JPS63283215A - Piezoelectric component - Google Patents

Abstract

PURPOSE:To evade the deviation of a frequency, by connecting in series a capacitor to a piezoelectric element, and setting the temperature coefficient of the inter-terminal capacitance of the piezoelectric element and that of the inter-terminal capacitance of the capacitor so as to show a specific relational equation. CONSTITUTION:The temperature coefficient (alpha) of the inter-terminal capacitance Cd of the piezoelectric element 2 and the temperature coefficient (beta) of the inter-terminal capacitance Cx of the capacitors 3 and 4 are set at relation as beta=-alpha/{N-alpha(1+N)} (where, N=Cx/Cd>>1 in equation). And as the capacitor Cx to be connected in series to a piezo-resonator, the capacitor having the temperature coefficient (beta) to satisfy the equation is selected. And the superposing planes of the piezoelectric element 2 and first and second capacitor units 3 and 4 are bonded with a bonding agent 14 keeping a prescribed interval to permit the vibration of vibration electrodes 6a and 7a. Thus, since the capacitors 3 and 4 are connected in series to the piezoelectric element 2 and the capacitor which satisfies the above stated equation is selected, it is possible to evade the characteristic change of the piezoelectric element due to temperature change.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a piezoelectric component that utilizes energy-trapped thickness vibration, and particularly relates to a piezoelectric component that can avoid fluctuations in frequency-impedance characteristics due to temperature changes. The present invention is suitable for a piezoelectric resonator employed in, for example, an F'M demodulation circuit, and will be described below using this as an example.

[Conventional technology]

Generally, an FM demodulation circuit inputs an FM signal output from a limiter amplifier at the final stage of an FM signal amplifier and a signal obtained by shifting the phase of the FM signal through a phase shift circuit to a multiplier, and converts these two signals. The phase difference is detected by the multiplier and its output is passed through a low-pass filter to obtain an FM demodulated signal. Conventionally, as the above-mentioned phase shift circuit employed in such an FM demodulation circuit, there has been one shown in FIG. This is a two-terminal piezoelectric resonator 20 that uses an energy-trapped thickness vibration mode.
and a constant resistor r constitute a bridge circuit. Note that 21 is a power supply, and 22 is an output terminal.

In the above phase shift circuit, if the capacitance between the two terminals of the piezoelectric resonator 20 is Cd, then r-1/ωs'cd ω・m(ωr+ωa)/2 ωo: angular frequency corresponding to r, ωr: resonance angular frequency ,
The circuit configuration is based on the relational expression of ωa two anti-resonant angular frequencies.

A phase shift circuit employing the piezoelectric resonator 20 has an hour wheel configuration and has excellent FM demodulation performance, so it has been widely used in recent years.

[Problem that the invention seeks to solve]

However, the conventional piezoelectric resonator 20 described above has a problem in that when the temperature changes, the capacitance 11cd between the two terminals of the piezoelectric resonator 20 changes, and the frequency-impedance characteristic changes.

FIG. 6 is a characteristic diagram showing the relationship between the angular frequency ω of the piezoelectric resonator 20 and the impedance 2, where the curve A shows the original impedance characteristic and the curve fiB shows the impedance characteristic changed due to temperature change.

As is clear from the figure, when the inter-terminal capacitance Cd changes due to temperature change, the angular frequency corresponding to the constant resistance r changes to ω
. From ω. It can be seen that the capacitance Cd between the terminals of the piezoelectric resonator 20 is generally 0.2 to 0.5.
%/°C, which is the only drawback of the FM demodulation circuit using the piezoelectric resonator 20.

The object of the invention is to reduce the angular frequency ω due to temperature changes.

An object of the present invention is to provide a piezoelectric component that can avoid misalignment.

[Means for solving problems]

In view of this, the present invention provides a piezoelectric substrate having two opposing main surfaces with the substrate sandwiched therebetween. In a piezoelectric component formed by connecting a capacitor in series to a piezoelectric element formed with a second vibrating electrode film, a temperature coefficient α of the inter-terminal capacitance Cd of the piezoelectric element,
The temperature coefficient β of the terminal capacitance Cx of a capacitor has the following formula: β--α/(N-α(1+N)), where N-value Cχ/Cd>>1. It is said that

Here, the reason for arriving at the above relational expression of the present invention will be explained in detail based on FIG.

