JP4525273B2 - Pressure wave generator - Google Patents

Description

  The present invention relates to a pressure wave generator that generates a pressure wave such as a sound wave targeting a speaker, an ultrasonic wave, or a monopulse density wave.

  2. Description of the Related Art Conventionally, an ultrasonic generator using mechanical vibration due to a piezoelectric effect is widely known. As this type of ultrasonic generator, 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 generator 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 influenced by external vibrations and fluctuations in external pressure.

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

  As shown in FIG. 5, this type of pressure wave generator 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.

  In the pressure wave generator described above, the thickness of the heating element layer 3 is set to about 30 nm. 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 generator having the configuration shown in FIG. 6 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 an ultrasonic sound source or a sound source of a speaker.
Japanese Patent Laid-Open No. 11-3000274

  However, as a result of intensive studies, the inventors of the present application have found that when the pressure wave generator described above is used for an application that requires strong ultrasonic waves (high output ultrasonic waves), the heating element is energized when the heating element layer 3 is energized. The knowledge that the temperature of the layer 3 becomes a very high temperature exceeding 1000 ° C. was obtained. An example of the findings is shown in FIG. The horizontal axis of the graph of FIG. 7 shows the maximum value of the input power when the peak value of the sine wave voltage is changed variously when the sine wave voltage having a frequency of 60 kHz is applied between the pair of pads 4, 4. 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.

  Accordingly, the inventors of the present application have examined a pressure wave generator that employs a refractory metal such as tungsten as the material of the heating element layer 3. However, the pressure wave generator described above 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. It is an object of the present invention to provide a possible pressure wave generator.

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. And a pressure wave generating element chip having a pair of pads formed in contact with the heating element layer on the one surface side of the support substrate, and a heating element associated with energization of the heating element layer via the pair of pads A pressure wave generator that generates a pressure wave by heat exchange between the layer and the medium, and is thermally coupled to each pad as a heat radiating means for radiating the heat of each pad to the outside of the pressure wave generating element chip; e Bei a pair of electrically conductive contact electrically connected to the conductive contact is thus provided overlap in the thickness direction of the pressure wave generating device chip to the pads on the ends of the heating element layer It is characterized by that.

According to the present invention, Bei example a pair of conductive contacts are thermally coupled with and electrically connected to the respective pads as a radiator means for radiating the respective pads heat to the pressure wave generating device chip external, Since the conductive contact is provided so as to overlap the pad on the end of the heating element layer in the thickness direction of the pressure wave generating element chip, when the heating element layer is energized, The temperature rise near the boundary with the pad can be suppressed, and the heat of the heating element layer and each pad does not react when the heating element layer is energized, and the heat of each pad is passed through the conductive contact to the outside of the pressure wave generating element chip. The heat generation layer can be prevented from being disconnected due to the temperature rise of the heat generation layer, and pressure waves in the ultrasonic range can be stably generated over a long period of time. Preparative it is, thereby an increase in the amplitude of the pressure wave by increasing the power applied to the heating element layer when energized.

  According to a second aspect of the present invention, in the first aspect of the present invention, the conductive contact has a thickness direction that coincides with the pressure wave generating element chip, and one end thereof overlaps the pad in the thickness direction of the pressure wave generating element chip. In this manner, the conductive plate is electrically connected to the pad and has the other end portion located on the side of the pressure wave generating element chip.

  According to this invention, the surface area of the conductive contact can be increased to improve heat dissipation.

  According to a third aspect of the present invention, in the first aspect of the invention, a synthetic resin mold part that covers the pressure wave generating element chip in a form in which the surface of the heating element layer in the pressure wave generating element chip is exposed, and a mold Each of the pads has a pair of lead terminals electrically connected to each pad and the other end exposed to the outside of the mold part, and each lead terminal also serves as the conductive contact It is characterized by being.

  According to this invention, since the mold portion is formed so as to cover the pressure wave generating element chip in a form in which the surface of the heating element layer in the pressure wave generating element chip is exposed, the pressure wave generating element chip The pressure wave generating element chip can be protected from the external environment without interfering with the generated pressure wave, the deterioration of the pressure wave generating element chip due to the external environment can be prevented, and the heat of each pad can be prevented. Heat is radiated to the outside through lead terminals for electrical input.

