JP3870968B2 - Image display device - Google Patents

Description

  The present invention relates to an image display device that displays an image using electron-emitting devices and phosphors arranged in a matrix.

  A field emission display (hereinafter referred to as “FED”) is an intersection of electrode groups orthogonal to each other. A pixel is provided with an electron-emitting device, and the amount of emitted electrons is adjusted by adjusting the voltage applied to each electron-emitting device. Then, the emitted electrons are accelerated in vacuum, and then irradiated on the phosphor, so that the irradiated portion of the phosphor emits light. Examples of the electron-emitting device include those using a field emission type cathode, those using a MIM (Metal-Insulator-Metal) type electron source, those using a carbon nanotube cathode, and those using a diamond cathode.

The carbon nanotube cathode emits electrons by applying an electric field to a linear material having a diameter of several to several tens of nanometers made of carbon, and is described in Non-Patent Document 1, for example. Electron emission occurs even when the externally applied electric field is as low as about 0.7 V / μm. Therefore, the drive voltage can be lowered, and a bright display device can be realized. is doing.

The diamond cathode causes electron emission by applying an external electric field to diamond, and is described in Non-Patent Document 2, for example. Similar to the carbon nanotube cathode, electron emission occurs even in an external electric field as low as about 3 V / μm. Therefore, it has excellent characteristics as an electron-emitting device for an image display device.

Materials Research Society Symposium Proceedings, Vol. 509 (1998) pp.107-112

IEEE Transaction Electron Devices, Vol.46, No.4 (1999) pp.787〜791

  Carbon nanotube cathodes and diamond cathodes have an excellent feature of emitting electrons even in a low external electric field, but conversely, the electron emission cannot be completely suppressed, and there is a problem that contrast is lowered when a matrix type display is manufactured. there were. The present invention provides an image display device that solves this problem.

  As a result of detailed examination of the prior art, we have clarified that the cause of the above-described contrast reduction is as follows.

FIG. 2 shows the structure of the carbon nanotube cathode. The cathode conductor 10 is formed on the substrate 14, the cathode 13 is formed thereon, and the gate 11 is formed around the insulating layer 12 having a thickness h. The diameter of the gate hole, that is, the portion where the cathode is formed is D. There is an anode 100 at a distance L from the cathode surface. Substrate 10-anode 1
Between 00 is a vacuum. The material of the cathode 13 is a carbon nanotube. Further, the diamond cathode uses a diamond thin film as the material of the cathode 13 in FIG. 2, and the other configurations are almost the same.

  Typical values are: insulation layer thickness h = 1-100 μm, gate hole diameter D = 1-100 μm (gate hole radius R = 0.5-50 μm), cathode-anode distance L = 1-3 mm. .

Now, the potential of the cathode conductor 10 is set to 0V. When a voltage Vg (> 0 V) is applied to the gate 11, an electric field is applied to the cathode surface, so that electrons are emitted from the cathode 13. The emitted electrons are accelerated by the acceleration voltage Va applied to the anode 100 and reach the anode 100. As will be described later in detail in the embodiment, the phosphor emits light by forming the phosphor on the anode 100.

In a broad field emission display composed of an electron-emitting device and a phosphor, selection of the phosphor and the acceleration voltage Va is important. This selection can be broadly divided into two types: using a low-energy electron beam-excited phosphor, Va = 400 to 800V (“low acceleration voltage type”), CRT phosphor or similar phosphor Va = 4 ~
It is about 8KV ("high acceleration voltage type"). Recent research has revealed that the high-acceleration voltage type is preferable because the lifetime deterioration of the phosphor is mainly governed by the injected charge amount (Coulomb degradation). Typical parameters for the high acceleration voltage type are Va = about 4-8 KV and L = 1-3 mm.

However, a cathode that emits electric field with a low electric field, such as a carbon nanotube cathode or a diamond cathode, causes the above-described problem of contrast reduction when a high voltage acceleration type configuration is used. Hereinafter, the mechanism of this contrast reduction will be described.

It was determined by simulation how the electric field intensity Ek applied to the surface of the cathode 13 changes depending on the gate voltage Vg. The parameters used in the simulation are L = 1 mm, Va = 6 KV, D = 20 μm (R = 10 μm), and h = 5 μm.

