Patent Application
20090072697
1. Field of the Invention
The present invention relates to an electron-emitting device adapted to a flat panel display and an image display apparatus using the electron-emitting device.
2. Description of the Related Art
A surface conduction electron-emitting device utilizes a phenomenon in which an electron emission is produced by flowing an electric current to a conductive film, which is formed on a substrate and has a small area, in parallel to the surface of the film. An electron-emitting portion is generally formed on the conductive film with an energizing process (forming) beforehand. Specifically, DC voltage or boosted voltage, which is boosted very slowly, such as in 1 V/min., is applied to the both ends of the conductive film, so as to locally destroy, deform or transubstantiate the conductive film, whereby an electron-emitting portion that is in electrically high-resistive state is formed. At the electron-emitting portion, a gap is formed at a part of the conductive film, so that electrons are emitted from the vicinity of the gap.
Japanese Patent Application Laid-Open (JP-A) No. H08(1996)-102251 discloses a technique in which a height regulating member having a sharp projecting shape is formed on a substrate, and a conductive film is formed thereon, in order to reduce electric power upon forming a gap.
JP-A No. 2006-66335 discloses an electron-emitting device having an electron-emitting portion on a convex surface.
According to the technique disclosed in JP-A No. H08(1996)-102251, an electric field can locally be increased upon the forming due to the sharp structure. However, the electron emission efficiency might greatly vary due to a slight positional deviation of the formed gap, with the result that control means for the position of the gap should be needed. In this technique, the effect of enhancing the electron emission efficiency of the electron-emitting device is small.
An object of the present invention is to enhance an electron emission efficiency without increasing a variation in the electron emission efficiency in an electron-emitting device that emits electrons from the vicinity of a gap formed on a conductive film.
The first aspect of the present invention is an electron-emitting device including a substantially linear convex portion forming a projection on a substrate; a first electrode and a second electrode formed on the substrate across the convex portion; a conductive film that connects the first electrode and the second electrode; and an electron-emitting portion that is composed of a gap formed on the conductive film and is present on the convex portion, wherein, supposing that a direction in which the convex portion extends is defined as a Y direction, a direction orthogonal to the Y direction on the substrate is defined as an X direction, and a normal direction of the substrate is defined as a Z direction, a top portion of the convex portion in X-Z section has a curved portion having a convex shape toward the projecting direction of the convex portion, and supposing that a voltage applied between the first electrode and the second electrode upon a electron emission is defined as Vf, a distance between an anode electrode, which is opposite to the substrate, and the substrate is defined as L, a voltage applied between the substrate and the anode electrode is defined as Va, a height from a surface of the substrate to the top of the convex portion is defined as H, a width of the convex portion at a bottom surface in the X direction is defined as W, and a distance between a center of the gap in the X direction and the top of the convex portion is defined as Xg,
H≧(Vf×L)/(π×Va)
|Xg|≦0.35 W
are established.
The present invention includes, as a preferable embodiment, that a radius of curvature of the curved portion at the top is not less than 0.5 W.
The second aspect of the present invention is an electron-emitting device including a substantially linear convex portion forming a projection on a substrate; a first electrode and a second electrode formed on the substrate across the convex portion; a conductive film that connects the first electrode and the second electrode; and an electron-emitting portion that is composed of a gap formed on the conductive film and is present on the convex portion, wherein, supposing that a direction in which the convex portion extends is defined as a Y direction, a direction orthogonal to the Y direction on the substrate is defined as an X direction, and a normal direction of the substrate is defined as a Z direction, a top portion of the convex portion in X-Z section has a plane portion whose width in the X direction is Wt, and a curved portion that is in contact with the plane portion and projects outwardly, and supposing that a voltage applied between the first electrode and the second electrode upon the electron emission is defined as Vf, a distance between an anode electrode, which is opposite to the substrate, and the substrate is defined as L, a voltage applied between the substrate and the anode electrode is defined as Va, a height from a surface of the substrate to the top of the convex portion is defined as H, a width of the convex portion at a bottom surface in the X direction is defined as W, and a distance between a center of the gap in the X direction and the top of the convex portion is defined as Xg,
H≧(Vf×L)/(π×Va)
|Xg|≦0.35 W+0.14 Wt
are established.
The present invention is also configured as an image display apparatus including a first substrate having plural electron-emitting devices according to the first aspect or the second aspect of the present invention; and a second substrate having an image forming member that emits light by the electrons emitted from an anode electrode, which is opposite to the substrate, and the electron-emitting devices.
