JP5283185B2 - Electret manufacturing method and manufacturing apparatus thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for manufacturing an electret that can shorten a time needed to manufacture the electret. <P>SOLUTION: The device 100 for manufacturing the electret includes: an upper chamber 101 into which a helium gas is injected; a lower chamber 102 in which an argon gas is added to air; a pedestal 104 for holding a silicon microphone 110; electrodes 105 and 106 provided to the pedestal 104; a DC power source 107 for applying a DC voltage between the electrodes 105 and 106; and an ionizing radiation generating device 108 for generating an ionizing radiation. The device 100 is configured to generate positive ions and negative ions by the ionizing radiation to electrostatically charge a silicon oxide film 132 provided to a back plate 130 to the negative polarity with the negative ions in a state wherein the DC voltage is applied to counter electrodes of the silicon microphone 110 in an atmosphere wherein the argon gas is added to the air. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an electret manufacturing method and an apparatus for manufacturing the same.

  Conventionally, as a method for producing a so-called electret in which a dielectric is held semipermanently, a corona discharge method, an electron beam method (for example, see Non-Patent Documents 1 and 2), a soft X-ray irradiation method ( For example, see Patent Documents 1 and 2). In addition, a sensor that uses an electret and can be operated without applying a voltage from the outside has been proposed (see, for example, Non-Patent Document 3).

  Of the above-described methods for producing electrets, the corona discharge method is often used industrially at present. Since the corona discharge method can be used without using a vacuum device as compared with the electron beam method, it is possible to manufacture an electret at a reduced equipment cost.

  However, (1) when performed in the atmosphere, harmful ozone is generated when generating the charge necessary for electretization that holds the electric charge in the dielectric. (2) Uniform in a curved surface shape. There are problems that it is difficult to manufacture electrets, and (3) an element having a structure in which ions cannot be supplied cannot be electretized.

  Therefore, as described in Patent Documents 1 and 2, an electret manufacturing method using ionizing radiation such as soft X-rays has been proposed. Although the above-mentioned problems have been solved by using this electret manufacturing method using ionizing radiation, a new problem arises that the time required for manufacturing the electret is longer than that of the corona discharge method. . In particular, as the distance between one electrode provided with the dielectric material to be electret and the other electrode becomes shorter, the number of ions generated by ionizing radiation in the gap between both electrodes decreases, so this problem is Remarkably appeared. As a result, there has been a problem in the industry that the equipment cost and the production cost increase due to an increase in the manufacturing time of the electret.

JP-A-11-117172 Japanese Patent Laid-Open No. 03-006500

"Electrostatic Handbook", Electrostatics Society, P1108, Ohmsha “Electrets” edited by G.M.Sessler, Lapracian Press “Microphone Technical Handbook” by Hiroo Takayanagi, P35, Kenrokukan Publishing

  The present invention has been made in view of the circumstances as described above, and an object of the present invention is to provide an electret manufacturing method and a manufacturing apparatus thereof that can shorten the time required for manufacturing the electret.

An electret manufacturing method according to the present invention includes: an ionizing radiation generating apparatus that generates ionizing radiation; a housing that houses an element having two substrates each formed with opposing electrodes; and a pedestal on which the element is disposed. , a electret production method using electret manufacturing apparatus having a, on one side facing either before Symbol pair counter electrode and a dielectric disposed disposing a dielectric, the element to the base Arranging and dividing the inside of the housing into a first chamber containing the ionizing radiation generator and a second chamber containing the other substrate by one of the two substrates, and transmitting the one substrate An ionizing radiation irradiating step for generating ionizing radiation to irradiate the dielectric; and a gas having a lower transmittance of the ionizing radiation than air in a predetermined energy range of the ionizing radiation. In a state of setting the second chamber to the free atmosphere, the counter electrode a DC voltage is applied between the dielectric by either one of the positive and negative ions generated between the counter electrode by said ionizing radiation And a dielectric charging step for charging the substrate.

  With this configuration, the electret manufacturing method of the present invention applies a DC voltage between the counter electrodes in an atmosphere containing a gas having a lower transmissivity of ionizing radiation than air, and applies ionizing radiation between the counter electrodes. Since the dielectric is charged by positive ions or negative ions generated between the counter electrodes, the time required for manufacturing the electret can be shortened.

  In the electret manufacturing method of the present invention, it is preferable that the gas is neon, argon, krypton, xenon, or a mixed gas thereof.

  Furthermore, in the method of manufacturing an electret according to the present invention, in the dielectric charging step, the potential of the other electrode is made lower than the electrode on the side where the dielectric is disposed, and the dielectric is charged negatively by the negative ions. It has the composition to make it.

  With this configuration, the electret manufacturing method of the present invention can manufacture a negatively charged electret.

  Furthermore, in the method of manufacturing an electret according to the present invention, in the dielectric charging step, the potential of the other electrode is made higher than the electrode on the side where the dielectric is disposed, and the dielectric is positively charged by the positive ions. It has the composition to make it.

  With this configuration, the electret manufacturing method of the present invention can manufacture a positively charged electret.

