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JP2009250928

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DESCRIPTION JP2009250928
An object of the present invention is a MEMS-type hot-wire type that can detect the particle
velocity of a medium that propagates sound waves over a wider frequency band than in the past,
and ensure design freedom of detection element spacing and miniaturize the device. To provide a
particle velocity detection element, a method of manufacturing the same, and an acoustic sensor.
A MEMS-type hot-wire type particle velocity detection element 10 includes a silicon substrate 11,
insulating films 12 and 13, an electrode pad 14, and particle velocity detection units 15 to 17.
The silicon substrate 11 transmits sound waves. The particle velocity detection units 15 to 17 are
respectively manufactured by the FIB-CVD method, and have free standing so as to bridge
between the respective convex portions. The pair of resistors are arranged in the X axis direction,
the Y axis direction, and the direction orthogonal to the Z axis direction. [Selected figure] Figure
1
MEMS-type hot-wire particle velocity detection device, method of manufacturing the same, and
acoustic sensor
[0001]
The present invention relates to a MEMS-type hot-wire particle velocity detecting element which
is formed using MEMS (Micro Electro Mechanical Systems: Micro-Electro-Mechanical Systems)
technology and detects particle velocity of a medium propagating acoustic waves, a
manufacturing method thereof and an acoustic sensor .
[0002]
05-05-2019
1
Heretofore, a MEMS type hot-wire particle velocity detection element manufactured using MEMS
technology and used for vibration analysis and acoustic analysis has been put to practical use
(see, for example, Non-Patent Document 1).
Sound is a compressional wave that travels in a medium (usually air), and the particles of the
medium are displaced as the sound propagates. The particle velocity detection element converts
the velocity of the particles of the medium into an electrical signal. Here, "particles" refers to
minute portions of a medium as virtual particles, and does not refer to a specific entity such as a
gas molecule.
[0003]
The conventional MEMS-type hot-wire particle velocity detection element (hereinafter simply
referred to as "particle velocity detection element" may be used. ) Has a configuration as shown
in FIG. 9, for example. FIGS. 9 (a) and 9 (b) are views of the conventional particle velocity
detecting element from the Z-axis direction and the X-axis direction, respectively. The illustrated
X, Y, and Z axis directions are directions defined for convenience of the description.
[0004]
As shown in FIGS. 9A and 9B, the conventional particle velocity detecting device includes the
silicon substrate 1, the recess 1a of the silicon substrate 1 which is a space through which sound
waves pass, and both ends of the upper surface of the silicon substrate 1. It comprises two
detection elements 3 and 4 formed to bridge each other, and an electrode pad 7 for connecting
the detection element 3 and an external circuit (not shown). Reference numeral 2 denotes an
insulating film.
[0005]
The detection element 3 has a configuration in which a resistor 5 made of a metal film such as
platinum is laminated on a support 6 made of an insulator such as silicon nitride. The resistor 5
is stacked on the support 6 because the metal film resistor 5 alone can not stand in space. The
size of the detection element 3 is, for example, 1 mm in the Y-axis direction, 2 ?m in the X-axis
direction, and 0.3 ?m in the Z-axis direction. Although not shown, the detection element 4 is
05-05-2019
2
also configured in the same manner as the detection element 3. Further, the distance between the
detection elements 3 and 4 in the X-axis direction is about 100 ?m.
[0006]
Next, a schematic manufacturing process of a conventional particle velocity detection element is
illustrated in FIG. In the figure, the AA 'cross section in each process is also described. First, in
order to form the support 6 and the insulating film 2, silicon nitride is deposited on both sides of
the silicon substrate 1 (FIG. 10A). Next, a platinum thin film resistor 5 is formed by the lift-off
method (FIG. 10 (b)). Next, the silicon nitride in the unnecessary portion of the substrate surface
is etched away by using an appropriate mask (FIG. 10 (c)). Then, using the silicon nitride as a
mask, the silicon substrate is etched to form a recess 1a (FIG. 10 (d)).
[0007]
Next, the operation of the particle velocity detecting element will be described with reference to
FIG.
[0008]
A constant current equal to the resistance of each of the two detection elements 3 and 4 is
applied to heat the detection elements 3 and 4.
In the steady state not exposed to sound waves, the temperature of the detection elements 3 and
4 is kept constant. When the detection element 3 is exposed to sound waves in the X-axis
direction, for example, the detection element 3 is deprived of heat by the medium at a certain
time. On the other hand, since the detection element 4 receives a part of the heat taken from the
detection element 3 through the medium, a temperature difference occurs between the detection
elements 3 and 4. Since the resistance value of the resistor changes due to temperature change, a
difference in resistance value from the steady state occurs in the resistors of the detection
elements 3 and 4. It has been confirmed that this resistance difference is approximately
proportional to the particle velocity of sound, and by detecting the resistance difference, the
particle velocity in the X-axis direction can be measured. On the other hand, with respect to the
particle velocity in the Y-axis and Z-axis directions, the temperature of the detection elements 3
and 4 changes similarly, so that there is no difference in resistance between the two detection
elements. Therefore, the particle velocity detection element has directivity.