  According to a fourth aspect of the present invention, in the first aspect of the invention, a pressure wave extraction window hole is formed in a portion corresponding to the heating element layer of the pressure wave generating element chip, and the pressure wave generating element chip is face down. A pair of conductor patterns each including a printed circuit board mounted and partially overlapping each of the pads in the thickness direction of the printed circuit board also serve as the conductive contact.

  According to the present invention, the pressure wave generating element chip is mounted face down on a printed circuit board in which a pressure wave extracting window hole is formed in a portion corresponding to the heating element layer of the pressure wave generating element chip. Since each of the pair of conductor patterns partially overlapping each of the pads in the thickness direction of the substrate also serves as the conductive contact, each of the pads without interfering with the pressure wave generated from the pressure wave generating element chip. Heat can be dissipated.

  In the invention of claim 1, 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 generator 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. 1B) are in contact with each other. Each of the pads 4 and 4 is provided as a heat radiating means for dissipating the heat of each of the pads 4 and 4 to the outside of the pressure wave generating element chip. A pair of conductive contacts 5 and 5 are provided that are thermally coupled and electrically connected to each other. In the present embodiment, the semiconductor substrate 1 constitutes a support substrate. The outer peripheral shape of each of the semiconductor substrate 1, the heat insulating layer 2, and the heating element layer 3 is a rectangular shape, and the outer peripheral shape of each pad 4, 4 is the direction in which the pads 4, 4 are arranged side by side (FIG. 1B). The shape is an elongated rectangular shape with the direction perpendicular to the horizontal direction as the longitudinal direction.

  Here, the pressure wave generating element chip is 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. Is generated. 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 chip in the present embodiment, a p-type silicon substrate is used as the semiconductor substrate 1, and the thermal insulating layer 2 is formed 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). Note that the thermal 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.

  In the pressure wave generating element chip in this embodiment, the thickness of the thermal insulating layer 2 is 10 μm, the thickness of the heating element layer 3 is 50 nm, and the thickness of the pad 4 is 1 μm. However, there is no particular limitation.

  Hereinafter, a method for manufacturing a pressure wave generating element chip will be briefly described. However, for convenience of description, the semiconductor substrate 1 will be described as meaning a wafer unless otherwise specified.

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, the current-carrying electrode is an anode, the platinum electrode 21 as a cathode, a predetermined current density (in this case, 20 mA / cm ²⁾ between the current source 20 between the anode and the negative pole current at a predetermined time (here, the The thermal insulating layer 2 having a predetermined thickness (here, 10 μm) is formed at a predetermined portion on the one surface side of the semiconductor substrate 1 by performing an anodic oxidation process for 8 minutes. 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.

  After the heat insulating layer forming step, the heat generating layer forming step for forming the heat generating layer 3 and the pad forming step for forming the pads 4 and 4 are sequentially performed, and then the dicing step is performed. The chip is completed. In the heating element layer forming step and the pad forming step, for example, the film may be formed by various sputtering methods, various vapor deposition methods, various CVD methods, and the like.

  By the way, as described above, the pressure wave generating device of the present embodiment is thermally coupled to each of the pads 4 and 4 as heat radiating means for radiating the heat of each of the pads 4 and 4 to the outside of the pressure wave generating element chip. And a pair of electrically conductive contacts 5 and 5 which are electrically connected. Here, the conductive contacts 5 and 5 are electrically connected to the pads 4 and 4 in such a manner that the thickness direction coincides with the pressure wave generating element chip and one end thereof overlaps the pads 4 and 4 in the thickness direction of the pressure wave generating element chip. And the other end is formed of a rectangular plate-like conductive plate positioned on the side of the pressure wave generating element chip. The conductive plates constituting the conductive contacts 5 and 5 are formed by applying gold plating to a phosphor bronze plate, and are fixed to the pads 4 and 4 with a conductive paste.

