JPH0686325U - Variable capacitor - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a variable capacitance capacitor which has a small capacitance even if it is miniaturized and has a good withstand voltage. [Structure] After the surface of the silicon substrate 1 is thermally oxidized to form a pattern, anisotropic etching is performed to form chevron-shaped irregularities. A silicon nitride film 16 as a protective film is deposited on this uneven surface by low pressure CVD (chemical vapor deposition). A window for impurity diffusion described below is formed in a part of the silicon nitride film 16, and impurities such as boron and phosphorus are thermally diffused in the silicon oxide film to reduce the resistance, and the lower electrode 2 is used. Next, thermal oxidation is performed on this surface to form an oxide film 3, which is deposited while introducing impurities into the oxide film 3 and patterned to perform sacrifice layer.
13 is etched with hydrofluoric acid to form the void 4 and the uneven upper electrode 5. As a result, the variable capacitor 20 including the electrodes 2 and 5 having a large surface area is obtained.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a variable capacitor used for frequency adjustment and the like.

[0002]

[Prior art]

 FIG. 6 shows an example of a conventional variable capacitance capacitor for frequency adjustment. In this variable capacitor 15, a flat plate-shaped upper electrode 10 and a flat plate-shaped lower electrode 11 face each other in parallel through a space 4, and the left and right edge portions of the upper and lower electrodes 10 and 11 are supported by a fixed portion 12. Has been. When a voltage is applied to both electrodes 10 and 11 to control the applied voltage, the electrode spacing between electrodes 10 and 11 is changed by the Coulomb force. This adjusts the capacitor capacity. By this capacitance adjustment, it is possible to finely adjust the frequency in a frequency oscillator circuit or the like.

[0003]

[Problems to be solved by the device]

 By the way, in recent years, in particular, as the circuit parts (electronic parts) have become lighter, thinner, shorter, and smaller, the variable capacitance capacitor 15 also tends to be downsized. If the conventional variable capacitor 15 is downsized, the electrode areas of the upper and lower electrodes 10 and 11 are reduced. However, the capacitance value of this type of capacitor is proportional to the electrode area and inversely proportional to the inter-electrode distance, so that the capacitance decreases as the electrode area decreases. Therefore, in order to prevent the decrease of the capacitance, if the distance between the electrodes is reduced, the capacitance is inversely proportional to the distance between the electrodes, and the capacitance is reduced by reducing the distance between the electrodes even if the electrode area becomes small. Although it is possible to prevent this, when the distance between the electrodes becomes small, a new problem arises that the dielectric strength voltage decreases.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a variable capacitance capacitor that does not decrease in capacitance even if it is miniaturized and has no problem in terms of withstand voltage. is there.

[0005]

[Means for Solving the Problems]

 The present invention is configured as follows in order to achieve the above object. That is, the present invention is a variable capacitor having at least a pair of electrodes facing each other and adjusting the voltage by controlling the voltage applied to the electrodes to adjust the capacitance. Is characterized in that it has concaves and convexes for increasing the surface area and increasing the capacitance.

[0006]

[Action]

 By providing irregularities on the opposing electrode surfaces of a pair of opposing electrodes, the electrode area is expanded even if the outer dimensions of the electrodes are reduced, and the capacitance increases without reducing the inter-electrode distance. This achieves the production of a small variable capacitor.

[0007]

【Example】

 Embodiments of the present invention will be described below with reference to the drawings. The variable capacitance capacitor of the present invention is used for frequency adjustment as in the conventional example, and has a pair of electrodes facing each other, and the capacitance is adjusted by varying the electrode interval by controlling the voltage applied to this electrode. I will do it.

