Plasma processing apparatus

Abstract

To efficiently diffuse active species generated at a plasma electrode into the air without the need for a fan.SOLUTION: A plasma processing apparatus comprises: a plasma generating unit 110 that includes at least one pair of upper layer electrodes 112 and lower layer electrodes 113 and an upper dielectric layer 111a and a lower dielectric layer 111b provided between the pair of upper layer electrodes 112 and lower layer electrodes 113, and generates plasma; an AC power supply unit 101 that applies an AC voltage to the upper layer electrode 112 and the lower layer electrode 113; a DC power supply unit 103 that is arranged on one side in the axial direction of the upper layer electrode 112 and the lower layer electrode 113 and has a DC electrode 102 that generates ion wind toward end portions 114, 114 on one side of the upper layer electrode 112 and the lower layer electrode 113; and a tapped transformer 104 that is electrically connected to the AC power supply unit 101 and the DC power supply unit 103, respectively.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a plasma processing apparatus. [Background technology]

[0002] In recent years, a technique called dielectric barrier discharge (DBD) has been developed in plasma processing technology, making it possible to generate low-temperature plasma at atmospheric pressure. As a result, the range of applications of plasma processing has expanded, and it is increasingly being used in a variety of applications. The purposes of plasma processing include sterilization, deodorization, surface modification, and decomposition of chemical substances. Furthermore, the substances that can be subjected to plasma processing can be solid, liquid, or gaseous.

[0003] Various plasma processing apparatuses have been developed to perform continuous plasma processing while flowing air. For example, Patent Document 1 discloses a plasma blower having a fan that generates wind by rotation, a rotating electrode that rotates together with the fan by a motor, and a fixed electrode that the rotating electrode periodically approaches. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-104361 Summary of the Invention [Problem to be solved by the invention]

[0005] In conventional plasma processing apparatuses, activated species generated at a plasma electrode are diffused into the air using a fan such as that disclosed in Patent Document 1. Examples of such fans include centrifugal fans (such as sirocco fans, radial fans, and turbo fans), axial flow fans (such as propeller fans), mixed flow fans (such as line fans), cross flow fans, and blowers.

[0006] When active species are diffused using a fan, which is a mechanical element, the following problems arise. For example, because a fan has a mechanical structure, it has a limited lifespan due to wear and tear and is highly likely to cause breakdowns. For example, foreign matter may get into the mechanical structure of the fan, and dust or liquid may get into the bearing part of the rotating shaft. Another problem is that the sound generated by the rotation of the fan is relatively loud, making it difficult to use in environments where quietness is required.

[0007] The present invention has been made in consideration of the above points, and aims to provide a plasma processing apparatus that does not require a fan and can efficiently diffuse active species generated at a plasma electrode into the air. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention is characterized by comprising: a plasma generation unit having at least a pair of electrode layers and a dielectric layer provided between the pair of electrode layers, and generating plasma; an AC power supply unit that applies an AC voltage to the pair of electrode layers; a DC power supply unit that is arranged on one side in the axial direction of the electrode layers and has a DC electrode that generates an ionic wind toward one end of the electrode layer; and a tapped transformer or a transformer circuit using multiple transformers that are electrically connected to the AC power supply unit and the DC power supply unit, respectively.

[0009] According to the present invention, because of the fanless structure that does not use a fan, the air flow caused by the ionic wind can efficiently diffuse the active oxygen species generated by the plasma processing in the desired direction in the air. As a result, the present invention has no mechanical moving parts and can improve the reliability of the plasma processing apparatus, which can avoid the problems described in the section on problems to be solved by the invention.

[0010] Furthermore, it is preferable that the pair of electrode layers have an upper electrode layer and a lower electrode layer, and an air layer through which ionic wind flows is provided between the upper electrode layer and the lower electrode layer which are arranged apart from each other.

[0011] According to the present invention, an air layer is provided between the upper electrode layer and the lower electrode layer, thereby generating a wind flow through the air layer, and this wind flow can efficiently diffuse the active oxygen species generated by the plasma treatment in a desired direction in the air.

[0012] Furthermore, it is preferable that the pair of electrode layers have an upper electrode layer and a lower electrode layer, and that a dielectric layer is filled between the upper electrode layer and the lower electrode layer.

[0013] Furthermore, it is preferable that the outer edge of the dielectric layer has an extension portion that extends outward beyond the outer edge of the electrode layer, and the DC electrode is disposed on the extension portion. According to the present invention, by disposing the DC electrode on the extension portion, the DC electrode for generating ion wind can be made with the same structure as the electrode for generating plasma. This reduces the number of parts and the assembly man-hours.

[0014] Furthermore, it is preferable that the dielectric layer has an upper dielectric layer and a lower dielectric layer, and the DC electrode is disposed on at least one of the upper dielectric layer and the lower dielectric layer.

[0015] Furthermore, it is preferable that the plasma generating unit is configured with two or more pairs of the electrode layers. According to the present invention, by configuring the pair of electrode layers with two or more pairs, the reaction between the plasma and the gas can be further promoted, and the plasma utilization efficiency can be improved.

