JP4617803B2 - Pressure wave generator - Google Patents

Description

  The present invention relates to a pressure wave generating element that generates a pressure wave such as a sound wave targeted for a speaker, an ultrasonic wave, or a monopulse density wave.

  2. Description of the Related Art Conventionally, an ultrasonic wave generating element using mechanical vibration due to a piezoelectric effect is widely known. As this type of ultrasonic generating element, for example, one having a structure in which electrodes are provided on both sides of a crystal made of a piezoelectric material such as barium titanate is known. By applying mechanical energy to generate electrical vibration, a medium such as air can be vibrated to generate ultrasonic waves.

  The ultrasonic generating element using the mechanical vibration as described above has a problem that the frequency band is narrow because it has a specific resonance frequency, and it is easily affected by external vibration and fluctuations in external pressure.

  On the other hand, in recent years, a pressure wave generating element using a method of forming air density by thermal excitation that applies heat to a medium has been proposed as an element that can generate ultrasonic waves without mechanical vibration ( For example, Patent Document 1).

  As shown in FIG. 4, this type of pressure wave generating element comprises a semiconductor substrate 1 made of a single crystal silicon substrate and a porous silicon layer formed from one surface in the thickness direction of the semiconductor substrate 1 to a predetermined depth. A heat insulating layer 2 having a sufficiently small thermal conductivity and heat capacity compared to the semiconductor substrate 1 and a heat generating layer 3 made of an aluminum thin film formed on the heat insulating layer 2, and an alternating current to the heat generating layer 3 The pressure wave is generated by heat exchange between the heating element layer 3 and the medium (for example, air) accompanying energization.

  Incidentally, in the pressure wave generating element described above, the thickness of the heating element layer 3 is set to about 30 nm, and in order to energize the heating element layer 3, as shown in FIG. A pair of pads 4, 4 that are in contact with both ends of each of the two pads 4, 4 may be provided, and a fine metal wire (bonding wire) may be wire bonded to each pad 4, 4.

The pressure wave generating element having the configuration shown in FIG. 5 can change the frequency of the generated pressure wave over a wide range by adjusting the frequency of the alternating voltage (drive voltage) applied to the heating element layer 3. For example, it is expected as a sound source of an ultrasonic sound source or a speaker.
Japanese Patent Laid-Open No. 11-3000274

  However, as a result of diligent research, the inventors of the present application have found that the temperature of the heating element layer 3 is 1000 ° C. when the heating element layer 3 is energized when the pressure wave generating element described above is used for an application that requires strong ultrasonic waves. We obtained the knowledge that the temperature would be very high. An example of the findings is shown in FIG. The horizontal axis of the graph of FIG. 6 shows the maximum value of the input power when the sine wave voltage having a frequency of 60 kHz is applied between the pair of pads 4 and 4 and the peak value of the sine wave voltage is variously changed. The axis is the output sound pressure measured at a position 30 cm away from the surface of the heating element layer 3, and the vertical axis on the right side is the temperature of the surface of the heating element layer 3. The pressure, “B”, indicates the temperature.

  Therefore, the inventors of the present invention have examined a pressure wave generating element that employs a refractory metal such as tungsten as the material of the heating element layer 3. However, the above pressure wave generating element is used for applications that require strong ultrasonic waves. In this case, the heating element layer 3 made of tungsten and the pad 4 made of aluminum react with each other to cause a missing portion due to partial aggregation or a high resistance portion, It has been found that there is a problem that the heating element layer 3 is disconnected due to concentration. Furthermore, it has been found that the material of the pad 4 that reacts with the heating element layer 3 reacts with the thermal insulating layer 2 and part of the thermal insulating layer 2 is easily destroyed.

  The present invention has been made in view of the above-mentioned reasons, and its purpose is to stably prevent generation of pressure waves in the ultrasonic region over a long period of time by preventing disconnection of the heating element layer due to temperature rise of the heating element layer. The object is to provide a possible pressure wave generating element.

