JP2001275190A - Piezoelectric speaker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric speaker that can ensure stable reliability by preventing deterioration or the like in sound pressure due to an ambient temperature change without causing cost increase. SOLUTION: In the piezoelectric speaker provided with a piezoelectric element 11 formed by arranging electrodes 11a, 11b to both sides of a piezoelectric ceramics 11c that is polarization-processed, a flat piezoelectric diaphragm 10 formed by adhering the piezoelectric element 11 to a metallic plate 12, a support frame 20 supporting the piezoelectric diaphragm 10, and a relay board 30 having a couple of external connection possible signal input terminals 31a, 31b respectively electrically connected to both side electrodes 11a, 11b and mounted on the support frame 20, a film resistor 35 is placed between the signal input terminals 31a, 31b of the relay board 30.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric speaker used for various kinds of portable electronic devices, in particular, a piezoelectric element obtained by applying a polarization treatment to piezoelectric ceramics is bonded to a metal diaphragm, and this is supported with a relay board. The present invention relates to a piezoelectric speaker supported on a frame.

[0002]

2. Description of the Related Art Conventional loudspeakers used in small electronic devices can be roughly classified into piezoelectric speakers and electrodynamic speakers, but the electrodynamic speakers require a voice coil and a magnet like ordinary electrodynamic speakers. On the other hand, a piezoelectric speaker is a plate-like body in which a piezoelectric element is bonded to a metal plate, so that it is suitable for reduction in size and weight, and is widely used in various portable terminals in recent years.

As a conventional piezoelectric speaker of this type, for example, there is a piezoelectric speaker as shown in FIG. 5. In this piezoelectric speaker, a thin plate-shaped piezoelectric element 101 is provided on one side with a conductive adhesive 103 on a metal plate 102. To form a piezoelectric vibration plate 100 as a sound-generating component, which is supported by a frame (not shown). Piezoelectric element 101
Has been subjected to an electric polarization process by applying a voltage so that it is polarized in the thickness direction, and electrodes 101 a and 101 b are formed on both surfaces of the piezoelectric element 101. These two electrodes 1
The method of forming the electrodes 01a and 101b is, for example, to screen-print a paste-like electrode material containing a silver component on the thin piezoelectric ceramic substrate 11c, and then bake it to form an electrode having a thickness of about 2 μm. With the recent increase in sensitivity of piezoelectric speakers, the thickness of electrodes has been reduced, and metal thin films of about 2 μm or less have been formed as electrodes by vapor deposition or sputtering.

FIG. 6 is a circuit diagram showing the configuration of an electric circuit of the piezoelectric vibration plate 100. The circuit configuration is such that the signal input terminals 122a and 122b for electrodes are connected to the electric capacitance 121 formed by the piezoelectric element 101. . Note that electrical insulation is secured between the electrode signal input terminals 122a and 122b by the relay board mounted on the frame.

However, piezoelectric speakers used in small electronic devices such as mobile phones and laptop computers are required to have high reliability (weather resistance, etc.) against environmental changes. The reliability is tested by an accelerated deterioration test taking into account the above.

FIG. 7 shows a test profile of an accelerated deterioration test for such a piezoelectric speaker for an information terminal. In this test, the piezoelectric speaker subjected to the performance test before the start of the test is set between the room temperature (20 ° C.) and the upper and lower limits of the storage environment temperature range (85 ° C., −40 ° C.) set in the product specification. A test that causes a short-term environmental temperature change between
After cooling from room temperature to −40 ° C. in 0 minutes and leaving it in a low temperature environment, it is left for a predetermined time until the environment temperature is stabilized at room temperature, and then heating from room temperature to 85 ° C. environment in 30 minutes. The process of leaving the device in a high-temperature environment is defined as one cycle, and this process is repeated for 80 cycles.
Thereafter, a performance test similar to the performance test before the start of the test is performed to determine the presence or absence of performance degradation.

In such a test, a rapid environmental temperature change occurs. However, when the electrode signal input terminals 122a and 122b are open as in the product state of the piezoelectric speaker,
The crystal of the piezoelectric ceramic substrate 11c absorbs heat to cause an electric polarization phenomenon, and the electric charge accumulated by the electric polarization in the piezoelectric element 101 is released. That is, the spontaneous polarization in the piezoelectric element 101, which has been aligned by the polarization processing, is broken by the pyroelectric effect of the piezoelectric element 101, so that the sound pressure sensitivity is reduced (hereinafter, this phenomenon is referred to as a pyroelectric drop phenomenon).

For example, when the environmental temperature is changed as shown in FIG. 7, each electrode 101a, 1a of the piezoelectric element 101 is changed.
A phenomenon in which excessive positive and negative voltages are alternately applied to both ends of 01b occurs, and the sound pressure sensitivity decreases due to the capacity deterioration of the piezoelectric element 101.