[0016] Furthermore, it is preferable to generate plasma between the DC electrode and the electrode layer. According to the present invention, more plasma can be generated than simply blowing air with a fan only to a plasma generating electrode of the same size. [Effects of the Invention]

[0017] According to the present invention, it is possible to obtain a plasma processing apparatus that does not require a fan and can efficiently diffuse activated species generated at a plasma electrode into the air. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 2 is a perspective view for explaining a plasma generating unit. [Figure 2] FIG. 2 is a perspective view for explaining a plasma generating unit. [Figure 3] FIG. 2 is a cross-sectional view illustrating a plasma generating unit. [Figure 4] FIG. 10 is a perspective view for explaining a plasma generating unit according to a first modified example. [Figure 5] FIG. 10 is a perspective view for explaining a plasma generating unit according to a second modified example. [Figure 6] FIG. 10 is a cross-sectional view illustrating a plasma generating unit according to a third modified example. [Figure 7] 1 is a schematic cross-sectional circuit diagram illustrating a plasma processing apparatus according to a first embodiment of the present invention. [Figure 8] 8 is a partially schematic cross-sectional circuit configuration diagram showing a modified example of the plasma processing apparatus of FIG. 7. [Figure 9] FIG. 4 is a partially schematic cross-sectional circuit configuration diagram showing a plasma processing apparatus according to a second embodiment of the present invention. [Figure 10] FIG. 10 is a partially schematic cross-sectional circuit configuration diagram showing a plasma processing apparatus according to a third embodiment of the present invention. [Figure 11] FIG. 10 is a schematic cross-sectional circuit diagram illustrating a plasma processing apparatus according to a fourth embodiment of the present invention. [Figure 12] 12 is a partially schematic cross-sectional circuit configuration diagram showing a modified example of the plasma processing apparatus of FIG. 11. FIG. [Figure 13] FIG. 11 is an equivalent circuit diagram of FIG. 10 using two transformers instead of the single tapped transformer. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, embodiments of the present invention will be described in detail, but the embodiments of the present invention are not limited to the embodiments described below. Each embodiment and modified example can be applied in appropriate combination. Furthermore, directions such as "upper" and "lower" in the description are used for convenience of explanation and do not limit the directions of the present invention.

[0020] The plasma processing apparatus of this embodiment is configured to perform continuous plasma processing of gases by including a multilayer plasma generation unit having a dielectric layer, an electrode layer, and an optional mask layer; an AC power supply unit capable of applying an AC voltage between a pair of electrode layers; a DC power supply unit having a DC electrode disposed on one side of the pair of electrode layers in the axial direction and generating an ion wind directed toward one end of the pair of electrode layers; and a tapped transformer electrically connected to the AC power supply unit and the DC power supply unit, respectively. In dielectric barrier discharge, a dielectric layer is provided between two electrode layers, and an AC voltage is applied between the two electrode layers to generate plasma within the dielectric layer sandwiched between the two electrode layers. First, the plasma generation unit will be described.

[0021] <Basic structure of the plasma generation unit> As shown in Figures 1 and 2, the plasma generating unit 10 includes a dielectric layer 11, an upper electrode 12, a lower electrode 13, an upper mask layer 14, and a lower mask layer 15. The plasma generating unit 10 is a thin-film member and is flexible. For convenience, the dielectric layer 11 is expressed as a single dielectric, but it may also be a laminate of one or more dielectrics containing air. The mask layer is provided to protect the electrodes and improve the ease of assembly of the electrodes, and may be omitted. Furthermore, by appropriately selecting the thickness and position of the mask layer, excessive electric field concentration on the electrodes can be prevented, thereby extending the life of the electrodes.

[0022] As shown in FIGS. 1 to 3, the dielectric layer 11 is a layer member disposed between the upper electrode 12 and the lower electrode 13. The material of the dielectric layer 11 is an insulating material with a large breakdown voltage so that discharge does not easily occur between the upper electrode 12 and the lower electrode 13. Furthermore, since the material of the dielectric layer 11 will be exposed to the generated plasma, it is preferable that the material be durable against the active substances generated in the plasma. The material of the dielectric layer 11 is preferably a material selected mainly from glass, ceramics, and synthetic resins. The term "mainly" means that the component composition is 50 mass % or more (the same applies hereinafter).

[0023] Examples of glass include soda-lime glass (soda glass), borosilicate glass, quartz glass, lead glass, and oxide glass.

[0024] Synthetic resins include thermoplastic resins and thermosetting resins. Examples of thermoplastic resins include general-purpose resins such as polyolefin, polystyrene, polyvinyl acetate, polyurethane, polylactic acid, ABS resin, AS resin, acrylic resin, polyvinyl chloride, and polyvinylidene chloride; engineering plastics such as polyamide, polyacetal, polycarbonate, modified polyphenylene ether, polyester, and cyclic polyolefin; polyphenylene sulfide, polysulfone, polyethersulfone, polyarylate, liquid crystal polymer, polyetheretherketone, polyimide, polyamideimide, polyetherimide, fluorine-based resin, unsaturated polyester resin, and polyurethane resin. Among these synthetic resins, silicone-based resins and polyimides, which have excellent durability, are particularly preferred. The thickness of the dielectric layer 11 is not particularly limited, but is preferably 0.1 mm to 5.0 mm, more preferably 0.1 mm to 3.0 mm, and even more preferably 0.1 mm to 1.0 mm, in order to achieve lightweight and compactness.

[0025] As shown in FIGS. 2 and 3, the upper electrode (electrode layer) 12 and the lower electrode (electrode layer) 13 are layer members disposed on the front and back of the dielectric layer 11. The upper electrode 12 and the lower electrode 13 are each provided with a through-hole 16 penetrating in the thickness direction. In this embodiment, the through-holes 16 are oval in plan view, and five through-holes 16 are formed, but the shape and number are not limited. The through-holes 16 may be omitted, but providing the through-holes 16 as in this embodiment makes it easier to generate plasma and facilitates the creation of a power supply circuit. Furthermore, contact with gas at the through-holes 16 enables plasma processing of the gas.