FIG. 1 shows the configuration of the main part of the variable capacitance capacitor of the first embodiment. The variable capacitor 20 has a low-resistance lower electrode 2 formed by thermally diffusing, for example, boron or phosphorus in a silicon material on a silicon substrate 1. The lower electrode 2 has a mountain-shaped uneven surface on the center side. Are formed. Fixing portions 12 made of a dielectric material such as silicon oxide (sio ₂ ) are provided on both ends of the unevenness forming portion, and the upper electrode 5 on which the chevron-shaped unevenness surface is similarly formed is formed on the lower electrode 2. It is mounted at a position facing each other with a space of 4. Like the lower electrode 2, the upper electrode 5 is a low resistance electrode formed by thermally diffusing boron or phosphorus in a silicon material.

Next, a manufacturing process of the variable capacitor 20 of the first embodiment will be described with reference to FIGS. 1 and 4. First, the surface of the silicon substrate {crystal face (100) face} 1 is thermally oxidized. As shown in FIG. 4A, a pattern is formed on the oxide film 3 of the silicon substrate 1, and the oxide film 3 other than the pattern forming portion is removed by hydrofluoric acid. Next, as shown in FIG. 4 (b), the silicon substrate 1 is anisotropically etched to form a mountain-shaped uneven portion on the silicon substrate 1, and then the pattern is formed as shown in FIG. 4 (c). The oxide film 3 in the forming portion is removed with hydrofluoric acid. Next, as shown in FIG. 1, a silicon nitride film (siN film) 16 is deposited as a protective film on the surface of the si substrate 1 having a mountain shape by low pressure CVD (chemical vapor deposition).

Next, a window for diffusing impurities such as boron and phosphorus is opened in a part of the silicon nitride film 16 by a photoetching method, and the silicon oxide film under the silicon nitride film 16 is covered with a film of boron, phosphorus, etc. Impurities are thermally diffused to form the lower electrode 2 having a low resistance. This heating is continued to grow and deposit the silicon oxide film 3 to form a deposition layer for the fixing portion 12, and then further deposit while introducing impurities into the silicon oxide film 3 and perform patterning. The layer 13 is removed by etching with hydrofluoric acid to form the void 4 and the lower electrode 2 and the upper electrode 5 having the mountain-shaped uneven surface.

According to the first embodiment, since the mountain-shaped unevenness is formed on the counter electrode surface of the pair of electrodes facing each other to increase the surface area and the electrostatic capacitance, the distance between the electrodes can be increased. Since the capacitance can be increased without reducing the capacitance, it is possible to manufacture a variable capacitance capacitor that has a good withstand voltage and whose capacitance can be easily adjusted.

In addition, since the mountain-shaped irregularities are formed on the surface of the electrode to increase the capacitance, the external dimensions of the electrode can be reduced by the amount of the increased surface area due to the mountain-shaped structure. A lightweight variable capacitor can be manufactured.

FIG. 2 shows the configuration of the main part of the variable capacitance capacitor of the second embodiment. In this variable capacitor 20, a silicon oxide film 3 is formed on the upper surface of a silicon substrate 1, and a lower metal electrode 7 is provided on the upper surface of this silicon oxide film 3. Then, a silicon nitride film 16 as a protective film is formed on the lower electrode 7. A fixed portion 12 made of the silicon oxide film 3 is formed on the left and right edge portions of the silicon nitride film 16, a silicon nitride film 16 is formed on the fixed portion 12, and an upper metal electrode is formed on the silicon nitride film 16. 6 is formed, and the silicon oxide film 3 is formed on the upper electrode 6.

A manufacturing process of the variable capacitor of the second embodiment will be described with reference to FIGS. First, as in the case of the first embodiment, the steps of FIGS. 4A, 4B, and 4C are advanced to form chevron-shaped irregularities on the surface of the silicon substrate 1. The surface of the silicon substrate 1 is thermally oxidized to form a silicon oxide film 3, and a lift-off method (resist pattern formation is performed on the silicon oxide film 3 and a metal layer is formed on the pattern by vapor deposition or the like, and then with acetone or the like. The metal lower electrode 7 is formed by a method of removing the resist) or an etching method.

