capacitor

Abstract

To provide a capacitor that suppresses the generation of leakage current flowing between an anode and a cathode.SOLUTION: The capacitor has a first surface and a second surface that are facing each other. The capacitor includes a cathode having a groove formed on the first surface, an internal anode arranged inside the groove, and an insulation film spaced apart from the internal anode and arranged on the inner wall surface of the groove. When a predetermined voltage is applied between the internal anode and the cathode, the insulation film covers the cathode in an area where electrons are emitted from the cathode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a capacitor. [Background technology]

[0002] A capacitor with a space between the anode and cathode can withstand a higher voltage than a capacitor with a dielectric material between the anode and cathode. For example, a capacitor with a vacuum between the anode and cathode (hereinafter also referred to as a "vacuum capacitor") is used (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. WO2011 / 031189 Summary of the Invention [Problem to be solved by the invention]

[0004] When a high voltage is applied between the anode and cathode of a vacuum capacitor, a leakage current flows between the anode and cathode. The leakage current reduces the withstand voltage of the vacuum capacitor.

[0005] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a capacitor in which the occurrence of leakage current flowing between the anode and the cathode is suppressed. [Means for solving the problem]

[0006] A capacitor according to one aspect of the present invention includes a cathode having a first surface and a second surface facing each other and having a groove formed in the first surface, an internal anode disposed inside the groove, and an insulating film disposed on an inner wall surface of the groove and spaced apart from the internal anode. The insulating film covers the cathode in a region where electrons are emitted from the cathode when a predetermined voltage is applied between the internal anode and the cathode. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a capacitor in which the occurrence of leakage current flowing between the anode and the cathode is suppressed. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic cross-sectional view showing the configuration of a capacitor according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram showing a simplified model of the structure of a capacitor of a comparative example. [Figure 3] FIG. 3 is a schematic diagram showing a simple model of the structure of the capacitor according to the embodiment. [Figure 4] FIG. 4 is a graph showing the relationship between the inter-electrode distance and the breakdown voltage. [Figure 5] FIG. 5 is a graph showing the relationship between the relative dielectric constant of an insulating film and the electric field generated in the insulating film. [Figure 6] FIG. 6 is a graph showing the relationship between the electric field generated in the vacuum region and the relative dielectric constant of the insulating film. [Figure 7] FIG. 7 is a schematic cross-sectional view (part 1) illustrating the method for manufacturing the capacitor according to the embodiment. [Figure 8] FIG. 8 is a schematic cross-sectional view (part 2) illustrating the method for manufacturing the capacitor according to the embodiment. [Figure 9] FIG. 9 is a schematic cross-sectional view (part 3) illustrating the method for manufacturing the capacitor according to the embodiment. [Figure 10] FIG. 10 is a schematic cross-sectional view (part 4) illustrating the method for manufacturing the capacitor according to the embodiment. [Figure 11] FIG. 11 is a schematic cross-sectional view (part 5) illustrating the method for manufacturing the capacitor according to the embodiment. [Figure 12] FIG. 12 is a schematic cross-sectional view (part 6) illustrating the method for manufacturing the capacitor according to the embodiment. [Figure 13]FIG. 13 is a schematic cross-sectional view (part 7) illustrating the method for manufacturing the capacitor according to the embodiment. [Figure 14] FIG. 14 is a schematic cross-sectional view for explaining the method for manufacturing the capacitor according to the embodiment (part 8). [Figure 15] FIG. 15 is a schematic cross-sectional view (part 9) illustrating the method for manufacturing the capacitor according to the embodiment. [Figure 16] FIG. 16 is a schematic cross-sectional view (part 10) illustrating the method for manufacturing the capacitor according to the embodiment. [Figure 17] FIG. 17 is a schematic cross-sectional view (part 11) illustrating the method for manufacturing the capacitor according to the embodiment. [Figure 18] FIG. 18 is a schematic cross-sectional view (part 12) illustrating the method for manufacturing the capacitor according to the embodiment. [Figure 19] FIG. 19 is a schematic cross-sectional view (part 13) illustrating the method for manufacturing the capacitor according to the embodiment. [Figure 20] FIG. 20 is a schematic cross-sectional view (part 14) illustrating a method for manufacturing a capacitor according to an embodiment. [Figure 21] FIG. 21 is a schematic cross-sectional view (part 15) illustrating the method for manufacturing the capacitor according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] The embodiments will be described with reference to the drawings. In the description of the drawings, the same parts are designated by the same reference numerals and the description thereof will be omitted.

[0010] As shown in FIG. 1 , a capacitor 1 according to an embodiment of the present invention has a first surface 11 and a second surface 12 facing each other. The cathode 10 has a groove 100 formed in the first surface 11, and an internal anode 21 disposed within the groove 100. An insulating film 30 is disposed on the inner wall surface of the groove 100, spaced apart from the internal anode 21. By applying a voltage between the internal anode 21 and the cathode 10, which face each other within the groove 100, electrostatic energy is accumulated in the capacitor 1. Unlike capacitors in which a dielectric material is disposed between the anode and cathode, the capacitor 1, which has a space between the internal anode 21 and the cathode 10, suppresses dielectric breakdown due to a voltage applied between the electrodes. Therefore, the withstand voltage of the capacitor 1 can be improved compared to capacitors in which a dielectric material is disposed between the anode and cathode.