05-05-2019
3
[0009]
As described above, the particle velocity detecting element can detect the particle velocity of the
medium transmitting the sound wave based on the difference in resistance value between the
resistors of the detecting elements 3 and 4. As an application of this particle velocity detecting
element, for example, a microphone and a medium flow meter have been proposed (see, for
example, Non-Patent Document 2 and Patent Document 1). "AN OVERVIEW OF MICROFLOWN
THE CNOLOGIES", H.-E. Bree, ACTA ACUSTICA UNITED WITH ACUSTICA, 89 (1), pp. 163-172,
JAN-FEB 2003. H.-E. de Bree et al., Proc. 109th AES Convention, Los Angels, 2000 JP-A-11326003
[0010]
By the way, the particle velocity of sound is very slow. For example, when the sound wave is a
plane wave, even if the sound pressure is 1 Pa (very loud sound), the particle speed is 2.4 mm / s,
the sound pressure is 20 ?Pa (human's least audible At the limit) the particle velocity is only
0.048 ?m / s. In addition, the human audio frequency band is said to be approximately 20 Hz to
20 kHz. That is, as the particle velocity detecting element, one capable of detecting extremely
slow sound particle velocity over a wide band is desirable. For that purpose, the heat capacity of
the detection element must be extremely small so that the temperature changes rapidly
according to the particle velocity of the sound.
[0011]
However, in the conventional particle velocity detection element, the detection element is
composed of a resistor and a support due to the restriction on the structure and the
manufacturing method, and among these, the support becomes a useless load that does not
contribute to heat generation. The heat capacity of the Therefore, in the conventional particle
velocity detection element, there is a problem that the sensitivity is lowered at a high frequency.
Thus, for example, a microphone provided with a conventional particle velocity detection element
can be used in combination with other microphones because only the sound in the low frequency
band can be detected due to the narrow band nature of the particle velocity detection element It
stayed in use.
05-05-2019
4
[0012]
Further, as described above, since the particle velocity detection element has directivity, when it
is applied to a device such as a nondirectional microphone, for example, the X, Y, Z axis
directions (hereinafter simply referred to as ?three axis directions?) Sometimes. The three
particle velocity detection elements must be combined with each other or three pairs of detection
elements must be built in one particle velocity detection element in three axial directions, which
has the following problems.
[0013]
First, in the prior art, when three particle velocity detecting elements are combined in three axial
directions, a space for providing them is required, which makes it difficult to miniaturize an
apparatus provided with the particle velocity detecting elements. There was a problem called.
[0014]
Next, when it is attempted to build three sets of particle velocity detection elements in one axial
direction into one particle velocity detection element by a conventional manufacturing method,
one of the elements in one axial direction is the front side of the silicon substrate. , I have to form
another one on the back side.
In this case, the thickness of the substrate must be the distance between the detection elements,
and there is a problem that the design freedom of the distance between the detection elements,
which is an important parameter for the performance of the particle velocity detection element,
is limited.
[0015]
The present invention has been made to solve the conventional problems, and is capable of
detecting the particle velocity of the medium propagating the sound wave over a wider frequency
band than in the prior art, and having the design freedom of the detection element spacing. It is
an object of the present invention to provide a MEMS type hot-wire type particle velocity
detecting element capable of securing and miniaturizing a device, a method of manufacturing the
same, and an acoustic sensor.
05-05-2019
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[0016]
The MEMS-type hot-wire particle velocity detecting element according to the present invention is
a MEMS-type hot-wire type particle velocity detecting element formed using MEMS technology,
and comprises at least one pair only of a medium that transmits sound waves and a resistor that
exchanges heat with the medium. First and second heat transfer means, a first electrode
electrically connecting one end of each of the first and second heat transfer means, and the first
and second heat transfer It has the composition provided with the 2nd electrode which
electrically connects the other end of each of means, and the substrate in which the 1st and 2nd
electrodes were formed.
[0017]
With this configuration, the heat transfer means of the MEMS type heat wire type particle
velocity detection device of the present invention consists of only the resistor, so the heat
capacity of the heat transfer means is reduced compared to the conventional one in which the
resistor is laminated on the support. The structure can also be simplified.
Further, with this configuration, the first heat transfer means and the second heat transfer means
can be arranged side by side at a predetermined axial direction at an arbitrary interval on one
side of the substrate.
[0018]
Therefore, the MEMS-type hot-wire particle velocity detecting element of the present invention
may be referred to as the particle velocity of a medium that propagates an acoustic wave
(hereinafter simply referred to as ?particle velocity of acoustic wave?).
Can be detected over a wider frequency band than in the past, and the design freedom of the
detection element interval can be ensured and the device can be miniaturized.
[0019]
Further, in the MEMS-type hot-wire type particle velocity detecting element of the present
invention, the first and second heat transfer means are each curved in a predetermined direction
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between the one end and the other end. Have a configuration that is
[0020]
According to this configuration, the MEMS type hot-wire type particle velocity detecting element
of the present invention can reduce the influence of thermal strain generated when the first and
second heat transfer means are heated.
[0021]
Furthermore, in the MEMS-type hot-wire type particle velocity detecting element of the present
invention, the first and second heat transfer means are each bent in a predetermined direction
between the one end and the other end. Have a configuration that is
[0022]
By this configuration, the MEMS type hot-wire type particle velocity detecting element of the
present invention has directivity in a specific direction.
[0023]
Further, in the MEMS type hot wire particle velocity detection element of the present invention,
each of the first and second heat transfer means includes a branch portion for branching a path
from the one end to the other end into a plurality of branches. It has a configuration.
