JP5982793B2 - Acoustic element - Google Patents

Description

  The present invention relates to an acoustic element such as a microphone or a speaker.

  In recent years, various small acoustic elements that can be mounted on mobile devices such as mobile phones and laptop computers have been proposed. For example, in Patent Document 1, an electret condenser microphone is proposed as an example.

JP 2000-50393 A

  However, the electric charge accumulated in the electret condenser microphone electrifier is emitted from the electret by heating. For this reason, for example, if a process such as reflow mounting is performed on the microphone, the charge escapes, and the sensitivity of the microphone decreases. Therefore, since the electret condenser microphone does not have a heat resistance sufficiently high enough to withstand reflow mounting, there is a problem that a heat treatment process such as reflow mounting cannot be used.

  On the other hand, Micro Electro Mechanical Systems (MEMS) microphones are excellent in heat resistance and can be reflow mounted. However, in the MEMS microphone, a high voltage must always be applied to the diaphragm. For this reason, the MEMS microphone consumes a large amount of power. Furthermore, in order to apply a high voltage to the diaphragm, it may be necessary to provide a booster circuit. In this case, there is a problem that the size and cost are increased. There is also a problem that noise generated from the booster circuit affects the acoustic characteristics.

  The main object of the present invention is to provide a novel acoustic element having excellent heat resistance.

  The acoustic element according to the present invention includes a vibration film, a piezoelectric layer, and a pair of electrodes. The piezoelectric layer is disposed on the vibration film. The pair of electrodes sandwich the piezoelectric layer.

  In a specific aspect of the acoustic element according to the present invention, the acoustic element includes a plurality of piezoelectric layers.

  In another specific aspect of the acoustic element according to the present invention, the piezoelectric layer includes at least one of aluminum nitride and scandium aluminum nitride.

  In another specific aspect of the acoustic element according to the present invention, the acoustic element further includes a casing covering one side of the piezoelectric layer. The casing is formed with an opening disposed at a position different from the piezoelectric layer when viewed from the stacking direction of the piezoelectric layer and the electrode.

  In still another specific aspect of the acoustic element according to the present invention, the casing shields infrared light.

  In still another specific aspect of the acoustic element according to the present invention, the piezoelectric layer includes scandium aluminum nitride. The acoustic element has a plurality of laminates of vibration films and piezoelectric layers. The plurality of stacked bodies include a stacked body in which the directions of the piezoelectric layers with respect to the vibration film are opposite.

  According to the present invention, a novel acoustic element having excellent heat resistance can be provided.

1 is a schematic cross-sectional view of an acoustic element according to a first embodiment. It is a schematic sectional drawing of the acoustic element which concerns on 2nd Embodiment. It is a schematic sectional drawing of the acoustic element which concerns on 3rd Embodiment. It is a graph showing the relationship between the power applied to the sputtering apparatus and the film stress of the scandium nitride aluminum film (Sc content: 37 at%) to be formed. FIG. 6 is a schematic cross-sectional view of an acoustic element according to a fourth embodiment. It is a schematic sectional drawing of the acoustic element which concerns on 5th Embodiment.

  Hereinafter, an example of the preferable form which implemented this invention is demonstrated. However, the following embodiment is merely an example. The present invention is not limited to the following embodiments.

  Moreover, in each drawing referred in embodiment etc., the member which has a substantially the same function shall be referred with the same code | symbol. The drawings referred to in the embodiments and the like are schematically described, and the ratio of the dimensions of the objects drawn in the drawings may be different from the ratio of the dimensions of the actual objects. The dimensional ratio of the object may be different between the drawings. The specific dimensional ratio of the object should be determined in consideration of the following description.

(First embodiment)
FIG. 1 is a schematic cross-sectional view of an acoustic element 1 according to the first embodiment. The acoustic element 1 is an element used as, for example, a microphone or a speaker.

  The acoustic element 1 includes a piezoelectric element 10. The piezoelectric element 10 includes a vibration film 11. The vibration film 11 can be made of an elastic material such as a resin such as polyimide resin or polyethylene terephthalate (PET) resin. From the viewpoint of imparting high heat resistance to the vibration film 11, the vibration film 11 is preferably made of a resin material having high heat resistance such as polyimide resin.

  The thickness of the vibration film 11 can be, for example, about 1 μm to 100 μm.

