JPS6321786A - Manufacture of thin film electroluminescence device - Google Patents

Abstract

(57) [Abstract] 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 a method for manufacturing a thin film electroluminescent (hereinafter referred to as EL) element used in display devices and the like.

[Prior Art] This type of thin film EL device has a light emitter layer and an adjacent insulating layer interposed between a pair of electrodes, at least one of which is transparent and usually one of which is patterned. It has a similar structure. The above insulating layer may be provided only on one side of the light emitting layer (table insulation structure) or on both sides (double insulating structure), and the above light emitting layer is not limited to one layer. Two or more layers may be stacked with an insulating layer in between. Such an EL element is driven by applying an alternating current electric field higher than the light emission starting voltage of the light emitter layer between the negative pair of electrodes to cause the element to emit light, and by causing the emitted light color to appear on the surface of the substrate on the transparent electrode side. This is to display a predetermined pattern.

By the way, it is desirable that the insulating layer of the above-mentioned EL element has a high dielectric strength voltage, and also that the voltage applied to the element is inversely proportional to the capacitance of the luminescent layer and the insulating layer. Therefore, in order to effectively apply voltage to the light emitter layer and to reduce the voltage applied to the entire device, it is necessary to use dielectric properties that have a high relative dielectric constant and low dielectric loss. It is hoped that it will be of excellent quality.

As an insulating layer that relatively satisfies these required characteristics,
In particular, tantalum oxide thin films formed by high-frequency sputtering have been proposed as having superior dielectric properties compared to conventional insulating layers made of thin films of yttrium oxide, silicon nitride, etc. formed by electron beam evaporation or sputtering. (Japanese Unexamined Patent Publication No. 172692/1983,
8-71590).

[Problem that the invention seeks to solve]

However, although the conventional thin film EL device using the tantalum oxide thin film proposed above as an insulating layer has advantages such as a low emission starting voltage due to the excellent dielectric properties of the thin film as described above, , the difference between the emission start voltage and the breakdown voltage at which the element breaks down, that is, the margin, is small, so when trying to increase the applied voltage to increase the emission brightness, the maximum brightness will be low, and when driving the element. There were difficulties in setting the applied voltage, and disadvantages in use could not be avoided.

Therefore, the present invention increases the margin, which is the difference between the light emission starting voltage and the breakdown voltage, without impairing the above-mentioned advantages of the thin film EL element using the tantalum oxide thin film as an insulating layer according to the above proposal. The purpose is to increase the efficiency of the device and to facilitate the driving of the device.

[Means for solving problems]

As a result of intensive studies to achieve the above object, the inventors found that the tantalum oxide thin film proposed above was formed by high-frequency sputtering, that is, this sputtering was performed using plasma under a low vacuum. Due to the deposition in the gas, gas molecules are mixed into the thin film, and the dielectric properties of tantalum oxide (Ta205) are not as expected (in addition, the surface on which the thin film is formed is exposed to plasma). As a result, the surfaces of the electrodes and light emitter layer, which are the formation surfaces, are easily affected by plasma, and these factors interact in a complex manner, leading to a decrease in the breakdown voltage of the device and a narrowing of the margin. It was determined that this is the case.

Therefore, as a result of further investigation into a thin film forming method that would not cause the above-mentioned problems, we decided to form a tantalum oxide thin film using a specific ion beam sputtering method instead of the high-frequency sputtering proposed above. I learned that thin-film EL elements with a thin film as an insulating layer have a low emission start voltage and a high breakdown voltage, which increases the margin and greatly contributes to improving maximum brightness and facilitating drive. .

This invention was completed based on the above findings, and the gist thereof is to provide an insulating layer consisting of a light emitting layer and an adjacent tantalum oxide thin film between a pair of electrodes, at least one of which is transparent. Thin film type E with a structure in which
In the manufacturing method of the L element, a tantalum oxide thin film as an insulating layer is formed by ion beam sputtering using tantalum metal or tantalum oxide as a target and spraying oxygen gas directly or ionized onto the thin film formation surface. A method of manufacturing a thin film EL element is provided.

[Structure and operation of the invention] will be described in detail below with reference to the drawings. FIG. 1 shows an example of a thin film type EL device manufactured by the method of the present invention.

