JP2013017344A - Piezoelectric type fan - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric type fan which stably maintains wind force larger than a certain magnitude even when manufacturing variations and environmental changes such as temperature changes occur.SOLUTION: A piezoelectric type fan has: thin plates 1, 2, 3; a connection part 4 connecting the thin plates 1, 2, 3; piezoelectric elements 5, 6, 7 respectively installed on the thin plates 1, 2, 3. Each of the piezoelectric elements 5, 6, 7 has a piezoelectric material and a driving electrode installed so as to sandwich the piezoelectric material, and the respective thin plates are bent and vibrated by applying AC voltages to the driving electrodes. A piezoelectric element for monitor 8, including a monitor electrode, is installed at the connection part 4. The voltages applied to the driving electrodes of the piezoelectric elements 5, 6, 7 are individually adjusted by signals obtained from the monitor electrode of the piezoelectric element for the monitor 8.

Description

  The present invention relates to a piezoelectric fan using piezoelectric vibration used for cooling electronic devices.

  The piezoelectric fan is generally a blower that generates a wind by bending and vibrating a thin plate by bonding a piezoelectric body to a thin plate made of a light and high-strength material and applying an AC voltage to the piezoelectric body. Since it is necessary to increase the vibration amplitude of the thin plate in order to obtain a large wind force, it is advantageous to use a primary bending vibration mode when the thin plate is cantilevered.

  When compared to an electromagnetic fan that is a blower that rotates a metal or resin propeller using an electromagnetic motor, the piezoelectric fan consumes less power and does not generate electromagnetic noise that interferes with the electronic signals of peripheral devices. In addition, it has advantages such as being quiet, but has a disadvantage that the wind force is small.

  Currently, in order to make use of the above-mentioned characteristics, piezoelectric fans are being studied for practical use, for example, for cooling electronic components mounted on portable devices, and obtaining large wind power is an important practical issue. It has become.

  As a conventional technique for obtaining a large wind force, for example, a tuning fork type vibrator structure described in Patent Document 1 is known. FIG. 7 is a plan view of a vibrator used in the conventional piezoelectric fan described in Patent Document 1. FIG. In FIG. 7, piezoelectric elements 36 a and 36 b are joined to the thin plate 31, and piezoelectric elements 37 a and 37 b are joined to the thin plate 32. The thin plates 31 and 32 are cantilevered at one end of the connecting portion 34. The other end of the connecting portion 34 is fixed. By applying an AC voltage to each of the piezoelectric elements 36a, 36b, 37a, 37b, the so-called tuning fork vibration in which the thin plates 31, 32 bend and vibrate in opposite directions in the X-axis direction is excited. By adopting such a tuning fork type structure, the Q value of the vibrator is increased, the oscillation is stabilized, the wind power is increased, and at the same time, the leakage of vibration from the connecting portion 34 which is a support fixing portion is reduced. By reducing the leakage of vibration from the support fixing portion, it is possible to suppress a decrease in vibration amplitude and an adverse effect on peripheral devices.

  Patent Document 2 describes a structure in which three thin plates of a piezoelectric fan vibrator are arranged in a plane. FIG. 8 is a plan view of a vibrator used in the conventional piezoelectric fan described in Patent Document 2. FIG. In FIG. 8, piezoelectric elements 45, 46, and 47 are joined to thin plates 41, 42, and 43, respectively, and are cantilevered and fixed by a connecting portion 44. An AC voltage is applied to each piezoelectric element, and the outer thin plates 41 and 43 are bent and vibrated in the Z-axis direction with the same phase and the central thin plate 42 with the opposite phase. If the structure of the thin plate and the piezoelectric element is designed so that the vibration energy of the outer thin plates 41 and 43 and the central thin plate 42 are equal, vibration leakage from the connecting portion 44 that is a support fixing portion can be reduced. An effect equivalent to that of the vibrator can be obtained. Furthermore, since the vibrator of FIG. 8 has a planar structure, it can be easily assembled.

