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JP2006094399

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DESCRIPTION JP2006094399
The present invention provides a pressure wave generating element capable of achieving high
output as compared with the case of employing gold as a material of a heat generating body
layer. A heat insulating layer 2 made of a porous silicon layer is provided between a supporting
substrate 1 made of a silicon substrate and a heat generating body layer 3 provided on one
surface side of the supporting substrate 1. The pressure wave generating element generates a
pressure wave by heat exchange between the heat generating body layer 3 and the air according
to the temperature change of the heat generating body layer 3 due to heat treatment, and the
Young's modulus does not fall below 170 GPa A metal material (for example, Pt, Mo, Ir, W) is
used. [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
piezoelectric effect is widely known.
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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, 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, as a pressure wave generator capable of generating a pressure wave such as
an ultrasonic wave by thermal excitation without mechanical vibration, as shown in FIG. 5, a
support substrate 1 ′ and a support substrate 1 ′. A heat insulating layer 2 ′ having a
thermal conductivity and a heat capacity sufficiently smaller than a supporting substrate 1 ′
formed on one surface side, and a heat generating layer 3 ′ formed on the heat insulating layer
2 ′; There have been proposed pressure wave generating elements that generate pressure
waves by heat exchange between the heat generating body layer 3 'and air accompanying the
application of alternating current to the layer 3' (Patent Documents 1, 2 and 3).
[0005]
In the pressure wave generating element having the configuration shown in FIG. 5, since the heat
insulating layer 2 'is formed immediately below the heat generating body layer 3', heat
generation can be achieved by energizing the heat generating layer 3 'with AC, for example.
While the temperature of the heat generating body layer 3 'changes in accordance with the input
waveform applied to the body layer 3', efficient heat exchange occurs with the air in the vicinity
of the heat generating body layer 3 'to expand the air As a result of compression, pressure waves
such as ultrasonic waves are generated.
In the pressure wave generating element having the configuration shown in FIG. 5, the frequency
of the generated pressure wave can be changed over a wide range by adjusting the frequency of
the alternating current supplied to the heating element layer 3 '. It can be used as a sound source
of a sound wave source or a speaker.
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In short, in the pressure wave generating element having the configuration shown in FIG. 5, the
waveform of the electrical input (voltage applied to the heating element layer 3 'or current
supplied to the heating element layer 3') applied to the heating element layer 3 'is By changing
the waveform by changing the period of the periodic wave as a periodic wave (for example, a sine
wave, a square wave, etc.), the frequency of the pressure wave to be generated can be changed
over a wide range, and If the waveform of the electrical input applied to the '' is a solitary wave, a
monopulse compressional compression wave (impulse sound wave) can be generated as a
pressure wave.
[0006]
Here, in the pressure wave generating element described in Patent Documents 1 and 2, the
supporting substrate 1 'is formed of a single crystal silicon substrate, and the heat insulating
layer 2' is anodizing a part of the silicon substrate. It is comprised by the porous silicon layer
formed by making it porous. In the above Patent Document 1, it is desirable to reduce the
thermal conductivity and heat capacity of the thermal insulation layer 2 ′ compared to the
thermal conductivity and thermal capacity of the support substrate 1 ′, and the thermal
conductivity and thermal capacity of the thermal insulation layer 2 ′ It is described that it is
preferable to make the product of V.sub.2 smaller than the product of the thermal conductivity
and the heat capacity of the support substrate 1 '.
