CN1152568C - Thin Film Field Emission Flat Panel Display - Google Patents

Abstract

The present invention belongs to the technical field of a panel display which is composed of an upper glass board, a lower glass board, ring seal glass and a supporting structure, wherein the upper glass board is coated with fluorescent powder and an anodic aluminium film, the lower glass board is prepared with a cathode grid for emitting electron, and the middle of the present invention is kept in an ultrahigh vacuum state. The present invention is characterized in that the cathode grid in turn comprises an earth metal lower electrode, an alkaline earth sulphide insulating layer, an upper electrode, an electron emission layer and a row/column confluence electrode which is printed on the lower glass board for connecting the upper electrode and the lower electrode. The present invention has the advantages of low capacitance, long service life, cost reduction of drive circuit, etc., and is especially suitable for large-screen high definition televisions.

Description

Thin Film Field Emission Flat Panel Display

Technical Field The present invention belongs to the technical field of display devices, and in particular relates to the structure of a novel electron-emitting flat panel display device.

Background Art Electron emission flat panel display devices include metal microtip field emission display devices (FED), surface conduction emission display devices (SED), vacuum fluorescent display devices (VFD) and various metal-insulator-metal (MIM) or metal - Field emission flat panel display devices of insulator-semiconductor-metal (MISM) structure. Wherein, the MIM device structure is shown in FIG. 1 . It includes: an upper plate 11 coated with phosphor powder 12 and an anode aluminum mold 13, a lower plate 18 with an electron-emitting cathode grid on it, a ring sealing glass and a supporting structure (not shown in the figure). The structure of the cathode grid is successively the lower electrode 17 of the metal film, the insulating layer (electron transport layer) 16 and the upper electrode 15 of the metal film. The device is in a vacuum state during operation. Its working principle is: electrons are emitted from the lower electrode 17 of the cathode grid through the insulating layer 16 and then reach the upper electrode 15 of the cathode grid, and part of the electrons pass through the upper electrode to form emitted electrons 14 . The emitted electrons are accelerated by the anode voltage to reach the anode 13 and bombard the phosphor 12 to emit light.

In the published MIM field emission devices, aluminum, molybdenum, gold, platinum, etc. are generally used for the metal lower electrode, and anti-oxidation metal films such as aluminum, gold, iridium, platinum, etc. are used for the upper electrode. The insulating layer mostly uses aluminum oxide and silicon oxide. For example, in the field emission display device developed by Hitachi, the lower electrode uses an aluminum film, the upper electrode uses an iridium-platinum-gold three-layer composite film electrode, and the middle insulating layer uses an aluminum oxide film formed by anodic oxidation.

In the above structure, whether it is alumina or silicon dioxide, the mean free path of electrons when moving in it is generally not more than 1.5 nanometers. In order for a sufficient number of electrons to obtain enough energy to overcome the work function of the upper electrode and be emitted, the electric field strength in the insulating layer should reach about one volt per nanometer (1v/nm). The above requirements can be met when aluminum and gold are used as the lower electrode, and aluminum oxide or silicon dioxide is used as the insulating layer. There are two fatal weaknesses in this structure. One is the contradiction between the driving voltage and the device capacitance. The thinner the insulating layer, the lower the driving voltage. Generally, the thickness of the insulating layer is within the range of 20 nanometers, so the device capacitance is relatively large, so the area of the display device cannot be too large. The above structure is only suitable for small-sized displays. The second is that because the electric field in the insulating layer is too high, it is easy to form the so-called "formation" structure, that is, some metal filaments are formed, which makes the device easy to break down, so the service life is short and the practical application is limited.

SUMMARY OF THE INVENTION The object of the present invention is to overcome the deficiencies of the prior art and propose a new thin-film field emission display device starting from materials and structural dimensions. It has the advantages of low device capacitance, long device life, and can reduce the cost of the driving circuit, and is especially suitable for large-screen high-definition televisions.

The present invention proposes a field emission flat panel display, which consists of an upper glass plate coated with phosphor powder and an anode metal film, a lower glass plate prepared with a cathode grid for emitting electrons, a ring sealing glass and a supporting structure, and an ultra-high vacuum is maintained in the middle , it is characterized in that, said cathode grid comprises rare earth metal thin film lower electrode, alkaline earth metal sulfide insulating layer, upper electrode and electron emission layer in sequence, and also includes printing on said lower glass plate and connecting said upper and lower electrodes The row and column bus electrodes.

