JP2008027781A - Diamond electron emitting element, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electron emitting element using diamond having excellent characteristics as an electron emitting material which has an excellent electron emitting capacity in high output operation. <P>SOLUTION: The electron emitting element 1 has an electron emitting part 10 consisting of a projected diamond and a gate electrode 20 to impress electric field on the electron emitting part provided on an insulating layer 21. An electron supply part 11 to supply electrons is installed at the side on the surface of the projected electron emitting part 10, and at least the surface of the electron supply part is made of a material which is not etched by hydrofluoric acid. The electron supply part is made of at least two layers and the layer of the side near the electron emitting part is made of a layer with better adhesion with diamond, and the layer with better adhesion may be covered with a second electron supply part made of a material which is hardly etched by hydrofluoric acid. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electron-emitting device made of diamond and a method for manufacturing the same.

  In recent years, cold cathodes have been developed as electron-emitting devices. An electron-emitting device such as a cold cathode has an electron-emitting portion made of, for example, molybdenum, carbon nanotube, or diamond. In particular, an electron-emitting device having diamond as an electron-emitting portion has a negative electron affinity, is extremely chemically stable, has a high thermal conductivity, etc. Has attracted attention as a source.

In the case of using diamond as an electron source, it is known that the n-type having many electrons as carriers has better electron emission characteristics such as electron emission from a low voltage. However, these are stories in which the current is on the order of μA. When the total current increases, the p-type electron-emitting device operates at a lower voltage than the n-type electron-emitting device. This is because n-type diamond has so far only been obtained with a low efficiency of about several hundred Ωcm.
JP 2001-266736 A JP 2004-1119018 A

  An object of the present invention is to provide an electron-emitting device using diamond having excellent characteristics as an electron-emitting material and having an excellent electron-emitting capability in high output operation.

  In order to solve the above problems, an electron-emitting device according to the present invention has an electron-emitting portion 10 made of protruding diamond and a gate electrode 20 for applying an electric field to the electron-emitting portion with an insulating layer 21 with reference to FIG. In the electron-emitting device 1 provided above, an electron supply portion 11 that supplies electrons is provided on a side surface of the surface of the protruding electron emission portion 10, and at least the surface of the electron supply portion is not etched with hydrofluoric acid It is characterized by comprising.

  Since the electron-emitting device having such a structure has a sharp tip, electron emission can be extracted at a low voltage due to electric field concentration, and the series resistance of diamond increased by sharpening can be reduced by the electron supply unit, so that a large current region can be obtained. The high electron emission ability of diamond can be maintained. Further, when such an electron supply unit is provided, it is difficult to form an electrode structure such as a gate. However, by using a material in which at least the surface of the electron supply portion is not etched with hydrofluoric acid, the etching selectivity with the gate electrode, insulating layer, etc. formed in the periphery can be increased. The electron-emitting device of the invention can be formed.

  In addition, as shown in FIG. 2, the electron supply part is composed of at least two layers 11 and 12, the side close to the electron emission part is composed of a layer 12 having good adhesion to diamond, and the layer having good adhesion is made of hydrofluoric acid. You may coat | cover with the 2nd electron supply part 11 which consists of material which is not etched.

  Since diamond is chemically stable, adhesion to other materials such as metals, particularly Mo and Si that are not etched with hydrofluoric acid, is not necessarily good. In particular, in an electron-emitting device, heat, applied voltage, and the like change in a harsh environment. If the adhesion is weak, the device can easily be destroyed. Therefore, by sandwiching a layer having good adhesion with diamond between the surface layer of such an electron supply section and diamond, high adhesion can be maintained and a stable diamond electron-emitting device can be obtained. Examples of such materials include Ti, Zr, Hf, V, Nb, and Ta. In addition, the material forming the carbide, such as W, can maintain high adhesion.

  Furthermore, as shown in FIG. 3A, the electron supply section may be composed of at least two layers, and the side in contact with the insulating layer 21 may be a material 13 having good adhesion to the insulating layer. Further, as shown in FIG. 3B, the material having good adhesion to the insulating layer may be the material 12 having good adhesion to the diamond.