[0011] In the capacitor 1, an insulating film 30 covers the cathode 10 in a region where electrons are emitted from the cathode 10 when a predetermined voltage is applied between the internal anode 21 and the cathode 10. The predetermined voltage applied to the internal anode 21 and the cathode 10 is set according to the desired electrostatic energy to be stored in the capacitor 1. In the capacitor 1 shown in FIG. 1, the insulating film 30 is provided only on the side surface of the groove 100 in the cathode 10. However, the insulating film 30 may also be provided on the bottom surface of the groove 100. On the other hand, if a sufficient distance is secured between the cathode 10 and the internal anode 21 at the bottom of the groove 100, it is not necessary to provide the insulating film 30 on the bottom surface of the groove 100, as shown in FIG. 1. For example, if the bottom surface of the groove 100 and the internal anode 21 are separated by a distance sufficient to prevent electrons emitted from the bottom surface of the groove 100 from reaching the internal anode 21, the insulating film 30 need not be provided on the bottom surface of the groove 100.

[0012] In the following description, the direction from the second surface 12 to the first surface 11 is referred to as the upward direction, and the direction from the first surface 11 to the second surface 12 is referred to as the downward direction. The surface facing upward is also referred to as the "upper surface," and the surface facing downward is also referred to as the "lower surface." For example, the first surface 11 of the cathode 10 is the upper surface of the cathode 10, and the second surface 12 is the lower surface of the cathode 10.

[0013] In the remaining area excluding the area where the groove 100 is formed, a first support portion 51 is disposed on the first surface 11 of the cathode 10. The first support portion 51 is made of an insulating material.

[0014] A second support 52 is disposed between the bottom of the groove 100 and the internal anode 21. The second support 52 supports the internal anode 21 inside the groove 100. The second support 52 is made of an insulating material, and the internal anode 21 and the cathode 10 are electrically insulated from each other.

[0015] An external anode 22 is disposed on the first surface 11 side of the cathode 10. The external anode 22 is electrically connected to the internal anode 21 and electrically insulated from the cathode 10. The external anode 22 has a first region 221 and a second region 222.

[0016] The first region 221 is disposed above the opening of the groove 100. The first region 221 has a connecting portion 2211 disposed inside the opening formed in the first support portion 51, and the connecting portion 2211 is connected to the internal anode 21.

[0017] The second region 222 is disposed on the upper surface of the first support portion 51 and faces the first surface 11 of the cathode 10. The first support portion 51 electrically insulates the second region 222 of the external anode 22 from the cathode 10. The second region 222 is separated from the first region 221 by the release hole 220 and is disposed around the first region 221.

[0018] The release hole 220 is formed so as to penetrate the external anode 22 and separate the first region 221 from the second region 222. The release hole 220 is in communication with the inside of the groove 100. As will be described later, the release hole 220 is used to form the groove 100 during the manufacturing process of the capacitor 1.

[0019] The capacitor 1 further includes a positive electrode portion 41 and a negative electrode portion 42. The positive electrode portion 41 is electrically insulated from the cathode 10 and is disposed on the side of the first surface 11 of the cathode 10. The negative electrode portion 42 is electrically connected to the cathode 10 and is disposed on the side of the second surface 12 of the cathode 10. The positive electrode portion 41 and the negative electrode portion 42 are made of a conductive material, and for example, a metal material or the like is suitably used for the positive electrode portion 41 and the negative electrode portion 42.

[0020] The positive electrode portion 41 is disposed on the upper surface of the external anode 22 so as to fill the opening of the release hole 220. The positive electrode portion 41 and the external anode 22 are electrically connected. Since the positive electrode portion 41 is disposed on the upper surface of the external anode 22 across the first region 221 and the second region 222, the first region 221 and the second region 222 are electrically connected via the positive electrode portion 41. The cathode 10 and the positive electrode portion 41 are electrically insulated by the first support portion 51.

[0021] Because the internal anode 21 and the first region 221 are electrically connected and the first region 221 and the second region 222 are electrically connected via the positive electrode portion 41, the internal anode 21 and the external anode 22 are at the same potential as the positive electrode portion 41. In other words, the anode of the capacitor 1 is composed of the internal anode 21 and the external anode 22. In the capacitor 1, the positive electrode portion 41 is electrically connected to the internal anode 21 while being electrically insulated from the cathode 10.

[0022] The negative electrode portion 42 is disposed on the second surface 12 and is electrically connected to the cathode 10. Therefore, by applying a voltage between the positive electrode portion 41 and the negative electrode portion 42 disposed on the outside of the cathode 10, a voltage can be applied between the internal anode 21 and the cathode 10.