FIG. 1 (bl shows the electrical equivalent circuit of the piezoelectric resonator 20, which shows the equivalent award amount L1 and equivalent compliance C7 when the mechanical vibration of the resonator 20 is replaced with an electric circuit.
and equivalent resistance r are connected in series, and the capacitance C0 of the piezoelectric resonator 20 is connected in parallel.

FIG. 1 fal is a circuit diagram in which a capacitor Cx is connected in series to the piezoelectric resonator 20.

First, in the case of only the piezoelectric resonator 20, in the equivalent circuit of FIG.
1+C+/C,-= (2) CI +C@-Cd
... The relational expression (3) holds true, and this expression ill, +21. From +31, CI
= (1-(ωr/ωa)”)Cd...(41
Ll m (a+a/ωr)" / (aha" -c
r”)Cd・
...(5).

Here, when a capacitor Cx is connected in series to the above equivalent circuit, the anti-resonant angular frequency ωa does not change, and only the resonant angular frequency ωr changes to ωr-ωrn. This ωrrl is expressed by the following formula.

(ωrn/ωr)'-1+ (1-(ωr/ωa)"
)Cd/Cx
・ ・ ・ (6) At this Niyama), Cd, C
Since x is a finite value, the right side is greater than or equal to 1, so ωr
n is always larger than cr. On the other hand, since the angular frequency range required for FM demodulation is limited between ωrn and ω3, it is better that ωrn not become larger than cr at the end of the spectrum. To satisfy this point, the above equation In (6), it is sufficient if Cx/Cd −N>>1.

Also, if the capacitance between the two terminals of the connected body when Cx is connected is Cdn, then Cdn = Cd - Cx/ (Cd + CX) - N - Cd
” / (Cd+N -Cd)-N-Cd/(1+N)
··· (sword .

becomes.

Now, due to temperature change, the capacitance between each terminal becomes Cd-α・C
d, Cx→β・CI, the above equation (the latter is expanded into the following equation).

Cdnma-β・Cd1x/ (cr ・Cd+β・C
I)-N・α・β・Cd” / (α・Cd+NβCd
)−N・α・β・Cd/ (α+Nβ) ・ ・
(8) Here, in the present invention, the above formula (7) and formula (8
) should be the same, so Cd-Cx/ (Cd+Cx) = N ・a-β・C
d/(α1N・β)...
・(9), and if β is represented by α and N in the formula (9), β--α/(N-α(1+N)l...
It will become a theme. In other words, the capacitor Cx connected in series with the piezoelectric resonator should have a temperature coefficient βΦ that satisfies the above formula α0.

[Effect]

According to the piezoelectric component according to the present invention, a capacitor is connected in series to the piezoelectric element, and the temperature coefficient of the capacitance between terminals of the piezoelectric element is
Since the temperature coefficient of the capacitance between the terminals of the capacitor and the temperature coefficient are set to meet a predetermined relational expression, in other words, capacitors with a temperature coefficient that can cancel out changes in the frequency-impedance characteristics due to temperature changes of the piezoelectric element are connected in series. Therefore, frequency deviation can be avoided.

〔Example〕

Examples of the present invention will be described below.

In this example, the relational expression β−−α/(NC1(1
+N)), Cx/Cd-N>>1, and design a piezoelectric resonator by applying specific values.

Now, ωr −10,35KH2, (IJ a−11,0
5MHz, ω. =10.70KH2, Cd=18PF,
If we choose Cx-18X17-3061F (N-17), the resonance angular frequency after connecting the capacitors in series is (ωrn)''-10,387 from the above equation (6).
MH2 tare 4° This value is the resonance angular frequency ωr = 10°3 before the above connection
5M) only 37KH2 (0,36%) compared to 12
This means that no deviation occurs.

On the other hand, if the temperature coefficient α of the piezoelectric resonator is 0.5%/℃, then from the above formula OI, β--0,005/(17-0,005(1+17)
1--0.0296%/°C.

As a result, the temperature coefficient β of the capacitor is -0,0296%
/'cs -30PpM/°C.

2 to 4 show the structure of the piezoelectric resonator according to this embodiment. In FIG. 0, reference numeral 1 indicates a chip-type piezoelectric resonator that utilizes energy-confined thickness vibration. This includes, from the top, the first capacitor unit 3°, the piezoelectric element 2. It is constructed by sequentially stacking second capacitor units 4.

