JP2007323028A - Driving method of image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driving method of an image display device in which the decrease of luminance is ameliorated by ameliorating the deterioration of diode current and emission efficiency of a thin film type electron source. <P>SOLUTION: The thin film type electron source ELS constitutes an MIM diode from a laminated structure of an image signal wiring (d) which is a lower electrode, a tunnel insulating layer TAO which is an electron acceleration layer and a connecting electrode ELC which is an upper electrode. An inversion pulse voltage is applied between the connecting electrode ELC and the image signal wiring (d) and electrons are released from the surface of the connecting electrode ELC. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for driving an image display device using a thin film type electron source having a three-layer structure of metal-insulator-metal or metal-insulator-semiconductor and emitting electrons in a vacuum.

  For example, a field emission display (FED) is known as a display device using a cold cathode array in which cold cathodes are formed at intersections of mutually orthogonal electrode groups. In the FED, a large number of field emission cathodes are arranged in each pixel, and field emission electrons from the field emission cathodes are accelerated in a vacuum and then irradiated to a phosphor to emit light.

  On the other hand, a thin film type electron source is a three-layered thin film structure composed of an upper electrode, an insulating layer, and a lower electrode, and a voltage at which the upper electrode becomes a positive voltage is applied between the upper electrode and the lower electrode. Electrons are emitted from the surface into a vacuum. Further, as this type of thin film type electron source, an MIM (metal-insulator-metal) type electron source using a metal for the upper electrode and the lower electrode, or a MIS (metal-insulator) using a semiconductor for at least one of the electrodes. -Semiconductor) type electron source.

  As another thin film type electron source, there is a structure using a laminated body of an insulator and a semiconductor instead of an insulating layer, that is, a four-layer structure of an upper electrode-insulating layer-semiconductor layer-lower electrode as a whole. Furthermore, there is a structure using a porous semiconductor such as porous silicon instead of the insulating layer.

  In these thin film type electron sources, a high electric field is applied to all insulating layers or layers that substitute for the insulating layers to generate hot electrons and emit them from the surface of the upper electrode. Yes. Therefore, as described later, it has a property that charges are easily accumulated in an insulating layer or a layer that replaces the insulating layer.

  Compared with a field emission cathode used in an FED, a thin film type electron source has characteristics preferable for a display device such as being resistant to surface contamination and having a low operating voltage. Further, this thin film type electron source has a simple element structure, and therefore can be easily processed finely. For example, the thin film type electron source has preferable characteristics as an electron source of an electron beam application apparatus such as an electron beam exposure apparatus. However, the conventional thin film type electron source has a problem that its operating life is short.

  As a solution to such a problem of shortening the lifetime, a driving method in which the operating lifetime is improved by applying a voltage whose polarity is reversed to a thin film electron source is disclosed in Patent Document 1 below. That is, when a positive voltage is applied to the upper electrode of the thin film electron source with respect to the lower electrode (hereinafter referred to as positive polarity), electrons are emitted from the upper electrode into the vacuum. When a negative voltage (negative polarity) is applied to the upper electrode with respect to the lower electrode, it is possible to prevent trap electrons from accumulating in impurity levels and defect levels in the insulating layer, thereby reducing the length of the thin-film electron source. Life expectancy is achieved.

  However, according to such a driving method, since voltages having the same polarity are always applied to each electron source, there is a problem that charges are accumulated in the insulating layer of the thin film electron source and the device characteristics deteriorate. .

  As a solution to such a problem, a driving method in which the operating life of a thin film electron source matrix is improved by applying a negative pulse voltage to the thin film electron source is disclosed in Patent Document 2 below.

  According to such a driving method, the charge accumulated in the insulating layer is extracted by applying a negative pulse voltage. At this time, since a negative pulse having a constant voltage is always applied, if the negative pulse voltage is shifted to a relatively high direction due to the influence of the displayed image, the electron conduction at the time of the positive pulse voltage is performed. Instead, ion conduction occurs. As a result, a metal conduction path is formed in the insulating layer, causing a short circuit between the scanning signal wiring and the image signal wiring, which makes it impossible to display an image.

