JPS60257098A - Thin film electroluminescent element and method of producingsame - 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 a thin film light emitting device that emits electroluminescence, and can be applied as an easy-to-read, high-definition flat panel display device such as a computer terminal device.

Conventional technology and its problems Electroluminescent elements (hereinafter referred to as EL) that emit light by applying an alternating current electric field
The device has a structure in which a dielectric thin film layer is provided on one or both sides of a phosphor thin film layer, and this is sandwiched between two electrode layers. The phosphor layer used here is ZnS+
(2) Mn or rare earth fluoride is added as a luminescent center to a matrix such as Zn5e and ZnF. In a Zns phosphor element doped with Mn as a luminescent center, a maximum of 3500
~5000”% brightness has been achieved.

Dielectric materials include Y2O3, Sin, St, N,
Representative examples include Ag, 03 and Ta205. The thickness of each layer is approximately 5,000 to 7,000 for the ZnS layer and 14,000 to 8,000 for the dielectric layer.

When driving with AC, the voltage applied to the element is divided between the ZnS layer and the dielectric layer. Since an EL element is equivalent to two capacitors connected in series, 6% -'z
Vz/lz (where, Si is the relative permittivity of the dielectric, tj is the thickness of the dielectric, ■ is the voltage applied to the dielectric, and ε2 is Zn5O
From the relationship between relative dielectric constant, tz and thickness of ZnS, and Vz is the voltage applied to Zns, each partial pressure is t7-tz
If so, it is inversely proportional to the dielectric constant. Therefore, the above Y
For a dielectric material such as 2O3, the average temperature is about 4 to 25. εZ of ZnS
is about 9, so only about 60% of the total applied voltage is applied to the ZnS layer. Therefore, in such an element,
At present, a voltage of 200 V or more is applied by pulse drive of several TG (z). This high voltage places a great burden on the drive circuit, and a special high voltage drive IC is required, which increases the cost. It is connected to the up.

Next, we will discuss what characteristics the dielectric layer should have in order to lower the driving voltage. Due to the already mentioned voltage division relationship, five cans must be large.

After light emission begins, a large amount of voltage is applied to the dielectric layer, so unless VIB (dielectric breakdown voltage of the dielectric layer) is also large, it cannot be said to be an excellent dielectric thin film. Therefore, the performance of the dielectric layer, index γ, is r = ε<Vjb, 4. = ε<Eib(E:<b
! dielectric breakdown electric field strength of the dielectric film).

As shown from the equation, γ is equal to the charge accumulated per unit area when the dielectric film undergoes dielectric breakdown. The larger γ is, the more stable low voltage driving can be performed. This is because, in two types of EL elements with the same phosphor film thickness and the same dielectric film thickness, one element has a dielectric film and the other has a dielectric film of ε1=50. Eib-U×10
6, γ = 1'50X1.06 If the characteristics are as follows, of course the thickness of the dielectric is the same, so the former εj = 1
00 emits light at a much lower voltage. However, Si”
50. Since the dielectric breakdown voltage of E7b=306Vcm is higher, if the withstand voltage is set to be the same as the former, the film thickness can be reduced to 1. As a result, the capacitance of the dielectric material triples, equivalently becoming ε (=150). Therefore, regardless of Si, a device with a higher figure of merit can produce a lower voltage light emitting device.

The value of r is as large as possible, and as a guideline for low voltage emission, Z
ε2 of nS=9. 1 from r=114
It is desired that it be 0 times or more.

The figure of merit of a conventionally known dielectric film is, for example, Y2
Approximately 50 x 106'V/c1n for O3, approximately 30 for A03
X 10"l'cm.

Si3N, which is small at about 70 x 106"7cm, is not suitable for low voltage light emission.In recent years, PbTi0J and pb(
Ti1. , -XzrX)03, etc. as the dielectric layer(5) was proposed. Although these have a Si content of 150 or more, their Eib is as small as 5 x 105 V/crt, so it is necessary to make the film thickness significantly thicker than conventionally used dielectric materials. Therefore, 6 of ZnS
000 people, the thickness of the dielectric thin film described above is generally required to be 15,000X or more in terms of device reliability.In general, with such materials, the substrate temperature during thin film formation is high, so particles in the film grow. Easy to become cloudy. In an XY matrix display using such a cloudy film, light is emitted even from non-light emitting segments by scattering light emitted from other segments, resulting in poor image quality.

In view of the above, the inventors have developed Eib and Eil
We have already proposed an EL device using a dielectric thin film mainly composed of 5rTIO3, which has a high product of both ) and Si and is suitable for low-voltage driving and does not become cloudy. It is preferable to lower the drive voltage from the viewpoint of reliability and cost of the drive circuit. In this respect, a sufficient technical solution has not yet been achieved. In particular, in order to increase the luminance of the phosphor thin film layer, heat treatment is performed after the thin film is formed (6), but if there is a dielectric layer under the phosphor thin film layer, heat treatment may be performed at the same time. receive. As a result, when the film thickness of the dielectric layer is approximately O,'5ttm or more, defects occur in the dielectric film and the withstand voltage decreases. Another disadvantage is that the dielectric breakdown state is easily propagated and self-recovery is difficult.

OBJECTS OF THE INVENTION The inventors have further investigated the composition of the S rTi 03 dielectric film in an attempt to obtain a dielectric film that is more suitable for low voltage driving and has higher reliability.

The structure of the invention is characterized in that a dielectric thin film layer is provided on at least one side of a phosphor thin film layer, and two electrode layers, at least one of which is transparent, connect the phosphor thin film layer to the dielectric thin film layer. The thin film electroluminescent device is configured such that a voltage is applied to the dielectric thin film layer, and the thin film electroluminescent device is characterized in that a potassium tank niobate film is used as the dielectric thin film layer.