In the present invention, the convex portion having a specific shape is formed on the substrate, and the gap is formed on the conductive film on the convex portion, whereby an electric field in which electrons are accelerated toward the anode electrode is multiplied, resulting in that the electron emission efficiency is enhanced. Since the multiplication of the electric field at the top of the convex portion is uniform, the variation in the electron emission efficiency is small. Accordingly, the present invention provides an image display apparatus that can display a high-quality image by plural electron-emitting devices having uniform electron emission efficiency.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
An electron-emitting device according to the present invention is formed on a substrate. An anode electrode is arranged with a distance L from the surface of the substrate. The electron-emitting device according to the present invention includes a first electrode and a second electrode arranged on the substrate with a space and a conductive film that connects the first and second electrodes, wherein a gap is formed on the conductive film so as to emit electrons. For example, a surface conduction electron-emitting device is a preferable embodiment to which the present invention is applied.
The feature of the present invention is that a convex portion having a specific sectional shape is formed on the surface of the substrate between the pair of electrodes. In the first invention, the top of the convex portion is a curved portion projecting outwardly, while in the second invention, the top of the convex portion is composed of a plane portion and a curved portion that is continuous with the plane portion and projects outwardly.
A preferable embodiment of the present invention will be specifically explained below, taking a surface conduction electron-emitting device as an example.
As shown in
In the present invention, the direction parallel to the surface of the substrate 1 and parallel to the opposite end sides of the electrodes 3 and 4 is defined as a Y direction, the direction parallel to the surface of the substrate 1 and orthogonal to the Y direction is defined as an X direction, and the normal direction of the surface of the substrate 1 is defined as a Z direction.
In the present invention, the anode electrode 8 is arranged with a distance L from the surface of the substrate so as to be opposite to the electron-emitting device. The device emits electrons from the vicinity of the gap 6 when a voltage Vf is applied between the first electrode 3 and the second electrode, and a voltage Va is applied between the conductive film 5 and the anode electrode.
The feature of the present invention is that a convex portion 2 is formed on the surface of the substrate 1, and the gap 6 is formed on the conductive film 5 on the convex portion 2. As shown in
The convex portion 2 in the present invention is a substantially linear portion extending in the Y direction. However, when the aforesaid H, W, Xg and Y are not uniform at each point in the Y direction, the convex portion is specified by the average values of them.
The gap 6 formed on the conductive firm 5 is formed along the Y direction as serpentining within the width Ws.
Each component of the electron-emitting device according to the present invention will be described below.
A glass (quartz glass, glass in which an impurity content such as Na is reduced, soda-lime glass) can be used as the substrate 1. Further, a substrate on which an SiO2 film is laminated on a glass substrate by such as a sputtering method, a ceramic substrate such as alumina, Si substrate, or the like can be used as the substrate 1. If necessary, the substrate is fully cleaned, and then, a hydrophobic process is performed onto the surface of the substrate by using a silane coupling agent.
It is necessary that the surface of the convex portion 2 formed on the substrate 1 is made of at least an insulating material so as to prevent the conductive film 5 from short-circuiting at the gap 6. Accordingly, the convex portion 2 may be a part of the substrate 1, or may be formed by patterning an insulating material that is different from the substrate 1. An etching method, a blasting method, laser processing method, photolithography method or the like are preferably used for processing the substrate 1 and forming the convex portion 2. The convex portion 2 can be formed in such a manner that an insulating material is laminated onto the substrate 1, and patterned with a printing method or photolithography method.
A general conductive material can be used for the material of the electrodes 3 and 4. For example, the material of the electrodes 3 and 4 can appropriately be selected from metals such as Ni, Cr, Au, Mo, W, Pt, Ti, Al, Cu, Pd, or the like. The thickness of the electrodes 3 and 4 may be set within the range of 1 nm or more and 1 μm or less. The electrodes 3 and 4 are formed in such a manner that a constituent material of the electrodes 3 and 4 is formed on the substrate 1 with a vacuum deposition method, and the resultant is patterned by a photolithography technique.
Examples of the conductive film 5 include a metal such as Pd, Pt, Ru, Ag, Au, Ti, In, Cu, Cr, Fe, Zn, Sn, Ta, W, Pb, etc., or oxide conductor such as PdO, SnO2, In2O3, PbO, Sb2O3, etc. Further, a nitride such as TiN, ZrN, HfN, etc., can be used.
It is preferable that a fine-grain film made of fine grains is used for the conductive film 5 in order to obtain satisfactory electron emission efficiency. The thickness thereof can be set within the range of 10 Å (1 nm) or more and 100 nm or less. The width of the conductive film 5 can be set within the range of 1 μm or more and 100 μm or less.