JP-A-62-55500 Japanese Utility Model Publication No. 3-35298

  However, in the conventional piezoelectric fan vibrator, when environmental changes such as manufacturing variations and temperature changes occur, the balance of vibration energy of multiple thin plates is lost, and as a result, vibration leaks from the support fixing part to the outside. There is a risk that the air blowing capability may be reduced or the peripheral devices may be adversely affected.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a piezoelectric fan that can stably maintain wind power of a certain magnitude or more even when environmental variations such as manufacturing variations and temperature changes occur.

  In order to solve the above problems, a piezoelectric fan of the present invention includes a plurality of thin plates, a connecting portion that connects the plurality of thin plates, and a piezoelectric body that is installed on at least a part of the plurality of thin plates. In a piezoelectric fan using a vibrator, the piezoelectric fan includes a plurality of drive electrodes for bending and vibrating the plurality of thin plates, and a monitor electrode installed in the connecting portion, and a signal obtained from the monitor electrode, The voltage applied to the plurality of drive electrodes is individually adjusted.

  Here, the plurality of thin plates and the connecting portion may be integrally formed in the same flat plate, and the plurality of drive electrodes and the monitor electrode may be formed on the same surface of the flat plate.

  Also, the output voltage obtained from the oscillation circuit or the voltage obtained by inverting the output voltage obtained from the oscillation circuit and the voltage obtained by passing the signal obtained from the monitor electrode through the current detection circuit and the phase shift circuit are added. Then, it may be applied to the plurality of drive electrodes.

  As described above, in the present invention, a monitor electrode is provided in a connecting portion that is a support portion of a plurality of thin plates, and a voltage applied to a drive electrode for vibrating each thin plate based on a signal obtained from the monitor electrodes Were adjusted individually. As a result, even when environmental changes such as manufacturing variations and temperature changes occur, it can be adjusted to always maintain the balance of vibration energy of multiple thin plates, so there is no vibration leakage to the support fixing part, A piezoelectric fan that can stably maintain wind power of a certain size or larger can be obtained.

  Moreover, the structure of the vibrator can be simplified by forming a plurality of thin plates and connecting portions integrally in the same flat plate, and forming a plurality of drive electrodes and monitor electrodes on the same surface of the flat plate, A piezoelectric fan that is easy to manufacture and can stably maintain wind power of a certain size or larger can be obtained.

  Furthermore, in the present invention, an output voltage obtained from the oscillation circuit, or a voltage obtained by inverting the output voltage obtained from the oscillation circuit, and a voltage obtained by passing a signal obtained from the monitor electrode through the current detection circuit and the phase shift circuit, Can be added to the plurality of drive electrodes to simplify the circuit for controlling the drive of the vibrator, and the wind power of a certain size or more can be stabilized stably including the control unit. A piezoelectric fan that can be maintained is obtained.

  As described above, according to the present invention, it is possible to obtain a piezoelectric fan that can stably maintain a wind force of a certain magnitude or more even when manufacturing variations or environmental changes such as temperature changes occur.

