JP2671017B2 - Method for manufacturing piezoelectric ceramics - Google Patents

Description

TECHNICAL FIELD The present invention relates to piezoelectric ceramics, and more particularly to a method for manufacturing piezoelectric ceramics used in mechanical filters for communication and similar applications.

[Prior Art] The basic requirements required for piezoelectric ceramics used in conventional communication mechanical filters are as follows.

I) Related to the bandwidth of the target filter 45
A relatively high coupling coefficient of over%.

II) Mechanical Q related to filter insertion loss should be as high as possible. (Generally> 2000) III) Dielectric constant is related to input / output impedance, but there is a wide range depending on the design target, but there is no particular general restriction, but 800-1500
Degree is standard.

IV) The temperature coefficient of the resonance frequency is a factor that determines the temperature coefficient of the mechanical filter, and there is some entanglement with the temperature coefficient of the Erinbar used, but the required value is somewhat different, but generally ± 100 ppm / ° C ( 0 to 60 ° C) is required.

V) The temperature coefficient of the dielectric constant is preferably small in relation to the input / output impedance band special temperature characteristics of the filter, and is generally 2000 ppm / ° C or less.

The above are the basic conditions required for piezoelectric ceramics used in communication mechanical filters, and various binary and ternary materials based on lead titanate and lead zirconate have been developed according to their respective purposes. Has been put into practical use.

[Problems to be Solved by the Invention] Conventionally, these piezoelectric ceramics have been
After being polarized in an electric field of up to 4 kV / mm, it is processed into a predetermined shape to form a piezoelectric ceramic element, which is generally bonded to an element of a constant elastic alloy Erinvar to form an input / output electromechanical transducer of a mechanical filter element.

There are various types of driving methods for such transducers: 1. Using flexural vibration of a constant elastic alloy plate 2. Using vertical vibration of a constant elastic alloy rod 3. Twisting of a constant elastic alloy rod There are some that use vibration, and the shapes of the elements used are different, but the common point is that the bonding process is required to form the decoding oscillator by joining with the constant elastic alloy. is there. There are two methods of bonding, one is using an organic adhesive and the other is soldering. The latter is superior in terms of reliability. However, in general, soldering exposes the piezoelectric ceramic element at a temperature of 200 ° C. or higher for at least a few seconds, which causes deterioration of various characteristics of the piezoelectric ceramic.

Even if the characteristics of the piezoelectric ceramics used when designing the filter are measured in advance, there is a problem in that there is a discrepancy between the finished filter and the finished filter due to characteristic deterioration due to soldering. . Further, a slight change in the soldering condition at this time causes a change in the characteristic deterioration degree, which also causes a variation in the filter characteristics.

Conventionally, it was general to design in advance empirically with regard to the characteristic deterioration due to soldering, but considering the improvement of design accuracy and quality variation, the piezoelectric with less characteristic deterioration due to soldering It is ideal to use ceramics, and development of piezoelectric ceramics satisfying such requirements has been required. Therefore, the technical problem of the present invention
It is an object of the present invention to provide a method for manufacturing a piezoelectric ceramic, which is less likely to have characteristic deterioration due to soldering or the like.

[Means for Solving the Problems] According to the present invention, the chemical composition is Pb {(Mn _1/3 Nb _2/3 ) _0.05.
Zr _x Ti _0.95−x } O ₃ + y wt% La ₂ O ₃ (however, 0.44 ≦ x ≦ 0.4
6,0 ≤ y ≤ 0.5) After polarization treatment of the ternary oxide represented by the three-component oxide, within the temperature range of 250 ℃ ~ 330 ℃ 15
A method for producing a piezoelectric ceramic is obtained which is characterized by performing a heat treatment for 120 minutes. That is, the present inventor investigated deterioration of various characteristics of various piezoelectric ceramics due to heat, and found that the final chemical composition was Pb {(Mn _1/3 Nb _2/3 ).
_0.05 Zr _x Ti _0.95−x } O ₃ + y wt% La ₂ O ₃ (however, 0.44 ≦ x ≦
0.46,0 ≤ y ≤ 0.5) As shown in the formula, after sintering a three-component oxide in the range of 1200 ° C to 1300 ° C for 2 to 3 hours, 10
For the one polarized at an electric field strength of 2.0 to 4 kV / mm in the temperature range of 0 to 200 ° C, this is 5 in the temperature range of 250 ° C to 330 ° C.
After heat treatment for ~ 120 minutes, it is necessary to satisfy the conditions required for piezoelectric ceramics for mechanical filters with the values of the basic characteristics thereafter, and to significantly reduce the characteristic deterioration at high temperature due to the soldering process. It has been found.