[0007]
Moreover, in the pressure wave generating element described in Patent Documents 1 and 2
above, the heat generating body layer 3 'is located on the heat insulating layer 2' inside the outer
periphery of the heat insulating layer 2 ', and the heat generating body layer 3' The structure in
which the surface of the surface (the upper surface of the heating element layer 3 'in FIG. 5) and
the part of the heat insulating layer 2' (the part where the heating element layer 3 'is not
laminated) is exposed is Patent Document 2 also describes a structure in which the heat
insulating layer 2 'is formed by subjecting the porous silicon layer to a rapid thermal oxidation
process, instead of forming the heat insulating layer 2' with a porous silicon layer. Further, in the
pressure wave generating element described in Patent Document 3, a structure in which the
surface of the heat generating body layer 3 'is covered with an insulating protective layer made
of a SiO2 film is employed. Further, in the above Patent Documents 1 and 2, an embodiment in
which the heat generating body layer 3 'is formed of an aluminum thin film is described, and in
the Patent Document 3, an embodiment in which the heat generating body layer 3' is formed of a
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tantalum nitride film is described. ing. In the example of Patent Document 3, the film thickness of
the tantalum nitride film forming the heating element layer 3 'is set to 0.5 μm, and the film
thickness of the SiO 2 film forming the insulating protective layer is set to 1.5 μm. It is done. JPA-11-300274 JP-A-2002-186097 JP-A-3-140100
[0008]
By the way, in the pressure wave generating element having the configuration shown in FIG. 5,
the inventors of the present invention have, for example, a plane surface of a portion generating
the pressure wave (a portion where the pad is not formed and the surface is exposed) in the
heating element layer 3 '. When ultrasonic waves with a frequency of 60 kHz are generated with
a size of 5 mm □, the temperature of the heating element layer 3 'is about 400 ° C. to obtain a
sound pressure of about 15 Pa at a position 30 cm away from the pressure wave generating
element. It was necessary to raise the temperature to about 30 Pa, and to obtain an acoustic
pressure of about 30 Pa, it was necessary to raise the temperature of the heat generating body
layer 3 'to a high temperature exceeding 1000.degree.
[0009]
Therefore, in the pressure wave generating devices described in Patent Documents 1 and 2
described above, a large number (48 types) of materials listed in paragraph [0030] of Patent
Document 3 above as materials of the heating element layer 3 ′ for increasing output. It is
possible to adopt materials other than aluminum among the metal materials in the above), but it
is considered that film forming equipment necessary for film formation, conditions for film
forming conditions, and acquisition of materials are examined Since it is difficult from the
viewpoint, the inventors focused on gold having a high melting point and excellent oxidation
resistance as compared to aluminum as a starting point, and the heat generating layer 3 ′ was a
10 nm chromium film on the heat insulating layer 2 ′ and the like. A 40 nm gold film on a
chromium film was used to examine the relationship between the input power to the heat
generating body layer 3 'and the output sound pressure.
As a result, when the above-mentioned plane size was set to 20 mm □, a sound pressure of 48
Pa was obtained as the maximum output sound pressure (sound pressure immediately before
dielectric breakdown).
[0010]
However, when industrial use is considered, if the chip size of the pressure wave generating
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element is reduced for the purpose of, for example, cost reduction and directivity reduction, the
planar size of the part generating the pressure wave is also small. And the sound pressure is also
reduced (for example, if the plane size of the portion generating the pressure wave is 5 mm □, it
becomes 1/16 of the sound pressure of 20 mm □), so gold as the heat generating body layer 3 '
It is considered that a pressure wave generating element having a high maximum output sound
pressure is required (in other words, a pressure wave generating element having a higher output
is required) than the pressure wave generating element adopting.
[0011]
Further, in the pressure wave generating element described in Patent Document 3, a SiO2 film is
adopted as the heat insulating layer 2 ', and tantalum nitride is adopted as the material of the
heat generating body layer 3'. Since the resistance is higher than that of metal, when driving with
a constant voltage, it becomes necessary to apply a high voltage to the heating element layer 3
'compared to the pressure wave generating element described in the above-mentioned Patent
Documents 1 and 2, and the input power (Ie, it is difficult to reduce power consumption).
