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JP2006088124

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DESCRIPTION JP2006088124
The present invention provides a pressure wave generating element capable of preventing a
break in a heat generating body layer caused by a temperature rise of a heat generating body
layer and stably generating pressure waves in an ultrasonic wave area for a long period of time.
A semiconductor substrate 1 made of a silicon substrate as a supporting substrate, a heating
element layer 3 formed on one surface side of the semiconductor substrate 1, a semiconductor
substrate 1 and a heating element layer on the one surface side of the semiconductor substrate 1
And a pair of pads 4, 4 formed in contact with the heat generating body layer 3. While tungsten
is employed as the material of the heat generating layer 3, aluminum is employed as the material
of the pads 4, 4, and the semiconductor substrate 1 reacts with the heat generating layer 3 when
the heat is applied to the heat generating layer 3. Furthermore, a pair of heat radiation layers 5
and 5 are provided which are made of a material different from each of the pads 4 and 4 and
which radiates the heat of the pads 4 and 4. [Selected figure] Figure 1
Pressure wave generator
[0001]
The present invention relates to, for example, a pressure wave generating element for generating
a pressure wave such as an acoustic wave intended for a speaker or an ultrasonic wave or a
single pulse compression wave.
[0002]
Conventionally, an ultrasonic wave generating element using mechanical vibration by a
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piezoelectric effect is widely known.
As this type of ultrasonic wave 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. In this ultrasonic wave generating element, the space between both electrodes
is known. By applying electrical energy to generate mechanical vibration, a medium such as air
can be vibrated to generate ultrasonic waves.
[0003]
The ultrasonic wave generating element utilizing mechanical vibration as described above has
problems such as a narrow frequency band and being susceptible to external vibration and
fluctuations in external pressure since it has an inherent resonance frequency.
[0004]
On the other hand, in recent years, as an element capable of generating an ultrasonic wave
without mechanical vibration, a pressure wave generating element has been proposed which
utilizes a method of forming air density by thermal excitation which applies heat to a medium (
For example, Patent Document 1).
[0005]
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 to a
predetermined depth from one surface of the semiconductor substrate 1 in the thickness
direction. The heat insulating layer 2 having a sufficiently small thermal conductivity and heat
capacity as compared with the semiconductor substrate 1 and the heat generating body layer 3
formed of an aluminum thin film formed on the heat insulating layer 2 The pressure wave is
generated by the heat exchange between the heat generating body layer 3 and the medium (for
example, air) accompanying the energization.
[0006]
By the way, in the above-mentioned pressure wave generating element, the film thickness of the
heat generating body layer 3 is set to about 30 nm, and in order to energize the heat generating
body layer 3, as shown in FIG. A pair of pads 4 and 4 may be provided in contact with the
respective end portions of each of the two, and metal fine wires (bonding wires) may be wirebonded to the respective pads 4 and 4.
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[0007]
The pressure wave generating element having the configuration shown in FIG. 5 can change the
frequency of the pressure wave to be generated over a wide range by adjusting the frequency of
the AC voltage (driving 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 Application Publication No. 11-300274
[0008]
However, as a result of intensive studies, the inventors of the present application have found that,
when the above-described pressure wave generating element is used for applications requiring
strong ultrasonic waves, the temperature of the heating element layer 3 is 1000 ° when the
heating element layer 3 is energized. It has been found that the temperature becomes very high
exceeding C.
An example of the knowledge is shown in FIG.
The horizontal axis of the graph in FIG. 6 represents the maximum value of the input power
when the peak value of the sine wave voltage is variously changed when applying a sine wave
voltage with a frequency of 60 kHz between the pair of pads 4 and 4. The axis is the output
sound pressure measured at a position 30 cm away from the surface of the heat generating layer
3, the vertical axis on the right is the temperature of the surface of the heat generating layer 3,
and "i" in FIG. Pressure, "ro" indicates the temperature.
[0009]
Therefore, although the inventors of the present invention examined a pressure wave generating
element adopting high melting point metal such as tungsten as a material of the heating element
layer 3, the above-mentioned pressure wave generating element is used for applications
requiring strong ultrasonic waves. In this case, the heating element layer 3 composed of tungsten
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and the pad 4 composed of aluminum react with each other to generate a missing part or a high
resistance part due to partial aggregation, resulting in a current It has been found that there is a
problem that the heating element layer 3 is broken due to concentration.
Furthermore, it has been found that the material of the pad 4 that has reacted with the heating
element layer 3 reacts with the heat insulating layer 2 and a part of the heat insulating layer 2 is
easily broken.
[0010]
The present invention has been made in view of the above-mentioned problems, and its object is
to prevent breakage of the heating element layer due to the temperature rise of the heating
element layer and stably generate pressure waves in the ultrasonic range over a long period of
time It is an object to provide a possible pressure wave generating element.