Said insulating layer material can be made of alkaline earth metal sulfide, such as strontium sulfide, calcium sulfide and magnesium sulfide, with a thickness in the range of 50-500 nanometers.

The said lower electrode adopts rare earth metal film.

Said electron emission layer can adopt N-type semiconductor material with low electron affinity.

Said row-column bus electrodes are printed by silk printing method, and the insulating layer can be printed by silk screen printing method on the intersections thereof for isolation.

Said upper pole plate can adopt colored fluorescent powder, and add graphite black base between colored fluorescent powder stripes, form black matrix.

Said support structure may be placed on the row bus electrodes.

Principle of the present invention is described as follows in conjunction with Fig. 2,3,4:

The thin film field emission flat panel display structure of the present invention includes an upper plate 21 , a lower plate 29 , a support structure 211 in the middle that resists atmospheric pressure, and the like. There are anodic aluminum film 214, black matrix 213, fluorescent powder 22, etc. on the upper plate. There is a cathode grid on the lower electrode plate, and the detailed structure of the cathode grid is a lower electrode 24, an insulating layer 28, an upper electrode 23 and an electron emission layer 31 in sequence. In order to reduce the electrode resistance, bus electrodes 25 and 26 are respectively added to the upper and lower electrodes of the cathode grid, so that the electrode resistance is less than 100 ohms. The support structure between the upper and lower glass plates. Since the device works in a vacuum, a support structure is necessary to resist atmospheric pressure. The support structure is generally called a support column or a support wall, and the material is generally a high-strength ceramic or a single crystal material, such as a zirconia single crystal.

The electron emission transport system composed of the lower electrode of the rare earth metal film and the alkaline earth metal sulfide starts to form the transport electrons in the insulating layer at a field strength of less than 0.3 volts per nanometer, which is more than three times smaller than the usual MIM system, so the drive The voltage is greatly reduced and the life is greatly increased. Since the mean free path of electrons in rare earth sulfides is much larger than that in alumina and silicon dioxide, the energy obtained by electrons is actually greater, which is conducive to the emission of electrons from the upper electrode.

The upper and lower electrodes of the cathode grid are row electrodes and column electrodes respectively, forming a matrix structure of rows and columns. The intersection of the row and column electrodes is a sub-pixel, and the intersection of three column electrodes and one row electrode constitutes a pixel.

Figure 4 shows the row and column electrodes of a display, where electrons are emitted at the intersections. The numbers of rows and columns are N and 3M respectively (one row and three columns correspond to one color pixel), and the number of formed pixels is M×N. In a specific device, the row electrodes may be on top, or the column electrodes may be on top. Calculations and experiments show that electrons have a self-focusing effect in one direction, which can reduce the divergence of electrons and help improve resolution. If the row electrodes are on the top, there is a focusing effect in the row direction, and vice versa, there is a self-focusing effect in the column direction. The specific selection can be based on the performance requirements of the device.

Positive voltage is applied to the upper electrode and negative voltage is applied to the lower electrode. Electrons are emitted from the lower electrode into the insulating layer through the tunnel effect and accelerated therein. After passing through the upper electrode and the emission layer, they are emitted into the vacuum. After being accelerated by the anode voltage, the bombardment phosphor emits light. As shown in Figure 4, when a certain row is displayed, the electrodes of other rows are grounded. Depending on how high or low the column voltage is, the intersections emit different amounts of electrons. On grounded rows, the column voltage is insufficient to cause electron emission. It is shown line by line that the function of the emission layer above the upper electrode is to reduce the effective work function and obtain a larger emission current.

The present invention has following characteristics:

(1) The capacitance of the device is low, thereby realizing a large-area device, which is suitable for a large-size display.

(2) The electric field intensity in the insulating layer is low, and the service life of the device is long, reaching a practical level.

Description of drawings

Figure 1 is a schematic diagram of the structure of the existing DC drive MIM.

Fig. 2 is a structural principle diagram of the present invention, wherein (a) is a structural schematic diagram; (b) is a working principle diagram.

Fig. 3 is a specific structure diagram of the cathode grid of the present invention.

