JPS6244989A - Thin film el element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an AC-driven thin film EI and element used as a light emitting display device or a surface light source, and particularly relates to a thin film BL stack with low voltage drive and high reliability. It's about children.

(Prior art) Figure 2 shows the cross-sectional structure of a typical AC-driven thin film HL element (Nis.I.D.74 Digest of
Technical Havers 84 fA +5ID74
digest of technical pap
ers).

As shown in the figure, the thin film EL element has a transparent glass substrate 21.
On top there is a transparent electrode 22 made of an ITO film or a NESA film, a thin lower insulator layer 23, and ZnS: Mn + ZnS.
: Light emitting layer 24 such as TbF, thin film, etc. Furthermore, a thin film upper insulator layer 25 is formed thereon. A: It has a multilayer thin film structure consisting of a back electrode 26 such as a thin film. Light emission is obtained by applying an alternating current voltage between both electrodes of this element (θ) The light emission is raised to the conduction band by a high electric field of about 2 MV/cps,
It is generated when electrons in the light-emitting layer accelerated at high speed collide and excite light-emitting centers such as Mn. The color of the emitted light is determined by the energy level difference between the excited state and the bottom state.For example, Mn emits a yellow color, while Tb emits green light. This prevents excessive DC current from flowing through the light-emitting layer and destroying the device, and also improves luminous efficiency and increases nonlinearity in voltage-luminance characteristics due to the effect of superimposing the electric field due to polarization on the externally driven AC electric field. The use of this insulating layer made it possible to make thin Y&EI devices practical for the first time. YIOH has traditionally been used as an insulator layer.
A1205g 8isNi, T"t05sSm103+
'rio,, BaTi01.8rTi03. Pb
Ti0. Thin films such as these are formed and used by the real-time process or sputtering method.

(Problems to be Solved by the Invention) The insulator layer is very important for an AC-driven thin IEL device.In terms of the operating characteristics of an OEL device, the insulator layer can be understood in terms of an equivalent circuit as a capacitor. That is, the external voltage applied between both electrodes is dividedly applied to each layer in inverse proportion to the capacitance of the insulator layer and the light emitting layer. 0 is not effectively applied to the emissive layer, so a very high external voltage is required.In addition, the current flowing in the emissive layer in an alternating current and contributing to light emission is proportional to the capacitance of the insulating layer. If the capacitance of the body layer is small, high-intensity light emission cannot be obtained. Therefore, increasing the capacitance of the insulator layer is important for driving EL hydrogen atoms at a low voltage and increasing brightness. Y, 0.0, which is usually used to realize a large capacity insulation layer. , A
The strategy of making the film thickness of /llO,, St, N4, etc. extremely thin is inappropriate because it causes significant BL hydrogen dielectric breakdown, and it is not possible to construct the insulator layer with a material other than dielectric #L4. preferable. For example, about 20
It has been reported that a low-voltage drive EL device can be realized by employing a Pb'l'i0B N film with a dielectric constant of 0 as an insulating layer (I.E.E. Trans. Electronics on Electron Devices, IEEE Trans, Electron
Devices ED-28, P698 (1981), (
In order to form a PbTiOs film with a high dielectric constant for a BL element by sputtering, the composition associated with sputtering film formation is as reported in the above literature. It is suitable for film formation on large-area substrates necessary for zero display panels, which require a very high substrate temperature of about 600°C to obtain a crystalline phase with a high dielectric constant and to avoid misalignment. However, the above-mentioned problems are extremely severe, and it is difficult to achieve sufficient productivity. Furthermore, %pb'rio, (7) sputtering film formation caused problems such as corrosion of the substrate glass and blackening of the T TO transparent electrode, making it difficult to use as an insulator layer for thin film EL devices. Furthermore, even if a relatively thick PbTiO film is adopted due to its high dielectric constant, it is difficult to completely eliminate minute defects such as pinholes in a film created by a film forming method such as sputtering. There was a piece of duck meat that was likely to cause element destruction due to energization with this defective part as the nucleus. Therefore, PbTi
Adopting a thin film with a high dielectric constant, such as Omdera, as an insulator layer is attractive due to the characteristics of EL.
It was difficult to adopt it industrially.Therefore, instead of sputtering and vapor deposition methods, organic metals...8
) E in which a thin film of a high dielectric constant oxide containing Ti, such as PB'RTO, is formed as a lower insulating layer by solution coating and baking.
I. I have been considering elements. More specifically, for example, Pb
'rto, in which the film is an insulating layer, tetrabutoxytitanium: Tl (OC41(1)4 and lead oxide: PbO
A pre-formation driving solution of Pb'rtos is prepared by dissolving and reacting in acetylacetone so that the Ti/Pb ratio is 1, and this is applied to a glass substrate on which an ITO transparent electrode is formed by immersion method or spin method. It is coated using a cord, roller coat, spray method, etc., and then heated and baked at a temperature of about 500°C. −
A film with a thickness of several 100X to 2000X is formed in several steps, and this process can be repeated multiple times as necessary to obtain a PbTiOs film with a predetermined thickness. PbTi0. The film has a dielectric constant of about 200 and is formed from a solution, and because it is coated and fired multiple times, it is difficult to obtain a good film as a lower insulator layer without pinholes. can. ZnS on top of this:
1Jn is formed by a vapor deposition method, and further Y, 0. YaTa101
A thin @EL element is obtained by forming an upper insulating layer and a back electrode. The thin film EL device produced in this way operates at low voltage and has the advantage of being less likely to cause dielectric breakdown, and is also advantageous in terms of film formation process for increasing the area and reducing costs. .

