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DESCRIPTION JPH1194810

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DESCRIPTION JPH1194810
[0001]
TECHNICAL FIELD The present invention relates to an ultrasonic probe. More particularly, the
present invention relates to ultrasound probes particularly suitable for use in devices utilizing
high frequency sonic energy.
[0002]
2. Description of the Related Art Ultrasonic probes are widely used in the medical field as well as
in industrial nondestructive testing. Generally, an ultrasonic probe used for such purpose applies
an electric signal to electrodes disposed on both sides of a piezoelectric element to generate an
ultrasonic wave, and this ultrasonic wave is transmitted to the subject. The ultrasonic waves
emitted from the subject are emitted by the piezoelectric element, converted into an electrical
signal, and the internal structure of the subject is analyzed from the result of the converted
signal.
[0003]
An example of a conventionally used ultrasonic probe is shown in FIG. In FIG. 6, reference
numeral 31 denotes a piezoelectric element. An upper electrode 32 is disposed on one surface of
the piezoelectric element 31 and a lower electrode 33 is disposed on the other surface. By
applying an electric signal such as a pulse signal between the upper electrode and the lower
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electrode, the piezoelectric element 31 is vibrated to generate an ultrasonic wave. A lens layer 34
is provided in contact with the upper electrode 32. This lens layer has an ultrasonic matching
function to focus the ultrasonic waves. In addition, an ultrasonic absorbing layer 35 is provided
in contact with the lower electrode 33. Reference numerals 37 and 38 indicate insulating layers,
and reference numeral 36 indicates a housing.
[0004]
In the conventional ultrasonic probe shown in FIG. 6, the cable 39 for applying an electric signal
to the piezoelectric element 31 is electrically connected to the lower electrode 33 through the
cable line 41, and the upper electrode 32 is connected to the lower electrode 33. In contrast, the
cable 39 is electrically connected to the housing 36 by the solder portion 42 and is electrically
connected through the cable wire 40. The cable wire 40 is connected to the upper electrode 32
by the solder 43, and the cable wire 41 is connected to the lower electrode 33 by the solder 44.
[0005]
The method of using solder for conductive connection with the lower electrode and the upper
electrode has the following disadvantages. A load is generated due to hardening and shrinkage of
the solder and the electrical characteristics of the piezoelectric element are degraded. The
thermal distortion of soldering causes micro cracks in the piezoelectric element. The heating
during soldering depolarizes a part of the piezoelectric element. The workability is bad and the
number of manufacturing steps is increased. Since a concentrated mass due to solder is loaded
on a part of the piezoelectric element, vibration modes other than the desired thickness vibration
are easily excited, and the characteristics vary depending on the soldering position.
[0006]
SUMMARY OF THE INVENTION Therefore, the object of the present invention is to solve the
above-mentioned drawbacks of the prior art, and without causing deterioration of the
piezoelectric element accompanying soldering, the load of concentrated mass accompanying
wiring It is an object of the present invention to provide an ultrasound probe which can avoid
variations due to the above and can sufficiently bring out the characteristics of the piezoelectric
element.
[0007]
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[Means for Solving the Problems] In order to solve the above-mentioned problems, an Au / Cr
vapor deposition film which is conducted to the upper surface of the acoustic lens is provided on
the outer periphery of the acoustic lens, and low melting point solder is interposed As a result,
the lower electrode of the ultrasonic oscillator and the housing are electrically connected.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION In the ultrasonic probe according to the
present invention, since the lead wire is not directly connected to the ultrasonic oscillator by
soldering, the ultrasonic oscillator is not deteriorated, and the ultrasonic wave is not It is possible
to provide a high performance ultrasonic probe with little variation among probes.
[0009]
FIG. 1 is a cross-sectional view of an acoustic lens 5 used in the ultrasonic probe of the present
invention.
As illustrated, the lower electrode lead-out portion 4 is continuously provided on the upper
surface and the outer peripheral side wall surface of the acoustic lens 5.
The lower electrode lead-out portion 4 can be made of, for example, an Au / Cr film.
Other metal films can also be used. The Au / Cr film can be formed by vapor deposition such as
vacuum evaporation or sputtering. Such film formation methods are known to those skilled in the
art. The deposition order of the Au layer or the Cr layer is not particularly limited. It is preferable
to form a Cr layer on the wall surface side of the acoustic lens 1 and an Au layer on this Cr layer.