[0024]
With this configuration, the MEMS-type hot-wire particle velocity detection device of the present
invention has a detection portion of the same length in a smaller space than a conventional
particle velocity detection device provided with a pair of linear-shaped detection devices. Since
the device can be disposed, the device can be miniaturized.
[0025]
Furthermore, in the MEMS-type heat wire type particle velocity detection element of the present
invention, the first and second heat transfer means transfer the heat in at least one axial direction
of three axes orthogonal to each other. It has a configuration.
[0026]
According to this configuration, the MEMS type hot-wire type particle velocity detecting element
05-05-2019
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of the present invention can detect at least one of the components in the three axial directions of
the particle velocity of the sound wave.
[0027]
The acoustic sensor according to the present invention comprises a MEMS-type hot-wire type
particle velocity detecting element, a heating means for heating the first and second heat transfer
means to a predetermined temperature, and the first heat transfer means. And a particle velocity
measuring means for measuring the particle velocity of the medium propagating the sound wave
based on the difference between the temperature and the temperature of the second heat
transfer means.
[0028]
According to this configuration, the acoustic sensor of the present invention has the first and
second heat transfer means consisting of only the resistors, so that the particle velocity of the
sound wave can be detected over a wider frequency band than before, and It is possible to secure
design freedom of the detection element interval and miniaturize the apparatus.
[0029]
A method of manufacturing a MEMS heat ray type particle velocity detection device according to
the present invention is a method of manufacturing a MEMS heat ray type particle velocity
detection device formed by using a MEMS technique, which is a resistance that exchanges heat
with a medium propagating sound waves. Generating at least a pair of first and second heat
transfer means consisting only of the body by focused ion beam chemical vapor deposition, and
electrically connecting one end of each of the first and second heat transfer means Forming on
the substrate a first electrode connected to the second electrode and a second electrode
electrically connected to the other end of each of the first electrode and the second electrode.
[0030]
According to this configuration, the method of manufacturing the MEMS type hot-wire type
particle velocity detecting element according to the present invention generates the first and
second heat transfer means consisting only of the resistor, so that the resistor is stacked on the
support. The heat capacity of the first and second heat transfer means can be reduced and the
structure can also be simplified.
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Further, with this configuration, the first heat transfer means and the second heat transfer means
can be arranged side by side at a predetermined axial direction at an arbitrary interval on one
side of the substrate.
[0031]
Therefore, the method of manufacturing the MEMS-type hot-wire particle velocity detecting
element of the present invention can detect the particle velocity of sound waves over a wider
frequency band than in the prior art, and ensure the design freedom of the detecting element
interval and the device It is possible to provide a MEMS type hot-wire type particle velocity
detection element which can be miniaturized.
[0032]
The present invention is capable of detecting the particle velocity of a medium that propagates
sound waves over a wider frequency band than in the prior art, and ensuring the design freedom
of the detection element spacing and downsizing of the device. It is possible to provide a MEMS
type hot-wire type particle velocity detection device, a method of manufacturing the same, and
an acoustic sensor.
[0033]
Hereinafter, embodiments of the present invention will be described using the drawings.
[0034]
First Embodiment First, the configuration of a MEMS-type hot-wire type particle velocity
detection device according to a first embodiment of the present invention will be described.
[0035]
As shown in FIG. 1, the MEMS type hot-wire type particle velocity detecting element 10 in the
present embodiment is provided with a silicon substrate 11, insulating films 12 and 13, an
electrode pad 14, and particle velocity detecting portions 15 to 17. ing.
[0036]
The silicon substrate 11 has four convex portions of height L and one concave portion 11a, and
is configured to allow sound waves to pass between the convex portions and the concave portion
05-05-2019
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11a.
An insulating film 12 is provided on the upper surface of each convex portion.
In addition, an insulating film 13 is provided on the lower surface of the silicon substrate 11.
An electrode pad 14 is formed on the insulating film 12.
The electrode pad 14 is connected to an external circuit (not shown).
[0037]
The particle velocity detection units 15 to 17 each include only a pair of resistors formed in a
self-supporting manner so as to bridge the respective convex portions, and both ends of the pair
of resistors are connected to the electrode pad 14.
Further, a current for heating the particle velocity detecting units 15 to 17 to be a predetermined
temperature is supplied to the particle velocity detecting units 15 to 17 through the respective
electrode pads 14. ing.
The particle velocity detectors 15 to 17 constitute heat transfer means according to the present
invention.
[0038]
Here, among the particle velocity detectors 15 to 17, the particle velocity detector 15 is taken as
an example, and the relationship between the particle velocity detector 15 and the electrode pad
14 will be described.
[0039]
05-05-2019
10
The particle velocity detection unit 15 includes a pair of particle velocity detection units 15a and
15b formed only of a medium that transmits a sound wave and a resistor that exchanges heat.
In addition, the electrode pad 14 includes electrode pads 14 a to 14 d to which the particle
velocity detectors 15 a and 15 b are electrically connected.
[0040]
Specifically, one ends of the particle velocity detectors 15a and 15b are electrically connected to
the electrode pads 14a and 14b, respectively.
The other ends of the particle velocity detectors 15a and 15b are electrically connected to the
electrode pads 14c and 14d, respectively.
Here, the particle velocity detectors 15a and 15b respectively constitute first and second heat
transfer means according to the present invention.
The electrode pads 14a and 14b constitute a first electrode according to the present invention.
The electrode pads 14c and 14d constitute a second electrode according to the present
invention.