[0011]
According to the first aspect of the present invention, there is provided a support substrate, a
heat generating body layer formed on one surface side of the support substrate, and a thermal
insulation layer interposed between the support substrate and the heat generating body layer on
the one surface side of the support substrate. A pair of pads formed in contact with the heat
generating body layer on the one surface side of the support substrate, and heat exchange
between the heat generating body layer and the medium accompanying energization of the heat
generating body layer through the pair of pads A pressure wave generating element for
generating a pressure wave, characterized by comprising a heat dissipation layer which does not
react with the heat generating body layer when current is supplied to the heat generating body
layer and which is made of a material different from each pad and dissipates the heat of the pad.
Do.
[0012]
According to the present invention, since the heat dissipation layer does not react with the heat
dissipation layer when current is supplied to the heat loss layer, and the heat dissipation layer
which dissipates the heat of the pad is made of a material different from each pad. The
temperature rise near the boundary of the heat source can be suppressed, and the heat of each
pad can be dissipated to the outside through the heat dissipation layer without the heat
generating body layer and each pad reacting with each other when the heat generating layer is
energized. It is possible to prevent the disconnection of the heat generating body layer due to the
temperature rise of the body layer, stably generate pressure waves in the ultrasonic range over a
long period of time, and prolong the life, and give to the heat generating body layer at the time of
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energization. The amplitude of the pressure wave can be increased by increasing the power.
[0013]
The invention of claim 2 is characterized in that, in the invention of claim 1, the heat dissipation
layer is formed in such a manner as to cover the exposed portions where the heat generating
body layer and the respective pads are in contact with each other.
[0014]
According to the present invention, the heat of each pad can be dissipated to the outside without
increasing the contact resistance between the heating element layer and each of the pads, and
the heat dissipation area can be made relatively wide.
Moreover, it becomes possible to suppress the output fall accompanying the temperature fall of
the said heat generating body layer by having provided the said thermal radiation layer.
[0015]
According to the invention of claim 3, in the invention of claim 1, the heat dissipation layer is
formed in such a manner that a portion is interposed between the heating element layer and
each of the respective pads and the surface of the remaining portion is exposed. It is
characterized by becoming.
[0016]
According to this invention, the heat in the vicinity of the interface between the heat generating
body layer and each of the pads can be dissipated to the outside through the exposed surface of
the heat dissipation layer. The reaction between the layer and each of the pads is less likely to
occur.
Further, compared with the second aspect of the present invention, the contact area between the
heating element layer and each of the pads can be reduced, and reactive power can be reduced.
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[0017]
The invention of claim 4 is characterized in that, in the invention of claims 1 to 3, the material of
the heat dissipation layer is an insulating material.
[0018]
According to the present invention, current does not flow to the heat dissipation layer when
current is applied to the heat generating body layer, so that the heat of each of the pads can be
effectively dissipated, and electric power due to current flow to the heat dissipation layer It is
possible to prevent the occurrence of loss.
[0019]
The invention of claim 5 is characterized in that, in the invention of claims 1 to 4, the support
substrate is made of a silicon substrate, and the heat insulation layer is made of a porous silicon
layer.
[0020]
According to the present invention, the product of the thermal conductivity and the thermal
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 pressure waves to be generated can be increased.
[0021]
According to the first aspect of the present invention, it is possible to prevent the disconnection
of the heat generating body layer due to the temperature rise of the heat generating body layer,
and to stably generate the pressure wave in the ultrasonic region over a long period of time.
[0022]
Embodiment 1 As shown in FIGS. 1 (a) and 1 (b), the pressure wave generating element of this
embodiment is a semiconductor substrate 1 and one surface (upper surface in FIG. 1 (b)) side of
the semiconductor substrate 1 The heat insulating layer 2 formed on the heat generating layer 3
formed on the heat insulating layer 2 and both ends of the heat generating layer 3 on the one
surface side of the semiconductor substrate 1 (left and right ends in FIG. Part 4) A pair of pads 4
and 4 formed in contact with each other, and does not react with the heating element layer 3
when the heating element layer 3 is energized, and is made of a material different from each pad
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4 and 4 And a pair of heat dissipation layers 5 and 5 for releasing the heat of heat.
In the present embodiment, the semiconductor substrate 1 constitutes a support substrate.
[0023]
The pressure wave generating element of the present embodiment is a pressure wave (for
example, an ultrasonic wave) by heat exchange between the heat generating body layer 3 and a
medium (for example, air) accompanying the energization (supply of electric energy) to the heat
generating body layer 3. Etc.).
For example, when a sinusoidal AC voltage is applied from the AC power supply to the heat
generating layer 3 through the pair of pads 4 and 4, the temperature of the heat generating layer
3 changes due to the generation of Joule heat. The pressure wave (sound wave) is generated
along with the temperature change of.