Japanese Patent Laid-Open No. 7-226146 JP 11-95716 A

Therefore, the present invention has been made to solve the above-described conventional problems, and its purpose is to improve the reduction in luminance by improving the deterioration of the diode current and emission efficiency of the thin-film electron source. Another object of the present invention is to provide a method for driving the image display apparatus.

  In order to achieve such an object, the image display apparatus driving method according to the present invention applies an inversion pulse voltage between a pair of metal electrodes when the acceleration electrode is turned off and all the electron sources are turned on. It is characterized by that.

  According to the present invention, since the diode current and emission efficiency of the electron source are not deteriorated, it is possible to obtain an extremely excellent effect that it is possible to realize an image display device in which the luminance is less reduced by long-time driving.

  Hereinafter, the present invention will be described in detail with reference to the drawings of the embodiments.

  FIG. 1 is a schematic plan view for explaining the configuration of an image display device for explaining an embodiment of the driving method of the image display device according to the present invention. In FIG. 1, image signal wirings d (d1, d2, d3,... Dn) are formed on the inner surface of the rear substrate SUB1 constituting the rear panel, and scanning is performed thereon via an insulating film (not shown). Signal wirings s (s1, s2, s3,... Sm) are formed to intersect. In FIG. 1, a partition wall (also referred to as a spacer) SPC formed of a ceramic material or a glass material molded body or the like is provided on the scanning signal wiring s1, and the thin film electrons are disposed downstream of the partition wall SPC in the vertical scanning direction VS. A source ELS is provided, and power is supplied from the scanning signal wiring s (s1, s2, s3,... Sm) through the connection electrode ELC which is a power supply electrode.

  Further, an anode electrode AD is provided on the inner surface of the front substrate SUB2 constituting the front panel. A phosphor layer PH (PH (R), PH (G), PH (B)) is formed on the front panel. The phosphor PH (PH (R), PH (G), PH (B)) is partitioned by a light shielding layer (black matrix) BM. The anode electrode AD is shown as a solid electrode (planar electrode), but the stripe electrode is divided for each pixel column by intersecting the scanning signal wiring s (s1, s2, s3,... Sm). It can also be. The electrons radiated from the thin film electron source ELS are accelerated and projected onto the phosphor layer PH (PH (R), PH (G), PH (B)) constituting the corresponding subpixel. As a result, the phosphor layer PH emits light of a predetermined color, and is mixed with the light emission color of the phosphor of the other subpixel to form a color pixel of a predetermined color.

  FIG. 2 is a schematic diagram showing the configuration of the back panel of the image display apparatus shown in FIG. 2, a plurality of image signal wirings d1, d2, d3,... Dn extend in the y direction and are arranged in parallel in the x direction on the back substrate SUB1 in FIG. Then, a plurality of scanning signal wirings s1, s2, s3,... Sm extend in the x direction so as to intersect with the image signal wirings d1, d2, d3,. Yes.

  Further, one row of thin film electron sources ELS is connected to each of the scanning signal wirings s1, s2, s3,. An image signal is applied from the image signal wiring to the thin film electron source ELS connected to the selected scanning signal wiring. A scanning signal to each scanning signal wiring s1, s2, s3,... Sm is supplied from a scanning signal line driving circuit (scanning driver) SDR, and an image to each image signal wiring d1, d2, d3,. The signal is supplied from an image signal line driving circuit (data driver) DDR. The scanning signal wiring is sequentially selected in the vertical scanning direction.

  A partition wall SPC that is long in the extending direction (x direction) is provided on the scanning signal wiring s2. Although the partition wall SPC may be installed on all the scanning signal wirings, it is actually installed for each of the plurality of scanning signal wirings. In addition, it is preferable from the viewpoint of ease of manufacturing that the partition wall SPC is not divided into one along the scanning signal wiring but is divided into several. In FIG. 2, the partition wall SPC is illustrated as being divided into two parts on the scanning signal wiring s2.