  Furthermore, in the method of manufacturing an electret according to the present invention, in the ionizing radiation irradiation step, the space from the ionizing radiation generating device that generates the ionizing radiation to the electrode on the ionizing radiation device side of the counter electrode in the energy range. It has the structure made into the atmosphere containing the gas whose transmittance | permeability of the said ionizing radiation is higher than air.

  With this configuration, the electret manufacturing method of the present invention can reduce the probability that ionizing radiation is absorbed in the space from the electrode on the side of the ionizing radiation device to the ionizing radiation generating device in the counter electrode. Radiation can pass through the electrode on the side of the ionizing radiation irradiation device, and the number of ions generated between the counter electrodes can be increased.

The electret manufacturing apparatus of the present invention is an ionization that irradiates the dielectric disposed on the opposing surface side of any one of the opposing electrodes with each other through the electrodes of the opposing electrodes and irradiates with ionizing radiation. A radiation generator , an element having two substrates each formed with the counter electrode, a housing for housing the ionizing radiation generator, a pedestal on which the element is disposed, and a DC voltage applied between the counter electrodes And a gas generating means for generating a gas having a lower transmittance of the ionizing radiation than air in a predetermined energy range of the ionizing radiation, and one of the two substrates has the element By being arranged on the pedestal, the inside of the housing is divided into a first chamber containing the ionizing radiation generator and a second chamber containing the other substrate, Means is for supplying the generated gas into the second chamber, the DC power source, positive ions between the counter electrode is generated between the counter electrode and the ionizing radiation in the presence of the atmosphere containing the gas In addition, the dielectric is charged by one of negative ions and negative ions.

  With this configuration, the electret manufacturing apparatus of the present invention applies a DC voltage between the counter electrodes in an atmosphere containing a gas having a lower transmittance of ionizing radiation than air, and applies a DC voltage between the counter electrodes. Since the dielectric is charged by positive ions or negative ions generated between the counter electrodes, the time required for manufacturing the electret can be shortened.

  Furthermore, the electret manufacturing apparatus of the present invention has a configuration in which the first chamber contains a gas having a higher transmittance of the ionizing radiation than air in the energy range.

  With this configuration, the electret manufacturing apparatus of the present invention can reduce the probability that ionizing radiation is absorbed in the space from the electrode on the side of the ionizing radiation irradiation device to the ionizing radiation irradiation device among the counter electrodes. It is possible to increase the number of ions generated between the counter electrodes by allowing the ionizing radiation to pass through the electrode on the ionizing radiation irradiation device side.

  The present invention can provide an electret manufacturing method and an apparatus for manufacturing the electret having an effect that the time required for manufacturing the electret can be shortened.

The figure which shows the structure of the experimental apparatus regarding the manufacturing apparatus of the electret in 1st Embodiment of this invention. The figure which shows each transmittance | permeability, such as air and oxygen, in the range whose energy of a soft X-ray is 3 keV-9.5 keV The figure which shows the transmittance | permeability of helium, neon, argon, krypton, xenon, and air in the soft X-ray energy in the range of 3 keV to 9.5 keV. Diagram showing the relationship between the surface potential of the sample and the argon mixing ratio Diagram showing the relationship between sample surface potential and irradiation time The figure which shows the inside of the housing | casing of the manufacturing apparatus of the electret in 1st Embodiment of this invention. The figure which shows the inside of the housing | casing of the manufacturing apparatus of the electret in 2nd Embodiment of this invention. The figure which shows the inside of the housing | casing of the manufacturing apparatus of the electret in 3rd Embodiment of this invention.

  The inventor of the present invention, as a result of repeated examinations to solve the above-mentioned problems, irradiates between one electrode provided with a dielectric and the other electrode when irradiating with ionizing radiation. It has been found that an atmosphere containing a gas having a lower transmittance than air in the energy range of ionizing radiation is effective in solving the problem. Then, before describing embodiment of this invention, the experiment regarding the manufacturing method of the electret which concerns on this invention is demonstrated.

  FIG. 1 is a diagram illustrating a configuration of an experimental apparatus. FIG. 2 shows the transmittance of standard air (hereinafter referred to as “air”) and oxygen constituting the air when the soft X-ray energy is in the range of 3 keV to 9.5 keV when ionizing radiation is used. FIG. Further, FIG. 3 shows the transmittance of neon, argon, krypton, and xenon, which has a soft X-ray transmittance lower than that of air, and the transmittance of helium, which has a soft X-ray transmittance higher than that of air, in the energy range described above. FIG.

  As will be described later, according to the experimental results, since the total number of ions generated in the atmosphere containing the noble gas is increased in the atmosphere containing the rare gas than in the atmosphere containing only the air, the electret can be formed in a short time. It turns out that it becomes possible to manufacture. This is because (1) the rare gas has a higher absorption rate of soft X-rays than oxygen in the air, and therefore has a high probability of ionization, and (2) the rare gas absorbs soft X-rays and becomes positive ions. This is probably because electrons emitted from rare gas molecules act on oxygen in the air and the like, and the number of positive and negative ions generated from oxygen in the air also increases.

