JP4765648B2 - Micro plasma jet generator - Google Patents

Description

  The present invention relates to a microplasma jet generator, and more particularly to a microplasma jet generator that can generate a microplasma jet with high reliability.

  Conventionally, vacuum plasma generators and atmospheric pressure plasma generators are large in size and cannot be applied to devices that are mounted on a robot and operated. However, in recent years, micro induction under atmospheric pressure has been impossible. A small microplasma jet generator that generates a combined plasma jet has been proposed (see, for example, Patent Document 1).

  As shown in FIG. 14, the microplasma jet generator includes a substrate 31, a corrugated microantenna 32 disposed on the substrate 31, and a discharge tube 33 disposed in the vicinity of the microantenna 32. By using the plasma chip 30 provided, gas is supplied from one end of the discharge tube 33 by the gas supply means 34, and high-frequency power in the VHF band is supplied from the high-frequency power source to the microantenna 32. The plasma P which is satisfactorily stabilized in the minute space in the discharge tube 33 with low power is generated and blown out as a microplasma jet.

Further, as a method of disposing the microantenna 32 on the substrate 31, a manufacturing process as shown in FIG. 15 is disclosed. In FIG. 15, a resist mask 35 having an opening 34 in the shape of a microantenna 32 is first formed on a substrate 31 as shown in (a), and then the substrate is formed by RF magnetron sputtering as shown in (b). A metal material 36 for forming the microantenna 32 is plated on 31. At this time, a chromium layer is preferably provided as an adhesive layer. Next, as shown in (c), the metal material 36 in the shape of the micro antenna 32 is left by lift-off, and electrolytic plating is performed thereon to form the micro antenna 32 having a desired thickness. Finally, as shown in (d), the plasma chip 30 is manufactured by adhering a plate material 37 of the same material to the back surface of the substrate 31 and sealing and forming the discharge tube 33.
Japanese Patent No. 3616088

  By the way, when microplasma is generated using the plasma chip 30 disclosed in Patent Document 1, there are the following problems. First, when 50 W of electric power is supplied to the microantenna 32, the temperature rises to 70 ° C. if the substrate 31 is alumina and 320 ° C. if the substrate 31 is quartz. This is as high frequency as possible to increase the plasma intensity. The resistance heat generation of the microantenna 32 adjusted to increase the amplitude of the current and the heat dissipation through the substrate 31 are balanced to reach the temperature, and the microantenna 32 itself rises above that temperature. However, it is like an electric heater. Therefore, when plasma is generated for a long time, there is a problem that the microantenna 32 is lifted from the substrate 31 to deteriorate the heat dissipation state, and the pattern portion of the microantenna 32 may be burned out.

  Second, the resistance of the microantenna 32 increases as the temperature rises, and as the resistance increases, the resistance becomes higher, the balance of the matching circuit is lost, and the reflected wave from the microantenna 32 changes significantly. There is a problem that the power supplied to the power source is reduced and the plasma intensity is reduced.

  Third, as the high frequency power to be supplied, a VHF frequency band typified by 100 MHz is used. When such a frequency band is reached, the current flows through the conductor surface and the thickness of the conductor from the conductor surface through which the current flows. More than twice the depth is required, and the thickness of the micro antenna 32 made of copper plating is required to be about 100 μm at 100 MHz, but to form the micro antenna 32 having a thickness of 100 μm by electroplating. The electroplating of several hours is required, and there is a problem that productivity is poor.

  Fourth, as a structure in which the discharge tube 33 is disposed in the vicinity of the microantenna 32, a plate material 37 is bonded to the back surface of the substrate 31 on which the microantenna 32 is disposed, and the groove formed on the back surface of the substrate 31 is sealed. Although the discharge tube 33 is formed, the microantenna 32 and the discharge tube 33 cannot be arranged close to each other in order to secure the strength of the substrate 31, and there is a limit to increasing the plasma generation efficiency. Have a problem.