[0026] The upper electrode (electrode layer) 12 and the lower electrode (electrode layer) 13 are formed of a conductive material, and may be a metal plate (including metal foil), a conductive paint, a conductive polymer, a conductive film, etc. The thickness of the upper electrode 12 and the lower electrode 13 is not particularly limited, but is preferably 5 μm to 1.0 mm, more preferably 5 μm to 0.2 mm, and even more preferably 5 μm to 0.1 mm, respectively, in order to provide a flexible, lightweight, and compact processing device.

[0027] The dielectric layer 11, the upper electrode 12, and the lower electrode 13 may be laminated without using an adhesive, or may be bonded with an adhesive. The adhesive is preferably a material that is durable against active substances generated in plasma. Examples of adhesives include epoxy, acrylic, urethane, phenol, urea, silicone, cyanoacrylate, rubber, and vinyl acetate adhesives. Among these, silicone adhesives and UV-curable epoxy adhesives are preferred from the viewpoint of durability, with polyamide adhesives, polyimide adhesives, and silicone adhesives being more preferred. The thickness of the adhesive is preferably 0.01 to 0.2 mm, and more preferably 0.01 to 0.1 mm.

[0028] As shown in FIG. 3 , the upper mask layer 14 and the lower mask layer 15 are components disposed on the outer sides of the upper electrode 12 and the lower electrode 13, respectively. More specifically, the upper mask layer 14 is disposed on the upper surface of the upper electrode 12. The lower mask layer 15 is disposed on the lower surface of the lower electrode 13. The upper mask layer 14 and the lower mask layer 15 are each provided with through holes 17. In this embodiment, the through holes 17 are oval and five in number are formed, but the shape and number are not limited thereto. The through holes 17 may be omitted, but for ease of manufacturing, it is preferable that the through holes 17 are the same as the through holes 16, although this is not limitative.

[0029] As shown in Figures 2 and 3, through hole 17 has the same shape as through hole 16, and they communicate with each other. It is not necessary that through hole 17 and through hole 16 have the same shape. Through holes 16, 17, dielectric layer 11 is exposed to the outside. In other words, the surface of dielectric layer 11 is exposed to the outside at multiple locations where through holes 16, 17 are formed. In addition, hole walls (cross-sectional portions) 16a, 17a of through holes 16, 17 are also exposed to the outside. Furthermore, through holes 16, 17 may be provided on only one side.

[0030] The upper mask layer 14 and the lower mask layer 15 are formed of an insulating material. The hardness of the upper mask layer 14 and the lower mask layer 15 is preferably equal to or less than that of the upper electrode 12 and the lower electrode 13. If the plasma generation unit 10 is manufactured using a thin material, it may be difficult to handle. However, providing the upper mask layer 14 and the lower mask layer 15 improves ease of handling. The upper mask layer 14 and the lower mask layer 15 also protect the thin conductor from mechanical and physical shocks during manufacture and use, as well as deterioration caused by the surrounding environment. Furthermore, they provide mechanical protection against scratches that may occur during manufacture. Considering that the plasma generation unit 10 will be installed on an object to be attached, the upper mask layer 14 and the lower mask layer 15 preferably have a hardness that allows for easy installation along the object and also improves ease of handling. Furthermore, by dividing the dielectric layer 11 into two, the upper and lower structures of the plasma generating unit 10 can be made symmetrical. Manufacturing can be easily achieved by assembling the upper and lower structures and bonding them together in the center. In this case, the dielectric layer 11 is divided into three layers: the upper layer, the lower layer, and the adhesive layer, but can be considered electrically as a single dielectric.

[0031] The thicknesses of the upper mask layer 14 and the lower mask layer 15 are not particularly limited, but in order to provide a flexible, lightweight, and compact processing device, they are preferably 5 μm to 1.0 mm, more preferably 5 μm to 0.2 mm, and even more preferably 5 μm to 0.1 mm. The thicknesses of the upper mask layer 14 and the lower mask layer 15 may be set as appropriate, but in this embodiment they are formed to be larger than the thicknesses of the upper-layer electrode 12 and the lower-layer electrode 13.

[0032] The plasma generating unit 10 is very thin and flexible, which can make it difficult to handle during assembly. Furthermore, the upper electrode 12 and the lower electrode 13 are made of conductive materials, such as conductive metals and conductive dielectrics. Metals, for example, can be corroded by liquids and gases. For example, the upper electrode 12 and the lower electrode 13 are oxidized by highly oxidizing gases and corroded by sulfuric acid and hydrochloric acid. Resin-based conductive materials can also be deteriorated by humidity and acid. Furthermore, the plasma generating unit 10 is designed to be installed according to the shape of the target object. However, if only the upper electrode 12 and the lower electrode 13 are installed without the upper mask layer 14 and the lower mask layer 15, thin metal electrodes can wrinkle or create gaps between the electrodes and the dielectric layer 11. Gaps between the upper electrode 12 and the lower electrode 13 and the dielectric layer 11 can cause abnormal or partial discharges.