In order to suppress the deterioration of the capacity of the piezoelectric speaker and the deterioration of the sound pressure sensitivity, it is necessary to prevent an excessive charge from flowing into the piezoelectric element due to a change in environmental temperature. . Therefore, conventionally, the signal input terminal 122a,
There is one in which a conductive gel having an appropriate electric resistance component is applied between the electrodes 122b.

FIG. 8 shows an example of a piezoelectric diaphragm of a piezoelectric speaker for suppressing such a pyroelectric drop phenomenon. In the figure, a piezoelectric element 131 is composed of a piezoelectric ceramic 131c and electrodes 131a and 131b formed on both sides thereof. The piezoelectric element 131 is attached to a plate-shaped metal plate 132 by an adhesive 133 to form a piezoelectric vibrating plate 130. Has become. The piezoelectric vibrating plate 130 is provided with a conductive gel 134 having an appropriate electric resistance component and straddling the piezoelectric element 131 and the metal plate 132.

[0011]

However, in a piezoelectric speaker in which a conductive gel or the like having an electric resistance component is disposed between a piezoelectric element and a metal diaphragm as described above, the component of the conductive gel 134 is not included. Variation, furthermore, metal thin film electrode 1
Due to variations in the surface condition of the metal plate 31a and the metal plate 102,
There has been a problem that the value of the electric resistance provided between the signal input terminals varies, and it is difficult to ensure stable reliability of the piezoelectric speaker.

On the other hand, it is naturally possible to suppress variations in the components of the conductive gel 134 and variations in the surface conditions of the metal thin-film electrode 131a and the metal plate 132. However, it is inevitable that the cost increases. is there.

Accordingly, the present invention is to provide a piezoelectric speaker capable of ensuring stable and high reliability without increasing the cost.

[0014]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a piezoelectric element in which electrodes are disposed on both sides of a polarizing-processed thin plate-shaped piezoelectric ceramic, and the piezoelectric element is bonded to a metal plate. A flat plate-shaped piezoelectric vibrating plate, a support frame for supporting the piezoelectric vibrating plate, and a pair of externally connectable signal input terminals electrically connected to electrodes on both surfaces of the piezoelectric ceramic, respectively. And a relay board mounted thereon, wherein a film resistor is disposed between the signal input terminals of the relay board.

In this piezoelectric speaker, a film as a conductive resistance component having a small variation in conductivity or resistance value is provided between the signal input terminals of the relay board, which is not affected by the surface condition of the electrodes of the piezoelectric element or the metal plate. Since the resistance is formed, the required electric resistance component with little variation can be interposed between the signal input terminals for the electrodes of the piezoelectric element, and the work of individually mounting the component parts and the electric parts is unnecessary. Since, for example, an operation of soldering a resistance component is unnecessary, the cost does not increase.

Further, when the film resistor is made of a carbon film disposed between the signal input terminals, the film can be easily formed and a stable film resistance can be obtained.

Further, when the film resistor is a sintered body formed by sintering between the signal input terminals, a stable operation can be achieved even when the signal input terminals are electrically connected to the outside by soldering or the like. The film resistance state can be maintained, and the reliability is high.

[0018]

Preferred embodiments of the present invention will be described below with reference to the drawings.

1 to 4 are views showing a piezoelectric speaker according to an embodiment of the present invention.

In this piezoelectric speaker, as shown in FIGS. 1 to 3, a thin plate-shaped piezoelectric element 11 is bonded to a metal plate 12 on one side with an adhesive 13 to constitute a piezoelectric vibration plate 10. Is supported by a frame case 20 (support frame) made of metal or resin.

The piezoelectric element 11 has a structure in which electrodes 11a and 11b are formed on both surfaces of a piezoelectric body having high piezoelectric characteristics and a constant pyroelectric characteristic, for example, a thin plate-shaped piezoelectric ceramic substrate 11c made of piezoelectric ceramics. A predetermined voltage (for example, a voltage of 100 to 400 V (10 to 40 kV / cm)) is preliminarily applied to the piezoelectric ceramic substrate 11 c so as to be polarized in the thickness direction (not limited to this direction).
Is applied to perform an electric polarization process. Also,
The electrodes 11a and 11b of the piezoelectric element 11 are, for example, formed on a thin piezoelectric ceramic substrate 11c as metal thin-film electrodes of about 2 μm or less by a vapor deposition method or a sputtering method, or a silver component is formed on the piezoelectric ceramic substrate 11c. Is screen-printed and then baked to form an electrode having a film thickness of about 2 μm.

On the other hand, the frame case 20 has a rectangular recess 2.
1 is formed, and the electrode 11 of the piezoelectric element 11 is formed there.
A relay board 30 for connecting a and 11b to the outside is mounted.

As shown in the cross-sectional view of FIG. 4, the relay substrate 30 is formed as a signal land having a stable surface condition, and is connected to the piezoelectric element 11 through an electrode lead 32a.
A signal input terminal 31a on the piezoelectric element side connected to the upper electrode 11a is formed as a signal land having a stable surface condition, and the metal plate 12 is formed via an electrode lead 32b.
And a signal input terminal 31b on the metal plate 12 side, and a substrate 33 made of an insulating material that supports the signal input terminals 31a and 31b.