The Cr layer promotes bonding between the lens and the metal. On the other hand, when the Au
layer is exposed, chemical stability is enhanced. The thickness of the Au / Cr film of the lower
electrode lead-out portion 4 is not particularly limited due to the roughness of the deposition
surface and the like, but in general, the thickness is preferably 3 μm or more. If it is less than 3
μm, a sufficient bonding effect may not be obtained. On the other hand, although the upper limit
of the film thickness of the Au / Cr film depends on the thickness of the ultrasonic wave
oscillator used, it is preferable to be about 1/10 of the thickness of the ultrasonic wave oscillator.
For example, in the case of 25 MHz, the upper limit is about 8 μm. It is not preferable to use an
Au / Cr vapor deposition film 4 thicker than this because problems such as interface reflection
waves occur.
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[0010]
In the ultrasonic probe of the present invention, the ultrasonic oscillator 6 and the acoustic lens
1 are integrated by pressure welding. FIG. 2 is a cross-sectional view of the ultrasonic oscillator 6
and the acoustic lens 1 integrated by this pressure welding. The term "pressure welding" as used
throughout this specification means cleaning the surfaces to be joined, and then bringing the two
into contact at high pressure to cause diffusion and joining at the surfaces. .
[0011]
As shown in FIG. 2, the upper electrode 2 is provided on one surface of the ultrasonic wave
oscillator 1, and the lower electrode 3 is provided on the other surface. The upper electrode 2
can be formed of, for example, an Au / Cr film. Other metals can of course also be used. Although
the method of forming the upper electrode is not particularly limited, it can be formed, for
example, by a method such as vapor deposition such as sputtering or vacuum evaporation. The
thickness of the upper electrode 2 is not particularly limited, but generally, it is preferably in the
range of 0.3 μm to 0.5 μm. If it is less than 0.3 μm, the surface roughness of the ultrasonic
oscillator 1 causes inconveniences such as no place where the upper electrode 2 exists, and if it
is more than 0.5 μm, there is no problem, but it is uneconomical It is only. In addition, the lower
electrode 3 can be formed of an Au / Cr film in the same manner as the upper electrode 2. Other
metals can of course also be used. Although the method of forming the lower electrode 3 is not
particularly limited, it can be formed, for example, by a method such as vapor deposition such as
sputtering or vacuum evaporation. The thickness of the lower electrode 3 is not particularly
limited, but generally, it is preferably in the range of 0.3 μm to 0.5 μm. If it is less than 0.3 μm,
the surface roughness of the ultrasonic oscillator 1 causes inconveniences such as no place
where the upper electrode 3 exists, and if it is more than 0.5 μm, there is no problem, but it is
uneconomical It is only. Since the Au / Cr vapor deposition film is used as the material for
forming the lower electrode 3, the Au / Cr vapor deposition film 4 of the acoustic lens 5 and the
Au-Au junction at the time of bonding are preferable because they are chemically stable.
[0012]
The acoustic lens 5 is formed of quartz or sapphire. Quartz or sapphire is chemically very stable
and excellent in corrosion resistance. Thus, the corrosion problems that occur with metallic
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acoustic lenses do not occur at all. Further, since only an Au / Cr film is present between the
acoustic lens 5 and the ultrasonic wave oscillator 1, generation of a reflected wave caused by this
film is hardly occurred at the time of oscillation, and good acoustic characteristics can be
obtained.
[0013]
As a piezoelectric element constituting the ultrasonic oscillator 1, PZT (Pb (Zr, Ti) 03 series
ceramics) or PbTiO3 (lead titanate) can be used. Such materials are well known to those skilled in
the art.
[0014]
FIG. 3 is a schematic view illustrating one step of the method of manufacturing an ultrasonic
probe according to the present invention. In FIG. 2, reference numeral 1 is an ultrasonic
oscillator made of a piezoelectric element, 5 is an acoustic lens made of quartz or sapphire, 13a
and 13b are beam sources for generating an atom beam, and 14a and 14b are pressing jigs. ,
Which are disposed in the vacuum processing chamber 20. At an appropriate position of the
vacuum processing chamber 20, a duct 22 connected to an evacuation means (not shown) is
provided.
[0015]
First, the ultrasonic oscillator 1 and the acoustic lens 5 are mounted on the pressure jigs 14 a
and 14 b respectively, and the atmosphere in the vacuum processing chamber 20 is evacuated
from the duct 22. Next, an atom beam of argon is generated from the beam sources 13a and 13b,
and the same beam is irradiated to the bonding surface of the ultrasonic wave oscillator 1 and
the acoustic lens 5, respectively, and the contamination layer present on these bonding surfaces
(for example, natural oxidation Remove substances or physically adsorbed water). Since the
bonding surface becomes a clean and active surface by this operation, the bonding surfaces of
both members are closely attached using the pressure jigs 14a and 14b, and by continuing
pressing for a predetermined time, diffusion is caused at the bonding surfaces of both members.
