JPH0764490A - Light emitting display element - Google Patents

Abstract

PURPOSE:To drive a light emission display element by relatively low voltage and improve its accuracy as a coloring or display element by providing a light emitting element for emitting light by means of electrons discharged from a strong dielectric by impressing alternating voltage. CONSTITUTION:A lower electrode layer 3, a strong dielectric layer 4, and an upper electrode layer 5 are laminated on the surface of the base plate 2 in a cell 1. A phospher layer 7 is formed inside the glass cell 6 opposite to the upper electrode layer 5 in the cell 1. When alternating pulse voltage is impressed on the lower electrode layer 3 from an electric power supply 8, remaneuce of the strong dielectric is inverted in the strong dielectric layer 4, and a strong electric field is generated accompanying this. When the strong electric field is impressed on the strong dielectric, electrons in the strong dielectric are drawn out by the upper electrode layer 5 following to a tunnel effect, and discharged outward. The phospher emits a light by radiating the electrons discharged from the upper electrode layer 5 to the phospher.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel light emitting display device using a ferroelectric thin film.

[0002]

2. Description of the Related Art Conventionally, as a light emitting display element, for example,
Fluorescence that excites the phosphor by ultraviolet rays generated by the discharge of the enclosed gas, plasma display that uses the emitted three primary colors as a light source, and accelerates and controls the thermoelectrons emitted from the heated filament surface to irradiate the phosphor to emit light. Display tube,
An EL (electroluminescence) display utilizing high electric field light emission of a semiconductor in which a high electric field is applied to a semiconductor base material doped with an emission center substance can be cited.

[0003]

However, the above-described conventionally known light emitting display elements have respective merits and demerits in practical characteristics such as light emission luminance, life, colorization, and large area. That is, the plasma display can be colored, but requires high driving power of 250 V or more,
The fluorescent display tube is driven by a low electric power of 150 V or less, but it is difficult to make it fine, and the EL display is also driven by a low voltage of 250 V or less, but it is difficult to colorize and increase the area of the display element. There's a problem.

It is an object of the present invention to provide a novel light emitting display device which can be driven at a relatively low voltage and which can be made into a color display or a fine display device.

[0005]

As a result of repeated studies of light emitting elements used for display elements, the present inventors have found that when an alternating voltage is applied to the ferroelectric substance, the remanent polarization of the ferroelectric substance is reduced. Focusing on the phenomenon that a strong electric field is generated due to the reversal and the emission of electric field electrons is observed, a ferroelectric substance, an electrode for applying an alternating voltage to the ferroelectric substance, and the ferroelectric substance by applying the alternating voltage It has been found that the above object can be achieved by using, as a light emitting display element, an array of a plurality of cells each including a phosphor that emits light by the emitted electrons.

The structure of the light emitting display device of the present invention will be described below with reference to the drawings. The light emitting display device of the present invention is composed of an assembly of a plurality of cells, and a typical structure of the single cell is shown in FIG. In the cell 1, the lower electrode layer 3, the ferroelectric layer 4, and the upper electrode layer 5 are sequentially laminated on the surface of the substrate 2. Further, a phosphor layer 7 is formed inside the glass cell 6 facing the upper electrode layer 5 in the cell 1. Further, the lower electrode layer 3 is a power source 8
The upper electrode layer 5 is connected to the ground (ground), and more preferably, the bias electrode 9 is formed on the back surface of the phosphor layer 7. The inside of the cell is kept under a vacuum of about 10 ^-2 torr or less. Further, in this example, the upper electrode layer 5 is composed of a mesh-shaped (grid) electrode.

In the cell having the above structure, the lower electrode layer 3
When an alternating pulse voltage of about 50 V or more is applied to the power source 8, the remanent polarization of the ferroelectric substance is inverted in the ferroelectric layer 4, and a strong electric field is generated accordingly. 1 for ferroelectric
When a strong electric field of 0 ⁷ V / cm or more is applied, the electrons in the ferroelectric substance are extracted by the upper electrode layer 5 by the tunnel effect and are emitted to the outside. This is a so-called field electron emission phenomenon. Then, the phosphor can be made to emit light by irradiating the phosphor with electrons emitted from the upper electrode layer 5.

