JP2007294858A - Method and device for electret - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To permit the electret of a dielectric film to an objective amount of electric charge with a high accuracy without investigating the condition of electric charge previously or even when the size of sound hole of a fixed electrode is small, in a condenser microphone formed through micro procession of a silicon substrate. <P>SOLUTION: The dielectric film 32 is used as an earth potential and, on the other hand, the fixed electrode 31 is used as another potential different from the earth potential. Thereafter, ion, generated by corona discharge, is arrived at the dielectric film 32 via the plurality of sound holes 35 provided on the fixed electrode 31 whereby the electret of the dielectric film 32 is effected. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electretization method and electretization apparatus for a dielectric film in a condenser microphone formed by using a silicon microfabrication technique.

  Electret condenser microphone (ECM) is a small acoustoelectric converter that detects the change in capacitance of the condenser due to sound waves as an electrical signal and uses an electret film with semi-permanent polarization, eliminating the need for a DC bias of the condenser. Device.

  The electret film (dielectric film at least partially polarized) in the ECM is made of an organic dielectric film such as FEP (fluoroethylene / propylene), for example. It is formed. Due to the electric field formed by the electric charges injected into the dielectric film, a potential difference is generated between the two electrodes of the capacitor sandwiching the dielectric film. In addition, injecting electric charges into the dielectric film and fixing it is called electretization.

  The dielectric film (electret film) is composed of a thin film such as FEP, and a metal such as gold or nickel is attached to the outer surface of the thin film by vapor deposition or the like.

  As a conventional method of injecting charges into a dielectric film for forming an electret, there are methods shown in FIGS. 6 and 7 (see, for example, Patent Document 1).

  FIG. 6 is a cross-sectional view of a main part of a conventional apparatus for generating a corona discharge by using a needle-like electrode to electret a dielectric film.

  In the apparatus of FIG. 6, a FEP (fluoroethylene / propylene) thin film 4 is placed on a ground electrode (metal tray) 5, and a direct current corona discharge is generated by an acicular electrode 6 connected to a high voltage power source 7. Is injected into the FEP thin film 4 and fixed to perform electretization.

  FIG. 7 is a cross-sectional view of a main part of a conventional apparatus that uses a wire electrode to generate corona discharge and convert the dielectric film into an electret. In FIG. 7, parts that are the same as those in the apparatus of FIG.

  In the apparatus of FIG. 7, a FEP (fluoroethylene / propylene) thin film 4 is placed on a ground electrode (metal tray) 5, a direct current corona discharge is generated by a wire electrode 21 connected to a high voltage power source 7, and ions are generated. Electretization is performed by injecting and fixing to the FEP thin film 4. In the apparatus of FIG. 7, since the wire electrode 21 has a two-dimensional spread, there is an advantage that ions can be irradiated over a wide range.

  Therefore, in general, when manufacturing ECM, considering mass productivity, a large number of FEP thin films (dielectric films) are arranged on a metal tray and subjected to corona discharge by the apparatus of FIG. The thin film is electretized. However, in this method, since the ion irradiation may not be performed uniformly, the electret amount of the FEP thin film may vary depending on the position on the tray. As a result, the microphone sensitivity varies. In addition to those caused by variations in the electret amount, variations in microphone sensitivity may occur due to variations in parasitic capacitance, FET capacitance, and the like.

  In the above conventional example, the dielectric film itself, which is the target of electretization, is taken out and electretized. Such a conventional technique can be said to be a technique based on an ECM configured by assembling mechanical parts.

  On the other hand, in recent years, there has been proposed a technique for forming an ultra-small condenser microphone by micro-processing a silicon substrate instead of assembling mechanical parts (for example, Patent Document 2, Patent Document 3, and Patent Document 4). reference).

  A silicon condenser microphone manufactured by using a so-called MEMS (micro electro mechanical system) element manufacturing technique is called a “silicon microphone (or silicon microphone)”, and the mobile phone is becoming smaller and thinner. It attracts attention as an ECM manufacturing technique for mounting on a telephone terminal or the like (see, for example, Patent Document 2).

  Here, since the silicon microphone is manufactured by processing a silicon substrate using a semiconductor process technology, electretization processing unrelated to semiconductor processing cannot be incorporated into the manufacturing process of the silicon microphone. . That is, it is not possible to take out only the dielectric film and make it an electret individually.