The top view of the vibrator | oscillator used for 1st Embodiment of the piezoelectric fan by this invention. Sectional drawing of the Example of the vibrator | oscillator used for 1st Embodiment of the piezoelectric fan by this invention. The block diagram which shows an example of the drive circuit used for 1st Embodiment of the piezoelectric fan by this invention. The top view of the vibrator | oscillator used for 2nd Embodiment of the piezoelectric fan by this invention. The top view of the vibrator | oscillator used for 3rd Embodiment of the piezoelectric fan by this invention. The figure which shows the measurement result of the temperature characteristic of the vibration amplitude of the thin-plate front-end | tip of the piezoelectric fan by this invention, and the conventional piezoelectric fan. The top view of the vibrator | oscillator used for the conventional piezoelectric fan. The top view of the vibrator | oscillator used for the conventional piezoelectric fan.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a plan view of a vibrator used in the first embodiment of the piezoelectric fan according to the present invention. In FIG. 1, the vibrator of the present embodiment has three thin plates, a thin plate 1, a thin plate 2, a thin plate 3, a connecting portion 4 that connects these thin plates, and thin plates 1, 2, and 3. It has installed piezoelectric elements 5, 6, 7. Each of the piezoelectric elements 5, 6, and 7 has a piezoelectric body and drive electrodes that are disposed so as to sandwich the piezoelectric body. By applying an AC voltage to these drive electrodes, each thin plate is bent and vibrated. It is configured to let you. In addition, the connecting portion 4 is provided with a monitoring piezoelectric element 8 having a monitor electrode. As shown in FIG. 1, in the vibrator of the present embodiment, three thin plates, thin plates 1, 2, 3 and a connecting portion 4 are integrally formed in the same flat plate, and three piezoelectric elements 5, The drive electrodes 6 and 7 and the monitor electrode of the monitor piezoelectric element 8 are formed on the same plane of the flat plate. In the piezoelectric fan of the present embodiment, the voltage applied to the drive electrodes of the piezoelectric elements 5, 6, and 7 is individually adjusted by a signal obtained from the monitor electrode of the monitor piezoelectric element 8. In the present embodiment, driving is performed so that the thin plate 1 and the thin plate 3 and the thin plate 2 of the vibrator are in opposite phases and cause a primary bending vibration mode in the Z-axis direction. In this case, the signal obtained from the monitor electrode of the monitor piezoelectric element 8 is fed back to the individual drive voltage signals applied to the drive electrodes of the piezoelectric elements 5, 6, 7, and the total vibration energy of the thin plate 1 and thin plate 3 and the thin plate By equalizing the vibration energy of 2, vibration leakage from the connecting portion 4 can be suppressed.

  FIG. 4 is a plan view of a vibrator used in the second embodiment of the piezoelectric fan according to the present invention. In FIG. 4, the vibrator of the present embodiment includes two thin plates, a thin plate 11 and a thin plate 12, a connecting portion 14 that connects these thin plates, and a piezoelectric element installed on each of the thin plates 11 and 12. 16 and 17. Each of the piezoelectric elements 16 and 17 has a piezoelectric body and drive electrodes installed so as to sandwich the piezoelectric body. By applying an AC voltage to these drive electrodes, each thin plate is bent and vibrated. It is configured. In addition, the connecting portion 14 is provided with a monitoring piezoelectric element 18 having a monitor electrode. As shown in FIG. 4, in the vibrator of the present embodiment, the two thin plates 11 and 12 and the connecting portion 14 are integrally formed in the same flat plate, and the drive electrodes of the two piezoelectric elements 16 and 17 are formed. And the monitor electrode of the monitor piezoelectric element 18 are formed on the same surface of the flat plate. Further, in the piezoelectric fan of the present embodiment, the voltage applied to the drive electrodes of the piezoelectric elements 16 and 17 is individually adjusted by a signal obtained from the monitor electrode of the monitoring piezoelectric element 18.

  The vibrator of the piezoelectric fan according to the present embodiment is a vibrator using two thin plates. In the piezoelectric fan according to the present embodiment, by applying an AC voltage having a reverse phase to the piezoelectric elements 16 and 17, bending vibrations in the Z-axis direction that are opposite to each other are excited on the thin plates 11 and 12. By inverting the output of the monitoring piezoelectric element 18 provided in the connecting portion 14 and feeding it back to the piezoelectric elements 16 and 17, the balance of vibrations excited on the thin plates 11 and 12 can be controlled, and manufacturing variations, temperature changes, etc. Even when an environmental change occurs, a high amplitude can be stably maintained. The present invention can be realized as long as the vibrator has two or more thin plates, and the number of thin plates may be four or more.

  FIG. 5 is a plan view of a vibrator used in the third embodiment of the piezoelectric fan according to the present invention. In FIG. 5, the vibrator of the present embodiment includes two thin plates, a thin plate 21 and a thin plate 22, a connecting portion 24 that connects these thin plates, and piezoelectric elements 26 a and 26 b that are joined so as to sandwich the thin plate 21. And piezoelectric elements 27 a and 27 b joined so as to sandwich the thin plate 22. Each of the piezoelectric elements 26a, 26b, 27a, and 27b has a piezoelectric body and driving electrodes installed so as to sandwich the piezoelectric body. By applying an AC voltage to the driving electrodes, each thin plate is formed. It is configured to bend and vibrate. The connecting portion 24 is provided with monitor piezoelectric elements 28a and 28b having monitor electrodes. As shown in FIG. 5, the vibrator of the present embodiment has the same structure as the conventional tuning fork vibrator structure shown in FIG. 7, except for the monitor piezoelectric elements 28a and 28b. In the piezoelectric fan of the present embodiment, the voltages applied to the drive electrodes of the piezoelectric elements 26a, 26b, 27a, and 27b are individually adjusted by signals obtained from the monitor electrodes of the monitor piezoelectric elements 28a and 28b.