[0041]
Although the description is omitted, the relationship between each of the particle velocity
detecting units 16 and 17 and the electrode pad 14 is also similar to the relationship between
the particle velocity detecting unit 15 and the electrode pads 14a to 14d.
Further, for example, the electrode pads 14c and 14d may be shared by one electrode pad, and
the common electrode pad may be connected to the ground.
05-05-2019
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[0042]
The pair of resistors constituting the particle velocity detection unit 15 are arranged in the
direction orthogonal to the X-axis direction shown in the drawing.
Further, the pair of resistors constituting the particle velocity detection unit 16 are arranged in a
direction orthogonal to the Y-axis direction shown in the drawing.
Further, a pair of resistors constituting the particle velocity detection unit 17 are arranged in a
direction orthogonal to the Z-axis direction shown in the drawing.
With this configuration, the particle velocity detectors 15 to 17 can respectively detect the X-axis
component, the Y-axis component and the Z-axis component of the particle velocity of the sound
wave.
The illustrated X, Y, and Z axis directions are directions defined for convenience of the
description.
[0043]
The pair of resistors constituting the particle velocity detection units 15 to 17 are respectively
manufactured by a FIB-CVD (Focused-ion-beam Chemical Vapor Deposition) method. The FIBCVD method is described in the literature "" Free-space-wiring fabrication in nano-space by
focused-ion-beam chemical vapor deposition ", T. Morita et al., J. Vac. Sci. Technol. B 21 (6), pp.
2737-2741 (2003) ?, but the outline will be described below.
[0044]
The FIB-CVD method locally generates a chemical reaction by irradiating an ion beam to the
injected source gas while injecting the source gas from a fine nozzle in vacuum, and the minute
on the space above the substrate This is a method of forming a wiring (for example, a resistor
05-05-2019
12
mainly composed of carbon). According to this method, by controlling the relative position
between the substrate and the nozzle and the ion beam, it is possible to form a threedimensionally freestanding fine resistor (including a curve) of free shape, so that the
conventional manufacturing technology In this case, the degree of freedom in forming the
particle velocity detection units 15 to 17 is dramatically increased. In addition, the material of
the resistor which comprises the particle | grain speed detection parts 15-17 is not limited to
carbon, What is necessary is just a material which a resistor can self-support.
[0045]
Next, the operation of the MEMS type hot-wire type particle velocity detecting element 10 in the
present embodiment will be described with reference to FIG. In order to simplify the description,
the particle velocity detection units 15a and 15b constituting the particle velocity detection unit
15 will be described as an example for the sound waves propagating in the arrow direction of the
X axis shown in FIG.
[0046]
First, a constant current is respectively applied to the particle velocity detectors 15a and 15b by
a power source (heating unit) (not shown) connected to the electrode pad 14 to heat them.
[0047]
In the steady state not exposed to the sound wave, the particle velocity detecting units 15a and
15b emit the heat equal to each other and receive a part of the heat of the other equal to each
other through the medium, so the particle velocity detecting unit 15a And the temperature of
15b is kept constant.
[0048]
Next, when the particle velocity detectors 15a and 15b are exposed to sound waves propagating
in the X-axis direction, for example, the particle velocity detector 15a is deprived of heat by the
medium at a certain time, and the particle velocity detector 15b detects the particle velocity
Since a part of the heat taken from the unit 15a is received through the medium, a temperature
difference occurs between the particle velocity detection units 15a and 15b.
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13
Since the resistance value of the resistor changes due to the temperature change, a difference in
resistance value from the steady state occurs between the particle velocity detection units 15a
and 15b.
Since this resistance difference is approximately proportional to the particle velocity of sound, it
is possible to detect the particle velocity of the sound wave propagating in the X-axis direction by
detecting the resistance difference. it can.
[0049]
Similar to the particle velocity detector 15 described above, the particle velocity detectors 16 and
17 also operate. Therefore, the MEMS heat ray type particle velocity detecting element 10 is
applied to, for example, a device for determining the direction of particle velocity by comparing
or combining the outputs of the particle velocity detecting units 15 to 17 or non-directionality It
can be used as a microphone.
[0050]
Next, a method of manufacturing the MEMS type hot-wire type particle velocity detection
element 10 according to the present embodiment will be described with reference to FIG. FIG. 2
is an explanatory view of a manufacturing process for forming the MEMS type hot-wire type
particle velocity detecting element 10 by the MEMS technology, and conceptually shows cross
sections in the AA ? direction and the BB ? direction shown in FIG. FIG.
[0051]
First, insulating films 12 and 13 such as silicon nitride and silicon oxide are formed on both sides
of the silicon substrate 11 by, for example, chemical vapor deposition or thermal oxidation (FIG.
2A).
[0052]
Next, the insulating films 12 and 13 are patterned, for example, by combining photolithography
and etching to form the openings 12a and 13a (FIG. 2B).
05-05-2019
14
[0053]
Next, the silicon substrate 11 is etched using the insulating films 12 and 13 as a mask by a
highly anisotropic etching method such as dry etching, for example, to form the concave portion
11 a and the convex portion of the step L in the silicon substrate 11.
The recess 11a can be formed by etching from the front and back of the silicon substrate 11
(FIG. 2 (c)).
[0054]
Next, a metal electrode pad 14 is formed by, for example, a mask vapor deposition method (FIG.
2 (d)).