  Moreover, since noble gas is used, there is no problem of generation of corrosion or harmful gas. It has also been found that charges can be accumulated using positive ions generated from a rare gas. This not only increases the number of ions by acting on oxygen in the air as described above, but the positive ions generated from the rare gas themselves contribute to the charging of the dielectric, so that they can usually be obtained in the air. It becomes possible to manufacture an electret having a difficult surface potential.

  Hereinafter, based on the block diagram shown in FIG. 1, the content of an experiment is demonstrated concretely.

  First, a sample 10 in which a silicon oxide film 12 and a silicon nitride film 13 were sequentially stacked on a silicon substrate 11 was prepared. The surface potential of Sample 10 was measured in advance, and it was confirmed that the surface potential was 0V.

  Next, in the sealed casing 25, the sample 10 was placed on the metal plate 21, and a mesh-like grid electrode 23 made of SUS was disposed on the metal plate 21 at intervals so as not to touch the sample 10. Here, the distance from the grid electrode 23 to the surface of the sample 10 was 2.5 mm.

  Next, a DC power source 24 provided outside was connected to the grid electrode 23 (the polarity will be described later). The metal plate 21 was set to ground potential. An ionizing radiation generator 22 that generates soft X-rays having an energy of 3 keV to 9.5 keV is disposed above the grid electrode 23. Here, the distance from the ionizing radiation generator 22 to the surface of the sample 10 was 15 mm. In addition, an argon cylinder 31 was connected to the housing 25 via a valve 32, a flow meter 33 and a tube 34, and an air cylinder 35 was connected via a valve 36, a flow meter 37 and a tube 34. The argon cylinder 31 constitutes gas generating means according to the present invention.

  In the above-described configuration, argon gas and air are mixed at a predetermined ratio using the flow meters 33 and 37 and the valves 32 and 36, and the mixed gas is injected from the inlet 26 of the casing 25. A predetermined voltage was applied to the grid electrode 23 by the DC power supply 24 after a time necessary for sufficiently replacing the gas inside. Thereafter, the sample 10 was irradiated with soft X-rays, and the irradiation was stopped after a certain period of time. Then, voltage application by the DC power source 24 was stopped, the sample 10 was taken out from the housing 25, and the surface potential of the electret sample 10 was measured.

(Experiment 1)
Experiment 1 is an experiment in which the potential of the grid electrode 23 is set to −50 V and the sample 10 is irradiated with soft X-rays. Specifically, this is an experiment in which soft X-rays are irradiated on the sample 10 for 30 seconds, and the influence of the mixing ratio of argon gas and air on the surface potential of the sample 10 is examined. The result is shown in FIG.

  According to the results shown in FIG. 4, when argon gas was not added to the air, the surface potential of the sample 10 was only changed from 0V to -17V. However, the surface potential of sample 10 increased in the negative direction as the proportion of argon gas was increased, and increased most negatively to −31 V when the argon gas was increased to 80%. This corresponds to 3/5 of the applied voltage. Thereafter, when the argon gas was increased to 99.5%, the surface potential of the sample 10 became -21 V on the contrary.

  On the other hand, in the case where the sample 10 was irradiated with soft X-rays in the air without adding argon gas, in order to obtain a surface potential of −31 V as in the condition of adding 80% of argon gas to the air, FIG. As shown, it took about 300 seconds.

  From the above results, in the electret manufacturing method using soft X-rays, the time required to increase the charge amount of the dielectric material can be greatly shortened by arranging the dielectric material in an atmosphere containing argon gas. I understood.

(Experiment 2)
Experiment 2 is an experiment in which the potential of the grid electrode 23 is set to +50 V and the sample 10 is irradiated with soft X-rays as in Experiment 1.

  As a result of this experiment, when argon was not added to the air, the surface potential increased only to +7 V even when irradiated with soft X-rays. On the other hand, it was found that when the proportion of argon gas was increased to 99.5%, the surface potential increased to + 40V. This result corresponds to 4/5 of the applied voltage and shows that it is larger than the limit value 3/5 obtained in the air.

  On the other hand, from the results of the above-described Experiment 1 (FIGS. 4 and 5), the surface potential of the sample 10 is saturated at about −31 V when the mesh grid potential is −50 V regardless of the addition of argon. It turned out that it did not rise any more in the negative direction.

  On the other hand, according to the result of this experiment 2, when the potential of the grid electrode 23 is set to +50 V and the mixing ratio of argon is increased, the surface potential exceeding 3/5, which is the limit value obtained in air, is obtained. It turns out that it is obtained. This is presumably because a large amount of argon ions (positive ions) generated in addition to positive ions generated from the components in the air contribute to the injection of electric charges into the dielectric. For this reason, in an electret manufacturing method using soft X-rays, argon gas is generated between both electrodes without greatly increasing the voltage applied between one electrode provided with a dielectric and the other electrode. It was found that a surface potential larger than that obtained in the air can be obtained by making the atmosphere contained.

