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JPS63238799

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DESCRIPTION JPS63238799
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
method of manufacturing a piezoelectric thin film moving member used in a sensor application.
[Prior Art] When a frequency voltage is applied to a piezoelectric element from the outside, the
piezoelectric element causes an expansion and contraction motion at a unique resonance
frequency determined by the element shape. It is a so-called piezoelectric vibrator that utilizes
the characteristics of such a piezoelectric element. Specific applications thereof include an
ultrasonic wave generator, a sound generator such as a pressure speaker, a buzzer, and a
piezoelectric speaker, various types of sensors, and the like. In any of these applications, it is
necessary to bond the piezoelectric element to one side or both sides of a vibrating substrate
usually made of a thin metal plate by some bonding or bonding method. In the present invention,
bonding of the diaphragm and the piezoelectric element, that is, a method of manufacturing the
piezoelectric vibrator will be described by taking as an example a density sensor used for flow
measurement of gas such as air and its control. The structure of the dense 1f sensor is as shown
in Fig. 1, and it is a pressure type device having Ag'α electrodes on the front and back sides on
the both sides of the base plate l made of a thin metal plate such as e) Ni alloy or stainless steel. 2
is pasted together and it becomes what is called a piezoelectric imaging element. The end of the
diaphragm 1 is fixed by a metal housing 3. In this structure, when a voltage is applied to the
piezoelectric element 2 from the outside, the imaging plate is driven accordingly. そして。 The
diaphragm driven in a constant voltage application state has an increase in the mass of the
equivalent of the diaphragm 1 in response to a change in the flow rate of the fluid (air) in the
horn portion 4, so that the moving plate 1 Change frequency (f ') of This relationship is shown by
the following equation. Mm = mechanical system amount Ma-acoustic system quality + =-(density) Kmm bi-directional spring constant Also, the electrical equivalent circuit of this
peristaltic yarn is as shown in Fig. 2, and the co-temperature frequency of the diaphragm Has a
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characteristic that the phase advances by π / 2. Therefore, by correcting the phase difference
and performing positive feedback, the moving plate oscillates at the same 6 frequency of the selfoscillation, so that the density can be measured from the oscillation frequency. In the
piezoelectric image pickup element of the density sensor driven by the principle, it is desired to
have the following characteristics. (1) High sensitivity. (2) A wide operating temperature range
(preferably usable at -50 "C to + 120 ° C). (31 The temperature change of the resonance
frequency is almost linear, and the hysteresis due to the temperature history is small. (41
Vibration resistance, heat resistance (heat cycle), moisture resistance. Excellent resistance to
pollution.
[Problems to be Solved by the Invention] By the way, in the manufacture of a conventional
density sensor, an imaging plate and a piezoelectric element are joined by using an organic
adhesive agent or a sander (pb-8n system) and a piezoelectric vibration is generated. I was a
child. The method using an organic adhesive has the advantages that the adhesive has a low
density (light t) and that the layering operation can be performed at around normal temperature.
