JP2010212968A - Piezoelectric acoustic element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric acoustic element capable of obtaining frequency characteristics of a plurality of sound pressure levels in only one diaphragm about the piezoelectric acoustic element made of a laminated body including a piezoelectric thin film formed on a silicon substrate. <P>SOLUTION: In the piezoelectric acoustic element in which a piezoelectric thin film 403 is formed in the diaphragm 421 provided in the silicon substrate 411, upper electrodes 404a and 404b and a lower electrode 402 are provided vertically on the top surface and the bottom surface of the piezoelectric thin film 403, respectively to give voltage to the piezoelectric thin film 403. The upper electrode 404a and the lower electrode 402 form one pair of electrodes, and further, the upper electrode 404b and the lower electrode 402 form another pair of electrodes. It is possible to obtain frequency characteristics of the plurality of sound pressure levels by providing two pairs or more of electrodes provided vertically on the piezoelectric thin film. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a piezoelectric acoustic element formed of a laminate including a piezoelectric thin film formed on a silicon substrate.

  Currently, small speakers are often used in electronic devices such as mobile phones, personal computers, PDAs, headphones, and earphones. The small speakers used here are mainly classified into two types of speakers. One is a dynamic speaker, which generates sound by vibrating a diaphragm by a magnetic coupling of a voice coil and a permanent magnet (for example, see Non-Patent Document 1). The other is a piezoelectric speaker that uses the inverse piezoelectric effect of a piezoelectric body, and applies a voltage to the piezoelectric body to generate sound using a phenomenon that the piezoelectric body deforms (for example, Non-patent document 2). In recent years, there have been some developments that try to make speakers even smaller by micromachine technology (see Non-Patent Document 3, for example). In any case, a generally small speaker is provided with one electrode pair, and by applying a signal voltage to this electrode pair, a sound corresponding to the frequency characteristic of a single sound pressure level is generated.

  On the other hand, by dividing the electrodes formed on both sides of the flexible piezoelectric film into a plurality of parts on the surface of the film, a signal is supplied to each of the divided electrodes, and a piezoelectric in a small section is partially provided. There is a speaker in which a film speaker is formed and a divided vibration region is increased to enable a wide band (see Patent Document 1). This is a piezoelectric acoustic element having a plurality of diaphragms, each of which is provided with a pair of electrodes to form a different frequency characteristic, thereby enabling a wide band.

JP 2003-143694 A

Sonion A / S, “Product data sheet of MX20”, pp.1-2, 2004 Murata Manufacturing Co., Ltd., “Catalog of Piezoelectric Sound Components”, pp.5-6, 2006 K.W.Cho, S.H.Yi, Y.H.Son, and S.Y.Kweon, “Characteristics of Piezoelectric Micro-Speaker Fabricated with ZnO Thin Film”, Integrated Ferroelectrics, 89, pp.141-149, 2007

  Conventional speakers have only one electrode pair for controlling the vibration of the diaphragm for one diaphragm as a sound source. Therefore, only one frequency characteristic of the sound pressure level with respect to the control signal of the speaker can be obtained. When an application requires a sound source having a plurality of frequency bands, a plurality of diaphragms and the same number of electrode pairs are necessary, which hinders the downsizing of the application and raises the problem of cost increase. To explain with specific examples, mobile phones are currently equipped with two types of speakers called receivers and sounders. The receiver emits a reception sound during a call, and the sounder emits a ringing sound during reception. The receiver has an audio frequency band of about 300 Hz to 5 kHz, and the sounder has a frequency band of up to about 10 kHz to emit music. Both frequency characteristics are different.

  The present invention is small, and without increasing the number of speakers, a single diaphragm provided on a silicon substrate, and a plurality of electrode pairs are provided, and a plurality of pairs of electrodes are controlled to control a plurality of signals. An object of the present invention is to provide a piezoelectric acoustic element capable of obtaining a frequency characteristic of a sound pressure level.

  In order to solve the above problems, the present inventor provides a plurality of electrode pairs for controlling a piezoelectric thin film formed on a single diaphragm, and gives a signal voltage to each electrode pair. It has been found that there is a frequency characteristic of the pressure level, and the present invention has been made.

  The invention according to claim 1 is a piezoelectric acoustic element having a silicon substrate and a laminate formed on the silicon substrate, the laminate being provided on each of the piezoelectric thin film and both surfaces of the piezoelectric thin film. The upper electrode and the lower electrode are formed, and the support layer is formed on the lower electrode side. The lower electrode is formed as a single layer in the same plane, and the upper electrode is formed in two in the same plane. It is characterized by being divided into the above parts.

