emission of R, G, or B, and includes three layers each including an organic compound that selectively emits R, G, and B. Full color with EL elements.

In addition, a protective layer 817 is formed to seal the EL element 818. As the protective layer 817, an insulating film mainly containing silicon nitride or silicon nitride oxide obtained by sputtering (DC method or RF method) or PCVD method, or a thin film mainly containing carbon (DLC film, CN film, etc.) ) Or a laminate of these. If a silicon target is used and formed in an atmosphere containing nitrogen and argon, a silicon nitride film having a high blocking effect against impurities such as moisture and alkali metals can be obtained. A silicon nitride target may be used. Further, the protective layer may be formed using a film forming apparatus using remote plasma.

In addition, in order to seal the EL element 818, a sealing substrate 804 is bonded with a sealant 805 in an inert gas atmosphere. A concave portion formed in advance by a sandblast method or the like is formed in the sealing substrate 804, and a desiccant 807 is attached to the concave portion. Note that an epoxy resin is preferably used as the sealant 805. In addition, the sealant 805 is desirably a material that does not transmit moisture and oxygen as much as possible.

Further, in this embodiment, as a material constituting the sealing substrate 804 having a recess, a metal substrate, a glass substrate, a quartz substrate, FRP (Fiberglass-Reinforced Plastics), PVF (polyvinyl fluoride), Mylar, polyester, acrylic, or the like A plastic substrate made of can be used. It is also possible to seal with a metal can with a desiccant attached inside.

In this embodiment, an example of a light emitting device having a top emission structure is illustrated. The schematic is shown in FIG.

9A is a top view illustrating the light-emitting device, and FIG. 9B is a cross-sectional view taken along line A-A ′ in FIG. 9A. Reference numeral 901 indicated by a dotted line denotes a source signal line driver circuit, 902 denotes a pixel portion, and 903 denotes a gate signal line driver circuit. Reference numeral 904 denotes a transparent sealing substrate, reference numeral 905 denotes a first sealing material, and the inside surrounded by the first sealing material 905 is filled with a transparent second sealing material 907. Note that the first sealing material 905 contains a gap material for maintaining the distance between the substrates.

Note that reference numeral 908 denotes wiring for transmitting signals input to the source signal line driver circuit 901 and the gate signal line driver circuit 903, and a video signal and a clock signal are received from an FPC (flexible printed circuit) 909 serving as an external input terminal. receive. Although only the FPC is shown here, a printed wiring board (PWB) may be attached to the FPC.

Next, the cross-sectional structure will be described with reference to FIG. A driver circuit and a pixel portion are formed over the substrate 910. Here, a source signal line driver circuit 901 and a pixel portion 902 are shown as the driver circuits.

Note that the source signal line driver circuit 901 is a CMOS circuit in which an n-channel TFT 923 and a p-channel TFT 924 are combined. The TFT forming the driving circuit may be formed by a known CMOS circuit, PMOS circuit or NMOS circuit. Further, in this embodiment, a driver integrated type in which a drive circuit is formed on a substrate is shown, but this is not always necessary, and it can be formed outside the substrate.

Further, the pixel portion 902 is formed of a plurality of pixels including a switching TFT 911, a current control TFT 912, and a first electrode (anode) 913 electrically connected to the drain thereof. The current control TFT 912 may be an n-channel TFT or a p-channel TFT, but is preferably a p-channel TFT when connected to the anode. In addition, it is preferable to appropriately provide a storage capacitor (not shown). Note that here, only a cross-sectional structure of one pixel among the infinitely arranged pixels is shown, and an example in which two TFTs are used for the one pixel is shown. However, three or more TFTs are appropriately used. , May be used.

Here, since the first electrode 913 is in direct contact with the drain of the TFT, the lower layer of the first electrode 913 is a material layer that can be in ohmic contact with the drain made of silicon, and a layer containing an organic compound. It is desirable that the uppermost layer in contact is a material layer having a large work function. For example, when a three-layer structure of a titanium nitride film, a film containing aluminum as a main component, and a titanium nitride film is used, the resistance as a wiring is low, a good ohmic contact can be obtained, and the film can function as an anode. . The first electrode 913 may be a single layer such as a titanium nitride film, a chromium film, a tungsten film, a Zn film, or a Pt film, or may be a stack of three or more layers.