However, since the stiffness (Young's modulus) is low and the temperature dependency is large,
the change in the cogrip frequency at high m (about 100 ° C.) deviates from the linearity, and
the hysteresis due to the temperature history is also thick. In addition, there is a disadvantage
that the moisture resistance is also poor. On the other hand, a piezoelectric vibrator constituted
by using a solder has good temperature dependency of the holding frequency and a small
hysteresis, but has a disadvantage that the sensitivity is easily lowered due to the influence of the
high density of the solder. In addition to the above method, a method of forming a piezoelectric
thin film directly on an imaging plate by a high-frequency buffer link has been proposed. In this
method, a diaphragm is fixed on the anode electrode side disposed in a chamber of a high
frequency sputtering apparatus, a piezoelectric body serving as a target is disposed on the
cathode electrode side, and the chamber is filled with a mixed gas of argon and oxygen. After
that, applying a high frequency voltage between the anode and the cathode electrode causes a
thin film having a piezoelectric crystal to adhere to the surface of the moving plate, and an
electrode is formed on the thin film to obtain a piezoelectric moving electrode. It is. The
piezoelectric vibrator according to this method has an advantage that the temperature
dependency of the coincidence frequency is good, the hysteresis is small, and the sensitivity is
large because no contact layer is present. However, there are the following problems in
manufacturing. (It is difficult to obtain a thin film having a piezoelectric crystal unless the
diaphragm installed on the side of the 11 anode electrode is heated to a certain temperature or
higher. (2) When the diaphragm is heated, it is in an atmosphere containing oxygen, so the
diaphragm is oxidized to form an oxide film of Fe 2 O 3, Cr 2 O 3, NiO or the like on the surface,
and adhesion with the thin film Decreases. (3) The piezoelectric thin film formed by sputtering
the piezoelectric body without heating the diaphragm is likely to be in an amorphous state. The
amorphous thin film can also be made to have a piezoelectric crystal by heat treatment in the
atmosphere at a temperature of 500 ° to 900 ° C. However, since it is heating in the
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atmosphere, the moving plate is oxidized. The piezoelectric thin film tends to fall off. Therefore,
in the method of forming a piezoelectric thin film by forming a piezoelectric thin film on a
diaphragm by high frequency sputtering, it is desired to prevent oxidation of the imaging plate
and improve adhesion between the piezoelectric thin film and the diaphragm.
The present invention improves the method of attaching a piezoelectric thin film to a diaphragm
by high frequency sputtering and applying a pressure M and a thin lossy resonator, and the
temperature dependency of the resonance frequency is almost linear and the temperature
hysteresis is used. An object of the present invention is to provide a pressure IIt thin vibrator for
density sensor application which exhibits a characteristic with small hysteresis and further
excellent moisture resistance. [Means for Solving the Problems] The above object is to apply an
alcoholate solution containing Si or Ti to the surface of a diaphragm made of a thin plate of Fe-Ni
alloy or stainless steel, and heat and bake it. Or the first step 1 of forming a 5 in 2 or TiO 2 film
by high frequency sputtering 11 using Si02 or Ti0z # thin film target as a target Next, the
imaging plate which has undergone the first step is mainly composed of Pb (Zr, Ti) 03 Can be
achieved by performing a second step of depositing a piezoelectric thin film by performing highfrequency buffer 7 j1) using a target piezoelectric material as a target. [Operation] The inventor
of the present invention has previously formed an oxide thin film in physical and thermal
consistency with the piezoelectric thin film on the surface of the diaphragm as a means for
preventing oxidation of the metal tearing moving plate. If the diaphragm is heated, high
frequency sputtering can be performed, and even if it is an amorphous piezoelectric thin film,
piezoelectricity can be imparted to the thin film by performing heat treatment in the air after
high frequency sputtering. , I thought that the manufacturing yield of the piezoelectric thin
vibrator will also be improved. And as a result of various examinations from the above viewpoint,
it was confirmed that manufacture of a piezoelectric thin imaging actuator for density sensor is
possible according to the fifth condition. (1) The material of the moving plate is Fe-42N i alloy or
stainless steel, and its thickness is preferably in the range of 20-50 μm. (The oxide formed on
the surface of the 21 diaphragm is most preferably 5i02 or TiO2. And the following two methods
are suitable as the formation method. One of the methods is to apply an alcoholate solution
containing Si or Ti, heat-process it at a temperature of 150 'to SOO ° C, and obtain a film of
5i02, TiO2, and high frequency sputtering using a Sio2 or Ti0z sintered body as a target. Is a
method of forming the film. The thickness of the film formed on the surface of the diaphragm is
preferably in the range of 1 to 5 μm in view of the adhesion with the diaphragm and the
piezoelectric thin film. The oxide film can also be deposited on the metal ring diaphragm by
thermal spraying.
