JP2004056351A - Piezoelectric microphone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric microphone employing a ferroelectric thin film formed by baking a high purity PZT thin film or the like on a thin sintered substrate with a thickness of about 10μm. <P>SOLUTION: After a ferroelectric raw material is coated on the substrate 6e, a calcined layer 6c calcined at a temperature lower than a phase transition temperature of the ferroelectric raw material or a temperature of the same degree is stacked on the substrate, after the ferroelectric raw material is coated on the calcined layer 6c or a ferroelectric thin film 6c baked at a high temperature of the phase transition temperature of the ferroelectric raw material or over without coating the ferroelectric raw material is used for a diaphragm 6. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric microphone, and more particularly, to a piezoelectric microphone using a polarization-processed ultra-thin ferroelectric thin film as a diaphragm.
[0002]
2. Description of the Related Art Conventionally, the applicant of the present invention has invented a "condenser microphone" (Japanese Patent Laid-Open No. 2001-8293) (hereinafter referred to as a conventional example). This conventional example,
"<Claims>
<Claim 1> A terminal board on which an IC element comprising a diaphragm, a back electrode, and a microphone FET is fixed is housed in a casing having a sound hole in a top plate in order from the top surface side while maintaining a predetermined interval. In the condenser microphone, a contact ring also serving as a spacer made of a conductive material is interposed between the back surface of the back electrode and the surface of the terminal board, and an insulating film is formed between the outer peripheral surface of the contact ring and the inner peripheral surface of the casing. A condenser microphone characterized by being insulated by interposing
<Claim 2> The insulating film is formed of an insulating material integrally having an insulating tubular portion along the inner peripheral surface of the casing and a spacer ring portion integrally protruding inside the top of the insulating tubular portion. 2. The condenser microphone according to claim 1, wherein the capacitor microphone is interposed between the diaphragm and the back electrode, and is insulated between the back electrode and the contact ring and the casing by an insulating cylinder.
<Claim 3> The condenser microphone according to claim 1, wherein the insulating film is formed of an insulating film attached to an inner surface of the casing. 』
As shown in FIG. 5, the upper surface of a casing 120 forming a housing is formed by forming a plurality of sound holes 122 in a top plate 121. Further, in the casing 120, a diaphragm 124 is provided so as to be sandwiched between a plate-shaped diaphragm ring 125 having a donut shape disposed on the lower surface of the top plate 121 and a spacer ring 129 having the same shape. Further, a back electrode 126 is provided below the spacer ring 129 with a slight gap provided between the diaphragm 124 and the diaphragm 124.
[0003]
In the conventional example, when the vibrating plate 124 thus provided is vibrated by air vibration propagating from the sound hole 122 provided in the top plate 121, the back electrode and the vibrating plate 124 that are not vibrated by the air vibration. The voltage across the formed electrical capacitor will change. Then, the electric change is electrically output by the IC element 133 fixed to the terminal plate 131 in the casing 120. On the other hand, a ferroelectric thin film that has been subjected to a polarization process is known to generate a voltage when a stress is applied to a dielectric and cause a voltage change depending on the amount of the deformation. In the case of a conventional ferroelectric thin film, for example, a ferroelectric PZT thin film, it is formed on a metal substrate serving as a sintered substrate of about 1.5 mm to 0.04 mm. That is, conventionally, a method of forming a thin film on a foil serving as a metal substrate by using a sol-gel method has been used, and there has been an example in which a 650 nm PZT thin film is formed on a 0.05 mm thick titanium foil (Ti).
Hereinafter, a conventional example of firing a PZT thin film on a titanium foil will be described.
[0004]
First, a metal substrate made of titanium foil is placed on a turntable for applying a PZT raw material, and is fixed by suction and adsorption. The PZT raw material is applied by spin coating on the metal substrate thus placed to form a film of the PZT raw material. Next, the metal substrate on which the PZT raw material film is formed is heated to a high temperature of 500 to 600 degrees Celsius, which is the sintering temperature of PZT, and the PZT raw material is sintered to form a PZT thin film. When it is desired to increase the thickness of the PZT thin film, the process of applying the PZT raw material by spin coating on the sintered PZT thin film and sintering again at a high temperature of 500 to 600 ° C. or more is repeated to obtain a desired thickness. Of the PZT thin film was obtained.
As described above, the metal substrate for sintering the PZT raw material is not only a titanium foil but also a metal substrate such as a 0.04 mm stainless steel (SUS304) foil, a 1.2 mm brass sheet, and a 1.5 mm nickel alloy. Used to form PZT thin films, respectively.