The conductive film 5 can be formed in the manner that an organic metal solvent is applied onto the substrate 1 on which the electrodes 3 and 4 are formed so as to form an organic metal film. A solution of organic compound having the material of the conductive film 5 as a main component can be used for the organic metal solvent. This organic metal film is heated and sintered, and patterned with a liftoff, etching, laser processing, or the like, so as to form the conductive film 5. Usable methods for forming the conductive film 5 include a vacuum deposition method, sputtering method, chemical vapor deposition method, dispersion and application method, dipping method, spinner method, or the like.
A so-called “forming process” is performed for forming the gap 6 on each conductive film 5. The forming process is performed by producing a potential difference between the pair of the electrodes 3 and 4 so as to energize (flow electric current to) the conductive film 5.
Specifically, when a voltage is applied between the electrodes 3 and 4, a joule heat is generated in the conductive film 5, and the gap 6 is formed on the conductive film 5. It is preferable that the voltage upon the forming process has a pulse waveform. The forming process can be ended at the time when a resistance, which is obtained by measuring the flowing current according to the application of voltage of about 0.1 [V], becomes not less than 1 [MΩ]. As shown in
It is preferable that a so-called “activation treatment” is performed to the electron-emitting device to which the forming process is completed. The activation treatment is performed by applying a voltage in the form of a pulse between the electrodes 3 and 4 like the forming process, under the atmosphere containing gas of an organic material. By this activation treatment, a later-described device current If and emission current Ie remarkably increase. A carbon film that covers the conductive film 5 in the gap 6 and in the vicinity of the gap 6 is formed by the activation treatment. A gap that is narrower than the gap 6 is formed into the gap 6 of the carbon film, so that the electrons are emitted from this narrow gap.
Finally, it is preferable that a stabilization process is performed to the electron-emitting device obtained through the aforesaid process. The stabilization process is to exhaust and reduce unnecessary materials such as an organic material in the vacuum device.
The gap 6 is a high-resistance portion formed at a part of the conductive film 5. The gap 6 depends upon the thickness, characteristic, and material of the conductive film 5 and a later-described technique such as an energizing forming process. Conductive fine grains of which diameter is several Å (several hundred pm) to several ten nm might be present in the gap 6. The conductive fine grains contain some of or all elements constituting the conductive film 5. The gap 6 and the conductive film 5 in the vicinity of the gap 6 can contain carbon or carbon compound.
Next, an effect of enhancing the electron emission efficiency and an effect of preventing the variation in the electron emission efficiency according to the present invention will be explained. Supposing that the current flowing through the conductive film is defined as the device current If, and the current flowing from the conductive film 5 to the anode electrode 8 is defined as the emission current Ie, the electron emission efficiency is represented by Ie/If.
Firstly, a potential distribution that affects the trajectory of the electrons emitted from the electron-emitting device in a general surface conduction electron-emitting device will be explained with reference to
It is supposed that the voltage Vf is applied to the conductive film 5, the left end of the conductive film 5 in the figure is 0 [V], and the right end is Vf [V].
ds=(Vf/π)×(L/Va) (1)
(The distance from the center of the gap 6 to this point is referred to as ds hereinafter).
The position where the electric field Evf and the electric field Eva are equal to each other is generally referred to as a stagnation point. The electrons emitted beyond the stagnation point almost reach the anode electrode 8 without dropping onto the conductive film 5, and contribute to the emission current Ie. On the other hand, the electrons that cannot reach the stagnation point drop onto the conductive film 5, and scatter there at least once, whereby some of the scattered electrons reach the anode electrode 8 and contribute to the emission current Ie. It is mentioned that the electrons that can again fly into the vacuum after the scattering are 20 to 30% among the collided electrons. Therefore, if the energies of the electrons are the same, the electrons having shorter ds can reach the stagnation point with reduced number of times of the scattering, whereby the electron emission efficiency can be enhanced. It is understood from the equation (1) that the electron emission efficiency is enhanced by reducing the distance L or increasing the voltage Va, since this reduces ds.
On the other hand, when the gap 6, which serves as the electron-emitting portion, is actually arranged at the top of the convex portion 2, the height H of the convex portion 2 and the position Xg of the gap 6 affect the electron emission efficiency. Next, the height H of the convex portion 2 and the position Xg of the gap 6 will be explained.
