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JPH02268593

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DESCRIPTION JPH02268593
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
acoustic wave receiving diaphragm which can exhibit high sensitivity particularly in the vicinity
of an ultrasonic wave region or an upper limit of an audible region, and an acoustic wave sensor
using the same. [The prior art and the problem to be solved by the invention] The ultrasonic
sensor can measure the distance and position of objects such as people and cars, but with the
recent automation of various devices, it is more sensitive and smaller. However, conventional
products can not meet the demand. For example, an ultrasonic sensor using a Be film as a
diaphragm not only carries the danger of beryllia that is highly toxic at the time of manufacture,
but also has a lower sensitivity in the ultrasonic region when it is miniaturized. is there. In
addition, although a thin plate made of a hard material such as A1203 or the like is known as a
sound wave receiving diaphragm, this too can not meet the above-mentioned request.
Furthermore, it has been proposed relatively recently that a diamond whisker is used as a
diaphragm (Japanese Utility Model Application Publication Nos. 59-38890 and 59-38891), but
these have satisfactory characteristics in the high frequency region. It is not something to do. The
present invention has been made to solve the above problems. That is, (1) The object of the
present invention is to exhibit high sensitivity etc. especially in the ultrasonic region and in the
vicinity of the upper limit of the audible region, to easily realize miniaturization, and vibration for
sound wave reception without any concern of toxicity It is in providing a board and an acoustic
sensor which uses it. [Means for Solving the Problems] The present invention for solving the
above problems is a diaphragm for sound wave reception characterized in that the diaphragm is
formed of a film made of diamonds. It is a sound wave sensor characterized by having the abovementioned diaphragm for sound wave reception. Hereinafter, the present invention will be
described in more detail. In the present invention, a thin film made of diamonds is used. In a state
of being laminated on a substrate, or a thin film made of diamonds itself is configured as a
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diaphragm for receiving sound waves. As a substrate used for forming a thin film of diamonds,
any substrate can be used as long as it can form diamonds on its surface, and for forming a
diamond thin film by vapor phase synthesis method And, according to the purpose, it can be
appropriately selected from various substrates such as a substrate known as an acoustic
diaphragm. Examples of the substrate include metals such as silicon, manganese, vanadium,
thallium, aluminum, titanium, tungsten, molybdenum, germanium and chromium, oxides, nitrides
and carbides thereof, alloys thereof, A1203-F @ system, TH1l Examples thereof include cermets
such as knee Ni-based, TiC-GO-based and 84C-Fe-based, and various ceramics.
Further, in the case of forming the diaphragm for sound wave reception with a thin film of
diamonds itself, it is necessary to remove the substrate on which the diamond thin film is formed
on the surface of the substrate by etching. A possible material, for example, the above-mentioned
various metals, is preferable, and the etching process is unnecessary when it is composed of the
substrate and a thin film of diamonds formed on the surface thereof as a diaphragm for receiving
sound waves. These substrates may be subjected to surface treatment or coating treatment to
further improve adhesion to a thin film of diamonds formed by vapor phase synthesis, and, for
example, tungsten, titanium, tantalum, alumina An intermediate layer of silicon or the like may be
provided, and the adhesion between the diamond thin film and the substrate can be further
improved by appropriately performing such treatment. However, such a process may not be
particularly necessary when forming a sound wave receiving diaphragm with a thin film of
diamonds alone. The shape of the substrate is also not particularly limited, but a known shape
can be adopted as the diaphragm, and examples thereof include a flat plate shape and a curved
surface shape. In the present invention, examples of diamonds include diamond, diamond-like
carbon (DLC) and mixtures of diamond and diamond-like carbon. Diamonds can be formed on a
substrate as follows. That is, the gas obtained by exciting the carbon source gas is brought into
contact with the substrate. As the carbon source gas, gases such as various hydrocarbons,
halogen-containing compounds, oxygen-containing compounds, and nitrogen-containing
compounds can be used. Examples of hydrocarbon compounds include paraffin hydrocarbons
such as methane, ethane, propane and butane; olefin hydrocarbons such as ethylene, propylene
and methylene; acetylene hydrocarbons such as acetylene and allylene and the like: diolefin
carbonization such as butadiene Hydrogen; Alicyclic hydrocarbons such as cyclopropane,
cyclobutane, cyclopentane, cyclohexane, etc .; Cyclobutadiene, benzene, toluene. Aromatic
hydrocarbons such as xylene and naphthalene; and halogenated hydrocarbons such as methyl
chloride, methyl bromide, methylene chloride and carbon tetrachloride can be mentioned.
