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DESCRIPTION JP2006217059

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DESCRIPTION JP2006217059
The present invention provides a pressure wave generator improved in response to an input to a
heat generating body layer as compared with the prior art. A support substrate 1, a heating
element layer 3 formed on one surface side of the support substrate 1, and heat interposed
between the support substrate 1 and the heating element layer 3 on the one surface side of the
support substrate 1 And an insulating layer 2. The thickness d [m] of the thermal insulating layer
2 is the thermal conductivity of the thermal insulating layer 2 α i [W / (m · K)], and the thermal
capacity of the thermal insulating layer 2 is Ci [J / (m · K)] The drive input waveform given to the
heating layer 3 is a sine wave, and the frequency twice the frequency f [Hz] of the sine wave is
the ideal frequency f [Hz] of the temperature oscillation generated in the heating layer 3
Assuming that the angular frequency of vibration is ω = 2πf [rad / s], the condition of 0.05D <d
<D is satisfied for the thermal diffusion length D [m] defined by D = (2αi / ωCi) It is set to be
satisfactory. [Selected figure] Figure 1
Pressure wave generator
[0001]
The present invention relates to, for example, a pressure wave generator 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 generator using mechanical vibration due to the piezoelectric
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effect is widely known.
As this type of ultrasonic wave 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. In this ultrasonic wave generator, 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 generator using mechanical vibration as described above has problems such
as narrow frequency band since it has an inherent resonance frequency, and is susceptible to
external vibration and fluctuations in external pressure.
[0004]
On the other hand, in recent years, as a pressure wave generator 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]
This pressure wave generator comprises a heating element layer and air as a medium according
to a temperature change of the heating element layer according to a drive input waveform
consisting of a driving voltage waveform or a driving current waveform applied to the heating
element layer through a pair of pads. Generates a pressure wave such as an ultrasonic wave by
heat exchange with the
In the above Patent Document 1, the thickness of the thermal insulating layer is set to a thickness
greater than the thermal diffusion length determined by the frequency of the temperature
vibration of the heat generating layer, the thermal conductivity of the thermal insulating layer,
and the thermal capacity of the thermal insulating layer. In addition, it is described that the
thermal conductivity and the thermal capacity of the thermal insulating layer are sufficiently
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smaller than the thermal conductivity and the thermal capacity of the support substrate.
Moreover, it is described in the said patent document 1 that you may use a polymeric material as
a material of a heat insulation layer.
[0006]
In the above-described pressure wave generator, for example, when the drive input waveform is a
sine wave, ideally, the frequency of the temperature vibration generated in the heating element
layer is twice the frequency of the drive input waveform, and the drive input waveform A
pressure wave of twice the frequency of the frequency of In short, in the above-described
pressure wave generator, ideally, the frequency of the pressure wave generated can be changed
by changing the frequency of the drive input waveform by changing the frequency of the drive
input waveform as a sine wave, and driving If the input waveform is a solitary wave, a single
pulse compressional compression wave (impulse sound wave) can be generated as a pressure
wave, and if it is used as a transmission element of an ultrasonic sensor, the distance is measured
by the ultrasonic sensor for distance measurement. This is effective for improving the accuracy,
and is effective for separating and detecting a plurality of objects in an ultrasonic sensor for
object detection.