The invention of claim 1 includes a support substrate, a heating element layer formed on one surface side of the support substrate, and a heat insulating layer interposed between the support substrate and the heating element layer on the one surface side of the support substrate. A pair of pads formed in contact with the heating element layer on the one surface side of the support substrate, and by heat exchange between the heating element layer and the medium accompanying energization of the heating element layer via the pair of pads a pressure wave generating device for generating a pressure wave, heat radiation to dissipate the heat of the pad consists of a different material than the and the pad does not react with fever body layer made of a refractory metal upon energization of the heat generating layer The layer is formed so as to cover each exposed portion where the heating element layer and each pad are in contact with each other.

  According to the present invention, since the heat-dissipating layer that does not react with the heat-generating element layer when energized to the heat-generating element layer and is made of a material different from each pad and dissipates the heat of the pad is provided, The temperature rise near the boundary of the heating element can be suppressed, and the heat of the heating element layer and each pad can be dissipated outside through the heat dissipation layer without reaction between the heating element layer and each pad when the heating element layer is energized. It is possible to prevent disconnection of the heating element layer due to the temperature rise of the body layer and to stably generate pressure waves in the ultrasonic range over a long period of time, and to extend the life, and to the heating element layer when energized The amplitude of the pressure wave can be increased by increasing the electric power.

  According to the present invention, the heat of each pad can be radiated to the outside and the heat radiation area can be made relatively wide without increasing the contact resistance between the heating element layer and each pad. Moreover, it becomes possible to suppress the output fall accompanying the temperature fall of the said heat generating body layer by providing the said thermal radiation layer.

The invention according to claim 2 is a support substrate, a heating element layer formed on one surface side of the support substrate, and a heat insulating layer interposed between the support substrate and the heating element layer on the one surface side of the support substrate, A pair of pads formed in contact with the heating element layer on the one surface side of the support substrate, and by heat exchange between the heating element layer and the medium accompanying energization of the heating element layer via the pair of pads A pressure wave generating element that generates a pressure wave, a heat dissipation layer that does not react with a heating element layer made of a refractory metal when energizing the heating element layer and is made of a material different from each pad and dissipates heat from the pad. some between each respective and fever body layer pad characterized by comprising formed in a manner to expose the surface of the remaining part interposed.

According to the present invention, since the heat-dissipating layer that does not react with the heat-generating element layer when energized to the heat-generating element layer and is made of a material different from each pad and dissipates the heat of the pad is provided, The temperature rise near the boundary of the heating element can be suppressed, and the heat of the heating element layer and each pad can be dissipated outside through the heat dissipation layer without reaction between the heating element layer and each pad when the heating element layer is energized. It is possible to prevent disconnection of the heating element layer due to the temperature rise of the body layer and to stably generate pressure waves in the ultrasonic range over a long period of time, and to extend the life, and to the heating element layer when energized The amplitude of the pressure wave can be increased by increasing the electric power. Further, according to this invention, since the vicinity of the interface heat between said respective pads and said heat generating layer can be radiated to the outside through the exposed surface of the heat dissipation layer, as compared to the first aspect of the present invention Reaction between the heating element layer and each pad is less likely to occur. Further, as compared with the invention of claim 1, the contact area between the heating element layer and each of the pads can be reduced, and the reactive power can be reduced.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the material of the heat dissipation layer is an insulating material.

  According to the present invention, since no current flows to the heat dissipation layer when the heating element layer is energized, it is possible to effectively dissipate the heat of each pad, and the power generated by the current flowing to the heat dissipation layer. Loss can be prevented from occurring.

According to a fourth aspect of the present invention, in the first to third aspects of the invention, the support substrate is a silicon substrate, and the thermal insulation layer is a porous silicon layer.

  According to this invention, the product of the thermal conductivity and the heat capacity of the thermal insulating layer is sufficiently smaller than the product of the thermal conductivity and the thermal capacity of the support substrate, and the heat resistance of the thermal insulating layer is high. The output of the generated pressure wave can be increased.

In the invention of claim 1 or claim 2, there is an effect that it is possible to prevent disconnection of the heating element layer due to the temperature rise of the heating element layer and to stably generate pressure waves in the ultrasonic region over a long period of time.