In addition, insulators (called banks, partition walls, barriers, banks, or the like) 914 are formed on both ends of the first electrode (anode) 913. The insulator 914 may be formed using an organic resin film or an insulating film containing silicon. Here, as the insulator 914, an insulator having a shape shown in FIG. 9 is formed using a positive photosensitive acrylic resin film.

In order to improve the coverage, a curved surface having a curvature is formed at the upper end portion or the lower end portion of the insulator 914. For example, in the case where positive photosensitive acrylic is used as a material for the insulator 914, it is preferable that only the upper end portion of the insulator 914 has a curved surface with a radius of curvature (0.2 μm to 3 μm). As the insulator 914, either a negative type that becomes insoluble in an etchant by photosensitive light or a positive type that becomes soluble in an etchant by light can be used.

Alternatively, the insulator 914 may be covered with a protective film made of an aluminum nitride film, an aluminum nitride oxide film, a thin film containing carbon as its main component, or a silicon nitride film.

Further, a layer 915 containing an organic compound is selectively formed on the first electrode (anode) 913 by a vapor deposition method using a vapor deposition mask or an ink jet method. Note that the layer 915 containing an organic compound in this embodiment refers to the three layers of the electroluminescent film 103, the floating electrode 104, and the electron transport auxiliary layer 105 in FIG. Specifically, a structure as shown in Embodiment 2 may be formed. However, the floating electrode is preferably applied separately for each pixel in order to prevent crosstalk.

Further, a second electrode (cathode) 916 is formed over the layer 915 containing an organic compound. As the cathode, a material having a small work function (Al, Ag, Li, Ca, or an alloy thereof, MgAg, MgIn, AlLi, CaF ₂ , or Ca ₃ N ₂ ) may be used. Here, a thin metal film, a transparent conductive film (ITO (indium tin oxide alloy), indium oxide zinc oxide alloy (In ₂ ) are used as the second electrode (cathode) 916 so as to transmit light. O ₃ —ZnO), zinc oxide (ZnO), or the like) is used. In this manner, the EL element 918 of the present invention including the first electrode (anode) 913, the layer 915 containing an organic compound, and the second electrode (cathode) 916 is formed. Here, since the EL element 918 emits white light, a color filter including a colored layer 931 and a light-shielding layer (BM) 932 (for the sake of simplicity, an overcoat layer is not shown here) is provided.

In addition, if each layer containing an organic compound capable of emitting R, G, and B light is selectively formed, a full color display can be obtained without using a color filter.

In addition, a transparent protective layer 917 is formed to seal the EL element 918. As this transparent protective layer 917, an insulating film mainly composed of silicon nitride or silicon nitride oxide obtained by sputtering (DC method or RF method) or PCVD method, a thin film mainly composed of carbon (diamond-like carbon: DLC film) , Carbon nitride: CN film, or the like) or a laminate of these. If a silicon target is used and formed in an atmosphere containing nitrogen and argon, a silicon nitride film having a high blocking effect against impurities such as moisture and alkali metals can be obtained. A silicon nitride target may be used. The transparent protective layer may be formed using a film forming apparatus using remote plasma. Moreover, in order to allow light emission to pass through the transparent protective layer, it is preferable that the thickness of the transparent protective layer be as thin as possible.

In addition, in order to seal the EL element 918, the sealing substrate 904 is bonded by the first sealing material 905 and the second sealing material 907 in an inert gas atmosphere. Note that an epoxy-based resin is preferably used as the first sealing material 905 and the second sealing material 907. In addition, the first sealing material 905 and the second sealing material 907 are desirably materials that do not transmit moisture and oxygen as much as possible.

Further, in this embodiment, a plastic substrate made of FRP (Fiberglass-Reinforced Plastics), PVF (polyvinyl fluoride), Mylar, polyester, acrylic, or the like is used as a material constituting the sealing substrate 904 as a material constituting the sealing substrate 904. be able to. Further, after the sealing substrate 904 is bonded using the first sealing material 905 and the second sealing material 907, it is also possible to seal with a third sealing material so as to cover the side surface (exposed surface).