[0023] In the capacitor 1, the positive electrode portion 41 fills the opening of the release hole 220, thereby isolating the inside of the groove 100 from the outside of the capacitor 1. In other words, the inside of the groove 100 is sealed by the positive electrode portion 41. By sealing the inside of the groove 100, the air pressure inside the groove 100 is maintained constant. For example, the inside of the groove 100 is maintained at atmospheric pressure or a vacuum state lower than atmospheric pressure. In the following description, a capacitor 1 is described in which the inside of the groove 100 is maintained in a vacuum state and the cathode 10 functions as a vacuum container. However, even if the inside of the groove 100 is at atmospheric pressure, the operation of the capacitor 1 is the same as when the inside of the groove 100 is in a vacuum state.

[0024] When the capacitor 1 is used, a negative potential is set to the negative electrode portion 42 relative to the positive electrode portion 41. By applying a voltage between the positive electrode portion 41 and the negative electrode portion 42, electrostatic energy is stored in the capacitor 1.

[0025] Before describing the details of the operation of capacitor 1, we will explain comparative capacitor 1M shown in Figure 2. Figure 2 shows a simplified model of the structure of comparative capacitor 1M, a vacuum capacitor of a comparative example. Comparative capacitor 1M has a configuration in which vacuum region 140 is disposed between anode 120 and cathode 110.

[0026] In the comparison capacitor 1M, the inside of a body 200 made of insulating material is maintained in a vacuum state. A cathode 110 is installed inside the body 200, and an anode 120 is installed outside the body 200. When a voltage is applied between the anode 120 and the cathode 110, electrons are emitted from the cathode 110 toward a vacuum region 140. The comparison capacitor 1M confines the electrons emitted from the cathode 110 in the vacuum region 140 and stores them as electrostatic energy. The comparison capacitor 1M is used, for example, as a battery.

[0027] The electrostatic energy stored in the comparison capacitor 1M (hereinafter referred to as "energy P") is calculated by equation (1): P=CV 2 / twenty one) In equation (1), C is the capacitance of the comparison capacitor 1M, and V is the voltage applied between the anode 120 and the cathode 110. Hereinafter, the voltage applied between the anode and the cathode is also referred to as the "interelectrode voltage."

[0028] The capacitance C is calculated by equation (2): C=kεS / d (2) In equation (2), ε is the vacuum permittivity, S is the electrode facing area, d is the inter-electrode distance, and k is the relative permittivity between the electrodes. Here, the "electrode facing area" is the area where the anode and cathode face each other. The "inter-electrode distance" is the distance between the anode and cathode. When there is a vacuum between the electrodes, k=1.

[0029] From equations (1) and (2), energy P is proportional to inter-electrode voltage V and capacitance C. To increase capacitance C, the inter-electrode distance d can be reduced. On the other hand, as shown in equation (1), the square of inter-electrode voltage V is proportional to energy P, so by increasing inter-electrode voltage V, energy P can be increased more effectively than by increasing capacitance C. The maximum value of inter-electrode voltage V is the value obtained by multiplying the electric field at which insulation between the electrodes breaks down (hereinafter referred to as the "breakdown electric field") by the inter-electrode distance d.

[0030] Since the space between the electrodes of a vacuum capacitor is a vacuum, the insulation between the electrodes theoretically does not break down, and the breakdown field of the vacuum capacitor can therefore be made infinite. However, if an inter-electrode voltage V is applied that exceeds a certain value in the electric field between the electrodes, a phenomenon occurs in which electrons emitted from the cathode reach the anode without electrostatic energy being accumulated in the vacuum region 140 (hereinafter also referred to as the "field emission phenomenon"). The field emission phenomenon causes leakage current to flow between the electrodes, reducing the withstand voltage of the vacuum capacitor. As such, there is a limit to the inter-electrode voltage V of the comparison capacitor 1M. In other words, there is a limit to the amount of energy P that can be accumulated in the comparison capacitor 1M.

[0031] On the other hand, the capacitor 1 shown in FIG. 1 can store more energy P than the comparative capacitor 1M, as will be described below.

[0032] 3 shows a simplified model of the structure of capacitor 1 shown in FIG. 1 when the inside of groove 100 is a vacuum. Anode 120, cathode 110, and insulating film 30 shown in FIG. 3 represent the internal anode 21, cathode 10, and insulating film 30 of capacitor 1. In the simplified model shown in FIG. 3, the inside of body 200 made of insulating material is maintained in a vacuum state. Cathode 110 and insulating film 30 are installed inside body 200, and anode 120 is installed outside body 200.

[0033] As shown in FIG. 3, by covering the cathode 110 with the insulating film 30, electrons are not emitted from the cathode 110. In other words, the capacitor 1 can prevent electrons emitted from the cathode 110 from reaching the anode 120. Therefore, the capacitor 1 can apply a high voltage between the electrodes of the anode 120 and the cathode 110 without causing the field emission phenomenon. That is, in equation (1), V 2 The value of can be increased to increase the energy P stored in capacitor 1.