  The invention described in claim 2 is characterized in that a signal voltage is applied to a pair of electrodes constituted by at least one of the upper electrodes and the lower electrode.

  The invention described in claim 3 is characterized in that a signal processing circuit for driving the pair of electrodes is provided.

  According to these inventions, in a single diaphragm provided on a silicon substrate, frequency characteristics of different sound pressure levels can be obtained depending on how to select a pair of electrodes for applying a signal voltage. Therefore, in an application that requires sound sources in a plurality of frequency bands, a plurality of speakers having different characteristics are not required, contributing to downsizing and space saving of the application, and further reducing costs. Moreover, the wiring which gives a signal voltage can be simplified by making a lower electrode into a single layer and making one of electrode pairs common. Further, since the patterning of the lower electrode is unnecessary, manufacturing costs and mask costs can be suppressed.

It is a figure which shows an example 100 of the piezoelectric acoustic element by a prior art. It is the figure which looked at the piezoelectric acoustic element 100 shown in FIG. 1 from the upper surface. FIG. 2 is a diagram showing the relationship between the vibration displacement in the z-axis direction at the center of the diaphragm of the piezoelectric acoustic element 100 shown in FIG. It is a figure which shows an example 400 of the piezoelectric acoustic element which has a pair of two electrodes by Example 1 of this invention. It is the figure which looked at the piezoelectric acoustic element 400 shown in FIG. 4 from the upper surface. It is a figure which shows the calculation result of the frequency characteristic by simulation of the piezoelectric acoustic element 400 shown in FIG. It is a figure which shows the example 700 of a piezoelectric acoustic element which has a pair of three electrodes by Example 2 of this invention. It is the figure which looked at the piezoelectric acoustic element 700 shown in FIG. 7 from the upper surface. It is a figure which shows the calculation result of the frequency characteristic by simulation of the piezoelectric acoustic element 700 shown in FIG. It is a figure which shows an example of the signal processing circuit 1041 which controls the piezoelectric acoustic element 1031 which has a pair of n electrodes by Example 3 of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a view showing an example 100 of a piezoelectric acoustic element according to the prior art, and shows a cross section thereof.
A piezoelectric thin film 103 is formed on a diaphragm 121 provided on the silicon substrate 111. An upper electrode 104 and a lower electrode 102 are provided above and below the piezoelectric thin film 103. In this case, there is one electrode pair composed of the upper and lower electrodes. The diaphragm 121 includes a support layer 101, a piezoelectric thin film 103, an upper electrode 104, and a lower electrode 102 from which the thick silicon substrate 111 that supports the entire element is removed. When an AC signal voltage is applied to the upper electrode 104 and the lower electrode 102 and the piezoelectric thin film 103 is periodically deformed, the diaphragm 121 vibrates and generates a sound. In particular, when the frequency of the AC signal voltage applied to the piezoelectric thin film 103 becomes a resonance frequency determined by the structure of the diaphragm 121, the diaphragm vibrates strongly and generates a loud sound.

  FIG. 2 is a top view of the conventional piezoelectric acoustic element 100 shown in FIG. The upper electrode 104 is disposed at the center of the diaphragm 121.

  FIG. 3 is a result of calculating the relationship between the displacement oscillating in the z-axis direction when the center point of the diaphragm 121 in FIGS. 1 and 2 is the primary resonance and the tertiary resonance and the coverage of the upper electrode 104 by simulation. is there. The coverage of the upper electrode represents the ratio of the area occupied by the upper electrode to the area of the diaphragm. The size of the diaphragm 121 used in the simulation is a square of 5 [mm] × 5 [mm], the support layer 101 has an oxide film of 1.0 [μm], the piezoelectric thin film 103 has an aluminum nitride of 1.2 [μm], and the upper part. The calculation was performed assuming that the electrode 104 was aluminum 0.15 [μm] and the lower electrode 104 was tungsten 0.2 [μm]. From this structure, the primary resonant frequency was 1 [kHz], and the tertiary resonant frequency was 3.5 [kHz]. 3 shows that when the coverage of the upper electrode 104 is 41 [%], the displacement of the primary resonance becomes the maximum and the displacement of the tertiary resonance becomes small. Further, it was found that when the coverage of the upper electrode 104 is 64 [%], the displacement of the third resonance is the maximum, and the displacement of the primary resonance is about 20% lower than the coverage 41 [%]. The present inventor has realized that the size of a plurality of resonance peaks can be changed depending on the coverage of the upper electrode 104, and by arranging a plurality of upper electrodes on a single diaphragm, a plurality of sound pressure levels can be obtained. It has been found that the frequency characteristics can be obtained. Specific examples of the present invention will be described below.