[0033] In this regard, according to this embodiment, the upper mask layer 14 and the lower mask layer 15 can protect the upper electrode 12 and the lower electrode 13, and the plasma generation unit 10 can be easily handled, improving workability and assembly. Furthermore, the provision of the upper mask layer 14 and the lower mask layer 15 allows the plasma generation unit 10 to be installed on an object without forming wrinkles or gaps. Furthermore, in the case of a multi-stage structure, the upper mask layer 14 and the lower mask layer 15 also serve as part of the dielectric that constitutes the barrier discharge, making it less likely that abnormal discharge will occur even if gaps are formed during installation.

[0034] The outer edges of upper layer electrode 12 and lower layer electrode 13 may be sealed with an insulator (not shown) to prevent deterioration over time due to exposure to the outside world and to prevent discharge from occurring via the outer edges other than through-hole 16. When a resin or the like is used as the mask layer, the mask layer has the effect of spreading thinly over not only upper layer electrode 12 and lower layer electrode 13 but also the upper and lower surfaces of dielectric 11.

[0035] Similarly, the outer edges of the upper mask layer 14 and the lower mask layer 15 may be sealed with an insulator (not shown) to prevent their outer edges from being exposed to the outside world and reacting with external substances to deteriorate over time, and to prevent discharge from occurring through the outer edges other than the through holes 17.

[0036] Furthermore, an insulating layer (not shown) may be provided on the outside of the upper mask layer 14 and the lower mask layer 15 .

[0037] When the longitudinal direction of the through holes 16 and 17 is parallel to the gas flow direction, the resistance to the gas flow is small and the gas flows smoothly. On the other hand, when the longitudinal direction of the through holes 16 and 17 is perpendicular to the gas flow direction, the resistance to the gas flow is large, the gas flow is disturbed, and the gas is agitated.

[0038] The shape, number, and direction of the through holes 16, 17 relative to the gas flow can be selected appropriately depending on the purpose of the plasma processing, the effect of the plasma processing, etc. The shapes of the through holes may be different between the front and back sides of the plasma generating unit 10. Alternatively, the through holes may be provided on the front side of the plasma generating unit 10 and not on the back side.

[0039] <First Modification of Plasma Generation Unit> 4 is a perspective view for explaining a plasma generating unit according to a first modified example. The plasma generating unit 10A according to the first modified example differs from the basic structure described above in that it does not have an upper mask layer 14. As in the plasma generating unit according to the first modified example, the mask electrode (mask electrode layer) may be provided only on one side of the plasma generating unit 10A.

[0040] <Second Modification of Plasma Generation Unit> FIG. 5 is a perspective view illustrating a plasma generating unit according to a second modified example. The plasma generating unit 10B according to the second modified example differs from the basic structure described above in that it does not include the upper mask layer 14 and the lower mask layer 15. As in the plasma generating unit B according to the second modified example, the upper mask layer 14 and the lower mask layer 15 may be omitted. In other words, by configuring the plasma generating unit 10B with the dielectric layer 11, the upper electrode 12, and the lower electrode 13, it is possible to further reduce the size and the number of parts. Furthermore, by making the dielectric layer 11, the upper electrode 12, and the lower electrode 13 thin, the electrodes themselves can be made flexible, allowing them to be manufactured to fit curved surfaces.

[0041] Furthermore, as in the first and second modified examples, by omitting both or one of the upper mask layer 14 and the lower mask layer 15, the upper electrode 12 and the lower electrode 13 can be brought into direct contact with the gas, and the plasma and gas can be brought into contact at the ends of the electrodes, making it possible to easily extract the plasma gas (active species).

[0042] <Third Modification of Plasma Generation Unit> FIG. 6 is a cross-sectional view illustrating a plasma generating unit according to a third modified example. The plasma generating unit 10C according to the third modified example differs from the basic structure described above in that it does not include an upper mask layer 14 and a lower mask layer 15. Furthermore, the plasma generating unit 10C according to the third modified example does not have a monolithic dielectric layer, but is composed of an upper dielectric layer 18 and a lower dielectric layer 19, which are separated vertically and arranged facing each other. However, since air is also considered a type of dielectric, the upper dielectric layer 18, the air layer 20, and the lower dielectric layer 19 can be considered as a single dielectric layer 11, resulting in the same structure as the plasma generating unit 10B. An upper electrode 12 is provided on the upper surface of the upper dielectric layer 18, and a lower electrode 13 is provided on the lower surface of the lower dielectric layer 19. An air layer 20 is provided between the upper dielectric layer 18 and the lower dielectric layer 19. In the third modified example, plasma can also be generated in the air layer 20. For convenience, this embodiment does not show supports with pillars, grooves, protrusions, or the like that structurally support the air layer 20, which is made of air. These may be either conductive or insulating, provided they are positioned a sufficient distance from the electrodes, but insulating materials are preferred. Furthermore, structures may be placed to divide, control, or change the flow rate of fluid passing through the interior. Furthermore, if these structures are made of a dielectric material, they can control the electric field to suppress electric field concentration in specific areas, or conversely, intentionally concentrate the electric field.