  In the pressure wave generator of the present embodiment described above, each pad 4, 4 is thermally coupled to each pad 4, 4 as a heat radiating means for radiating the heat of each pad 4, 4 to the outside of the pressure wave generating element chip. Since the pair of conductive contacts 5 and 5 connected to each other is provided, the temperature rise near the boundary between the heating element layer 3 and each of the pads 4 and 4 can be suppressed when the heating element layer 3 is energized. The heat generating layer 3 and the pads 4 and 4 do not react when the heat generating layer 3 is energized, and the heat of the pads 4 and 4 is radiated to the outside of the pressure wave generating element chip through the conductive contacts 5 and 5. Therefore, disconnection of the heating element layer 3 due to the temperature rise of the heating element layer 3 can be prevented, and pressure waves in the ultrasonic range can be stably generated with high output over a long period of time, thereby extending the life. At the same time An increase in the amplitude of the pressure wave by increasing the power applied to the heating layer 3 improved. Therefore, even when the temperature of the heating element layer 3 rises to a temperature exceeding 1000 ° C., it is possible to prevent the heating element layer 3 from being disconnected. Further, since the conductive contacts 5 and 5 are formed of the above-described conductive plate, the surface area of the conductive contacts 5 and 5 can be increased to improve heat dissipation.

(Embodiment 2)
Hereinafter, the pressure wave generator of the present embodiment will be described with reference to FIGS. 3 (a) and 3 (b).

  The pressure wave generating device of this embodiment includes a pressure wave generating element chip including the semiconductor substrate 1, the thermal insulating layer 2, the heating element layer 3, and the pair of pads 4 and 4 described in the first embodiment, and the pressure Mold part 6 made of a synthetic resin (for example, a resin generally used as a sealing material in an IC or the like) that covers the pressure wave generating element chip with the surface of the heating element layer 3 in the wave generating element chip exposed. And a pair of lead terminals 7 and 7 each having one end electrically connected to each of the pads 4 and 4 in the mold portion 6 and the other end exposed to the outside of the mold portion 6.

  The mold part 6 is formed with a pressure wave extraction window hole 6a on the surface side of the heating element layer 3 in the pressure wave generating element chip. Here, the window hole 6 a is formed in a rectangular shape that exposes most of the surface of the heating element layer 3. Therefore, the pressure wave generated from the pressure wave generating element chip is output through the window hole 6a.

  Each of the lead terminals 7 and 7 is formed in an L-shaped cross section, and is arranged along a horizontal piece embedded so that the thickness direction of the pressure wave generating element chip coincides with the thickness direction of the pressure wave generating element chip. A vertical piece that is disposed and partially protrudes from the back surface of the mold portion 6 is formed continuously and integrally. In other words, the horizontal piece of each lead terminal 7 is arranged along a plane parallel to the one surface of the pressure wave generating element chip, and the vertical piece is arranged along a plane parallel to the side surface of the pressure wave generating element chip. It is arranged.

  In the present embodiment, each of the lead terminals 7 and 7 also serves as a heat dissipation means including a pair of conductive contacts that are thermally coupled to and electrically connected to the pads 4 and 4, respectively. Here, the lead terminals 7 and 7 may be formed of the same material as a general lead frame (for example, a nickel-based alloy, a copper-based alloy, etc.).

  Therefore, in the pressure wave generating device of the present embodiment, the mold portion 6 is formed so as to cover the pressure wave generating element chip in a form in which the surface of the heating element layer 3 in the pressure wave generating element chip is exposed. The pressure wave generating element chip can be protected from the external environment without interfering with the pressure wave generated from the pressure wave generating element chip, the deterioration of the pressure wave generating element chip due to the external environment can be prevented, and the heating element The heat of each pad 4, 4 is radiated to the outside through the lead terminals 7, 7 for electric input when the layer 3 is energized, thereby preventing the heating element layer 3 from being disconnected due to the temperature rise of the heating element layer 3. The pressure wave in the ultrasonic region can be stably generated at a high output over a long period of time, the life can be extended, and the pressure by increasing the power applied to the heating element layer 3 when energized Attained of an increase in the amplitude. Therefore, even when the temperature of the heating element layer 3 rises to a temperature exceeding 1000 ° C., it is possible to prevent the heating element layer 3 from being disconnected.