[0024]
In the pressure wave generating element of the present embodiment, a p-type silicon substrate is
used as the semiconductor substrate 1, and the heat 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 the p-type silicon substrate as the semiconductor substrate 1 in the electrolytic solution,
and the conditions of the anodizing treatment The porosity can be changed by appropriately
changing it.
In the porous silicon layer, the thermal conductivity and the heat capacity decrease as the
porosity increases, and the thermal conductivity can be sufficiently reduced as compared with
single crystal silicon by appropriately setting the porosity.
According to Patent Document 1, a single crystal silicon substrate having a thermal conductivity
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of 168 W / (m · K) and a heat capacity of 1.67 × 10 <6> J / (m <3> · K) is anodized. The porous
silicon layer formed with 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). It has been reported.
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.
[0025]
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, or not limited to p-type, and may
be n-type or non-doped The conditions of the anodizing treatment may be appropriately changed
according to the type of the substrate 1.
Therefore, the porous semiconductor layer constituting the heat insulating layer 2 is not limited
to the porous silicon layer, and, for example, a porous polycrystalline silicon layer formed by
anodizing polycrystalline silicon, or a semiconductor material other than silicon It may be a
porous semiconductor layer.
[0026]
In addition, although tungsten, which is a type of refractory metal, is used as the material of the
heat generating layer 3, the material of the heat generating layer 3 is not limited to tungsten, and
the melting point is relatively higher than 1000 ° C. Any metal having a melting point may be
used, and for example, a refractory metal such as tantalum or molybdenum or a noble metal such
as iridium may be employed.
[0027]
Each of the pads 4 and 4 is formed to extend over the end of the heat generating layer 3 and the
one surface of the semiconductor substrate 1.
Here, Al is adopted as a material of each pad 4.
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[0028]
Each heat dissipation layer 5 is formed in such a manner as to cover the exposed portions where
the heat generating layer 3 and the pads 4 and 4 are in contact with each other.
In other words, the heat dissipation layer 5 is formed across a part of one surface (upper surface
in FIG. 1B) of the pad 4 and a part of the surface of the heating element layer 3. Here, SiO 2 is
adopted as a material of each heat dissipation layer 5. 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
respective materials of the heat generating body layer 3 and the pad 4. Also, carbides such as
HfC, NbC, ZrC, TiC, VC, WC, ThC, and SiC, and oxides other than SiO 2 such as Al 2 O 3 may be
used.
[0029]
In the pressure wave generating element of this embodiment, the thickness of the heat insulating
layer 2 is 10 μm, the thickness of the heat generating 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 Although the thickness is 1.5
μm, these thicknesses are an example and are not particularly limited. The width of the heat
dissipation layer 5 in the juxtaposing direction of the pads 4 and 5 is 0.5 mm, and the width of
the portion formed on the pad 4 and the portion formed on the heating element layer 3 in the
juxtaposing direction Although the widths are made to be substantially the same, these widths
are also an example and are not particularly limited.
[0030]
Hereinafter, the manufacturing method of the pressure wave generating element of the present
embodiment will be briefly described.
[0031]
First, an energizing electrode (not shown) used for anodizing treatment is formed on the other
surface (lower surface in FIG. 1B) side of the semiconductor substrate 1 made of a single crystal
p-type silicon substrate, as shown in FIG. By performing anodizing treatment using such an
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anodizing treatment apparatus, the heat insulating layer 2 made of a porous silicon layer is
formed.
Here, the step of anodizing treatment is the step of forming a heat insulating layer, and in the
anodizing treatment, as shown in FIG. A platinum electrode is immersed in the electrolyte (for
example, a mixed solution of a 55 wt% hydrogen fluoride aqueous solution and ethanol mixed at
1: 1) B and then connected to the negative side of the current source 20 through a wire 21 is
disposed in the electrolytic solution B so as to face the one surface side of the semiconductor
substrate 1. Subsequently, a current-carrying electrode is an anode, a platinum electrode 21 is a
cathode, and a current of a predetermined current density (here, 20 mA / cm <2>) is supplied
from the current source 20 to the anode and the cathode 21 for a predetermined time (here
Then, by performing anodizing treatment by flowing for 8 minutes, the heat insulating layer 2 is
formed on the one surface side of the semiconductor substrate 1 to a predetermined thickness
(10 .mu.m in this case) where the thickness other than the peripheral portion is constant. Form.
The conditions at the time of anodizing treatment are not particularly limited, and the current
density may be appropriately set, for example, in the range of about 1 to 500 mA / cm <2>. It
may be appropriately set according to the predetermined thickness.