[0043] First Embodiment Next, a plasma processing apparatus according to a first embodiment of the present invention will be described. FIG. 7 is a partially schematic cross-sectional circuit diagram showing the plasma processing apparatus according to the first embodiment of the present invention. The plasma processing apparatus 100 according to the first embodiment of the present invention includes a plasma generation unit 110, an AC power supply unit 101, a DC power supply unit 103 having a DC electrode 102, and a tap transformer 104 electrically connected to the AC power supply unit 101 and the DC power supply unit 103. The plasma generation unit 110 of this embodiment does not have either an upper or lower mask layer, as in the third modified example described above, and an air layer 105 is provided between the upper dielectric layer 111a and the lower dielectric layer 111b, penetrating along the axial direction of the plasma generation unit 110. While this embodiment uses a single tap transformer 104, this is not limiting. Instead of the single tap transformer 104, a transformer circuit using multiple transformers may be used, as shown in FIG. 13 (described later).

[0044] The plasma generating unit 110 includes an upper dielectric layer 111a, a lower dielectric layer 111b, an upper electrode (electrode layer) 112, and a lower electrode (electrode layer) 113. Between the upper dielectric layer 111a and the lower dielectric layer 111b, an air layer 105 is provided through which air (gas) flows from one side to the other along the axial direction of the plasma generating unit 110 (a direction parallel to the upper electrode 112 and the lower electrode 113). As shown in FIG. 7, the upper dielectric layer 111a and the lower dielectric layer 111b each have a uniform thickness and are layered. The thicknesses of the upper dielectric layer 111a and the lower dielectric layer 111b are preferably set larger than the thicknesses of the upper electrode 112 and the lower electrode 113 to prevent abnormal discharge. That is, the upper dielectric layer 111a and the lower dielectric layer 111b are disposed inside the upper electrode 112 and the lower electrode 113, respectively.

[0045] The upper electrode 112 is disposed on the upper dielectric layer 111a and preferably has a smaller thickness than the upper dielectric layer 111a.

[0046] Lower electrode 113 is disposed under and overlapping lower dielectric layer 111b. The thickness of lower electrode 113 is preferably smaller than the thickness of lower dielectric layer 111b.

[0047] Although not shown in Fig. 7, the upper layer electrode 112 and the lower layer electrode 113 are each provided with a through-hole penetrating in the thickness direction. For example, as shown in Fig. 1, these through-holes have an oval shape in a plan view, and five of them are formed, but the shape and number are not limited thereto.

[0048] Since the temperature of the plasma processing apparatus 100 changes during use, if there is a large difference in the thermal expansion coefficient between the materials constituting the multilayer structure, there is a concern that problems such as peeling may occur over time. Therefore, the materials and adhesives constituting the upper dielectric layer 111a and the lower dielectric layer 111b, which are laminated with the upper electrode 112 and the lower electrode 113, are preferably highly flexible materials that can follow dimensional changes of the upper electrode 112 and the lower electrode 113. As such materials, synthetic resin-based materials are preferred, and it is preferable to select and use an appropriate material from among the synthetic resin-based materials.

[0049] To manufacture the plasma generating unit 110 of the plasma processing apparatus 100 of this embodiment, the upper dielectric layer 111a and the upper electrode 112, and the lower dielectric layer 111b and the lower electrode 113 are laminated together. Methods for laminating the layers include known methods such as pressure bonding, thermocompression bonding, and adhesive application, and any method can be appropriately selected and used.

[0050] The tapped transformer 104 boosts the voltage depending on the winding ratio between the primary and secondary sides, and can adjust the voltage of the AC power supply unit 101 to a voltage at which plasma can be generated according to the winding ratio. The AC power supply unit 101 is electrically connected to the primary side of the tapped transformer 104. The positive electrode of the DC power supply unit 103 is electrically connected to the secondary side of the tapped transformer 104, and the negative electrode of the DC power supply unit 103 is electrically connected to the DC electrode 102. The tap can be, for example, a center tap, but is not limited to a center tap.

[0051] The secondary side of tapped transformer 104 is electrically connected to upper layer electrode 112 and lower layer electrode 113, which face each other with upper dielectric layer 111a and lower dielectric layer 111b therebetween. An AC voltage boosted by tapped transformer 104 is applied between upper layer electrode 112 and lower layer electrode 113.

[0052] Furthermore, the positive electrode of DC power supply unit 103 is electrically connected to a tap of tapped transformer 104. Therefore, the potential on the positive side of DC power supply unit 103 is the same as the AC voltage divided by the tap ratio and winding ratio of tapped transformer 104. For example, if AC voltage is generated from AC power supply unit 101 and the tap position of tapped transformer 104 is set to the center, the intermediate voltage between the voltages applied to upper layer electrode 112 and lower layer electrode 113 and the potential on the positive side of DC power supply unit 103 will be the same.

[0053] The DC electrode 102 has a substantially cylindrical shape and is arranged so that the side circumferential surface of the cylinder faces one end of the upper electrode 112 and one end of the lower electrode 113. The DC electrode 102 is arranged in a horizontal or substantially horizontal position (facing the air layer 105) on one side along the axial direction of the plasma generation unit 110. A DC voltage (for example, 10 to 30 kV) is applied to the DC electrode 102 from a DC power supply unit 103.

[0054] There are no particular limitations on the AC power supply unit 101, and any known power supply device can be used as long as it can apply an AC voltage of a predetermined voltage at a predetermined frequency to each electrode of the plasma generation unit 110. The frequency of the AC voltage is preferably 50 Hz to 30 MHz, and more preferably 50 Hz to 100 kHz. The AC voltage is preferably 0.1 to 50 kV, and more preferably 0.2 to 10 kV.