  The present invention solves the above-described conventional problems, and an object of the present invention is to provide a microplasma jet generator that can reliably prevent an abnormal temperature increase of a microantenna and can generate a plasma jet with high reliability. And

Microplasma jet generating device of the present invention includes a micro-antenna wavy form of multi-turn, and discharge electric tube, and a high-frequency power source for supplying high frequency power to the micro-antenna, a gas supply for supplying gas to one end of the discharge tube A micro-plasma jet generator that generates plasma from the other end of the discharge tube by an inductively coupled method using a high-frequency current flowing through the micro-antenna. A groove for a discharge tube is formed at a position facing one side of the pair of substrates on one surface of the pair of substrates facing the micro-antenna on the surface facing the other substrate. The discharge tube is constituted by a dielectric plate made of a dielectric material disposed between them.

  According to this configuration, since the microantenna is sandwiched between the pair of substrates, even if a high-frequency current flows through the microantenna and generates heat, both surfaces of the microantenna are restrained by the substrate and are not lifted from the substrate. Since heat is effectively dissipated through both substrates in contact with each other, there is no risk of the microantenna becoming abnormally hot and burning out. There is no fear that the balance will be lost, the reflected wave will become stronger, the input of high frequency power will decrease, and the plasma intensity will decrease, and the micro antenna is manufactured by processing a metal plate. Compared with production by electroplating, it can be manufactured at a much lower cost and with higher productivity.

The microantenna includes a plurality of winding-shaped micro-antennas, a discharge tube, a high-frequency power source that supplies high-frequency power to the micro-antenna, and a gas supply unit that supplies gas to one end of the discharge tube. In a microplasma jet generator that generates plasma from the other end of the discharge tube by an inductively coupled method using a flowing high-frequency current, the microantenna manufactured by processing a metal plate is disposed between a pair of substrates, and In one of the pair of substrates, a discharge tube groove is formed at a position facing the micro-antenna on the surface facing the other substrate, and a tube made of a dielectric is disposed in the groove to form the discharge tube. This makes it possible to place the discharge tube close to the microantenna simply by placing the dielectric tube in the groove of the substrate. It can, it is possible to generate a plasma at a high efficiency by more simple and cheap structure. In addition, by extending the dielectric tube from the side of the substrate to an appropriate length, an arbitrary interval can be provided between the plasma blowing position and the substrate, and the degree of freedom in design of the plasma jet blowing position. Further, the degree of freedom in designing the blowing position of the plasma jet can be further increased by bending the extending portion of the tube into an L shape or the like .

Further, in the other substrate, a concave portion that accommodates the microantenna is formed on a surface facing the one substrate in accordance with the shape of the microantenna, and preferably, in the one substrate, A shallow groove-like recess is formed to accommodate and place the dielectric plate, so that high-density plasma is stably generated with low power, and the plasma blows out from the other end of the discharge tube to generate a plasma jet. To do .

  According to the microplasma jet generator of the present invention, since the microantenna is sandwiched between a pair of substrates, even if the microantenna generates heat, it is effectively dissipated through both substrates without being lifted from the substrate, There is no risk of burning the micro antenna at an abnormally high temperature, and since the micro antenna does not reach a higher temperature than specified, the matching circuit is unbalanced due to an increase in resistance, reducing the input of high-frequency power and reducing the plasma intensity. In addition, since the micro antenna is manufactured by processing a metal plate, it can be manufactured at a much lower cost and with higher productivity as compared with the case where it is manufactured by conventional electroplating.

  Hereinafter, each embodiment of the microplasma jet generator of the present invention will be described with reference to FIGS.

(First embodiment)
First, a first embodiment of the microplasma jet generator of the present invention will be described with reference to FIGS.

  As shown in FIGS. 1 and 2, the microplasma jet generator 1 according to the present embodiment is formed in a pair of alumina substrates 2 and 3 and a plurality of windings in a wavy form, and between the substrates 2 and 3. A microantenna 4 sandwiched between, a discharge tube 5 disposed in the vicinity of the microantenna 4, and a gas supply means 6 for supplying a plasma generating gas G such as an inert gas to one end of the discharge tube 5; And a high frequency power source (not shown) for supplying the microantenna 4 with high frequency power in the VHF frequency band.

  Both substrates 2 and 3 are fixed integrally with an adhesive or the like with the micro-antenna 4 sandwiched between them, a method of fastening and fixing with bolts and nuts or screws, a method of fixing with other appropriate fixing tools, etc. It is integrated with. The high-frequency power source (not shown) outputs a high frequency in the VHF band having a frequency of about 100 to 500 MHz, for example, and the output is about 20 to 100 W. A matching circuit (not shown) that adjusts the input of the reflected wave from the micro antenna 4 to the high frequency power source near zero is interposed between the high frequency power source and the micro antenna 4.