On the other hand, in the case of |Xg/W|>0.35, the inequality of ds>ds0 is established, which means that the electron emission efficiency is reduced compared to the case in which the convex portion 2 is not formed. Further, it is understood that the electron emission efficiency greatly changes due to the value of Xg/W. Thus, it is understood that |Xg|≦0.35 W is preferable for the position Xg of the gap 6 in order to stably enhance the electron emission efficiency. This relationship is applicable to
In the case of the surface conduction electron-emitting device taken as an example, it has been found that the gap 6, which serves as the electron-emitting portion, might serpentine depending upon the fabrication condition or the condition of the conductive film as shown by the enlarged view of
The similar operation and effect can be obtained even if a part of the top is plane over the width Wt as shown in
As for the radius of curvature R of the curved portion of the top, the variation in the electron emission efficiency due to the positional deviation of the gap becomes small as the R increases. Specifically, it has been found that the effect of the present invention can more stably be obtained in the case of R≧0.5 W. In the present embodiment, the explanation about the convex portion 2 is made only with the sectional view. However, since the sectional shape is continuous in the Y direction, the effect of the present invention can be obtained over the whole length of the convex portion 2. Particularly, when the sectional shape varies along the Y direction as shown in
In the present invention, an image display apparatus can be configured such that aforesaid plural electron-emitting devices are arranged on the same substrate, and an anode electrode is arranged at the position opposite to the substrate. More specifically, plural electron-emitting devices according to the present invention are arranged on the same substrate, and wirings for applying a voltage to each electrode are mounted to form a rear plate (first substrate). On the other hand, an image forming member such as a phosphor film is formed on a transparent insulating substrate such as a glass substrate, and an anode electrode serving as a metal back is formed thereon by vapor deposition of such as Al. The resultant is defined as a face plate (second substrate). The rear plate and the face plate are arranged so as to be opposite to each other in such a manner that the anode electrode and the electron-emitting devices are opposite to each other with a predetermined distance. The surrounding is sealed, whereby an image display apparatus can be manufactured. Electrons are emitted from each electron-emitting device by applying a drive voltage through the wirings. The emitted electrons are accelerated by the voltage Va between the anode electrode and the conductive film, and collide with the image forming member (phosphor film). Thus, the image forming member emits light, whereby a desired image is formed.
The present invention will be explained in more detail with reference to the specific examples.
In this Example, a glass was used as the substrate 1, and an SiO2 film with a thickness of 2 μm was applied thereon. Then, resist was applied and patterned. Subsequently, the region other than the region where the convex portion 5 was formed was removed by etching so as to form the convex portion 2. The convex portion 2 had the semicircular sectional shape in the X direction as shown in
A Pt film with a thickness of 20 nm was formed on the glass substrate by a sputtering method so as to form the electrodes 3 and 4. The space between the electrodes 3 and 4 was set to 10 μm.
After the substrate was well cleaned, a palladium oxide (PdO) film with a thickness of 10 nm at the maximum was obtained. Then, the palladium oxide was reduced under the vacuum atmosphere containing a hydrogen gas to form a conductive film 5 made of palladium. Next, the conductive film 5 was energized and heated, whereby a first gap was formed at a part of the conductive film 5. The gap was formed at substantially the center of the conductive film 5, and somewhat serpentined, but the serpentine width Ws was not more than 2 μm. The center of the serpentine was substantially the center of the width of the convex portion 2 (Xg=0).
Subsequently, tolunitrile was introduced into the vacuum atmosphere, and the energizing process was performed to the conductive film 5 under the vacuum atmosphere of 1.3×10−4 Pa. Thus, a carbon or carbon compound was deposited in the vicinity of the first gap to form a second gap (gap 6).
The substrate 1 (hereinafter referred to as rear plate) thus obtained and the face plate having the anode electrode 8 formed on the glass substrate were arranged in the vacuum such that the distance L between the substrate 1 and the anode electrode 8 became 1.6 mm.
As shown in
Next, a palladium oxide film was formed in the same mariner as in the Example 1. Then, in this Example, the palladium oxide film was energized and heated under the vacuum atmosphere containing a slight amount of hydrogen gas in order to reduce electric power upon the energization for forming the first gap. Thus, the palladium oxide was reduced to form the conductive film 5 made of palladium, and simultaneously, the gap 6 was formed at a part of the conductive film 5. The formed gap 6 had the width larger than the gap 6 in the Example 1, and its serpentine width Wm was about 3.5 μm. The center of the serpentine was substantially at the center of the width of the convex portion 2 (Xg=0).
