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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
diaphragm for a speaker having excellent acoustic characteristics in a high frequency range.
2. Description of the Related Art Various types of sound speakers are used, among which
dynamic speakers are most frequently used. This type is based on the principle of converting an
electrical signal into sound by means of a diaphragm connected to a moving coil moving in
magnetic flux. Loudspeakers with different frequency ranges are used together, such as for bass,
medium tone, and high tone. The dimensions are different, and the characteristics required for
the diaphragm are also different. The most widely used material for the diaphragm is paper.
While this is an inexpensive, lightweight and suitable material, its low stiffness makes accurate
conversions difficult above several hundred hertz. In order to improve this, various diaphragm
materials have been studied.
When the Young's modulus of the diaphragm material is E and the density is ρ, the larger the E
/ ρ material, the better the conversion characteristics in the high frequency range. That is, the
higher the Young's modulus and the smaller the density, the better the high-pitched sound
characteristics. For example, Be has been proposed as a substitute for paper. The E / こ れ of this
is 50 × 10 10 dyn · cm / g, which is excellent. However, Be is highly toxic and must be carefully
considered in the manufacturing process to avoid the toxicity. Moreover, processability is bad.
Moreover, Ti is also proposed as a diaphragm. However, E / 密度 is small because the density is
Japanese Patent Publication No. 57-29919 proposes silicon Si as a diaphragm. E / ρ of this is
about 50 × 10 10 dyn · cm / g, and the internal loss is also as large as 0.012. Also proposed is a
diaphragm of SiB alloy by alloying boron B into silicon, or a diaphragm of silicon carbide alloy
SiC in which carbon is alloyed into silicon. It is assumed that these E / ρ reach about 140 × 10
10 dyn · cm / g. These utilize the fact that the density ρ of silicon is small (ρ = 2.3 g / cm 3).
However, the diaphragms of Si, SiB, and SiC also have small E / が and can not obtain sufficient
high-pitched characteristics. Japanese Patent Publication No. 55-33237 proposes a diaphragm
made of a diamond-shaped carbon molded film obtained by ion beam deposition of carbon ions.
This uses diamond-like carbon to increase E / ρ. A substrate is made of Al, Ti or plastic, is
brought to a negative potential of -40 V, and is bombarded with argon at a carbon electrode with
argon in a high vacuum of 10 -5 to 10 -6 Torr. And deposit a carbon film on the substrate.
However, this can form only a conductive porous carbon film, and is considered not to be a
diamond but an amorphous carbon film having graphite as a main component.
The diamond E / ρ is high, reaching 300 × 10 10 dyn · cm / g. If a speaker diaphragm is made
of diamond, it should be excellent in high-pitched sound characteristics. However, the speaker
diaphragm must be as thin as 20 μm or 50 μm. In addition, it requires a considerable area such
as 20 to 30 mm in diameter. Of course, it is not possible to make such a wide thin plate from
naturally occurring diamond grains as a raw material.
[Means for Solving the Problems] The speaker diaphragm of the present invention is
characterized by being made of only diamond produced by a chemical vapor deposition method
and processed into the shape of a speaker diaphragm. I assume.
[Summary of operation] The outline of the manufacturing method is as follows: a substrate made
of Si processed into the shape of the diaphragm for a speaker, or a substrate coated with Si on a
metal processed into the shape of the diaphragm for the speaker; The substrate is placed in a
vacuum chamber, and the substrate is heated to grow a diamond film on the substrate by
chemical vapor deposition while flowing a raw material gas containing hydrocarbon, and the
substrate and the diamond film are cooled and taken out of the vacuum chamber, The substrate
is dissolved and removed to obtain a diaphragm-shaped diamond film.
Since the diaphragm is a hemispherical shell (dome shape), a diamond film must be grown on
such a dome shaped substrate.
The substrate may be entirely made of silicon Si, or the metal may be processed into a dome
shape and the surface thereof may be coated with Si.
Of course, the whole made of Si is the best. FIG. 1 shows an example of the shape of the
substrate. The whole is made of polycrystalline Si and has, for example, an outer diameter of 25.5
mm and a height of 7 mm. Generally, the outer diameter of the dome substrate is about 20 to 30
mm and the height is about 5 to 10 mm.
Such a substrate is placed in a chemical vapor deposition apparatus (CVD) to coat a diamond
film. FIG. 2 shows a process chart. First, a substrate is prepared. This may be Si as a whole as
shown in FIG. 1, or Si on metal as shown in FIG.