  FIG. 4 is a view showing an example of a piezoelectric acoustic element 400 having two electrode pairs according to the first embodiment of the present invention. The piezoelectric acoustic element 400 in which a piezoelectric thin film 403 is formed on a diaphragm 421 provided on a silicon substrate 411. The cross section of is shown. In order to apply a voltage to the piezoelectric thin film 403, upper electrodes 404a and 404b and a lower electrode 402 are provided above and below the piezoelectric thin film 403. The upper electrode 404a and the lower electrode 402 form one electrode pair, and the upper electrode 404b and the lower electrode 402 form another electrode pair. In this case, there are two electrode pairs.

  FIG. 5 is a top view of the piezoelectric acoustic element 400 shown in FIG. 4 so that the positional relationship between the upper electrodes 404a and 404b can be easily understood. The shape of the diaphragm 421 shown here is a square, but is not limited to a square, and the shape may be a rectangle, a circle, an ellipse, or the like. The upper electrode 404a is disposed at the center of the diaphragm 421, and the upper electrode 404b is disposed so as to surround it.

  FIG. 6 shows the frequency characteristics when a signal voltage is applied to the upper electrode 404a and the lower electrode 402 calculated by simulation, and when the signal voltage is applied between the lower electrode 402 with the upper electrodes 404a and 404b at the same potential. The frequency characteristics of are shown. Here, the vertical axis in FIG. 6 represents the square of the sound pressure, which is obtained by squaring and summing the speed in the z-axis direction at each position of the diaphragm. Is correlated with the square of the sound pressure. In the simulation, the calculation is performed such that the coverage of the upper electrode 404a is 41 [%] and the total coverage of the upper electrodes 404a and 404b is 64 [%]. From the calculation result of FIG. 6, the result of the upper electrode 404a and the result of setting the upper electrodes 404a and 404b to the same potential both have the same magnitude of the square of the sound pressure of the primary resonance. It can be seen that the square of the sound pressure of the secondary resonance is slightly larger than the primary resonance in the result of the upper electrode 404a and lower than the primary resonance in the result of setting the upper electrodes 404a and 404b to the same potential. . From this result, for example, when it is desired to lower the sound pressure at a high frequency, it is preferable to select a combination in which the upper electrodes 404a and 404b are set to the same potential and a signal voltage is applied between the lower electrodes. Here, the peak of the square of the sound pressure stands discretely. However, when the degree of damping is increased, each peak decreases and the half-value width tends to increase. That is, when the degree of damping is increased, the frequency characteristic tends to become flat.

  FIG. 7 is a diagram illustrating an example of a piezoelectric acoustic element 700 having three electrode pairs according to Embodiment 2 of the present invention. The second embodiment is an example different from the first embodiment, and shows a cross section of a piezoelectric acoustic element in which a piezoelectric thin film 703 is formed on a diaphragm 721 provided on a silicon substrate 711. In order to apply a voltage to the piezoelectric thin film 703, upper electrodes 704c, 704d, and 704e and a lower electrode 702 are provided above and below the piezoelectric thin film 703. Each of the upper electrodes 704c, 704d, and 704e forms an electrode pair with the lower electrode 702, and there are three electrode pairs.

  FIG. 8 is a top view of the piezoelectric acoustic element shown in FIG. 7 so that the positional relationship between the upper electrodes 704c, 704d, and 704e can be easily understood. The shape of the diaphragm 721 shown here is a square, but is not limited to a square, and this shape may be a rectangle, a circle, an ellipse, or the like. The upper electrode 704c is disposed at the center of the diaphragm 721, and the upper electrodes 704d and 704e are disposed so as to sandwich the upper electrode 704c.

  9 shows frequency characteristics when a signal voltage is applied to the upper electrode 704c and the lower electrode 702 calculated by simulation, frequency characteristics when a signal voltage is applied to the upper electrode 704d and the lower electrode 702, and the upper electrode 704c, Frequency characteristics when 704d and 704e are set to the same potential and a signal voltage is applied to the lower electrode 702 are shown. In the simulation, the total electrode area is calculated as three equal parts so that the total coverage of the upper electrodes 704c, 704d, and 704e is 64 [%]. From the calculation result of FIG. 9, it can be seen that the peak of the square of the sound pressure is not seen at a frequency of 13 [kHz] or higher in the result of setting the upper electrodes 704c, 704d, and 704e to the same potential. On the other hand, the result of the upper electrode 704d and the result of the upper electrode 704c show a peak even at a frequency of 13 [kHz] or higher. It can also be seen that the number of peaks of 13 [kHz] or less is large in the result of the upper electrode 704d. In any case, the frequency characteristics are different, and an appropriate electrode pair is selected according to the frequency characteristics required by the application, and a signal voltage may be applied.

