JPH05251784A - Thickness-wise longitudinal-vibration piezoelectric porcelain transformer and manufacture thereof - Google Patents

Abstract

PURPOSE:To manufacture a piezoelectric transformer capable of being operated in a high-frequency band, particularly a piezoelectric transformer for an on- board power supply, in which miniaturization and the reduction of noises are required, and to enable multi-outputs and multi-inputs. CONSTITUTION:A high impedance section 17 and a low impedance section 16 are formed integrally by alternately laminating internal electrodes and piezoelectric porcelain layers in the thickness direction. Kerfs 18 are formed to the low impedance section 16, and three independent low impedance sections 11, 12, 13 are shaped, thus manufacturing a piezoelectric porcelain transformer with a plurality of output sections or input sections.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric transformer capable of operating in a high frequency band, and more particularly to a piezoelectric ceramic transformer for an on-board power supply, which requires miniaturization and low noise, and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, an electromagnetic transformer is used as a switching power supply in order to miniaturize a power supply circuit of an electronic device, and it is desirable to increase the switching frequency to reduce the size of the switching power supply. However, when the switching frequency is increased, the hysteresis loss of the magnetic material used for the electromagnetic transformer, the eddy current loss, and the loss due to the skin effect of the conductor wire are rapidly increased, and the efficiency of the transformer is extremely low. Therefore, the upper limit of the practical frequency band of the electromagnetic transformer is at most 500 kHz. On the other hand, the laminated piezoelectric transformer is used in a resonance state, and compared with a general electromagnetic transformer, (1) the energy density is high at the same frequency, so that the piezoelectric transformer can be downsized, and (2) noncombustible. 3) It has many advantages such as no noise due to electromagnetic induction.

FIG. 5 shows the structure of a conventional Rosen type piezoelectric transformer, which is a typical laminated type piezoelectric transformer. Hereinafter, description will be given with reference to the drawings. When a high voltage is to be taken out, in the piezoelectric plate having electrodes provided on the surface, a portion indicated by 61 is a low impedance driving portion of the piezoelectric transformer, and electrodes 63 and 64 are provided on the upper and lower surfaces thereof. It is polarized in the thickness direction as indicated by 66 in the figure. Also,
Similarly, a portion indicated by 62 is a high-impedance power generation portion, an electrode 65 is provided on the end face thereof, and the power generation portion 62 is polarized in the length direction of the piezoelectric plate as indicated by 67 in the figure. The operation of this piezoelectric transformer is as follows.
When a voltage is applied to 64, longitudinal vibration is excited by the electromechanical coupling coefficient k _{31 in the} transverse effect 31 mode, and the entire transformer vibrates. Further, in the power generation portion 62, a high voltage is taken out from the output electrode 65 by the longitudinal effect longitudinal vibration mode (33 mode) due to the electromechanical coupling coefficient k ₃₃ . On the other hand, when a high voltage is input and a low voltage is output, the vertical effect high impedance portion 62 may be the input side and the horizontal effect low impedance portion 61 may be the output side. The other types of piezoelectric transformers also use the same extension vibration of a flat plate and radial vibration of a circular plate as in the Rosen type, and the applicable frequency is up to about 200 kHz.

On the other hand, the present inventors first filed Japanese Patent Application 1
The piezoelectric ceramic transformer disclosed in Japanese Patent No. 139525 has a structure in which piezoelectric ceramic plates polarized in the thickness direction are stacked, and can be operated in the MHz band by driving at the resonance frequency of longitudinal vibration of thickness.

[0005]

As shown in the above-mentioned conventional example, the applicable frequency range of the Rosen type piezoelectric transformer is only in the low frequency range of 200 kHz or less.
Further, the Rosen type piezoelectric transformer has a drawback that the bandwidth is small because it is unavoidable to use the electromechanical coupling coefficient k ₃₁ of the transverse effect vibration mode which is remarkably smaller than the electromechanical coupling coefficient of the longitudinal effect. Furthermore, Japanese Patent Application No. 1-13952
Since the piezoelectric ceramic transformer disclosed in No. 5 has a single input and a single output, it can be used only in a limited place and cannot be applied in various and wide ranges. The present invention has been made to overcome the above drawbacks.