Next, this is heated in a CVD apparatus, a source gas containing carbon and hydrogen is
introduced, the gas is excited by some method, and a diamond film is coated on the heated
substrate. This must have a considerable film thickness and a film thickness of about 20 μm to
100 μm. If this is too thin, the rigidity is insufficient and it can not maintain its own shape. If it is
too thick, the high-pitched sound characteristics will be rather worse and the cost will be high.
When the predetermined thickness is reached, the growth of diamond is stopped. That is, the
supply of the source gas is stopped, and the heating temperature of the substrate is gradually
lowered. After reaching room temperature, open the CVD apparatus and take out the substrate.
Then, the substrate Si or metal and Si are dissolved and removed by an appropriate chemical.
This leaves a dome-shaped diamond film. This is a single diamond diaphragm.
The reason for making the substrate Si is as follows. When a metal other than Si is used as the
substrate, the defect density is extremely large because the difference in thermal expansion
coefficient with the diamond film is large. When the substrate is dissolved and removed, the
diamond film may be broken apart. This is not useful. The growth of diamond is performed at a
high temperature of 850 to 1000 ° C. However, it is necessary to cool down to room
temperature after film formation. Many metals have a large coefficient of thermal expansion.
During the cooling process, a strong compressive stress is generated in the diamond. Because of
this stress, if the temperature is lowered, many cracks and cracks occur in the diamond film in
the vertical and horizontal directions, and the diamond is decomposed if it is severe.
The coefficient of linear expansion of diamond is extremely small and is 1.times.10@-6 K @ -1 at
ordinary temperature (20 DEG C.) and 5.8.times.10@-6 K @ -1 at 1380 DEG C and increases with
temperature. The linear expansion coefficient of Si is also sufficiently small, and is about 2.5 ×
10 −6 K −1 at normal temperature and about 4 × 10 −6 K −1 at 530 ° C. For example,
when cooled from 1000 ° C. to 20 ° C., the difference in linear expansion coefficient between
Si and diamond in this process is much smaller than in the other combinations. Therefore, if the
entire substrate is made of Si or the substrate surface is made of Si, the compressive stress
generated on the surface of the diamond in the gradual cooling process becomes smaller, and the
probability of cracking, cracking and defects also decreases.
As the chemical vapor deposition (CVD) method, it is possible to use: filament CVD method
microwave plasma CVD method thermal plasma CVD method. In the filament CVD method,
current such as W or Ta is passed through a current to generate thermions, thereby exciting the
source gas. In microwave plasma CVD, microwaves of 2.45 GHz are introduced into a vacuum
chamber through a dielectric window, electrons are vibrated at microwave frequencies, neutral
atoms and molecules are struck by electrons, and these are plasmatized. In the thermal plasma
CVD method, the nozzle is an electrode, positive and negative voltages are applied, and a source
gas is flowed to the nozzle to cause an arc discharge to be a plasma.
EXAMPLES Example 1 Polycrystalline silicon was machined into a speaker diaphragm shape by
cutting. A 25 μm-thick diamond film was formed on this surface by a known microwave plasma
CVD method. After that, the silicon substrate was dissolved in a mixture of hydrofluoric acid and
nitric acid at room temperature. Thus, a 25 μm thick diamond diaphragm was obtained. The
treble resonance frequency of this diaphragm was 65,000 Hz. The treble resonance frequency of
the diaphragm of the same shape is 28,000 Hz, and the treble resonance frequency of Al2 O3 is
35,000 Hz. It can be seen that the high frequency characteristics of the diamond diaphragm of
the present invention are extremely excellent.
Example 2 Mo was cut and processed into a diaphragm shape for a speaker. On the surface, Si, Ti
and W were vapor-deposited to a thickness of 1 μm to make three types of substrates. A sample
of Mo alone and a deposited layer was combined with these three types of substrates, and a
diamond film was coated to a thickness of 10 μm by a known microwave plasma CVD method
for four types of samples. This was cooled and the defect density was measured as it is. After this,
the Mo substrate was removed by a mixed solution of hydrochloric acid, hydrofluoric acid and
nitric acid. Thin films of Mo and Si, Ti, W, etc. were dissolved and only diamond remained. Some
were able to maintain a dome-like shape, but some were broken apart. The results are shown in
Table 1.