  The microantenna 4 is made of a metal having a low specific resistance value, for example, copper (specific resistance: 17.2 nΩm (20 ° C.), temperature coefficient: 0.004 / ° C.), silver (specific resistance: 16.2 nΩm (20 ° C.), temperature Coefficient: 0.004 / ° C., gold (specific resistance: 24.0 nΩm (20 ° C.), temperature coefficient: 0.0034 / ° C.), aluminum (specific resistance: 28.2 nΩm (20 ° C.), temperature coefficient: 0.00. (004 / ° C.) or the like, and is formed by punching or cutting a metal thin plate or metal foil. The material of the microantenna 4 is most preferably copper, and the thickness thereof is more than twice the depth from the surface through which the high-frequency current flows. For example, when the frequency of the high-frequency current is 100 MHz, the thickness is about 100 μm. That is preferred.

  In this embodiment, as shown in FIG. 3, the microantenna 4 is accommodated in an arrangement recess 7 formed on the surface of one substrate 2 facing the other substrate 3, and an adhesive is used as necessary. Are sandwiched from both sides by a pair of substrates 2 and 3 in a state where they are bonded and fixed together. The arrangement recess 7 of the substrate 2 is formed by processing according to the shape of the microantenna 4, and the depth is preferably processed to be equal to or slightly shallower than the thickness of the microantenna 4.

  The discharge tube 5 includes a groove 8 formed at a position facing the micro antenna 4 on the surface of the other substrate 3 facing the one substrate 2, and a dielectric disposed between the groove 8 and the micro antenna 4. The dielectric plate 9 is configured such that the thickness of the dielectric plate 9 is the distance between the microantenna 4 and the discharge tube 5. Further, a shallow groove-like recess 10 for accommodating and arranging the dielectric plate 9 is formed at a position where the dielectric plate 9 of the other substrate 3 is arranged, and the other substrate is accommodated in the state where the dielectric plate 9 is accommodated in the shallow groove-like recess 10. 3, the surface facing the one substrate 2 is substantially flush.

  In the above configuration, by supplying high-frequency power to the microantenna 4 while supplying the gas G from one end of the discharge tube 5, a dielectric magnetic field generated by a high-frequency current flowing through the microantenna 4 in the minute discharge tube 5 at atmospheric pressure. In the inductive coupling method, a part of ions and electrons are efficiently captured, a high-density plasma P is stably generated with a small electric power, the plasma P blows out from the other end of the discharge tube 4, and a plasma jet is generated. appear.

  According to the microplasma jet generator 1, since the microantenna 4 is sandwiched between the pair of substrates 2 and 3, even if a high-frequency current flows through the microantenna 4 and generates heat, both sides of the substrate 2 and 3 Since the heat is effectively dissipated from both sides through the substrates 2 and 3 made of alumina having good thermal conductivity without being lifted from the substrates 2 and 3, the microantenna 4 becomes an abnormally high temperature and burns out. In addition, the resistance of the micro-antenna 4 increases as the microantenna 4 becomes higher than a predetermined temperature, the matching circuit is unbalanced, the reflected wave becomes stronger, the input of high-frequency power is reduced, and the plasma intensity is reduced. There is no fear of such a situation. Moreover, since the micro antenna 4 is manufactured by cutting a thin metal plate or metal foil by laser cutting or stamping, etc., the cost is much lower than that of conventional electroplating. Can be manufactured with good productivity.

  The discharge tube 5 includes a groove 8 formed on the other substrate 3 and a dielectric plate 9 made of a dielectric disposed between the groove 8 and the microantenna 4. Since it is sandwiched between the substrates 2 and 3, there is no problem in strength even if a thin dielectric plate 9 is used. As a result, only the thin dielectric plate 9 is interposed between the microantenna 4 and the discharge tube 5. The distance between the microantenna 4 and the discharge tube 5 is shortened, and the plasma P can be generated with high efficiency.