However, in the thermal spraying, a dense film was not obtained, and the adhesion of the
diaphragm was not good either. (3) The composition of the piezoelectric material used as a target
for forming the piezoelectric thin film is desirably a material having a high electromechanical
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coupling coefficient (Kr), a small mechanical quality coefficient (Qm) and a small temperature
coefficient of resonant frequency . すなわち。 Pb(Zr、
Ti)O3−Pb(Sb3ANb3A)O3、Pb(Zr。 Ti) O3-Pb (Mg3ANb%) O3. Pb (Zr,
Ti) O3-Pb (Mg% W%) O3 etc. are in accordance with the object of the present invention. (4) As a
condition of high frequency sputtering, when a piezoelectric material is subjected to high
frequency sputtering while heating an imaging plate installed on the end node electrode side to
400 ° to 700 ° C., a piezoelectric thin film having a piezoelectric crystal (perovskite phase) It
could be formed. The piezoelectric thin film obtained when the holding temperature of the
diaphragm was less than or equal to the season temperature was amorphous. On the other hand,
if the holding temperature is 700 "C or more, the thin film is likely to be cracked or the like, and
it is difficult to obtain a good film quality. (5) The piezoelectric v-film, which was amorphous, is
made to appear a perovskite phase having piezoelectricity by performing treatment in the
atmosphere at a temperature of 5000 to 850 ° C. for 0.5 to 3 hours after sputtering. We
confirmed that we could do t-X-ray. (6) The pressure in the thin-film piezoelectric actuator for
density sensors was practically usable if the thickness of the thin film was 15 to 30 μm.
EXAMPLES The detailed examples of the present invention will be described below. (Example 1)
A diaphragm with a flange having a thickness of 30 Bm (7) Fe-42 wt. T N i and i% of i 2 '2 S + I
11 is converted into a silicon alcoholate solution CS + (U, C5 Ht □) 4]. After immersion to
uniformly apply the solution to the surface of the diaphragm, heat treatment was performed at
350 ° C. for 1 hour in the air to form a 1.5 μm thick film of SiO2. Thereafter, an imaging plate
with a 5i 02 film was disposed on the anode electrode side of the high-frequency sputtering
apparatus, and the imaging plate was heated to 550 ° C. by a heater disposed on the anode
electrode portion. In this condition, high-frequency sputtering 11 is performed under
predetermined conditions using a piezoelectric material of a thickness of 3 dragons and a 50-fil
diameter composition of pb (Zr, Ti) 03 Pb (Sb% Nb 5 A%) 3 as a target. A thin film of thickness n
μm was ruptured on the front and back of the When this piezoelectric thin film was subjected to
X-ray diffraction, it was confirmed to be a light-perovskite phase.
The density sensor having the same configuration as that of FIG. 1 was farmed using the
piezoelectric thin vibrator obtained in the above steps. As a comparative product to the product
of the present invention, the composition is Pb (Zr) in the imaging plate of the same shape as that
described above. Ti)O3−pb(Sb3/2. A piezoelectric vibrator was used in which a
pressure 11 L element having a thickness of 50 μm and a diameter of 231 was bonded with an
epoxy-based adhesive. An external frequency voltage of 5 was applied to the pressure 'is element
of the density sensor from the outside to drive the diaphragm, and the temperature dependency
of the resonance frequency (fr) at that time and the hysteresis due to the temperature history
were measured. The temperature cycle was in the order of 頷 ° C →-(9) ° C → m ° C → 100
° C → 頷 ° C. FIG. 3 shows the relationship between the resonant frequency and the
temperature in the range of 30 ° C. to 100 ° C. The resonance frequency of the product of the
present invention shown by the solid line 11 increases at the low temperature side and decreases
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at the high temperature, but the change with temperature is almost linear. On the other hand, in
the case of the comparative product using the epoxy adhesive shown by the solid line 12, the
decrease of the resonance frequency becomes large and the linearity is deteriorated at around 前
後 ° C. Also, the hysteresis of the resonance frequency (fr2 to fr 1 / fl s) when subjected to a
temperature history of 20 ° C. (frl) → − (° C.) 20 ° C. → 100 ° C. → 20 ′ ′ C (fr 2) When
X 100) was calculated, the product of the present invention was 100%, the OS%, and the
comparative product was + 0.78%, and the product of the present invention showed small