  Conventionally, in a silicon microphone, for example, if a desired voltage of the electret is 1, a voltage greatly exceeding 1 has to be applied between the vibrating electrode serving as a grid and the fixed electrode. Specifically, to obtain a voltage of 1, an applied voltage of about 5/3 was required. In addition, when a voltage of a certain level or more is applied, the vibrating electrode and the fixed electrode are attracted by electrostatic attraction, and in some cases, the vibrating electrode is destroyed. Therefore, a high voltage cannot be applied during manufacture of the electret, and the desired surface potential is It was not obtained. On the other hand, the result of this experiment 2 has shown that the manufacturing method of the electret which concerns on this invention can solve these problems.

(First embodiment)
Next, a first embodiment of an electret manufacturing apparatus according to the present invention will be described. In the present embodiment, an example of producing an electret condenser silicon microphone (hereinafter simply referred to as “silicon microphone”) electret among silicon electret elements formed by a semiconductor microfabrication technique and provided with opposing electrodes facing each other will be given. A case where the dielectric film provided on the silicon microphone is negatively charged will be described.

  First, the structure of the electret manufacturing apparatus in the present embodiment will be described. FIG. 6 is a diagram showing the inside of the housing of the electret manufacturing apparatus 100 in the present embodiment, and the housing itself is not shown.

  As shown in FIG. 6, the electret manufacturing apparatus 100 has a configuration in which the inside of the housing is divided into upper and lower parts, and an upper chamber 101 located at the upper portion of the housing and a lower chamber located at the lower portion of the housing. 102, and a partition plate 103 that partitions the upper chamber 101 and the lower chamber 102. Note that the upper chamber 101 and the lower chamber 102 constitute a first chamber and a second chamber according to the present invention, respectively. Further, the partition plate 103 constitutes a housing internal dividing means according to the present invention.

  In addition, the electret manufacturing apparatus 100 is provided on a pedestal 104 that holds the silicon microphone 110, an electrode 105 provided on the surface of the pedestal 104 on the upper chamber 101 side, and a surface of the pedestal 104 on the lower chamber 102 side. The electrode 106, a DC power source 107 that applies a DC voltage between the electrodes 105 and 106, and an ionizing radiation generator 108 that generates ionizing radiation. Note that the pedestal 104 constitutes a housing internal dividing means according to the present invention.

  The silicon microphone 110 has a structure in which the silicon substrate 111 on which the vibration film 120 is formed and the back plate 130 on which the sound hole 135 is formed face each other. Hereinafter, each surface where the vibration film 120 and the back plate 130 face each other is referred to as an “opposing surface”.

  The vibration film 120 has a thickness of about 2000 nm, and a gap of 10,000 nm or more is provided between the vibration film 120 and the back plate 130 with an insulating spacer 112 interposed therebetween.

  Further, as shown in the enlarged view, the vibration film 120 includes silicon 121 and an aluminum thin film 122 as an electrode formed on the outer surface of the silicon 121 (the back surface of the facing surface). The thickness of the aluminum thin film 122 is about 50 nm to 100 nm.

  As shown in the enlarged view, the back plate 130 includes silicon 131, a silicon oxide film 132 as a dielectric provided on the opposite surface side of the silicon 131, and a silicon nitride film 133 as a moisture-proof film provided on the upper surface thereof. I have. Further, an aluminum thin film 134 as an electrode is formed on the back surface of the facing surface of the silicon 131. Here, the thicknesses of the silicon oxide film are about 1000 nm, the silicon nitride film is about 200 nm, and the aluminum thin film 134 is about 50 nm to 100 nm, for example.

  In the upper chamber 101, an ionizing radiation generator 108 is disposed, and the back surface of the facing surface of the vibration film 120 through which the ionizing radiation emitted from the ionizing radiation generator 108 is transmitted, that is, the surface of the aluminum thin film 122 is exposed. .

  In the lower chamber 102, a back plate 130 having a silicon oxide film 132 that is a dielectric is exposed and the opposed surface of the vibration film 120 is exposed.

  The upper chamber 101 and the lower chamber 102 can individually inject an arbitrary gas.

  Specifically, it is preferable to inject the upper chamber 101 with a gas having a higher transmittance of ionizing radiation than air in a predetermined energy range of ionizing radiation, for example, helium gas. With this configuration, the probability that ionizing radiation is absorbed in the space from the ionizing radiation generator 108 to the vibrating membrane 120 can be reduced, so that a larger amount of ionizing radiation passes through the vibrating membrane 120 and the vibrating membrane 120 and the back plate The number of ions generated between 130 can be increased. The upper chamber 101 may be filled with only air.

  On the other hand, the lower chamber 102 is filled with a gas obtained by adding 20% to 95%, preferably 70% to 90%, argon to the air. At this time, for the sake of convenience, a gas nozzle is installed directly below the back plate 130 without using a sealed casing, and a mixed gas of air and argon gas is passed between the vibrating membrane 120 and the back plate 130 through the sound hole 135. It is good also as a structure sprayed on a space | gap. Alternatively, a gas nozzle may be installed on the side surface of the silicon microphone 110 and sprayed into the gap between the vibration film 120 and the back plate 130. Note that the lower chamber 102 may be 100% argon gas.