As a result, the ultrasonic oscillator 1 and the acoustic lens 2 can be pressure-bonded. The
pressing jig is for performing pressure welding between the respective members, and can be
constituted by a hydraulic cylinder or the like.
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[0016]
When the pressure welding of the ultrasonic oscillator 1 and the acoustic lens 5 is completed, the
ultrasonic oscillator 1 and the pressing jig 14a are separated. Then, as shown in FIG. 4, the
ultrasonic absorbing material 7 is attached to the pressing jig 14 a. While maintaining the
vacuum pressure at the time of pressure welding of the ultrasonic oscillator 1, the beam source
13a and the joint surface of the other joint surface of the ultrasonic oscillator 1 not jointed to the
acoustic lens 5 and the ultrasonic absorption material 7 The atom beam of argon generated from
13b is irradiated to remove the contamination layer (eg, native oxide or physisorbed water, etc.)
present on these bonding surfaces. Since the bonding surface becomes a clean and active surface
by this operation, the bonding surfaces of both members are closely attached using the pressure
jigs 14a and 14b, and by continuing pressing for a predetermined time, diffusion is caused at the
bonding surfaces of both members. As a result, the ultrasonic wave oscillator 1 and the ultrasonic
wave absorbing material 7 can be press-bonded to each other. Thus, the acoustic lens 5 and the
ultrasonic absorbing material 7 are integrally press-bonded integrally with the ultrasonic
oscillator 1 interposed therebetween without using the conventional epoxy resin-based organic
adhesive. it can.
[0017]
In the present invention, an ion beam or an atom beam is used as a means for cleaning the
bonding surfaces of the ultrasonic wave generator 1, the acoustic lens 5 and the ultrasonic wave
absorbing material 7. The reason is that the surface active under vacuum conditions. In the same
chamber while maintaining the state. The surface cleaning means may be plasma, organic solvent
or ultrapure water, but it is most preferable to use ion beam or atom beam to carry out surface
activation and bonding in the same chamber. For example, a beam of argon or the like can be
suitably used as the ion beam or the atom beam.
[0018]
The vacuum processing chamber 20 is used to efficiently perform the ion beam or atom beam
cleaning process. The vacuum pressure suitable for this purpose is not particularly limited, but
generally, it is preferably about 10 −6 Torr. If the vacuum pressure in the vacuum processing
chamber 20 is lower than this, recontamination of the bonding surface can not be prevented, and
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if it is higher than this, the effect of the cleaning processing itself can be further enhanced. It is
only uneconomical because it can not be done.
[0019]
As the beam sources 13a and 13b, for example, an apparatus known to those skilled in the art
such as a beam gun commercially available from ATOMTECH can be used. The power of the ion
beam or atom beam required for the cleaning process of the bonding surface is not particularly
limited. It may be an output that can obtain a degree of cleanliness sufficient to establish
pressure welding between members. As a general index, it is preferable that the output of the ion
beam or atom beam be about 1 keV, 25 mA. If the output is less than 1 keV, 25 mA, the junction
surface may be poorly cleaned. On the other hand, when the output greatly exceeds 1 keV and
25 mA, it is not preferable because a disadvantage such as formation of a large void or the like
occurs in the junction surface. The beam irradiation time is not particularly limited as long as it
has a sufficient length for cleaning the bonding surface. The beam power and the beam
irradiation time have an inverse relationship to obtain the desired degree of interface cleaning.
For example, if a high power beam is used, the irradiation time will be short, while if a low power
beam is used, the irradiation time will be long. As a mere general index, the irradiation time is
about 600 seconds when using a beam with an output of about 1 keV and 25 mA.
[0020]
The pressing pressure and pressing time of each member by the pressing jigs 14a and 14b may
be any size and length as long as they are necessary and sufficient to form the pressure welding
between the members, and is not particularly limited. Generally, when a pressure of 12.5 MPa or
more is used, the pressure time is about 30 seconds. If the pressure is too high, the quartz
acoustic lens 5 may be damaged. Generally, the upper limit of the applied pressure is determined
by the object to be bonded.