  A piezoelectric layer 12 is disposed on the vibration film 11. The type of the piezoelectric material constituting the piezoelectric layer 12 is not particularly limited. The piezoelectric layer 12 may be composed of at least one of aluminum nitride, scandium aluminum nitride, lead zirconate titanate (PZT), zinc oxide, potassium sodium niobate, PVDF (polyvinylidene fluoride), polylactic acid, and the like. it can. In particular, the piezoelectric layer 12 is preferably made of at least one of aluminum nitride and scandium aluminum nitride substantially free of lead. Aluminum nitride and scandium / aluminum nitride have both excellent heat resistance and excellent moisture resistance. Therefore, the heat resistance and moisture resistance of the acoustic element 1 can be improved by forming the piezoelectric layer 12 with at least one of aluminum nitride and scandium / aluminum nitride.

  The thickness of the piezoelectric layer 12 can be about 0.1 μm to 10 μm, for example.

  The piezoelectric layer 12 is sandwiched between the first electrode 13a and the second electrode 13b. Each of the first and second electrodes 13a and 13b is made of, for example, at least one metal such as gold, platinum, tungsten, aluminum, copper, molybdenum, ruthenium, titanium, chromium, nickel, and alloys thereof. Can do.

  The thicknesses of the first and second electrodes 13a and 13b can be set to about 0.05 μm to 1 μm, respectively.

  In the present embodiment, the laminated body of the piezoelectric layer 12 and the vibration film 11 is sandwiched between the first and second electrodes 13a and 13b. However, the present invention is not limited to this configuration. For example, only the piezoelectric layer 12 is sandwiched between the first and second electrodes 13a and 13b, and the vibration film 11 may not be sandwiched between the first and second electrodes 13a and 13b. For example, the vibration film 11 may be disposed on the main surface of the first or second electrode 13a, 13b opposite to the piezoelectric layer 12. Furthermore, the vibration film 11 may be made of a metal foil, and the first electrode 13a may be omitted. The manufacturing cost of the piezoelectric element can be reduced by configuring the vibration film 11 with the aluminum foil.

  The piezoelectric element 10 is sandwiched between a support member 21 provided on the substrate 22 and a support member 24 provided on a casing 23 fixed to the substrate 22. The piezoelectric element 10 is supported by support members 21 and 24 apart from the substrate 22 and the casing 23.

  In the present embodiment, the support members 21 and 24 and the casing 23 are made of a conductive material such as a metal, and the control member 25 disposed on the substrate 22 via the support members 21 and 24 and the casing 23. Is electrically connected. The control member 25 is electrically connected to a terminal electrode 26 disposed on the surface of the substrate 22 opposite to the piezoelectric element 10. In addition, the control member 25 can be comprised by IC, for example.

  Next, the operation of the acoustic element 1 when the acoustic element 1 is used as a microphone will be described.

  When a sound wave is emitted toward the acoustic element 1, the sound wave reaches the piezoelectric element 10 through a plurality of openings 23 a provided in a matrix on the casing 23. As a result, sound pressure is applied to the piezoelectric element 10 and the piezoelectric element 10 vibrates. Thereby, electric charges are generated in the piezoelectric layer 12 of the piezoelectric element 10. The generated charge is converted into a voltage in the control member 25, and an electrical signal corresponding to the sound pressure is output from the terminal electrode 26.

  On the other hand, when the acoustic element 1 is used as a speaker, a voltage corresponding to the sound to be generated is applied to the piezoelectric element 10 by the control member 25. As a result, the piezoelectric element 10 vibrates and a sound wave is emitted.

  As described above, in the acoustic element 1, the sound pressure is converted into electric charges by the piezoelectric layer 12. The piezoelectric layer 12 has heat resistance superior to, for example, an electret. Unlike the electret, the piezoelectric layer 12 does not have a reduced sound pressure-to-charge conversion function even at a high temperature. Therefore, the acoustic element 1 has excellent heat resistance and can be reflow mounted.

  Further, unlike the MEMS microphone, it is not always necessary to apply a voltage to the vibration film 11. Therefore, since the drive voltage of the acoustic element 1 can be lowered, low power consumption can be realized.

  As described above, according to the acoustic element 1, it is possible to achieve both excellent heat resistance and a low driving voltage.

  From the viewpoint of further improving the heat resistance, the piezoelectric layer 12 preferably contains at least one of aluminum nitride and scandium aluminum nitride.