[Table 1]
From these results, it can be seen that the one having a diamond film formed by vapor-depositing
Si on a substrate has few defects, and the state after dissolving and removing the substrate is also
sound, and is excellent as a speaker diaphragm .
EXAMPLE 3 Diamond was grown on a dome-like substrate by a known filament CVD apparatus.
FIG. 3 shows a schematic configuration of the filament CVD apparatus.
A cooling support 2 is provided in the vacuum chamber 1. Cooling water 3 is passed through
this. The base 4 is placed on the cooling support 2. A filament 5 is stretched horizontally on the
substrate 4 and supported by electrodes 6, 6 at both ends. An electric current flows from the
external power source 7 to the filament 5 through the electrodes 6 and 6. The source gas flows
into the vacuum chamber 1 from the upper gas inlet 8. The filament 5 is heated to generate
thermions, which plasmify the source gas. The substrate is heated by the radiant heat of the
filament 5 and heated. Exhaust gas is exhausted from the vacuum exhaust port 9. The process is
as shown in FIG.
As a substrate, a Si polycrystal processed into a dome shape was used as a substrate. This is
shown in FIG. 1, but it has a near-hemispherical shape like a sphere cut by a small circle (a circle
not passing through the center). The diameter is 25.5 mmφ, and the height from the bottom to
the top is 7 mm. The surface of this dome-shaped Si substrate was scratched with # 600 diamond
The dome-shaped Si substrate 4 was placed on a sufficiently cooled support 2. The inside of the
vacuum chamber 1 is evacuated to a sufficiently high vacuum. Thereafter, 100 sccm of hydrogen
gas and 20 sccm of methane gas were fed into the vacuum chamber 1 from the raw material gas
inlet 8 and maintained at a pressure of 50 Torr. The filament 5 was tungsten W and was
energized so as to reach 2,100 ° C. The radiant heat of the filament heats the Si substrate to a
temperature suitable for vapor deposition. Since the thermoelectrons are emitted from the
filament, the methane gas is excited by this to become a plasma consisting of positive ions,
neutral radicals (active species) and electrons. This reacts in a gas phase on the Si substrate to
grow polycrystalline diamond.
When a diamond film of a predetermined thickness is formed, the supply of the source gas is
stopped and the temperature of the substrate is gradually lowered. After reaching the normal
temperature, the Si substrate was taken out and immersed in a solution in which hydrofluoric
acid and nitric acid were mixed in a 1: 1 ratio to dissolve and remove only the Si substrate. The
diamond did not melt, so a dome-shaped diamond remained. This dome shaped diamond weighed
60 mg.
The acoustic characteristics were measured as a diaphragm for a speaker. The frequency sound
pressure characteristics are shown in FIG. The acoustic characteristics of the Ti speaker
diaphragm having the same shape thickness are measured under the same conditions for
comparison, and the results are shown in FIG. In each case, the horizontal axis is frequency (Hz)
and the vertical axis is sound pressure level (dB). It can be seen that the diamond diaphragm
according to the present invention has a sufficient sound pressure level even at 20,000 Hz or
higher, and the high sound resonance frequency is 70,000 Hz. It can play up to 70,000 Hz (70
kHz) treble. However, it is understood that the resonance frequency is 17,000 Hz in the
diaphragm of Ti, and high sound of 25,000 Hz or more can not be reproduced with sufficient
EXAMPLE 4 A diamond film was formed under the same conditions as in Example 3 with the
substrate being Mo coated with Si. A filament CVD apparatus was used. The substrate is obtained
by coating 5,000 Å (0.5 μm 2) of Si by sputtering on hemispherically shaped Mo having an
outer diameter of 30.5 mm and a height of 7.5 mm. FIG. 6 shows a cross sectional view. The
surface of the dome-like substrate was scratched with # 600 diamond powder. This was placed in
the apparatus of FIG. 3 and a diamond film was grown under the same conditions as in Example
3. After cooling, the substrate was taken out and dissolved. Mo is first dissolved in aqua regia
(hydrochloric acid: nitric acid = 3: 1). After this, Si is dissolved away with 1: 1 fluoronitric acid. In
this way, a single diamond vibrating plate with a weight of 60 mg was obtained. The acoustic
characteristics of this diaphragm were measured. As in Example 3, it was found that the
reproduction capability in the high range was significantly improved.