[0034] However, when the anode 120 is covered with an insulating film, the occurrence of the field emission phenomenon cannot be suppressed for the following reason. That is, when a large number of electrons are emitted from the cathode 110 due to the inter-electrode voltage, the electrons adhere to the insulating film covering the anode 120. Because the insulating film to which the electrons adhere becomes an electrode, the dielectric breakdown field of the insulating film becomes the dielectric breakdown field of the capacitor. Therefore, when the anode 120 is covered with an insulating film, it is not possible to utilize the large dielectric breakdown field obtained by leaving a space between the electrodes.

[0035] Figure 4 shows the relationship between the gap between the cathode and anode and the breakdown voltage (see M Radmilovic-Radjenovic and B Radjenovic, Europhysics Letters, 83, 25001 (2008)). The voltage that can be applied between the electrodes is lower than the breakdown voltage. The dashed line L1 in Figure 4 is Paschen's theoretical line, which indicates that the shorter the electrode distance, the higher the voltage that can be applied between the electrodes. The solid line L2 is the calculated value using an analytical equation. The circles (◯) and squares (□) in Figure 4 represent experimental values. When the electric field generated between the electrodes (hereinafter referred to as the "generated electric field") is equal to or higher than the field indicated by the slope of the line LE connecting the origin of the graph in Figure 4 to the experimental value, the voltage that can be applied between the electrodes is lower than the theoretical value due to field emission. The electric field indicated by the slope of the line LE is 0.08 MV / cm. Capacitor 1 capable of suppressing the field emission phenomenon can apply a higher voltage between the electrodes than a capacitor without insulating film 30, particularly when the generated electric field is 0.08 MV / cm or higher. In other words, capacitor 1 has an advantage in energy density, particularly when the generated electric field is 0.08 MV / cm or higher.

[0036] However, when the generated electric field is lower than 0.08 MV / cm, field emission is unlikely to occur, so there is no need to reduce the interelectrode voltage. In other words, when the generated electric field is lower than 0.08 MV / cm, it is possible to use a capacitor without the insulating film 30. Below, we compare Capacitor 1 with Comparative Capacitor 1M, which does not have the insulating film 30, for cases where the generated electric field is low and field emission does not occur. Because the capacitance of Capacitor 1 is the series capacitance of the vacuum region and the insulating film 30, Capacitor 1 is smaller than Comparative Capacitor 1M. On the other hand, Capacitor 1 is larger in size due to the presence of the insulating film 30. Since the interelectrode voltages of Capacitor 1 and Comparative Capacitor 1M can be made the same, the energy density of Capacitor 1 is lower than that of Comparative Capacitor 1M. Therefore, when used in a generated electric field where field emission does not occur, the Comparative Capacitor may be used in terms of energy density.

[0037] On the other hand, capacitor 1 has an advantage in energy density over a capacitor without insulating film 30 when used in a range where the electric field generated in vacuum region 140 is 0.08 MV / cm or more.

[0038] Below, we will consider the electric field generated between the electrodes of the capacitor 1. In the simplified model of the capacitor 1 shown in FIG. 3, when an inter-electrode voltage V is applied between the cathode 110 and the anode 120, the inter-electrode voltage V is divided into a voltage applied to the vacuum region 140 and a voltage applied to the insulating film 30. Here, the length of the vacuum region 140 in the direction of the inter-electrode distance is defined as a first distance d1, and the length of the insulating film 30 is defined as a second distance d2. In this case, when the cathode 110 is set to 0 V and the inter-electrode voltage V is applied to the anode 120, the first voltage V1 applied to the vacuum region 140 is calculated using equation (3), and the second voltage V2 applied to the insulating film 30 is calculated using equation (4): V1={(k2 / d2) / (k1 / d1+k2 / d2)}×V (3) V2={(k1 / d1) / (k1 / d1+k2 / d2)}×V (4) In the formulas (3) and (4), k1 is the relative dielectric constant of a vacuum, 1, and k2 is the relative dielectric constant of the insulating film 30.

[0039] Using the first voltage V1, the second voltage V2, and the first distance d1 and the second distance d2, the first electric field E1 generated in the vacuum region 140 is calculated by equation (5), and the second electric field E2 generated in the insulating film 30 is calculated by equation (6): E1=V1 / d1 (5) E2=V2 / d2 (6)

[0040] Substituting equation (3) into equation (5) gives equation (7), and substituting equation (4) into equation (6) gives equation (8): E1={k2 / (d1×d2) / (k1 / d1+k2 / d2)}×V (7) E2={k1 / (d1×d2) / (k1 / d1+k2 / d2)}×V (8)

[0041] Dividing equation (7) by equation (8) gives equation (9): E1 / E2=k2 / k1 (9)

[0042] 5 shows the relationship between the relative dielectric constant k2 of the insulating film 30 and the second electric field E2 generated in the insulating film 30 when the first electric field E1 generated in the vacuum region 140 is 200 MV / cm, 90 MV / cm, 60 MV / cm, and 40 MV / cm. In FIG. 5, characteristic S200 is the characteristic when the first electric field E1=200 MV / cm, characteristic S90 is the characteristic when the first electric field E1=90 MV / cm, characteristic S60 is the characteristic when the first electric field E1=60 MV / cm, and characteristic S40 is the characteristic when the first electric field E1=40 MV / cm. Hereinafter, characteristic S200, characteristic S90, characteristic S60, and characteristic S40 will be collectively referred to as "characteristic S."