FIG. 3 shows the position dependence of the cathode surface of the electric field strength Ek (V / μm) on the cathode surface. The horizontal axis represents a value r / R obtained by normalizing the position r (see FIG. 2) with the gate hole center as 0 by the gate hole radius R. When Vg = 50 V, Ek = 7 to 9 V / μm, and an electric field sufficient to cause electron emission is applied to the entire cathode surface. On the other hand, when Vg = 0, Ek is close to 0 in the peripheral part of the gate hole (r / R˜1) and electron emission is suppressed, but Ek = 2.5 in the central part of the gate hole (r / R = 0). Since V / μm is reached, electron emission occurs.

Consider the case where there is no gate electrode. In this case, the average electric field E0 between the cathode and the anode is Va / L = 6 V / μm. This exceeds the electron emission threshold of low field electron emission materials such as carbon nanotubes. That is, when a low field electron emission material is used, this electric field E0 must be “shielded” by the gate electrode so as not to reach the cathode surface. When the Spindt-type cathode is used, such a problem does not occur because the electron emission threshold is higher than E0. The result of FIG. 3 is because the shielding effect by the gate electrode is not sufficient at the center of the gate hole.

  FIG. 4 shows a conventional driving method of a field emission display in which low field electron emission cathodes are arranged in a matrix. Although not shown, an acceleration voltage Va = 6 KV is always applied to the anode 100.

A scanning signal 501 (voltage -Vs) is sequentially applied to the cathode 13 as a scanning signal. Depending on the image to be displayed, a data pulse 502 (voltage + V _{d) is} applied to the gate electrode 11 as a data signal.
) Is applied. In the pixel to which the scan pulse and the data pulse are simultaneously applied, a voltage of (V _d + Vs) is applied between the gate 11 and the cathode 13 of the corresponding electron source element, so that electrons are emitted and the phosphor emits light.

In the conventional driving method, the voltage between the gate 11 and the cathode 13 in a state not selected by the scanning signal (a state in which -Vs is not applied) is 0 V when V _d is not applied to the gate electrode 11. When a voltage of V _d is applied to the electrode 11, it becomes V _d . Therefore, as is apparent from the results of FIG. 3, electron emission occurs even when the scanning signal is not selected, which causes a decrease in contrast.

  As the number N of scanning lines increases and the number of non-selected scanning lines (number (N-1)) increases, the contribution of unnecessary electron emission from there increases, and the contrast decreases remarkably.

  The present invention solves the above problem by setting the gate application voltage to a potential lower than the cathode application voltage for the electron-emitting device on the scanning electrode in the non-selected state.

  The second aspect of the present invention solves the above problem by supplying power from the scan electrode to the cathode and driving the non-selected scan electrode with a higher impedance than the selected scan electrode. To do.

FIG. 5 shows the dependence of the cathode surface electric field Ek on the gate voltage Vg by simulation. The parameters are the same as in FIG. The thin line is the Ek value at the periphery of the gate hole (r / R to 0.8), and the thick line is the Ek value at the center of the gate hole (r / R to 0).
As can be seen from FIG. 5, when Vg = -25 V, Ek = 0 even at the center of the gate hole. That is, for the electron-emitting device on the scanning electrode in the non-selected state, the gate voltage may be set to a voltage lower than the cathode applied voltage. This is the first solution.

  The second solution is to supply power from the scan electrode to the cathode, and to set the output state of the scan drive circuit that supplies power to the scan electrode to a high impedance state in the scan electrode in the non-selected state. In this way, the electron flow from the cathode is blocked, so that electron emission can be reduced.

  According to the present invention, in an image display apparatus using a carbon nanotube cathode, a diamond cathode, or the like as a low-field electron-emitting device as an electron-emitting device, it is possible to prevent a decrease in contrast and display a good image.

  The image display apparatus according to the present invention will be described below in more detail with reference to embodiments of the invention according to some examples shown in the drawings.