[0055] <Action and effect> Next, the effects of the plasma processing apparatus 100 according to this embodiment will be described. First, DC power supply unit 103 is switched from an off state to an on state to apply a DC voltage to DC electrode 102, and AC power supply unit 101 is switched from an off state to an on state to apply an AC voltage between upper electrode 112 and lower electrode 113. A potential difference is generated between DC electrode 102 to which the DC voltage is applied and upper electrode 112 and lower electrode 113 to which the AC voltage is applied. This potential difference generates an electrostatic force.

[0056] This electrostatic force attracts ions (electrons) from the DC electrode 102, generating an ion wind (electron flow) from the DC electrode 102 toward one end 114, 114 of the upper electrode 112 and the lower electrode 113. The ion wind is composed of an ion wind W1 directed toward one end (edge) 114 of the upper electrode 112 and an ion wind W2 directed toward one end (edge) 114 of the lower electrode 113 (see FIG. 7). This ion wind generates a wind flow from one side to the other around the plasma generation unit 110. This wind flow is composed of wind flow A flowing along the upper surface of the upper electrode 112, wind flow B flowing along the lower surface of the lower electrode 113, and wind flow C flowing along the air layer 105 provided between the upper dielectric layer 111a and the lower dielectric layer 111b.

[0057] On the other hand, when an AC voltage is applied between upper electrode 112 and lower electrode 113 with upper dielectric layer 111a and lower dielectric layer 111b sandwiched therebetween, plasma is generated in the vicinity of the upper surface of upper electrode 112 and the lower surface of lower electrode 113. Active oxygen species are also generated at the contact surfaces between the plasma-treated gas and upper electrode 112 and lower electrode 113. These active oxygen species are efficiently diffused in desired directions in the air by wind flows A, B, and C caused by the ionic wind.

[0058] In this embodiment, since the fanless structure does not use a fan, the active oxygen species generated by the plasma processing can be efficiently diffused in the desired direction in the air by the wind flows A, B, and C caused by the ionic wind. As a result, in this embodiment, there are no mechanical moving parts, and the plasma processing apparatus 100 can be made more reliable, thereby avoiding the problems described in the section on problems to be solved by the invention.

[0059] Furthermore, since the present embodiment has no mechanical moving parts, it is highly quiet, and can efficiently pump out gas (reactive oxygen species) generated by plasma processing in environments where quietness is required, such as bedrooms.

[0060] Furthermore, in this embodiment, a tapped transformer 104 is used to generate a DC electric field between the intermediate voltage between the upper layer electrode 112 and the lower layer electrode 113 and the DC electrode 102 that creates the ionic wind, thereby making it possible to easily create an ionic wind (flow of electrons).

[0061] Furthermore, in this embodiment, the DC voltage between the DC electrode 102 that creates the ion wind and the upper and lower electrodes 112 and 113 is sufficiently higher than the voltage applied between the upper and lower electrodes 112 and 113 that generates plasma.

[0062] Furthermore, in this embodiment, the amount of ionic wind can be changed by adjusting the DC power supply unit 103 to change the voltage of the DC electrode 102 that generates the ionic wind.

[0063] The plasma-treated gas kills microorganisms present in the gas and decomposes chemical substances due to the active oxygen species generated by the plasma, thereby sterilizing and deodorizing the gas.

[0064] Furthermore, active oxygen species remain in the plasma-treated gas, so by spraying the plasma-treated gas generated by the plasma processing apparatus of this embodiment onto an object, microorganisms present in the object are killed and chemical substances are decomposed, thereby sterilizing and deodorizing the object.

[0065] Functions exhibited by plasma processing of gas using the plasma processing apparatus 100 of this embodiment include sterilization, virus inactivation, deodorization, surface modification, and decomposition of chemical substances. The mechanism by which these functions are exhibited is thought to be that reactive oxygen species (ROS) such as singlet oxygen, hydrogen peroxide, OH radicals, peroxide radicals, and ozone are generated in the gas by the plasma processing, and these kill target microorganisms or decompose and modify chemical substances through oxidation reactions or the like. Examples of microorganisms include various bacteria, viruses, and mold.

[0066] By utilizing these functions, the plasma processing apparatus 100 of this embodiment can be used for purposes such as deodorization, odor removal, sterilization, disinfection, and air purification in many industrial fields, including medicine (fiberscopes, endoscopes, various small cameras, etc.), housing, civil engineering, construction, agriculture, fisheries, livestock farming, food processing, transportation, storage, and retail.

[0067] 8 is a partial cross-sectional circuit diagram showing a plasma processing apparatus according to a modification of this embodiment. The plasma processing apparatus 100a shown in FIG. 8 differs from this embodiment in that the upper dielectric layer 111a disposed below the upper electrode 112 is removed. Even with this modification, the same effects as those of the embodiment shown in FIG. 7 can be obtained.

[0068] Second Embodiment Next, a plasma processing apparatus according to a second embodiment of the present invention will be described. From the second embodiment onward, differences from the first embodiment will be mainly described. As shown in FIG. 9, a plasma processing apparatus 200 according to this embodiment is different in that the upper electrode 112 and the lower electrode 113 are covered with a single, integrally formed dielectric layer 202, and the air layer 105 as in the first embodiment is not provided. In other words, the difference is that the single dielectric layer 202 is filled between the upper electrode 112 and the lower electrode 113.