However, several problems arose during the production of the #film EL device mentioned above. One of them was that it was impossible to perform high-temperature heat treatment on the light-emitting layer to improve its characteristics. Normally, the higher the heat treatment, the higher the luminance and luminance. The opening voltage is set and heat treatment at about 500 to 600°C is carried out after forming the ZnS:Mn emissive layer. When the film was then subjected to 1IiIi thermal treatment, a phenomenon of blackening of the film was observed, and the luminescent properties were even worse. Therefore, high-temperature heat treatment was not possible, and the temperature was limited to around 400°C, and the characteristics could not be sufficiently improved by heat treatment.Furthermore, even in long-term luminescence tests conducted in a dry atmosphere of the EL element created as described above, the brightness gradually decreased. As a result, deterioration was observed over time, posing a practical problem.

The present invention aims to solve the above-mentioned problems and provide a BL display device that is driven at low voltage, emits high brightness, and has high reliability. In a thin film EL element with a lower insulating layer made of a high dielectric constant oxide thin film containing Ti, ion diffusion is achieved between the lower insulating layer and the light emitting layer by coating an organic metal precursor solution and heating and baking it. It is characterized in that an intervening layer such as a thin oxide film is formed to prevent the damage.

(Function) An EL structure in which a thin oxide film containing Ti, such as PbTi0°, created by coating and firing a precursor solution is used as the lower insulating layer, and a light-emitting layer, such as ZnS:Mn, is directly formed on the lower insulating layer.
The cause of deterioration that occurs with heat treatment and long-term operation in devices is thought to be due to diffusion reactions of some kind of ions, etc.Residues and impurities such as C and C-H groups from thermal decomposition reactions of organic metals in the insulator layer , or free 'ri-? In the present invention, an intervening layer is formed between the lower insulating layer and the light emitting layer to prevent the diffusion (7) of the hard particles that are thought to have diffused ions such as Pb or Zn from the light emitting layer. This is what I did. As the intervening layer, A/20as Yt01+ sio, e 8i0s
Oxides and nitrides such as TatOse8mtO@y8i-N are preferred. In addition, increasing the thickness of the intervening layer detracts from the advantage of using a C-wave compound thin film containing Ti with a high dielectric constant as an insulating layer, and the intervening layer should not be unnecessarily thick. Depends on the material used, but 0
．． By inserting an intervening layer such as ⊚, which preferably has a value of about 0.01 to 0.1 μm, no blackening was observed even after high-temperature heat treatment, and the light emitting characteristics were improved and the life characteristics were also good.