As shown in FIG. 4 (bl), the piezoelectric element 2 has first and second vibrating electrodes 6a and 7a formed approximately at the center of the upper and lower surfaces of a ceramic piezoelectric substrate 5 and facing each other with the substrate 5 in between. Then, the first vibrating electrode 6a on the upper surface is led out to the center edge 5a of the right long side of the piezoelectric substrate 5 in the drawing by an extraction amount i6b, and the second vibrating electrode 7a on the lower surface is led out to the left side of the substrate 5 by an extraction electrode 7b. It is configured to be led out to the central edge 5b of the long side.

The first capacitor unit 3 has the above-mentioned temperature coefficient β, and as shown in FIG. 10a, and the capacitor electrode 9a on the upper surface is led out to the central edge 8a of the short side on the upper side of the substrate 8 in the drawing by an extraction electrode 9b, and the capacitor electrode 10a on the lower surface is led out to the right side of the substrate 8 by an extraction amount 110b. It is configured to be led out to the central edge 8b of the side.

Furthermore, the second capacitor unit 4 also has the above-mentioned temperature coefficient β, and as shown in FIG. . The extraction electrode 12b of the capacitor electrode 12a on the upper surface is located at the center edge 11a of the left long side of the capacitor unit 40 substrate 11 in the drawing.
At the same time, the extraction electrode 13b of the capacitor electrode 13a on the lower surface is connected to the center edge 1 of the lower short side of the substrate 11.
1b.

Then, the piezoelectric element 2 and the first . The overlapping surface of the second capacitor unit 3.4 is the vibrating electrode 6a.

7a and capacitor electrodes 10a and 12a,
In other words, the vibrating electrodes 6a, 7a are bonded together with an adhesive 14 with a predetermined gap that allows vibration of the vibrating electrodes 6a, 7a.

As a result, the extraction electrode 10b of the capacitor electrode 10a and the extraction electrode 6b of the vibrating electrode 6a, and the extraction electrode i7b of the vibrating electrode 7a and the extraction electrode 12b of the capacitor electrode 12a are connected.
are located on the same long side, respectively, and the extraction electrodes 9b and 13b of the capacitor electrodes 9a and 13a are respectively drawn out on the opposite short side, and both short sides of the piezoelectric resonator 1 A conductive external electrode 15 is attached to the side surface of the connector, and a relay bridge 16 is attached to the central portion of both long sides. As a result, the lead electrode 10b of the first capacitor unit 3 and the lead electrode 6b of the piezoelectric element 2 are connected, and the lead electrode 7b of the piezoelectric element 2 and the lead electrode 12b of the second capacitor unit 4 are connected. In this way, the piezoelectric element 2 receives the first. A piezoelectric resonator 1 is realized in which second capacitor units 3 and 4 are connected in series.

〔Effect of the invention〕

As described above, according to the piezoelectric component according to the present invention, a capacitor is connected in series to a piezoelectric element, and the temperature coefficient β of the capacitance Cx between the terminals of the capacitor and the temperature coefficient β of the capacitance Cd between the terminals of the piezoelectric element are determined as follows. α and β−−1α/(N−α(1
Since we selected a capacitor that satisfies the relationship: +N)), it is possible to avoid changes in the characteristics of the piezoelectric element due to temperature changes.

[Brief explanation of drawings]

FIG. 1 (al and FIG. 1 m) is an equivalent circuit diagram of a piezoelectric resonator for explaining the process of making the present invention, and FIGS. 2 to 4 are diagrams of piezoelectric resonators for realizing the present invention. show, second
The figure is a perspective view, FIG. 3 is a sectional view taken along the line m-m1a in FIG. 2, and FIGS. 5 is a bridge circuit diagram composed of a piezoelectric resonator and a constant resistor, and FIG. 6 is a characteristic diagram showing the relationship between impedance and angular frequency. In the figure, l indicates the piezoelectric resonator. (piezoelectric component), 2 is a piezoelectric element, 3.4 is a capacitor unit (capacitor), 5 is a piezoelectric substrate, 5a and 7a are first and second vibrating electrodes. Patent applicant Murata Manufacturing Co., Ltd. Agent Patent attorney Tsutomu ShimobuFigure 1Figure 3Figure 4

Claims (1)

[Claims] (1) In a piezoelectric element, first and second vibrating electrode films are formed on opposing main surfaces of a piezoelectric substrate with the substrate interposed therebetween,
In a piezoelectric component formed by connecting capacitors in series, the temperature coefficient α of the capacitance Cd between the terminals of the piezoelectric element and the temperature coefficient β of the capacitance Cx between the terminals of the capacitor are expressed by the following formula, β=-α/{N-α (1+N)}, where N=Cx/Cd>>1.