[0043] In order to prevent the insulating film 30 from being broken down by the inter-electrode voltage V, the second electric field E2 generated in the insulating film 30 must be lower than the breakdown electric field of the material of the insulating film 30. The breakdown electric field Emax of the insulating film 30 is calculated by the approximation formula (10): Emax=(400 / k2) 0.5 ···(10) The breakdown field Emax calculated by equation (10) is shown in FIG. 5, overlapping with the characteristic S.

[0044] For the capacitor 1 to operate normally, the second electric field E2 generated in the insulating film 30 must be smaller than the breakdown electric field Emax of the insulating film 30. In other words, the relative dielectric constant k2 of the insulating film 30 must be in a range larger than the relative dielectric constant k2 at the intersection where the characteristic S intersects with the breakdown electric field Emax in FIG.

[0045] FIG. 6 shows the relationship between the relative dielectric constant k2 at the intersection of the characteristic S and the breakdown electric field Emax and the first electric field E1 generated in the vacuum region 140. The horizontal axis of FIG. 6 represents the first electric field E1, and the vertical axis represents the relative dielectric constant k2 of the insulating film 30. From FIG. 10, an approximate expression for the relationship between the relative dielectric constant k2 of the insulating film 30 and the first electric field E1 generated in the vacuum region 140 is expressed by the following equation (11): k2=0.0025×E1 2 ···(11) That is, when an interelectrode voltage is applied between the internal anode 21 and the cathode 10, the electric field generated in the space between the internal anode 21 and the insulating film 30 is E, and the relative dielectric constant k2 of the insulating film is 0.0025×E 2 When the dielectric breakdown field Emax is larger than the dielectric breakdown field Emax, the electric field generated in the insulating film 30 is lower than the dielectric breakdown field Emax. By making the electric field generated in the insulating film 30 lower than the dielectric breakdown field Emax, it is possible to prevent dielectric breakdown of the insulating film 30. Furthermore, by making the electric field generated in the insulating film 30 lower than the dielectric breakdown field Emax, it is possible to extend the life of the insulating film 30 and improve the reliability of the capacitor 1.

[0046] A silicon substrate, for example, is used for the cathode 10 of the capacitor 1. A silicon nitride film, for example, with a thickness of 10 nm, is formed as the insulating film 30 on the sidewall surface of the groove 100. The distance between the internal anode 21 and the insulating film 30 inside the groove 100 is, for example, 100 nm. In this case, a vacuum region 140 with a first distance d1 of 100 nm and an insulating film 30 with a second distance d2 of 10 nm are disposed between the internal anode 21 and the cathode 10.

[0047] Below, we will explain a method for manufacturing capacitor 1 with reference to the drawings. Note that the method for manufacturing capacitor 1 described below is just one example, and it goes without saying that capacitor 1 can be realized by various other manufacturing methods, including variations thereof.

[0048] First, as shown in FIG. 7, a first support portion 51 is formed on the first surface 11 of the cathode 10. For example, a conductive silicon substrate is used for the cathode 10, and a silicon oxide film is deposited on the first surface 11 as the first support portion 51. Thermal CVD (Chemical Vapor Deposition) or plasma CVD may be used as a deposition method for the first support portion 51. The thickness of the first support portion 51 needs to be such that the second region 222 of the external anode 22 and the cathode 10 are electrically insulated when a predetermined interelectrode voltage is applied between the internal anode 21 and the cathode 10. The thickness of the first support portion 51 is, for example, 2 μm or more.

[0049] 8, openings 510 are formed in the first support portion 51 so as to expose regions in which the grooves 100 are to be formed on the first surface 11 of the cathode 10. For example, the openings 510 are formed by patterning the first support portion 51 using a photolithography technique.

[0050] Although not shown in the drawings, patterning using photolithography is performed, for example, as follows (the same applies to the patterning steps using photolithography in the following steps). That is, a photoresist film is formed on the upper surface of the first support section 51. Next, the photoresist film is selectively exposed to light and patterned. Then, using the photoresist film as an etching mask, the first support section 51 is patterned by anisotropic etching or the like. A dry etching method such as reactive ion etching may be used for the anisotropic etching. After patterning the first support section 51, the photoresist film is removed using oxygen plasma, sulfuric acid, or the like.

[0051] Next, using the first support portion 51 as an etching mask, a portion of the upper portion of the cathode 10 is etched away to form the groove 100 as shown in FIG. 9. The groove 100 may be formed, for example, by anisotropic dry etching. Because the depth of the groove 100 affects the capacitance of the capacitor 1, the size of the groove 100 may be designed depending on the application of the capacitor 1. Here, the depth of the groove 100 is set to 5 μm. The width of the groove 100 is set to 5 μm, for example. By using a silicon substrate for the cathode 10, the groove 100 can be easily formed in the cathode 10 using photolithography or the like.