Incidentally, the present invention is not limited by the presence or absence, material, and structure of the upper insulating layer formed after forming the light emitting layer. shows the cross-sectional structure of
This will be explained below. Corning 7059 Glass Substrate 1.1
A transparent electrode 12 was formed by forming a film of about 0.2 microns of ITO thereon. Tetrapoxytita/:Ti(QC,He)4
and lead acetate: P b (CI(,COO), and Ti/
It was weighed so that the pb ratio was 1, and reacted by heating it in paraxylene at 130 to 140°C to obtain a powdery reaction product: Pb-Ti01 (QC4I(,)1). This was dissolved in acetylacetone to obtain Pb-Ti01 (QC4I(,)1). b T i Os equivalent concentration 12 times ii % 0) PbTi0. The prepared precursor solution was applied to the substrate using a roller coater. Then, it was heated and fired in a tunnel furnace maintained at 500°C. The holding time at the heating temperature of 500° C. is about 30 minutes. This coating and firing process was repeated 5 times to form a lower insulator Jd1 of PbTi0B film with a thickness of 0.6 microns.
I got 3. The relative dielectric constant of this film was about 200, and a large dielectric constant was achieved for a thin film.F)Sr-N The film was formed into a 0.02 micron film. After that, a ZnS:Mnn layer containing 1 mole of Mn was formed to a thickness of 0.3 micron by vacuum evaporation method to form the light emitting layer 15, and then heated at 550°C for 2 hours. Heat treatment was performed in Ar. (2) The film did not darken due to heat treatment, demonstrating the effectiveness of the intervening layer.

Then Ylo, 0.15 micron top insulator It116
Formed as an AI! The thin gBL element of this example was obtained by forming a back electrode by vapor deposition of . Also,
Since the intervening layer was thin, the emission start voltage did not increase, and on the contrary, it was able to be lowered by several volts due to the effect of high temperature heat treatment. In addition, in the life test, it showed good characteristics with little decrease in brightness.

In addition to the St-N film, the effect of the intervening layer such as
In addition to ZnS:Mn, ZnSe:
Similar effects were obtained when Mn + ZnS aTbF, etc. were used.

In this embodiment, fL has been described with respect to a double insulation type element as shown in FIG. 1, but it is equally effective for an element with a single insulation type structure in which the upper insulating layer is removed.

C) Effects of the invention) Luminescence characteristics of a thin film EL device according to the invention, in which a precursor solution containing an organic metal is coated, heated and baked, and an oxide thin film containing Ti having a high dielectric constant is used as a lower insulating layer.

The lifespan characteristics have been improved.0 This makes it possible to realize a highly reliable thin film EL display device driven at low voltage.0

[Brief explanation of the drawing]

FIG. 1 shows the cross-sectional structure of a thin 1-digL element according to an embodiment of the present invention, and FIG. 2 shows a general conventional thin J[E
11.21...Glass substrate, 12.22...Transparent electrode, 13...Lower insulator layer (oxide containing Ti formed from precursor solution), 23
-... lower insulator layer, 14... intervening layer, 15.24.
...Light emitting layer, 16.25...Top insulator layer, 17.2
6...Back electrode bottom 1 Figure 72

Claims (1)

[Claims] Zn between a pair of electrodes, at least one of which is translucent
It consists of a thin film light emitting layer such as S:Mn or ZnS:TbF_3 and an insulating layer sandwiched on one or both sides of the light emitting layer, and at least the lower insulating layer formed prior to the light emitting layer of the insulating layer is In a thin film EL device consisting of a high dielectric constant oxide thin film containing Ti, which is formed by coating an organic metal precursor solution and heating and baking, an insulator such as an oxide or nitride is used between the lower insulating layer and the light emitting layer. A thin film EL device characterized by having a structure including an intervening layer.