[0005]
However, in the condenser microphone shown in the conventional example, the diaphragm 124 and the back electrode 126 are indispensable for the condenser for detecting a change in sound. Further, in order to accurately detect a change in sound, it is required that the diaphragm 124 vibrates due to the vibration of air, which is a sound, but the back electrode 126 must not vibrate due to the vibration.
That is, the diaphragm 124 is required to vibrate even by a slight change in sound, that is, the vibration, and in order to realize this, the substrate is required to be thin.
On the other hand, since the back electrode 126 must not vibrate in response to the vibration of air, it is required to be robust. Then, in order to form the back electrode 126 robustly, it was necessary to make the back electrode thick.
As described above, in the conventional condenser microphone, the thickness of the back electrode 126 limits the size reduction of the entire microphone.
[0006]
On the other hand, in a conventional ferroelectric thin film, even a metal substrate which is a sintered substrate having a minimum thickness is about 0.04 mm (40 μm), and a PZT thin film cannot be formed on a thin metal substrate having a thickness of 10 μm or less. That is, if the thickness of the metal substrate is reduced to about 10 μm, irregularities are generated on the metal substrate when the PZT raw material is sucked and adsorbed on a turntable during spin coating when applying the PZT raw material. There is a problem that wrinkles are generated during sintering. Further, when the sintering of the PZT raw material at a temperature of 500 to 600 degrees Celsius is repeated a plurality of times in order to obtain the thickness of the PZT thin film, wrinkles generated at the first time further increase and strain is accumulated. Not only the strain but also cracks are generated, and the integrity of the generated high dielectric thin film, PZT thin film, is reduced, so that there is a problem that a high purity PZT thin film cannot be formed. As described above, since a thin film ferroelectric substance could not be obtained, there was a problem that it was difficult to form a piezoelectric microphone that was small and had good followability.
[0007]
Accordingly, it is an object of the present invention to provide a piezoelectric microphone using a ferroelectric thin film obtained by sintering a high-purity PZT thin film or the like on a thin sintered substrate of about 10 μm and using a polarization treatment.
[0008]
Means for Solving the Problems The present invention provides:
After the ferroelectric material is applied on the substrate, a calcined layer that is baked at a temperature lower than the sintering temperature of the ferroelectric material is laminated, and the ferroelectric material is applied on the calcined layer or after the ferroelectric material is applied. A piezoelectric microphone characterized in that a ferroelectric thin film that is sintered at a temperature at which the ferroelectric material is sintered without applying the body material is subjected to polarization processing to form a diaphragm,
[0009]
as well as,
[0010]
A casing having a sound hole in the top plate, a diaphragm sandwiched between the upper diaphragm ring and the lower diaphragm ring, and a diaphragm provided inside the casing of the top plate such that the upper diaphragm ring is on the top plate side; A terminal board provided inside the casing to fix the IC element composed of a microphone FET, a contact ring made of conductive material and interposed between the lower diaphragm ring and the surface of the terminal board, and an outer peripheral surface of the contact ring and the casing. The diaphragm consists of an insulating film interposed so as to insulate it from the inner peripheral surface. The vibrating plate is a calcined layer that is fired at a temperature lower than the sintering temperature of the ferroelectric material after applying the ferroelectric material on the substrate. The ferroelectric thin film is sintered at a temperature at which the ferroelectric material is sintered after the ferroelectric material is applied on the calcined layer or without applying the ferroelectric material. Piezoelectric microphone, characterized in that it consists of those treated,
I will provide a.
[0011]
According to the present invention, in order to solve the above-mentioned problem, a terminal in which an IC element including a diaphragm, a contact ring, and a microphone FET is fixed in a casing having a sound hole in a top plate in order from the top surface side. The board is accommodated with a predetermined interval maintained, the diaphragm is sandwiched between the upper diaphragm ring and the lower diaphragm ring, and a contact made of a conductive material is also provided between the upper diaphragm ring and the terminal board surface. A ring is interposed, and the outer peripheral surface of the contact ring and the inner peripheral surface of the casing are insulated with an insulating film interposed therebetween.
The ferroelectric thin film forming the diaphragm is formed by applying a ferroelectric material on a substrate, and sintering the substrate on which the ferroelectric material is applied at a temperature lower than a sintering temperature. Form a calcined layer of the body. By a series of these steps, a calcined calcined layer is gradually formed on the substrate. Then, when the calcined layer on the substrate has a desired thickness, the calcined layer is sintered at the sintering temperature of the ferroelectric material to obtain a ferroelectric thin film.