Further, in the pressure wave generating element described in Patent Document 3, since the heat
capacity of the heat generating body layer 3 'is larger than that of the pressure wave generating
element described in the Patent Documents 1 and 2, The response of the temperature change to
the waveform of the applied electrical input is delayed and the temperature of the heat
generating body layer 3 'is less likely to rise, which makes it difficult to achieve high output and
high response speed.
[0012]
The present invention has been made in view of the above problems, and an object thereof is to
provide a pressure wave generating element capable of achieving high output as compared with
the case of employing gold as a material of a heat generating body layer.
[0013]
According to the first aspect of the present invention, the heat insulating layer formed of the
porous silicon layer is provided between the silicon substrate and the heat generating body layer
provided on the one surface side of the silicon substrate, and A pressure wave generating
element that generates a pressure wave by heat exchange between a heat generating body layer
and air with temperature change, and using a metal material whose Young's modulus does not
fall below 170 GPa as a material of the heat generating body layer It features.
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[0014]
According to the present invention, compared with the case where gold is adopted as the
material of the heat generating body layer, the breakdown power becomes high, and high output
can be achieved.
[0015]
The invention of claim 2 is characterized in that, in the invention of claim 1, the metal material is
a metal having a Vickers hardness of not less than 160 Hv.
[0016]
According to the present invention, the breakdown power can be further increased, and the
reliability can be improved.
[0017]
The invention of claim 3 is characterized in that, in the invention of claim 1 or claim 2, the metal
material is a noble metal.
[0018]
According to this invention, it is possible to prevent the oxidation of the heating element layer
and to prolong the life.
[0019]
According to the invention of claim 4, in the invention of claims 1 to 3, the heat insulation layer
is formed on a predetermined region on the one surface side of the silicon substrate, and the heat
generating body layer is formed on the heat insulation layer. An insulating film formed inside the
outer periphery of the heat insulating layer and laminated on a portion other than the
predetermined region on the one surface side of the silicon substrate, and the heat generating
layer and the insulating film on the one surface side of the silicon substrate And a protective film
for preventing oxidation of the heat insulation layer.
[0020]
According to this invention, oxidation of the heat insulation layer can be prevented by the
protective film, output reduction due to oxidation of the heat insulation layer can be prevented,
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and reliability can be improved.
[0021]
In the invention of claim 5, in the invention of claims 1 to 3, the heat insulating layer is formed
on a predetermined region on the one surface side of the silicon substrate, and the heat
generating body layer is formed on the heat insulating layer. An insulating film formed inside the
outer periphery of the heat insulating layer and laminated on a portion other than the
predetermined region on the one surface side of the silicon substrate, and both ends of the heat
generating layer on the one surface side of the silicon substrate And a pair of pads formed in
contact with each other, and a part of the pad is interposed between each end of the heat
generating body layer and the insulating film on the one surface side of the silicon substrate, and
the heat is generated A protective film is formed between the heat generating body layer and the
insulating film on the one surface side of the silicon substrate on the periphery of the body layer
and on which the pad is not formed to prevent oxidation of the heat insulating layer. To be done
And features.
[0022]
According to the present invention, the oxidation of the heat insulating layer can be prevented by
a part of each pad and the protective film, and a decrease in output due to the oxidation of the
heat insulating layer can be prevented and the reliability is improved. Can.
[0023]
According to the invention of claim 6, according to the invention of claim 4 or claim 5, the
protective film is a material selected from the group of carbides, nitrides, borides and silicides,
and which has a melting point higher than that of silicon. It is characterized by being formed by
Here, carbides having a melting point higher than that of silicon include, for example, TaC, HfC,
NbC, ZrC, TiC, VC, WC, ThC, and SiC, and nitrides having a melting point higher than silicon
include, for example, HfN. And borides having a melting point higher than that of silicon, such as
HfB, TaB, ZrB, TiB, NbB, WB, VB, MoB, CrB, etc., which are higher than silicon. As the silicide of
the melting point, there are, for example, WSi2, MoSi2, TiSi2, and the like.