  That is, if the monitor signals obtained from the monitor piezoelectric elements 28a and 28b are fed back to the individual drive voltage signals of the drive piezoelectric elements 26a, 26b, 27a and 27b, the balance of vibrations excited on the thin plates 21 and 22 is achieved. Therefore, even when an environmental change such as a manufacturing variation or a temperature change occurs, a high amplitude can be stably maintained. In addition, as the piezoelectric body of the vibrator of the piezoelectric fan of the present embodiment, a bulk piezoelectric body obtained by normal firing or the like is used, and the piezoelectric body is attached to a thin plate to constitute the vibrator.

  Hereinafter, a specific example of the vibrator used in the first embodiment of the piezoelectric fan according to the present invention shown in FIG. 1 will be described in detail. In the present embodiment, the thin plates 1, 2, 3 and the connecting portion 4 are integrally formed of a single crystal silicon flat plate. In addition, lead zirconate titanate (hereinafter referred to as PZT) was used as the piezoelectric body constituting the piezoelectric elements 5, 6, 7 and the monitoring piezoelectric element 8.

  A specific manufacturing method is as follows. First, a silicon oxide film having a thickness of 100 nm is formed on the surface of a 4-inch single crystal silicon substrate having a mirror surface by polishing, and then titanium having a thickness of several tens of nanometers serving as a lower electrode. A film and a platinum film with a thickness of 100 nm, a PZT film with a thickness of 2 μm serving as a piezoelectric body, and a platinum film with a thickness of 100 nm serving as an upper electrode were sequentially formed by sputtering. The method of forming each electrode or PZT film is not limited to sputtering. For example, in the case of a PZT film, a sol-gel method, an ion plating method, a hydrothermal synthesis method, an MOCVD method, an aerosol deposition method, screen printing The film can also be formed by a method or the like. With respect to a film forming method in which the crystal is not grown by heat treatment during film formation, it is necessary to perform heat treatment after the film formation in order to increase the piezoelectricity of PZT. The heat treatment temperature is preferably about 600 ° C., although it is necessary to consider peeling due to internal stress of PZT, PZT composition shift due to silicon diffusion, and the like.

  After the above film formation, a resist was formed into a desired pattern by using a general photolithography technique consisting of resist coating, exposure, and development steps. Note that the mask pattern used for exposure was laid out so that about one hundred piezoelectric vibrators could be produced on a 4-inch single crystal silicon substrate.

  Next, after removing the platinum film layer on the outermost surface where the resist is opened by dry etching, the resist is removed. Similarly, unnecessary portions of the PZT film layer, the platinum film layer, the titanium film layer, and the silicon layer were sequentially removed by photolithography and dry etching.

  FIG. 2 is a cross-sectional view of an example of the vibrator used in the first embodiment of the piezoelectric fan according to the present invention, and shows a cross-sectional view of the ZX plane including the piezoelectric elements 5, 6, and 7 in FIG. . The upper electrodes 5a, 6a and 7a are the outermost platinum film layers. The piezoelectric films 5b, 6b, and 7b are PZT film layers. The lower electrodes 5c, 6c, and 7c are platinum film layers having a titanium film as a base. The thin plates 1, 2, and 3 are silicon single crystal substrates having an oxide film formed on the surface. The connecting portion 4 where the monitoring piezoelectric element 8 is installed also has a similar cross-sectional structure. After fabrication of the vibrator, a high electric field of 10 V / μm was applied between the lower electrode and the upper electrode for several minutes to perform a polarization treatment for enhancing piezoelectricity. Through the steps as described above, the vibrator used in the first embodiment of the piezoelectric fan according to the present invention was manufactured.