The ferroelectric thin film thus obtained is subjected to polarization processing to impart piezoelectricity to use as a diaphragm, and when an external stress is applied to the piezoelectric thin film by the vibration of air, a voltage characteristic of the piezoelectric material is generated. By detecting a change in voltage caused by the vibration of air, waveform information of a sound wave is obtained in the form of an electric signal.
Incidentally, the insulating film may be constituted by an insulating film adhered to the inner peripheral surface of the casing.
[0012]
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view of a piezoelectric microphone according to an embodiment of the present invention, FIG. 2 is a transverse sectional view of the same, and FIG. 3 is a diagram showing a procedure for forming a diaphragm according to an embodiment of the present invention. FIG. 4 is an explanatory view showing the coating step in FIG.
The piezoelectric microphone 1 has a casing 2 made of aluminum or nickel-white molded into a cylindrical shape with a bottom by drawing, and the casing 2 has a bottom plate formed by a top plate 3 forming an upper surface. The top plate 3 is formed with a plurality of sound holes 4 and formed so that sound from the outside of the casing 2 propagates inside. A diaphragm 6 for detecting vibration of the sound transmitted from the sound hole 4 is provided below the top plate 3 inside the casing 2.
[0013]
The vibrating plate 6 is made of a piezoelectric thin film obtained by polarizing a ferroelectric thin film. The vibrating plate 6 is stretched from above and below by vibrating plate rings 7 and 26 which are in contact with the inner surface of the top plate 3 having a donut ring shape. It is pinched and fixed. Since the diaphragm 6 is sandwiched between the diaphragm rings 7 and 26 in this manner, the diaphragm 6 is housed at a distance from the top plate 3 by the diaphragm rings 7 and 26, and can vibrate by sound transmitted from the sound hole 4. .
Further, the casing 2 is bent by crimping the hem portion 5 of the cylindrical surface to the inside to prevent the members such as the diaphragm 6 housed therein from coming off.
[0014]
The diaphragm rings 7 and 26 located above and below the diaphragm 6 are accommodated in a cylindrical insulating material 9 inserted in contact with the inner surface of the casing 2 to insulate the casing 2 from each other. The insulating material 9 is formed in a tubular shape to form an insulating film, and maintains the lower diaphragm ring 8 and the casing 2 in an insulated state.
The lower end of the lower diaphragm ring 8 is in contact with the upper end of a cylindrical contact ring 10, the lower end of the contact ring 10 is in contact with and overlapped with the terminal board 11, and the lower surface of the terminal board 11 is provided with the bottom of the casing 2. 5 is crimped. At this time, the contact ring 10 and the casing 2 are insulated from each other, but may be formed by extending the cylindrical insulating material 9 to the hem portion 5 and maintaining the insulating state by the insulating material 9. good.
The inside of the contact ring 10 forms a back space 12, in which electronic components such as an IC element 13 composed of a field effect transistor (FET) are fixed and housed on the upper surface of the terminal board 11. The ring 10 also serves as a spacer between the lower diaphragm ring 8 and the terminal board 11.
Hereinafter, details of the diaphragm 6 will be described.
[0015]
The diaphragm 6 is made of a polarized piezoelectric thin film. When an external stress is applied to the piezoelectric thin film forming the diaphragm 6 by the vibration of air, a voltage characteristic of the piezoelectric body is generated. The change in the voltage of the piezoelectric thin film caused by the vibration of the air is detected and electrically converted, so that the sound applied to the diaphragm 6 can be reproduced.
The vibration plate 6 is a piezoelectric thin film made of a PZT thin film, and as shown in part A of FIG. 1, a titanium foil 6a forming a base of a metal substrate and a platinum film formed on the titanium foil 6a. An electrode layer 6b, a lead zirconate titanate (hereinafter referred to as PZT) thin film 6c formed on the platinum electrode layer 6b by sintering, and a gold electrode layer 6d formed as an upper electrode on the PZT thin film 6c.
The titanium foil 6a is formed as a substrate of the diaphragm 6, and has a metal foil shape having a thickness of 10 μm or less whose surface is subjected to a thermal oxidation treatment. In this embodiment, the titanium foil 6a has a thickness of 10 μm or less, but may have a thickness of 10 μm or more, such as 18 μm, depending on the application of the diaphragm 6, and may have any desired thickness. The thickness may be appropriately selected and used from the strength and the response when vibrated by air.
The platinum electrode layer 6b is formed in a layered form on the upper surface of the titanium foil 6a by sputtering, and functions as a lower electrode which is one electrode of the diaphragm 6. The platinum electrode layer 6b and the titanium foil 6a form a substrate 6e.