EXAMPLE 5 Diamond films were grown while changing the synthesis conditions and the material
of the substrate. This is mainly to examine how the material of the substrate affects the diamond
film. Here, a filament CVD method and a microwave plasma CVD method were used. FIG. 7 shows
a schematic view of a microwave plasma CVD apparatus. A base 13 is set by a support 12 in a
non-metallic (eg quartz) vacuum chamber 11. The source gas is introduced from the gas inlet 14
and exhausted from the vacuum exhaust port 15. There is a heater (not shown) in the support 12
to heat the substrate 13 to a suitable temperature. At the side of the vacuum chamber 11 is a
magnetron 16. From this, microwaves of 2.45 GHz are generated and propagate in the
waveguide 17. On the opposite side is a plunger 18 which holds the plate of the conductor in an
retractable manner. The effective length of the waveguide 17 is determined by the plunger 18, in
which a standing wave of the lowest order mode (or a mode close to it) is established. Since the
electrons in the source gas are vibrated by the microwaves, they excite the gas to form plasma
The sample is NO. 1 to NO. It is up to seven. The substrate is NO. 1 is Si only, NO. 2 is Si / Mo
(coated with Si on Mo), NO. 3 is Si / W, NO. 4 is Si only, NO. 5 is Mo only, NO. 6 is Mo only, NO. 7
is W only. The source gases are hydrogen and methane. The pressure is maintained between 40
and 80 Torr. And the presence or absence of generation | occurence | production of the crack at
the time of melt | dissolution removal of a base | substrate was investigated. Furthermore, NO.
The Raman spectrum of the sample No. 3 was examined, and the spectrum is shown in FIG. NO.
2, NO. The thickness of the Si coating layer 3 is 5000 Å (0.5 μm). Table 2 shows the results of
this experiment.
[Table 2]
Sample No. 1 by the method of the present invention. 1 to NO. In No. 4, a dome-shaped good
diamond diaphragm is produced.
In any of these, the substrate is Si or the substrate surface is Si. On the other hand, NO. 5 to NO.
7 uses a non-Si substrate. In these cases, there were cracks in the diamond coating and cracks in
the diamond film at the end of the coating. And when the substrate is dissolved, NO. 5 to NO. All
of the samples of 7 were broken and could not be made into a diaphragm. From this it can be
seen that the substrate must be either entirely Si or that the surface is covered by Si.
FIG. 8 shows sample NO. 3 is a Raman spectrum of 3; The horizontal axis is wave number (cm-1)
and the vertical axis is intensity. There is a sharp peak at 1333 cm -1, which is the signal from
crystalline diamond, and it can be seen that crystalline diamond is abundant. The signal from
amorphous carbon is widely distributed in this wave number range, but if there is a large amount
of amorphous carbon, the peak at 1333 cm -1 is low and the other part is a widely raised
spectrum. Since this is almost absent, it is clear that the sample is composed of crystalline
diamond with almost no amorphous carbon.
According to the present invention, it is possible to provide a speaker diaphragm made of high
quality diamond alone. The diamond can be used as a diaphragm with E / ρ much larger than
Be, Ti, Al 2 O 3, etc. and excellent in high-pitched sound characteristics, and high-pitched sound
of 80 kHz (80,000 Hz) can be reproduced without distortion. It is an excellent invention.
Brief description of the drawings
1 is a front view of a Si substrate used to produce the diamond diaphragm of the present
2 is a process diagram when manufacturing a diamond diaphragm of the present invention.
3 is a schematic diagram of a filament CVD apparatus used to manufacture the diamond
diaphragm of the present invention.
FIG. 4 is a frequency sound pressure characteristic diagram of the diamond diaphragm
manufactured by the method of the present invention.
5 is a frequency sound pressure characteristic diagram of a known titanium diaphragm.
FIG. 6 is a cross-sectional view of a substrate obtained by coating a metal substrate with Si.
7 is a schematic configuration diagram of a microwave plasma CVD apparatus used in the
present invention.
8 is a Raman spectrum of the diamond diaphragm manufactured by the method of the present
Explanation of sign
Reference Signs List 1 vacuum chamber 2 cooling support 3 cooling water 4 base 5 filament 6
electrode 7 power supply 8 gas inlet 9 vacuum outlet 10 pressure gauge 11 vacuum chamber 12
support 13 base 14 gas inlet 15 vacuum outlet 16 magnetron 17 wave guide Tube 18 plunger
19 plasma
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