Description of Examples (7) The present invention is characterized by the discovery of a new composition for dielectric thin films used in conventional thin film light emitting devices. By using potassium acid, it was possible to obtain a dielectric film with εi of 100 or more and Eib of 2X10"%n. In the experiment, the thin film was formed using magnetron RF sputtering method, and its removal was The target used is a sintered ceramic target. Potassium tantalate niobate used in the present invention is a solid solution of potassium tantalate and potassium niobate, and is an oxide ferroelectric material with a perovskite structure. One point is
Potassium niobate is about 11-20υ, but when niobium is replaced with tantalum, the Curie point moves to the lower temperature side.
When replaced with 0 molar tantalum, the value decreases to nearly -80υ. Therefore, if a composition with a high dielectric constant or dielectric strength is selected, the resulting potassium tantalum niobate will have a single Curie point near room temperature, and the amount of tantalum substituted in that case will be in the range of 50 to 70 mole percent. Become.

(8) For example, K (Ta O,6Nb O,'i ) O,
When looking at
It was confirmed that the value was higher than that of the rTiO3 film. or,
The formed film is transparent with no clouding due to grain growth, and when used as a dielectric thin film for EL devices, it is possible to obtain EL devices with good image quality and to produce highly reliable EL devices with high yields. It can be manufactured with.

Next, a method for manufacturing a thin film electroluminescent device of the present invention will be explained with reference to the drawings and according to the process used in the experiment.

As shown in the figure, ITO transparent conductor! (Glass substrate provided with 21 (111, K(TaO,6NbO,'
l) The dielectric film (3) with the composition 03 was placed in a magnetron R.
Deposit to a thickness of 5000X using the F sputter link method.

As the sputtering gas, a mixed gas of 02 and Ar (
02 partial pressure 25%) was used. Gas pressure during sputtering is O
, BPa. As a target, a ceramic plate mixed with the above composition and sintered at 1200 υ was used. The substrate temperature is 600υ(9). The thin film thus obtained was transparent and no clouding was observed. At the time when the dielectric film (3) is formed, εz
(!: EibO value was checked. After that, ZnS and Mn were simultaneously deposited on the dielectric thin film (3) by electron beam evaporation method, and a phosphor layer (4) of ZnS:Mn was formed to a thickness of 500 mm.
After forming a ZnS:Mn film, a heat treatment was performed in a vacuum for one hour at 600υ, and a Ta205 film (5
) was deposited to a thickness of qooX by electron beam evaporation.

A PbNb2O6 film (6) was deposited thereon to a thickness of 1000× by magnetron RF sputtering. As the sputtering gas at this time, an Ar mixed gas containing 25% 02 was used, and the sputtering gas pressure was 3 Pa. PbNb,.06 ceramic was used as the target, and the substrate temperature was set to 380υ. Finally, an AQ film (7) was deposited as an upper electrode to a thickness of 1000λ using resistance heating vapor deposition, completing the electroluminescent device.

The electroluminescent device manufactured as described above was driven with alternating current pulses with a repetition frequency of 5 KHz, and the voltage-luminance characteristics were measured. As a result, the electrical characteristics were that ζ was 120. Eib
is 2 X I O""7cm, e6 X Eib is 2
40 x 106(/,)(10), and the luminescence characteristics were: - Saturation luminance was 38oO (0 condition), and the applied voltage at this time was 110V. As is clear from the above results, both the electrical properties and luminescent properties of 5rTi
It has been demonstrated that it is far superior to e.

In addition, in the compositional formula of K(TaxNbneyX)03, if the value of was found to have a figure of merit of

From the above barrier, 5rTi0 can be used as a dielectric film of a low-voltage driven electroluminescent device in the range of composition formula T O, 5≦X≦0.7, which is K (TaxNb, X) 03.
A thin film superior to that of the 5BaTi03 film can be obtained.

Effects of the Invention As described above, according to the present invention, the dielectric thin film layer of the thin film electroluminescent device is made of K (ThxNb 1)O.
By constructing a dielectric material with a high figure of merit and a high crack resistance with a composition of 11) It is industrially effective in terms of improved reliability and cost.

[Brief explanation of the drawing]

The figure is a cross-sectional view of one embodiment of the thin film electroluminescent device of the present invention. (1)...Glass substrate, (2)...Transparent electrode, (
3) --- Dielectric film, (41.=ZnS:Mn
Fluorescent film, (5)-Ta20□ film, 16)...Pb
Nb2O6 film, (7) --- Name of AQ short electrode representative
Patent attorney Etsuji Yoshizaki (12)

Claims (1)

[Scope of Claims] 1. A phosphor thin film layer and a dielectric thin film layer provided on at least one side of the phosphor thin film layer, at least one of the two electrode layers is 1. A thin film electroluminescent device configured to apply a voltage through two transparent electrode layers, characterized in that the dielectric thin film layer is made of a potassium tank niobate film. 2. The thin film electroluminescent device according to claim 1, wherein the potassium tantalum niobate film constituting the dielectric thin film is a sputtered potassium tantalum niobate film formed in an oxygen partial pressure. . ), a thin film electroluminescent element in which (1) a transparent electrode layer, a first dielectric film, a phosphor thin film layer, a second dielectric film, and an electrode are sequentially stacked on a substrate; In the manufacturing process, the first dielectric film is coated with a transparent electrode layer in an oxygen atmosphere using tankurium niobate porcelain having a single point near room temperature and a perovskite structure as a target. A method for manufacturing a thin film electroluminescent device, characterized in that the device is formed by sputtering on a substrate.