  FIG. 3 is a block diagram showing an example of a drive circuit used in the first embodiment of the piezoelectric fan according to the present invention. First, all the lower electrodes are connected to ground or a reference power source. The output of the oscillation circuit 51 was input to the adder circuit 53, the output of the adder circuit 53 was connected to the upper electrode of the piezoelectric element 6, and an alternating drive voltage signal was applied between the upper electrode and the lower electrode of the piezoelectric element 6. At the same time, the output was input to the addition circuits 54 and 55 via the inversion circuit 52 that inverts the phase of the drive voltage signal, and the outputs of the addition circuits 54 and 55 were connected to the piezoelectric element 5 and the piezoelectric element 7, respectively. In this case, self-excited oscillation could be achieved by monitoring the drive current. It should be noted that the phase characteristics and filter characteristics of the oscillation circuit, and the piezoelectric element 5, so that the thin plate 1 and the thin plate 3 and the thin plate 2 of the vibrator are in reverse phase and resonate in the first bending vibration mode in the Z-axis direction 6 and 7 shapes need to be designed. Here, for example, in the above embodiment, when a small vibrator is configured with the thin plate of the vibrator having a length of 2 mm and a thickness of 80 μm, the resonance frequency of the primary bending vibration is 23 kHz. The self-excited oscillation may be performed at the frequency. The output of the monitoring piezoelectric element 8 is input to the adder circuits 53, 54, and 55 via the current detection circuit 56 and the phase shift circuit 57.

  If the total width of the thin plates 1 and 3 and the width of the thin plate 2 are substantially equal, the total vibration energy of the thin plates 1 and 3 and the vibration energy of the thin plate 2 during driving vibration can be approximately equal. The vibration energy can be efficiently reflected, that is, a resonance state with little attenuation can be obtained. In this case, vibration leakage occurring in the connecting portion 4 can be suppressed, and a decrease in vibration amplitude due to vibration leakage from the support fixing portion, that is, a decrease in wind power and an adverse effect on peripheral devices can be suppressed. In addition, since the vibration of the vibrator is complicated due to a torsional element in addition to the bending, the thin plate 1 is actually used by using a finite element method analysis or the like so that the vibration amplitude of the connecting portion 4 is minimized. A few shapes need to be designed strictly.

  The monitoring piezoelectric element 8 provided in the vicinity of the support fixing portion of the connecting portion 4 has a generated charge of 0 (zero) in an ideal state where there is no vibration leakage. Precisely, the distortion of the connecting part that occurs when the outer thin plate is bent and the distortion of the connecting part that occurs when the central thin plate bends are mixed in the connecting part, and the total generated charge Became 0 (zero).

  Actually, vibration leakage may occur due to processing errors of the vibrator, or even if there is no vibration leakage at normal temperature, vibration leakage may occur due to material constant changes accompanying temperature changes. Electric charges are generated in the monitoring piezoelectric element 8. For example, when the vibration energy of the outer thin plate is larger than the vibration energy of the central thin plate, the monitor piezoelectric element 8 has a signal having the same phase as the drive voltage signal of the driving piezoelectric elements 5 and 7 for driving the outer thin plate. Was to occur. On the contrary, when the vibration energy of the central thin plate is large, a signal having the same phase as the drive voltage signal of the piezoelectric element 6 is generated from the monitoring piezoelectric element 8.

  Therefore, in order to suppress the vibration leakage, the driving voltage of the thin plate having a large vibration energy may be lowered. Therefore, the output of the monitoring piezoelectric element 8 is transferred to the piezoelectric elements 5, 6 and 7 via the current detection circuit and the phase shift circuit. Give feedback. Basically, the voltage obtained by reversing the charge generated by the monitor piezoelectric element 8 may be added to the drive voltage signals of the drive piezoelectric elements 5, 6, 7. Specifically, as shown in FIG. 3, the generated charge from the monitoring piezoelectric element 8 is converted into a voltage by the current detection circuit 56 and the phase is adjusted via the phase shift circuit 57, and the oscillation circuit The output of 51 and the output of the inverting circuit 52 are added by the adder circuits 53, 54 and 55, respectively, and these outputs are applied to the respective driving piezoelectric elements. In the drive circuit of FIG. 3, if an auto gain control circuit capable of automatically varying the amplification factor so that the output of the current detection circuit 56 is reduced is added, even if the processing error of the vibrator varies and individual differences occur. Alternatively, even if the material constants of silicon and PZT change with temperature, the vibration energy of each thin plate is automatically adjusted, and vibration leakage can be reduced automatically.