[0006]

According to the present invention, a plurality of internal electrode layers and piezoelectric ceramic layers are alternately laminated, and the piezoelectric ceramic layers adjacent to each other via the internal electrode layers are polarized in directions opposite to each other in the thickness direction. In a laminated body, in a thickness longitudinal vibration piezoelectric ceramic transformer consisting of a low impedance portion in which a large number of thin piezoelectric ceramic layers are laminated and a high impedance portion in which a single thick or small number of thick piezoelectric ceramic layers are laminated, a low impedance portion and And / or a thickness longitudinal oscillating piezoelectric ceramic transformer having a structure in which a high impedance portion is divided into a plurality of portions by cut grooves formed in the thickness direction. In addition, the manufacturing method includes a step of producing a green sheet from a slurry composed of a piezoelectric material, a dispersion medium and a binder, a step of printing internal electrodes on the green sheet, laminating and thermocompression bonding, and performing binder removal and firing. A step of cutting into a predetermined shape, a step of forming a cut groove in a low impedance portion and / or a high impedance portion, a step of forming an external electrode, a step of applying a voltage to the external electrode to polarize, and a parallel plane polishing. And a step of adjusting the resonance frequency.

[0007]

EXAMPLES Next, examples of the present invention will be described. Figure 1
Is a perspective view of an example of the piezoelectric ceramic transformer of the present invention, and FIG. 2 is a cross-sectional connection diagram thereof. 1 and 2, the piezoelectric ceramic transformer of the present invention has a low impedance portion 16 in which a large number of piezoelectric ceramic layers 19 polarized in opposite directions in the thickness direction are laminated via internal electrode layers 14 and 15, and in the middle thereof. The high impedance portion 17 is composed of a single piezoelectric ceramic layer 10 formed via an insulating layer. Further, the low impedance portion 16 is provided with a cut groove 18 perpendicular to the stacking direction. The external electrode terminals are, as shown in FIG. 2, output terminals 21, 22, 25, 26, 27, 28 formed by alternately connecting the internal electrode layers 14 of the low impedance portion 16 outside.
Then, the input terminals are taken out from the internal electrode layers 15 located above and below the high impedance portion 17, and are designated as 23 and 24.
The total thickness of the piezoelectric ceramic layers of the high impedance portion 17 and the total thickness of the piezoelectric ceramic layers of the low impedance portion 16 are the same. Here, the piezoelectric ceramic layers of the low impedance portion are arranged such that the polarization directions of adjacent layers are opposite. Also, the cut groove 18
By providing, the three independent low impedance portions 11, 12, 13 and one high impedance portion are configured as one laminated body.

The electrode terminals 23 of the high impedance part 17,
When a high voltage having a frequency equal to the resonance frequency of the thickness longitudinal vibration is applied between 24, the entire piezoelectric ceramic transformer mechanically resonates, and the low impedance section 16 generates a voltage having the same frequency as the input voltage due to the positive piezoelectric effect. , Electrode terminals 21,2
It outputs to 2, 25, 26, 27, 28. At that time, due to the difference in impedance between the input side and the output side, the output terminal 2
The voltage between 1, 22 and between 25, 26 and 27, 28 is lower than the voltage between the input terminals 23, 24. Further, different voltages can be freely output by changing the electrode interval of the low impedance part. When converting a low voltage to a high voltage, between terminals 21 and 22, 25 and 26
If a low voltage is applied between terminals 27 and 28, terminals 23 and 2
High voltage is output from between 4. In this way, a piezoelectric transformer having multiple outputs or multiple inputs can be realized with an integrated type laminated body, and it is very effective in downsizing the power supply and reducing costs.

The resonance frequency of the thickness longitudinal vibration is expressed by the following equation, ignoring the decrease of the resonance frequency due to the piezoelectric longitudinal effect. to _{f r = n · v t /} 2t (n = 1,2,3 ···) Here, f _r: the resonance frequency of the thickness longitudinal vibration n: mode order v _t: of the longitudinal wave in the thickness direction speed of sound t: Thickness Here, if a piezoelectric ceramic transformer can be manufactured so that v _t and t are constant, the resonance frequency f _r of the thickness longitudinal vibration is also constant, but the resonance frequency is not always the designed resonance frequency due to variations in contraction rate during integral firing. Don't Therefore, a structure capable of adjusting the resonance frequency after firing is desirable. It is not easy to adjust after firing with a piezoelectric transformer that has electrodes on the upper and lower main surfaces, but by arranging a frequency adjustment layer that can be polished up and down, the desired resonance frequency can be obtained by polishing after firing. , It is possible to exactly match the drive frequency of the external circuit.