  FIG. 3 is a diagram for explaining the timing of the vertical scanning signal supplied to the scanning signal wiring. The vertical scanning signal is sequentially applied to the scanning signal wirings s1, s2, s3,... Sm in the scanning direction VS in FIG. A pulse RSP having a polarity opposite to that of the scanning pulse SP is added to each scanning signal wiring at least once in one frame period. Further, a pulse RDP having a polarity opposite to that of the data pulse DP may be applied to each image signal wiring at least once within one frame period. Pulses RSP and RDP having opposite polarities are applied to one or both of the scanning signal wiring and the image signal wiring.

  4 is a cross-sectional view of a main part cut in the y direction of FIG. In FIG. 4, image signal wirings d (d1, d2, d3,... Dn) are formed on the inner side surface of the back panel PNL1, and the scanning signal wirings s ( s1, s2, s3,... sm) are formed to intersect. In FIG. 4, a partition wall SPC is provided on the scanning signal line s2, and a thin film electron source ELS1 is provided upstream of the partition wall SPC in the vertical scanning direction VS. A thin film electron source ELS2 is provided on the downstream side in the vertical scanning direction VS, and the thin film electron source ELS includes an upper electrode ELC, an insulating layer TAO, and a lower electrode.

Further, an anode electrode AD is provided on the inner side surface of the front panel PNL2, and the corresponding phosphor layer is accelerated by accelerating electrons e ⁻ emitted from the electron sources ELS (ELS1, ELS2, ELS3,...). Projection is made to PH (PH1, PH2, PH3...). As a result, the phosphor layer PH (PH1, PH2, PH3...) Emits light with a predetermined color light, and is mixed with the light emission color of the phosphor of another sub-pixel to constitute a color pixel of a predetermined color. In the present embodiment, the connection electrode also serves as the upper electrode, and the image signal wiring d also serves as the lower electrode.

  FIG. 5 is an enlarged cross-sectional view of a main part for explaining the configuration of the thin film electron source ELS (ELS1, ELS2, ELS3) shown in FIG. As shown in FIG. 5, the thin film electron source ELS is a MIM diode having a laminated structure of an image signal wiring d as a lower electrode, a tunnel insulating layer TAO as an electron acceleration layer, and a connection electrode ELC as an upper electrode. Electrons are emitted from the surface of the connection electrode ELC by applying a drive voltage between the image signal wiring d and the connection electrode ELC.

  The thin film electron source ELS is formed as follows. First, aluminum (Al) is formed on the insulating rear substrate SUB1 as an image signal wiring d to a thickness of about 15 nm by, for example, RF magnetron sputtering. Next, the surface of the Al film is anodized to form a tunnel insulating layer ATO. Next, gold is deposited on the tunnel insulating layer ATO to a thickness of about 5 nm by, for example, RF magnetron sputtering or vapor deposition to form a connection electrode ELC.

  The MIM diode thus formed exhibits I (current) -V (voltage) characteristics as shown in FIG. In order to obtain the emission current, as shown in FIG. 7A, a positive pulse Vp having a constant voltage equal to or lower than the threshold voltage Vth from the power source P is applied to the connection electrode ELC, and the image signal wiring d is illustrated in FIG. A negative pulse Vn having a voltage corresponding to the desired luminance is applied.

As a result, a tunnel current Id flows through the tunnel insulating film TAO, and a part of the tunnel current Id reaches the anode electrode AD shown in FIG. 4 as an emission current Ie. At this time, the emission efficiency is defined as η = Ie / Id. At the same time, as shown in FIG. 8, tunnel electrons e ⁻ move by the electric field, and the MIM capacitor using the tunnel insulating film TAO as a dielectric is charged.

  As shown in FIG. 9, the electric charge E stored in the tunnel insulating film TAO generates an electric field E2 that acts in a direction to cancel the internal electric field E1 due to the applied voltage. As a result, the threshold voltage Vth fluctuates and the IV characteristic does not change, and the diode current and emission efficiency deteriorate.

