JPH04167900

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DESCRIPTION JPH04167900
[0001]
Industrial Application Field of the Invention The present invention (I, 'for HiFi audio, in particular,
it can be used as a diaphragm of a speaker (generally called Skoker or tweeter) that reproduces
high frequencies of 2 to 3 kHz or more. Diamond diaphragm using diamond thin film and its
synthesis method Also regarding the synthesis device Conventional technology Recently,
equipment using digital recording such as compact disc and DAT became popular, and software
recorded faithfully from low to high range In response to this, it has become desirable to have a
system that can reproduce faithfully over a wide band of speakers. In order to faithfully
reproduce the high-pitched range, it is desirable that the diaphragm of the speaker be light in
weight, high in rigidity, and provided with an appropriate internal loss. Therefore, various
materials have been studied so far. Beryllium titanium, alumina-based ceramic-containing
titanium boronate, etc. are used as the material of the high-rigidity diaphragm (for example, JP-A58-223999, etc.). Recently, a thin film of diamond can be synthesized by vapor phase synthesis,
and its application as a diaphragm has been studied (for example, JP-A 60-141697). Diamond is
expected to be one of the hardest and chemically stable materials among the materials and to be
one of the most suitable materials to realize a diaphragm with high rigidity and little change with
time. Also, a plasma jet (for example, JP-A-58-135117) using an extremely high frequency or
microwave has been reported as a thermal filament method (for example, JP-A-59-27753) using
heat of filament. There is. However, among these methods, it has been possible to synthesize a
diamond thin film into a dome-shaped diaphragm shape (Problems to be solved by the invention
which was only the thermal filament method) A base metal of a conventional diaphragm is used
as a material ζ 交 Force bonding produced by a method of pressing a thin metal plate with a
mold There is a limit in thinning the thickness of the metal plate, and wrinkles and forming
distortion are likely to occur and cause irregular vibration. Furthermore, the Young's modulus of
the material itself is smaller than that of diamond etc., and there is a limit to the reproduction of
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the high region due to the occurrence of split resonance etc. Also the sound unique to the
material because the internal loss is small (specific squeal (Also called) is often generated, and
sometimes a material with a large internal loss has to be used in combination to prevent this.
Also, a diamond thin film is used as a diaphragm. 4 & (1) Relieving internal stress and
maintaining film uniformity to maintain the shape as a diaphragm and improving film uniformity
(2) Two points of film forming process with excellent mass productivity to supply at low cost is
necessary.
The thermal filament method can freely set the shape of the filament according to the shape of
the substrate, and is a method suitable for producing a dome-shaped diamond diaphragm, with a
film deposition rate of at most 5 μm or less. Because it is very slow, for example, it takes 6 hours
or more to create a diaphragm with a thickness of 30 μm, and it has the problem of poor mass
productivity and high manufacturing cost. Then, maintenance was required that the filament had
to be replaced, and the diamond-like thin film synthesized by methods other than the thermal
filament had a large internal stress, and when the substrate was removed, damage or omission
due to film deformation was likely to occur. There is a problem that it is difficult to use as a
diaphragm. The present invention 41 solves the above-mentioned problems and mass
productivity is high. It aims at providing a diamond diaphragm excellent in characteristics. Means
for Solving the Problems The present invention LL Inclusion of graphite and amorphous carbon
in the grain wall portion of diamond, or incorporation of nitrogen in the diamond layer and
vibration of diamond by utilizing thermal plasma jet Manufacture a board. It is an object of the
present invention to solve the above problems and provide a diamond diaphragm having high
mass productivity and excellent acoustic characteristics. The internal stress of the diamond thin
film is significantly reduced by mixing graphite and amorphous carbon in the grain wall portion
of the working diamond. The same effect can be obtained by mixing nitrogen into the diamond
thin film. Thus, if the diamond thin film is synthesized by reducing the internal stress, the film
will not be deformed and damaged even if the substrate is dissolved and removed, and a speaker
diaphragm of only the diamond thin film can be obtained. When graphite or amorphous carbon
is mixed into the wall of the diamond grain, the internal loss is appropriately increased, and a
speaker diaphragm having excellent acoustic characteristics is obtained. In the present invention,
thermal plasma jet is used for synthesizing the diamond thin film. Since the temperature of the
thermal plasma jet is high, the decomposition of the source gas is promoted and the diamond
thin film can be synthesized at high speed. At this time, by adjusting the distance between the
nozzle of the plasma jet nozzle and the substrate, the introduction position of the source gas, and
the concentration of the source gas as necessary, it is possible to realize the diamond thin film of
the configuration to reduce the internal stress at high speed. EXAMPLE FIG. 1 shows a schematic
of the thermal plasma generator used in the examples of the present invention. The arc 4 is
generated between the water-cooled cathode 1 and the water-cooled anode 2 by the DC power
supply 3, the Ar gas 5 fed from the rear is heated by the DC arc 4, and the high temperature
plasma 6 is transferred from the nozzle 7 to the substrate 10. It spouts.