Example 1
A first embodiment will be described with reference to FIGS. The display panel of the display device includes a substrate on which a thin film electron source matrix is formed and a face plate on which a phosphor or the like is formed. FIG. 6 is a cross-sectional view of the display panel. A cathode conductor 10 is formed on a substrate 14 made of an insulating material such as glass or ceramics. The cathode conductors 10 are formed by the number of scanning lines of the display device. A gate electrode 11 is formed through the insulating layer 12. The gate electrodes 11 are formed orthogonal to the cathode conductors 10 and are formed by the number of columns of the display device. A plurality of gate holes are formed in a region where the gate electrode 11 and the cathode conductor 10 intersect, and a cathode 13 is formed at the bottom of the gate hole. The cathode 13 uses carbon nanotubes.

An enlarged view of the gate electrode-cathode conductor intersection (dotted line portion in FIG. 6) is shown in FIG. FIG. 12B is a plan view, and FIG. 12A is a cross-sectional view taken along the line AB. A resistance layer may be formed between the cathode 13 and the cathode conductor 10 as necessary. This substrate is formed by, for example, Materials Research Society Symposium Proceeding
s, Vol. 509 (1998) pp. 107-112. Parameters such as the size of each gate hole provided in the intersecting region of the gate electrode 11 and the cathode conductor 10 and the thickness of the insulating layer 12 are as described above. The number of gate holes provided in the intersection region, that is, the number of gate holes per pixel is usually several tens to several thousand.

A black matrix 120 is formed on a face plate 110 made of a light-transmitting material such as glass, and a red phosphor 114A, a green phosphor 114B, and a blue phosphor 114C are formed in a pattern. Examples of phosphors include Y ₂ O ₂ S: Eu (P22-R) in red and ZnS: Cu, Al (P22 in green).
-G), ZnS: Ag (P22-B) may be used for blue.

Next, after filming with a film such as nitrocellulose, Al is deposited on the entire face plate 110 to a thickness of 50 to 300 nm to form a metal back 122. Then face plate 1
10 is heated to about 400 ° C. to thermally decompose organic substances such as a filming film and PVA. In this way, the face plate 110 is completed.

The face plate 110 and the substrate 14 manufactured in this way are sealed in an inert gas atmosphere using frit glass with a spacer 60 (not shown) interposed therebetween. The positional relationship between the phosphors 114A, 114B, 11C formed on the face plate 110 and the substrate 14 is as shown in FIG. Considering that the electron beam emitted from the electron-emitting device is somewhat spatially spread, the width of the region for forming the gate hole (denoted as “W” in the figure) is the phosphor 11.
Designed to be narrower than the width of 4.

  The distance between the face plate 110 and the substrate 14 is about 1 to 3 mm. The spacer 60 is inserted in order to prevent damage to the panel due to external force at atmospheric pressure when the inside of the panel is evacuated. Therefore, when manufacturing a display device having a display area of about 4 cm wide × 9 cm long using glass having a thickness of 3 mm for the substrate 14 and the face plate 110, the atmospheric pressure is determined by the mechanical strength of the face plate 110 and the substrate 14 itself. Therefore, it is not necessary to insert the spacer 60. The spacer 60 is made of glass or ceramics, and plate-like or columnar columns are arranged side by side.

The sealed panel is evacuated to a vacuum of about 1 × 10 ⁻⁶ to 1 × 10 ⁻⁷ Torr and sealed. In order to maintain the degree of vacuum in the panel at a high vacuum, a getter film is formed or a getter material is activated at a predetermined position (not shown) in the panel immediately before or after sealing. For example, in the case of a getter material mainly composed of Ba, a getter film can be formed by high frequency induction heating. In this way, the display panel is completed.

FIG. 7 is a connection diagram to the drive circuit of the display panel manufactured as described above. The cathode conductor 10 is arranged in the row direction and connected to the scanning drive circuit 41. The gate electrode 11 is arranged in the column direction and connected to the data driving circuit 42. Metal back 122 is the acceleration electrode drive circuit 4
Connect to 3. The dot at the intersection of the nth electrode 10Rn in the row direction and the mth electrode 15Cm in the column direction is represented by (n, m). 7 shows only 3 × 3 electron-emitting devices 301, but in an actual display panel, several hundred to several thousand cathode conductors 10 and several hundred to several thousand gate electrodes are formed. .