(Embodiment 1)
As shown in FIGS. 1A and 1B, the pressure wave generating element of this embodiment includes a semiconductor substrate 1 and heat formed on one surface (the upper surface in FIG. 1B) of the semiconductor substrate 1. The insulating layer 2, the heating element layer 3 formed on the thermal insulating layer 2, and both ends of the heating element layer 3 on the one surface side of the semiconductor substrate 1 (left and right ends in FIG. 1A) are in contact with each other. The pair of pads 4 and 4 formed in a shape and the heating element layer 3 do not react with the heating element layer 3 when energized, and the pads 4 and 4 are made of a different material and radiate the heat of the pads 4 and 4. A pair of heat radiation layers 5 and 5 are provided. In the present embodiment, the semiconductor substrate 1 constitutes a support substrate.

  Note that the pressure wave generating element of the present embodiment has a pressure wave (for example, an ultrasonic wave) by heat exchange between the heating element layer 3 and a medium (for example, air) accompanying energization (supply of electric energy) to the heating element layer 3. Etc.). For example, when a sinusoidal AC voltage is applied from the AC power source to the heating element layer 3 via the pair of pads 4 and 4, the temperature of the heating element layer 3 changes due to the generation of Joule heat, and the heating element layer 3. A pressure wave (sound wave) is generated along with the temperature change.

In the pressure wave generating element of the present embodiment, a p-type silicon substrate is used as the semiconductor substrate 1, and the thermal insulating layer 2 is composed of a porous silicon layer. Here, the porous silicon layer constituting the heat insulating layer 2 is formed by anodizing a part of a p-type silicon substrate as the semiconductor substrate 1 in an electrolytic solution. By changing appropriately, the porosity can be changed. The porous silicon layer has a smaller thermal conductivity and heat capacity as the porosity increases, and the thermal conductivity can be made sufficiently smaller than that of single crystal silicon by appropriately setting the porosity. In Patent Document 1, a single crystal silicon substrate having a thermal conductivity of 168 W / (m · K) and a heat capacity of 1.67 × 10 ⁶ J / (m ³ · K) is formed by anodizing. It has been reported that a porous silicon layer having a porosity of 60% has a thermal conductivity of 1 W / (m · K) and a heat capacity of 0.7 × 10 ⁶ J / (m ³ · K). The heat insulating layer 2 is not limited to the porous silicon layer, and may be formed of, for example, a SiO ₂ film or a Si ₃ N ₄ film.

  Here, the semiconductor substrate 1 is not limited to a single-crystal p-type silicon substrate, but may be a polycrystalline or amorphous p-type silicon substrate, and is not limited to a p-type, and may be n-type or non-doped. What is necessary is just to change the conditions of an anodizing process suitably according to the kind of board | substrate 1. FIG. Therefore, the porous semiconductor layer constituting the heat insulating layer 2 is not limited to the porous silicon layer. For example, a porous polycrystalline silicon layer formed by anodizing polycrystalline silicon or a semiconductor material other than silicon is used. It may be a porous semiconductor layer.

  In addition, tungsten, which is a kind of high melting point metal, is used as the material of the heating element layer 3, but the material of the heating element layer 3 is not limited to tungsten, and the melting point is relatively higher than 1000 ° C. For example, a refractory metal such as tantalum or molybdenum or a noble metal such as iridium may be employed.

  Each pad 4, 4 is formed so as to straddle the end of the heating element layer 3 and the one surface of the semiconductor substrate 1. Here, Al is adopted as the material of each pad 4.

Each heat dissipation layer 5 is formed so as to cover each exposed portion where the heating element layer 3 and each of the pads 4 and 4 are in contact with each other. In other words, the heat dissipation layer 5 is formed so as to straddle a part of one surface (the upper surface in FIG. 1B) of the pad 4 and a part of the surface of the heating element layer 3. Here, as a material of each heat radiation layer 5, SiO ₂ is adopted. However, the material of the heat dissipation layer 5 is not limited to SiO ₂ , and may be any material that does not react with the materials of the heating element layer 3 and the pad 4. For example, Si ₃ N ₄ , TaN, HfN, TiN, BN, etc. Nitride, carbides such as TaC, HfC, NbC, ZrC, TiC, VC, WC, ThC, SiC, and oxides other than SiO ₂ such as Al ₂ O ₃ may be used.