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At this time, although hydrogen gas 8 is introduced into the high temperature plasma in the
vicinity of the nozzle 7, a port 11 into which the source gas 9 is introduced is provided between
the nozzle 7 and the substrate 10. A moving mechanism is installed at the source gas
introduction port 11, and it is configured to be able to move continuously between the nozzle 7
and the substrate 10 in the vertical direction as shown by the arrow. The substrate 10 is
mounted on a substrate mount 12 provided with a cooling mechanism, and the movable
mechanism mounted on the substrate mount 12 allows the distance between the nozzle 7 and
the substrate 10 to be freely set. An embodiment using such a thermal plasma jet apparatus will
be described in detail below. (First Embodiment) FIG. 2 shows a first embodiment. The same
figure (a) shows the appearance of the diamond diaphragm, and the same figure (b) is an
enlarged view of the same part A. This is an amorphous carbon partially containing graphite in
the grain wall portion of the diamond crystal grains 14 The diamond thin film 13 mixed with is
used as a vibrating plate. An example of film forming conditions of this embodiment is shown in
Table 1 in which methane gas is used as lO-source gas. The use of the first surface thermal
plasma jet increases the deposition rate, and in this experiment, the diamond thin film can be
synthesized at a synthesis rate of 200 to 300 μm / min. In the conventional thermal plasma jet
apparatus, the source gas is Ar gas or hydrogen. It is a common practice to mix and introduce the
gas (in this apparatus, it is introduced from the introduction port 11 between the nozzle 7 and
the substrate 10). As a result, the arc discharge can be stabilized, and it is possible to prevent the
adhesion of soot-like deposits due to the decomposition of the source gas on the surfaces of the
cathode 1 and the anode 2. As a result, it was possible to stably generate arc discharge for a long
time under this condition for 10 minutes of film formation (on the surface of the dome-shaped
substrate 10 made of titanium, on the grain wall portion of the diamond microcrystalline grain
14). The diamond thin film 13 mixed with amorphous carbon partially containing graphite was
synthesized to about 35 μm, and then the dome-shaped substrate 10 was dissolved and
removed to measure the characteristics as a diaphragm of only the diamond thin film. 6x 10 @ m
'/ see ", with an internal loss of 0.02, a high specific elastic modulus and a relatively large
internal loss, and a diaphragm with excellent acoustic characteristics can be realized, and the
specific elastic modulus affecting the acoustic characteristics The internal loss is closely related
to the amorphous carbon 15 including a part of graphite mixed in the wall of the diamond crystal
grain 14. That is, when the amorphous carbon 15 decreases, the specific modulus increases but
the internal loss decreases. Conversely, when the amorphous carbon 15 increases, the internal
loss increases but the specific modulus decreases.