[0055]
Next, a particle velocity detection unit 16 mainly composed of carbon is formed between the
electrode pads 14 using the FIB-CVD method (FIG. 2 (e)).
Although not shown, the particle velocity detectors 15 and 17 can be manufactured as well as
the particle velocity detector 16.
[0056]
When a silicon wafer having a large number of the above structures is fabricated into chips by
dicing, for example, the particle velocity detection units 15 to 17 are chipped without damage by
using a known laser-type dicing method. It is possible.
[0057]
As described above, by using the FIB-CVD method, it is possible to form a three-dimensionally
curved or bent detection element which has not been possible in the past.
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Thereby, the XYZ three sets of detection elements can be formed in the same process as the
process of forming one set of detection elements on one side of the substrate.
[0058]
Next, it will be specifically described that the detection element (particle velocity detection units
15 to 17) according to the present invention can reduce the heat capacity as compared with the
conventional detection element.
[0059]
The heat capacity CL per unit length of the detection element (J и K <?1> и m <?1>) can be
calculated by [Equation 1].
[0060]
[Equation 1] CL = Cv О detector cross section
[0061]
Here, Cv indicates the heat capacity per unit volume of the detection element (J и K <?1> и m
<?3>), and can be expressed by [Equation 2].
Cm represents molar heat capacity (J и K <-1> и mol <-1>), M represents molar mass (kg и mol <1>), and ? represents density (kg и m <-3>) .
[0062]
[Equation 2] Cv = Cm / M О ?
[0063]
First, consider the following configuration as an example of a conventional detection element.
In addition, the numerical value illustrated here is a document "JW van Honschoten et al.,"
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16
Analytic model of a two-wire thermal sensor for flow and sound measurements ", J. Micromech.
Microeng. 14 (2004) pp. 1468-1447.
It is excerpted from ".
[0064]
(1) Configuration Example of Conventional Detection Element Resistor: platinum, thickness 0.1
?m, width 2 ?m, Cv (platinum) = 2.85 О 10 <6> (J и K <?1> и m <?3) >) Support: Silicon
nitride, thickness 0.2 ?m, width 2 ?m, Cv (silicon nitride) = 1.66 О 10 <6> (J и K <-1> и m <-3>)
Substituting in [Equation 1], the heat capacity CL (platinum) of platinum per unit length and the
heat capacity CL (silicon nitride) of silicon nitride become values shown in [Equation 3] and
[Equation 4], respectively.
[0065]
[Equation 3] CL (platinum) = 2.85 О 10 <6> (J и K <?1> и m <?3>) О 0.1 О 10 <?6> (m) О 2
О 10 < -6> (m) = 0.57 О 10 <-6> (J и K <-1> и m <-1>)
[0066]
[Equation 4] CL (silicon nitride) = 1.66 О 10 <6> (J и K <?1> и m <?3>) О 0.2 О 10 <?6> (m)
О 2 О 10 <-6> (m) = 0.66 О 10 <-6> (J и K <-1> и m <-1>)
[0067]
Therefore, the heat capacity CL (conventional element) per unit length of the conventional
detection element is a value represented by [Equation 5].
[0068]
[Equation 5] CL (conventional element) = CL (platinum) + CL (silicon nitride) = 1.23 О 10 <-6> (J
и K <?1> и m <?1>)
[0069]
05-05-2019
17
Next, the following configuration is considered as a detection element according to the present
invention.
Here, since the thin line produced by the FIB-CVD method generally has a radius of about 50 nm,
this value is used.
In addition, the values of the molar heat capacity and the density of the carbon-based resistor
manufactured by the FIB-CVD method are substituted with the values of diamond (extracted from
the science chronology).
[0070]
(2) Example of configuration of detection device according to the present invention Resistor:
Carbon-based material, radius 50 nm Cm (carbon) = 16 (J и K <-1> и mol <-1>): value at a
temperature of 600 K of diamond M (carbon) = 0.012 (kg и mol <-1>): value of diamond ((carbon)
= 3.5 О 10 <3> (kg и m <-3>): value of diamond
[0071]
Substituting the above value into [Equation 2], the heat capacity Cv (carbon) of carbon per unit
volume becomes a value shown in [Equation 6].
[0072]
[Equation 6] Cv (carbon) = 16 (J и K <?1> и mol <?1>) / 0.012 (kg и mol <?1>) О 3.5 О 10 <3>
(kg иии) m <-3>) = 4.7 О 10 <6> (J и K <-1> и m <-3>)
[0073]
Next, when this value is substituted into [Equation 1], the heat capacity CL (this element) of the
detection element according to the present invention per unit length becomes the value shown in
[Equation 7].
[0074]
[Equation 7] CL (this element) = 4.7 О 10 <6> (J и K <?1> и m <?3>) О ? О (50 О 10 <?9>)
<2> (m <2>) = 3.7 О 10 <-8> (J и K <?1> и m <?1>)
05-05-2019
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[0075]
(3) Comparison results Comparing the heat capacity of the conventional element shown in
[Equation 5] with the heat capacity of the present element shown in [Equation 7], the heat
capacity CL per unit length in this element is 1/1 of that of the conventional element. It is 33 that
the heat capacity CL can be made much smaller than that of the conventional element.
[0076]
As described above, according to the MEMS-type hot-wire particle velocity detecting element 10
in the present embodiment, the particle velocity detecting units 15 to 17 are formed by only the
resistors that are self-supporting using the FIB-CVD method. The heat capacity of the particle
velocity detection units 15 to 17 can be reduced and the structure can be simplified as compared
with the conventional case where the resistor is laminated on the support.