  Furthermore, in the acoustic element 1, it is not always necessary to provide a booster element that causes noise generation in the MEMS microphone. Therefore, the acoustic element 1 can realize low noise as compared with the MEMS microphone.

  Hereinafter, other examples of preferred embodiments of the present invention will be described. In the following description, members having substantially the same functions as those of the first embodiment are referred to by the same reference numerals, and description thereof is omitted.

(Second and third embodiments)
FIG. 2 is a schematic cross-sectional view of the acoustic element 2 according to the second embodiment. FIG. 3 is a schematic cross-sectional view of the acoustic element 3 according to the third embodiment. The acoustic elements 2 and 3 are different from the acoustic element 1 according to the first embodiment in the configuration of the piezoelectric element 10.

  As shown in FIG. 2, in the acoustic element 2 according to the second embodiment, the piezoelectric element 10 includes a plurality of piezoelectric layers. Specifically, the piezoelectric element 10 includes a piezoelectric layer 12a and a piezoelectric layer 12b whose polarization directions are opposite to each other. A first electrode 13a is disposed between the piezoelectric layer 12a and the piezoelectric layer 12b. The cross-sectional shape is substantially U-shaped so as to cover the surface of the piezoelectric layer 12a opposite to the first electrode 13a and the surface of the piezoelectric layer 12b opposite to the first electrode 13a. The vibration film 11a is arranged. A second electrode 13b having a substantially U-shaped cross section is disposed outside the vibration film 11a. Further, a vibration film 11b having a substantially U-shaped cross section is disposed outside the second electrode 13b.

  As shown in FIG. 3, also in the acoustic element 3 according to the third embodiment, the piezoelectric element 10 includes a piezoelectric layer 12a and a piezoelectric layer 12b whose polarization directions are opposite to each other. The piezoelectric layer 12a is disposed on the vibration film 11a. The piezoelectric layer 12a and the vibration film 11a are sandwiched between a pair of electrodes 13a1 and 13b1. The piezoelectric layer 12b is disposed on the vibration film 11b. The piezoelectric layer 12b and the vibration film 11b are sandwiched between a pair of electrodes 13a2 and 13b2. The electrode 13b2 and the electrode 13b1 are electrically connected.

  By providing a plurality of piezoelectric layers 12a and 12b like the acoustic elements 2 and 3, the amount of electric charges generated in the piezoelectric element 10 can be increased. Therefore, it is possible to increase the sensitivity of the acoustic elements 2 and 3 when used as a microphone and to increase the output of the acoustic elements 2 and 3 when used as a speaker.

  FIG. 4 is a graph showing the relationship between the RF power applied to the sputtering apparatus and the film stress of the scandium aluminum nitride film (Sc content: 37 at%) formed. A positive value indicates tensile stress, and a negative value indicates compressive stress. As shown in FIG. 4, for example, in the case of an aluminum nitride film not containing scandium, the film stress can be made substantially zero by adjusting the RF power input to the sputtering apparatus. For this reason, for example, even when a piezoelectric layer made of aluminum nitride is formed on a very thin and highly flexible vibrating membrane, the occurrence of warpage can be suppressed by adjusting the formation conditions of the piezoelectric layer. it can.

  In contrast, the scandium aluminum nitride film has almost no change in the film stress of the formed film even when the RF power applied to the sputtering apparatus is changed. Regardless of the RF power applied to the sputtering apparatus, film stress is generated in the scandium nitride / aluminum film. Therefore, when the piezoelectric layer containing scandium / aluminum nitride is formed on the vibration film, the laminate of the vibration film and the piezoelectric layer is greatly warped. In particular, since the compressive stress film generates a slack of the diaphragm, the acoustic characteristics may be affected as a result.

  Here, in the second and third embodiments, a plurality of laminated bodies of vibration films and piezoelectric layers are provided. The plurality of stacked bodies include a stacked body in which the directions of the piezoelectric layer with respect to the vibration film are opposite. Therefore, the film stresses of the piezoelectric layer whose direction is opposite to the vibration film cancel each other, and the warpage of the multilayer body including the vibration film, the piezoelectric layer, and the pair of electrodes is suppressed.