A material whose surface is not etched by hydrofluoric acid, such as Mo, does not necessarily have good adhesion to the insulating layer, and poor adhesion to an oxide insulating layer such as SiO ₂ . Therefore, a diamond electron-emitting device with a long lifetime can be obtained by forming a material having good adhesion to the insulating layer with a separate contact portion with the insulating layer. Examples of such materials include Ti, Zr, Hf, V, Nb, and Ta.

  Moreover, it is preferable that the electron supply unit 11 covers the protruding electron emission unit 10 to a distance of 500 nm or less from the tip of the protruding electron emission unit. Since the protruding diamond has an elongated shape, the series resistance is high, and when the end of the electron supply portion is far from the tip of the electron emission portion, the resistance becomes high, so that a large current cannot be obtained. It is desirable to form the electron supply part to a distance of 500 nm or less that allows electrons to move without being scattered when a high voltage is applied. Desirably, a distance of 200 nm or less with less electron scattering is preferable.

  Further, as shown in FIG. 4, the radius of curvature of the tip of the electron emission unit 10 is r, the film thickness of the electron supply unit is d, and the distance from the tip of the electron emission unit to the end of the electron supply unit is L. It is preferable that L> 2r and L> 2d. In order to reduce the series resistance, it is desirable that the electron supply portion be as close as possible to the tip of the electron emission portion. However, if it is too close, the electric field applied to the gate electrode is blocked, and it is found that a high emission current cannot be obtained. As an optimum structure for the electron supply portion, the electric field of the gate electrode is effectively reduced by 2 r or more apart from the radius of curvature r of the electron emission portion and 2 d or more than the film thickness d of the electron supply portion. Applied to the tip, a high electron emission current can be obtained.

  The diamond is preferably n-type. Although p-type diamond also has a high electron emission capability, the series resistance, which was an n-type problem, can be reduced by forming the above-described electron supply portion, and an electron having an effectively high electron emission capability. An emission element can be obtained.

  The diamond surface is preferably terminated with oxygen. When diamond is terminated with oxygen, the adhesion with other materials becomes higher, and a long-life and stable electron-emitting device can be obtained as an electron-emitting device having the structure of the present invention. In particular, in the case of n-type diamond, when the surface is terminated with hydrogen, carriers in the electron emission portion are reduced by the p-type conductive layer on the surface. Therefore, by terminating oxygen, n-type diamond can exhibit a high electron emission capability.

  The method for manufacturing an electron-emitting device of the present invention includes a step of preparing a protruding diamond, a step of forming an electron supply portion on the protruding diamond, a step of coating a photoresist on the protruding diamond, It consists of a step of immersing the protruding diamond in an etching solution to etch the electron supply part at the tip of the protrusion. By adopting such a process, it becomes possible to arbitrarily control the distance between the electron supply part and the electron emission part tip by changing the film thickness of the photoresist to be coated, thereby forming an optimum structure for the present invention. can do.

  In addition, after forming the first electron supply portion by the manufacturing method, forming a second or more electron supply portion, coating the photoresist on the protruding diamond, and the protruding shape It is preferable that the manufacturing method does not expose the first electron supply part by immersing diamond in an etching solution to etch the electron supply part at the tip of the protrusion. By adopting such a process, it becomes possible to arbitrarily control the position of the electron supply unit consisting of two or more layers as described above, and the layer having good adhesion is a surface layer that is not etched with hydrofluoric acid. The electron-emitting device of the present invention can be obtained by reliably coating.

  The processing method for stabilizing the electron-emitting device of the present invention is characterized by heating in a vacuum at 200 ° C. to 600 ° C. for 30 minutes or more. According to the manufacturing method of the present invention, residues such as an etching solution remain at the tip of the electron emission portion, but these substances can be removed by heating to 200 ° C. or higher in vacuum to obtain a stable emission current. . Further, by limiting the temperature to 600 ° C. or lower, it is possible to prevent the diffusion of the metal in the stacked electron supply section, and to prevent damage to the electron-emitting device.