[0024]
According to the present invention, the protective film can be formed by a general thin film
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forming method used in a semiconductor manufacturing process such as a sputtering method, a
vapor deposition method, and a CVD method.
[0025]
According to the first aspect of the present invention, compared to the case where gold is used as
the material of the heat generating body layer, the breakdown power is increased, and the output
can be increased.
[0026]
In the pressure wave generating element of the present embodiment, as shown in FIG. 1, the heat
generating layer 3 is provided on one surface side of the supporting substrate 1, and the heat
insulating layer 2 is formed between the supporting substrate 1 and the heat generating layer 3.
A pair of pads 4 and 4 which are provided and which are in contact with both end portions (left
and right end portions in FIG. 1) of the heating element layer 3 on the one surface side of the
support substrate 1 are provided.
[0027]
Here, in the pressure wave generating element of the present embodiment, the heat insulating
layer 2 is formed in a predetermined region on the one surface side of the support substrate 1,
and the heat generating layer 3 is formed on the heat insulating layer 2 from the outer periphery
of the heat insulating layer 2. In addition, an insulating film 5 formed of an SiO 2 film laminated
on a portion other than the predetermined region on the one surface side of the support
substrate 1 and the heating element layer 3 on the one surface side of the support substrate 1. A
protective film 6 is provided, which is partially interposed between the insulating film 5 to
prevent oxidation of the heat insulating layer 2.
The protective film 6 is formed so as to cover the surface of a portion of the heat insulating layer
2 where the heating element layer 3 is not stacked and the insulating film 5, and the pad 4
extends over the heating element layer 3 and the protective film 6. It is formed in the form.
[0028]
The pressure wave generating element of the present embodiment has a temperature of the heat
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generating body layer 3 corresponding to the waveform of an electrical input (voltage applied to
the heat generating body layer 3 or current supplied to the heat generating body layer 3) applied
to the heat generating body layer 3 With the change, a pressure wave is generated by heat
exchange between the heat generating body layer 3 and the air.
The outer peripheral shape of the support substrate 1 is a rectangular shape, and the outer
peripheral shapes of the heat insulating layer 2 and the heat generating layer 3 are also formed
in a rectangular shape.
[0029]
In the present embodiment, a single crystal silicon substrate is used as the support substrate 1
and the heat insulating layer 2 is formed of a porous silicon layer having a porosity of
approximately 70%. Therefore, the silicon substrate used as the support substrate 1 The porous
silicon layer to be the heat insulating layer 2 can be formed by anodizing the above-mentioned
predetermined region, which is a part of the above, in a hydrogen fluoride aqueous solution.
Here, the porosity and thickness of the porous silicon layer to be the heat insulating layer 2 can
be set to desired values by appropriately setting the conditions of the anodizing treatment (for
example, current density, current passing time, etc.).
In the porous silicon layer, the thermal conductivity and the thermal capacity decrease as the
porosity increases. For example, the thermal conductivity is 148 W / (m · K) and the thermal
capacity is 1.63 × 10 <6> J / (m < The porous silicon layer having a porosity of 60% formed by
anodizing a single crystal silicon substrate of 3> · K) has a thermal conductivity of 1 W / (m · K)
and a heat capacity of 0.7 × 10 It is known that <6> J / (m <3> · K).
In the present embodiment, as described above, the heat insulating layer 2 is formed of a porous
silicon layer having a porosity of approximately 70%, and the heat conductivity of the heat
insulating layer 2 is 0.12 W / (m · K), The heat capacity is 0.5 × 10 <6> J / (m <3> · K).