By encapsulating the EL element in the first sealing material 905 and the second sealing material 907 as described above, the EL element can be completely blocked from the outside, and deterioration of the organic compound layer such as moisture and oxygen from the outside can be performed. It can prevent the urging substance from entering. Therefore, a highly reliable light-emitting device can be obtained.

Note that when a transparent conductive film is used for the first electrode 913, a double-sided light-emitting device can be manufactured.

The light-emitting device of the present invention described in Example 4 and Example 5 is a light-emitting device with a good yield and excellent life and driving voltage. Therefore, the electric appliance using the light-emitting device of the present invention has an advantage that the yield is good and the length is kept long. Especially for electrical appliances such as portable devices that use a battery as a power source, low power consumption is directly linked to convenience (battery is unlikely to run out), so the light emitting device of the present invention with excellent driving voltage is extremely useful. is there.

Examples of electric appliances include video cameras, digital cameras, head mounted displays (goggles type displays), car navigation systems, projectors, car stereos, personal computers, personal digital assistants (mobile computers, mobile phones, electronic books, etc.), and the like. It is done. Examples of these are shown in FIGS.

FIG. 10A illustrates a personal computer, which includes a main body 1001, an image input portion 1002, a display portion 1003, a keyboard 1004, and the like.

FIG. 10B shows a video camera, which includes a main body 1101, a display portion 1102, an audio input portion 1103, operation switches 1104, a battery 1105, an image receiving portion 1106, and the like.

FIG. 10C illustrates a mobile computer, which includes a main body 1201, a camera unit 1202, an image receiving unit 1203, an operation switch 1204, a display unit 1205, and the like.

FIG. 10D shows a player using a recording medium (hereinafter referred to as a recording medium) in which a program is recorded, and includes a main body 1401, a display portion 1402, a speaker portion 1403, a recording medium 1404, an operation switch 1405, and the like. This player uses a DVD (Digital Versatile Disc), CD, or the like as a recording medium, and can enjoy music, movies, games, and the Internet.

FIG. 10E shows a digital camera, which includes a main body 1501, a display unit 1502, an eyepiece unit 1503, an operation switch 1504, an image receiving unit (not shown), and the like.

FIG. 11A shows a mobile phone, which includes a main body 1601, an audio output unit 1602, an audio input unit 1603, a display unit 1604, operation switches 1605, an antenna 1606, an image input unit (CCD, image sensor, etc.) 1607, and the like.

FIG. 11B illustrates a portable book (electronic book), which includes a main body 1701, display portions 1702 and 1703, a storage medium 1704, operation switches 1705, an antenna 1706, and the like.

FIG. 11C shows a display, which includes a main body 1801, a support stand 1802, a display portion 1803, and the like.

Note that the display shown in FIG. 11C is a medium or small size display, for example, a screen size of 5 to 20 inches. Further, in order to form a display portion having such a size, it is preferable to use a substrate having a side of 1 m and perform mass production by performing multiple chamfering.

As described above, the scope of application of the present invention is extremely wide and can be applied to electric appliances in various fields.

The figure which shows the basic composition of this invention. The figure which shows the basic composition of this invention. The figure explaining the operation | movement principle of this invention. The figure explaining the operation | movement principle of this invention. FIG. 11 illustrates an EL element and a light-emitting device manufacturing apparatus using the EL element. The figure which shows the data of Example 1 and Comparative Example 1. The figure which shows the data of Example 2 and Comparative Example 2. 3A and 3B are a top view and a cross-sectional view of a light-emitting device. 3A and 3B are a top view and a cross-sectional view of a light-emitting device. The figure which shows the specific example of an electric appliance. The figure which shows the specific example of an electric appliance. The figure which shows the basic composition of this invention.