[0069] In this embodiment, the generation of ion wind from DC electrode 102 is the same, but the wind flow caused by the ion wind from one side to the other around plasma generating unit 204 is made up of wind flow A flowing along the upper surface of upper electrode 112 and wind flow B flowing along the lower surface of lower electrode 113. Plasma-treated gas (active oxygen species) is generated by contact with gas outside upper electrode 112 and lower electrode 113, and this plasma-treated gas can be sent out in direction D opposite the negative electrode of DC electrode 102 by wind flow A and wind flow B.

[0070] Third Embodiment Next, a plasma processing apparatus 300 according to a third embodiment of the present invention will be described. As shown in Fig. 10, the plasma processing apparatus 300 according to this embodiment differs in that it has an upper extension 302 extending outward beyond the outer edge of the upper-layer electrode 112 at the outer edge of the upper dielectric layer 111a, and a lower extension 304 extending outward beyond the outer edge of the lower-layer electrode 113 at the outer edge of the lower dielectric layer 111b. Another difference is that DC electrodes 306 and 308 are disposed on the upper extension 302 and the lower extension 304, respectively.

[0071] In this embodiment, the DC electrodes 306 and 308 are disposed on both the upper extension portion 302 and the lower extension portion 304, respectively. However, this is not limiting and the DC electrodes may be disposed on at least one of the upper extension portion 302 (upper dielectric layer 111a) and the lower extension portion 304 (lower dielectric layer 111b). In this embodiment, the DC electrode 306 is disposed on the lower surface of the upper extension portion 302 of the upper dielectric layer 111a, and the DC electrode 308 is disposed on the upper surface of the lower extension portion 304 of the lower dielectric layer 111b. However, this is not limiting. For example, provided that a sufficient physical distance can be maintained, a similar effect can be obtained even if one DC electrode 306 is disposed on the same surface as the upper-layer electrode 112 (the upper surface of the upper extension portion 302) and the other DC electrode 308 is disposed on the same surface as the lower-layer electrode 113 (the lower surface of the lower extension portion 304).

[0072] In this embodiment, by forming DC electrodes 306, 308 for generating ion wind into the same structure as upper electrode 112 and lower electrode 113 for generating plasma, it is possible to reduce the number of parts and the number of assembly steps. Furthermore, upper dielectric layer 111a and lower dielectric layer 111b can function as structures that support upper electrode 112 and lower electrode 113, in addition to functioning as dielectric layers.

[0073] <Fourth embodiment> Next, a plasma processing apparatus 400 according to a fourth embodiment of the present invention will be described. As shown in Fig. 11, the plasma processing apparatus 400 according to this embodiment differs from the previous embodiments in that a plasma generating unit 402 for generating plasma is composed of two or more pairs of electrode layers.

[0074] The plasma generation unit 402 is composed of two sets of electrode layers: a first upper-layer electrode 404 and a first lower-layer electrode 406 arranged on the upper side, and a second upper-layer electrode 408 and a second lower-layer electrode 410 arranged on the lower side. A first upper dielectric layer 412 is arranged on the upper surface of the first upper-layer electrode 404, and a first lower dielectric layer 414 is arranged on the upper surface of the first lower-layer electrode 406. A second upper dielectric layer 416 is arranged on the upper surface of the second upper-layer electrode 408, and a second lower dielectric layer 418 is arranged on the upper surface of the second lower-layer electrode 410.

[0075] Furthermore, a first air layer 420 is provided between the first upper electrode 404 and the first lower dielectric layer 414, spaced a predetermined distance apart in a direction perpendicular to the axis of the plasma generating unit 402. A second air layer 422 is provided between the first lower electrode 406 and the second upper dielectric layer 416, spaced a predetermined distance apart in a direction perpendicular to the axis of the plasma generating unit 402. A third air layer 424 is provided between the second upper electrode 408 and the second lower dielectric layer 418, spaced a predetermined distance apart in a direction perpendicular to the axis of the plasma generating unit 402.

[0076] In this embodiment, an ion wind is generated toward one end (edge) 426 of first upper layer electrode 404 and first lower layer electrode 406, and also toward one end (edge) 426 of second upper layer electrode 408 and second lower layer electrode 410. As a result, this ion wind generates a wind flow from one side to the other around plasma generation unit 402. This wind flow is made up of wind flow E flowing through first air layer 420 along the lower surface of first upper layer electrode 404, wind flow F flowing through second air layer 422 along the lower surface of first lower layer electrode 406, wind flow G flowing through third air layer 424 along the lower surface of second upper layer electrode 408, and wind flow H flowing outside second lower layer electrode 410 along the lower surface of second lower layer electrode 410.

[0077] In this embodiment, two pairs of electrode layers are provided to form a multi-stage structure, which improves the plasma generation efficiency and allows the active oxygen species generated by plasma processing to be diffused more efficiently by the air flows E, F, G, and H. Furthermore, the first upper-layer electrode 404, the first lower-layer electrode 406, the second upper-layer electrode 408, and the second lower-layer electrode 410 are arranged with electrodes of different polarities alternately. This allows plasma to be generated not only in the first air layer 420 and the third air layer 424, but also in the second air layer 422 between the first lower-layer electrode 406 and the second upper-layer electrode 408. Furthermore, according to this embodiment, the plasma processing apparatus 400 can be easily manufactured by simply stacking multiple basic units (components each having an electrode disposed on the lower surface of a dielectric layer) at intervals. Note that the number of pairs of electrode layers may be three or more. This further improves the plasma generation efficiency and the diffusion efficiency of active oxygen species.