  Therefore, for example, the silicon microphone described in Patent Document 3 is a condenser microphone that does not include an electret film.

  However, the silicon microphone cannot be electretized. For example, in the silicon microphone described in Patent Document 4, the dielectric film can be electretized.

  That is, the silicon microphone described in Patent Document 4 includes a first silicon substrate (microphone film) including a dielectric film formed on a substrate and a second silicon substrate (a microphone film) bonded to the first silicon substrate ( The dielectric film is electretized at the end of the manufacturing process of the first silicon substrate, and then the second silicon substrate is bonded to the first silicon substrate.

  Further, in the silicon microphone and the manufacturing method thereof described in Patent Document 5, the dielectric film can be electretized in the silicon microphone having a structure in which the dielectric film is not exposed, which is made of a single silicon substrate. Yes.

  That is, according to the method for converting a silicon microphone into an electret described in Patent Document 5, after a capacitor microphone chip formed by finely processing a silicon substrate is mounted on a mounting substrate, a dielectric film that is a component of the capacitor microphone is used. In which the dielectric film is electretized by individually performing at least one corona discharge by one acicular electrode on one condenser microphone.

Further, in the electretization method described in Patent Document 6, when corona discharge is performed, the movement of ions is controlled by arranging a grid electrode between the electrode that performs corona discharge and the electretization object. While doing electretization. Thereby, the amount of electretization can be controlled.
JP-A-56-58220 Japanese Patent Laid-Open No. 11-88992 JP 2005-20411 A JP 2000-508860 Publication PCT / JP2006 / 31248 JP 2003-282360 A

  As described above, when trying to manufacture a silicon microphone by micro-processing a silicon substrate using a semiconductor manufacturing process, it is essentially impossible to take out only a dielectric film and make it an electret. It is difficult to manufacture (electret condenser microphone).

  Further, as in the technique described in Patent Document 4, for example, a method of manufacturing a silicon microphone by performing a manufacturing process on each of two substrates and finally bonding the two substrates together is a dielectric film. However, there is a problem that the manufacturing process of the silicon microphone is complicated.

  In addition, when microfabrication of a silicon substrate is performed, variations in device dimensions are likely to occur, and variations in the performance of electronic components such as FETs (field effect transistors) mounted on a mounting substrate may not be ignored. Therefore, the sensitivity of the silicon microphone varies. However, the above-mentioned Patent Document 4 does not describe any countermeasures against such variations in sensitivity of silicon microphones.

  In addition, as in the technique described in Patent Document 5, in a method in which at least one corona discharge by one needle-like electrode is individually performed on one condenser microphone, the target charge amount is electretized. At this time, various adjustment conditions (corrosion distance (distance between the corona discharge electrode and dielectric film), corona discharge applied voltage, etc.) when performing corona discharge are tested in advance, Therefore, it is necessary to determine the charging conditions for obtaining the target charging amount.

  Furthermore, in the method described in Patent Document 5, since the ions generated by corona discharge pass through a sound hole provided in the fixed electrode and reach the dielectric film, electretization is performed. When the size of the hole is reduced, ions generated by corona discharge cannot reach the dielectric film not only when the wire electrode is used but also when the needle electrode is used.

  The present invention has been made on the basis of the above-described considerations. The purpose of the present invention is to fix a capacitor microphone formed by micro-processing a silicon substrate without checking the charging conditions in advance. Even when the size of the sound hole of the electrode is small, the dielectric film can be formed into an electret with high accuracy to the target charge amount.

  In order to achieve the above object, according to the present invention, a corona discharge is performed above a fixed electrode in a condenser microphone in a state where the dielectric film is set to the ground potential and the fixed electrode is set to a potential different from the ground potential. The film is electretized.