  In order to prevent this, it is effective to apply a reverse bias voltage so as to discharge the charged electric charge to the driven thin film electron source. However, when a negative pulse Vn is applied to the image signal wiring d, a reverse bias voltage is applied to the non-driving cell. That is, a voltage is applied to an uncharged thin film electron source.

  The charge moving in the tunnel insulating film TAO when a positive bias voltage is applied is an electron, but when a reverse bias voltage is applied, ions move. As a result, a metal filament (conduction path) extending from the connection electrode ELC toward the image signal wiring d is formed, and a short circuit occurs between the connection electrode ELC and the image signal wiring d.

  The short circuit caused by the metal filament caused by the application of the reverse bias voltage is burned out by the inflow current when a high positive bias voltage is applied, so that the original insulation state can be recovered.

  Therefore, as a countermeasure against a short circuit due to a reverse bias voltage, the entire cell may be periodically driven. That is, it is effective to light the panel in white. However, since the entire lighting is not an image that should be displayed, it is sufficient to drive only the cells in a state where a high voltage is not applied to the anode electrode AD.

That is,
(1) A frame for driving the entire surface of the cell with a high voltage of 0 V every predetermined time is formed.
(2) When the power is turned on, make a frame that turns on the entire cell by setting the high voltage to 0V before applying the high voltage.
(3) When the power is turned off, create a frame that turns on the entire cell by reducing the high voltage to 0V.
It is sufficient to provide a positive bias voltage supply means for driving such as to prevent a short circuit due to a reverse bias voltage.

  According to such a driving method, by applying a positive bias voltage, it is possible to prevent a short-circuit path from growing due to ion conduction. Even when the short circuit path is established, the short circuit portion can be burned out and repaired by applying a positive bias current.

  FIG. 10 is a front view of a surface disposed inside the front panel, and FIG. 11 is a cross-sectional view taken along the line II of FIG. An anode electrode AD is formed on the front substrate SUB2. The anode electrode AD is formed in a strip shape in parallel with the image signal wiring on the rear panel. The anode voltage applied to the anode electrode may be controlled for each anode electrode formed in a divided manner. By controlling the voltage for each anode electrode, it is possible to cut the short-circuited portion by the metal filament for each electron source element facing each anode electrode.

  According to such a configuration, it is not necessary to drive all the electron sources simultaneously. That is, it is possible to cut the short-circuit portion by driving only the necessary electron source without causing the pixels to emit light. Further, abnormal discharge can be controlled by controlling the anode voltage for each divided anode electrode. The anode electrodes may be electrically connected to each other. In this case, although the divided anode electrodes cannot be individually controlled, the capacitance can be reduced because the anode electrodes are divided.

  FIG. 12 is a front view of another example of the surface of the front panel on which the anode electrode is formed. The anode electrode AD is formed in a strip shape parallel to the scanning signal wiring on the rear panel. The anode voltage applied to the anode electrode AD may be controlled for each anode electrode formed in a divided manner. By applying a voltage to each anode electrode, the short-circuited portion of the metal filament can be cut for each electron source element facing each anode electrode.

  According to such a configuration, it is not necessary to drive all the electron sources simultaneously. That is, it is possible to cut the short-circuit portion by driving only the necessary electron source without causing the pixels to emit light. Since the anode electrode AD extends along the scanning signal wiring, it is easy to control the anode electrode AD. Since the vertical scanning period is longer than the horizontal scanning period, it is easy to switch the supply voltage. Further, since the anode electrode AD is divided, the capacitance can be reduced. Further, abnormal discharge can be controlled by controlling the anode voltage for each divided anode electrode.

  In the drive for cutting the metal filament, the same voltage as when electrons are emitted is applied to the first electrode and the second electrode arranged with the insulating layer interposed therebetween. More preferably, the electron-emitting device is driven in the same manner as when the phosphor screen emits peak luminance. However, since the anode voltage is not supplied to the anode electrode even when the electron-emitting device is driven, the phosphor does not emit light.

