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JP2007228305

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DESCRIPTION JP2007228305
To provide a pressure wave generating element capable of stably generating a pressure wave of
larger sound pressure and a method of manufacturing the same. A support substrate 1 made of a
silicon substrate, a heating element layer 3 made of a metal thin film (for example, an iridium
thin film) provided on one surface side of the support substrate 1, and support on the one
surface side of the support substrate 1 A thermal insulating layer 2 interposed between the
substrate 1 and the heat generating body layer 3, and a pair of pads 4 and 4 electrically
connected to both end portions of the heat generating body layer 3 on the one surface side of the
support substrate 1. Equipped with The heat insulating layer 2 is composed of a porous silica
layer which is a porous layer formed of a material having electrical insulation. The heat
insulating layer 2 is formed on the one surface side of the support substrate 1 by a coating
method. [Selected figure] Figure 1
Pressure wave generating element and method of manufacturing the same
[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, and a method of manufacturing the same.
[0002]
Conventionally, an ultrasonic wave generating element using mechanical vibration by a
piezoelectric effect is widely known.
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1
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, the medium (eg, 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 a pressure wave generating element capable of generating
pressure waves such as ultrasonic waves without mechanical vibration, a supporting substrate
made of a single crystal silicon substrate and one surface side of the supporting substrate A heat
insulating layer formed of the porous silicon layer, a heat generating layer formed of an
aluminum thin film formed on the heat insulating layer, and a pair electrically connected to the
heat generating layer on the one surface side of the support substrate And a pad having the
following are proposed (for example, see Patent Document 1).
[0005]
The pressure wave generating element applies thermal shock to the medium (air) by the
temperature change of the heat generating body layer according to the drive input waveform
consisting of the drive voltage waveform or the drive current waveform applied to the heat
generating body layer through the pair of pads. Generates pressure waves such as ultrasonic
waves.
In the pressure wave generating element disclosed in Patent Document 1, the thermal diffusion is
determined by the thickness of the thermal insulation layer determined by the frequency of the
temperature vibration of the heating layer, the thermal conductivity of the thermal insulation
layer, and the thermal capacity of the thermal insulation layer. Since the heat conductivity and
heat capacity of the heat insulating layer are sufficiently smaller than the heat conductivity and
volumetric heat capacity of the support substrate while being set to a longer thickness or more,
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2
the heat generated in the heat generating body layer is the support substrate It becomes difficult
to escape to the side, and the temperature rise of the heat generating body layer can be
increased, and an ultrasonic wave can be generated by applying a thermal shock to the medium.
Japanese Patent Application Publication No. 11-300274
[0006]
However, in the pressure wave generating element disclosed in Patent Document 1 described
above, a silicon substrate is used as a support substrate, and the heat insulating layer is formed
of a porous silicon layer. When the input power is increased to generate a pressure wave with a
large sound pressure, a leak current flows to each of the support substrates, a large current by a
local leak flows in the porous silicon layer, and a porous silicon is generated by a local heat
generation. There has been a problem that the partial destruction of the layer occurs and the
heating element layer is damaged accordingly and the device does not function as an element.
[0007]
The present invention has been made in view of the above-mentioned problems, and an object
thereof is to provide a pressure wave generating element capable of stably generating a pressure
wave of larger sound pressure and a method of manufacturing the same.
[0008]
According to the first aspect of the present invention, the heat insulating layer is interposed
between the heat conductive support substrate and the heat generating body layer provided on
the one surface side of the support substrate, and the heat generating body layer accompanying
the current flow to the heat generating body layer. A pressure wave generating element that
generates a pressure wave by applying a thermal shock to the medium by a temperature change
of the heat insulating layer, and the heat insulating layer is made of a porous layer formed of an
electrically insulating material. Do.
[0009]
According to the present invention, since the heat insulating layer is formed of the porous layer
formed of the material having electrical insulation, not only the heat permeability is small and the
pressure wave generation efficiency is high, but also the current to the heat generating body
layer is supplied. At the same time, it is possible to suppress the flow of leakage current to the
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thermal insulation layer, so it stabilizes the pressure wave with a larger sound pressure
compared to the conventional case where the thermal insulation layer is made of a porous silicon
layer. Can be generated.
The pressure wave generation efficiency is a value defined by the ratio of the sound pressure of
the pressure wave generated to the input power.
[0010]
The invention of claim 2 is characterized in that, in the invention of claim 1, the heat insulating
layer is composed of a porous silica layer.