hysteresis. On the other hand, in the salt spray test carried out separately and the cold heat
resistance test repeating 1 cycle between 40 ° C. and 120 ° C., the product of the present
invention can be compared with conventional organic adhesives and density sensors using
solder. No problems were found either. (Example 2) Using the same members as in Example 1,
high frequency sputtering was performed in a state where the imaging plate disposed on the
anode electrode side was not heated, and a piezoelectric thin film with a thickness of 5 μm was
attached to the front and back of the diaphragm. . This was subjected to X-ray diffraction, but the
presence of amorphous and piezoelectric crystals was not observed. The resultant was heattreated at 650 ° C. for 1 hour in the air, and X-ray diffraction was performed again. As a result,
it was confirmed that a perovskite phase exhibiting piezoelectricity was formed. In addition, the
phenomenon which a diaphragm and a piezoelectric thin film peel at the time of heat processing
was not recognized at all. A density sensor was configured using the above piezoelectric thin
vibrator, and the same experiment as in Example 1 was performed to measure the temperature
dependency of the resonant frequency and the hysteresis due to the temperature history. As a
result, it was confirmed that the properties of the product of the present invention were
equivalent to those of the product of the present invention shown in Example 1.
(Example 3) Using the same moving plate as in Example 1, high frequency sputtering 11 was
performed with the SiO sintered body as a target, and a film of 1.3 μm in thickness was
deposited. This is further placed on the anode electrode side and heated to lake C. State Te Pb
(Zr, Ti) O3-Pb (Sb%). Nb station) High frequency sputtering was performed using O3 as a target
to form a 4 μm thick piezoelectric thin film. It was confirmed by X-ray diffraction that this
piezoelectric thin film was a perovskite phase. And it confirmed experimentally that the density
sensor using this had the outstanding characteristic more than the conventional product. Note
that a thin piezoelectric transducer made by depositing a thin film of Ti02 on the imaging plate
by the same method as above and forming a piezoelectric thin film by high frequency sputtering
with a piezoelectric body as a target is also used for a density sensor It confirmed that it had the
outstanding characteristic. [Effects of the Invention] As described above, according to the present
invention, a thin plate made of metal having a coating of 5i02 or TiO2 formed on the surface is
used to target a piezoelectric material mainly composed of pb (Zr, Ti) O3 as a high frequency
target. Since the method of forming a piezoelectric thin film by sputtering 11 is not oxidized even
if the diaphragm is heated in an oxidizing atmosphere, high frequency sputtering is possible in a
state where the diaphragm is heated, and after high frequency sputtering, it is in the air. It is also
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possible to impart piezoelectric crystallinity to the H film which was amorphous by heat
treatment, and a piezoelectric thin film excellent in adhesion to the diaphragm can be provided.
And since the piezoelectric thin vibrator can be manufactured without using a bonding material
such as an organic adhesive or solder as in the prior art if it is the method of the present
invention, the temperature of the resonance frequency when used in a density sensor The
characteristics are linear, the hysteresis caused by the temperature history is small, and the
moisture resistance, the fouling resistance, the heat resistance, etc. are also excellent, so it is
possible to provide a highly sensitive and reliable density sensor. Have. In addition, the method of
the present invention has an advantage that it can be applied as a piezoelectric thin vibrator of
fine and precise functional parts as well as a density sensor.
[0002]
Brief description of the drawings
[0003]
1 is a cross-sectional view of the structure of the density sensor, FIG. 2 is an equivalent circuit
diagram of the density sensor, and FIG. 3 is a graph showing the relationship between the
resonant frequency and temperature measured by the density sensor.
1: imaging plate, 2: piezoelectric element, 3: housing, 4: horn, 11: resonance frequencytemperature curve of the invention, 12: resonance frequency-temperature curve of the
comparison product. / ′ ′ 1-generation, ヱ, 連 山 '' '(' HG, ','; M 十 十 M 、, complement to 2 Cp:
勧, 柿 3 荀 7 婢 客Second Ward 云 j 辰 (Hz)
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