  Moreover, since the thickness of the micro antenna 4 is set to about 100 μm and is set to be twice or more the depth from the surface through which the high frequency current of 100 MHz flows, the micro antenna 4 can be made to the minimum necessary thickness. In addition, since the microantenna 4 is accommodated in the arrangement recess 7 formed on the one substrate 2, the arrangement fixing of the microantenna 4 to the substrate is accommodated in the arrangement recess 7 of the one substrate 2 and the other substrate 3. The manufacturing process can be reduced by reducing the number of assembly steps, and the thickness of the microantenna 4 can be reduced as described above, so that the processing of one substrate 2 can be reduced and the cost can be reduced. be able to.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIGS. In the following description of the embodiments, components that are the same as those in the preceding embodiment are denoted by the same reference numerals, description thereof is omitted, and only differences will be mainly described.

  In the present embodiment, as shown in FIG. 4, wiring boards 11 a and 11 b that supply high-frequency power to the microantenna 4 are integrally attached to a pair of substrates 2 and 3. Specifically, as shown in FIGS. 5 and 6, part of the wiring boards 11 a and 11 b so that the ends of the wiring boards 11 a and 11 b overlap the terminal parts 4 a and 4 b at both ends of the microantenna 4. Is inserted and fixed between the substrates 2 and 3 and sandwiched between the substrates 2 and 3. In order to sandwich a part of the wiring boards 11a and 11b between the boards 2 and 3 without creating a gap between them, the wiring boards 11a and 11b are placed on the other board 3 as shown in FIG. Shallow housing recesses 12a and 12b are formed for housing a part of each.

  According to this configuration, since the wiring boards 11a and 11b for supplying power to the microantenna 4 are arranged between the pair of substrates 2 and 3, the wiring boards 11a and 11b are arranged in a compact configuration. In addition, the connection portion of the wiring boards 11a and 11b with the micro-antenna 4 that generates the most heat is effectively cooled through the substrates 2 and 3, and the increase in resistance due to the high temperature of the wiring boards 11a and 11b is also suppressed. And power can be supplied efficiently.

  In addition to the microantenna 4 and the dielectric plate 9, the wiring boards 11a and 11b are also sandwiched between the pair of substrates 2 and 3 while being accommodated in the accommodating recesses 12a and 12b formed on the other substrate 3. Therefore, by simply sandwiching the micro antenna 4, the dielectric plate 9, and the wiring boards 11a and 11b between the pair of boards 2 and 3, these can be arranged and fixed on the boards 2 and 3, and the number of assembly steps can be reduced and manufactured. Cost can be reduced.

(Third embodiment)
Next, a third embodiment of the present invention will be described with reference to FIGS.

  In the first embodiment, the arrangement recess 7 that accommodates and arranges the micro antenna 4 is formed on one substrate 2, and the shallow groove-like recess 10 that arranges the dielectric plate 9 that forms the discharge tube 5 on the other substrate 3. In the present embodiment, as shown in FIGS. 7 and 8, the micro antenna 4 is formed between the flat substrate 2 and the substrate 3 in which the grooves 8 constituting the discharge tube 5 are formed. The microplasma jet generator 1 is configured by sandwiching a thin flat intermediate dielectric plate 13 made of a dielectric material and fixing the substrates 2 and 3 to each other.

  Specifically, the microantenna 4 is positioned and arranged at a predetermined position on the surface of the substrate 2 facing the substrate 3 and bonded and fixed with an adhesive. With the dielectric plate 13 interposed, the substrate 2, the intermediate dielectric plate 13, and the substrate 3 are fastened together by screws 14 or the like and integrally fixed. 14 a is a screw hole provided in the substrate 3, and 14 b is a through hole of the screw 14 provided in the substrate 2 and the intermediate dielectric plate 13. Note that the microantenna 4 may be adhered to the intermediate dielectric plate 13 with an adhesive, and thermal conductivity is provided in a gap between the substrate 2 and the intermediate dielectric plate 13 corresponding to the thickness of the microantenna 4. The intermediate dielectric plate 13 and the substrate 3 may be bonded and fixed, and the whole may be bonded and fixed integrally.

  According to the present embodiment, since the microantenna 4 is fixed to the substrate 2 with an adhesive, it is not necessary to form the arrangement recess 7 for accommodating and arranging the microantenna 4, and the substrate 3 is also grooved. No. 8 is formed, and it is not necessary to form the shallow groove-like concave portion 10 that accommodates and arranges the dielectric plate 9, and it is not necessary to perform complicated processing on the substrates 2 and 3. Can do.