In the above structure, the bias electrode 9
Is applied with a positive bias voltage of 10 V or more, and electrons emitted from the upper electrode layer 9 are accelerated to reach the phosphor layer 7, whereby the light emission of the phosphor layer 7 is further increased.

According to the present invention, the phosphor layer 7 is required to be formed on the opposite side of the upper electrode layer 5 from the ferroelectric layer 4 based on the above-mentioned mechanism of light emission, and the bias is applied. When the electrode 9 is provided, the phosphor layer 7 may be disposed between the upper electrode layer 5 and the bias electrode 9, and therefore the phosphor layer 7 is not the inner surface of the glass cell as described above. Alternatively, it may be formed directly on the upper electrode layer 5.

In the present invention, the ferroelectric layer 4 is specifically made of Pb (ZrTi) O ₃ , (PbLa) (ZrT).
i) It is composed of O ₃ or a composite oxide composed of a compound obtained by adding a dopant such as Nb. It is desirable that the ferroelectric layer 4 has a thickness of 5 μm or less in order to cause field electron emission at a low voltage. The lower electrode layer 3, the upper electrode layer 5 and the bias electrode 9 are made of platinum (P
t), Au, Al. Further, the phosphor layer 7 may be made of a well-known phosphor, and can emit light of any color by changing the type of phosphor. For example, Y ₂ SiO ₅ : Tb phosphor is used as a phosphor for green (G), Y ₂ O ₂ S: Eu phosphor is used for red (R), and ZnS: Cl is used for blue (B). ) Can emit light.

According to the present invention, as shown in FIG. 2, the single cells shown in FIG. 1 are arranged in a matrix in a matrix form, and, for example, an alternating voltage is applied to the lower electrode layer 3 of each cell. The control means 10 controls the positive voltage application to the bias electrode 9 by the control means 11 so that any single cell in the matrix can emit light. That is,
As shown in FIG. 4, since the electric field electron density from the ferroelectric substance varies depending on the applied voltage to the bias electrode, the lower electrode layer 3 and the bias voltage are set to emit light only when a predetermined voltage is applied at the same time. By controlling ON-OFF of the voltage applied to the electrodes and the application of the alternating voltage to the ferroelectric, only a predetermined single cell can emit light.

According to the present invention, the phosphor layer 7 of the single cell 1 is replaced with a phosphor having a different emission wavelength as described above, and as shown in FIG. 3, red (R), green (G), Blue (B)
A flat color light emitting display element can be manufactured by arranging a plurality of the single segments 12 by arranging a group of three single cells that emit light in a single segment 12.

[0013]

According to the structure of the present invention, a ferroelectric substance and an electrode are laminated in a single cell, and an alternating pulse voltage of a relatively low voltage of 50 V or more is applied to the electrode, whereby the electric field of the ferroelectric substance is increased. Due to the electron emission phenomenon, electrons are emitted at a high field electron density of about 1.0 A / cm ² . The emitted electrons cause the phosphor to emit light. Further, according to the present invention, a bias electrode is formed in the cell, and a positive voltage is applied to the bias electrode to accelerate the emitted electrons,
The emission brightness of the phosphor can be controlled, and the emission of any single cell can be controlled in the display device including a matrix of a plurality of cells by controlling the applied voltage of the bias voltage and the applied voltage to the ferroelectric. can do.

In addition, since the above-mentioned layer structure constituting the single cell can be formed by a thin film method or the like, the laminated structure can be thinned and the cell can be miniaturized. It is possible to manufacture a flat and thin display element as well as the definition. In addition, by changing the type of the phosphor layer, it is possible to easily color the phosphor layer, and it can be widely used as various display elements.