[0078] 11, in this embodiment, plasma can also be generated in the region (area surrounded by dashed lines) between the DC electrode 102 that generates the ion wind and the first and second upper-layer electrodes 404, 408 and the first and second lower-layer electrodes 406, 410 that generate plasma. Therefore, this embodiment has the advantage of being able to generate more plasma than simply blowing air with a fan only to plasma generating electrodes (upper-layer electrode and lower-layer electrode) of the same size.

[0079] 12 is a partial cross-sectional schematic circuit diagram showing a plasma processing apparatus according to a modification of this embodiment. Plasma processing apparatus 400a shown in FIG. 12 differs from this embodiment in that multiple (two) DC electrodes 102a, 102b (negative electrodes) for generating ionic wind are arranged in accordance with the overall thickness of the electrodes for generating plasma. In this modification, the same effects as this embodiment can be obtained, and ionic wind can be generated more efficiently, and the wind flow resulting from this ionic wind can be efficiently directed between the multiple electrodes for generating plasma.

[0080] FIG. 13 is an equivalent circuit diagram of FIG. 10 , in which two transformers are used instead of the single tapped transformer. While the embodiments and modifications of the present invention use a single tapped transformer 104, this is not limiting. For example, in the plasma processing apparatus 300a shown in FIG. 13 , two transformers 104a and 104b may be used instead of the single tapped transformer 104, and two AC power supply units 101a and 101b may be electrically connected to each of the transformers 104a and 104b. Note that the two AC power supply units 101a and 101b must be appropriately synchronized in frequency and phase. Alternatively, two identical high-frequency oscillators may be used and connected to each of the transformers 104a and 104b. Although the equivalent circuit diagram shown in FIG. 13 uses a transformer circuit using two transformers 104a and 104b, this is not limiting and a transformer circuit using multiple transformers may be used.

[0081] In each embodiment of the present invention, the fluid, particularly the air, passing through the air layers 105, 420, 422, and 424 is assumed to flow from the right to the left in the figure, and not in the vertical direction of the arrows (air flows E, F, and G). Therefore, to actually create such a device, a structure is required to stop the flow of fluid in the vertical direction of the arrows, and a structure is required to physically hold the electrodes 112, 113, etc. in the correct positions. These may be either conductors or insulators (or dielectrics) as long as they are sufficiently far from the electrodes, but insulators are preferable.

[0082] Furthermore, a high voltage is applied to upper layer electrode 112 and lower layer electrode 113, and a mechanism (not shown) for protecting them or for safety reasons is also required. For example, safety can be improved by placing a sufficiently thick insulator (or dielectric) containing air outside upper layer electrode 112 and lower layer electrode 113. Furthermore, safety can be further improved by placing a conductor with a potential similar to the ground potential outside the insulator (or dielectric).

[0083] Although the embodiments and modifications of the present invention have been described above, appropriate design changes are possible within the scope of the present invention. [Explanation of symbols]

[0084] 100, 100a, 200, 300, 300a, 400, 400a Plasma processing apparatus 101 AC power supply section 102, 102a, 102b, 306, 308 DC electrode 103 DC power supply section 104 Tapped transformer 104a, 104b transformer 105, 420, 422, 424 Air layer 110, 110a, 402 plasma generating unit 111a upper dielectric layer 111b Lower dielectric layer 112, 404, 408 Upper layer electrode (layer) 113, 406, 410 Lower electrode (layer) 114, 426 End 202 Dielectric layer 302 Upper extension part 304 Lower extension part W1, W2, W3, W4 Ion Wind A, B, C, E, F, G, H Wind flow

Claims

1. a plasma generating unit that has at least a pair of electrode layers and a dielectric layer provided between the pair of electrode layers and generates plasma; an AC power supply unit that applies an AC voltage to the pair of electrode layers; a DC power supply unit disposed on one side of the electrode layer in the axial direction and having a DC electrode that generates an ionic wind directed toward one end of the electrode layer; a tapped transformer electrically connected to the AC power supply unit and the DC power supply unit, or a transformer circuit using a plurality of transformers; A plasma processing apparatus comprising:

2. 2. The plasma processing apparatus according to claim 1, The pair of electrode layers includes an upper electrode layer and a lower electrode layer, A plasma processing apparatus characterized in that an air layer through which the ion wind flows is provided between the upper electrode layer and the lower electrode layer which are arranged apart from each other.

3. 2. The plasma processing apparatus according to claim 1, The pair of electrode layers includes an upper electrode layer and a lower electrode layer, The plasma processing apparatus is characterized in that the dielectric layer is filled between the upper electrode layer and the lower electrode layer.

4. 3. The plasma processing apparatus according to claim 2, an outer edge of the dielectric layer has an extension portion that extends outward beyond an outer edge of the electrode layer; The plasma processing apparatus is characterized in that the DC electrode is disposed on the extension portion.

5. 5. The plasma processing apparatus according to claim 4, the dielectric layer includes an upper dielectric layer and a lower dielectric layer; The plasma processing apparatus is characterized in that the DC electrode is disposed on at least one of the upper dielectric layer and the lower dielectric layer.

6. 2. The plasma processing apparatus according to claim 1, The plasma processing apparatus is characterized in that the plasma generating unit is composed of two or more pairs of the electrode layers.

7. 2. The plasma processing apparatus according to claim 1, The plasma processing apparatus is characterized in that the DC electrode is composed of one or more electrodes.

8. 2. The plasma processing apparatus according to claim 1, A plasma processing apparatus characterized in that plasma is generated between the DC electrode and the electrode layer.

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