A silicon nitride film 16 as a protective film is deposited on the lower electrode 7 by plasma CVD and patterned. The silicon oxide film 3 is deposited on the silicon nitride film 16 by plasma CVD, or SOG (spin on glass) is spin-coated on the silicon nitride film 16 to form the silicon oxide film 3. A silicon nitride film 16 is deposited on the film 3 by plasma CVD. Then, a metal upper electrode 6 is formed by a lift-off method or an etching method, a silicon oxide film 3 is deposited on the upper electrode 6 by plasma CVD, and after patterning, the sacrificial layer 13 is etched to form a void 4. Then, a variable capacitor is manufactured.

In the second embodiment, a mountain-shaped unevenness is formed on the electrode surfaces of the pair of electrodes 6 and 7 facing each other to increase the surface area, and a metal film is formed on the surface of this mountain-shaped uneven surface. Therefore, the capacitance can be increased without reducing the distance between the electrodes. As a result, it is possible to manufacture a variable capacitance capacitor which has a good withstand voltage as in the first embodiment and whose capacitance can be easily adjusted.

The present invention is not limited to the above-mentioned embodiments, and can take various modes. For example, in the above embodiment, the shape of the electrode surface was formed by mountain-shaped irregularities. However, as shown in FIG. 3, the vertex may be P and the pyramidal irregularities composed of the bottom surface 18 may be formed. As shown in FIG. 5, a silicon substrate 1 having a crystal plane of 110 may be anisotropically etched to form an uneven shape perpendicular to the 110 plane. May be dry-etched by RIE (reactive ion etching) to form an uneven shape perpendicular to the substrate surface, and the uneven shape is not limited to that of the embodiment.

Further, in the above embodiment, the variable capacitance capacitor is formed by the pair of counter electrodes. However, a plurality of capacitance capacitors having the counter electrodes are stacked and connected in parallel to manufacture a large capacitance capacitor. You may.

Furthermore, in the above-mentioned embodiment, the description was made for frequency adjustment, but the variable capacitor of the present invention can be applied to other uses.

[0020]

[Effect of device]

 Since the present invention has a structure in which unevenness is formed on the opposite electrode surface of a pair of electrodes facing each other to increase the surface area and increase the electrostatic capacitance, it is possible to increase the electrostatic capacitance without reducing the distance between the electrodes. Therefore, it is possible to obtain a variable capacitance capacitor which has a good withstand voltage and whose capacitance can be easily adjusted.

Further, since the electrode surface is made uneven so as to increase the capacitance, the size of the electrode can be reduced and a small and lightweight variable capacitance capacitor can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective explanatory diagram of a main part configuration of a variable capacitor according to a first embodiment.

FIG. 2 is an explanatory diagram of a main part configuration of a variable capacitor according to a second embodiment.

FIG. 3 is an explanatory view of an electrode shape of another configuration of the variable capacitor according to the present invention.

FIG. 4 is an explanatory diagram of a manufacturing process of an electrode shape of the variable capacitor according to the first and second embodiments.

FIG. 5 is an explanatory view of a manufacturing process of another constituent electrode shape of the variable capacitor according to the present invention.

FIG. 6 is an explanatory diagram of an example of a conventional variable capacitor.

[Explanation of symbols]

 1 Silicon Substrate 2 Lower Electrode 3 Silicon Oxide Film 4 Void 5 Upper Electrode 6 Upper Metal Electrode 7 Lower Metal Electrode 12 Fixed Part 13 Sacrificial Layer 16 Silicon Nitride Film 20 Variable Capacitor

Claims (1)

[Scope of utility model registration request] 1. A variable capacitance capacitor having at least a pair of electrodes facing each other, the capacitance being adjusted by varying an electrode interval by controlling a voltage applied to the electrodes, wherein a surface area is provided on a surface of the facing electrode of the facing electrode. A variable capacitance capacitor characterized in that irregularities are formed to increase the capacitance to increase the capacitance.