  The outer periphery of the pedestal 104 is coupled to the partition plate 103, and a through hole having a stepped portion is formed inside the pedestal 104. The pedestal 104 is made of an insulator, and the silicon microphone 110 is set on the stepped portion of the pedestal 104 so that the vibrating membrane 120 side becomes the ionizing radiation generator 108 side. When the silicon microphone 110 is set on the pedestal 104, the upper chamber 101 and the lower chamber 102 are separated from each other with the vibration film 120 as a boundary, and the aluminum thin film 122 and the electrode 105 of the vibration film 120 and the aluminum thin film 134 of the back plate 130 are separated. And the electrode 106 are electrically connected to each other.

  Next, the manufacturing method of the electret in this embodiment is demonstrated.

  First, the silicon microphone 110 on which the silicon oxide film 132 is not charged is set on the stepped portion of the pedestal 104. At that time, the aluminum thin films 122 and 134 are electrically connected to the electrodes 105 and 106 provided above and below the pedestal 104, respectively. This step is a step of disposing a silicon oxide film 132 as a dielectric on the aluminum thin film 134 side of the aluminum thin films 122 and 134 as counter electrodes facing each other (dielectric disposing step).

  Subsequently, helium gas is injected into the upper chamber 101 of the housing from an inlet (not shown). In addition, a mixed gas obtained by adding argon gas to air is injected into the lower chamber 102 of the housing from an inlet (not shown).

  Next, soft X-rays are irradiated from the ionizing radiation generator 108 toward the silicon microphone 110 (ionizing radiation irradiation step). The irradiated soft X-rays pass through the vibration film 120 including the aluminum thin film 122. Here, when the film thickness of the silicon vibration film 120 is 2000 nm, the transmittance of soft X-rays having an energy of 6.5 keV, for example, is approximately 95%. The soft X-rays that have passed through the vibrating membrane 120 ionize the mixed gas between the vibrating membrane 120 and the back plate 130.

  Next, a voltage is applied to the aluminum thin films 122 and 134 by the DC power source 107. Here, when the silicon oxide film 132 is negatively charged, the polarity of the DC power source 107 is set so that the aluminum thin film 134 (back plate 130 side electrode) has a positive potential with respect to the aluminum thin film 122 (vibration film 120 side electrode). Set. When ionizing radiation is applied in this state, not only oxygen in the air is ionized and ions are generated between the vibrating membrane 120 and the back plate 130, but also argon absorbs the ionizing radiation and becomes positive. The electrons ionized and released at that time act on oxygen in the air and the number of ions increases. At this time, positive ions including argon ions are attracted to the vibration film 120, negative ions are attracted to the back plate 130, and the silicon oxide film 132 provided on the back plate 130 is negatively charged (dielectric charging process).

  As described above, in the electret manufacturing apparatus 100 according to the first embodiment, the gap between the opposed electrodes of the vibration film 120 and the back plate 130 is arranged in the lower chamber 102, and the lower chamber 102 added argon gas to the air. Since the atmosphere is configured to irradiate the silicon oxide film 132, which is a dielectric, with soft X-rays, the amount of ions generated between the counter electrodes increases, so the surface of the silicon oxide film 132 provided on the back plate 130 The potential rises in a short time, and the time required to obtain a predetermined surface potential in normal air can be reduced to 1/10 (300 seconds → 30 seconds: see Experiment 1).

  Therefore, the electret manufacturing apparatus 100 according to the present embodiment can reduce the time required for manufacturing the electret.

  In addition, since the electret manufacturing apparatus 100 according to the present embodiment uses a rare gas, there is no problem of corrosion or generation of harmful gas.

In the above-described embodiment, the gap between the counter electrodes of the vibration film 120 and the back plate 130 has been described as an example of an atmosphere in which argon gas is added to air, but the present invention is limited to this. It is not a thing. That is, the space between the counter electrodes may be an atmosphere containing a gas having a lower transmittance than air, or may be a mixture of air and CO ₂ .

  When the dielectric is negatively charged as in the above-described embodiment, it is preferable to use a gas that generates more negative ions than in the air when irradiated with ionizing radiation. Examples of the gas that easily generates negative ions include chlorine-based and fluorine-based gases. However, when chlorine-based or fluorine-based gas is used, it is preferable that the dielectric or the like is made of a material resistant to these gases.

  Further, in the above-described embodiment, soft X-rays are taken as an example of ionizing radiation, but the present invention is not limited to this, and the same effect can be obtained by using X-rays, γ-rays, and the like.

  In the above-described embodiment, the example in which the silicon oxide film 132 as the dielectric is provided on the back plate 130 has been described. However, the present invention is not limited to this, and the dielectric is arranged on the vibration film 120 side. The same effect can be obtained with the configuration provided in FIG.