[0052] After forming the trench 100, an insulating film 30 is formed on the inner wall surface of the trench 100, as shown in FIG. 10 . For example, a silicon nitride film is deposited as the insulating film 30 on the entire inner wall surface of the trench 100. A low-pressure CVD method or the like is preferably used as a method for depositing the insulating film 30, which can form a silicon nitride film with good coverage inside the trench 100. The thickness of the insulating film 30 is set so that electrons emitted from the cathode 10 do not reach the internal anode 21. For example, the thickness of the insulating film 30 is about 10 nm.

[0053] 11, the insulating film 30 formed on the upper surface of the first support 51 is removed by anisotropic etching. The anisotropic etching in this process removes the insulating film 30 on the upper surface of the first support 51 and the insulating film 30 at the bottom of the groove 100, but does not remove the insulating film 30 on the sidewall surface of the groove 100.

[0054] Thereafter, as shown in FIG. 12 , an insulating film is formed on the bottom of the groove 100 to form the second support portion 52. For example, a silicon oxide film is formed on the bottom of the groove 100 as the second support portion 52 by silicon thermal oxidation. For example, the cathode 10 is reacted with water vapor by heating in a water vapor atmosphere at 1100°C for 8 hours, forming a silicon oxide film on the bottom of the groove 100. In the process of forming the second support portion 52, the sidewall surface of the groove 100 is covered with the insulating film 30, and the first surface 11 of the cathode 10 is covered with the first support portion 51. Therefore, no silicon oxide film is formed on the sidewall surface of the groove 100 or the first surface 11. The thickness of the second support portion 52 needs to be such that the internal anode 21 and the cathode 10 are electrically insulated from each other when a predetermined interelectrode voltage is applied between them. The thickness of the second support portion 52 is, for example, approximately 2 μm.

[0055] Next, as shown in FIG. 13 , a first sacrificial film 310 is formed on the surfaces of the insulating film 30, the first support portion 51, and the second support portion 52. The first sacrificial film 310 may be, for example, a silicon oxide film. A low-pressure CVD method, which can deposit a silicon oxide film with good coverage inside the trench 100, is preferably used as a deposition method for the first sacrificial film 310. The first sacrificial film 310 is removed in a later process, and the area from which the first sacrificial film 310 is removed becomes a space between the internal anode 21 and the insulating film 30. In other words, the thickness of the first sacrificial film 310 determines the width of the space. The thicker the first sacrificial film 310, the smaller the capacitance of the capacitor 1. On the other hand, if the first sacrificial film 310 is thin, there is a possibility that the etchant will not penetrate the entire first sacrificial film 310 during the process of removing the first sacrificial film 310, which will be described later. The thickness of the first sacrificial film 310 is, for example, approximately 100 nm.

[0056] After forming the first sacrificial film 310, as shown in FIG. 14, a first conductive film 410 for forming the internal anode 21 and the connection portion 2211 is formed so as to fill the groove 100. For example, a polysilicon film may be used as the first conductive film 410. The following describes an example in which the first conductive film 410 is a polysilicon film. A low-pressure CVD method may also be used to form the polysilicon film. The thickness of the polysilicon film is preferably greater than half the width of the groove 100. By making the thickness of the polysilicon film greater than half the width of the groove 100, the inside of the groove 100 can be filled with the polysilicon film. For example, if the width of the groove 100 is 5 μm, the thickness of the polysilicon film should be greater than 2.5 μm. After the polysilicon film is deposited, a process is performed to make the polysilicon film conductive. For example, an annealing process is performed in which the polysilicon film is heated at 950°C in a phosphorus oxychloride (POCl3) atmosphere. This annealing step dopes the polysilicon film with phosphorus atoms to form an N-type polysilicon film, and the first conductive film 410 becomes conductive.

[0057] 15, the upper part of the first conductive film 410 is etched away until the first sacrificial film 310 is exposed. For example, the etching amount of the first conductive film 410 is set to 2.5 μm, which corresponds to the film thickness of the first conductive film 410.

[0058] Next, as shown in FIG. 16 , a region near the outer edge of the first conductive film 410 is selectively etched away to form a hole region 415. The hole region 415 is formed to facilitate etching and removal of the first sacrificial film 310 formed on the sidewall surface of the groove 100. The aforementioned photolithography technique may be used to form the hole region 415. The first conductive film 410 remaining inside the hole region 415 is the connection portion 2211. The first conductive film 410 remaining below the hole region 415 is the internal anode 21 after the first sacrificial film 310 is removed. The amount of etching of the first conductive film 410 is approximately equal to the sum of the thickness of the first support portion 51 and the thickness of the first sacrificial film 310. If the first conductive film 410 is etched more than this sum, the opposing area between the internal anode 21 and the cathode 10 will be reduced. The smaller the opposing area between the internal anode 21 and the cathode 10, the less electrostatic energy can be stored in the capacitor 1.

