JP3426185B2 - Piezo speaker - Google Patents

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 in various portable electronic devices, and in particular, a piezoelectric element obtained by subjecting piezoelectric ceramics to polarization treatment is attached to a metal vibrating plate, which is supported by a relay substrate. The present invention relates to a piezoelectric speaker supported by a frame.

[0002]

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

A conventional piezoelectric speaker of this type is shown in FIG. 5, for example. In this piezoelectric speaker, a thin flat plate-shaped piezoelectric element 101 is provided on one side with a conductive adhesive 103 to form a metal plate 102. The piezoelectric vibrating plate 100, which is a sounding component, is configured by being attached to the above, and is supported by a frame (not shown). Piezoelectric element 101
Has been electrically polarized by applying a voltage so as to be polarized in the plate thickness direction, and electrodes 101a and 101b are formed on both surfaces of the piezoelectric element 101. Both electrodes 1
The method of forming 01a and 101b is, for example, screen-printing a paste-like electrode material containing a silver component on a thin piezoelectric ceramic substrate 11c, and then firing the electrode material to form an electrode having a film thickness of about 2 μm. It is to be noted that with the recent increase in sensitivity of piezoelectric speakers, thinning of electrodes has progressed, 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 a configuration of an electric circuit of the piezoelectric diaphragm 100, which has a circuit configuration in which electrode capacitance signal input terminals 122a and 122b are connected to an electric capacity 121 formed by a piezoelectric element 101. . In addition, electrical insulation is secured between the signal input terminals 122a and 122b for electrodes by a relay board mounted on the frame.

By the way, piezoelectric speakers used for 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 in consideration of.

FIG. 7 shows a test profile of an accelerated deterioration test for such a piezoelectric speaker for information terminals. This test is performed at room temperature (20 ° C) and the upper and lower limits (85 ° C, -40 ° C) of the storage environment temperature range set in the product specifications, with respect to the piezoelectric speaker subjected to the performance test before the start of the test. The test that causes a short cycle of environmental temperature changes between 3
After cooling from normal temperature to −40 ° C. in 0 minutes and leaving it in the low temperature environment, it is left for a predetermined time at ambient temperature until the environmental temperature stabilizes, and then in 30 minutes from normal temperature to 85 ° C. heating. The process of leaving it in the high temperature environment is set as one cycle, and this is repeated for 80 cycles.
After that, the same performance test as the performance test before the start of the test is performed to determine the presence or absence of performance deterioration.

In such a test, abrupt environmental temperature changes occur, but 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 generate an electric polarization phenomenon, and the electric charge accumulated by the electric polarization in the piezoelectric element 101 escapes. That is, the spontaneous polarization in the piezoelectric element 101, which has been aligned by the polarization process, is destroyed by the pyroelectric effect of the piezoelectric element 101, resulting in a decrease in sound pressure sensitivity (hereinafter, referred to as a pyroelectric drop phenomenon).

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

In order to suppress the capacity deterioration as 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 the change of the environmental temperature. . Therefore, conventionally, the signal input terminals 122a,
There is one in which a conductive gel having an appropriate electric resistance component is applied between 122b.

FIG. 8 shows an example of a piezoelectric diaphragm of a piezoelectric speaker that suppresses such a pyroelectric drop phenomenon. In the figure, a piezoelectric element 131 comprises a piezoelectric ceramics 131c and electrodes 131a and 131b formed on both surfaces thereof. The piezoelectric element 131 is attached to a plate-shaped metal plate 132 with an adhesive 133 to form a piezoelectric vibrating plate 130. Has become. The piezoelectric vibrating plate 130 is provided with a conductive gel 134 which has an appropriate electric resistance component and which extends over the piezoelectric element 131 and the metal plate 132.

[0011]

However, in the piezoelectric speaker in which the conductive gel or the like having the electric resistance component is arranged between the piezoelectric element and the metal diaphragm as described above, the component of the conductive gel 134 is Variation, and further metal thin film electrode 1
31a and the variation of the surface state of the metal plate 102,
There is a problem that the value of the electric resistance arranged between the signal input terminals varies, and it is difficult to secure stable reliability of the piezoelectric speaker.

On the other hand, it is naturally conceivable to suppress variations in the components of the conductive gel 134 and variations in the surface state of the metal thin film electrode 131a and the metal plate 132, but this inevitably results in high costs. is there.

Therefore, the present invention provides a piezoelectric speaker which can secure stable and high reliability without increasing the cost.