[0007]
By the way, conventionally, an ultrasonic sensor for detecting an object or measuring a distance
to an object has been proposed and put into practical use by receiving a reflected wave of the
transmitted ultrasonic wave by the object. In particular, in an ultrasonic sensor for detecting an
object at a specific point such as FA application, high distance accuracy is required, and an
ultrasonic source capable of transmitting impulse ultrasonic waves and having high directivity is
required. Here, the directivity of the ultrasonic wave depends on the frequency of the ultrasonic
wave and the directivity becomes higher as the frequency becomes higher. Therefore, realization
of an ultrasonic wave generator capable of generating an ultrasonic wave of about 400 kHz, for
example, is expected . Japanese Patent Application Publication No. 11-300274
[0008]
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In the pressure wave generator disclosed in Patent Document 1, the heat capacity of the thermal
insulation layer is large and the thickness of the thermal insulation layer is larger than the
thermal diffusion length, so the first rise period of the drive input waveform and the drive input
waveform If the temperature of the heat generating body layer can not follow the time change of
the heat amount generated in the heat generating body layer, for example, when the heat amount
reaches the peak value, when the frequency of A delay occurs when the temperature of the body
layer reaches the peak value, and a pressure wave of a desired frequency (a frequency twice the
frequency of the drive input waveform) according to the frequency of the drive input waveform
can not be generated The In particular, the higher the frequency of the drive input waveform, the
lower the responsiveness to the drive input waveform.
[0009]
For example, when a sine wave with a frequency of 40 kHz as shown in FIG. 5A is input to the
heat generating body layer as the driving voltage waveform, the heat quantity generated in the
heat generating body layer follows the voltage change and the figure ( Although the temperature
changes as shown in b), the temperature of the heating element layer can not follow the change
in the amount of heat and changes as shown in (c) in the figure, and the generated pressure wave
has a waveform as shown in (d) in the figure. As can be seen from the comparison between FIG.
(A) and (d), the time (one cycle) required for one frequency on the left side of the pressure wave
in FIG. (D) is longer than the half cycle of the drive voltage waveform. It will The time (one cycle)
required for one frequency approaches the half cycle of the driving voltage waveform from the
right one frequency in the pressure wave of FIG.
[0010]
As another example, when a solitary wave as shown in FIG. 6A (here, a half cycle waveform of a
sine wave having a frequency of 40 kHz) is input as a drive voltage waveform to the heating
element layer, heat generation is generated. The amount of heat generated in the body layer
changes as shown in (b) following the change in voltage, but the temperature of the heat
generating body layer changes as shown in (c) without being able to follow the change in the
amount of heat, The generated pressure wave has a waveform as shown in (d), and as can be
seen from the comparison between (a) and (d), the generation period of the pressure wave is
from the start of the rise of the drive voltage waveform. It will be longer than the period until the
end of the fall (input period).
[0011]
The present invention has been made in view of the above-mentioned problems, and an object
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thereof is to provide a pressure wave generator having an improved response to an input to a
heat generating body layer as compared with the prior art.
[0012]
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. And a pressure wave generator that generates a
pressure wave with the temperature change of the heat generating body layer accompanying the
energization of the heat generating body layer, and the thermal conductivity of the heat
insulating layer is αi [W / (m · K). ], The heat capacity of the heat insulating layer is Ci [J / (m
<3> · K)], the drive input waveform given to the heating element layer is a sine wave, and the heat
is generated twice the frequency f1 [Hz] of the sine wave. Assuming that the frequency f2 of the
temperature vibration generated in the body layer is Hz and the angular frequency of the
temperature vibration is ω = 2πf rad / s, then D = (2αi / ωCi) <1/2> It is characterized in that
the thickness d [m] of the heat insulating layer is smaller than the thermal diffusion length D [m].
[0013]
According to the present invention, since the thickness d of the thermal insulation layer is
smaller than the thermal diffusion length D, even if the first rise period of the drive input
waveform or the frequency of the drive input waveform is changed to a higher frequency in the
middle, etc. The temperature change of the heat generating body layer can be made to
substantially follow the time change of the heat generated in the heat generating body layer.
That is, the thermal diffusion length D is one period of temperature oscillation (temperature
change) of the heat generating body layer when the heat transferred from the heat generating
body layer heated periodically to the heat insulating layer is diffused in the heat insulating layer.