[0011]
According to the present invention, since the heat insulation layer is formed of a porous silica
layer, the heat conductivity and the volume heat capacity can be reduced as compared with the
case where the material of the heat insulation layer is SiO 2, and the heat permeation is achieved.
Rate can be reduced, and the material of the heat insulating layer can realize a smaller heat
permeability than in the case of porous silicon, and the heat insulating property of the heat
insulating layer can be improved, and pressure waves can be achieved. The generation efficiency
can be improved.
[0012]
According to the invention of claim 3, the heat insulating layer is interposed between the heat
conductive support substrate and the heat generating body layer provided on the one surface
side of the support substrate, and the heat generating body layer accompanying the energization
of the heat generating body layer. A pressure wave generating element that generates a pressure
wave by applying a thermal shock to the medium by a temperature change of the heat insulating
layer, and the heat insulating layer is formed of an organic material having electrical insulation.
[0013]
According to the present invention, since the heat insulating layer is formed of an organic
material having electrical insulation, it is possible to suppress a leak current from flowing into
the heat insulating layer when current is supplied to the heat generating body layer. As
compared with the case where the heat insulating layer is made of a porous silicon layer as in the
above, a pressure wave with a larger sound pressure can be generated stably.
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[0014]
The invention of claim 4 is characterized in that, in the invention of claim 3, the organic material
of the heat insulating layer is made of a polyimide resin, a parylene resin or a fluorocarbon resin.
[0015]
According to this invention, the heat resistance of the heat insulating layer can be made relatively
high while using an organic material as the material of the heat insulating layer, and a pressure
wave with a larger sound pressure can be stably generated. it can.
[0016]
The invention of claim 5 is characterized in that, in the invention of claim 4, the heat insulating
layer is made of a porous layer formed of the organic material.
[0017]
According to the present invention, the heat insulating property of the heat insulating layer can
be improved, and a pressure wave with a larger sound pressure can be generated stably.
[0018]
The invention of claim 6 is characterized in that, in the invention of claims 1 to 5, the support
substrate has an electrical insulating property.
[0019]
According to the present invention, it is possible to more reliably prevent the leak current from
flowing to the support substrate when the heat generating body layer is energized, and to
generate a pressure wave with a larger sound pressure stably.
[0020]
The invention according to claim 7 is the method for manufacturing a pressure wave generating
element according to any one of claims 1 to 6, wherein a thermal insulating layer is formed on
one surface side of a support substrate. It is characterized by including a process and a heat
generating body layer forming process which forms a heat generating body layer on a heat
insulation layer.
[0021]
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According to the present invention, it is possible to provide a pressure wave generating element
capable of stably generating a pressure wave with a larger sound pressure.
[0022]
The invention of claim 8 is characterized in that in the invention of claim 7, the heat insulation
layer is formed by a coating method or a CVD method in the heat insulation layer forming step.
[0023]
According to the present invention, the restriction of the size of the support substrate is reduced,
and it is possible to provide a larger pressure wave generating element and reduce the
manufacturing cost.
[0024]
According to the first aspect of the present invention, there is an effect that a pressure wave with
a larger sound pressure can be generated stably.
[0025]
According to the seventh aspect of the present invention, it is possible to provide a pressure
wave generating element capable of stably generating a pressure wave with a larger sound
pressure.
[0026]
(Embodiment 1) As shown in FIG. 1, the pressure wave generating element of the present
embodiment includes a supporting substrate 1 having thermal conductivity, and a metal provided
on one surface (upper surface in FIG. 1) side of the supporting substrate 1. A heat generating
layer 3 made of a thin film, a heat insulating layer 2 interposed between the support substrate 1
and the heat generating layer 3 on the one surface side of the support substrate 1, and a heat
generation on the one surface side of the support substrate 1 A pair of pads 4 and 4 electrically
connected to both ends of the body layer 3 are provided.
[0027]
In the pressure wave generating element of the present embodiment, the pressure wave is
generated by applying a thermal shock to air as a medium by the temperature change of the heat
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generating body layer 3 accompanying the energization of the heat generating body layer 3
through the pair of pads 4 and 4. generate.
That is, in the pressure wave generating element of the present embodiment, the pressure is
applied by applying a thermal shock to air by the temperature change of the heat generating
body layer 3 according to the drive input waveform formed of the drive voltage waveform or
drive current waveform applied to the heat generating body layer 3. It can generate waves.
The planar shape of the support substrate 1 is a rectangular shape, and the planar shapes of the
heat insulating layer 2 and the heat generating layer 3 are also formed in a rectangular shape.