  Further, the processing method for stabilizing the electron-emitting device may be to apply a pulsed voltage to the gate electrode. By applying such a voltage as a pre-process before the full-scale operation of the electron-emitting device, the residue at the tip of the electron-emitting portion is thermally desorbed by the emitted electrons, electric field evaporation, etc. through the manufacturing process of the present invention. As a result, the emission electrons are increased and a stable emission current can be obtained. At this time, the pulse width is desirably 5 msec or less, and the duty ratio is desirably 10% or less. By doing in this way, the stabilization process of an electron-emitting device can be performed effectively, preventing arc discharge etc. At this time, the electric field applied to the tip of the electron emission portion is preferably 20 V / μm or more. By using such an electric field, the stabilization process can be accelerated and a stable electron-emitting device can be obtained at an early stage.

  By forming the electron supply portion in diamond having excellent properties as an electron emission material, it is possible to obtain an electron emission capability superior to that of a conventional electron emission device in a high output operation. Such a field emission type electron source can improve the performance of microwave tubes such as traveling wave tubes and klystrons, high-frequency amplification elements, electron beam equipment such as SEMs and electron beam exposure machines, and light-emitting elements such as FEDs. it can.

  Although the form for implementing this invention is demonstrated concretely by an Example, the scope of the present invention is not limited by this Example.

Phosphorus-doped diamond was formed on a high-pressure synthetic Ib (111) single crystal diamond substrate using microwave plasma CVD. Hydrogen (H ₂ ) flow rate 200 sccm, methane / hydrogen (CH ₄ / H ₂ ) concentration 0.05%, phosphine / methane (PH ₃ / CH ₄ ) concentration 20%, pressure 13.3 kPa, substrate temperature 870 ° C. The film thickness was 5 μm.

Next, SiO ₂ was deposited on the phosphorus-doped diamond by ICP-CVD, and dots having a diameter of 1.5 μm were formed by photolithography. This was etched by the RIE method to form a circular SiO ₂ mask. The RIE reaction conditions were a CF ₄ flow rate of 20 sccm, a pressure of 1.3 Pa, and an RF power of 100 W. Next, the diamond was etched using a SiO ₂ mask to form a diamond having a protruding electron emission portion. RIE reaction conditions were an oxygen flow rate of 50 sccm, a CF ₄ / O ₂ concentration of 2%, a pressure of 2 Pa, and an RF power of 250 W. The height of the formed protrusion is 2 μm.

  After immersing the diamond having the projection shape in hydrofluoric acid, it was put into a solution in which nitric acid and sulfuric acid were mixed at 1: 3 and heated at 200 ° C. for 30 minutes to terminate the surface with oxygen. Next, in order to form a layer having good adhesion with diamond as an electron supply portion, a Ti film having a thickness of 50 nm was formed on the side having the protrusions by sputtering. A photoresist was spin-coated on the diamond surface. This was put into buffered hydrofluoric acid and exposed to a distance of 1 μm from the tip of the protrusion. Next, in order to form an electron supply portion that is not etched with hydrofluoric acid, a 50 nm-thick Mo film was formed by sputtering. Similarly, a photoresist was spin-coated and exposed to a distance of 200 nm from the tip of the protrusion with aqua regia. Next, in order to form a layer having good adhesion to the insulating layer, a resist having a thickness of 3 μm was applied to the electron supply portion and exposed, and Ti was deposited to a thickness of 50 nm by a vapor deposition method and lift-off was performed.

Next, in order to form a gate structure, ₂ μm of SiO ₂ was formed as an insulating layer using an ICP-CVD method, and 200 nm of Mo was formed as a gate electrode using a sputtering method. A photoresist was spin-coated on this, and a gate structure having a diameter of 2 μm was formed around the electron emission portion using aqua regia and buffered hydrofluoric acid. Further, a photoresist was applied and exposed, and gate electrode separation was performed by etching.

An anode electrode was placed on the electron-emitting device, put in a vacuum chamber and evacuated to 10 ⁻⁷ Pa, and then heated at 300 ° C. for 1 hour to remove residues such as degassing that damaged the operation of the device. Next, a voltage pulse having a voltage of 150 V, a pulse width of 2 msec, and a frequency of 10 Hz was applied 4000 times to the gate electrode. The transition of the emission current at this time is shown in FIG.