  According to the present invention, corona discharge is performed above the fixed electrode while the fixed electrode in the capacitor microphone chip is set to a potential different from the ground potential. As a result, ions generated by corona discharge reach the dielectric film via the sound holes of the fixed electrode while being controlled by the potential of the fixed electrode, whereby the dielectric film can be electretized. Further, the dielectric film is electretized until the potential of the dielectric film caused by the charging becomes equal to the potential of the fixed electrode. For this reason, the dielectric film can be accurately electretized to the target charge amount without investigating the relationship between the conditions of electret charging and the voltage electretized on the dielectric film (potential of the dielectric film by the charging). Can be

  In the first to third embodiments of the present invention, as described later, corona discharge is performed above the fixed electrode in a state where the fixed electrode in the condenser microphone is set to a potential different from the ground potential. As a result, ions generated by corona discharge reach the dielectric film via the sound holes of the fixed electrode while being controlled by the potential of the fixed electrode, whereby the dielectric film can be electretized. Further, the dielectric film is electretized until the potential of the dielectric film caused by the charging becomes equal to the potential of the fixed electrode. For this reason, the dielectric film can be accurately electretized to the target charge amount without investigating the relationship between the conditions of electret charging and the voltage electretized on the dielectric film (potential of the dielectric film by the charging). Can be

  Further, in the second embodiment of the present invention, as will be described later, the microphone is charged by charging the dielectric film before mounting the microphone chip on the mounting substrate. There is no need to electrically connect the chip for mounting and the mounting substrate by bonding wires or the like.

  Furthermore, in the second embodiment of the present invention, as described later, the following effects can be obtained by charging the dielectric film before mounting the microphone chip on the mounting substrate. It is done. That is, by performing the sensitivity inspection and the electretization amount inspection of the condenser microphone in a state where it is not mounted, a defective chip can be detected before mounting, so that the disposal loss of the mounting substrate and the mounting element is reduced.

  Further, in the third embodiment of the present invention, as will be described later, by using a wire electrode for corona discharge, it becomes possible to simultaneously charge the dielectric films of a plurality of microphones. Productivity is improved.

(First embodiment)
Hereinafter, an electretization method and an electretization apparatus according to a first embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view of a device for explaining the structure of a silicon microphone manufactured by micro-processing a silicon substrate.

  As shown in FIG. 1, the silicon microphone 43 includes a silicon substrate (silicon diaphragm) 34, a vibration film 33 provided so as to cover a removal region of the silicon substrate 34 and functioning as one electrode of a capacitor, And a fixed electrode 31 which is supported by a spacer portion 37 on the silicon substrate 34 so as to face the vibration film 33 and functions as the other electrode of the capacitor. And. The fixed electrode 31 is provided with a plurality of sound holes (openings for guiding sound waves to the vibration film 33) 35. In addition, an air gap 36 formed by etching the sacrificial layer is interposed between the vibration film 33 and the fixed electrode 31. The vibration film 33, the fixed electrode 31, and the inorganic dielectric film 32 constituting the silicon microphone 43 are manufactured using a silicon microfabrication technique and a CMOS (complementary field effect transistor) manufacturing process technique.

  FIG. 2 is a cross-sectional view showing an electret microphone mounting structure (structure after case sealing) using a silicon substrate. In FIG. 2, parts that are the same as those in FIG. In FIG. 2, the silicon microphone (semiconductor device) 43 is illustrated in a simplified manner (the actual structure is as shown in FIG. 1).

  As shown in FIG. 2, a silicon microphone (semiconductor device) 43 and other electronic components (FET, resistor, amplifier, etc.) 45 are mounted on a mounting substrate 42 made of plastic or ceramic.

  A ground pattern 46 and a microphone signal output pattern 47 are disposed on the back surface of the mounting substrate 42. As shown in FIG. 2, in the mounting mode, the silicon microphone 43 is mounted on the mounting substrate 42. The vibration film 33 forming one pole of the capacitor is electrically connected to the other electronic component 45 through the bonding wire 44a. The other electronic components 45 are electrically connected to the wiring pattern 60b on the mounting substrate 42 through bonding wires 44c. The fixed electrode 31 forming the other pole of the capacitor is electrically connected to the wiring pattern 60a on the mounting substrate 42 via the bonding wire 44b. The wiring patterns 60a and 60b are electrically connected to a ground pattern 46 and a microphone signal output pattern 47 provided on the back surface of the mounting board 42 via wirings L1 and L2 inside the mounting board 42, respectively. Yes.

  The shield case 41 is attached on the mounting substrate 42 after the electretization process is completed. The shield case 41 is provided with a wide opening 49 as a sound hole for guiding sound waves.

  FIG. 3 is a diagram illustrating a configuration of a main part of the electretization apparatus according to the present embodiment. In FIG. 3, the same reference numerals are given to portions common to FIGS. 1 and 2, and redundant description is omitted.