(Embodiment 3)
Hereinafter, the pressure wave generator of this embodiment will be described with reference to FIGS. 4 (a) and 4 (b).

  The pressure wave generating device of this embodiment includes a pressure wave generating element chip including the semiconductor substrate 1, the thermal insulating layer 2, the heating element layer 3, and the pair of pads 4 and 4 described in the first embodiment, and the pressure There is provided a printed circuit board 8 in which a pressure wave extraction window hole 8a is formed at a portion corresponding to the heating element layer 3 of the wave generating element chip and the pressure wave generating element chip is mounted face down. Here, the pads 4 and 4 of the pressure wave generating element chip are fixed to the conductive patterns 9 and 9 formed on the surface of the printed circuit board 8 facing the pressure wave generating element chip by a conductive die bond paste.

  Although the base material of the printed circuit board 8 is not particularly limited, in the present embodiment, a pair of conductor patterns 9 and 9 each partially overlapping each of the pads 4 and 4 in the thickness direction of the printed circuit board 8 are respectively connected to the pads 4 and 4. 4 also serves as a heat dissipation means composed of a pair of conductive contacts that are thermally coupled and electrically connected to each of them. From the viewpoint of heat dissipation, a high thermal conductivity ceramic substrate is used as the base material of the printed circuit board 8. It is particularly preferable that the conductor patterns 9, 9 are thicker.

  Thus, in the pressure wave generating device of the present embodiment, the pressure wave generating element chip is formed on the printed circuit board 8 in which the pressure wave extracting window hole 8a is formed at a portion corresponding to the heating element layer 3 of the pressure wave generating element chip. A pair of conductor patterns 9 and 9 which are mounted face down and partially overlap each of the pads 4 and 4 in the thickness direction of the printed circuit board 8 also serve as conductive contacts. Since the heat of the pads 4 and 4 is radiated to the outside without interfering with the pressure wave to be generated, disconnection of the heating element layer 3 due to the temperature rise of the heating element layer 3 can be prevented, and the pressure wave in the ultrasonic range over a long period of time Can be stably generated at a high output, the life can be extended, and the amplitude of the pressure wave can be increased by increasing the power applied to the heating element layer 3 during energization. Therefore, even when the temperature of the heating element layer 3 rises to a temperature exceeding 1000 ° C., it is possible to prevent the heating element layer 3 from being disconnected.

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). Embodiment 3 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 Conductive contact

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 A pressure wave generating element chip having a pair of pads formed in contact with the heating element layer on the side, and 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 that generates a pressure wave by means of a pair of heat pads that are thermally coupled to and electrically connected to each pad as heat radiating means for radiating the heat of each pad to the outside of the pressure wave generating element chip. e Bei the conductive contact, the conductive contact, the pressure wave, characterized in that thus provided overlap in the thickness direction of the pressure wave generating device chip to the pads on the ends of the heating element layer Generator.   The conductive contact is electrically connected to the pad such that the thickness direction coincides with the pressure wave generating element chip and one end overlaps the pad in the thickness direction of the pressure wave generating element chip. 2. The pressure wave generator according to claim 1, comprising a conductive plate located on a side of the pressure wave generating element chip.   A synthetic resin mold part covering the pressure wave generating element chip with the surface of the heating element layer in the pressure wave generating element chip exposed, and one end portion of each of the pads in the mold part being electrically connected 2. The pressure wave generation according to claim 1, further comprising a pair of lead terminals that are connected to each other and the other end portions are exposed to the outside of the mold portion, and each lead terminal also serves as the conductive contact. apparatus.   The pressure wave generating element chip includes a printed circuit board in which a pressure wave extraction window hole is formed at a portion corresponding to the heating element layer and the pressure wave generating element chip is mounted face down, in the thickness direction of the printed circuit board. 2. The pressure wave generator according to claim 1, wherein each of the pair of conductor patterns partially overlapping each of the pads also serves as the conductive contact.

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