If the thickness d of the thermal insulation layer is made smaller than the thermal diffusion
length D, the heat transferred to the thermal insulation layer is thermally insulated until the next
period of the temperature change of the heating element layer. The heat can be dissipated to the
outside of the layer (here, the support substrate), and the temperature rise of the thermal
insulation layer due to the heat accumulation in the thermal insulation layer can be suppressed.
Therefore, it is possible to reduce the influence of the temperature change of the heat insulating
layer on the temperature change of the heat generating body layer, and it is possible to make the
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temperature change of the heat generating body layer substantially follow the time change of the
heat generated in the heat generating body layer. It becomes possible to suppress the occurrence
of a delay when the temperature of the heat generating body layer reaches the peak value with
respect to the time when the heat generated in the heat generating body layer reaches the peak
value. It is possible to improve the responsiveness to the input of
As the thickness d of the heat insulating layer decreases, the heat generated in the heat
generating layer easily escapes to the supporting substrate and the peak value of the
temperature of the heat generating layer decreases, and the pressure of the generated pressure
wave (sound pressure The thickness d of the heat insulating layer is preferably greater than 0.05
D because
[0014]
The invention of claim 2 is characterized in that, in the invention of claim 1, when the frequency
f1 of the sine wave is higher than 10000 Hz, the condition of d <0.5 D is satisfied.
[0015]
According to the present invention, heat release from the heat generating layer to the support
substrate is started when the peak value is reached at the latest in the first half period from the
start of the rise to the peak value at the time of rise of heat in the heat generating layer.
Therefore, even if the frequency f1 of the sine wave is higher than 10000 Hz, the time when the
temperature of the heat generating layer reaches the peak with respect to the time when the heat
generated in the heat generating layer reaches the peak It is possible to suppress the occurrence
of a delay in time t, and to improve the responsiveness to the input to the heating element layer
as compared with the prior art.
As the thickness d of the heat insulating layer decreases, the heat generated in the heat
generating layer easily escapes to the supporting substrate and the peak value of the
temperature of the heat generating layer decreases, and the pressure of the generated pressure
wave (sound pressure The thickness d of the heat insulating layer is preferably greater than 0.05
D because
[0016]
The invention of claim 3 is characterized in that, in the invention of claim 1 or claim 2, the drive
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input waveform is a solitary wave.
[0017]
According to this invention, it is possible to make the period from the start of the rise of the drive
input waveform to the end of the fall substantially coincide with the generation period of the
pressure wave.
[0018]
The invention of claim 4 relates to the invention according to claims 1 to 3, wherein the thermal
conductivity of the support substrate is αs [W / (m · K)], and the heat capacity of the support
substrate is Cs [J / (m < When 3> · K)] is satisfied, the condition of (αiCi) <(0.1αsCs) is satisfied.
Here, αiCi, which is the product of the thermal conductivity αi of the thermal insulation layer
and the thermal capacity Ci of the thermal insulation layer, is a heat that is an index of the ability
of the thermal insulation layer to take heat away from the heat source (the heating element layer)
Permeability = (αiCi) <1/2>, which is the product of the thermal conductivity αs of the support
substrate and the heat capacity Cs of the support substrate, αsCs corresponds to the heat source
of the support substrate It corresponds to the square of the thermal effusivity = (αsCs) <1/2>
which is an index of the ability to take heat from the layer).
[0019]
According to the present invention, the heat permeability of the support substrate becomes a
value larger than approximately 3.2 times the heat permeability of the heat insulating layer, and
the case where the relationship of (αiCi) <(0.1αsCs) is not satisfied. In comparison, heat is easily
transmitted from the heat insulating layer to the support substrate, and the temperature change
of the heat generating body layer can follow the change of the heat quantity generated in the
heat generating body layer, and the input to the heat generating body layer The responsiveness
to can be improved.
[0020]
The invention of claim 5 is characterized in that, in the invention of claims 1 to 4, the heat
insulating layer comprises a porous layer of an inorganic material.
