Patent Application
20120091881
1. Field of the Invention
The present invention relates to a field emission type electron emitting device for use in an image display apparatus or the like.
2. Description of the Related Art
A vertical type electron emitting device discusses in Japanese Patent Application Laid-Open No. 2010-146915, and a Spindt type electron emitting device are known as a field emission type electron emitting device for use in an image display apparatus or the like. It is known that the surface configuration of each of a cathode and a gate of the field emission type electron emitting device contribute largely to electron emitting characteristics thereof. Particularly, the surface configuration of the cathode relates directly to electron emitting. Accordingly, numerous improvements have been made thereto. On the other hand, improvements have been made to the gate to solve problems in a manufacturing process, rather than to improve the electron emitting characteristics to which the gate relates directly.
Japanese Patent Application Laid-Open No. 5-21002 discusses a method of forming oxidized film on each of an emitter tip (i.e., a cathode) made of metallic molybdenum and a gate layer made of metallic molybdenum and adjusting, in a process of removing the oxidized film, an edge shape of the emitter tip and a distance between the emitter tip and the gate layer. Japanese Patent Application Laid-Open No. 9-306339 discusses a method of forming MoO3 film on a surface of a molybdenum cathode and cleaning the surface of the cathode by heating and removing the MoO3 film when the cathode is mounted on the device.
Field emission type electron emitting devices which excel in electron emitting characteristics are demanded.
According to an aspect of the present invention, an electron emitting device includes a cathode, and a gate onto which electrons field-emitted from the cathode are irradiated. The gate includes at least a layer containing molybdenum and oxygen provided at a portion onto which the electrons field-emitted from the cathode are irradiated. The layer has peaks in a range of 397 electron-volts (eV) to 401 eV, a range of 414 eV to 418 eV, a range of 534 eV to 538 eV, and a range of 540 eV to 547 eV, respectively, in a spectrum measured by electron energy loss spectroscopy using a transmission electron microscope.
Further features and aspects of the present invention will become apparent from the following detailed description of exemplary embodiments with reference to the attached drawings.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments, features, and aspects of the invention and, together with the description, serve to explain the principles of the invention.
Various exemplary embodiments, features, and aspects of the invention will be described in detail below with reference to the drawings.
An exemplary embodiment is described in detail below with reference to the drawings. The scope of the present invention is not limited only to dimensions, materials, shapes and relative arrangements of components described in the exemplary embodiment, unless otherwise specifically described.
First, an example of a configuration of an electron emitting device according to the present exemplary invention is described with reference to
The protruding portion 16 is provided on a corner portion 32 serving as a boundary portion between the side surface (i.e., the surface 3f illustrated in
In the example described here, the cathode 6 has a plurality of protruding portions 16, as illustrated in
A gap 8 which is an air gap is provided between the gate 5 and the protruding portion 16. A voltage is applied between the cathode 6 and the gate 5 so that a potential-level of the gate 5 is higher than a potential-level of the cathode 6. Thus, electrons are field-emitted from each protruding portion 16 of the cathode 6.
A position at which the gate 5 is located is not limited to that illustrated in
In the example described here, the insulating member 3 is configured by a laminated body of a first insulating layer 3a and a second insulating layer 3b. However, the insulating member 3 can be configured with a single insulating layer. Furthermore the insulating member 3 can be configured with three or more insulating layers.
In the configuration illustrated in
When the insulating member 3 is configured with the first insulating layer 3a and the second insulating layer 3b, the first top surface corresponds to a top surface 3g of the second insulating layer 3b. The second top surface corresponds to a part of the top surface 3e of the first insulating layer 3a, which is exposed to the concave portion 7. The side surface connecting the first top surface and the second top surface to each other corresponds to the side surface 3d of the second insulating layer 3b. Thus, in the configuration illustrated in
In the configuration illustrated in
The gate 5 is separated from the cathode 6, connected to a part of the top surface of the insulating member 3, which is not covered with the cathode 6, and supported by the insulating member 3. The gate 5 includes the base portion 5-1, and the protruding portion 5-2 which protrudes from the base portion 5-1 to be close to the cathode 6 (particularly, to each protruding portion 16 of the cathode 6). Generally, if the surface of the substrate 1 is flat, the protruding portion 5-2 of the gate 5 protrudes in (substantially) parallel to the surface of the substrate 1.
A protruding direction in which the protruding portion 5-2 of the gate 5 protrudes intersects with a protruding direction in which each protruding portion 16 of the cathode 16 protrudes. In other words, as illustrated in
The base portion 5-1 and the protruding portion 5-2 are concepts used to facilitate understanding. The present invention can employ a configuration in which the base portion 5-1 and the protruding portion 5-1 are formed integrally with each other, in other words, a configuration in which there is no clear boundary therebetween.