FIG. 1 shows a waveform of a voltage generated by each drive circuit. Although not shown in FIG. 1, a voltage of about 6 KV is constantly applied to the metal back 122.
In FIG. 1, the state where the scanning pulse 501 is applied is “a scanning line in a selected state”.
The others are “unselected scanning lines”. The voltage −Vs is applied to the scanning line in the selected state, and the reverse bias voltage Vr is applied to the scanning line in the non-selected state.
In this embodiment, Vr = 25V.

When a data pulse 502 having an amplitude V _d is applied to the gate electrode 11 while the scanning line is in a selected state, a voltage of (V _d + Vs) is applied between the gate electrode 11 and the cathode 13 at the electron emission element at the intersection. As a result, electron emission occurs, causing the phosphor to emit light.
The waveform of the data pulse 502 changes depending on the image to be displayed, and in the case of the waveform of FIG. 1, the hatched pixels in FIG. 7 emit light. In the case of a color display, one “pixel” is formed by a combination of “subpixels” corresponding to red, blue, and green. In this specification, subpixels are also referred to as pixels.
Although only waveforms up to the third of R1, R2, and R3 are shown in FIG. 1, this scanning is actually continued for the number of scanning lines. When the entire scanning line has been scanned, the process returns to R1 again, and the scanning is repeated. One screen scan is performed during one field period (1 / f). In the case of an NTSC television signal, one field period is 16.7 ms.
When displaying a video with gradation, it is only necessary to change the voltage amplitude of the data pulse 502 in accordance with the video signal or to change the pulse width of the data pulse 502.
In the drive waveform of FIG. 1, the maximum value of the voltage of the data pulse 502 is 0V. Therefore, the difference (Vg−Vk) between the gate electrode 11 potential Vg and the cathode 13 potential Vk of the electron-emitting device 301 connected to the scanning line in the non-selected state is in the range of − (V _d + Vr) to −Vr. Become. That is, the voltage between the gate electrode 11 and the cathode 13 is at most −Vr = −25V.
Therefore, as can be seen from FIG. 5, no electron emission occurs from the electron-emitting devices on the scanning lines in the non-selected state, and the contrast does not decrease.

In this embodiment, an example in which carbon nanotubes are used as the cathode 13 is shown. However, when a diamond cathode is used, a diamond film may be used as the cathode 13. The substrate manufacturing method in this case is described, for example, in IEEE Transaction Electron Devices, Vol. 46, No. 4 (1999) pp. 787 to 791.

Example 2
A second embodiment using the present invention will be described with reference to FIG. 8, FIG. 9, and FIG. The display panel of the display device includes a substrate on which a thin film electron source matrix is formed and a face plate on which a phosphor or the like is formed. FIG. 8 is a cross-sectional view of the display panel. The display panel used in this embodiment has substantially the same configuration as that used in the first embodiment, but the gate electrode 11 is arranged in the row direction and the cathode conductor 10 is arranged in the column direction.

  The structure of the gate electrode-cathode conductor intersection (dotted line portion in FIG. 8) is almost the same as that in FIG. In FIG. 12, the cathode conductor 10 and the insulating layer 12 may be read in the column direction, and the gate electrode 11 may be read in the row direction. The manufacturing method of the display panel shown in FIG. 8 is the same as that of the first embodiment.

FIG. 9 is a diagram showing a method of connecting the display panel and the drive circuit. The gate electrode 11 is arranged in the row direction and connected to the scan drive circuit 41. The cathode conductors 10 are arranged in the column direction and connected to the data driving circuit 42. The metal back 122 is connected to the acceleration electrode drive circuit 43. The dot at the intersection of the nth electrode 10Rn in the row direction and the 15th electrode 15Cm in the column direction (n,
m). Although only 3 × 3 electron-emitting devices 301 are illustrated in FIG. 9, in an actual display panel, several hundred to several thousand cathode conductors 10 and several hundred to several thousand gate electrodes are formed. .

FIG. 10 shows the waveform of the voltage generated by each drive circuit. Although not shown in FIG. 10, a voltage of about 6 KV is constantly applied to the metal back 122.
In FIG. 10, a state in which a scan pulse 501 is applied is a “selected scanning line”, and the other is a “non-selected scanning line”. The voltage + V is applied to the selected scanning line.
The reverse bias voltage −Vr is applied to the scanning line to which s is applied and is not selected. In this example, −Vr = −25V.