Claims (26)

An electroluminescent device in which an anode, an electroluminescent film containing an organic compound that emits light, a floating electrode, an electron transport auxiliary layer, and a cathode are sequentially laminated,
An electroluminescent device comprising a hole blocking material in at least one of the electroluminescent film and the electron transport auxiliary layer. An electroluminescent device in which an anode, an electroluminescent film containing an organic compound that emits light, a floating electrode, an electron transport auxiliary layer, and a cathode are sequentially laminated,
An electroluminescent element comprising a hole blocking material in the electron transport auxiliary layer. 3. The electroluminescent device according to claim 1, wherein the cathode includes a conductive film formed by a sputtering method. 3. The electroluminescent device according to claim 1, wherein the cathode includes a conductive film which is light-transmitting and formed by a sputtering method. 4. An electroluminescent device comprising a cathode, an electron transport auxiliary layer, a floating electrode, an electroluminescent film containing an electroluminescent organic compound, and an anode, sequentially laminated,
An electroluminescent device comprising a hole blocking material in at least one of the electroluminescent film and the electron transport auxiliary layer. An electroluminescent device comprising a cathode, an electron transport auxiliary layer, a floating electrode, an electroluminescent film containing an electroluminescent organic compound, and an anode, sequentially laminated,
An electroluminescent element comprising a hole blocking material in the electron transport auxiliary layer. The electroluminescent element according to claim 1, wherein the hole blocking material has an ionization potential of 5.8 eV or more. 8. The electroluminescent device according to claim 1, wherein the hole blocking material is an organic compound containing a phenanthroline skeleton or a pentacoordinate metal complex having a group 13 element as a central metal. An electroluminescent element characterized by the above. 8. The electroluminescent device according to claim 2, wherein the cathode is made of a conductor having a work function of 3.5 eV or more. . An electroluminescent device comprising an anode, an electroluminescent film containing an organic compound that emits light, an electron transport layer, a floating electrode, an electron transport auxiliary layer, and a cathode, which are sequentially stacked. An electroluminescent device in which an anode, an electroluminescent film containing an organic compound that emits electroluminescence, an electron transport layer, a floating electrode, an electron transport auxiliary layer, and a cathode are sequentially stacked,
An electroluminescent device comprising a hole blocking material in at least one of the electroluminescent film and the electron transport auxiliary layer. An electroluminescent device in which an anode, an electroluminescent film containing an organic compound that emits electroluminescence, an electron transport layer, a floating electrode, an electron transport auxiliary layer, and a cathode are sequentially stacked,
An electroluminescent element comprising a hole blocking material in the electron transport auxiliary layer. The electroluminescent element according to claim 10, wherein the cathode includes a conductive film formed by a sputtering method. 13. The electroluminescent device according to claim 10, wherein the cathode includes a light-transmitting conductive film formed by a sputtering method. 1. An electroluminescent device comprising a cathode, an electron transport auxiliary layer, a floating electrode, an electron transport layer, an electroluminescent film containing an organic compound that emits light, and an anode, which are sequentially stacked. An electroluminescent device in which a cathode, an electron transport auxiliary layer, a floating electrode, an electron transport layer, an electroluminescent film containing an electroluminescent organic compound, and an anode are sequentially laminated,
An electroluminescent device comprising a hole blocking material in at least one of the electroluminescent film and the electron transport auxiliary layer. An electroluminescent device in which a cathode, an electron transport auxiliary layer, a floating electrode, an electron transport layer, an electroluminescent film containing an electroluminescent organic compound, and an anode are sequentially laminated,
An electroluminescent element comprising a hole blocking material in the electron transport auxiliary layer. The electroluminescent device according to claim 11, wherein the hole blocking material has an ionization potential of 5.8 eV or more. . The electroluminescent device according to claim 11, wherein the hole blocking material is an organic compound containing a phenanthroline skeleton, or a group 13 element as a central metal. An electroluminescent element characterized by being a coordination type metal complex. 18. The electroluminescent device according to claim 12, wherein the cathode is made of a conductor having a work function of 3.5 eV or more. 21. The electroluminescence device according to claim 1, wherein the electron transport auxiliary layer includes an electron transport material having a higher electron mobility than a hole mobility. element. The electroluminescent element according to any one of claims 1 to 21, wherein the floating electrode is made of a conductor having a work function of 3.5 eV or less. 23. The electroluminescent device according to claim 1, wherein the floating electrode is provided on an insulating film provided on a side in contact with the electroluminescent film and on a side in contact with the electron transport auxiliary layer. An electroluminescent element comprising the conductive film. The electroluminescent device according to any one of claims 1 to 23, wherein the electron transport auxiliary layer has a thickness of 10 nm to 1 µm. 25. A light-emitting device using the electroluminescent element according to any one of claims 1 to 24. An electric appliance using the light-emitting device according to claim 25.

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