Further, in the pressure wave generating element of this embodiment, the thickness of the
support substrate 1 is 525 μm, the thickness of the heat insulating layer 2 is 1.5 μm, the
thickness of the heat generating layer 3 is 50 nm, and the thickness of each pad 4 is Although
the value is 0.5 μm, each of these values is an example and is not particularly limited.
[0028]
As the support substrate 1, a single crystal silicon substrate is used.
The heating element layer 3 is formed of iridium, which is a kind of high melting point metal, but
the material of the heating element layer 3 is not limited to iridium, and for example, other high
melting point metals such as tantalum, molybdenum and tungsten. It may be adopted.
Moreover, although aluminum is employ | adopted as a material of each pad 4, it does not limit
to aluminum and materials other than aluminum may be employ | adopted.
[0029]
By the way, the pressure wave generating element of the present embodiment is constituted of a
porous silica layer which is a porous layer in which the heat insulating layer 2 is formed of a
material having electrical insulation.
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Therefore, in the pressure wave generating element of this embodiment, since the heat insulating
layer 2 is made of a porous layer formed of a material having electrical insulation, the heat
permeability is small and the pressure wave generation efficiency is high. Since it is possible to
suppress the flow of leakage current in the heat insulating layer 2 when the heat generating
layer 3 is energized, the heat insulating layer is porous as in the conventional pressure wave
generating element described in Patent Document 1 above. A pressure wave with a larger sound
pressure can be stably generated as compared to the case where the quality silicon layer is used.
The pressure wave generation efficiency is a value defined by the ratio of the sound pressure of
the pressure wave generated to the input power (pressure wave generation efficiency = {sound
pressure [Pa] / input power [W]}).
[0030]
Further, in the pressure wave generating element of the present embodiment, since the heat
insulating layer 2 is formed of a porous silica layer as described above, the case of employing SiO
2 having heat insulating property and electrical insulating property as the material of the heat
insulating layer 2 The thermal conductivity and the volumetric heat capacity can be reduced as
compared with the above, and the thermal penetrability can be reduced, as in the conventional
pressure wave generating element described in Patent Document 1 above. As compared with the
case where the material is porous silicon, the heat permeability of the heat insulating layer 2 can
be made smaller, the heat insulating property of the heat insulating layer 2 can be improved, and
the pressure wave generation efficiency can be improved.
In the case where the heat insulating layer 2 is formed of a porous silica layer, the thermal
conductivity is set to 1/10 or less and the volumetric heat capacity is set to 2/3 or less as
compared to the case of forming a porous silicon layer. It is possible to significantly reduce the
heat transfer rate.
[0031]
To further explain the porous silica layer constituting the heat insulating layer 2, the average
value of the pore diameter is 5 nm or less in order to suppress the adsorption of moisture in the
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air into the pores of the porous silica layer. It is desirable to have.
Thus, by setting the average value of the pore diameters of the porous silica layer constituting
the heat insulating layer 2 to 5 nm or less, it is difficult for moisture in the air to be adsorbed in
the pores of the porous silica layer, and the heat insulating layer It is possible to prevent an
increase in volumetric heat capacity including the holes 2 and to suppress a decrease in pressure
wave generation efficiency.
In addition, since it is possible to suppress the adsorption and aggregation of moisture in the
pores of the porous silica layer, the pores of the porous layer (in the present embodiment, the
porous silica layer) constituting the heat insulating layer 2 can be suppressed. A leak current can
be prevented from flowing through the aggregated water, and a pressure wave with a large
sound pressure can be stably generated even under a high humidity atmosphere.
In addition, it is possible to prevent the heat penetrability of the heat insulating layer 2 from
changing with time due to the reaction product by the moisture adsorbed in the pores of the heat
insulating layer 2, and improve the time stability of the output. be able to.
As the average value of the pore diameter of the porous silica layer constituting the heat
insulating layer 2 becomes smaller, the moisture is more difficult to be adsorbed, but when it
becomes too small, the heat insulating property becomes low, so the average pore diameter of
the porous silica layer is reduced. The value is preferably a smaller value within the range in
which the desired heat permeability of the heat insulating layer 2 can be obtained.
[0032]
Hereinafter, the manufacturing method of the pressure wave generation element of this
embodiment is explained.
[0033]
First, a thermal insulation layer forming step of forming the thermal insulation layer 2 on one
surface (upper surface in FIG. 1) side of the support substrate 1 made of a silicon substrate is
performed.
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Here, in the heat insulation layer forming step, the heat insulation layer 2 is formed by a coating
method.