If the voltage of the cathode conductor 10 is 0 V when the scanning line is in the selected state, the electron emission element at the intersection is applied with a voltage of Vs between the gate electrode 11 and the cathode 13, so that electron emission occurs. The phosphor is caused to emit light. Also, if you do not want to emit light at a pixel on a scanning line in the selected state applies a corresponding V _d becomes voltage to the cathode conductor 10. Then, the voltage between the gate electrode 11 and the cathode 13 becomes (Vs−V _d ), and no emitted electrons are emitted or only a sufficiently small amount of electrons are emitted. That is, data pulse 50
The waveform of 2 changes depending on the image to be displayed, and in the case of the waveform of FIG. 10, the hatched pixels in FIG. 9 emit light. In the case of a color display, one “pixel” is formed by a combination of “subpixels” corresponding to red, blue, and green. In this specification, subpixels are also referred to as pixels.

In FIG. 10, only waveforms up to the third of R1, R2, and R3 are shown, but in practice, this scanning is continued by the number of scanning lines. When the entire scanning line has been scanned, the process returns to R1 again, and the scanning is repeated. One screen scan is performed during one field period (1 / f). In the case of an NTSC television signal, one field period is 16.7 ms.
When displaying an image with gradation, alters the combined voltage amplitude V _d of the data pulses 502 in the video signal may be either by changing the pulse width of the data pulse 502.

In the drive waveform of FIG. 10, the minimum value of the voltage of the data pulse 502 is 0V.
Therefore, the gate electrode 1 of the electron-emitting device 301 connected to the scanning line in the non-selected state
The difference (Vg−Vk) between 1 potential Vg and cathode 13 potential Vk is in the range of − (V _d + Vr) to −Vr. That is, the voltage between the gate electrode 11 and the cathode 13 is at most −Vr = −25V.
Therefore, as can be seen from FIG. 5, no electron emission occurs from the electron-emitting devices on the scanning lines in the non-selected state, and the contrast does not decrease.
In this embodiment, an example in which carbon nanotubes are used as the cathode 13 is shown. However, when a diamond cathode is used, a diamond film may be used as the cathode 13. The substrate manufacturing method in this case is described, for example, in IEEE Transaction Electron Devices, Vol. 46, No. 4 (1999) pp. 787 to 791.

Example 3
Next, a third embodiment using the present invention will be described with reference to FIGS. The display panel used in this example is the same as that in the first example, as shown in FIG. The connection method to the drive circuit is the same as that in the first embodiment, as shown in FIG.

FIG. 11 shows the waveform of the voltage generated by each drive circuit. Although not shown in FIG. 11, a voltage of about 6 KV is constantly applied to the metal back 122.
In FIG. 11, the state where the scanning pulse 501 is applied is a “selected scanning line”, and the other is a “non-selected scanning line”. The voltage + V is applied to the selected scanning line.
s is applied and the scanning line in the non-selected state is kept in the high impedance state. In FIG. 11, the dotted line indicates the high impedance state. In this embodiment, the output impedance of the drive circuit is 10 MΩ in the high impedance state.
When a data pulse 502 having an amplitude V _d is applied to the gate electrode 11 while the scanning line is in a selected state, a voltage of (V _d + Vs) is applied between the gate electrode 11 and the cathode 13 at the electron emission element at the intersection. As a result, electron emission occurs, causing the phosphor to emit light.
The waveform of the data pulse 502 changes depending on the image to be displayed. In the case of the waveform of FIG. 11, the pixels in the shaded area in FIG. 7 emit light. In the case of a color display, one “pixel” is formed by a combination of “subpixels” corresponding to red, blue, and green. In this specification, subpixels are also referred to as pixels.
In FIG. 11, only waveforms up to the third of R1, R2, and R3 are shown, but in practice, this scanning is continued for the number of scanning lines. When the entire scanning line has been scanned, the process returns to R1 again, and the scanning is repeated. One screen scan is performed during one field period (1 / f). In the case of an NTSC television signal, one field period is 16.7 ms.
When displaying a video with gradation, it is only necessary to change the voltage amplitude of the data pulse 502 in accordance with the video signal or to change the pulse width of the data pulse 502.
The scanning line in the non-selected state is in a high impedance state. Accordingly, since the electron flow (current) from the scan drive circuit 41 is limited, electron emission from the corresponding cathode 13 into the vacuum is limited, and unnecessary electron emission that causes a decrease in contrast can be reduced. .