  In the driving for cutting the metal filament, the voltage applied to the anode electrode does not necessarily have to be 0V. The off voltage applied to the anode electrode in the present embodiment is not a problem as long as it is a voltage that does not cause electrons to collide with the phosphor to emit light.

  In the first embodiment, the MIM type structure has been described as the thin film type electron source. However, the present invention is not limited to this, and the present invention is also applicable to the image display apparatus using the various thin film type electron sources described above. The same applies.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic plan view illustrating a configuration of an image display device for explaining a first embodiment of a driving method of the image display device according to the present invention. It is a schematic diagram which shows the structure of the back panel of FIG. It is a figure explaining the timing of the vertical scanning signal supplied to a scanning signal wiring. It is principal part sectional drawing which shows the structure of a thin film type electron source cut | disconnected in the y direction of FIG. It is a principal part expanded sectional view which shows typically the detailed structure of the thin film type electron source of FIG. It is a figure which shows the current-voltage characteristic of a MIM diode. FIG. 7A is a diagram showing a pulse voltage waveform applied to the thin film type electron source of FIG. 4, FIG. 7A is a positive pulse waveform on the scanning signal wiring side, and FIG. 7B is a negative pulse waveform on the signal wiring side. . It is a schematic cross section which shows the state of the electric charge accumulate | stored in the tunnel insulating film of a thin film type electron source. It is a schematic cross section which shows the state of the electric charge accumulate | stored in the tunnel insulating film of a thin film type electron source. It is a front view of the surface arrange | positioned inside a front panel. It is sectional drawing along the II line | wire of FIG. It is a front view of the other example of the surface in which the anode electrode of the front panel was formed.

Explanation of symbols

SUB1 ... rear substrate, SUB2 ... front substrate, s (s1, s2, ... sm, s11, s12, ... s1m, s21, s22, ... s2m) ... scanning signal wiring, d (d1, d2, d3,... dn) ... image signal wiring, ELS ... electron source, ELC ... connection electrode, TAO ... tunnel insulating film, AD ... anode electrode, BM ... Black matrix, PH (PH (R), PH (G), PH (B)) ... phosphor layer, SDR ... scanning signal line driving circuit, DDR ... image signal line driving circuit, AR: image display area, SPC: partition wall.

Claims (5)

A back panel in which an electron source having an electrode structure in which an insulating layer is sandwiched between a pair of opposing metal electrodes is arranged in a matrix;
A front panel on which phosphors and acceleration electrodes are formed facing the back substrate;
In a method for driving an image display device comprising:
A driving method of an image display device, characterized in that a voltage that turns off the acceleration electrode and turns on the electron source is applied.   The electron source has a lower electrode and an upper electrode, and an electron acceleration layer sandwiched between the lower electrode and the upper electrode, and a voltage is applied between the lower electrode and the upper electrode to 2. The method for driving an image display device according to claim 1, wherein the driving method is a thin-film electron source that emits electrons from an electrode.   The method of driving an image display device according to claim 2, wherein the lower electrode is an image signal wiring.   The image display device driving method according to claim 2, wherein the upper wiring is a connection electrode connected to the scanning signal wiring. In the driving method of the image display device configured by the display panel that holds the internal space in which the back panel and the front panel face each other at a predetermined interval in a predetermined vacuum state,
The back panel includes a plurality of scanning signal lines that extend in one direction and are arranged in parallel in another direction orthogonal to the one direction and sequentially apply a scanning signal in the other direction, and extend in the other direction and A back substrate on which a plurality of image signal wirings arranged in parallel in the one direction so as to intersect a scanning signal wiring, and a thin film electron source connected to the scanning signal wiring and the image signal wiring are formed;
The front panel has a front substrate on which a phosphor layer and an acceleration electrode for accelerating electrons emitted from the electron source so as to be directed to the phosphor layer,
A driving method of an image display device, wherein the electron source is driven in a state where the acceleration electrode is not driven.

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