[0077]
Further, according to the MEMS-type hot-wire type particle velocity detecting element 10 in the
present embodiment, as shown in FIG. 1, the particle velocity detecting portions 15 to 17 are
provided side by side at arbitrary intervals in three axial directions on one side of the substrate. It
can be configured.
[0078]
Therefore, the MEMS-type hot-wire particle velocity detecting element 10 according to the
present embodiment can detect the particle velocity of the sound wave over a wider frequency
band than in the prior art, and ensures the design freedom of the detecting element interval and
the device Miniaturization can be achieved.
[0079]
Further, according to the MEMS type hot-wire type particle velocity detecting element 10 in the
present embodiment, three sets of particle velocity detecting portions 15 to 17 can be easily
formed on one surface of the substrate by using the FIB-CVD method. it can.
With this configuration, the MEMS hot-wire type particle velocity detection device 10 can be
suitably applied to an acoustic sensor, for example, a nondirectional microphone.
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As the acoustic sensor, the MEMS type heat ray type particle velocity detecting element 10, a
power supply as a heating means for supplying an electric current to heat the three sets of
particle velocity detecting portions 15 to 17 to predetermined temperatures, and particle velocity
detection It may be configured to include particle velocity measuring means for measuring the
particle velocity of the sound wave based on the temperature difference of each of the resistors
constituting the units 15 to 17.
[0080]
In the above-mentioned embodiment, although what detected the sound wave of the direction of
the X-axis, the direction of the Y-axis, and the direction of the Z-axis was mentioned as an
example and explained, the present invention is not limited to this.
[0081]
For example, as shown in FIG. 3, the concave portion 11b is provided in the silicon substrate 11
so that sound waves in one axial direction of the three axial directions, for example, in the X-axis
direction pass through. It is good also as composition which detects a direction ingredient.
[0082]
Here, as shown in FIG. 4, it is preferable that the resistor of the particle velocity detection unit 15
be curved in, for example, the Z-axis direction to form a curved shape.
The resistor of the particle velocity detector 15 has a temperature of several hundred degrees
when it is energized, so that a thermal strain occurs in the resistor of the particle velocity
detector 15.
At this time, if the resistor of the particle velocity detection unit 15 has a curved shape, thermal
strain does not concentrate on a specific location of the resistor, and the possibility of
disconnection of the resistor due to thermal strain can be reduced. It is because it can.
[0083]
In addition, the MEMS type hot-wire type particle velocity detecting element according to the
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present invention can be configured as shown in FIG. 5, for example.
The MEMS-type hot-wire type particle velocity detecting element shown in FIG. 5 has a silicon
substrate 11 provided with a through hole 11c for passing sound waves in the Z-axis direction
and two convex portions, and a pair of particle velocities having a bent shape. And a detection
unit 18.
The pair of particle velocity detection units 18 are each manufactured using the FIB-CVD method
in the same manner as the particle velocity detection units 15 to 17 described above, and detect
the X-axis direction component of the particle velocity of sound waves. A detection unit 18a, a
detection unit 18b that detects a Y-axis direction component, and a detection unit 18c that
detects a Z-axis direction component are provided.
[0084]
The detection units 18a to 18c respectively detect X, Y, and Z axial components of the particle
velocity of the sound wave, but since these are one set of continuous resistors, the output of the
particle velocity detection unit 18 is X, The components in the Y and Z axis directions are added.
For example, if the lengths of portions that detect the X, Y, and Z axis components of particle
velocity are made equal to one another, the particle velocity can be detected, for example, the
sensitivity of [XYZ] in the [111] direction can be increased. A special directivity can be given by
the routing shape of the portion 18.
When the particle velocity detection element is incorporated into a system and used, the
mounting direction of the particle velocity detection element is often limited. In this case, it is
effective to impart directivity to a specific direction of the silicon substrate in advance. It is.
[0085]
In addition, as shown in FIG. 4, each of the detection units 18 a to 18 c may have a curved shape.
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This configuration is preferable because the possibility of disconnection of each of the detection
units 18 a to 18 c due to the influence of thermal strain can be reduced.
[0086]
As described above, the FIB-CVD method makes it possible to form a curved or bent particle
velocity detection unit which has not been possible in the prior art.
As a result, the possibility of disconnection of the detection element due to the influence of
thermal strain can be reduced, or a particle velocity detection element having directivity in a
specific direction with respect to the substrate can be provided.
[0087]
Second Embodiment First, the configuration of a MEMS heat ray particle velocity detection device
according to a second embodiment of the present invention will be described with reference to
FIG.
FIGS. 6A and 6B are views of the MEMS type hot-wire type particle velocity detecting device
according to the present embodiment as viewed from the Z-axis direction and the X-axis
direction, respectively.
The illustrated X, Y, and Z axis directions are directions defined for convenience of the
description.
Further, the description overlapping with the description in the first embodiment is omitted.
[0088]
As shown in FIGS. 6A and 6B, the MEMS type hot-wire type particle velocity detecting element
20 according to the present embodiment includes the insulator substrate 21, the electrode pad
22, and the particle velocity detecting unit 23. There is.
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[0089]
The insulator substrate 21 is made of, for example, glass, and has a recess 21 a through which
sound waves pass in the X-axis direction.