In the figure, 1 is a transparent substrate made of a glass plate, etc., and 2 is In2O3-5nO□ with a thickness of about 1,000 to 3,000A.
Transparent electrode made of thin film, such as ITO thin film, 3 is Al
Thickness of thin film or tTol film etc. is 500~3.0O
The back electrode is about OX and is patterned into a shape that corresponds to the display pattern.

4 contains a small amount of luminescence activator such as rare earth fluoride or manganese in a matrix made of zinc sulfide (ZnS), such as ZnS:TbF3 (green luminescence), ZnS
: SmF3 (red light emission), ZnS:Mn (yellow-orange light emission), ZnS:TmF3 (blue light emission), ZnS:Pr
The thickness is 5,000 to 1o, oOoi, consisting of F3 (white light emission), ZnS: Dy F3f: yellow light emission), etc.
It is a light emitter layer of about

Reference numeral 5.6 denotes an insulating layer made of tantalum oxide thin film with a thickness of about 2,000 to 5,000λ adjacent to the front and rear surfaces of the luminescent layer 4; The light-emitting layer 4 is also extended from the outside atmosphere, and the light-emitting layer 4 is completely isolated from the external atmosphere by this and the insulating layer 5 on the front side.

The transparent electrode 2, insulating layer 5, light emitter layer 4, insulating layer 6, and back electrode 3 in the thin film EL element configured in this manner are formed on the transparent substrate 1 in the above order. Of these, the transparent electrode 2, the light emitting layer 4, and the back electrode 3 are formed by a thin film forming method suitable for each, such as electron beam evaporation, high frequency sputtering, and resistance heating. There is nothing particularly different from the conventional one.

On the other hand, the insulating layers 5 and 6 are formed by ion beam sputtering, which is unique to the present invention, using a sputtering apparatus as shown in FIG. 2, for example. That is, first, a target 8 and a composite substrate 9 on which a thin film is to be formed are set in a vacuum chamber 7 in the above-mentioned apparatus.

Tantalum oxide made of Ta205 is used as the target 8, but tantalum metal may be used depending on the case. Further, the thin film forming surface IQ of the composite substrate 9 is the back surface of the electrode 2 of the composite substrate 9 consisting of the transparent substrate 1 and the transparent electrode 2 when forming the insulating layer 5, and is the back side of the electrode 2 when forming the insulating layer 6. The back side of the luminescent layer 4 of the composite substrate 9 consisting of the transparent substrate 1, the transparent electrode 2, the insulating layer 5, and the luminescent layer 4 (
and the side surface corresponding to the above-mentioned extension part, etc.).

Next, an inert gas Pi such as argon gas is introduced into the ion generation chamber 11 of the above device through the introduction valve 12 to ionize it, accelerate and converge it, and take it into the vacuum chamber 7 in the form of a beam to target the target. Collision with 8. At this time, it accelerates like a beam.

If the focused ions are made to collide with the target 8 after being neutralized by the electron generator 13, the rate of thin film formation on the composite substrate 9 will be significantly increased, so it is recommended to adopt such an additional means. desirable. The method of collision after neutralization will hereinafter be particularly referred to as neutral beam sputtering, but the ion beam sputtering referred to in this specification naturally includes the above-mentioned neutral beam sputtering.

The sputtered atoms generated by the collision are transferred to the heater 14
The gas reaches the thin film forming surface 10 of the composite substrate 9 which is usually heated by 200 to 400° C.Cl.
Oxygen gas P is blown onto the formation surface 10 through 6.
While being oxidized by Ta205 or an oxide composition close to Ta205, it is deposited on the formation surface 10. As a result, the tantalum oxide thin film as the insulating layer 5 or 6 is formed to a predetermined thickness within the above range.

Note that the oxygen gas P blown onto the thin film forming surface 10
o is indispensable in forming a tantalum oxide thin film with good dielectric properties, but instead of spraying oxygen gas directly in its molecular state, it is ionized by the side ion gun 17 shown in Fig. 2 and then sprayed. You can. By spraying in this ionized state, more desirable results such as a reduction in the emission start voltage of the resulting EL element can be obtained.