  In the present embodiment, when the wiring boards 11a and 11b are provided, a cutout (not shown) is provided in the intermediate dielectric plate 13 corresponding to the terminal portions 4a and 4b of the microantenna 4, and the cutout portions are provided. The connection end portions of the wiring boards 11a and 11b may be arranged on the board, and the wiring boards 11a and 11b may be sandwiched between the substrates 2 and 3 together with the intermediate dielectric plate 13. In this case, at least the connection end portions of the wiring boards 11 a and 11 b are set to have substantially the same thickness as the intermediate dielectric plate 13.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described with reference to FIGS.

In the present embodiment, as shown in FIGS. 9A and 9B, the discharge tube 5 is constituted by a dielectric tube 15 disposed in a groove 8 formed in the other substrate 3. . According to this configuration, the discharge tube 5 can be disposed close to the microantenna 4 simply by disposing the tube 15 made of a dielectric in the groove 8 of the substrate 3. Can generate plasma. When the dielectric tube 15 is used, the dielectric plate 9 used in FIG. 2 and the intermediate dielectric plate 13 used in FIG. 7 need not be used.

  Further, according to the configuration of the present embodiment, as shown in FIG. 9A, the plasma P blowing position is obtained by appropriately extending the tube 15 made of a dielectric material from the sides of the substrates 2 and 3. An arbitrary space can be provided between the substrate 2 and the substrate 2 and 3 and the degree of freedom in designing the blowing position of the plasma jet is increased. Furthermore, as shown in FIG. 10, the degree of freedom in designing the blowing position of the plasma jet can be further increased by bending the extending portion of the tube 15 made of a dielectric into an L shape or the like.

(Fifth embodiment)
Next, a fifth embodiment of the present invention will be described with reference to FIGS.

  In the present embodiment, as shown in FIG. 11, reactance elements 16 a and 16 b such as capacitors constituting the matching circuit 18 are formed on the outer surface of the substrate 2 or 3, that is, the surface not sandwiching the microantenna 4, and these reactance elements. Wiring boards 17a, 17b, and 17c made of copper plates that connect 16a and 16b, the microantenna 4, and the wiring boards 11a and 11b are disposed. As shown in FIG. 12, the matching circuit 18 is interposed between the microantenna 4 and the high frequency power source 19 to suppress the reflected wave from the microantenna 4 from being input to the high frequency power source 19 to near zero. is there. In FIG. 12, L is the inductance of the microantenna 4 and R is the internal resistance.

  According to the present embodiment, since the matching circuit 18 is disposed on the substrate 3, the matching circuit 18 can be disposed in the vicinity of the micro antenna 4, and the high frequency power in the VHF frequency band is supplied to the micro antenna 4. In addition, the distance between the matching circuit 18 and the microantenna 4 becomes long and power is not attenuated between them, so that the matching circuit 18 can be supplied efficiently and the matching circuit 18 is integrated on the substrate 3. Thus, the substrate 3 can be shared, and the microplasma jet generator 1 can be configured compactly.

(Sixth embodiment)
Next, a sixth embodiment of the present invention will be described with reference to FIG.

  In this embodiment, as shown in FIG. 13, one of the substrates 2 and 3, the substrate 2 in which the matching circuit 18 is not arranged in the illustrated example, is used as an apparatus made of an aluminum plate or a steel plate of the microplasma generator 1. The case 20 is arranged in surface contact. In FIG. 13, reference numeral 21 denotes an input connector provided on the outer surface of the device case 20, which is wired from a high-frequency power source with a coaxial cable and connected to the wiring board 11a. Further, the wiring board 11b is connected to the device case 20 so that the entire device case 20 is grounded. For this reason, a thin copper plate having good conductivity and low specific resistance is preferably disposed on the inner surface of the device case 20. Further, a thin copper plate may be disposed on the surface of the device case 20 in order to further reduce the resistance value between the device case 20 and the ground. Reference numeral 22 denotes a gas inlet provided on the outer surface of the apparatus case 20 and is connected to the discharge tube 5.