  The electretization apparatus of FIG. 3 performs electretization by irradiating ions to one silicon microphone by corona discharge using one needle-like electrode.

  As shown in FIG. 3, corona discharge using the needle electrode 51 is used for the electretization process of the present embodiment. That is, the needle-like electrode 51 is positioned above the silicon microphone (semiconductor device) 43. The acicular electrode 51 is connected to a high voltage power supply 53 for generating corona discharge. The high voltage power supply 53 applies a high voltage of, for example, about 5 to 10 kV to the needle electrode 51.

  In the electret charging process, wiring different from that in the mounting mode is made on the silicon microphone 43.

  Specifically, as shown in FIG. 3, even during the electret charging process, the silicon microphone 43 is mounted on the mounting substrate 42, but the vibrating membrane 33 forming one pole of the capacitor and the other pole of the capacitor are connected. The formed fixed electrodes 31 are electrically connected to the wiring patterns 60a and 60b on the mounting substrate 42 via bonding wires 44a and 44b, respectively, unlike the mounting mode shown in FIG. The wiring patterns 60a and 60b are electrically connected to a ground pattern 46 and a microphone signal output pattern 47 provided on the back surface of the mounting board 42 via wirings L1 and L2 inside the mounting board 42, respectively. Yes.

  Further, as shown in FIG. 3, a grounding pin (charging device pin) 52 is connected to the grounding pattern 46 on the back surface of the mounting substrate 42. The vibration film 33 of the silicon microphone 43 is electrically connected to the ground pattern 46 provided on the back surface of the mounting substrate 42 via the wire 44a, the wiring pattern 60a on the mounting substrate 42, and the wiring L1 inside the mounting substrate 42. Connected. Therefore, the vibration film 33, that is, the dielectric film 32 can be set to the ground potential by connecting the grounding pin (the charging device pin) 52 to the ground pattern 46.

  On the other hand, as shown in FIG. 3, a voltage application pin (charging device pin) 54 is connected to the microphone signal output pattern 47 on the back surface of the mounting substrate 42, and a voltage application pin (charging device pin). ) 54 is connected to a variable voltage machine 55. Further, as described above, the fixed electrode 31 of the silicon microphone 43 is provided on the back surface of the mounting substrate 42 via the wire 44b, the wiring pattern 60b on the mounting substrate 42, and the wiring L2 inside the mounting substrate 42. The microphone signal output pattern 47 is electrically connected. Therefore, the fixed electrode 31 can be set to a potential set by the variable voltage machine 55, that is, a potential different from the ground potential, by connecting the voltage application pin (the charging device pin) 54 to the microphone signal output pattern 47. .

  In the state shown in FIG. 3 described above, the inorganic dielectric film 32 (see FIG. 1) inside the silicon microphone 43 is irradiated with ions generated by corona discharge by the needle electrode 51. Thereby, the inorganic dielectric film 32 (see FIG. 1) of the silicon microphone 43 can be electretized with the voltage applied to the fixed electrode 31.

  By the way, in the conventional method, the fixed electrode is grounded or is in an electrically floating state. In this case, ions flow through the fixed electrode to the ground, and an appropriate amount of ions is not irradiated onto the dielectric film. In particular, as the sound hole provided in the fixed electrode becomes smaller, the amount of ions irradiated to the dielectric film decreases, and the dielectric film becomes less likely to be electretized.

  On the other hand, in the present embodiment, as shown in FIGS. 1 and 3, the fixed electrode 31 of the silicon microphone 43 is set to a potential different from the ground potential, so that the vibration film 33 and the fixed electrode 31 are interposed. A potential difference is generated, and as a result, ions generated by corona discharge by the needle-like electrode 51 are attracted to the dielectric film 32 through a plurality of sound holes 35 provided in the fixed electrode 31.

  The dielectric film 32 is gradually electretized and its potential (electret potential) increases, and finally the potential of the surface of the dielectric film 32 on the vibration film 33 and the potential of the fixed electrode 35 are equal. Become.

  When the potential of the dielectric film 32 and the potential of the fixed electrode 35 become equal, ions are no longer irradiated to the dielectric film 32 as in the conventional method. Therefore, the dielectric film 32 has a potential obtained by applying an electret potential to the fixed electrode 35. It becomes electret until it becomes equal to.