Next, efficiency will be considered. Most of the loss of the piezoelectric ceramic transformer is mechanical loss, and the mechanical loss is larger as the mechanical quality factor Qm is smaller. The mechanical quality factor Qm largely depends on the parallelism and flatness of the upper and lower principal surfaces. The surface of a piezoelectric transformer that has just been fired has poor parallelism and flatness, and its mechanical quality factor Qm is at most 1
00. On the other hand, by performing parallel plane polishing, it is possible to obtain parallelism and flatness within several μm, and a mechanical quality factor Qm of 1000 or more can be easily obtained. Further, in the piezoelectric transformer according to the present invention, the notch groove perpendicular to the main surface is formed. However, by making the interval of the notch groove such that the resonance frequency of the thickness longitudinal vibration to be used is avoided, the piezoelectric lateral effect can be obtained. Based on this, it is possible to drive the width spurious vibration out of the used band.

A piezoelectric ceramic transformer having such an internal multi-layer electrode and three independent low impedance parts in one laminated body is used in a laminated piezoelectric ceramic capacitor, a laminated piezoelectric actuator or the like. It can be manufactured by the (doctor blade method). In addition, as a method of forming the groove, it is possible to form the groove by using a dicing saw, a wire cut, or the like in the laminated body that is fired as in the present invention. In the piezoelectric ceramic transformer manufactured by such a method, the layer spacing is 25
It is possible to reduce the thickness to about μm. Therefore, 1 /
Even if the thickness longitudinal resonance vibration of the two-wavelength mode (fundamental mode with both ends free) or the one-wavelength mode (secondary mode with both ends free) is used, the laminated ceramic technique is used to
It is possible to realize a piezoelectric ceramic transformer that operates in the ultrahigh frequency region of 0 MHz band.

FIG. 3 is an explanatory view of a method of manufacturing the piezoelectric ceramic transformer having the structure shown in FIGS. The piezoelectric ceramic transformer shown in FIGS. 1 and 2 is a monolithic laminated type of a four-terminal type piezoelectric transformer having three independent low impedance portions, each of which uses a 2 MHz band thickness longitudinal secondary mode and uses piezoelectric material as a piezoelectric material. Uses a PbTiO ₃ based piezoelectric material. In the manufacturing method, as shown in FIGS. 3A to 3C, PbTiO ₃ -based piezoelectric ceramic powder as a piezoelectric material is first dispersed in a solvent together with an organic binder to form a slurry. A green sheet having a thickness of about 70 μm is produced by a casting method using a doctor blade. After that, it is punched and cut by a punching machine into a shape required for laminating and pressure bonding with a hot press machine, that is, a size suitable for a press die. The Pt paste composed of Pt, a binder, and an organic solvent is printed on the green sheet (piezoelectric ceramic layer) 10 as the internal electrode layer 14 by a screen printing method (FIG. 3A). After that, a plurality of green sheets are laminated and pressure-bonded by a heat press machine to obtain one green laminated body. This green laminated body is cut into a predetermined shape,
The binder is removed by heat treatment in air at 500 ° C. for 10 hours. After that, it is baked at 1200 ° C. for 2 hours and cut into a predetermined shape with a dicing saw to produce a laminated body as shown in FIG. After that, parallel-plane polishing is performed so as to have a thickness required for resonance frequency adjustment. In this embodiment, since the piezoelectric transformer is driven at 2 MHz, parallel plane polishing is performed so that the piezoelectric transformer has a thickness of 2.2 mm. Then, the low impedance portion is cut with a dicing saw so as to be perpendicular to the stacking direction, and a piezoelectric ceramic transformer element as shown in FIG. 3C is manufactured.

The internal electrodes are exposed on only one end face, and the external electrodes are baked on the end faces to connect the electrode terminals 21 to 28, respectively, as shown in FIG. Next, between the electrode terminals 23 and 24, between 21 and 22, between 27 and 28, 2
A DC voltage of 7 kV / mm is applied between 5 and 26 for polarization.