The PZT thin film 6c is formed by applying a raw material of PZT which is a ferroelectric material in which lead titanate (PbTiO ₃ ) and lead zirconate (PbZrO ₃ ) are dissolved on the upper surface of the substrate 6e and then sintering. Therefore, when spin coating, the PZT raw material is dropped as a PZT solution in which the PZT raw material is mixed into the solution, and is sintered at a high temperature after the spin coating to form the PZT thin film 6c.
The formation of the PZT thin film 6c is performed by a forming step S of the diaphragm 6 for forming the diaphragm 6, as shown in FIG.
[0016]
The forming step S includes a coating step S1, a calcination step S2, a repetition determination step S3, and a final sintering step S4.
The application step S1 is a step of applying a PZT raw material to the titanium foil 6a on which the platinum electrode layer 6b has been applied by spin coating. In the coating step S1, the titanium foil 6a provided with the platinum electrode layer 6b is placed and fixed on the coating table 16 of the spin coater 14 shown in FIG. 4 so that the platinum electrode layer 6b faces upward. At this time, the substrate 6e is fixed by adsorbing the solution 18 between the coating table 16 and the titanium foil 6a so that the platinum electrode layer 6b is on the upper surface. In general, in a suction method such as vacuum suction performed by the spin coater 14, irregularities are generated in the thin titanium foil 6a of about 10 μm as in this embodiment due to the suction force, and the firing of the PZT thin film 6c in the next and subsequent steps is performed as it is. Doing so will cause wrinkles. However, by mounting and fixing to the spin coater 14 with the solution 18 as in the present invention, the titanium foil 6a is not uneven, and a good PZT thin film 6c can be fired. Note that the solution 18 is made of a liquid such as alcohol, but may be another liquid as long as it does not affect the composition of the diaphragm 6 as well as the coating table 16.
[0017]
The coating table drive unit 15 of the spin coater 14 placed on the coating table 16 by liquid level adsorption is driven to rotate the coating table 16. Next, by dropping the PZT solution from the PZT original dropping device 17, the PZT solution is coated on the upper surface of the platinum electrode layer 6b on the titanium foil 6a.
Next, in the repetition determination step S3, it is determined whether the application step S1 has been repeated a predetermined number of times. The repetition determination step S3 is simply performed by the operator, but may be configured to automatically determine whether a predetermined number of times has been reached or not, and to perform automatic manufacturing.
Since the substrate 6e coated with the PZT solution has not been spin-coated a predetermined number of times, it is temporarily baked in the calcination step S2. That is, in the calcination step S2, calcination is performed at a temperature lower than or equal to the phase transition temperature of the PZT raw material forming the diaphragm 6 at 300 to 350 degrees Celsius.
This calcination step S2 is repeated until the number of times reaches a predetermined number in the repetition determination step S3 to obtain a PZT thin film 6c having a calcination layer having a desired thickness.
When the PZT thin film 6c has a desired thickness, a final sintering step S4 is performed.
[0018]
In the final sintering step S4, the PZT thin film 6c spin-coated in the final application step S1 together with the preliminarily fired layer preliminarily fired in the preliminarily firing step S2 is heated to 500 to 600 degrees Celsius, which is higher than the PZT sintering temperature. And sinter. Then, the PZT thin film 6c reaches the sintering temperature and is baked, so that a good PZT thin film 6c on ceramic is obtained.
As described above, even if the PZT thin film 6c is formed by spin coating a plurality of times, a sintered PZT thin film 6c with high purity and with little cracks, without accumulation of distortion, and high purity can be obtained.
In this embodiment, after the PZT thin film 6c is preliminarily baked to form a calcination layer, the PZT solution is applied again in the application step S1 and then the final sintering step S4 is performed. The final sintering step S4 may be performed in a state where the thin film 6c has formed the pre-fired layer.
[0019]
The gold electrode layer 6d is formed on the PZT thin film 6c formed as described above, and forms an upper electrode. The upper electrode is not limited to gold, and may be formed of other materials such as silver, platinum, iridium, and palladium. When there is a concern about chemical reaction with PZT or mutual diffusion of components, a buffer layer capable of suppressing chemical reaction and mutual diffusion is provided between the PZT layer and the electrode to form In ₂ O ₃ —SnO ₂ (ITO). ), An electrode may be formed using a material such as an oxide such as ZnO or a base metal such as Cu or Ni. The gold electrode layer 6d is formed by a general method like the conventional diaphragm 6. The gold electrode layer 6d may be formed after the final sintering step S4. The gold electrode layer 6d is placed on the spin-coated PZT solution before the final sintering step S4, and is integrated with the PZT thin film 6c by the final sintering step S4. May be formed.