[0030]
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The protective film 6 is formed of HfC having a melting point higher than that of silicon, but the
material of the protective film 6 is a material selected from the group of carbides, nitrides,
borides, and silicides, and has a melting point higher than silicon. The carbides having a melting
point higher than that of silicon may be TaC, HfC, NbC, NbC, ZrC, TiC, VC, WC, ThC, SiC or the
like, and nitrides having a melting point higher than that of silicon HfN, TiN, TaN, BN, Si3N4 etc.
can be adopted as the boride, HfB, TaB, ZrB, TiB, TiB, NbB, WB, VB, MoB, CrB etc. is adopted as
the boride having a melting point higher than that of silicon. It is possible to use WSi2, MoSi2,
TiSi2 or the like as the silicide having a melting point higher than that of silicon.
The material of the heat generating layer 3 will be described later.
Further, in the pressure wave generating element of this embodiment, the thickness of the heat
insulating layer 2 is 2 μm, the thickness of the heat generating layer 3 is 50 nm, and the
thickness of each pad 4, 4 is 0.5 μm. Is an example and is not particularly limited.
[0031]
Hereinafter, the manufacturing method of the pressure wave generating element of the present
embodiment will be briefly described.
[0032]
First, an energizing electrode (not shown) used for anodizing treatment is formed on the other
surface (lower surface in FIG. 1B) of the silicon substrate used as the support substrate 1, and
then the above predetermined is formed on one surface side of the silicon substrate Anodizing
treatment is performed to form an insulating film 5 having a portion corresponding to the region
and to form the heat insulating layer 2 made of a porous silicon layer by making the
predetermined region of the silicon substrate porous by anodizing treatment Perform the
process.
Here, in the anodizing treatment step, a processing solution mainly composed of a silicon
substrate can be placed in a processing bath using a mixed solution of a 55 wt% hydrogen
fluoride aqueous solution and ethanol mixed at 1: 1 as an electrolytic solution. The power source
is immersed in the electrolyte, and the current-carrying electrode is an anode, and the platinum
electrode oppositely disposed on the one surface side of the silicon substrate is a cathode, and a
current of a predetermined current density is supplied from the power source to the anode and
05-05-2019
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the cathode for a predetermined time. By flowing, the heat insulating layer 2 made of a porous
silicon layer is formed.
[0033]
After the anodizing process described above, the protective film formation process for forming
the protective film 6, the heating element layer formation process for forming the heating
element layer 3, and the pad formation process for forming the pads 4 and 4 are sequentially
performed. By performing the process, the pressure wave generating element is completed.
In the protective film forming step, the heating element layer forming step, and the pad forming
step, the film may be formed by, for example, various sputtering methods, various vapor
deposition methods, various CVD methods, etc. An etching technique may be used as appropriate.
[0034]
Next, the result of having examined the material of the heat generating body layer 3 is
demonstrated.
[0035]
With regard to the pressure wave generating element having the configuration of FIG. 1, the
planar size of the portion generating the pressure wave in the heating element layer 3 is 20 mm
□, and Au of the metal materials shown in Table 1 below as the material of the heating element
layer 3 The pressure wave generating element which adopted each of Pt, Mo, Ir, and W was made
as an experiment.
However, in a pressure wave generating element employing Au, the heating element layer 3 is
constituted of a 10 nm chromium film on the heat insulation layer 2 and a 40 nm gold film on
the chromium film, and Pt, Mo, Ir, W In the pressure wave generating element which adopted
each, the heat generating body layer 3 is comprised by the metal thin film which is 50 nm in
thickness, and consists of a single metal material.
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In addition, each numerical value of Table 1 is a value based on "metal data book" (Maruzen Co.,
Ltd., published on January 30, 1984, revised 2nd edition) edited by The Metals Society of Japan.
[0036]
FIG. 2 shows the results of measuring the output sound pressure when the input power to the
heat generating body layer 3 was variously changed for each of the pressure wave generating
elements produced on an experimental basis.
In FIG. 2, the horizontal axis is the peak value (maximum input) of the input power when the
peak value is changed variously with the sine wave voltage at a frequency of 30 kHz as an input,
and the vertical axis is from the surface of the heating element layer 3 The frequency measured
at a position separated by 30 cm is the sound pressure (output sound pressure) of ultrasonic
waves of 60 kHz.