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[0021]
According to the present invention, the heat resistance of the heat insulating layer can be
improved as compared with the case where the heat insulating layer is formed of a porous layer
of an organic material, and the heat generating layer is heated to a higher temperature. Can be
used to increase the pressure wave output.
[0022]
According to the first aspect of the present invention, the response to the input to the heating
element layer is improved as compared to the prior art.
[0023]
(Embodiment 1) As shown in FIGS. 1 (a) and 1 (b), the pressure wave generator according to this
embodiment includes a support substrate 1 made of a single crystal p-type silicon substrate and
one surface of the support substrate 1. Between the supporting substrate 1 and the heating
element layer 3 on the one surface side of the supporting substrate 1 and the heating element
layer 3 formed of a metal thin film (for example, a tungsten thin film) formed on the upper
surface side (FIG. 1B) And a pair of pads 4 and 4 electrically connected to both ends of the heat
generating body layer 3 on the one surface side of the support substrate 1, respectively. A
pressure wave is generated in accordance with the temperature change of the heat generating
body layer 3 accompanying the energization of the heat generating body layer 3 through the pair
of pads 4 and 4.
That is, in the pressure wave generator according to the present embodiment, the heat
generating body layer 3 and the medium are changed according to the temperature change of
the heat generating body layer 3 according to the drive input waveform consisting of the drive
voltage waveform or drive current waveform applied to the heat generating layer 3. Heat
exchange with certain air generates a pressure wave.
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.
[0024]
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By the way, in the present embodiment, as described above, a p-type 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 60%. A porous silicon layer to be the heat insulating layer 2 by
anodizing a part of the silicon substrate used as 1 in an electrolytic solution in which, for
example, a 55 wt% aqueous solution of hydrogen fluoride and ethanol are mixed approximately
1: 1 It can be formed.
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.) here. .
In the porous silicon layer, as the porosity increases, the thermal conductivity and the thermal
capacity decrease, and in Patent Document 1, the thermal conductivity is 168 W / (m · K) and the
thermal capacity is 1.67 × 10 <6>. The porous silicon layer having a porosity of 60% formed by
anodizing a J / (m <3> · K) single crystal silicon substrate has a thermal conductivity of 1 W / (m ·
K), and a heat capacity It is described that is 0.7 * 10 <6> J / (m <3> * K).
[0025]
The heating element layer 3 is formed of tungsten, which is a kind of refractory metal, and has a
thermal conductivity of 174 W / (m · K) and a heat capacity of 2.5 × 10 <6> J / (m <3). > · K).
The material of the heat generating body layer 3 is not limited to tungsten, and, for example,
tantalum, molybdenum, iridium or the like may be employed. 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.
[0026]
In the pressure wave generator of the present embodiment, the thickness of the support
substrate 1 is 525 μm, the thickness of the heat insulating layer 2 is 0.5 μm, the thickness of
the heat generating layer 3 is 50 nm, and the thickness of each pad 4 is It is 0.5 μm.
[0027]
Hereinafter, the manufacturing method of the pressure wave generator of this embodiment is
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demonstrated easily.
[0028]
First, an energizing electrode (not shown) used for anodizing treatment is formed on the other
surface (lower surface of FIG. 1B) of the silicon substrate used as the support substrate 1, and
then one surface of the silicon substrate (FIG. The heat insulating layer forming step of forming
the heat insulating layer 2 made of porous silicon is performed by making the formation
scheduled portion of the heat insulating layer 2 on the upper surface side of b) porous by
anodizing treatment.
Here, in the heat insulating layer forming step, for example, as shown in FIG. 2, an electrolytic
solution (for example, a 55 wt% hydrogen fluoride aqueous solution) in which the object S mainly
composed of a silicon substrate is contained in the treatment tank 30 And the platinum electrode
21 connected to the negative side of the current source 20 via a wire in the electrolyte 31;
Arrange so as to face.