  In the pressure wave generating element of this embodiment, the thickness of the thermal insulating layer 2 is 10 μm, the thickness of the heating element layer 3 is 50 nm, the thickness of the pad 4 is 0.5 μm, and the thickness of the heat dissipation layer 5 is 1. However, these thicknesses are only examples and are not particularly limited. In addition, the width of the heat dissipation layer 5 in the juxtaposed direction of the pads 4 and 4 is 0.5 mm, and the width of the part formed on the pad 4 and the part formed on the heating element layer 3 in the juxtaposed direction are as follows. The widths are substantially the same, but these widths are also examples and are not particularly limited.

  Hereinafter, the manufacturing method of the pressure wave generating element of this embodiment will be briefly described.

First, a current-carrying electrode (not shown) used for anodizing is formed on the other surface (the lower surface in FIG. 1B) of the semiconductor substrate 1 made of a single crystal p-type silicon substrate, and then shown in FIG. The thermal insulation layer 2 made of a porous silicon layer is formed by anodizing with such an anodizing apparatus. Here, the anodizing process is a thermal insulating layer forming process, and in the anodizing process, as shown in FIG. A platinum electrode immersed in the resulting electrolyte (for example, a mixture of 55 wt% aqueous hydrogen fluoride and ethanol mixed 1: 1) B, and then connected to the negative side of the current source 20 via a wiring 21 is arranged in the electrolytic solution B so as to face the one surface side of the semiconductor substrate 1. Subsequently, using a current-carrying electrode as an anode and a platinum electrode 21 as a cathode, a current having a predetermined current density (in this case, 20 mA / cm ² ) is supplied from the current source 20 to the anode and the cathode 21 for a predetermined time (here, The thermal insulating layer 2 is formed on the one surface side of the semiconductor substrate 1 so that the thickness of the portion other than the peripheral portion is a predetermined thickness (here, 10 μm). . The conditions during the anodic oxidation treatment are not particularly limited, and the current density may be appropriately set within a range of, for example, about 1 to 500 mA / cm ² , and the predetermined thickness of the thermal insulating layer 2 may be set for the predetermined time. What is necessary is just to set suitably according to it.

  By sequentially performing the heating element layer forming process for forming the heating element layer 3, the pad forming process for forming the pads 4 and 4, and the heat dissipation layer forming process for forming the heat dissipation layer 5 after the above-described thermal insulation layer forming process, A pressure wave generating element is completed. In the heating element layer forming step, the pad forming step, and the heat dissipation layer forming step, for example, the film may be formed by various sputtering methods, various vapor deposition methods, various CVD methods, and the like.

  In the pressure wave generating element according to the present embodiment described above, the heating element layer 3 does not react with the heating element layer 3 and is made of a material different from that of the pads 4 and 4 to dissipate heat from the pads 4 and 4. Since the heat dissipating layers 5 and 5 are provided, a temperature rise in the vicinity of the boundary (interface) between the heat generating layer 3 and each of the pads 4 and 4 can be suppressed. Since the heat of each pad 4, 4 can be radiated to the outside through the heat radiation layers 5, 5 without reacting with each pad 4, 4, It is possible to prevent disconnection and to stably generate a pressure wave in the ultrasonic range over a long period of time, to extend the life, and to increase the power applied to the heating element layer 3 during energization, the amplitude of the pressure wave Increase. In this embodiment, since the heat radiation layers 5 and 5 are formed so as to cover the exposed portions where the heat generating layer 3 and the pads 4 and 4 are in contact with each other, the heat generating layer 3 and each pad are formed. The heat of each pad 4, 4 can be radiated to the outside without increasing the contact resistance with each of 4, 4, and the heat radiation area can be made relatively wide. Moreover, it becomes possible to suppress the output fall accompanying the temperature fall of the heat generating body layer 3 by having provided the thermal radiation layers 5 and 5. FIG.

Further, by adopting an insulating material such as the above-described SiO ₂ as the material of each heat dissipation layer 5, current does not flow to each heat dissipation layer 5 when the heating element layer 3 is energized. Heat dissipation, and it is possible to prevent the occurrence of power loss due to the current flowing to each heat dissipation layer 5.