  As described above, according to the present embodiment, in the condenser microphone formed by micro-processing the silicon substrate, the size of the sound hole 35 of the fixed electrode 31 is not increased without checking the charging conditions in advance. Even if it is small, the dielectric film 32 can be electretized with high accuracy to the target charge amount.

  Further, according to the present embodiment, the charge amount of the dielectric film 32 can be adjusted by the magnitude of the potential of the fixed electrode 31 set by the variable voltage machine 55.

(Second Embodiment)
Hereinafter, an electretization method and an electretization apparatus according to a second embodiment of the present invention will be described with reference to the drawings.

  FIG. 4 is a diagram illustrating a configuration of a main part of the electretization apparatus according to the present embodiment. In FIG. 4, the same reference numerals are given to portions common to those in FIGS. 1 to 3, and redundant description is omitted.

  The electretization apparatus shown in FIG. 4 performs electretization by irradiating the chip of one silicon microphone 43 with ions by corona discharge using one needle-like electrode.

  As shown in FIG. 4, in this embodiment, the silicon microphone 43 is placed on the stationary fixing jig 81, and the vibration film 33 and the fixed electrode 31 of the silicon microphone 43 are connected to the grounding pin 52 and the voltage, respectively. It is electrically connected to the application pin 54. The grounding pin 52 is connected to the ground by a lead wire, so that the vibration film 33, that is, the dielectric film 32 can be set to the ground potential. The voltage application pin 54 is connected to the variable voltage machine 55 through a lead wire, and the fixed voltage 31 can be set to a potential different from the ground potential by the variable voltage machine 55.

  In the state shown in FIG. 4 described above, corona discharge is performed by the needle-like electrode 51 above the fixed electrode 31, and ions generated thereby are applied to the dielectric film 32 (see FIG. 1) inside the silicon microphone 43. The dielectric film 32 is converted into an electret.

  According to this embodiment, the same effect as that of the first embodiment can be obtained by the same charging process as that of the first embodiment. In addition, since the dielectric film 32 of the silicon microphone 43 is electretized before being mounted on the mounting substrate 42, the following effects are obtained. That is, it is not necessary to electrically connect the silicon microphone 43 and the mounting substrate 42 with bonding wires or the like. Moreover, since the sensitivity inspection and electretization amount inspection of the silicon microphone 43 can be performed by a single chip, in other words, the sensitivity inspection and electretization amount inspection of the silicon microphone 43 can be performed without mounting, Since the defective chip can be detected before mounting, the disposal loss of the mounting substrate and the mounting element is reduced.

(Third embodiment)
Hereinafter, an electretization method and an electretization apparatus according to a third embodiment of the present invention will be described with reference to the drawings.

  FIG. 5 is a diagram illustrating a configuration of a main part of the electretization apparatus according to the present embodiment. In FIG. 5, the same reference numerals are given to portions common to those in FIGS. 1 to 4, and redundant description is omitted.

  The electretization apparatus of FIG. 5 performs electretization by irradiating ions to the chips of the plurality of silicon microphones 43 by corona discharge using the wire electrode 91.

  As shown in FIG. 5, corona discharge using the wire electrode 91 is used for the electretization process of the present embodiment. That is, the wire electrode 91 is positioned above the silicon microphone (semiconductor device) 43. A high voltage power supply 53 for generating corona discharge is connected to the wire electrode 91. The high voltage power supply 53 applies a high voltage of, for example, about 5 to 10 kV to the wire electrode 91.

  A plurality of silicon microphones 43 mounted on the substrate are arranged below the wire electrode 91, and a ground pin 52 and a voltage application pin 54 are provided as in the first embodiment shown in FIG. These are connected electrically to the ground pattern 46 and the microphone signal output pattern 47 of the mounting substrate 42 on which the silicon microphones 43 are mounted. Thereby, in each silicon microphone 43, each fixed electrode 31 can be set to a potential different from the ground potential, and each vibration film 33, that is, each dielectric film 32 can be set to the ground potential.

  In the state shown in FIG. 5 described above, corona discharge is performed by the wire electrode 91, and ions generated thereby are irradiated to the dielectric film 32 (see FIG. 1) inside each silicon microphone 43. The dielectric film 32 is changed to an electret.