Fig. 4 is a schematic diagram of the row and column electrode arrangement structure and driving mode of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the thin film emitting flat panel display device of the present invention are described in detail as follows in conjunction with the accompanying drawings:

The structure and principle of this embodiment are shown in FIG. 2 . Its structure includes an upper glass plate 21, a lower glass plate 29, a support structure 211 in the middle that resists atmospheric pressure, and the like. There are anodic aluminum film 214, fluorescent powder 22, etc. on the upper glass plate. Display size 5 inches, monochrome, upper glass plate 21 and lower glass plate 29 thickness are 2 millimeters, be coated with green fluorescent powder 22 on the anode plate (upper glass plate 21).

There is a cathode grid on the lower glass plate, and the detailed structure of the cathode grid is a lower electrode 24 , an insulating layer 28 , an upper electrode 23 and an electron emission layer 31 in sequence. Said electron emission layer adopts N-type semiconductor material with low electron affinity, as shown in FIG. 3 . In this embodiment, the insulating layer 28 of the cathode grid has a thickness of 100 nanometers of magnesium sulfide, the thickness of the lower electrode 24 dysprosium film is 100 nanometers, the thickness of the composite film of the upper electrode 23 and the emission layer 31 is 8 nanometers, and the distance between the anode plate and the cathode grid plate is 3 mm. The upper and lower electrodes of the cathode grid are row electrodes and column electrodes respectively, forming a matrix structure of rows and columns. An insulating layer is printed on the intersection of the row and column bus electrodes to isolate them by screen printing. Zirconia single crystal is used for the support structure 211, the support structure is generally several centimeters long, 200 microns thick, and the height is equal to the distance between the plates. The support structure is placed on the row bus electrodes. The upper and lower glass plates are sealed with a 3 mm high glass frame 215 and low-melting point glass, and sealed off the exhaust platform after exhaust and baking to form a vacuum working condition. Colored fluorescent powder is used on the upper glass plate, and graphite black matrix is added between colored fluorescent powder strips to form a black matrix. During the test, the voltage of the row electrodes (lower electrodes) is -30 volts, and the maximum voltage of the column electrodes (upper electrodes) is 20 volts. The positive pressure is 5000 volts, and a stable, uniform and reliable display is obtained.

The upper electrode of this embodiment adopts a platinum-gold double-layer thin film, the metal with a high work function is on the bottom, and the metal with a low work function is on top. Electron emission is more than 5 times higher than that of single metal electrodes. Platinum upper electrode is used, and sulfide or nitride N-type semiconductor is used as the emission layer, and the emission is increased by more than 10 times. The divergence of the electron beam is very small, and in the non-self-focusing direction, the light-emitting area of the fluorescent screen is basically the same as that of the cathode. In the self-focusing direction, it is obvious that the light-emitting area is smaller than the electron-emitting area. When the positive pressure exceeds 5000 volts, the self-focusing effect is obviously weakened.

Claims (7)

1. A thin-film field emission flat-panel display, consisting of an upper glass plate coated with phosphor powder and anodic aluminum film, a lower glass plate prepared with a cathode grid for emitting electrons, a ring sealing glass and a supporting structure, and an ultra-high vacuum is maintained in the middle , it is characterized in that, said cathode grid comprises rare earth metal thin film lower electrode, alkaline earth metal sulfide insulating layer, upper electrode and electron emission layer in sequence, and also includes printing on said lower glass plate and connecting said upper and lower electrodes The row and column bus electrodes. 2. The thin film field emission flat panel display according to claim 1, wherein the thickness of said insulating layer is in the range of 50-500 nanometers. 3. The thin film field emission flat panel display according to claim 1, wherein the upper electrode is a double-layer metal thin film composite electrode, the metal with a high work function is on the bottom, and the metal with a low work function is on top. 4. The thin film field emission flat panel display according to claim 1, characterized in that said electron emission layer is made of N-type semiconductor material with low electron affinity. 5. The thin film field emission flat panel display as claimed in claim 1, characterized in that, said row-column bus electrodes are printed by screen printing, and an insulating layer is printed by screen printing on the intersections of the bus electrodes to isolate them. . 6. The thin film field emission flat panel display as claimed in claim 1, characterized in that said upper glass plate adopts colored fluorescent powder, and a graphite black matrix is added between the colored fluorescent powder stripes to form a black matrix. 7. The thin film field emission flat panel display as claimed in claim 1, wherein said supporting structure is placed on the row bus electrodes.

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