Subsequently, a current-carrying electrode is an anode, a platinum electrode 21 is a cathode, and
a current of a predetermined current density (here, 50 mA / cm <2>) is supplied from the current
source 20 to the anode and the cathode 21 for a predetermined time (here Then, the heat
insulating layer 2 having a predetermined thickness (here, 0.5 μm) is formed on the one surface
side of the silicon substrate to be the support substrate 1 by performing anodizing treatment of
flowing for 7 seconds). 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.
[0029]
After the above-described heat insulation layer formation step, a heating element layer formation
step of forming the heating element layer 3 is performed, and thereafter, a pad formation step of
forming the pads 4 and 4 is performed. 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.
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[0030]
By the way, although the thickness of the heat insulating layer 2 is set to 0.5 μm as described
above in the pressure wave generator according to the present embodiment, the thickness of the
heat insulating layer 2 is limited to 0.5 μm. Absent.
[0031]
However, the thickness d [m] of the thermal insulation layer 2 in the pressure wave generator of
this embodiment is the thermal conductivity of the thermal insulation layer 2 α i [W / (m · K)],
and the thermal capacity of the thermal insulation layer 2 Ci [J / (m <3> · K)], the drive input
waveform given to the heating element layer 3 is a sine wave, and the ideal frequency of the
heating element layer 3 is twice the frequency f1 [Hz] of the sine wave Assuming that the
frequency f2 (Hz) of the typical temperature vibration and the angular frequency of the
temperature vibration are ω = 2πf (rad / s), D = (2αi / ωCi) <1/2> (equation 1) For the thermal
diffusion length D [m] to be set, it is set so as to satisfy the condition of 0.05D <d <D (equation 2).
[0032]
For example, in order to generate a pressure wave having a frequency of 80 kHz, the frequency
f1 of the drive input waveform may be set to 40 kHz, and the porosity of the porous silicon layer
which is the heat insulating layer 2 is 60% as described above. In this case, if αi = 1 [W / (m · K)]
and Ci = 0.7 × 10 <6> [J / (m <3> · K)], the thermal diffusion length D is Since D 2.4 × 10 <-6>
[m] = 2.4 μm from this, 0.05D ≒ 0.12 × 10 <-6> [m] = 0.12 μm, and the heat is generated as
described above. By setting the thickness d of the insulating layer 2 to 0.5 × 10 <−6> [m] = 0.5
μm, the relational expression of 0.05D <d <D is satisfied.
[0033]
Thus, in the pressure wave generator of the present embodiment, the thickness d of the thermal
insulation layer 2 is smaller than the thermal diffusion length D, so the first rise period of the
drive input waveform and the frequency of the drive input waveform are higher in the middle.
Even when the frequency is changed, it becomes possible to make the temperature change of the
heat generating body layer 3 substantially follow the time change of the heat amount generated
in the heat generating body layer 3, so the heat amount generated in the heat generating body
layer 3 has a peak value It is possible to suppress the occurrence of a delay when the
temperature of the heat generating body layer 3 reaches the peak value with respect to the time
of reaching the point, and improve the responsiveness to the input to the heat generating body
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layer 3 compared to the conventional case. be able to.
As the thickness d of the heat insulating layer 3 becomes smaller, the heat generated in the heat
generating layer 3 tends to escape to the supporting substrate 1, and the peak value of the
temperature of the heat generating layer 3 becomes lower. Since the pressure (sound pressure) is
also reduced, the thickness d of the heat insulating layer 2 is desirably larger than 0.05 D as in
the above-mentioned equation 2.
[0034]
However, when the frequency f1 of the sine wave of the drive input waveform is set to a
frequency higher than 10000 [Hz] = 10 kHz as described above, it is preferable to satisfy the
condition of 0.05D <d <0.5D (Equation 3) For example, when the frequency f1 of the sine wave is
40 kHz as described above, 0.5D = 1.2 × 10 <-6> [m] = 1.2 μm, and the heat insulating layer 2
as described above The relational expression of 0.05D <d <0.5D is satisfied by setting the
thickness d of as 0.5 × 10 <−6> [m] = 0.5 μm.