  According to this embodiment, the same effect as that of the first embodiment can be obtained by the same charging process as that of the first embodiment. Further, since the dielectric films 32 (see FIG. 1) of the plurality of silicon microphones 43 can be electretized simultaneously with the voltage applied to the fixed electrode 31, the productivity of the silicon microphones can be improved.

  INDUSTRIAL APPLICABILITY The present invention provides an effect that a dielectric film can be electretized with high accuracy to a target charging potential in a silicon microphone (silicon microphone) using a semiconductor chip formed by finely processing a silicon substrate. The present invention is useful as an ultra-small silicon microphone mounted on a mobile communication device, an electret method thereof, and an electret device used for manufacturing the same.

FIG. 1 is a cross-sectional view for explaining the structure of a silicon microphone manufactured by micro-processing a silicon substrate. FIG. 2 is a cross-sectional view of the silicon microphone mounted on the substrate after enclosing the case. FIG. 3 is a diagram showing a configuration of a main part of the electretizing apparatus according to the first embodiment of the present invention. FIG. 4 is a diagram illustrating a configuration of a main part of an electretizing apparatus according to the second embodiment of the present invention. FIG. 5 is a diagram illustrating a configuration of a main part of an electretizing apparatus according to the third embodiment of the present invention. FIG. 6 is a cross-sectional view of a main part of a conventional electretizing apparatus. FIG. 7 is a cross-sectional view of a main part of a conventional electretizing apparatus.

Explanation of symbols

31 Fixed electrode 32 Inorganic dielectric film 33 Vibration film 34 Silicon substrate 35 Sound hole 36 Air gap 37 Spacer part 41 Shield case 42 Mounting substrate 43 Silicon microphones 44a, 44b, 44c Bonding wire 45 Electronic component 46 Ground pattern 47 Microphone signal output pattern 49 Opening 51 Needle-like electrode 52 Grounding pin 53 High voltage power supply 54 Voltage application pin 55 Variable voltage machine 60a, 60b Wiring pattern 81 Fixing jig 91 for electrode 91 Wire electrode L1, L2 Wiring

Claims (9)

A fixed electrode having a plurality of sound holes, a vibration film disposed so as to face the fixed electrode, and a dielectric provided on the vibration film so as to be positioned between the fixed electrode and the vibration film In a condenser microphone comprising a film, an electretization method for electretizing the dielectric film,
A step (a) of setting the dielectric film to a ground potential;
A step (b) of setting the fixed electrode to another potential different from the ground potential;
After the step (a) and the step (b), ions generated by corona discharge reach the dielectric film via the plurality of sound holes provided in the fixed electrode, thereby And (c) a step of electretizing the dielectric film. The electretization method according to claim 1,
The condenser microphone is mounted on a mounting board,
The step (a) includes the step of bringing the dielectric film to the ground potential through a first electrode provided on the mounting substrate.
The step (b) includes a step of setting the fixed electrode to the other potential via a second electrode provided on the mounting substrate. The electretization method according to claim 1,
The step (a) includes the step of bringing the dielectric film to the ground potential via a first probe pin,
The step (b) includes a step of bringing the fixed electrode to the other potential via a second probe pin. The electretization method according to claim 1,
The step (c) includes a step of generating the corona discharge using a wire electrode. The electretization method according to claim 1,
The step (c) includes a step of generating the corona discharge using a needle-like electrode. The electretization method according to claim 1,
The electretization method characterized in that the charge amount of the dielectric film in the step (c) is adjusted by the magnitude of the other potential of the fixed electrode in the step (b).   A condenser microphone comprising the dielectric film electretized by the electretization method according to claim 1. A fixed electrode having a plurality of sound holes, a vibration film disposed so as to face the fixed electrode, and a dielectric provided on the vibration film so as to be positioned between the fixed electrode and the vibration film In a condenser microphone comprising a film, an electretization device for electretizing the dielectric film,
An electrode for generating corona discharge;
A high voltage power supply for applying a high voltage to the electrode;
A voltage power source for setting the fixed electrode to another potential different from the ground potential;
A grounding pin for setting the dielectric film, which is a film to be electretized, to the ground potential;
An electretizing apparatus comprising: a voltage application pin for setting the fixed electrode to the other potential. In the electretization apparatus of Claim 8,
The electretization apparatus characterized in that the voltage power source can adjust the magnitude of the other potential.

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