Next, high-frequency and high-voltage signals for exciting the longitudinal secondary mode are input from the electrode terminals 23 and 24 of the high impedance section 17, respectively, and the electrical terminals 21, 22 and 25, 26 and 27 of the low impedance section 16 are inputted. , 28 were terminated with an appropriate resistance load, and evaluated as a step-down transformer for extracting the output. In the prototype integrated piezoelectric transformer, the resonance frequencies of the output parts (low impedance parts) 11, 12, and 13 are 1.98 to 2.06 MHz, the mechanical quality factor Qm value is 845 to 870, and the maximum energy conversion efficiency is 92. ~ 94
%, The power capacity achieved 5 W each, and three completely independent output voltages were obtained. Note that FIG. 4 shows measured values of the frequency-gain and efficiency characteristics of the piezoelectric ceramic transformer 11. It is clear that the prototyped piezoelectric transformer has realized the step-down function of the transformer and high energy conversion efficiency. It was also confirmed that the desired voltage can be obtained by changing the layer spacing of one layer in the low impedance part.

As described above, the piezoelectric ceramic transformer of the present invention has the transformer step-down function and high energy conversion efficiency, is very advantageous for downsizing the power supply and reducing the cost, and realizes multiple outputs. Is clear. It should be noted that the input terminal can be used as a step-up transformer by taking out the low impedance portion and the output terminal from the high impedance portion. In this case, needless to say, a large number of inputs can be realized. Further, in this embodiment, the low impedance portion is formed of three independent laminated bodies,
It is also possible to realize multi-input and multi-output by using three independent high-impedance layers.

[0016]

As described above, in the piezoelectric ceramic transformer according to the structure of the present invention, by integrating a plurality of low impedance parts or high impedance parts, the power supply can be downsized and the cost can be reduced. Very effective. Further, it is obvious that it can be used in a wide band in a high frequency band of 1 MHz or more, and it is small in size, highly efficient, and has a large number of inputs and a large number of outputs. Therefore, it can be applied to a wide variety of applications that conventional piezoelectric transformers do not have, and has great industrial value.

[Brief description of drawings]

FIG. 1 is a perspective view of an example of a thickness longitudinal vibration piezoelectric ceramic transformer of the present invention.

FIG. 2 is a cross-sectional connection diagram of an example of the piezoelectric ceramic transformer of the present invention.

FIG. 3 is an explanatory diagram of a manufacturing method of an example of the piezoelectric ceramic transformer of the present invention.

FIG. 4 is a frequency-gain and efficiency characteristic diagram of an example of a piezoelectric ceramic transformer according to the present invention.

FIG. 5 is a perspective view of an example of a conventional Rosen type piezoelectric transformer.

[Explanation of symbols]

10 Piezoelectric ceramic layer 11, 12, 13, 16, 61 Low impedance part 14, 15, Internal electrode layer 17,62 High impedance part 18 Notch groove 19 Piezoelectric ceramic layer 21, 22, 23, 24, 25, 26, 27, 28 electrode terminals 63, 64, 65 electrodes 66, 67 polarization direction

Claims (2)

[Claims] 1. A laminate in which a plurality of internal electrode layers and piezoelectric ceramic layers are alternately laminated, and piezoelectric ceramic layers adjacent to each other through the internal electrode layers are polarized in directions opposite to each other in the thickness direction,
In a thickness longitudinal vibration piezoelectric ceramic transformer composed of a low impedance part in which a large number of thin piezoelectric ceramic layers are laminated and a high impedance part in which a single thick piezoelectric ceramic layer is laminated or a small number of layers, a low impedance part and / or a high impedance part is provided. A thickness longitudinal oscillating piezoelectric ceramic transformer having a structure divided into a plurality of parts by cut grooves formed in the thickness direction. 2. The method for manufacturing a piezoelectric ceramic transformer according to claim 1, wherein a step of producing a green sheet from a slurry comprising a piezoelectric material, a dispersion medium and a binder, and an internal electrode is printed on the green sheet, Steps of stacking and thermocompression bonding, steps of removing the binder and firing to cut into a predetermined shape, steps of forming cut grooves in the low impedance section and / or high impedance section, steps of forming external electrodes, and external electrodes A method of manufacturing a thickness longitudinal oscillating piezoelectric ceramic transformer, comprising: a step of applying a voltage to the substrate to perform polarization, and a step of parallel-plane polishing to adjust a resonance frequency.