[0090]
As in the first embodiment, the particle velocity detection unit 23 is manufactured by the FIBCVD method, and includes only a pair of resistors formed in a self-supporting manner so as to
bridge over the concave portion 21a. Each end of the pair of resistors is connected to the
electrode pad 22.
A current for heating the temperature of the particle velocity detection unit 23 to a
predetermined temperature is supplied to the particle velocity detection unit 23 through each
electrode pad 22.
[0091]
Specifically, the particle velocity detection unit 23 includes a pair of particle velocity detection
units 23a and 23b formed of only a medium that transmits a sound wave and a resistor that
exchanges heat.
In addition, the electrode pad 22 includes electrode pads 22a to 22d to which the particle
velocity detectors 23a and 23b are electrically connected.
[0092]
One end of each of the particle velocity detectors 23a and 23b is electrically connected to the
electrode pads 22a and 22b, respectively.
The other ends of the particle velocity detectors 23a and 23b are electrically connected to the
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23
electrode pads 22c and 22d, respectively.
Here, the particle velocity detectors 23a and 23b respectively constitute first and second heat
transfer means according to the present invention. The electrode pads 22a and 22b constitute a
first electrode according to the present invention. The electrode pads 22c and 22d constitute a
second electrode according to the present invention. For example, the electrode pads 22c and
22d may be shared by one electrode pad, and the common electrode pad may be connected to
the ground.
[0093]
The particle velocity detectors 23a and 23b are arranged in the direction orthogonal to the Xaxis direction shown in the drawing. With this configuration, the particle velocity detection unit
23 can detect an X-axis component of the particle velocity of the sound wave.
[0094]
Next, a method of manufacturing the MEMS type hot-wire type particle velocity detecting
element 20 according to the present embodiment will be described with reference to FIG. Note
that an example in which a glass substrate is used as the insulator substrate 21 will be described.
[0095]
First, a glass substrate is prepared as the insulator substrate 21, a photoresist 24 is applied on
both surfaces thereof, and an opening 24a is formed on the surface of the substrate by
photolithography (FIG. 7A).
[0096]
Next, etching is performed using, for example, an etching solution of hydrofluoric acid to form a
recess 21a, and the photoresist 24 is removed (FIG. 7B).
[0097]
Next, a metal electrode pad 22 is formed by using, for example, a mask vapor deposition method
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(FIG. 7C).
[0098]
Next, a particle velocity detection unit 23 mainly made of, for example, carbon is formed between
the electrode pads 22 using the FIB-CVD method (FIG. 7 (d)).
[0099]
When a large number of the above structures are produced on a substrate and made into chips
by dicing, it is possible to make chips without damaging the particle velocity detection unit 23 by
using, for example, a known laser dicing method. is there.
[0100]
As described above, according to the MEMS-type hot-wire particle velocity detection element 20
in the present embodiment, since the insulator substrate 21 is used as the substrate, insulation of
the substrate surface is obtained as compared with the configuration using the silicon substrate.
A film, for example, the insulating films 12 and 13 shown in FIG. 3 is not necessary, the structure
can be simplified, and the manufacturing cost can be reduced.
[0101]
Third Embodiment The configuration in a third embodiment of the MEMS type hot-wire type
particle velocity detection device according to the present invention will be described with
reference to FIG.
The description overlapping with the description in the first and second embodiments is omitted.
[0102]
As shown in FIG. 8A, the MEMS type hot-wire type particle velocity detecting element 30 in the
present embodiment is provided with an insulator substrate 31, an electrode pad 32, and particle
velocity detecting units 33 and 34.
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The illustrated X, Y, and Z axis directions are directions defined for convenience of the
description.
[0103]
The insulator substrate 31 is formed with an opening 31a through which sound waves in the Zaxis direction pass.
[0104]
The particle velocity detectors 33 and 34 are each manufactured by FIB-CVD as in the first
embodiment, and are resistors formed in a self-supporting manner so as to bridge over the
opening 31a. Each end of each resistor is connected to the electrode pad 32.
A current for heating the temperature of the particle velocity detection units 33 and 34 to a
predetermined temperature is supplied to the particle velocity detection units 33 and 34 via the
electrode pads 32.
In addition, the electrode pad 32 includes electrode pads 32 a to 32 d to which the particle
velocity detection units 33 and 34 are electrically connected.
[0105]
In detail, the particle velocity detection unit 33 is configured as shown in FIG.
FIG. 8B is a view of the particle velocity detection unit 33 viewed from the Z-axis direction, and
the particle velocity detection unit 33 is a circle formed through a circle detection unit 33a and a
branch unit 33d. A linear portion 33b connected to the shape detection portion 33a, and a linear
portion 33c connected to the circular detection portion 33a via the branch portion 33e.
Similar to the particle velocity detection unit 33, the particle velocity detection unit 34 includes a
circular detection unit 34a and straight portions 34b and 34c.
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[0106]
As shown in FIG. 8A, one ends of the particle velocity detectors 33 and 34 are electrically
connected to the electrode pads 32a and 32b, respectively.
The other ends of the particle velocity detectors 33 and 34 are electrically connected to the
electrode pads 32c and 32d, respectively. Here, the particle velocity detectors 33 and 34
respectively constitute first and second heat transfer means according to the present invention.
The electrode pads 32a and 32b constitute a first electrode according to the present invention.