In this embodiment, an example in which carbon nanotubes are used as the cathode 13 is shown. However, when a diamond cathode is used, a diamond film may be used as the cathode 13. The substrate manufacturing method in this case is described, for example, in IEEE Transaction Electron Devices, Vol. 46, No. 4 (1999) pp. 787 to 791.

In field emission displays that combine low-field electron-emitting devices and phosphors by eliminating or reducing unnecessary electron emission from non-selected scanning-line electron-emitting devices, good image quality can be prevented. it can.

It is a figure for demonstrating the drive method of the image display apparatus which concerns on this invention. It is a figure for demonstrating the principle of operation of a low field electron emission element. It is the figure which showed the place dependence of the cathode surface electric field. It is a figure for demonstrating the drive method of the conventional image display apparatus. It is the figure which showed the gate voltage dependence of the cathode surface electric field. It is sectional drawing for demonstrating the structure of the display panel of the 1st Example of the image display apparatus which concerns on this invention. It is the figure which showed the connection to the drive circuit of the said display apparatus. It is sectional drawing for demonstrating the structure of the display panel of the 2nd Example of the image display apparatus which concerns on this invention. It is the figure which showed the connection to the drive circuit of the said display apparatus. It is a figure which shows the drive method of the 2nd Example of the image display apparatus which concerns on this invention. It is a figure which shows the drive method of the 3rd Example of the image display apparatus which concerns on this invention. It is a figure which shows the structure of the electrode crossing area | region of the display panel of the 1st, 2nd Example of the image display apparatus which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Space part, 11 ... Gate electrode, 12 ... Insulating layer, 13 ... Cathode, 14 ... Substrate, 41 ... Scanning drive circuit, 42 ... Data drive circuit, 43 ... Acceleration electrode drive circuit, 100 ... Anode, 110 ... Face plate, 114 ... phosphor, 120 ... black matrix, 122 ... acceleration electrode (
(Metal back), 301 ... Electron-emitting device, 501 ... Scanning pulse, 502 ... Data pulse.

Claims (4)

A plurality of electron-emitting devices arranged in a matrix that emits electrons from the cathode when a positive voltage is applied to the cathode to the gate electrode; A plurality of first electrodes arranged in one direction of the matrix for supplying power to the cathode; and a plurality of second electrodes arranged in a direction orthogonal to the one direction for supplying power to the gate electrode. A display element comprising a first substrate, a second substrate having a phosphor and an anode, first driving means for sequentially applying a scanning signal to the first electrode, and data for the second electrode An image display device comprising: a second driving unit that supplies a signal;
Assuming that the voltage applied to the first electrode is V1 and the voltage applied to the second electrode is V2, the relationship of (V2−V1) ≦ −25V during the period in which the first electrode is in a non-selected state. An image display device characterized by satisfying the above.   2. The image display according to claim 1, wherein a potential of the first electrode in a non-selected state among the first electrodes is a positive potential with respect to a maximum value of a voltage applied to the second electrode. apparatus. A plurality of electron-emitting devices arranged in a matrix that emits electrons from the cathode when a positive voltage is applied to the cathode to the gate electrode; A plurality of first electrodes arranged in one direction of the matrix for supplying power to the cathode; and a plurality of second electrodes arranged in a direction orthogonal to the one direction for supplying power to the gate electrode. A display element comprising a first substrate, a second substrate having a phosphor and an anode, first driving means for sequentially applying a scanning signal to the second electrode, and data for the first electrode An image display device comprising: a second driving unit that supplies a signal;
Assuming that the voltage applied to the first electrode is V1 and the voltage applied to the second electrode is V2, the relationship of (V2−V1) ≦ −25V during the period in which the second electrode is not selected. An image display device characterized by satisfying the above.   4. The image according to claim 3, wherein the potential of the second electrode in the non-selected state among the second electrodes is a negative potential with respect to the minimum value of the voltage applied to the first electrode. 5. Display device.

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