The base portion 5-1 is connected to a part of the top surface of the insulating member 3 (i.e., placed on the top surface of the insulating member 3). When the insulating member 3 is configured with the first insulating layer 3a and the second insulating layer 3b, as illustrated in
According to the example described here, when the electron emitting device is viewed from above (as illustrated in
From a viewpoint of position alignment with the protruding portion 16 of the cathode 6, it is desirable that at least the side surface 5a of the protruding portion 5-2 (particularly a part at a distal-end of the protruding portion 5-2, which is most distant from the base portion 5-1) is shaped like a circular arc (having a curvature).
The gate 5 includes a layer containing molybdenum and oxygen. The layer containing molybdenum and oxygen has peaks in a range of 397 eV to 401 eV, a range of 414 eV to 418 eV, a range of 534 eV to 538 eV, and a range of 540 eV to 547 eV, respectively, in a spectrum measured according to a transmission electron microscope (TEM) electron energy loss spectroscopy (EELS) method (TEM-EELS method) (see
As described above, the “TEM-EELS method” designates a method of performing microscope electron energy loss spectroscopy using a transmission electron microscope. The TEM-EELS method is discussed in Shunsuke Muto et al. (2002), “Structural Analysis for Local Region of Light Element Material Utilizing Inner Shell Excitation Spectrum in Transmission Electron Energy Loss Spectroscopy”, Surface Science, Vol. 23, No. 6, pp. 381-388.
The gate 5 can be configured only by the above layer. Alternatively, the gate 5 can be configured by providing a gate electrode and stacking the above layer (gate layer) on at least a part of the gate electrode, more specifically, on a portion onto which electrons emitted from a cathode are irradiated. In the configuration illustrated in
Thus the above layer may be useful to be provided on at least a side surface of the gate electrode. Moreover the gate layer may be more useful also to be provided on the bottom surface (more specifically, a part thereof facing the second top surface of the above insulating member 3 across an air gap (i.e., to be separated therefrom)) of the gate electrode. Accordingly, e.g., the protruding portion 5-2 illustrated in
When the electron emitting device according to the present invention is drove, an anode 20 is provided at a predetermined distance (e.g., several millimeters (mm)) from the electron emitting device, as illustrated in
Hereinafter, a specific exemplary example of the electron emitting device according to the present invention is described.
A first exemplary example of the electron emitting device according to the present invention is described hereinafter. A process of manufacturing an electron emitting device according to the present exemplary example is described hereinafter with reference to cross-sectional views illustrated in
In step 1, first, as illustrated in
Next, in step 2, a resist pattern (not illustrated) is formed on the electrically conductive layer 50 by photolithography techniques. Then, the electrically conductive layer 50, the insulating layer 40, and the insulating layer 30 are sequentially processed using a dry etching method (see
Then, in step 3, the resist is peeled off. Then, the insulating layer 40 is etched (see
Next, in step 4, a molybdenum (Mo) film was formed on each of the slope 3f and the top surface 3e of the first insulating layer 3a and the gate electrode 5 by an electron beam heating vapor deposition method such that at least the Mo film formed on the slope 3f of the first insulating layer 3a is 35 nm in thickness (see
Next, in step 5, wet etching (i.e., third etching) is performed on the conductive films 60A and 50B (see
Next, in step 6, the conductive films 60A and 50B are exposed to the atmosphere. More specifically, the substrate 1 subjected to the treatment in step 4 is taken into the atmosphere and left in the atmosphere at room temperature for 1 hour.
Finally, in step 7, a cathode electrode 2 is formed as illustrated in
Then, the TEM-EELS measurement was performed on vicinity (i.e., a portion covering the side surface 5a of the gate electrode 5) of a surface layer of a gate layer 5B. A measurement sample used therefor was a thin section obtained by cutting a portion close to a surface layer of a gate layer 5B of the produced electron emitting device, using a focused ion beam (FIB) processing apparatus, so as to have a cross-section perpendicular to the surface of the substrate 1, as illustrated in
A transmission electron microscope with an acceleration voltage of 200 kV was used for the TEM-EELS measurement. The measurement was performed by reducing a beam diameter to about 2 nm. A measured energy range extended from 360 eV to 560 eV. A spectrum illustrated in each of the drawings referred to in the following description was obtained by enlarging a part of a measured spectrum. The gate layer 5B is a film containing molybdenum and oxygen. Thus, attention energy ranges are a range extending from 380 eV to 430 eV, in which a spectrum due to molybdenum appeared, and another range extending from 520 eV to 570 eV, in which a spectrum due to oxygen appeared.
A large number of electron emitting devices (i.e., samples) were produced by a manufacturing method similar to the method according to the present exemplary embodiments. Then, the TEM-EELS measurement was performed on the gate layer 5B. Thus, it was found that the first peak was present in the range from 397 eV to 401 eV, that the second peak was present in the range from 414 eV to 418 eV, that the third peak was present in the range from 534 eV to 538 eV, and that a fourth peak was present in the range from 540 eV to 547 eV. It was also found that the FWHM of the first peak of each of all of the electron emitting devices ranged from 3 to 5 eV, that the FWHM of the second peak thereof ranged from 6 eV to 8 eV, that the FWHM of the third peak thereof ranged from 2 eV to 4 eV, and that the FWHM of the fourth peak thereof ranged from 9 eV to 14 eV.