(Other aspects of the first embodiment)
In the above description, the case where the silicon oxide film 132 as a dielectric is negatively charged has been described. Hereinafter, a case where the silicon oxide film 132 is positively charged will be described as another aspect of the first embodiment. In this embodiment, the atmosphere of the lower chamber 102 is different from the above-described configuration, and the other configurations are the same. Therefore, the description overlapping with the above description is omitted.

  First, the lower chamber 102 in the electret manufacturing apparatus of this embodiment is filled with a mixed gas in which argon is added to air at 50% or more, preferably 99% or more. Note that the lower chamber 102 may be 100% argon gas.

  Next, a voltage is applied to the aluminum thin films 122 and 134 by the DC power source 107. Here, when the silicon oxide film 132 is positively charged, the polarity of the DC power source 107 is set so that the aluminum thin film 134 (back plate 130 side electrode) has a negative potential with respect to the aluminum thin film 122 (vibration film 120 side electrode). Set. When ionizing radiation is applied in this state, not only oxygen in the air is ionized and ions are generated between the vibrating membrane 120 and the back plate 130, but also argon absorbs the ionizing radiation and becomes positive. The electrons ionized and released at that time act on oxygen in the air and the number of ions increases. At this time, negative ions are attracted to the vibrating membrane 120 side, positive ions including argon ions are attracted to the back plate 130 side, and the silicon oxide film 132 provided on the back plate 130 is positively charged (dielectric charging step).

  As described above, in the electret manufacturing apparatus according to another aspect of the first embodiment, in addition to the effects of the first embodiment, in the configuration in which the silicon oxide film 132 is positively charged, the atmosphere containing argon gas is oxidized with silicon. Argon ions greatly contribute to the increase of the surface potential of the silicon oxide film 132 by disposing the film 132, so that the surface potential (32/50 → 40/50: experiment) which is 25% larger than the surface potential normally obtained in air. 2).

(Second Embodiment)
Next, a second embodiment of the electret manufacturing apparatus according to the present invention will be described. In the present embodiment, an example of producing an electret condenser silicon speaker (hereinafter simply referred to as “silicon speaker”) among silicon electret elements formed by a semiconductor microfabrication technique and provided with opposing electrodes facing each other will be given.

  First, the structure of the electret manufacturing apparatus in the present embodiment will be described. FIG. 7 is a diagram showing the inside of the housing of the electret manufacturing apparatus 200 in the present embodiment, and the housing itself is not shown.

  As shown in FIG. 7, the electret manufacturing apparatus 200 includes a gas nozzle 201 that discharges a mixed gas in which argon and air are mixed, electrodes 202 to 204, a DC power source 205, and an ionizing radiation generator 206. ing.

  The silicon speaker 210 has a structure in which two silicon substrates 211 and 212 on which vibration films 220 and 230 are respectively formed and a fixed substrate 240 formed so as to be sandwiched between them are bonded together. The vibration films 220 and 230 have a thickness of about 2000 nm, for example, and a gap of 10,000 nm or more is provided between each of the vibration films 220 and 230 and the fixed substrate 240 with an insulating spacer 213 interposed therebetween. ing. The fixed substrate 240 is made of silicon having a thickness of about 50 μm, and has a resistivity of, for example, 0.1 Ωcm or less.

  As shown in the enlarged view, the vibration film 220 includes silicon 221 and an aluminum thin film 222 as an electrode formed on the outer surface (back surface of the facing surface) of the silicon 221. The thickness of the aluminum thin film 222 is about 50 nm to 100 nm. Although illustration is omitted, the configuration of the vibration film 230 is the same as that of the vibration film 220, and an aluminum thin film is formed symmetrically with respect to the fixed substrate 240.

  Further, as shown in the enlarged view, the fixed substrate 240 includes silicon 241, a silicon oxide film 242 as a dielectric formed on both sides of the silicon 241 (opposite sides of the vibration films 220 and 230), And a silicon nitride film 243 as a moisture-proof film formed on the upper surface. Here, for example, the silicon oxide film 242 has a thickness of about 1000 nm and the silicon nitride film 243 has a thickness of about 200 nm.

  The electrodes 202 and 203 are connected to the electrodes of the vibrating membranes 220 and 230, respectively. The electrode 204 is connected to the silicon 241 of the fixed substrate 240.

  Next, the manufacturing method of the electret in this embodiment is demonstrated.

  First, a silicon speaker 210 in which the silicon oxide film 242 is not charged is set in a predetermined jig (not shown) in the housing, and the vibration films 220 and 230 and the fixed substrate 240 are connected to the DC power source 205 via the electrodes 202 to 204. Connect to.

  In addition, a gas nozzle in which a mixed gas obtained by adding 20% to 95%, preferably 70% to 90% of argon gas to the air is installed in the gap between the vibration films 220 and 230 and the fixed substrate 240 on the side surface of the silicon speaker 210. Spray with 201. In addition, you may spray only argon gas, without using mixed gas.