[0015]

【Example】

Example 1 A specific explanation will be given using a ferroelectric substance of PbZrTiO ₃ (PZT). First, the lower electrode layer 3 made of Pt was formed to a thickness of 0.3 μm on the surface of the insulating substrate 2 by the sputtering method. Then, a PZT sol-gel solution is applied onto the Pt lower electrode layer 3 by a spin coating method, dried and then crystallized at 700 ° C. for 2 hours, and the above-described film forming process is repeated until a target film thickness is obtained. Repeated times, a ferroelectric layer 4 made of PZT (Zr / Ti molar ratio = 65/35) solid solution having a film thickness of 3 μm was formed. This ferroelectric layer 4 is
It had a remanent polarization of 20 μm / cm ² or more and a ferroelectric property of a coercive electric field of 100 kv / cm or less. Then, Pt is deposited on the ferroelectric layer 4 by the sputtering method.
The upper electrode layer 5 was formed. Further, as shown in FIG. 1, an ITO transparent electrode (bias electrode) 9 having a thickness of 0.5 μm is formed on the inner surface of the glass cell 6 by sputter deposition, and Y ₂ S is formed on the transparent electrode 9 by screen printing.
The iO ₅ : Tb phosphor layer 7 was formed to a thickness of 5 μm. The inside of the cell was set to a vacuum state of 10 ⁻⁴ torr and electrically connected as shown in FIG.

When an alternating pulse voltage of 2 kHz was applied to the lower electrode layer 3 of the device thus manufactured, the cell exhibited stable green light emission. In addition to this, the transparent electrode layer 9
A bias voltage of 30 V and 100 V was applied to the device and the emission brightness at that time was measured. The dependency of the emission brightness on the alternating pulse voltage and the bias voltage is shown in FIG. According to FIG. 4, it was found that the higher the bias voltage, the higher the emission luminance at the low alternating pulse voltage, and the emission luminance was almost saturated in the range of the alternating pulse voltage of 300 V or higher.

Example 2 Instead of the Y ₂ SiO ₅ : Tb phosphor of Example 1, Y ₂ O was used.
_{When a 2} S: Eu phosphor was similarly formed on the ITO transparent electrode layer 9 and an alternating pulse voltage of 2 kHz was applied to the lower electrode layer 3, stable red light emission was exhibited. Furthermore, Zn
When an S: Cl phosphor was formed, the cell emitted blue light. From this, it is understood that color can be easily obtained by changing the phosphor.

[0018]

As described above, according to the structure of the present invention, light can be emitted at a relatively low voltage, and the laminated structure can be thinned and the cell can be miniaturized. It is possible to manufacture a flat and thin display element along with refinement. In addition, by changing the type of the phosphor layer, it is possible to easily color the phosphor layer, and it can be widely used as various display elements.

[Brief description of drawings]

FIG. 1 is a diagram showing a typical structure of a single cell according to the present invention.

FIG. 2 is a diagram showing an example of a structure of a light emitting display element of the present invention.

FIG. 3 is a diagram showing an example of a structure of a light emitting color display element of the present invention.

FIG. 4 is a diagram showing the relationship between the emission luminance of a cell and the alternating pulse voltage and bias voltage in the present invention.

[Explanation of symbols]

 1 Single Cell 2 Substrate 3 Lower Electrode Layer 4 Ferroelectric Layer 5 Upper Electrode Layer 6 Glass Cell 7 Phosphor Layer 8 Power Supply 9 Bias Electrode

Claims (2)

[Claims] 1. A ferroelectric substance, an electrode for applying an alternating voltage to the ferroelectric substance, and a remanent polarization of the ferroelectric substance by the application of the alternating pulse voltage is inverted to generate a strong electric field. 2. A light emitting display device comprising a plurality of single cells arranged with a phosphor that emits light by field electrons emitted by. 2. The light emitting display device according to claim 1, wherein the single cell comprises an electrode for accelerating electrons emitted from the ferroelectric substance.