The electrode pads 32c and 32d constitute a second electrode according to the present
invention. For example, the electrode pads 32c and 32d may be shared by one electrode pad, and
the common electrode pad may be connected to the ground.
[0107]
As described above, the particle velocity detection unit 33 includes the branch portions 33d and
33e that branch the path from the electrode pads 32a to 32c into two. Similarly, the particle
velocity detection unit 34 is provided with a branch portion that branches the path from the
electrode pads 32 b to 32 d into two.
[0108]
In the MEMS-type hot-wire type particle velocity detecting element 30 according to the present
embodiment, the particle velocity detecting units 33 and 34 respectively oppose the circular
detecting unit 33 a and the circular detecting unit 34 a in the direction orthogonal to the Z-axis
direction. It is arranged side by side. With this configuration, the MEMS heat ray type particle
velocity detection element 30 can detect the Z-axis direction component of the particle velocity
of the sound wave. Here, the particle velocity detection units 33 and 34 have been described by
taking an example in which the particle velocity detection units 33 and 34 are arranged to face
each other in the direction orthogonal to the Z-axis direction, but the present invention is not
limited thereto.
[0109]
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FIG. 8C is a view showing an example of a method of manufacturing the particle velocity
detection unit 33. As shown in FIG. First, as shown in the upper side of FIG. 8C, the semicircular
portion of the circular detection portion 33a and the linear portions 33b and 33c are integrally
formed by using the FIB-CVD method. Although not shown, the straight portions 33b and 33c are
connected to the electrode pads 32a and 32c, respectively. Next, as shown in the lower side of
FIG. 8 (c), using FIB-CVD, both ends of the remaining semicircular portion of the circular
detection portion 33a are formed so as to be connected at branch portions 33d and 33e,
respectively. Thus, the particle velocity detection unit 33 is formed. In addition, since the
manufacturing method of the particle | grain speed detection part 34 is the same as the
manufacturing method of the particle | grain speed detection part 33, description is abbreviate |
omitted.
[0110]
As described above, according to the MEMS-type hot-wire particle velocity detection element 30
in the present embodiment, the branch portion for dividing the path from one end to the other
end of each of the particle velocity detection units 33 and 34 into two Since the configuration is
provided, compared with a conventional particle velocity detection element provided with a pair
of linear-shaped detection elements, detection sections of the same length can be disposed in a
smaller space. Therefore, the MEMS type hot-wire type particle velocity detecting element 30 in
the present embodiment can miniaturize the device that detects the particle velocity.
[0111]
In the above embodiment, although there are two branch parts 33d and 33e in one circular
detection part 33a, the present invention is not limited to this, and three or more branch parts
are It may be.
[0112]
In the above embodiment, the path from one end to the other end of each of the particle velocity
detection units 33 and 34 has been described as an example of being branched into two, but the
present invention is limited thereto Instead, the detection unit may be branched into three or
more at the branch portion.
[0113]
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28
In the above-described embodiment, the circular detection unit 33a has been described by taking
an example of one circular path, but the present invention is not limited to this. For example, two
concentric circular paths may be used. It may be a path or an elliptical path.
Moreover, although the circular detection part 33a gave and demonstrated the example formed
in planar shape, this invention is not limited to this.
[0114]
The perspective view which shows notionally the structure in 1st Embodiment of the MEMS heat
ray type | mold particle | grain speed detection element concerning this invention The
manufacturing method in 1st Embodiment of the MEMS type heat ray | wire type particle speed
detection element concerning this invention In the first embodiment of the MEMS hot-wire type
particle velocity detection device according to the present invention, a diagram conceptually
showing the configuration of the first other aspect of the present invention MEMS-hot-wire type
according to the present invention In the first embodiment of the particle velocity detection
element, the figure schematically showing the configuration of the second other aspect In the
first embodiment of the MEMS heat ray particle velocity detection element according to the
present invention, the third embodiment Fig. 5 is a perspective view conceptually showing the
configuration of the other embodiment of the present invention. Fig. 5 conceptually shows the
configuration of the second embodiment of the MEMS heat ray particle velocity detection device
according to the present invention. Second implementation of the detection element The
sectional view which shows notionally the manufacturing method in a form The figure which
shows notionally the structure in 3rd Embodiment of the MEMS type heat ray | wire type particle
velocity detection element based on this invention The structure of the conventional particle
velocity detection element is conceptualized Cross-sectional view conceptually showing a method
of manufacturing a conventional particle velocity detection element
Explanation of sign
[0115]
10, 20, 30 MEMS type hot-wire type particle velocity detecting element 11 silicon substrate
(substrate) 11a, 11b, 21a recessed part 11c through hole 12, 13 insulating film 12a, 13a, 24a
opening part 14, 22, 32 electrode pad 14a, 14b , 22a, 22b, 32a, 32b electrode pad (first
electrode) 14c, 14d, 22c, 22d, 32c, 32d electrode pad (second electrode) 15 to 17, 18, 23
Particle velocity detection unit (heat transfer means) ) 15a, 23a, 33 Particle velocity detector
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(first heat transfer means) 15b, 23b, 34 Particle velocity detector (second heat transfer means)
18a Detector for detecting X axial component 18b Y axial component Detection unit 18c that
detects a detection unit 21 that detects a component in the Z-axis direction 21 31 insulator
substrate (substrate) 24 photoresist 31a opening 33 , 34a circular detector 33b, 33c, 34b, 34c
linear portions 33d, 33e bifurcation
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