The signal input terminal 31 of the relay board 30
a, a film resistor 3 having a predetermined electric resistance
The film resistor 35 is formed between the signal lands of the signal input terminals 31a and 31b as shown in FIG. The film resistor 35 is a dried film made of carbon having an electric resistance component, and is a strip-shaped sintered carbon film formed by sintering.
Such a film resistance generally has a stable electric resistance value, and the film resistance 35 is set to an arbitrary resistance value from, for example, a range of 100 kΩ to 250 kΩ, and has a stable electric resistance value close to the set value. .

As shown in FIG. 2, the electric circuit configuration of such a piezoelectric speaker includes a signal input terminal 31a on the relay board 30 and an electric capacitance 41 formed by the piezoelectric element 11.
The signal input terminals 31a and 31b are short-circuited by interposing an electric resistance including a film resistor 35 between the signal input terminals 31a and 31b. It is preferable that both surfaces of the piezoelectric element 11 be covered with an insulating polymer film (not shown).

In the piezoelectric loudspeaker of this embodiment configured as described above, the signal input terminals 31a and 31b are short-circuited by the film resistance 35, which is a predetermined electrical resistance component. An electric component for interposing an electric resistance component between 31a and 31b is not required as a separate component, and the sound pressure sensitivity to an input signal voltage is reduced due to a pyroelectric effect of a piezoelectric speaker accompanying a change in environmental temperature. The phenomenon can be effectively suppressed.

Also, since no separate electric resistance component is used as a separate component, the number of components does not increase, and
Since it is not necessary to perform a soldering operation or the like for arranging the resistance component, the number of steps can be reduced as compared with the conventional case where the conductive gel is applied.

Further, since the film resistor 35 is made of a sintered carbon film having an electric resistance component, the signal input terminal 3
Even when 1a and 31b are electrically connected to the outside by soldering or the like, a stable film resistance state can be maintained, an electric resistance component having a stable resistance value can be interposed, and reliability can be improved.

In the embodiment described above, an electrical resistance component such as carbon is arranged between signal input terminals on the relay board by sintering in order to secure an electrical resistance value. The same operation can be performed by using other substances, for example, other substances that are printed in a film shape on a ceramic substrate and have a stable resistance value after quenching.

[0030]

As described above, according to the present invention, it is possible to suppress the deterioration of the capacitance and the sound pressure sensitivity due to the change of the environmental temperature, and to use the input device without using a separate electric resistance component. Since a relay board having a stable resistance component between signal terminals is used, it is possible to provide a piezoelectric speaker that can reduce the number of steps and the number of parts in an assembly process.

[Brief description of the drawings]

FIG. 1 is a plan view showing a piezoelectric speaker according to an embodiment of the present invention.

FIG. 2 is an electric circuit diagram of the piezoelectric speaker of one embodiment.

FIG. 3 is a sectional view of a piezoelectric element bonding portion in the piezoelectric speaker of one embodiment.

FIG. 4 is a sectional view of a relay board mounting portion in the piezoelectric speaker of one embodiment.

5A and 5B are views showing a conventional piezoelectric speaker, wherein FIG. 5A is a plan view thereof, and FIG. 5B is a sectional view taken along line B5-B5 of FIG.

FIG. 6 is an electric circuit diagram of a conventional piezoelectric speaker.

FIG. 7 is a diagram showing a profile of an accelerated deterioration test due to a change in environmental temperature of a piezoelectric speaker.

FIG. 8 is a view showing another conventional piezoelectric speaker, and FIG.
Is a plan view thereof, and (b) is a B8-B8 sectional view of (a).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Piezoelectric vibrating plate 11 Piezoelectric element 11a, 11b Electrode 11c Piezoelectric ceramic substrate (piezoelectric material) 12 Metal plate 13 Rubber adhesive 20 Frame case (supporting frame) 30 Relay board 31a, 31b Both signal input terminals (signal lands) 35 Film resistance (electric resistance component) 41 Electric capacity

Claims (3)

[Claims] 1. A piezoelectric element in which electrodes are respectively arranged on both sides of a polarizing-processed thin plate-shaped piezoelectric ceramic; a flat-plate-shaped piezoelectric diaphragm in which the piezoelectric element is bonded to a metal plate; and a support for the piezoelectric diaphragm. A support frame having a pair of externally connectable signal input terminals respectively electrically connected to electrodes on both surfaces of the piezoelectric ceramic, and a relay board mounted on the support frame, A piezoelectric speaker, wherein a film resistor is provided between the signal input terminals of the relay board. 2. The piezoelectric speaker according to claim 1, wherein the film resistor is made of a carbon film disposed between the signal input terminals. 3. The piezoelectric speaker according to claim 1, wherein the film resistor is a sintered body formed by sintering between the signal input terminals.