[0059] After forming the hole region 415, as shown in FIG. 17, a second sacrificial film 320 is formed on the upper surface of the first sacrificial film 310 so as to fill the hole region 415. The second sacrificial film 320 is, for example, a silicon oxide film. A low-pressure CVD method or the like is preferably used as a deposition method for the second sacrificial film 320, as it can form a silicon oxide film with good coverage inside the hole region 415. The thickness of the second sacrificial film 320 is set so as to completely fill the hole region 415. For example, if the width of the hole region 415 is 2 μm, the thickness of the second sacrificial film 320 can be set to 1 μm or more so that the hole region 415 can be filled with the second sacrificial film 320.

[0060] 18, the upper portion of the second sacrificial film 320 is etched away so as to expose the upper surface of the first conductive film 410. The amount of etching of the second sacrificial film 320 is approximately the same as the film thickness of the second sacrificial film 320.

[0061] Thereafter, as shown in FIG. 19 , a second conductive film 420 is formed over the upper surfaces of the first sacrificial film 310, the second sacrificial film 320, and the first conductive film 410. The second conductive film 420 is formed to define the first region 221 and the second region 222 of the external anode 22. The second conductive film 420 is, for example, a polysilicon film. The following describes, by way of example, a case in which the second conductive film 420 is a polysilicon film. The polysilicon film may be formed, for example, by low-pressure CVD. The second conductive film 420 has a thickness of, for example, about 1 μm. After the polysilicon film is deposited, the second conductive film 420 is made conductive by performing an annealing process similar to that for the first conductive film 410.

[0062] 20 , the second conductive film 420 is selectively etched to form a release hole 220. The upper surface of the second sacrificial film 320 is exposed inside the release hole 220. For example, photolithography can be used to form the release hole 220. By forming the release hole 220, the second conductive film 420 is divided into a first region 221 and a second region 222.

[0063] After the release holes 220 are formed, the second sacrificial film 320 and the first sacrificial film 310 are removed as shown in FIG. 21 . The second sacrificial film 320 and the first sacrificial film 310 are preferably removed by isotropic etching using an etchant such as hydrofluoric acid. The etchant is injected into the cathode 10 through the release holes 220. In the etching process for the second sacrificial film 320 and the first sacrificial film 310, etching conditions such as etching time are set so that at least a portion of the bottom of the groove 100 is exposed. Note that this etching process may cause the outer edge of the second support 52 to recede inward from the outer edge of the internal anode 21. By removing the first sacrificial film 310, a space is formed between the internal anode 21 and the insulating film 30.

[0064] Thereafter, the positive electrode portion 41 is formed over the upper surfaces of the first region 221 and the second region 222 of the external anode 22. A metal film such as an aluminum film is preferably used for the positive electrode portion 41. A sputtering method (hereinafter also referred to as "oblique sputtering") is preferably used to deposit material from an oblique direction relative to the upward direction in order to fill the opening of the release hole 220. In the capacitor 1 shown in FIG. 1 , the material is deposited from the upper right to the lower left of the page, so that the positive electrode portion 41 is attached to a portion of the side wall surface facing the right side of the release hole 220. The film thickness of the positive electrode portion 41 and the angle of the deposition direction relative to the upward direction in the oblique sputtering method are set so as to completely block the opening of the release hole 220. The degree of vacuum inside the groove 100 is the degree of vacuum in the sputtering process. While it depends on the specifications of the sputtering device, the degree of vacuum inside the groove 100 is, for example, 1×10 -5 It is in the Pa range.

[0065] Next, the negative electrode portion 42 is formed on the second surface 12 of the cathode 10. For example, the negative electrode portion 42 is formed by sputtering a metal film such as an aluminum film. The film thickness of the negative electrode portion 42 is, for example, about 2 μm. In this way, the capacitor 1 is completed. The first sacrificial film 310 left on the upper surface of the first support portion 51 functions as part of the first support portion 51. The first sacrificial film 310 left on the upper surface of the second support portion 52 functions as part of the second support portion 52.

[0066] The length of the second support 52 from the bottom of the groove 100 to the point where the second support 52 connects to the internal anode 21 is set to be longer than the distance between the internal anode 21 and the insulating film 30. In other words, the distance from the bottom of the groove 100 to the internal anode 21 is longer than the gap between the insulating film 30 and the internal anode 21. For example, the gap between the internal anode 21 and the insulating film 30 is approximately 100 nm, and the thickness of the second support 52 is approximately 2 μm. Because the distance from the insulating film 30 to the internal anode 21 is shorter than the distance from the bottom of the groove 100 to the internal anode 21, the electric field generated when a voltage is applied between the internal anode 21 and the cathode 10 is stronger between the insulating film 30 and the internal anode 21 than between the bottom of the groove 100 and the internal anode 21. As a result, electron emission from the bottom of the groove 100 is suppressed. This suppresses the field emission phenomenon caused by electrons emitted from the bottom of the groove 100.