[0032]
By sequentially performing the heat generating layer forming step of forming the heat generating
layer 3, the pad forming step of forming the pads 4 and 4, and the heat dissipation layer forming
step of forming the heat dissipation layer 5 after the above-described heat insulation layer
forming step. The pressure wave generating element is completed. In the heating element layer
formation step, the pad formation step, and the heat radiation layer formation step, for example,
films may be formed by various sputtering methods, various vapor deposition methods, various
CVD methods, or the like.
[0033]
In the pressure wave generating element of the present embodiment described above, it does not
react with the heat generating body layer 3 at the time of energization to the heat generating
body layer 3 and is made of a material different from each pad 4, 4 and dissipates the heat of the
pads 4, 4. Since the heat dissipation layers 5 and 5 are provided, the temperature rise near the
boundary (interface) between the heat generating body layer 3 and each of the pads 4 and 4 can
be suppressed. Since the heat of each of the pads 4, 4 can be dissipated to the outside through
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the heat dissipation layers 5, 5 without the reaction of each of the pads 4, 4 with each other, the
heating element layer 3 It is possible to prevent disconnection and stably generate pressure
waves in the ultrasonic region over a long period of time, and it is possible to achieve long life
and to increase the amplitude of the pressure waves by increasing the power applied to the
heating element layer 3 at the time of energization. It can be increased. Here, in the present
embodiment, since the heat dissipation layers 5 and 5 are formed to cover the exposed portions
where the heating element layer 3 and the pads 4 and 4 are in contact with each other, the
heating element layer 3 and the pads are formed. The heat of each pad 4, 4 can be dissipated to
the outside without increasing the contact resistance with each of 4, 4, and the heat dissipation
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.
[0034]
Further, by adopting the above-mentioned insulating material such as SiO 2 as the material of
each heat dissipation layer 5, no current flows to each heat dissipation layer 5 when the heat
generating layer 3 is energized, so the heat of each pad 4 is effectively applied. While being able
to radiate heat, generation | occurrence | production of the power loss by the electric current
flowing into each thermal radiation layer 5 can be prevented.
[0035]
By the way, in this embodiment, the semiconductor substrate 1 as a support substrate is
comprised by a silicon substrate, the heat insulation layer 2 is comprised by the porous silicon
layer, and the product of the heat conductivity of the heat insulation layer 2 and heat capacity is
Since the heat insulation of the thermal insulation layer 2 is sufficiently small (about 1/400) as
compared with the product of the thermal conductivity and the thermal capacity of the support
substrate, the output of the pressure wave to be generated can be increased, By providing the
layers 5 and 5, high-power ultrasonic waves can be stably output over a long period of time.
[0036]
Second Embodiment The basic configuration of the pressure wave generating element of the
present embodiment is substantially the same as that of the first embodiment, and as shown in
FIG. 3, the formation positions of the heat dissipation layers 5 are different.
That is, each of the heat radiation layers 5 and 5 in the present embodiment is formed such that
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a part is interposed between each end of the heat generating body layer 3 and each of the pads 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 generation layer 3 at positions slightly separated from the both ends of the heat generation
layer 3, and the respective pads 4 and 4 are the above-mentioned ones of the respective heat
radiation layers 5 and 5. It is formed to extend over the semiconductor substrate 1 and the upper
portion and the portion near both ends of the heating element layer 3 and the semiconductor
substrate 1. In addition, the same code | symbol is attached | subjected to the component similar
to Embodiment 1, and description is abbreviate | omitted.
[0037]
Thus, in the pressure wave generating element of the present embodiment, the heat radiation
layers 5 and 5 are partially interposed between the heat generating layer 3 and the pads 4 and 4
respectively, and the surface of the remaining portion is exposed. Since it is formed, heat in the
vicinity of the interface between heating element layer 3 and each of pads 4 and 4 can be
dissipated to the outside through the exposed surface of heat dissipation layer 5 and 5. The
reaction between the body layer 3 and each of the pads 4 and 4 is less likely to occur. Further,
the contact area between the heating element layer 3 and each of the pads 4 and 4 can be made
smaller than that of the first embodiment, and the reactive power can be reduced.
[0038]
1st Embodiment is shown, (a) is a schematic plan view, (b) is a D-D 'sectional view of (a). It is
explanatory drawing of the manufacturing method same as the above. Embodiment 2 is shown,
(a) is a schematic plan view, (b) is a D-D 'sectional view of (a). A prior art example is shown, (a) is
a schematic plan view, (b) is a D-D 'sectional view of (a). The other conventional example is
shown, (a) is a schematic plan view, (b) is a D-D 'sectional view of (a). FIG.
Explanation of sign
[0039]
Reference Signs List 1 semiconductor substrate 2 thermal insulation layer 3 heating element
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layer 4 pad 5 heat dissipation layer
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