  Next, soft X-rays are irradiated from the ionizing radiation generator 206 toward the silicon speaker 210 to ionize the mixed gas between the vibrating membranes 220 and 230 and the fixed substrate 240. At this time, since the vibration film 220 and the fixed substrate 240 are thin, soft X-rays are transmitted.

  Here, when the film thickness of the silicon vibration film 220 is 2000 nm, for example, the transmittance of soft X-rays having an energy of 6.5 keV is approximately 95%. Further, if the thickness of the fixed substrate 240 made of silicon is 50 μm, the transmittance of 6.5 keV soft X-rays is approximately 27%. The transmitted soft X-rays ionize the gas between the vibrating membranes 220 and 230 and the fixed substrate 240. If necessary, another ionizing radiation generator 206 may be prepared and irradiated with soft X-rays from the vibrating membrane 230 side. Thereby, when soft X-rays are irradiated from one direction, it is possible to prevent the number of generated ions from becoming asymmetric between the two counter electrodes due to the attenuation of ionizing radiation by the fixed substrate 240, and between the both surfaces of the fixed substrate 240. Can prevent the surface potential from being biased.

  Next, a voltage is applied to each electrode by the DC power source 205. Here, when the silicon oxide film 242 is negatively charged, the polarity of the DC power source 205 is set so that the electrode of the fixed substrate 240 has a positive potential with respect to the electrodes of the vibration films 220 and 230. When ionizing radiation is applied in this state, not only oxygen in the air is ionized and ions are generated between the vibrating membranes 220 and 230 and the fixed substrate 240, but argon absorbs the ionizing radiation. Then, the electrons are converted to positive ions, and the electrons released at that time act on oxygen in the air and the number of ions increases. At this time, positive ions including argon ions are attracted to the vibrating membranes 220 and 230 side, negative ions are attracted to the fixed substrate 240 side, and the silicon oxide film 242 provided on the fixed substrate 240 is negatively charged.

  As described above, in the electret manufacturing apparatus 200 according to the second embodiment, the silicon speaker 210 includes the fixed substrate 240 having the silicon oxide film 242 as a dielectric formed on both surfaces, and the vibration films 220 and 230. Since the gap between the vibration films 220 and 230 and the fixed substrate 240 is an atmosphere in which argon is added to air and the silicon oxide film 242 is irradiated with soft X-rays, the amount of ions generated between the counter electrodes increases. Therefore, the surface potential of the silicon oxide film 242 rises in a short time, and the time taken to obtain a predetermined surface potential in normal air can be reduced to 1/10 (300 seconds → 30 seconds: see Experiment 1). it can.

  Therefore, the electret manufacturing apparatus 200 in the present embodiment can reduce the time required for manufacturing the electret.

(Third embodiment)
Next, a description will be given of a third embodiment of the electret manufacturing apparatus according to the present invention. In this embodiment, the example which manufactures the electret of an electret filter is given.

  First, the structure of the electret manufacturing apparatus in the present embodiment will be described. FIG. 8 is a view showing the inside of the housing of the electret manufacturing apparatus 300 in the present embodiment, and the housing itself is not shown.

  As shown in FIG. 8, the electret manufacturing apparatus 300 includes a gas nozzle 301 that discharges a mixed gas in which argon and air are mixed toward an electret filter 310, a mesh electrode 302, a DC power supply 303, and ionizing radiation. Generator 304.

  The electret filter 310 includes a metal plate 311 arranged to face the mesh electrode 302 and a filter material 312 provided on the metal plate 311.

  The filter material 312 is processed into a fiber shape, a mesh shape, a nonwoven fabric shape, or the like made of a resin material such as polyolefin, polyester, polycarbonate, or polyvinyl chloride. In this embodiment, for example, a SUS mesh electrode 302 having an aperture ratio of about 50% and a metal plate 311 are used as the counter electrode, and the filter material 312 is installed on the counter surface of the metal plate 311. A potential difference of, for example, about 0 to 10 kV can be applied between the mesh electrode 302 and the metal plate 311 by the DC power source 303.

  Next, the manufacturing method of the electret in this embodiment is demonstrated.

  First, a mesh electrode 302 is prepared, and the mesh electrode 302 is arranged inside the housing and connected to the DC power source 303.

  Subsequently, a metal plate 311 provided with a filter material 312 is arranged to face the mesh electrode 302, and the metal plate 311 is grounded.

  Furthermore, soft X-rays are irradiated from the ionizing radiation generator 304, and the gas between the mesh electrode 302 and the metal plate 311 is ionized through the mesh electrode 302. As the gas, a mixed gas in which argon is added to air at 20% to 95%, preferably 70% to 90% is blown from the gas nozzle 301. In addition, you may spray only argon gas, without using mixed gas.

  Next, a voltage is applied to the mesh electrode 302 and the metal plate 311 by the DC power source 303. Here, when the filter material 312 is desired to be negatively charged, the polarity of the DC power supply 303 is set so that the metal plate 311 has a positive potential with respect to the mesh electrode 302. When soft X-ray irradiation is performed in this state, oxygen in the air is ionized between the mesh electrode 302 and the metal plate 311 to generate ions, and argon absorbs soft X-rays. Then, the electrons are converted into positive ions, and the electrons released at that time act on oxygen in the air and the number of ions increases. At this time, positive ions including argon ions are attracted to the mesh electrode 302, negative ions are attracted to the metal plate 311, and the filter material 312 provided on the metal plate 311 is negatively charged.