Examples of oxygen-containing compounds include ketones such as acetone, diethyl ketone and
benzophenone: Alcohols such as methanol, ethanol, propatrol and butanol: methyl ether, ethyl
ether, ethyl methyl ether, methyl propyl ether, ethyl propyl ether, phenol Ethers, acetals, ethers
of cyclic ethers (dioxane, ethylene oxide, etc.); acetone, binacholine, methyl oxide, aromatic
ketones (acetophenone, benzophenone, etc.), ketones such as diketones, cyclic ketones, etc .;
formaldehyde, acetaldehyde, butyraldehyde And aldehydes such as benzaldehyde; organic acids
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such as formic acid, acetic acid, propionic acid, succinic acid, butyric acid, oxalic acid, tartaric
acid and stearic acid; acids such as methyl acetate and ethyl acetate Ester ethers, ethylene glycol,
dihydric alcohols knee carbon oxide such as diethylene glycol, can be mentioned carbon dioxide.
Examples of the nitrogen-containing compound include 1; amines such as trimethylamine and
triethylamine. In addition, the carbon raw materials are not single substances, but are classified
into Class 4 dangerous substances specified by the Fire Service Law: first petroleum oils such as
gasoline, kerosene, turpentine oil, chamber oil, second petroleum oils such as pine oil, It is also
possible to use gases such as heavy oils and other third oils, gear oil, cylinder oils and other
fourth oils. In addition, various carbon compounds can be mixed and used. Among these carbon
sources, methane or paraffin hydrocarbons such as ethane and propane, olefin hydrocarbons
such as ethylene and propylene, ketones such as acetone and benzophenone, methanol and
ethanol And oxygenated compounds such as carbon oxides, carbon dioxide gas, etc. are
preferred. Also, if desired, a carrier gas such as hydrogen gas or inert gas can be used together
with the carbon source. The means for exciting the carbon source gas is not particularly limited
as long as it can form crystalline diamond by a vapor phase method, for example, a method of
plasma decomposition by direct current or alternating current arc discharge, high frequency
induction discharge Method of plasma decomposition, method of plasma decomposition by
microwave discharge (including magnetic field-CVD method), method of plasma decomposition
by light energy or ion decomposition or plasma decomposition is performed in an ion chamber or
ion gun, and ions are extracted by an electric field Any of a beam method, a thermal
decomposition method (including an EACVD method) which is thermally decomposed by heating
with a hot filament, a combustion flame method, a sputtering method and the like can be
employed. In the present invention, the reaction usually proceeds under the following conditions
to form a thin film of diamonds on the substrate. That is, since the temperature of the surface of
the substrate is different depending on the means for exciting the carbon source gas in the vapor
phase synthesis method and the cooling of the substrate, it can not be determined roughly. To
form a diamond thin film, the temperature is 200 to 1.200 ° C., preferably 300 to 1,100 ° C.
To form a DLC thin film, the temperature is usually room temperature to 500 ° C., preferably Is
from room temperature to 400.degree. The reaction pressure is usually 10-6 to 10 3 torr,
preferably 10-5 to 10 'tarr, when forming a diamond thin film, and 1-10 6-780 torr, preferably
10 when forming a DLC thin film. -4 to 10 torr.
If the reaction pressure is lower than 10-'torr, the diamond thin film may not be deposited. on the
other hand. Even if it is higher than 103 tart, the corresponding effect can not be obtained.
Similarly, when the reaction pressure is lower than 10 -6 Torr, the DLC thin film may not be
deposited. On the other hand, even if it is higher than 780 torr, the corresponding effect can not
be obtained. In addition, the total flow rate of the carbon source gas is usually 1 to 1.0003 CCM,
preferably 10 to 500 OCT4. The reaction time is different depending on the temperature 1
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reaction pressure of the surface of the substrate, the thickness of the required thin film of
diamonds, and the like, and can not generally be determined, but can usually be within 10 hours.
The diaphragm for sound wave reception can be manufactured by forming a thin film of
diamonds on the surface of the substrate. However, the substrate is removed by the etching
process described below, and only the thin film of diamonds is used as a diaphragm for sound
wave reception. You can also The etching process includes wet etching process and dry etching
process. In the wet etching process, the chemical solution used varies depending on the material
of the substrate. For example, when the material is Mo, hot concentrated sulfuric acid, and when
the material is An, dilute hydrochloric acid or sodium hydroxide aqueous solution, the material is
Si In some cases, it is appropriate to use a mixed acid of hydrogen fluoride and nitric acid. In the
case of dry etching, when the material is Si, dry etching with carbon tetrafluoride gas and
hydrogen is suitable. The thin film of diamonds thus formed is usually 3 to 501 Lm, and
preferably 10 to 50 JLm when removing the substrate. If it is less than pm, the mechanical
strength of the thin film may be weak, and if it exceeds 50 pm, the function as a diaphragm may
be weak. One sound wave sensor The sound wave sensor of the present invention is not
particularly limited in its kind as long as the sound wave receiving diaphragm can be used, for
example, electrokinetic type such as moving coil microphone, magne Examples include
electromagnetic types such as tick microphones, electrostatic types such as condenser
microphones, and piezoelectric types such as crystal microphones. The acoustic wave sensor of
the present invention is particularly suitable for ultrasonic wave reception. Since the thin film
made of diamond or diamond-like carbon or the laminate coated with this thin film in the form of
a substrate is used as a diaphragm for sound wave reception, the sound pressure sensitivity and
selectivity (S / N ratio, frequency selection Property), and in particular, exerts high sensitivity in
an ultrasonic range of 20 KHz or more.
