JPS6260799B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a thin film light emitting device that emits electroluminescence.

Conventional structure and its problems Thin film EL (electroluminescence) elements that emit light when an alternating current electric field is applied have 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. High brightness is obtained. An element having a single dielectric thin film layer is characterized by a simple structure and low driving voltage. A device with two dielectric thin film layers is characterized by being less prone to dielectric breakdown and having particularly high brightness. As phosphor materials, active material-added ZnS, ZnSe, _ZnF2, etc. are known, and in particular, ZnS-based materials are known.
For devices doped with Mn as the luminescent center, the highest
Brightness of 3500-5000 cd/ ^m2 has been achieved. _Dielectric materials _{include Y2O3} , SiO, _Si3N4 , _{Al2O3 ,} and
Typical examples include Ta ₂ O ₅ . ZnS has a thickness of 500~
700nm, relative permittivity is approximately 9, and the dielectric thin film has a thickness of
It has a wavelength of 400 to 800 nm and a relative dielectric constant of 4 to 25. When driving with AC, the voltage applied to the element is divided between the ZnS layer and the dielectric thin film layer, and only about 40 to 60% of the voltage is applied to the former. The voltage required for light emission is apparently increasing. In a device with dielectric thin film layers on both sides of the ZnS layer, 200 V can be achieved by pulse drive at several KHz.
Currently, higher voltages are being applied. This high voltage places a heavy burden on the drive circuit, requiring a special high-voltage integrated circuit (IC), which also leads to increased costs.

On the other hand, in order to lower the driving voltage, it has a high dielectric constant.
It has been proposed to use a thin film mainly composed of PbTiO ₃ or Pb(Ti _1-x Zr _x )O ₃ as a dielectric thin film layer. These thin films have a relative dielectric constant (hereinafter referred to as εr)
is over 100, while the dielectric breakdown electric field strength (hereinafter E _b
) is as small as 0.5 MV/cm, so it is necessary to make the film much thicker than conventionally used dielectric materials. In the case of a high-brightness device, the thickness of the ZnS layer is required to be about 0.6 μm, and from the viewpoint of device reliability, the thickness of the dielectric thin film layer is required to be 1.5 μm or more. When the film thickness is increased, particles in the film grow due to the high substrate temperature. As a result, the film becomes cloudy and the light transmittance decreases. Using such a cloudy membrane
When the EL element is made into an X-Y matrix, etc.,
Even non-emissive segments have the disadvantage of causing crosstalk by scattering the emitted light of other segments.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a thin film EL element with a luminance equal to or higher than that of conventional EL elements and a low driving voltage.

Structure of the Invention The present invention uses a general formula in which ε _r and E _b are large in the dielectric layer.
The above object was achieved by using a dielectric layer containing a complex oxide represented by AB ₂ O ₆ as a main component. Here A is Pb, Ca, Sr, Ba, Cd
B represents at least one of Ta and Nb.

In an AC driven thin film EL element, the voltage applied to the dielectric layer is determined by the thickness t _i of the dielectric thin film layer,
The product of the electric field strength E _i is t _i ·E _i . The smaller t _i ·E _i is, the more effectively the voltage is applied to the phosphor thin film layer. In order for the device to operate stably without causing dielectric breakdown, t _i can be considered to be inversely proportional to E _b of the dielectric thin film layer. E _i is the electric field strength E _z in the phosphor thin film layer, relative dielectric constant ε _z and ε _r of the dielectric thin film layer,
The relationship is E _i =E _z ·ε _z /ε _r . If E _z and ε _z are constant, E _i is inversely proportional to ε _r . Therefore, t _i・E _i is roughly the product of E _b and ε _r E _b・
It can be said that it is inversely proportional to ε _r . The larger E _b ·ε _r is, the better the dielectric thin film layer is.

The composite oxide thin film represented by the general formula AB ₂ O ₆ used in the present invention has a larger E _b ·ε _i than conventional materials and is excellent as a dielectric thin film for EL. Here, A is at least one kind of divalent metal elements such as Pb, Cd, Ba, Sr, and Ca, and B is one or both of Ta and Nb. The bulk ε _r of these composite oxides is large, for example, PbNb ₂ O ₆
is 300, _{PbTa2O6 is also 300} , _{( Pb0.55Sr0.45} ) _{Nb2O6 is}
A value of 1600 has been reported. When it is made into a thin film, it is difficult to obtain the same ε _r as the bulk, but an ε _r of 40 or more can be easily obtained by sputtering. Furthermore, the E _b of the thin film is as high as 2×10 ⁶ V/cm or more. The E _b・ε _r of these thin films is 80×10 ⁶ V/cm
The value is as follows. E of conventionally used materials
For example, _b・ε _r is approximately 50×10 ⁶ V/cm for Y ₂ O ₃ ,
30×10 ⁶ V/cm for Al ₂ O ₃ , 70×10 ⁶ V/cm for Si ₃ N ₄
cm, it can be seen that the composite oxide thin film represented by AB ₂ O ₆ used in the present invention is superior.

These excellent properties cannot be obtained with divalent metal element oxides or pentavalent metal oxides. for example
PbO and CdO are materials with low electrical resistance that cannot be called insulators, and naturally their withstand voltage is extremely low. CaO,
It is impossible to make chemically stable thin films with SrO and BaO, and their withstand voltage is low, making them impractical. On the other _hand , _Nb2O5
Thin films also have low electrical resistance and a very low withstand voltage.
The Ta ₂ O ₅ thin film has considerably better characteristics than the above materials, but its ε _r is about 25 and the breakdown voltage is 1.5 × 10 ⁶ V/cm or more, which is a problem during the formation of the anodic oxide film. It is difficult to obtain only in the polar direction.