  According to this embodiment, since heat can be efficiently radiated from the substrate 2 to the device case 20, the temperature increase of the microantenna 4 can be further suppressed via the substrate 2 and the substrate 2, and the above-described present invention. The effect of can be further exhibited.

  In the description of the above embodiment, an example in which the substrate 2 or 3 is arranged in direct contact with the device case 20 is shown, but the substrate 2 or 3 is arranged in surface contact with a heat sink (not shown), The heat radiating plate may be coupled to the device case 20. In this way, heat can be efficiently radiated from the substrate 2 or 3 to the heat radiating plate, and the temperature rise of the substrate 2 or 3 can be further suppressed by radiating heat from the heat radiating plate to the outside through the device case. High effect can be demonstrated. For the substrates 2 and 3, alumina is used in the above embodiment, but the present invention is not limited to this, and heat conductive materials such as sapphire, aluminum nitride, silicon nitride, boron nitride, and silicon carbide are used. Good materials may be used.

  According to the microplasma jet generator of the present invention, since the microantenna is sandwiched between a pair of substrates, heat can be effectively radiated, the microantenna is not burned out, and the resistance of the microantenna is increased to increase the high frequency power. Since the micro antenna is manufactured by processing a metal plate, it can be manufactured at low cost and with high productivity. In particular, it can be suitably used for a small microplasma jet generator mounted on various devices.

The perspective view of 1st Embodiment of the microplasma jet generator of this invention. The exploded perspective view of the embodiment. The disassembled perspective view of one board | substrate and microantenna of the embodiment. The perspective view of 2nd Embodiment of the microplasma jet generator of this invention. The exploded perspective view of the embodiment. The perspective view of the other board | substrate of the embodiment. The disassembled perspective view of 3rd Embodiment of the microplasma jet generator of this invention. The perspective view of the embodiment. The 4th Embodiment of the microplasma jet control apparatus of this invention is shown, (a) is a perspective view, (b) is a bottom view. The perspective view of the modification structural example of the embodiment. The perspective view of 5th Embodiment of the microplasma jet generator of this invention. The block diagram of the circuit structure of the embodiment. The perspective view of 5th Embodiment of the microplasma jet generator of this invention. The perspective view of the microplasma jet generator of a prior art example. The perspective view which shows the plasma chip manufacturing process in the prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Microplasma jet generator 2 Substrate 3 Substrate 4 Microantenna 5 Discharge tube 6 Gas supply means 7 Arrangement recessed part 8 Groove 9 Dielectric plate 10 Shallow groove-shaped recessed part 11a, 11b Wiring board 12a, 12b Housing recessed part 13 Intermediate dielectric plate 15 Dielectric Tube made of 19 high frequency power supply 20 device case P plasma G gas

Claims (4)

A high frequency current that flows through the microantenna, comprising a multi-turn corrugated microantenna, a discharge tube, a high frequency power source that supplies high frequency power to the microantenna, and a gas supply means that supplies gas to one end of the discharge tube In the microplasma jet generator for generating plasma from the other end of the discharge tube by an inductive coupling method with current,
The micro antenna manufactured by processing a metal plate is disposed between a pair of substrates, and one substrate of the pair of substrates is positioned at a position facing the micro antenna on a surface facing the other substrate. A microplasma jet generator comprising: a discharge tube formed by a dielectric plate made of a dielectric formed between a groove for the discharge tube and the microantenna. A high frequency current that flows through the microantenna, comprising a multi-turn corrugated microantenna, a discharge tube, a high frequency power source that supplies high frequency power to the microantenna, and a gas supply means that supplies gas to one end of the discharge tube In the microplasma jet generator for generating plasma from the other end of the discharge tube by an inductive coupling method with current,
Place the micro antenna manufactured by processing a metal plate between a pair of substrates,
In one of the pair of substrates, a discharge tube groove is formed at a position facing the microantenna on a surface facing the other substrate, and a tube made of a dielectric is disposed in the groove, thereby the discharge tube. luma to a characterized by being configured to Lee black plasma jet generator.   3. The microplasma jet generation according to claim 1, wherein a concave portion for accommodating the microantenna is formed on a surface of the other substrate facing the one substrate in accordance with the shape of the microantenna. apparatus.   2. The microplasma jet generator according to claim 1, wherein a shallow groove-like recess for accommodating and arranging the dielectric plate is formed on the one substrate.

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