EXAMPLES The present invention will next be described in more detail by way of examples.
Example 1 A molybdenum substrate having a thickness of 50 pm was placed in a reaction
chamber of a microwave plasma CVD apparatus. Next, a CO / H2 mixed gas (GO 7%
concentration) is introduced at a flow rate of 100 scc in this reaction chamber, and the pressure
of one reaction chamber is 40 Torr and a microwave power of 2.45 GHz frequency under the
conditions of a molybdenum substrate temperature of 880 ° C. It was set to 500W. When
plasma treatment was performed for 10 hours under these conditions, a diamond film with a film
thickness of 20 JLm could be formed on the molybdenum substrate. Next, the laminate thus
obtained was immersed in heated and melted paraffin, and then the laminate was pulled up to
remove the paraffin on the central surface. Subsequently, this laminated board was placed in a
hot concentrated sulfuric acid bath, subjected to electrolytic polishing, and then the laminated
board was placed in a triclen bath (or chloroform may be used) to dissolve the resist film. As a
result, the substrate was removed, and a diaphragm with a diamond film on the central surface
and a molybdenum outer periphery was obtained. Next, a sound wave sensor was manufactured
using this diaphragm, and when the frequency characteristic of the diaphragm was examined, the
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sound pressure sensitivity was flat at 5 to 80 KHz. Example 2 A water-cooled aluminum substrate
having a thickness of 804 m was placed in a reaction chamber of a microwave plasma CVD
apparatus. Next, a Co / H2 mixed gas (COIO% concentration) is introduced into this reaction
chamber at a flow rate of 100 gccm, the pressure in the reaction chamber is 40 ororr, the
aluminum substrate temperature is 500 ° C, and the microwave power is 2.45 GHz. Was set to
300W. When plasma processing was performed for 120 hours under these conditions, a
diamond film with a film thickness of 40 JLm could be formed on the aluminum substrate. Next,
the laminate thus obtained was immersed in heated and melted paraffin, and then the laminate
was pulled up to remove the paraffin on the central surface. Subsequently, the laminate was
placed in a 30% aqueous caustic soda solution heated to 80 ° C. to carry out electrolytic
polishing, and then the laminate was placed in a triclinic bath to dissolve the resist film. As a
result, the substrate was removed, and a diaphragm with a diamond film on the center surface
and an aluminum outer periphery was obtained. Next, a sound wave sensor was manufactured
using this diaphragm, and when the frequency characteristic of the diaphragm was examined, the
sound pressure sensitivity was flat at 5 to 50 KHz. Example 3 An alumina substrate with a
thickness of 40 pm is subjected to ultrasonic cleaning for 30 minutes in acetone in which a
diamond paste (particle size 10 to 20) has been dispersed beforehand, and then this substrate is
placed in the reaction chamber of a microwave plasma CVD apparatus. did.
Then, mixed gas (7% concentration of CO 7) of CO / H is introduced into the reaction chamber at
a flow rate of f00 sccm, the pressure of the reaction chamber is 40 Torr, and the alumina
substrate temperature is 900 ° C. Set to When plasma treatment was performed for 2 hours
under these conditions, a diamond film having a film thickness of 571 m could be formed on the
alumina substrate. The laminated board thus obtained was used as a diaphragm A, and an
alumina substrate not forming a diamond film was used as a diaphragm B. Acoustic wave sensors
were produced, and ultrasonic vibrations of 35 KHz and 55 KHz were detected by a detector of
the same shape. By the way, the output of the detector was larger than that of B as shown in the
following. Detector output (relative value) 35 KHz 55 KHz diaphragm A sensor 1.1 1.1
diaphragm B sensor 1.0 1.0 [effect of the invention] According to the present invention, as a
diaphragm for sound wave reception, diamond or diamond Since a thin film made of carbon
dioxide or a laminate coated with the film on a substrate is used, the loss of ultrasonic waves in
the diaphragm is small, the sound pressure sensitivity and selectivity are improved, especially in
the ultrasonic region and near the upper limit of the audible range It is possible to provide an
acoustic wave receiving diaphragm capable of exhibiting high sensitivity. Therefore, by using this
sound wave receiving diaphragm, it is possible to construct a sound wave sensor with good
sensitivity which can be easily miniaturized, which is large compared to the field of sensors of
various robots or a small distance meter. It is possible to make a contribution.
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