  As described above, in the electret manufacturing apparatus 300 according to the third embodiment, the electret filter 310 includes the metal plate 311 provided with the filter material 312 as a dielectric, the mesh electrode 302 prepared separately, and the metal plate Since the air gap with 311 is an atmosphere in which argon is added to air and the filter material 312 is irradiated with soft X-rays, the amount of ions generated between the counter electrodes increases, so the surface potential of the filter material 312 It rises in a short time, and the time taken to obtain a predetermined surface potential in normal air can be reduced to 1/10 (300 seconds → 30 seconds: see Experiment 1).

  Therefore, the electret manufacturing apparatus 300 according to the present embodiment can reduce the time required for manufacturing the electret.

10 Samples 11, 111, 211, 212 Silicon substrates 12, 132, 242 Silicon oxide films 13, 133, 243 Silicon nitride films 21, 311 Metal plates 22, 108, 206, 304 Ionizing radiation generator 23 Grid electrodes 24, 107, 205, 303 DC power supply 25 Case 26 Inlet 31 Argon cylinder (gas generating means)
32, 36 Valve 33, 37 Flow meter 34 Tube 35 Air cylinder 100, 200, 300 Electret manufacturing apparatus 101 Upper chamber (first chamber)
102 Lower room (second room)
103 partition plate (internal housing dividing means)
104 pedestal (case internal dividing means)
105, 106, 202-204 Electrode 110 Silicon microphone 112, 213 Spacer 120, 220, 230 Vibration membrane 121, 131, 221, 241 Silicon 122, 134, 222 Aluminum thin film 130 Back plate 135 Sound hole 201, 301 Gas nozzle 210 Silicon speaker 240 Fixed substrate 302 Mesh electrode 310 Electret filter 312 Filter material

Claims (7)

An electret manufacturing apparatus comprising: an ionizing radiation generating apparatus that generates ionizing radiation; a housing that houses an element having two substrates each formed with a counter electrode facing each other; and a pedestal on which the element is disposed. A method of manufacturing the electret used,
A dielectric disposed disposing a dielectric on one side facing either before Symbol pair counter electrode,
Dividing the inside of the housing into a first chamber containing the ionizing radiation generator and a second chamber containing the other substrate by placing one of the two substrates on the pedestal, and
An ionizing radiation irradiating step of generating ionizing radiation that passes through the one substrate and irradiating the dielectric;
In the state where the second chamber is set in an atmosphere containing a gas having a lower transmittance of the ionizing radiation than air in a predetermined energy range of the ionizing radiation, a DC voltage is applied between the counter electrodes, and the ionizing radiation And a dielectric charging step of charging the dielectric with one of positive ions and negative ions generated between the counter electrodes.   The method for producing an electret according to claim 1, wherein the gas is any one of neon, argon, krypton, and xenon, or a mixed gas thereof.   2. The dielectric charging step according to claim 1, wherein the potential of the other electrode is made lower than the electrode on the side where the dielectric is disposed, and the dielectric is charged negatively by the negative ions. Item 3. A method for producing an electret according to Item 2.   2. The dielectric charging step according to claim 1, wherein the potential of the other electrode is made higher than the electrode on the side where the dielectric is disposed, and the dielectric is positively charged by the positive ions. Item 3. A method for producing an electret according to Item 2.   In the ionizing radiation irradiation step, a space from the ionizing radiation generating device that generates the ionizing radiation to the electrode on the ionizing radiation device side of the counter electrode has a higher transmittance of the ionizing radiation than air in the energy range. The method for producing an electret according to any one of claims 1 to 4, wherein the atmosphere includes a gas. An ionizing radiation generator that irradiates ionizing radiation through one electrode of the counter electrode to a dielectric disposed on the opposite surface side of one electrode of the counter electrodes facing each other, and the counter electrode An element having two substrates each formed and a housing for accommodating the ionizing radiation generator, a pedestal on which the element is disposed, a DC power source for applying a DC voltage between the counter electrodes, and the ionizing radiation Gas generating means for generating a gas having a lower transmittance of the ionizing radiation than air in a predetermined energy range;
One of the two substrates is divided into a first chamber containing the ionizing radiation generator and a second chamber containing the other substrate by arranging the element on the pedestal and thereby the interior of the housing. Is what
The gas generating means supplies the generated gas to the second chamber;
The DC power source charges the dielectric with one of positive ions and negative ions generated between the counter electrodes by the ionizing radiation in a state where the counter electrodes are in an atmosphere containing the gas. An apparatus for producing electrets, characterized in that: The said 1st chamber contains the gas whose transmittance | permeability of the said ionizing radiation is higher than air in the said energy range, The manufacturing apparatus of the electret of Claim 6 characterized by the above-mentioned.

Images