[0037]
Here, when the material of the heat generating body layer 3 is Au / Cr, Pt, Mo, Ir, and W,
respectively, the maximum output sound pressures are 48 Pa, 150 Pa, 236 Pa, 226 Pa, and 264
Pa, respectively.
[0038]
The above results are summarized in Table 2 below.
Table 2 also shows the converted value of the maximum output sound pressure when assuming
that the above-mentioned plane size is 5 mm □.
[0039]
From Table 2, by adopting Pt or Mo or Ir or W as the material of the heat generating body layer
3, the breakdown power becomes high as compared with the case where gold is adopted as the
material of the heat generating body layer 3, high power It can be seen that it can be
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[0040]
By the way, in order to suppress the directivity of the pressure wave generated from the pressure
wave generating element and emit the ultrasonic wave in a wide area, it is necessary to reduce
the above-mentioned plane size, but the generated sound pressure is proportional to the abovementioned plane size If the plane size is too small, the absolute amount of sound pressure will be
small.
[0041]
If it is a pressure wave generated from a sound source and a reflected wave reflected by an
object is detected to detect a distance or direction to the object, a sound pressure of at least
about several Pa is required, for example, In order to detect a reflected wave using a detector
with a sensitivity of several mV / Pa, it is necessary to output a pressure wave at which a sound
pressure of at least about 8 Pa can be obtained from the sound source.
Here, as can be seen from Table 2, in the pressure wave generating element employing Pt, Mo, Ir,
or W as the material of the heat generating body layer 3, a sound pressure exceeding 8 Pa is
obtained even when the plane size is 5 mm □. It can be understood that
Therefore, as a result of comparing the relative magnitude relationship between Pt, Mo, Ir, W and
Au with respect to each physical property of Table 1, the present inventors have compared Au
with respect to all of Pt, Mo, Ir and W. We obtained the finding that Young's modulus can be
mentioned as a physical property that makes the magnitude relationship with the same.
That is, the Young's modulus of each of Pt, Mo, Ir, and W is a value higher than that of Au, and
the Young's modulus of Au is 88 GPa, whereas the Young's modulus of Pt, Mo, Ir, W is The rates
are 170 GPa, 327 GPa, 570 GPa and 403 GPa, respectively.
Therefore, by using a metal material whose Young's modulus does not fall below 170 GPa, which
is the Young's modulus of Pt, as the material of the heat generation layer 3, the breakdown
power is higher than when Au is employed as the material of the heat generation layer 3. It
becomes high, and high output can be achieved.
[0042]
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In addition, "the life test method of heating wire and band" has been standardized in the JIS
standard (JIS C 2524), and it is described that the life test is performed at an output of 1.2 times
the rating in this standard. Therefore, if the sound pressure rating of the pressure wave
generating element is 8 Pa, it is necessary to conduct the life test with the sound pressure set at
9.6 Pa, in accordance with this life test method.
Here, as for the pressure wave generating element having a plane size of 5 mm □, the material
of the heat generating layer 3 in the pressure wave generating element having a maximum
output sound pressure larger than 9.6 Pa is Mo, Ir, W, From the above Table 1, it was found that
hardness (here, Vickers hardness) can be mentioned as a physical property in which the
magnitude relationship with Pt is the same for all of Mo, Ir, and W. That is, the Vickers hardness
of each of Mo, Ir, and W is a value higher than that of Pt, and the Vickers hardness of Pt is 39 Hv,
while the Vickers hardness of each of Mo, Ir, and W is respectively , 160 Hv, 200 Hv, 360 Hv.
Therefore, by using a metal material whose Young's modulus does not fall below 170 GPa and
whose Vickers hardness does not fall below 160 Hv as the material of the heat generation layer
3, compared with the case where Au, Pt is adopted as the material of the heat generation layer 3,
The breakdown power can be increased to increase the output, and the reliability can be
improved.