In such a sputtering operation, the degree of vacuum in the vacuum chamber 7 is generally adjusted to 1O- It is assumed that the degree of vacuum is 4 Torr or less. In the proposed high frequency sputtering, 10 to 10
While it is necessary to have a low vacuum of Torr, since it is possible to have a high vacuum as mentioned above, the incorporation of gas molecules into the formed oxide tank thin film is suppressed and the dielectric properties are improved. can contribute. Moreover, since the substrate is not exposed to plasma, the thin film forming surface 1
When 0 is the transparent electrode 2 or the light emitting layer 4, there is no adverse effect of plasma on the surfaces thereof.For this reason, according to the present invention, the insulating layers 5 and 6 are made of tantalum oxide thin films formed by the above method. Thin-film EL elements have a low emission starting voltage of 5° and a high breakdown voltage.
The advantage is that the margin increases accordingly and the maximum brightness can be improved, and the range of allowable voltage during driving becomes wider, making handling easier.

In order to better express these effects,
In the sputtering operation, the ratio [(a)/β)] between the partial pressure hole of the oxygen gas Po, which is sprayed directly or ionized to the thin film forming surface 10 and the thin film forming speed CB), is preferably set within an appropriate range. That is, the partial pressure hole is generally in the range of IXIO''Torr to 3XIQ'Torr,
The thin film formation rate Q3) is usually selected in the range of 30 to 100 people/min, but in this case, the film formation rate Q3) is 1×10 to 5×10
By setting the voltage to Torr/A/min, the effect of increasing the breakdown voltage and increasing the margin is significantly exhibited.

Further, the above ratio [(A)/(B)] differs somewhat depending on whether the oxygen gas o is sprayed in its molecular state as it is or whether it is sprayed after being ionized.

When spraying in the molecular state, the above ratio is 5 × 10 ~
in the range of 5X10 Torr/A/min, particularly preferably 5
It is preferable to set it within the range of X10 to 3X10 Torr/A/min. On the other hand, in the case of ionizing and spraying, it is within the range of ■×10 to 5×1OTorr/A/min, particularly preferably 2×10 to 3×10'Torr/A/min.
It is best to set it within the range of X 7 minutes.

Setting the ratio between the partial pressure hole of oxygen gas Po and the thin film formation rate β) as described above not only increases the margin, but also allows the formation of a thin film with good dielectric properties inherent to tantalum oxide and the start of light emission. This is desirable also from the point of view of lowering the voltage.

In other words, if the above ratio becomes too small, the film turns black and develops metallic characteristics, making it difficult to emit light itself.
Furthermore, if the above ratio becomes too large, the film becomes porous and there is a risk that the breakdown voltage will be extremely reduced.

Note that the thin film formation rate (B) is determined by the rate of introduction of inert gas Pi, acceleration of ions generated in the ion generation chamber into a beam shape,
Since it is determined by the current and voltage value when the electrons are converged and introduced into the vacuum chamber 7, and the presence or absence of an electron generator, these conditions can be arbitrarily adjusted by appropriately selecting them.

The above is the first part of the method for manufacturing a thin film EL element of the present invention.
Although the structure shown in the figure has been explained as an example, the above manufacturing method of the present invention can also be applied to other structures, such as a type in which one of the insulating layers 5 and 6 is omitted, or a type in which the light emitting layer 4 is replaced with an insulating layer. The present invention can be similarly applied to thin-film EL elements having various configurations, such as those having two or more layers, and thereby the same effects as described above can be achieved.

[Effects of the Invention] As described above, in the present invention, the insulating layer made of the tantalum oxide thin film is formed by the above-mentioned specific ion beam sputtering, so that the emission starting voltage is low and the breakdown voltage is low. The effect is that it is possible to provide a thin film type EL element that has a high margin and therefore can contribute to improving maximum brightness and facilitating driving.

〔Example〕

EXAMPLES Below, examples of the present invention will be described in more detail.

Example 1 A transparent electrode made of ITO with a thickness of 1.500 mm was formed by vacuum evaporation on one surface of a substrate made of alkali-free glass with a thickness of 3 mm, and the electrode surface was the thin film forming surface. It was set in the sputtering apparatus shown in FIG. Ta205 was used as the target, and argon gas pressure was 5X1.
0 Torrs Partial pressure of oxygen gas blown onto the Vi film forming surface: 7×10 Torr.

Thin film formation speed: 70A, 7 minutes, substrate heating temperature: 200°C
By performing neutral beam scattering under these conditions and attaching an electron generator to neutralize beam-like ions, tantalum oxide ('ra , o,) An insulating layer made of a thin film was formed. The dielectric constant of this insulating layer is 28, and the dielectric loss (t
anδ) was 0.2%.

In addition, the partial pressure of oxygen gas in the above sputtering (ratio [(A)/(B)] between At and thin film formation rate (B)) is lXl0
'Torr/A/min.