The rear plate was formed in the same manner as in the Example 1 except that the convex portion 2 had a sectional shape in the X direction having a semicircular shape laminated on a rectangle as shown in
When the gap 6 serving as the electron-emitting portion was formed, the conductive film 5 made of the reduced palladium was heated and energized to form the gap 6 like the Example 1. The formed gap 6 serpentined with the serpentine width Ws of about 2 μm that was approximately the same as that in the Example 1. The center of the serpentine was substantially at the center of the width of the convex portion 2 (Xg=0).
The rear plate was formed in the same manner as in the Example 1 except that the convex portion 2 was formed whose height H and the width W varied at a predetermined cycle in the Y direction as shown in
When the gap 6 serving as the electron-emitting portion was formed, the conductive film 5 made of the reduced palladium was heated and energized to form the gap 6 like the Example 1. The formed gap 6 serpentined with the serpentine width Ws of about 2 μm that was approximately the same as that in the Example 1. The center of the serpentine was substantially at the center of the width of the convex portion 2 (Xg=0).
The rear plate was formed in the same manner as in the Example 1 except that the substrate 1 did not have the convex portion 2, and the surface thereof was flat. The gap 6, serving as the electron-emitting device, serpentined with the serpentine width Ws of about 2 μm that was approximately the same as that in the Example 1. The center of the serpentine was substantially at the center of the conductive film 5.
The rear plate was formed in the same manner as in the Example 1 except that section of the convex portion 2 in the X direction was in the shape of substantially an isosceles triangle. The height H of the convex portion 2 was 2 μm, the width W thereof was 4 μm, and the radius of curvature at the top was 0.2 μm. The convex portion 2 had a shape of a triangle pole in which the sectional shape was continuous in the Y direction. The gap 6 serving as the electron-emitting portion serpentined with the serpentine width Ws of about 1 μm about the top. The central position of the serpentine was substantially at the center of the width of the convex portion 2 (Xg=0).
The rear plate was formed in the same manner as in the Example 1 except that the convex portion 2 was formed into a semi-cylindrical shape such that the section thereof in the X direction was semicircular having the height H of 0.2 μm, the width W of 0.4 μm and the radius of curvature at the top of 0.2 μm, and this sectional shape extended in the Y direction. The formed gap 6 serving as the electron-emitting portion serpentined with the serpentine width Ws of about 2 μm that was approximately the same as that in the Example 1. The center of the serpentine was substantially at the center of the width of the convex portion 2 (Xg=0).
Voltage was applied to the devices obtained by the Examples 1 to 4 and the Comparative Examples 1 to 3 in such a manner that the electrode 3 had 0 V, the electrode 4 had 18 V, and the anode electrode 8 had 10 kV. As a result, it was confirmed that electric current flew through the anode electrode 8, and the electrons were emitted.
In order to confirm the effect of the present invention, the electron emission efficiency, which was obtained as the ratio of the device current If flowing between the electrodes 3 and 4 and the emission current Ie detected at the anode electrode 8, was measured for plural substrates. Table 1 shows the result.
In the case of Example 1, the electric field multiplication effect by the convex portion 2 effectively acts, so that the electron emission efficiency increases compared to the Comparative Example 1. Further, although the gap 6 serpentines, it is within the distance of 0.35 W from the top of the convex portion 2, whereby the variation in the electron emission efficiency is the same as that in the Comparative Example 1. In the case of Example 2, the electron emission efficiency and the variation in the electron emission efficiency are the same level in the Example 1, although the serpentine width Ws of the gap 6 in the Example 2 is larger than that in the Example 1.
In the case of Examples 3 and 4, the electron emission efficiency increases more than the Example 1, since the electric field multiplication efficiency of the convex portion 2 is greater than that in the Example 1. Further, although the gap 6 serpentines, it is within the distance of 0.35 W from the top of the convex portion 2, whereby the variation in the electron emission efficiency is the same as that in the Comparative Example.
In the Comparative Example 2, the electron emission efficiency increases from 0.7-fold to two-fold in the Comparative Example 1, which means the electron emission efficiency greatly varies. This is considered that, since the radius of curvature of the top of the convex portion 2 is small such as 0.1 W, which means that the convex portion 2 does not substantially have the curved portion, the electron emission efficiency greatly varies due to the serpentine of the gap 6, compared to the case in which the radius of curvature R at the top of the convex portion 2 is not less than 0.5 W like the Examples 1 to 4.
In the Comparative Example 3, the electron emission efficiency is the same level as that in the Comparative Example 1 although the convex portion 2 is formed. This is considered that a sufficient electric field multiplication effect cannot be obtained since the height H of the convex portion 2 is about ds0/10.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2007-242109, filed on Sep. 19, 2007, which is hereby incorporated by reference herein its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-242109 | Sep 2007 | JP | national |