[0014]

In order to solve the above-mentioned problems, the present invention relates to a piezoelectric element in which electrodes are arranged on both surfaces of a thin plate-shaped piezoelectric ceramic which is polarized, and the piezoelectric element is bonded to a metal plate. A flat plate-shaped piezoelectric vibrating plate, a supporting frame that supports the piezoelectric vibrating plate, and a pair of externally connectable signal input terminals that are electrically connected to the electrodes on both sides of the piezoelectric ceramics. In a piezoelectric speaker including a mounted relay board, a film resistor is arranged 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 substrate which is not affected by the surface state of the electrodes of the piezoelectric element or the metal plate. Since the resistance is formed, it is possible to interpose a required electrical resistance component with little variation between the signal input terminals for the electrodes of the piezoelectric element, and the work of individually mounting the component parts and electric parts is unnecessary. In addition, since the work of soldering the resistance component is unnecessary, the cost is not increased.

When the film resistance is made of a carbon film arranged between the signal input terminals, the film formation is easy and stable film resistance can be obtained.

Further, when the film resistance is a sintered body formed by sintering between the signal input terminals, it is stable 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]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 flat plate-shaped piezoelectric element 11 is attached to a metal plate 12 on one side thereof with an adhesive 13 to form a piezoelectric vibrating plate 10. Is supported by a frame body case 20 (support frame) made of metal or resin.

The piezoelectric element 11 is formed by forming electrodes 11a and 11b on both sides of a piezoelectric body having a high piezoelectric characteristic and a constant pyroelectric characteristic, for example, a thin plate-shaped piezoelectric ceramic substrate 11c made of piezoelectric ceramic. 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 11c so as to polarize in the plate thickness direction (not limited to this direction).
Is applied to apply electric polarization. Also,
The electrodes 11a and 11b of the piezoelectric element 11 are, for example, those formed as thin metal film electrodes of about 2 μm or less on a thin piezoelectric ceramic substrate 11c by a vapor deposition method or a sputtering method, or a silver component on the piezoelectric ceramic substrate 11c. After a paste-like electrode material containing is printed by screen, the electrode material is 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 sectional view of FIG. 4, the relay substrate 30 is formed as a signal land whose surface state is stable, and the piezoelectric element 11 is provided through the electrode lead wire 32a.
The metal plate 12 is formed as a signal input terminal 31a on the piezoelectric element side connected to the upper electrode 11a and a signal land whose surface condition is stable and through the electrode lead wire 32b.
It has a signal input terminal 31b on the side of the metal plate 12 connected to and a substrate 33 made of an insulating material that supports both signal input terminals 31a and 31b.

The signal input terminal 31 of the relay board 30 is also provided.
A film resistor 3 having a predetermined electric resistance between a and 31b
5, the film resistor 35 is formed across the signal lands of the signal input terminals 31a and 31b as shown in FIG. The film resistance 35 is a dry film-like film made of carbon having an electric resistance component, and is a belt-like 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 in the range of 100 kΩ to 250 kΩ, for example, 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 capacitance 41 formed by the piezoelectric element 11, a signal input terminal 31a on the relay board 30, and a signal input terminal 31a.
31b is connected, and an electric resistance composed of a film resistor 35 is interposed between the signal input terminals 31a and 31b to short-circuit the signal input terminals 31a and 31b. It is preferable that both surfaces of the piezoelectric element 11 are covered with an insulating polymer film (not shown).

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

Further, since an independent electric resistance component is not used as a separate component, the number of components does not increase, and moreover,
Since no soldering work or the like for disposing the resistance component is required, the number of steps can be reduced as compared with the conventional case where the conductive gel is applied.

Furthermore, 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 above embodiment, the electric resistance component such as carbon is arranged by sintering between the signal input terminals on the relay board to secure the electric resistance value. The same operation can be performed using other substances, for example, other substances that have a stable resistance value after being printed in a film on a ceramic substrate and quenched.

[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 without using the electric resistance component as a separate component. Since the relay board having a stable resistance component is used between the signal terminals, it is possible to provide a piezoelectric speaker that can reduce the number of steps in the assembly process and the number of parts.

[Brief description of 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 according to the embodiment.

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

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

5A and 5B are diagrams showing a conventional piezoelectric speaker, in which 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 acceleration deterioration test of a piezoelectric speaker due to a change in environmental temperature.

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

[Explanation of symbols]

10 Piezoelectric diaphragm 11 Piezoelectric element 11a, 11b electrodes 11c Piezoelectric ceramic substrate (piezoelectric material) 12 metal plate 13 Rubber adhesive 20 Frame case (support frame) 30 relay board 31a, 31b Both signal input terminals (signal land) 35 Film resistance (electrical resistance component) 41 Electric capacity

Claims (3)

(57) [Claims] 1. A piezoelectric element in which electrodes are arranged on both surfaces of a thin plate-shaped piezoelectric ceramic that has been polarized, a flat plate-shaped piezoelectric vibrating plate in which the piezoelectric element is attached to a metal plate, and the piezoelectric vibrating plate is supported. In a piezoelectric speaker comprising: a supporting frame; and a relay board mounted on the supporting frame, which has a pair of externally connectable signal input terminals electrically connected to electrodes on both surfaces of the piezoelectric ceramic, A piezoelectric speaker in which 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 resistance is made of a carbon film arranged 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.