[0043]
Here, the pressure at the time of initial driving is set for each of the pressure wave generating
element using Ir having the minimum maximum output sound pressure among Mo, Ir, and W,
and the pressure wave generating element using W having the maximum. The result of having
conducted the life test of several samples as 12 Pa is shown in FIG. In FIG. 3, the horizontal axis
is the number of times of driving, and the vertical axis is the sound pressure (output sound
pressure), and a1 to a5 in the same figure are continuous driving life characteristics of a sample
using Ir as the metal material of the heating layer 3. In the figure, b1 to b3 indicate the life
characteristics of the sample using W as the metal material of the heating element layer 3. The
downward arrows in FIG. 3 indicate the timing at which each of b1 to b3 is broken.
[0044]
From FIG. 3, according to the life characteristics, the pressure wave generating element using W
having a large maximum output sound pressure had a maximum number of times of driving of
80,000,000, while the pressure wave generating element using Ir has a maximum. It can be seen
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that even if the driving is performed 300 million times for all the samples, the heat source layer
3 is not broken and the sound pressure is stable, and the maximum output sound pressure is
larger than that of the pressure wave generating element using W. It can be seen that the
pressure wave generating element used is far superior in continuous drive life characteristics.
[0045]
Various conditions can be considered as the driving condition of the pressure wave generating
element. For example, assuming that the product which can be continuously driven once a
second, regardless of daytime / nighttime is 10 years, about 300 million times It is necessary to
guarantee the drive count.
Here, while the pressure wave generating element using W described above could only drive
about 80 million times, the pressure wave generating element using Ir driven up to 360 million
times for all samples. It has been confirmed that no disconnection occurs. The pressure wave
generating element using Ir as the material of the heating element layer 3 is superior to the
pressure wave generating element using W with respect to the continuous driving life
characteristics, although W is a refractory metal although it is While oxidation is likely to occur
at several hundred degrees C., it is considered that Ir is a noble metal, has higher oxidation
resistance than W, and can prevent the oxidation of the heating element layer 3.
[0046]
In the pressure wave generating element of the present embodiment, since the above-described
protective film 6 is provided on the one surface side of the support substrate 1, the oxidation of
the heat insulating layer 2 can be prevented. While being able to prevent the output fall, it is
possible to improve the reliability. Here, the protective film 6 is formed by sputtering using a
material selected from the group of carbides, nitrides, borides, and silicides and having a melting
point higher than that of silicon as the material of the protective film 6; It can form by the
general thin film formation method utilized by semiconductor manufacturing processes, such as
a vapor deposition method and CVD method.
[0047]
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By the way, in the example shown in FIG. 1, the protective film 6 is formed on the one surface
side of the support substrate 1 so as to surround the heating element layer 3 all around, but as
shown in FIG. A portion of the pads 4, 4 is interposed between the insulating film 5 and both end
portions (left and right end portions in FIG. 4B) of the heating element layer 3 on the one surface
side of the support substrate 1, The above-described protective film 6 may be formed around the
portion 3 where the pads 4 and 4 are not formed. When the configuration of FIG. 4 is adopted,
the oxidation of the heat insulating layer 2 can be prevented by a part of each of the pads 4 and
4 and the protective film 6, and the output decrease due to the oxidation of the heat insulating
layer 2 is prevented. And improve reliability.
[0048]
It is a schematic sectional drawing which shows embodiment. FIG. It is a lifetime characteristic
figure same as the above. The other structural example same as the above is shown, (a) is a
schematic plan view, (b) is an A-A 'sectional view of (a), (c) is a B-B' sectional view of (a). It is a
schematic sectional drawing which shows a prior art example.
Explanation of sign
[0049]
1 support substrate 2 thermal insulation layer 3 heating element layer 4 pad 5 insulation film 6
protective film
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