  Specifically, in the acoustic element 2 according to the second embodiment, the piezoelectric layer 12a is located on the z1 side of the portion of the vibration film 11a where the piezoelectric layer 12a is formed, while the piezoelectric layer 12b The film 11a is located on the z2 side of the portion where the piezoelectric layer 12b is formed. Accordingly, the film stress of the piezoelectric layer 12a and the film stress of the piezoelectric layer 12b cancel each other. Therefore, the curvature of the laminated body including the vibration films 11a and 11b, the piezoelectric layers 12a and 12b, and the electrodes 13a and 13b is suppressed.

  In the acoustic element 3 according to the third embodiment, the piezoelectric layer 12a is located on the z1 side of the vibration film 11a, while the piezoelectric layer 12b is located on the z2 side of the vibration film 11b. Accordingly, the film stress of the piezoelectric layer 12a and the film stress of the piezoelectric layer 12b cancel each other. Therefore, the curvature of the laminated body including the vibration films 11a and 11b, the piezoelectric layers 12a and 12b, and the electrodes 13a and 13b is suppressed.

  Thus, in the acoustic elements 2 and 3, since the curvature is suppressed, it is easy to obtain more excellent acoustic characteristics.

(Fourth embodiment)
FIG. 5 is a schematic cross-sectional view of the acoustic element 4 according to the fourth embodiment.

  The acoustic element 4 differs from the acoustic element 1 according to the first embodiment in the support mode of the piezoelectric element 10.

  In the acoustic element 4, the support member 21 is formed in a ring shape, and the support member 24 includes a portion having an inner diameter larger than the outer diameter of the support member 21. The piezoelectric element 10 is caulked by a support member 21 and a support member 24. In this case, an adhesive that inhibits vibration is not necessarily required for fixing the piezoelectric element 10. Therefore, the characteristics of the acoustic element 4 can be further improved.

(Fifth embodiment)
FIG. 6 is a schematic cross-sectional view of the acoustic element 5 according to the fifth embodiment.

  The acoustic element 5 differs from the acoustic element 1 according to the first embodiment in the arrangement of the control member 25. In the acoustic element 1, the control member 25 is disposed so as to overlap the piezoelectric element 10 in the z-axis direction that is the stacking direction of the piezoelectric elements 10. On the other hand, in the acoustic element 5, the control member 25 and the piezoelectric element 10 do not overlap in the z-axis direction. When viewed from the z-axis direction, the control member 25 and the piezoelectric element 10 are arranged at different positions. By doing so, the acoustic element 5 can be thinned.

  In the acoustic element 1, the opening 23 a overlaps the piezoelectric element 10 in the z-axis direction. On the other hand, in the acoustic element 5, the opening 23 a is provided at a position different from the piezoelectric element 10 when viewed from the z-axis direction. The piezoelectric element 10 is covered with a casing 23 that shields light such as visible light and infrared light.

  For this reason, it is difficult for infrared light or the like to enter the piezoelectric element 10. Therefore, even when the piezoelectric element 10 has pyroelectricity, generation of noise due to infrared light can be suppressed.

  Further, since the opening 23 a is provided at a position different from the piezoelectric element 10 when viewed from the z-axis direction, dust or the like hardly adheres to the piezoelectric element 10. Accordingly, it is possible to suppress the occurrence of noise due to the adhesion of dust or the like.

DESCRIPTION OF SYMBOLS 1-5 ... Acoustic element 10 ... Piezoelectric element 11, 11a, 11b ... Vibration film 12, 12a, 12b ... Piezoelectric layer 13a, 13a1, 13a2, 13b, 13b1, 13b2 ... Electrode 21, 24 ... Support member 22 ... Substrate 23 ... Casing 23a ... Opening 25 ... Control member 26 ... Terminal electrode

Claims (3)

A vibrating membrane made of an elastic resin material;
A piezoelectric layer disposed on the vibrating membrane;
A pair of electrodes sandwiching the piezoelectric layer and the vibrating membrane;
Bei to give a,
A plurality of laminates of the vibration film and the piezoelectric layer sandwiched between the pair of electrodes,
The piezoelectric layer includes scandium aluminum nitride;
The acoustic element, wherein the plurality of stacked bodies include a stacked body in which directions of the piezoelectric layer with respect to the vibration film are opposite . Further comprising a casing covering one side of the piezoelectric layer;
2. The acoustic element according to claim 1, wherein the casing is formed with an opening disposed at a position different from the piezoelectric layer when viewed from a stacking direction of the piezoelectric layer and the electrode. The acoustic element according to claim 2 , wherein the casing shields infrared light.

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