In the present invention, x is 0.44 to 0.46 because 0.44 <x <
When exceeding 0.46, the temperature coefficient of resonance frequency is 50ppm / ℃.
It was determined that it is not preferable as the material of the piezoelectric ceramic element for mechanical filter because it exceeds the above range. Similarly, the amount y of La ₂ O ₃ added is set to 0 to 0.5 wt% by weight for the purpose of improving the temperature coefficient. When the amount of La ₂ O ₃ addition exceeds 0.5 wt%, the electromechanical coupling coefficient deteriorates. It became larger than 40% and it was decided because it was not used as a material for piezoelectric ceramics elements for mechanical filters.

The heat treatment temperature is set to 250 ° C. to 330 ° C. because the effect of the present invention is small at 250 ° C. or lower, and when it is 330 ° C. or higher, the Curie point approaches and the piezoelectric property is significantly impaired.

EXAMPLES The present invention will be described in detail below with reference to the drawings. According to Table 1, Pb {(Mn _1/3 Nb _2/3 ) _0.05 Zr _x Ti _0.95−x } O ₃
+ Y wt% La ₂ O _{3 The} ternary oxide expressed by various x and y values in the composition range and its composition are sintered at 1200 ℃ ~ 1300 ℃ for 2-3 hours, then 100 ~ 200 ° C, 2.0-4kV / m
Polarized with an electric field strength of m. The basic characteristics of the obtained disc vibrator having a diameter of 20 mm and a thickness of 1 mm are measured and shown in Table 1. As can be seen from the table, in the case where La ₂ O ₃ is not added, the coupling coefficient (Kp) and the dielectric constant (ε ^T ₃₃ / ε ₀ ) gradually increase as the value of x increases, and x is around 0.47. Peaks and then descends again. The temperature coefficient (TK · fr) gradually decreases as x increases, but begins to rise again when it exceeds 0.46. However, when La ₂ O ₃ is added in each composition range, the temperature coefficient TK · fr is greatly improved and its value becomes smaller. On the other hand, when La ₂ O ₃ is added, the dielectric constant (ε ^T ₃₃ / ε ₀ ) and the coupling coefficient (K
p), deterioration of mechanical Q (Qm) was observed.

Next, for some of the samples selected from Table 1, 20
After heat-treating at a temperature of 0 ℃ ~ 350 ℃ for 15 ~ 120 minutes, it was left at room temperature for 24 hrs or more and then the basic characteristics were measured. Table 2 shows the results. In Table 2, as the heat treatment temperature increases, the dielectric constant tends to increase and the engagement coefficient tends to decrease, but the temperature coefficient (TK · fr) of mechanical Q and resonance frequency hardly changes. However, when the heat treatment temperature is 350 ° C, the dielectric constant and the electromechanical coupling coefficient Kp are rapidly deteriorated. There is little correlation with the heat treatment time, and the difference between 15 minutes and 60 minutes is small (7-1, 7-2, 7-3).

Next, on a hot plate controlled to 250 ° C ± 5 ° C, some of the samples shown in Tables 1 and 2 were heated for 10 seconds and then allowed to stand at room temperature for 24hrs or longer, then the electromechanical coupling coefficient Kp and the dielectric constant ε. ^T ₃₃ / ε ₀ was measured and indicated by the rate of change (%).

As is clear from the table, the rate of change of the heat-treated product at 250 ° C. or higher is extremely small and is 1% or less.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a method for manufacturing piezoelectric ceramics with little deterioration in characteristics after soldering with an Elinvar element, and its industrial value is great.

Claims (1)

(57) [Claims] 1. The chemical composition is Pb {(Mn _1/3 Nb _2/3 ) _0.05 Zr _x Ti.
_0.95−x } O ₃ + y wt% La ₂ O ₃ (However, 0.44 ≦ x ≦ 0.46,0 ≦
y ≦ 0.5), the sintered body composed of a three-component oxide is polarized, and then 15 to 12 within the temperature range of 250 to 330 ° C.
A method for producing a piezoelectric ceramic, characterized by performing a heat treatment for 0 minutes.