  By the way, in this embodiment, the semiconductor substrate 1 as a support substrate is comprised by the silicon substrate, the heat insulation layer 2 is comprised by the porous silicon layer, and the product of the heat conductivity and heat capacity of the heat insulation layer 2 is obtained. Although it is sufficiently smaller than the product of the thermal conductivity and the heat capacity of the support substrate (about 1/400) and the heat insulation layer 2 has high heat resistance, it is possible to increase the output of the generated pressure wave. By providing the layers 5 and 5, high output ultrasonic waves can be output stably over a long period of time.

(Embodiment 2)
The basic configuration of the pressure wave generating element of the present embodiment is substantially the same as that of the first embodiment, and the formation positions of the heat radiation layers 5 and 5 are different as shown in FIG. That is, each of the heat dissipation layers 5 and 5 in the present embodiment is formed in such a manner that a part is interposed between each end of the heating element layer 3 and each pad 4 and 4 and the surface of the remaining part is exposed. ing. In other words, in the present embodiment, the heat radiation layers 5 and 5 are formed on the heat generating body layer 3 at positions slightly separated from both ends of the heat generating body layer 3, and the pads 4 and 4 are arranged on the heat radiation layers 5 and 5. And over the semiconductor substrate 1 and over the vicinity of both ends of the heating element layer 3. In addition, the same code | symbol is attached | subjected to the component similar to Embodiment 1, and description is abbreviate | omitted.

  Thus, in the pressure wave generating element of the present embodiment, each of the heat dissipation layers 5 and 5 is partially interposed between the heating element layer 3 and each of the pads 4 and 4 and the surface of the remaining portion is exposed. Since it is formed, heat in the vicinity of the interface between the heating element layer 3 and each of the pads 4 and 4 can be radiated to the outside through the exposed surfaces of the heat dissipation layers 5 and 5. The reaction between the body layer 3 and each of the pads 4 and 4 is less likely to occur. Compared with the first embodiment, the contact area between the heating element layer 3 and each of the pads 4 and 4 can be reduced, and the reactive power can be reduced.

Embodiment 1 is shown, (a) is a schematic plan view, and (b) is a sectional view taken along the line D-D ′ of (a). It is explanatory drawing of a manufacturing method same as the above. Embodiment 2 is shown, (a) is a schematic plan view, (b) is a D-D 'cross-sectional view of (a). A prior art example is shown, (a) is a schematic plan view, and (b) is a sectional view taken along the line D-D 'of (a). Another example is shown, (a) is a schematic plan view, (b) is a D-D 'cross-sectional view of (a). It is characteristic explanatory drawing same as the above.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Thermal insulation layer 3 Heat generating body layer 4 Pad 5 Heat radiation layer

Claims (4)

A support substrate, a heating element layer formed on one surface side of the support substrate, a heat insulating layer interposed between the support substrate and the heating element layer on the one surface side of the support substrate, and the one surface of the support substrate Pressure waves that generate a pressure wave by heat exchange between the heating element layer and the medium when the heating element layer is energized through the pair of pads. a generating element, a heat radiation layer dissipating the heat of the pad consists of a different material than the and the pad does not react with fever body layer made of a refractory metal upon energization of the heat generating layer and the heat generating layer each A pressure wave generating element characterized by being formed so as to cover each exposed portion in contact with each pad . A support substrate, a heating element layer formed on one surface side of the support substrate, a heat insulating layer interposed between the support substrate and the heating element layer on the one surface side of the support substrate, and the one surface of the support substrate Pressure waves that generate a pressure wave by heat exchange between the heating element layer and the medium when the heating element layer is energized through the pair of pads. A heat generating layer that is a generating element and does not react with a heating element layer made of a refractory metal when energized to the heating element layer and is made of a material different from each pad, and dissipates the heat of the pad. pressure wave generating element, wherein a portion is formed in a manner to expose the surface of the remaining portion interposed between. The material of the heat dissipation layer, the pressure wave generator of the mounting serial to claim 1 or claim 2, characterized in that an insulating material. 4. The pressure wave generating element according to claim 1, wherein the support substrate is made of a silicon substrate, and the thermal insulation layer is made of a porous silicon layer .

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