[0035]
By setting the thickness d of the thermal insulation layer 2 so as to satisfy the relational
expression of the above-mentioned equation 3, the time from the start of rising to the peak value
arrival in the time change of the heat quantity generated in the heating element layer 3 Since
heat dissipation from the heat generating body layer 3 to the support substrate 1 is started at the
latest in the first half period as late as the peak value is reached, the amount of heat generated in
the heat generating body layer 3 even if the frequency f1 of the sine wave is higher than 10000
Hz. It is possible to suppress the occurrence of a delay when the temperature of the heating
element layer 3 reaches the peak value with respect to the time when the peak value is reached,
and the response to the input to the heating element layer 3 is It can be improved.
[0036]
As an example of the input response characteristic of the pressure wave generator according to
the present embodiment described above, when a sine wave having a frequency of 40 kHz as
shown in FIG. The amount of heat generated in the heat generating body layer 3 changes as
shown in FIG. 6B following the change in voltage, and the temperature of the heat generating
body layer 3 changes as shown in FIG. The generated pressure wave has a waveform as shown in
FIG.
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Here, in the input response characteristic of the conventional example shown in FIG. 5, the time
(one cycle) required for one frequency on the left side of the pressure wave is longer than the
half cycle of the drive voltage waveform, but As can be seen from FIGS. 3A and 3D, in the input
response characteristic of the pressure wave generator of the embodiment, the time required for
one frequency (one cycle) on the left side of the pressure wave is approximately equal to the half
cycle of the drive voltage waveform. At the same time, the time required for one frequency on the
right side (one cycle) is also substantially equal to the half cycle of the drive voltage waveform,
and a pressure wave having a frequency twice the frequency of the drive voltage waveform is
generated.
In short, in the pressure wave generator of the present embodiment, the responsiveness to the
input to the heating element layer 3 is improved as compared with the conventional pressure
wave generator.
[0037]
In addition, as another example of the input response characteristic of the pressure wave
generator of the present embodiment, a solitary wave (here, the frequency is 40 kHz as shown in
FIG. 4A as a drive voltage waveform to the heating element layer 3). When a sine wave (half cycle
waveform) is input, the amount of heat generated in the heat generating body layer 3 changes as
shown in (b) following the change in voltage, and the temperature of the heat generating body
layer 3 changes in heat amount. The pressure wave that follows and changes as shown in (c) in
the figure, and the generated pressure wave has a waveform as shown in (d) in the figure.
Here, in the input response characteristics of the conventional example shown in FIG. 6, the
generation period of the pressure wave is longer than the input period from the rise start time to
the fall end time of the drive voltage waveform. In the input response characteristics of the
pressure wave generator according to the embodiment, as can be seen from FIGS. 4A and 4D, the
period from the start of the rise of the drive input waveform to the end of the fall, and the
generation period of the pressure wave. Are almost identical.
In short, in the present embodiment, it is possible to make the period from the rise start time to
the fall end time of the drive input waveform consisting of a solitary wave substantially coincide
with the generation period of the pressure wave.
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[0038]
In the pressure wave generator according to this embodiment, the thermal conductivity of the
support substrate 1 is αs [W / (m · K)], and the heat capacity of the support substrate 1 is Cs [J /
(m <3> · K)]. If so, it is desirable to satisfy the condition of (αiCi) <(0.1αsCs) (Expression 4).
Here, αiCi, which is the product of the thermal conductivity αi of the thermal insulation layer 2
and the thermal capacity Ci of the thermal insulation layer 2, is a heat that is an index of the
ability of the thermal insulation layer 2 to take heat from the heating element layer 3 regarded as
a heat source. The coefficient αsCs, which is the product of the thermal conductivity αs of the
support substrate 1 and the heat capacity Cs of the support substrate 1 corresponding to the
square of the permeability = (αiCi) <1/2>, is a thermal insulation in which the support substrate
1 is regarded as a heat source It corresponds to the square of the thermal effusivity = (αsCs)
<1/2> which is an index of the ability to take heat from the layer 2.