  FIG. 10 is an example of a signal processing circuit 1041 that controls a piezoelectric acoustic element 1031 having a pair of n electrodes. The signal processing circuit 1041 includes a signal voltage source 1051, a switch group 1052, and a control device 1053 for controlling them. The piezoelectric acoustic element 1031 has n upper electrodes and one lower electrode on a single diaphragm, and constitutes a pair of n electrodes on the diaphragm. Each of the upper electrodes has a signal terminal so that a signal voltage is applied to each of the upper electrodes. The signal processing circuit 1041 generates a signal voltage serving as a sound source by the voltage signal source 1051, an appropriate switch of the switch group 1041 is closed by a command from the control device 1053, and a signal is sent to a selected signal terminal of the piezoelectric acoustic element 1031. A voltage is given. The signal voltage source 1051 is controlled by the controller 1053 so as to generate a signal voltage suitable for the frequency characteristic of the selected electrode pair. As a practical example, when the piezoelectric acoustic element 1031 has the characteristics of the receiver and the sounder, the switches of the switch group 1041 are closed so as to select the upper electrode suitable for the frequency characteristics of the receiver from the controller 1053. Then, a signal voltage in which a frequency characteristic in a lower frequency range is emphasized than the signal voltage source 1051 is generated, and the signal voltage is applied to the selected upper electrode. When it is desired to operate as a sounder, the switch of the switch group 1041 is closed so that the upper electrode suitable for the frequency characteristic of the sounder is selected, and the signal voltage that emphasizes the frequency characteristics in the higher range than the signal voltage source 1051. And a signal voltage is applied to the selected upper electrode.

  Regarding the materials constituting the diaphragm described so far, the piezoelectric thin films 103, 403, and 703 are not limited to aluminum nitride but may be zinc oxide or lead zirconate titanate. The lower electrode 102, 402, 702 and the upper electrode 104, 404a, 404b, 704c, 704d, 704e are made of any metal material of aluminum, titanium, polysilicon, gold, platinum, tungsten, molybdenum, or the above metal material. An alloy containing the main component is preferable. For the support layers 101, 401, and 701, a silicon compound film such as a silicon oxide film or a silicon nitride film or a laminated film thereof is preferably used. In order to form the diaphragms 121, 421, 721, the silicon substrates 111, 411, 711 may be excavated from the back surface opposite to the piezoelectric thin films 103, 403, 703, or the diaphragms 121, 421, 721 may be formed. Alternatively, an appropriate through hole may be opened and excavated from a surface that is the same surface as the piezoelectric thin films 103, 403, and 703.

  The signal processing circuit 1041 may be composed of discrete electronic components, or may be integrated as a semiconductor IC. Further, the signal processing circuit 1041 integrated as an IC may be packaged separately from the piezoelectric acoustic element 1031 or may be configured in the same packaging as the piezoelectric acoustic element 1031. In the case where the signal processing circuit 1041 and the piezoelectric acoustic element 1031 are packaged in the same package, they may be formed separately, or the signal processing circuit 1041 may be formed on the silicon substrate of the piezoelectric acoustic element 1031.

  As mentioned above, although embodiment in this invention was shown, it is clear that this invention can be implement | achieved with a various form further, and is not restrict | limited to embodiment mentioned above.

  The piezoelectric acoustic element of the present invention can be suitably used in the field of acoustic parts that require a reduction in the size of the system or a plurality of sound pressure level frequency bands, and the field of products in which the acoustic parts are mounted.

101, 401, 701 Support layer 102, 402, 702 Lower electrode 103, 403, 703 Piezoelectric thin film 104, 404a, 404b, 704c, 704d, 704e Upper electrode 111, 411, 711 Silicon substrate 121, 421, 721 Diaphragm 1031 Piezoelectric acoustic Element 1041 Signal processing circuit 1051 Signal voltage source 1052 Switch group 1053 Control device

Claims (3)

A silicon substrate;
A piezoelectric acoustic element having a laminate formed on the silicon substrate,
The laminate is a piezoelectric thin film;
An upper electrode and a lower electrode formed on each of both surfaces of the piezoelectric thin film;
A support layer formed on the lower electrode side,
The lower electrode is formed of a single layer in the same plane;
2. The piezoelectric acoustic element according to claim 1, wherein the upper electrode is divided into two or more parts in the same plane. At least one of the upper electrodes;
2. The piezoelectric acoustic element according to claim 1, wherein a signal voltage is applied to a pair of electrodes composed of the lower electrode.   The piezoelectric acoustic element according to claim 1, wherein a signal processing circuit that drives the pair of electrodes is provided.

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