The present invention is based on the discovery that a composite oxide having a composition of AB ₂ O ₆ , which is a composite of a divalent metal element oxide and a pentavalent metal element oxide, has excellent properties. Among them, element A of AB ₂ O ₆
PbTa ₂ O ₆ and PbNb ₂ O ₆ which are Pb are E _b・ε _r
is 150×10 ⁶ V/cm and 120×10 ⁶ V/cm, making it an excellent thin film material for EL. These thin films are formed by RF sputtering, targeting ceramics. The higher the substrate temperature, the higher ε _r a thin film can be obtained. E _b is a substantially constant value when the substrate temperature is below about 400° C., and gradually decreases as the substrate is heated above that temperature. The value of E _b ·ε _r becomes large when the substrate temperature is around 400°C. Within this temperature range, there is no adverse effect on the phosphor thin film layer, and the glass substrate can be used without problems such as thermal deformation. Furthermore, the thin film layer represented by the general formula AB ₂ O ₆ does not become cloudy due to grain growth.

Description of examples Next, embodiments of the present invention will be described using the drawings.

Note that a conventional example will also be described here for comparison.

As shown in FIG. 1 for a conventional example and FIG. 2 for an embodiment of the present invention, transparent electrodes 2 and 12 made of ITO (indium tin oxide) are provided on glass substrates 1 and 11. , Y ₂ O ₃ films 3 and 13 with a thickness of 40 nm were deposited by electron beam evaporation. On top of this, ZnS and
Mn was co-evaporated to form ZnS:Mn phosphor layers 4 and 14. The film thickness is 600 nm. The heat treatment was carried out in vacuum at 580°C for 1 hour. This element is divided into five parts, and element 1 is made of Y ₂ O ₃ with a thickness of 400 nm as shown in Fig. 1 as a conventional example for comparison.
A film 5 was formed. On the other hand, as shown in FIG. 2, in the device 2 as an embodiment of the present invention, a Ta ₂ O ₅ film 15 with a thickness of 30 nm is deposited by electron beam to protect ZnS:Mn, and PbNb ₂ A PbNb ₂ O ₆ film 16 was formed by magnetron RF sputtering using O ₆ ceramics as a target. The sputtering atmosphere was O ₂ :Ar=1:4 and the pressure was 0.6 Pa. The substrate temperature is 420°C and the film thickness is 700nm. In addition, as another embodiment of the present invention, element 3 uses PbTa ₂ O ₆ as a target instead of PbNb ₂ O ₆ ,
The other conditions were the same as in the case of element 2, and a PbTa ₂ O ₆ film was formed. The film thickness is 700nm.

In another embodiment of the invention, device 4 contains BaTa ₂ O ₆ as a target instead of PbNb ₂ O ₆ .
using the same conditions as for element 2,
A BaTa ₂ O ₆ film was formed. The film thickness is 500 nm.

Further, as an example of the present invention, SrTa ₂ O ₆ was used as a target in element 5 instead of PbNb ₂ O 6, and _the other conditions were the same as in the case of element 2.
A SrTa ₂ O ₆ film was formed. The film thickness is 450 nm.

PbNb ₂ O ₆ film and PbTa ₂ O ₆ produced under the above conditions
The characteristics of the film, BaTa ₂ O ₆ film, and SrTa ₂ O ₆ film are that E _b is 2.2×10 ⁶ V/cm, 2.6×10 ⁶ V/cm, and 4.2×, respectively.
10 ⁶ V/cm, 4.5×10 ⁶ V/cmε _r are 70 and 48, respectively.
25, 22. On the other hand, no clouding of the membrane was observed.

As shown in Figures 1 and 2, the light reflecting Al
A thin film of Al was deposited as electrodes 6 and 17.

The EL element fabricated as described above is 5KHz
When driven with a sine wave, element 1 has a voltage of approximately 150V.
The brightness is almost saturated at 100V for element 2, 110V for element 3, 125V for element 4, and 125V for element 5.
At 125V, the brightness was almost saturated and the light emitted stably. The saturated luminance was approximately 3000 cd/cm ² for all three elements.

Effects of the Invention The thin film light emitting device of the present invention has a lower driving voltage than conventional devices and operates stably.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a conventional thin film light emitting device, and FIG. 2 is a sectional view of a thin film light emitting device according to an embodiment of the present invention. 1,11...Glass substrate, 2,12...Transparent electrode, 3,13... _Y2O3 film, 4,14... _ZnS :
Mn film, 5...Y ₂ O ₃ film, 15... Ta ₂ O ₅ film, 16
...PbNb ₂ O ₆ film, 17...Al electrode.

Claims (1)

[Claims] 1. A dielectric thin film layer is provided on at least one surface of the phosphor thin film layer, and a voltage is applied to the thin film layer by two electrode layers, at least one of which is transparent to light. The dielectric thin film layer is represented by the general formula AB ₂ O ₆ , where A is at least one member selected from the group consisting of Pb, Ca, Sr, Ba and Cd, and B is 1. A thin film light emitting device comprising a dielectric material whose main component is a complex oxide of at least one of Ta and Nb.