[0039]
Therefore, by satisfying the condition of the above-mentioned equation 4, the heat permeability
of the support substrate 1 becomes a value larger than about 3.2 times the heat permeability of
the heat insulating layer 2, and (αiCi) <(0.1αsCs). Compared to the case where the relationship
of (1) is not satisfied, the heat is more easily transmitted from the heat insulating layer 2 to the
support substrate 1, and the temperature change of the heat generating body layer 3 can follow
the change of the heat quantity generated in the heat generating body layer 3. The
responsiveness to the input to the heating element layer 3 can be improved. As described above,
when the porosity of the porous silicon layer which is the heat insulating layer 2 is 60% and the
supporting substrate 1 is a silicon substrate, αi = 1 [W / (m · K)], Ci = 0. 7 × 10 <6> [J / (m <3> ·
K)], αs = 168 [W / (m · K)], Cs = 1.67 × 10 <6> [J / (m <3>) · K)], αiCi is about 400 times
smaller than αsCs (that is, αiCi is smaller than 0.1 times αsCs), the condition of the above
equation 4 is I meet.
[0040]
In the above-described embodiment, Si is used as the material of the support substrate 1, but the
material of the support substrate 1 is not limited to Si, and, for example, by anodic oxidation
treatment of Ge, SiC, GaP, GaAs, InP, etc. Other semiconductor materials that can be made porous
can also be used. In any case, since the heat insulating layer 2 is formed of the porous layer of
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the inorganic material, the heat insulating layer 2 is formed of heat as compared with the case
where the heat insulating layer 2 is formed of the porous layer of the organic material (polymer
material). The heat resistance of the insulating layer 2 can be improved, the heat generation layer
3 can be heated to a higher temperature, and the output of pressure waves can be increased.
[0041]
Second Embodiment The basic configuration of the pressure wave generator of the present
embodiment is substantially the same as that of the first embodiment, and the heat insulating
layer 2 is formed of a porous silica film formed on the one surface of the support substrate 1.
The other points are the same. The point that the heat insulating layer 2 is formed of a porous
layer of an inorganic material is the same as that of the first embodiment.
[0042]
Here, in the production of the pressure wave generator of the present embodiment, for example,
a solution in which organic component fine particles to be thermally decomposed are dispersed
in a SOG (Spin on Glass) method of hydrolyzing a monomer to obtain silica (SiO 2). Is applied
onto the one surface of the support substrate 1 and heat-treated to form the thermal insulation
layer 2 made of a porous silica film.
[0043]
Therefore, also in the pressure wave generator according to the present embodiment, the heat
resistance of the heat insulating layer 2 is improved as compared to the case where the heat
insulating layer 2 is formed of a porous layer of an organic material (polymer material).
Therefore, it is possible to heat the heating element layer 3 to a higher temperature, and the
output of pressure waves can be increased.
[0044]
As a method of forming the porous layer of the inorganic material, in addition to the anodizing
treatment described in the first embodiment and the method described in the second
embodiment, the inorganic material may be formed on the one surface side of the support
substrate 1. Another method is to deposit the particles in a gas.
[0045]
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15
1st Embodiment is shown, (a) is a schematic plan view, (b) is a X-X 'schematic sectional view of
(a).
It is explanatory drawing of the manufacturing method same as the above.
It is explanatory drawing of the input response characteristic same as the above.
It is explanatory drawing of the input response characteristic same as the above. It is explanatory
drawing of the input response characteristic of a prior art example. It is explanatory drawing of
the input response characteristic same as the above.
Explanation of sign
[0046]
1 support substrate 1 thermal insulation layer 3 heating element layer 4 pad
13-04-2019
16
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