  Next, a description will be given of results obtained by actually making a prototype of the vibrator used in the first embodiment of the piezoelectric fan according to the present invention by the above manufacturing method and evaluating the effect of the present invention. In the prototype of the prototype, the Qm value in the first-order bending vibration mode was 1600 at room temperature, and the vibration amplitude at the tip of the thin plate generated by applying the drive voltage signal of 1 Vp-p was 50 μm. The vibrator is bonded and mounted on a glass epoxy circuit board with an epoxy resin and connected to a circuit component by wire bonding. In the case where the piezoelectric fan according to the present invention is configured by using the above-produced vibrator and using a drive circuit that feeds back the signal of the monitor piezoelectric element 8 to the drive voltage signal of the piezoelectric elements 5, 6, and 7, The temperature characteristics of the vibration amplitude at the tip of the thin plate were evaluated in the case where a conventional piezoelectric fan that drives the piezoelectric elements 5, 6, and 7 without using the piezoelectric element 8 was configured. In this evaluation, an evaluation sample was set on a hot plate, the temperature was changed, and the vibration amplitude was measured with a laser Doppler vibrometer. FIG. 6 is a diagram showing the measurement results of the temperature characteristics of the vibration amplitude of the thin plate tips of the piezoelectric fan according to the present invention and the conventional piezoelectric fan. As shown in FIG. 6, in the piezoelectric fan according to the present invention, the degree of temperature change of the vibration amplitude based on the room temperature of 20 degrees can be reduced to about 1/10 compared with the conventional piezoelectric fan.

  It goes without saying that the present invention is not limited to the above-described embodiments and examples, and the design can be changed according to the purpose and application. For example, the shape and material of the thin plate, the structure and shape of the piezoelectric element and the piezoelectric element for monitoring, the arrangement location, the number of thin plates, etc. can be changed according to the application. In addition, all of the thin plate or only the portion that excites vibration can be a piezoelectric body. In this case, an electrode is provided in the vibration drive portion, and the functions of the piezoelectric element and the monitoring piezoelectric element are provided on the thin plate itself. Can be given.

1, 2, 3, 11, 12, 21, 22, 31, 32, 41, 42, 43 Thin plates 4, 14, 24, 34, 44 Connecting portions 5, 6, 7, 16, 17, 26a, 26b, 27a 27b, 36a, 36b, 37a, 37b, 45, 46, 47 Piezoelectric element
8, 18, 28a, 28b Piezoelectric elements 5a, 6a, 7a for monitoring Upper electrodes 5b, 6b, 7b Piezoelectric films 5c, 6c, 7c Lower electrode 51 Oscillation circuit 52 Inversion circuit 53, 54, 55 Addition circuit 56 Current detection circuit 57 Phase shift circuit

Claims (3)

  In a piezoelectric fan using a vibrator having a plurality of thin plates, a connecting portion for connecting the plurality of thin plates, and a piezoelectric body disposed on at least a part of the plurality of thin plates, each of the plurality of thin plates is bent. A plurality of drive electrodes for oscillating and a monitor electrode installed in the connecting portion, wherein a voltage applied to the plurality of drive electrodes is individually adjusted by a signal obtained from the monitor electrode Piezoelectric fan.   The plurality of thin plates and the connecting portion are integrally formed in the same flat plate, and the plurality of drive electrodes and the monitor electrode are formed on the same surface of the flat plate. The piezoelectric fan described in 1.   Add the output voltage obtained from the oscillation circuit or the voltage obtained by inverting the output voltage obtained from the oscillation circuit and the voltage obtained by passing the signal obtained from the monitor electrode through the current detection circuit and the phase shift circuit. The piezoelectric fan according to claim 1, wherein the piezoelectric fan is applied to the plurality of drive electrodes.

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