[0021]
In the present embodiment, although the members to be joined, ie, the piezoelectric element 1,
the acoustic lens 5 and the ultrasonic wave absorbing member 7 are all joined at room
temperature, the temperature of the joining surface is obtained by heating the members to be
joined using a heater or the like. When bonding is performed after raising to a range, bonding
strength further increases.
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[0022]
Although bonding is performed in vacuum in this embodiment, bonding may be performed after
the atmosphere is filled with an inert gas such as argon or nitrogen after irradiation with an atom
beam.
The formation of an inert gas atmosphere can prevent re-oxidation and re-contamination of
components.
[0023]
FIG. 5 is a cross-sectional view showing the final assembled structure of the ultrasonic probe of
the present invention. As described above, the piezoelectric element integrated by pressure
welding and the acoustic lens are inserted into the housing 10, and the low melting point solder
foil 24 is inserted in the gap between the housing 10 and the acoustic lens 5. The low melting
point solder foil 24 can be inserted between the housing 10 and the acoustic lens 5 by an
appropriate method such as, for example, winding on the Au / Cr film surface of the outer
peripheral side wall surface of the acoustic lens 5. Preferably, the solder foil 24 has a low melting
point (for example, 150 ° C. or less). When the melting point becomes high, heat is conducted at
the time of welding, and the ultrasonic oscillator 1 has an adverse effect such as generation of
micro cracks or depolarization, which is not preferable. As the solder having a melting point of
150 ° C. or lower, for example, a low-temperature solder having a composition ratio of 58% of
Bi and 42% of Sn (melting point of 117 ° C.) can be used. The thickness of the solder foil 24 is
not particularly limited, but generally, the thickness in the range of 300 μm to 500 μm is
preferable. If the thickness of the solder foil 24 is less than 300 μm, conduction failure of the
lower electrode may occur. On the other hand, when the thickness of the solder foil 24 is more
than 500 μm, when heating the housing 10 to melt the solder foil 24, the heat capacity becomes
large, and the heat is transmitted to the ultrasonic oscillator 1 through the lower electrode lead
portion 4 It is not preferable because it causes problems such as heating and the occurrence of
micro cracks.
[0024]
Thereafter, a temperature not higher than the melting point of the solder used from the outside
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of the housing 10 is applied to melt the solder foil 24 inside, and the acoustic lens 5 and the
housing 10 are welded. As a heating method, an appropriate method such as a method of
applying heat directly from the outside of the housing can be used.
[0025]
By welding the solder foil 24, the lower electrode 3 of the ultrasonic oscillator 1 and the housing
5 are conducted. Therefore, according to the present invention, the lower electrode 3 of the
ultrasonic oscillator 1 can be removed through the housing 5 without applying a thermal load.
Therefore, in FIG. 5, the ground lead wire 6 can be stably connected to the adjustment circuit 26,
and an ultrasonic probe with less variation can be manufactured and provided. The adjustment
circuit 26 adjusts the frequency and sensitivity with a transformer and a capacitor based on the
ground lead 6 and the signal lead 8. In addition, the code | symbol 9 in FIG. 5 is resin for fixation
(for example, epoxy resin), and the code | symbol 28 shows a connector part. These are well
known to those skilled in the art.
[0026]
As described above, according to the present invention, the piezoelectric element does not
deteriorate due to soldering, the variation due to the load of concentrated mass due to the wiring
is avoided, and the characteristics of the piezoelectric element are improved. An ultrasound
probe that can be fully withdrawn is obtained.
[0027]
Brief description of the drawings
[0028]
1 is a cross-sectional view of an acoustic lens used in the ultrasonic probe of the present
invention.
[0029]
2 is a schematic cross-sectional view of an example of the ultrasonic probe of the present
invention.
[0030]
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3 is a schematic view illustrating one step of the method of manufacturing an ultrasonic probe of
the present invention.
[0031]
4 is a schematic view illustrating another step of the method of manufacturing an ultrasonic
probe of the present invention.
[0032]
5 is a schematic cross-sectional view of an example of the assembly structure of the ultrasonic
probe of the present invention.
[0033]
6 is a schematic cross-sectional view of an example of the assembly structure of the conventional
ultrasonic probe.
[0034]
Explanation of sign
[0035]
Reference Signs List 1 ultrasonic oscillator 2 upper electrode 3 lower electrode 4 Au / Cr film 5
acoustic lens 6 grounding lead wire 7 ultrasonic wave absorbing material 8 signal lead wire 9
filling material 10 protective case 13a, 13b beam source 14a, 14b pressing jig 20 vacuum
processing chamber 22 exhaust duct 24 low melting point solder foil 26 adjustment circuit
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