In the case of this embodiment, the ratio of the flow rate of hydrogen gas and methane gas
(hereinafter referred to as methane concentration) most affects the content of amorphous
carbon, but if the methane concentration is less than 5%, the contained amorphous carbon is It
will be extremely low, resulting in a film with small internal loss. On the other hand, when the
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methane concentration is 20% or more, the contained amorphous carbon is increased and the
elastic modulus is lowered. It is necessary for the speaker diaphragm to be well-balanced, and in
the case of this embodiment, the methane concentration is preferably 5% to 20%, and more
preferably 10% to 15%. In the case of producing a diaphragm of a diamond thin film by plasma
jet, the internal stress of the film usually becomes large and the film is likely to be damaged or
missing when the substrate is dissolved and removed. % This is especially true for films
containing less impurities such as amorphous carbon. On the other hand, in this example, as a
result of adding nitrogen gas at the time of film formation, it became clear that the internal stress
of the film was relieved and damage / dropout was less likely to occur. It is presumed that the
internal stress is relaxed by mixing a very small amount of nitrogen into the crystal of. The
amount of nitrogen gas added is preferably 5 to 15% with respect to the concentration of
methane gas. If it is less than 5%, the effect of stress relaxation is weakened, and if it exceeds
15%, the quality and synthesis rate of the diamond thin film are reduced. For this reason, in this
embodiment, 10% nitrogen gas is added and 9 (the second embodiment) to the third figure
number. An embodiment of the diamond diaphragm of the present invention is shown. This is a
configuration in which diamond thin films having different contents of amorphous carbon are
laminated to each other, and the film forming method is the same as the first embodiment. Film
forming conditions 1 Even though the methane concentration is changed according to the
content of amorphous carbon, Table 2 shows the methane concentration when each film is
synthesized. Table 2 shows a film with a large internal loss which is synthesized under the
conditions of 20% and contains a large amount of amorphous carbon. While diamond thin film
Bl? Is a membrane with a large specific elastic modulus synthesized at a methane concentration
of 3%. The present embodiment takes advantage of the respective films by forming these films
into a laminated structure, and the specific elastic modulus is 2. A diamond diaphragm with the
characteristics of l x 10 "m '/ sec' and an internal loss of 0.022 could be realized, and for film
formation, only the methane concentration was changed as needed, and the first embodiment
Similar to the example, it can be synthesized at high speed. (Third Embodiment) FIG. 4 shows a
third embodiment of the present invention. This is a diamond diaphragm with a laminated
structure of a diamond thin film D19 containing nitrogen and a diamond thin film 20 containing
nothing. 4 As described above, when nitrogen gas is added when synthesizing a diamond thin
film by a thermal plasma jet, the inside of the film The stress is relieved so that even if the
substrate is dissolved and removed, damage to the film can be prevented. In the present Example
C, the diamond thin film D 19 containing nitrogen and the diamond thin film E 20 which is large
in specific modulus but easily damaged due to internal stress To realize a diamond diaphragm
having a specific elastic modulus close to that of single crystal diamond.
The film forming conditions 6 of the diamond thin film D19 are the same as the conditions
shown in Table 1 except that the methane concentration is 2.5%. On the other hand, the
synthesis of the diamond thin film E20 is carried out using a methane concentration of 1. With
this configuration, a diamond thin film D19 is synthesized 7 μm on a titanium dome-shaped
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substrate thinned to 0%, a diamond thin film E20 is synthesized 13 μm, and a diamond thin film
D19 is synthesized 10 μm, and then the dome-shaped substrate is dissolved away. There is no
loss or loss of film even if the substrate is dissolved and removed, and the specific elastic
modulus is also close to 2.8 × 10 ′ ′ m ′ / 5 ec2 and single crystal diamond (specific elastic
modulus 3.4 × 10 ′ ′ m ′ / see ′ ′) The characteristic diaphragm can be realized, and the
reproducible high frequency can be extended up to 55 KHz. For island = 17-film forming method,
it is only necessary to change the methane concentration or add nitrogen gas as required. After
that, it can be synthesized at the same high speed as the first embodiment. (Fourth embodiment)
Next embodiment. The fourth embodiment will be described. The thermal plasma shown in FIG.