[0067] Because electrons are not emitted from the bottom of the groove 100, it does not matter whether the insulating film 30 is disposed at the bottom of the groove 100. In other words, it is sufficient that the insulating film 30 covers the cathode 10 in a region of the cathode 10 that faces the internal anode 21 and retains electrons when a predetermined voltage is applied between the internal anode 21 and the cathode 10. In other words, the cathode 10 does not need to be covered with the insulating film 30 in a region where electrons are not emitted when a predetermined voltage is applied between the internal anode 21 and the cathode 10.

[0068] As described above, in the capacitor 1, the insulating film 30 is disposed in the region of the cathode 10 facing the internal anode 21, thereby suppressing the occurrence of field emission. To store electrostatic energy in the capacitor 1, the negative electrode portion 42 may be set to ground potential and a positive voltage may be applied to the positive electrode portion 41. For example, the inner wall surface of the groove 100 in the cathode 10 may be covered with the insulating film 30 made of silicon nitride. Since the relative dielectric constant of a silicon nitride film is approximately 7, the breakdown field Emax calculated using equation (10) is 7.6 MV / cm. Therefore, in the capacitor 1, from equations (3), (5), and (7), 500 V can be applied to the positive electrode portion 41 when the inter-electrode distance is 110 nm. Here, the breakdown field Emax is calculated under the conditions of the first distance d1 = 100 nm, the second distance d2 = 10 nm, and the relative dielectric constant k2 of the insulating film 30 = 7.

[0069] Under the above conditions, the total electric field generated between the internal anode 21 and cathode 10 of capacitor 1 is 50 mV / cm, and the second electric field E2 generated in the insulating film 30 is 7 MV / cm. Therefore, the second electric field E2 is smaller than the breakdown field of the insulating film 30. Furthermore, the voltage that can be applied to capacitor 1 is orders of magnitude larger than that of a vacuum capacitor with an inter-electrode distance of 110 nm or other types of capacitors in which the electrodes are separated by a dielectric material. According to equation (1), the electrostatic energy stored in a capacitor is proportional to the square of the inter-electrode voltage, so capacitor 1 can store more electrostatic energy than other types of capacitors.

[0070] Although the embodiments of the present invention have been described above, the descriptions and drawings that form part of this disclosure should not be understood to limit the present invention. Various alternative embodiments, examples, and operating techniques will become apparent to those skilled in the art from this disclosure.

[0071] For example, although the above description exemplifies a case where the inside of the groove 100 is a vacuum, the inside of the groove 100 may be at atmospheric pressure. Even when the inside of the groove 100 is at atmospheric pressure, the occurrence of the field emission phenomenon can be suppressed by covering the region of the cathode 10 from which electrons are emitted with the insulating film 30. [Explanation of symbols]

[0072] 1...Capacitor 10...Cathode 11...Side 1 12…Second side 21...Internal anode 22...External anode 30...Insulating film 41...Positive electrode 42...Negative electrode 51...First support part 52…Second support part 100...Groove 110...Cathode 120...Anode 140...Vacuum area 220...Release hole 221…First area 222…Second area 2211...Connection

Claims

1. a cathode having a first surface and a second surface facing each other, the first surface having a groove formed therein; an internal anode disposed within the groove; an insulating film disposed on an inner wall surface of the groove and spaced apart from the internal anode; Equipped with a capacitor in which the insulating film covers the cathode in a region where electrons are emitted from the cathode when a predetermined voltage is applied between the internal anode and the cathode;

2. When a voltage is applied to the internal anode and the cathode, and the electric field generated in the space between the internal anode and the insulating film is E, the relative dielectric constant of the insulating film is 0.0025×E 2 The capacitor of claim 1 .

3. a positive electrode portion electrically insulated from the cathode and disposed on the first surface side of the cathode, the positive electrode portion being electrically connected to the internal anode; a negative electrode portion electrically connected to the cathode and disposed on the second surface side of the cathode; The capacitor of claim 1 or 2, further comprising:

4. a first support portion disposed on the first surface in a remaining area excluding the area in which the groove is formed, The capacitor according to claim 3 , wherein the cathode and the positive electrode portion are electrically insulated by the first support portion.

5. a first region having a connection portion disposed within an opening formed in the first support portion and connected to the internal anode; a second region disposed on the first support portion and electrically connected to the first region; an external anode having The capacitor according to claim 4 , wherein the positive electrode portion is disposed on the external anode.

6. The capacitor according to claim 3 , wherein the inside of the groove is sealed by the positive electrode portion.

7. 7. The capacitor of claim 1, further comprising a second support disposed between the bottom of the groove and the internal anode, electrically insulating the internal anode from the cathode.

8. 8. The capacitor according to claim 7, wherein a length of the second support portion from a bottom of the groove to a point where the second support portion is connected to the internal anode is longer than a distance between the internal anode and the insulating film.

9. 9. The capacitor of claim 1, wherein the cathode is a silicon substrate.

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