[0020]
As described above, the diaphragm 6 has the lower electrode formed by the platinum electrode layer 6b, the upper electrode formed by the gold electrode layer 6d, and the sintered PZT thin film 6c formed in the middle part. Thereafter, a polarization process is performed to obtain the diaphragm 6. The platinum electrode layer 6b, which is the upper electrode, contacts the upper diaphragm ring 7 and further contacts the casing 2, and is connected to the terminal board 11 via the skirt 5 at the lower part of the casing 2, and is the lower electrode. The gold electrode layer 6d contacts the lower diaphragm ring 8, further contacts the contact ring 10, and the lower part of the contact ring 10 is connected to the terminal board 11 to form an electric circuit.
The diaphragm 6 is obtained by subjecting the PZT thin film 6c formed as described above to polarization processing.
[0021]
In the piezoelectric microphone 1 configured as described above, the vibration plate 6 vibrates due to the vibration of the sound that penetrates through the sound hole 4 through the air, and the movement thereof is moderate in compliance and moderation because the vibration plate 6 itself is a thin film. The change of the diaphragm 6 itself due to the vibration of the diaphragm 6 becomes a generated voltage difference, which is controlled by the compliance of the back space 12 having a small size, and the change is generated by the IC element 13 fixed on the terminal board 11. Then, it converts to low impedance and outputs it electrically.
[0022]
In this embodiment, PZT is used as the ferroelectric thin film, but it is possible to form a ferroelectric thin film by using the above-mentioned method by using other materials such as PLZT and ZnO.
[0023]
According to the present invention, a diaphragm is formed by forming a ferroelectric thin film on a substrate of about 2 μm to about 4 μm of 10 μm or less and performing polarization processing. The size of the piezoelectric microphone can be remarkably reduced, and a piezoelectric microphone having higher sensitivity and favorable f characteristics can be manufactured.
Since the ferroelectric thin film forming the diaphragm can obtain ferroelectric properties as long as the temperature is equal to or lower than the phase transition temperature, deterioration with respect to a temperature of about 260 degrees Celsius such as solder reflow is lower than that of a conventional condenser microphone. You get no microphone. Similarly, it can be used for high-temperature parts that could not be used conventionally because of high temperatures. In addition, since the back electrode in the condenser microphone is not required, the size and thickness can be further reduced.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a piezoelectric microphone according to an embodiment of the present invention. FIG. 2 is a transverse sectional view of the same. FIG. 3 is an explanatory view showing a procedure for forming a diaphragm according to an embodiment of the present invention. 4 is an explanatory view showing the coating step in FIG. 3 [FIG. 5] A conventional example view [Description of symbols]
DESCRIPTION OF SYMBOLS 1 Piezoelectric microphone 2 Casing 3 Top plate 4 Sound hole 5 Foot 6 Vibrating plate 6a Titanium foil 6b Platinum electrode layer 6c PZT thin film 6d Gold electrode layer 6e Substrate 7 Upper diaphragm ring 8 Lower diaphragm ring 9 Insulator 10 Contact ring 11 Terminal substrate 12 Back space 13 IC element 14 Spin coating device 15 Coating table drive unit 16 Coating table 17 PZT original liquid dropping device 18 Solution S Forming step S1 Coating step S2 Pre-baking step S3 Repeat determination step S4 Final sintering step

Claims (2)

After the ferroelectric material is applied on the substrate, a calcined layer that is fired at a temperature lower than the sintering temperature of the ferroelectric material is laminated, and the ferroelectric material is applied on the calcined layer or after the ferroelectric material is applied. A piezoelectric microphone characterized in that a ferroelectric thin film that is sintered at a temperature at which a ferroelectric material is sintered without applying a body material is subjected to polarization processing to form a diaphragm. A casing having a sound hole in the top plate;
A diaphragm sandwiched between the upper diaphragm ring and the lower diaphragm ring, the diaphragm provided inside the casing of the top plate such that the upper diaphragm ring is on the top plate side;
A terminal substrate provided inside the casing facing the top plate and fixing an IC element composed of a microphone FET;
A contact ring made of a conductive material and also serving as a spacer interposed between the lower diaphragm ring and the terminal board surface;
It consists of an insulating film interposed so as to insulate between the outer peripheral surface of the contact ring and the inner peripheral surface of the casing,
After applying the ferroelectric material on the substrate, a calcination layer that is fired at a temperature lower than the sintering temperature of the ferroelectric material is formed in a laminated structure, and after the ferroelectric material is applied on the calcination layer, Alternatively, a piezoelectric microphone comprising a ferroelectric thin film which is sintered at a temperature at which the ferroelectric material is sintered without applying the ferroelectric material, and polarization-processed.

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