  FIG. 6 shows a comparison of emission current between the electron-emitting device of the present invention formed as described above and an electron-emitting device having the same structure except that there is no electron supply portion. Thus, it can be seen that the electron-emitting device of the present invention has excellent characteristics.

  As described above, the electron-emitting device of the present invention has an electron-emitting capability superior to that of the conventional electron-emitting device by forming an electron supply portion in diamond having excellent properties as an electron-emitting material. be able to. Such a field emission type electron source can improve the performance of microwave tubes such as traveling wave tubes and klystrons, high-frequency amplification elements, electron beam equipment such as SEMs and electron beam exposure machines, and light-emitting elements such as FEDs. it can.

FIG. 3 shows a cross-sectional view of the electron-emitting device of the present invention. FIG. 6 shows another cross-sectional view of the electron-emitting device of the present invention. FIG. 6 shows another cross-sectional view of the electron-emitting device of the present invention. The enlarged view of the electron emission part of this invention is shown. The transition of the emission current of an example is shown. The comparison of the emission current of an Example is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electron emission element 10 Electron emission part 11 Electron supply part 12 Layer with good adhesiveness with diamond 13 Layer with good adhesiveness with insulating layer 20 Gate electrode 21 Insulating layer

Claims (15)

  In an electron-emitting device including an electron emission portion made of protruding diamond and a gate electrode for applying an electric field to the electron emission portion on an insulating layer, an electron supply portion for supplying electrons is formed on a side surface of the surface of the protruding electron emission portion. An electron-emitting device which is provided and is made of a material which is not etched with hydrofluoric acid at least on the surface of the electron supply portion.   The electron supply section is composed of at least two layers, the side close to the electron emission section is formed of a layer having good adhesion to diamond, and the good adhesion layer is covered with a second electron supply section made of a material that is not etched with hydrofluoric acid. The electron-emitting device according to claim 1.   The electron-emitting device according to claim 1, wherein the electron supply unit includes at least two layers, and a side in contact with the insulating layer is formed of a material having good adhesion to the insulating layer.   4. The electron-emitting device according to claim 1, wherein the electron supply unit covers the electron emission unit to a distance of 500 nm or less from a tip of the electron emission unit.   L> 2r and L>, where r is the radius of curvature of the tip of the electron emission portion, d is the thickness of the electron supply portion, and L is the distance from the tip of the electron emission portion to the end of the electron supply portion. The electron-emitting device according to claim 1, wherein the electron-emitting device is 2d.   6. The electron-emitting device according to claim 1, wherein the material that is not etched by hydrofluoric acid in the electron supply portion is made of either Mo or Si.   The electron-emitting device according to claim 1, wherein the layer having good adhesion to diamond in the electron-emitting portion is made of any one of Ti, Zr, Hf, V, Nb, and Ta.   The electron-emitting device according to claim 1, wherein the layer having good adhesion to diamond in the electron-emitting portion is a material that forms carbide.   The insulating layer is an oxide insulator, and the electron supply portion having good adhesion to the insulating layer is made of any one of Ti, Zr, Hf, V, Nb, and Ta. The electron-emitting device according to any one of the above.   The electron-emitting device according to claim 1, wherein the diamond is n-type.   The electron-emitting device according to claim 1, wherein the surface of the diamond electron-emitting portion is terminated with oxygen.   A step of preparing a protruding diamond, a step of forming an electron supply portion on the protruding diamond, a step of coating the protruding diamond with a photoresist, and a step of immersing the protruding diamond in an etching solution The manufacturing method of the electron-emitting device which consists of the process of etching the electron supply part.   Forming the second or more electron supply portions after forming the electron supply portion (first electron supply portion), coating the photoresist on the protruding diamond, and the protruding diamond; 13. The method of manufacturing an electron-emitting device according to claim 12, wherein the electron supply portion at the tip of the protrusion is etched by immersing the substrate in an etching solution and the first electron supply portion is not exposed.   A method for processing an electron-emitting device, comprising: heating an electron-emitting device including the electron supply unit in a vacuum at a temperature of 200 ° C. or higher and 600 ° C. or lower for 30 minutes or more. An electron-emitting device including the electron supply unit, wherein a pulse voltage is applied to a gate electrode.

Images