On the other hand, for comparison, TEM-EELS measurement similar to the above measurement was performed on commercially available standard samples (manufactured by KISHIDA CHEMICAL Co., Limited.) respectively made of Mo, MoO2, and MoO3.
The spectra illustrated in
Next, the spectra illustrated in
Next, the spectra illustrated in
Thus, it is found that the surface layer portion (i.e., the gate layer 5B) of the gate 5 onto which electrons emitted from the cathode 6 are irradiated has a special composition differing from that of each of pure Mo, MoO2, and MoO3.
A first comparative example is described hereinafter. According to the first comparative example, a method for forming the gate layer according to the first example was changed. More specifically, step 1 through step 3 of the first comparative example were performed, similarly to step 1 through step 3 of the first exemplary example. Hereinafter, step 4 and later steps of the first comparative example are described with reference to
Next, in step 4, a Mo film is formed on the slope 3f and the top surface 3e of the first insulating layer 3a and the gate electrode 5A by a directional sputtering method (see
In the above film formation step, an angle of a surface of the substrate 1 with respect to a sputter target was set to correspond to a horizontal direction. According to the first comparative example, a shield was provided between the substrate 1 and the target such that each sputtering particle was incident upon a surface of the substrate 1 at a limited angle (more specifically, 80° with respect to the surface of the substrate 1). In addition, argon plasma was generated at electric-power of 3 kilo-watts (kW), and a degree of vacuum of 0.1 Pa. The substrate 1 was arranged such that a distance between the substrate 1 and the Mo-target was 60 mm (i.e., equal to or less than a mean free path at a pressure of 0.1 Pa). Then, the Mo film was formed at a deposition rate of 10 nm per minute (nm/min) such that a thickness of the Mo film on the slope of the insulating layer 3 was 15 nm.
In step 5, a resist mask 100 is formed only on an electrically conductive film 50B1 to cover an electrically conductive film 50B1. Then, similar to the first exemplary example, a Mo film was formed on each of the slope 3f and the top surface 3e of the first insulating layer 3a and the gate electrode 5A by the electron beam heating vapor deposition method. Various conditions for the electron beam heating vapor deposition method are the same as those described in the description of step 4 according to the first exemplary example. In step 5, the electrically conductive film 60A2 covering an electrically conductive film 60A1, and an electrically conductive film 50B2 covering the mask 100 are formed. The conductive films 60A1 and 60A2 located on the slope 3f of the first insulating layer 3 were formed so that, similar to the conductive films according to the first exemplary example, a total thickness of the conductive films 60A1 and 60A2 was 35 nm.
Next, in step 6, wet etching (i.e., third etching) is performed on the conductive films 60A2 and 50B2, similarly to step 5 according to the first exemplary example. Various conditions for the wet etching are set to be similar to those set in step 5 in the first exemplary example.
Finally, in step 8, the resist mask 100 was peeled off. Thus, the gate layer 5B (or the conductive film 50B1) covering the top surface 5b and the side surface 5a of the gate electrode 5A was exposed. Then, the cathode electrode 2 was formed, similarly to that according to the first exemplary example (see
It was confirmed from a TEM image that the electron emitting device formed through the above steps and the electron emitting device according to the first exemplary example were equivalent to each other in the shape of the protruding portions 16 of the cathode 6 and in the width of the gap 8 serving as the shortest distance between the gate layer 5B and the cathode 6.
In a case where the electron emitting characteristics of the electron emitting device were measured similarly to those of the electron emitting device according to the first exemplary example, when the drive voltage applied between the cathode electrode 2 and the gate electrode 5A was 23 V, the electron emitting current Ie was 21 μA. The electron emitting characteristics of the device in this case are illustrated in
In a case where an electron emitting device according to a modification was produced, similarly to the first exemplary example except that the step 6 of exposing the conductive films to the atmosphere according to the first exemplary example was not performed, an EEL spectrum substantially similar to that of the electron emitting device according to the first comparative example was measured. In other words, no significant peaks due to oxygen were observed in the range of energy from 520 eV to 570 eV. The electron emitting device according to the modification was lower than the electron emitting device according to the first exemplary example in the electron emitting current Ie and the electron emitting efficiency η (i.e., a ratio of the electron emitting current (Ie) to electric current (If) (=Ie/If)) flowing between the cathode and the gate.
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 modifications, equivalent structures, and functions.
This application claims priority from Japanese Patent Application No. 2010-232626 filed Oct. 15, 2010, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-232626 | Oct 2010 | JP | national |
