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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
ceramic diaphragm used as a diaphragm for acoustic devices such as speakers and microphones
and a method of manufacturing the same.
2. Description of the Related Art Conventionally, there have been those using ceramic made of
silicon carbide, aluminum oxide or the like as diaphragms for acoustic equipment such as
speakers and microphones, and longitudinal waves are compared with metal diaphragms.
Propagation speed is large.
However, since the ceramic material itself has a Young's modulus smaller than that of diamond,
which has excellent characteristics as a material for a diaphragm for acoustic equipment, it has a
disadvantage that the propagation speed of longitudinal waves is small and the vibration
characteristic is inferior.
SUMMARY OF THE INVENTION The problem to be solved in the present invention is to solve the
drawbacks of such ceramic diaphragms, in particular, to increase the propagation velocity of the
longitudinal wave by eliminating the point where the Young's modulus is small. An object of the
present invention is to find a means for inexpensively manufacturing a diaphragm for an audio
device which satisfies the requirements.
SUMMARY OF THE INVENTION In the present invention, the above problems are solved by
forming a high energy ion irradiated layer by irradiating the surface of the ceramic diaphragm
with high energy ions.
Any ceramic can be used as a ceramic for forming the diaphragm, but since V = (E / ρ) 1/2 (V:
sound velocity, E: Young's modulus, :: density), the density In order to realize a diamond-like
sound velocity, it is preferable that the density is smaller than 5, and silicon carbide, silicon
nitride, aluminum nitride, sialon, aluminum oxide and the like are most preferable.
Means for irradiating high energy ions include ions of inert elements such as helium, neon, argon
and xenon, nonmetal elements such as boron, nitrogen, phosphorus and oxygen, and metal
elements such as aluminum, titanium and chromium. However, it is convenient from the
viewpoint that it is a gas at room temperature, is easy to vaporize, and is easy to accelerate easily,
and if the accelerating voltage of ions is smaller than 1 kV, the implantation depth is shallow and
compressive stress is sufficiently transmitted inside. There is no influence to improve Young's
modulus, acceleration voltage of 1 kV or more is necessary, and mechanical strength such as
bending strength is reduced by thermal effect if it is larger than 10 MV. Acceleration voltage is 1
kV to 10 MV The voltage is appropriate.
Furthermore, when the ion irradiation dose is less than 1 × 10 13 ions / cm 2, no improvement
in Young's modulus is observed.
The surface is made amorphous when larger than 1 × 10 19 ions / cm 2 and the Young's
modulus does not increase. Therefore, the ion irradiation amount is preferably 1 × 10 13 to 1 ×
10 19 ions / cm 2.
The Young's modulus increases even if the residual compressive stress layer is formed on one
side of the diaphragm, but the Young's modulus significantly improves if formed on both sides,
so it is better to irradiate ions on both sides of the diaphragm. preferable.
Although any ceramic material can be used as the ceramic, those containing silicon carbide,
silicon nitride, aluminum nitride, sialon or aluminum oxide as the main component are
chemically stable and have sufficient mechanical strength. And, since the density is relatively
small, it is a suitable material to increase the speed of sound like a diamond.
In addition, since a porous material which is broken by vibration is unsuitable and it is necessary
to have a non-porous and dense structure, a substrate formed by vapor phase chemical vapor
deposition is particularly advantageous.
If the thickness of the ion implantation layer by ion irradiation is thinner than 0.001 μm, no
increase in Young's modulus due to the formation of a residual compressive stress layer can not
be observed, and therefore, the thickness should be 0.001 μm or more.
It is also conceivable to provide a compressive stress layer on the surface of the ceramic
diaphragm by heat treatment or the like, but this method is not preferable because it lowers the
strength of the ceramic substrate itself.
By irradiating the ceramic surface with high energy ions, a layer having a compressive stress is
formed on the ceramic surface, which can increase the surface Young's modulus to that of a
diamond film.
The conventional ceramic diaphragm generally has a longitudinal wave speed higher than that of
a metal diaphragm, but has the disadvantage of being inferior in bending strength and impact
On the other hand, in the case of the present invention having a surface modification layer
implanted with high energy ions, strain of the lattice propagates to the inside due to the
implantation of high energy ions, and compressive stress acts not only on the surface but also
inside If so, bending strength and fracture toughness also improve.
Therefore, the diaphragm of the present invention responds to vibrations having a larger
amplitude than conventional ones, vibrations of high frequency or vibrations having large
vibration energy, and copes with vibrations of relatively low to high frequency without breaking.
it can.
Also, when the amount of high energy ions implanted is increased, the wrinkles (which become
the origin of breakage) formed by processing the surface of the ceramic diaphragm disappear or
reduce, or the particles are amorphized or semi-amorphized on the surface. The fracture
toughness and bending strength can be enhanced by the disappearance or reduction of the field,
and a ceramic diaphragm having high strength and high longitudinal wave propagation speed
can be obtained by appropriately selecting the injection amount.
And, the surface layer which has been reformed by injecting high energy ions has a fine
structure, and has a role of reducing vibration energy loss.
EXAMPLES The surface of a carbon substrate is coated with silicon carbide, aluminum oxide and
silicon nitride to a thickness of 30 μm each by CVD, and carbon is oxidized in an electric furnace
at a temperature of about 1000 ° C. The carbon substrate was oxidized and removed, and the
ash remaining on the surface was removed by mixed acid while applying ultrasonic vibration,
and 100 convex diaphragms each having a diameter of 30 mm were produced.
Nitrogen ions were irradiated at 1 × 10 12 to 1 × 10 19 N + / cm 2 on the surface of the
obtained diaphragm using an ion irradiation apparatus.
During ion irradiation, the sample temperature was kept at 100 ° C. or less.
The reason for setting the temperature to 100 ° C. or lower is because if the temperature
exceeds 100 ° C., the bending strength is reduced due to the thermal effect, or the strength is
decreased due to transformation or the like. The beam current was fixed at 0.1 mA.
The results of the comparison of the velocity of sound and the Young's modulus of the ceramic
diaphragm having a compressive residual stress layer on the surface thus obtained and the
conventional ceramic diaphragm (same shape, same lot material) are shown in Table 1 , Table 2
and Table 3 show.
[Table 1]
[Table 2]
[Table 3]
From this result, it is found that the diaphragm of the present invention has a Young's modulus
51 to 96% higher than that of the conventional one, and the velocity of sound is 23 to 41%
higher. You can see how fast the speed of sound is.
Further, as can be seen from this table, the density does not increase by irradiation with nitrogen
ions, but on the contrary, the density tends to decrease by expansion of a small volume, and a
residual compressive stress layer is provided on the surface of the ceramic diaphragm of the
present invention Considering as a method of obtaining a ceramic diaphragm, the strain for
which a method of forming a compressive strain is formed inside the ceramic diaphragm by ion
implantation does not disappear by the action of mechanical stress such as heat or vibration, so it
is extremely useful as a diaphragm. It is valid.
In addition, although various experiments were attempted by changing the direction of ion
irradiation, there was an effect of increasing the speed of sound regardless of the direction of
The effects of the present invention are not limited by this embodiment, and it is possible to
improve the physical characteristics by the ion irradiation conditions.
The following effects can be achieved by the present invention.
(1) A diaphragm having characteristics similar to those of a diamond film can be manufactured
(2) The obtained diaphragm does not change with time and is excellent in durability.
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