Finally, on the above insulating layer, by electron beam evaporation method,
The thickness was 7.5 cm under the conditions of a vacuum degree of 1X10 Torr, a substrate temperature of 180° C., and a deposition rate of 30 A/sec. A luminescent layer of oooX was formed. The luminescent material is ZnS with 3 TbF3
% by weight was used. After vacuum deposition, heat treatment was performed in vacuum at 500°C for 1 hour. Thereafter, an insulating layer made of a tantalum oxide thin film having a thickness of 3,000 λ was formed on this light emitting layer using a neutral beam scattering method exactly as described above. Finally, on this insulating layer, a thin film with a thickness of 2
By forming a back electrode in a desired pattern made of Al metal with a thickness of .000λ, a thin film type EL element according to the present invention having the configuration shown in FIG. 1 was obtained.Examples 2 to 5 Partial pressure diagram of oxygen gas and thin film formation speed (7) as shown in Table 1 below to obtain a thickness of 3. Four types of thin film EL devices according to the present invention were fabricated in exactly the same manner as in Example 1, except that an insulating layer made of an oooX tantalum oxide thin film was formed. The relative dielectric constant and dielectric loss of the insulating layer in each element were as shown in Table 1.

Table 1 Examples 6 to 8 A side ion gun is attached to ionize the oxygen gas to be sprayed onto the thin film formation surface so that the oxygen gas is sprayed in an ionized state, and the partial pressure diagram of the oxygen gas and the thin film formation rate ( Example 3 according to the present invention was prepared in exactly the same manner as in Example 1, except that B) was changed as shown in Table 2 below to form an insulating layer made of a tantalum oxide thin film with a thickness of 3,000×. A thin film type EL device was fabricated. The relative permittivity and dielectric loss of the insulating layer in each element were as shown in Table 2.

Table 2 Comparative Examples An insulating layer consisting of a tantalum oxide thin film with a thickness of 3,000 mm was formed by high-frequency sputtering at an argon gas pressure of lXl.
0 Torr, oxygen gas pressure 2X10 Torr.

A comparative thin film EL device was fabricated in the same manner as in Example 1, except that the substrate temperature was 200° C. and the thin film formation rate was 30×/min. The dielectric constant of the insulating layer of this device was 23, and the dielectric loss was 0.7%.

In order to investigate the characteristics of each EL element according to the above examples and comparative examples, a 5 KHz AC pulse voltage was applied, and the emission start voltage, maximum brightness, and margin (difference between the emission start voltage and breakdown voltage) were measured. The results were as shown in Table 3 below.

, -''/'/'' Table 3 As is clear from the results in Table 3 above, the thin film EL device obtained by the method of the present invention has a low emission start voltage, a large margin, and a high maximum luminance. It turns out that it is expensive.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of a thin film electroluminescent device obtained by the method of the present invention, and FIG. 2 is a schematic diagram showing an example of a sputtering apparatus for carrying out the method of the present invention. 2...Transparent electrode, 3...Back electrode, 4...Light emitter layer, 5.6...Insulating layer (tantalum oxide thin film), 7...Vacuum chamber, 8...Target, 10...Thin film Formation surface, 11.
...Ion generation chamber, 13...Electron generator, 17...
Side ion gun, Pi...inert gas, PO...
oxygen gas

Claims (3)

[Claims] (1) In a method for manufacturing a thin-film electroluminescent device having a structure in which a luminescent layer and an adjacent insulating layer made of a tantalum oxide thin film are interposed between a pair of electrodes, at least one of which is transparent, the insulating layer is A thin film electroluminescent device characterized in that a tantalum oxide thin film is formed using an ion beam sputter that targets tantalum metal or tantalum oxide and sprays oxygen gas directly or in ionized form onto the thin film formation surface. manufacturing method. (2) The beam-shaped ions are accelerated and focused from the ion generation chamber that ionizes the inert gas and taken into the vacuum chamber, and are neutralized by an electron generator before colliding with the target. A method for manufacturing a thin film electroluminescent device according to claim (1). (3) Partial pressure (A) of oxygen gas blown onto the thin film formation surface
and the thin film formation rate (B) [(A)/(B)] is 1×
A method for manufacturing a thin film electroluminescent device according to claim 1 or 2, wherein the torr/A/min range is 10 to 5×10^-^6 Torr/Å/min.