Using a jet apparatus. If the temperature and the density of the crystal grains of the synthesized
diamond thin film can be changed by controlling the temperature of the substrate 10, for
example, when the film is formed under the conditions of Table 1, crystals are produced at a
substrate temperature of 900.degree. While a dense film having a grain size of 10 μm or less is
formed, a porous film in which large crystal grains of 50 μm or more gather at a substrate
temperature of 1100 ° C. is formed. The same effect can be obtained even if the film forming
speed is changed. That is, the source gas is introduced near the nozzle 7 or the distance between
the nozzle 7 and the substrate 10 is made as large as possible within the reach of the torch. By
increasing the deposition rate to increase the deposition rate, a porous film in which large crystal
grains are gathered can be obtained. Conversely, if the deposition rate is decreased, a dense film
can be obtained. FIG. 5 also shows a cross section of the diaphragm according to the fourth
embodiment utilizing the above effects. This is a dome shaped substrate onto which a large
diamond crystal is produced by thermal plasma jet under the conditions of substrate temperature
1100 温度 methane concentration 3%. 21 is a diamond diaphragm in which a porous diamond
thin film in which 21 is collected is synthesized, then the substrate is dissolved and removed, and
an epoxy resin is impregnated between diamond crystals 21. The size of the crystal is about 50
μm, the specific elastic modulus is 2.0 × 10 ′ ′ m 27 sec ′, the internal loss is 0.025, and
the diamond gas plate is well balanced as described above. It is also possible to synthesize a
porous diamond thin film similarly by approaching the nozzle or separating the nozzle 7 and the
substrate 10 from each other.
Therefore, it is possible to manufacture a similar diaphragm not only by controlling the substrate
temperature but also by controlling at least one of the introduction position of the source gas
and the distance between the nozzle and the substrate. (Fifth Embodiment) FIG. 6 shows a cross
section of a diaphragm according to a fifth embodiment. First, move the source gas inlet port
close to the nozzle 7 to a dome-shaped substrate No. 7 and synthesize a dense diamond thin film
F23 with a particle diameter of about 5 μm under the conditions of substrate temperature 850t:
about 10 μm and then source gas inlet port Is separated from the nozzle 7 and a porous
diamond thin film G24 having a large particle diameter is synthesized to a thickness of about 40
μm under the condition of a substrate temperature of 1050 t :. Furthermore, after 7 μm of fine
diamond thin film F23 is synthesized thereon, the substrate is dissolved and removed. That is,
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this embodiment is a diaphragm having a structure in which a fine diamond thin film and a
porous diamond thin film are laminated to each other, the specific elastic modulus is 2.5×[email protected]
/ 5eC2, and the internal loss is 0.015. . The diamond thin film G24 is porous, so the internal
loss is large, and the diamond thin film F23 is monotonous and dense, so the specific elastic
modulus is large. B ° C. A diamond diaphragm having a high elastic modulus and a large
internal loss can be realized. The number of laminated layers is not limited. The outermost
surface of the diaphragm is preferably a fine diamond thin film F23 in order to increase the
specific elastic modulus. The present invention is not limited to the control of temperature, and
the distance between the nozzle and the substrate may be changed as described in the fourth
embodiment. And the like can be provided relatively inexpensively and in large quantities with a
diamond diaphragm having excellent acoustic characteristics, and its industrial value is very
large.
[0002]
Brief description of the drawings
[0003]
Fig. 2 is a schematic diagram of the thermal plasma jet apparatus used in the embodiment of the
present invention. Fig. 2 is a cross-sectional view showing a first embodiment of the present
invention = 21. Fig. 3 is a second embodiment. FIG. 4 is a sectional view showing the third
embodiment. FIG. 5 is a sectional view showing the fourth embodiment. FIG. 6 is a sectional view
showing the fifth embodiment.
4 · · · arc discharge 6 · · · high temperature plasma 7 · · · · 10 · · · K K · · · 14 microcrystalline
diamond 無 15 · amorphous carbon 秦 16 20 · · · diamond thin film 21 ・ ・ ・ Diamond crystal
22 ・ ・ ・ Epoxy resin 23, 24 ・ ・ ・ Name of diamond thin-fee agent Attorneys Attorneys
Osamu Kosumi 2 people size L /) t / ') (O 琳 諷 琳 諷= Alpha mouth alpha mouth city 1) l 14114 '
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