To explain further, in the heat insulating layer forming step, for example, a solution obtained by
dissolving any one of a thermally decomposable compound, a surfactant and a foamable
compound in a siloxane resin or an organic polymer resin having an aromatic hydrocarbon main
chain Is spin-coated on the one surface of the support substrate 1 and then pores are formed at
the time of curing to form the heat insulating layer 2 composed of a porous silica layer.
In the coating method, a method may be adopted in which pores are generated by utilizing a
chemical reaction when the solution is cured.
Moreover, the formation method of the heat insulation layer 2 in a heat insulation layer
formation process may employ | adopt not only the application method but CVD method.
[0034]
After the above-described heat insulation layer formation process, a heat generation body layer
formation process for forming a heat generation body layer 3 formed of a metal thin film (for
example, an iridium thin film) on the heat insulation layer 2 is performed. Perform the pad
formation process.
In the heating element layer forming step, the heating element layer 3 may be formed by
sputtering or evaporation using a metal mask or the like, and in the pad forming step, the
sputtering or evaporation may be performed using a metal mask or the like. The pads 4 and 4
may be formed by the like.
In the above-described manufacturing method, all steps up to the end of the pad forming step are
performed in the wafer state, and therefore, after the pad forming step is completed, it may be
divided into desired chip sizes by the dicing step.
[0035]
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In the method of manufacturing a pressure wave generating element according to the present
embodiment described above, since the heat insulating layer 2 made of the porous silica layer is
formed by the coating method or the CVD method in the heat insulating film forming step, There
is less restriction on the size (planar size), and it is possible to provide a larger pressure wave
generating element and reduce the manufacturing cost.
[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 the heat
insulating layer 2 is a porous layer formed of an organic material having electrical insulation. The
other configuration is the same as that of the first embodiment.
[0037]
Therefore, in the pressure wave generating element according to the present embodiment, the
heat insulating layer 2 is formed of an organic material having electrical insulation, so that a leak
current flows in the heat insulating layer 2 when the heat generating layer 3 is energized. As
compared with the conventional case where the heat insulating layer is made of a porous silicon
layer, a pressure wave with a larger sound pressure can be generated stably.
Further, since the heat insulating layer 2 is formed of a porous layer formed of an organic
material, the heat insulating property of the heat insulating layer 2 is improved, and a pressure
wave with a larger sound pressure can be generated stably.
[0038]
Here, if a polyimide-based resin, a parylene-based resin or a fluorocarbon resin is used as the
organic material which is the material of the heat insulating layer 2, the heat resistance of the
heat insulating layer 2 can be obtained while using the organic material as the material of the
heat insulating layer 2. It can be made relatively high, and a pressure wave of larger sound
pressure can be generated stably.
Melting point and glass transition temperature Tg are shown in Table 1 as data on heat
resistance of various organic materials.
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[0039]
[0040]
In Table 1, data of Teflon (registered trademark) is shown as an example of the fluorine resin.
[0041]
The method of manufacturing the pressure wave generating element of the present embodiment
is also substantially the same as that of the first embodiment, and the process of forming the heat
insulating layer 2 is different.
In the heat insulating layer forming step in the present embodiment, when the heat insulating
layer 2 is formed by a coating method, the carbon dioxide gas and the fluorocarbon substitute for
the volatile liquid are physically introduced into, for example, a polyimide resin and then foamed.
It forms a hole.
In addition, if a supercritical fluid of CO 2 is used as the fluid physically introduced into the
polyimide resin, the thermal insulating layer 2 is formed which is a porous layer with less
variation in the pore diameter and a smaller average value of the pore diameter. Can.
Moreover, the formation method of the heat insulation layer 2 in a heat insulation layer
formation process may employ | adopt not only the apply | coating method but CVD method.
[0042]
In the first and second embodiments, a silicon substrate is used as the support substrate 1.
However, if a substrate having electrical insulation is used instead of the silicon substrate, the
support substrate 1 can be used when the heating element layer 3 is energized. A leak current
can be more reliably prevented from flowing, and a pressure wave with a larger sound pressure
can be generated stably.
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Here, as the support substrate 1 having electrical insulation, for example, a ceramic substrate
such as an aluminum nitride substrate having high thermal conductivity and electrical insulation,
a glass-coated metal substrate (for example, Cu substrate), A silicon substrate or the like coated
with a SiO 2 film may be used.
[0043]
FIG. 2 is a schematic cross-sectional view of a pressure wave generating element in Embodiment
1. It is explanatory drawing of the manufacturing method of a pressure wave generation element
same as the above.
Explanation of sign
[0044]
1 support substrate 2 thermal insulation layer 3 heating element layer 4 pad
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