JPH0260221A - Piezoelectric vibrator - Google Patents

Abstract

PURPOSE:To easily generate the bulk wave piezoelectric vibrator of high connection, which has a basic wave mode vibration wave in a VHF band by setting the peripheral rotary angle theta of an electric axis to an angle within a specified range in a thickness longitudinal vibrator where a rotary Y plate or a X plate is used. CONSTITUTION:The thickness vertical vibrator is set by using the rotary Y plate or the rotary X plate of a Li2B4O7 single crystal, and the peripheral rotary angle of the electric axis is set within the range of 37 deg. to 45 deg.. The phase speed Vp of the rotary Y plate or the rotary X plate is such a high speed that it shows 7420<=Vp<=7540m/s. Consequently, the vibrator having the basic wave mode vibration wave in the VHF band can be manufactured. The thickness H of the vibrator when the frequency F is set to 30-150MHz goes to 24.2<=H<124mum. Since a grinding processing can sufficiently be executed in such value, the VHF band vibrator can easily be manufactured. Since the electric mechanical connection factor K<2> of the Y plate or the X plate shows 4%<K<25%, the thickness longitudinal vibrator of high connection can be obtained.

Description

[Detailed Description of the Invention] [Summary] Regarding a piezoelectric vibrator for the VHF band (30 to 150 MHz), the present invention aims to easily realize a highly coupled bulk wave piezoelectric vibrator having a fundamental mode vibration wave in the VHF band. The purpose is to use a thickness longitudinal oscillator using a rotating Y plate or rotating X plate of LitBaOt single crystal, and to set the rotation angle θ around the electric axis within the range of 37"<lθ1≦45". According to
Enables vibrational energy to be confined within the region between opposing electrodes.

[Industrial application field]

The present invention relates to a piezoelectric vibrator for the VHF band (30 to 150 MHz), and more particularly to a highly coupled bulk wave piezoelectric vibrator having a fundamental mode vibration wave in the VHF band.

[Prior art and problems to be solved by the invention] 30-1
As a VHFHF band around 50 MHz, there are known vibrators that use bulk waves, such as those that utilize higher-order modes (third or fifth order) of thickness shear waves or thickness torsional waves, and surface acoustic wave A grating-type SAW resonator (resonator) that uses a reflector to confine SAW energy on the surface is known.

Since the fundamental wave of the bulk wave oscillator has the optimum size in the HF band, it is necessary to pass higher-order modes in the VHF band for -C, but if you dare to apply the fundamental wave, It is necessary to make the thickness as thin as possible (10 to 20
μm), manufacturing becomes extremely difficult. Furthermore, even in the case of using a higher-order mode, a filter for filtering the fundamental wave is required in order to apply it to an oscillator, a filter, etc., and there is a drawback that the peripheral circuit becomes large. Furthermore, in the case of higher-order modes, the degree of coupling is small, making it difficult to apply to wide-band filters, oscillators with large variable widths, and the like.

On the other hand, the optimum frequency for SAW resonators is 200M
VHF band and UHF band above Hz, 100MH! If used in close proximity, the element becomes large, which hinders the miniaturization of oscillators and filters.

Further, since the grating type SAW resonator has a large capacitance ratio, it is not suitable for a wideband filter or an oscillator with a large variable width.

Therefore, an object of the present invention is to easily realize a piezoelectric vibrator having a fundamental mode vibration wave within the VHF band and having high coupling, that is, a large electromechanical coupling coefficient.

[Means to solve the problem]

In order to achieve the above object, in the present invention, LigB
A thickness longitudinal oscillator using a rotating Y plate or rotating X plate of aOt single crystal is used, and the rotation angle θ around the electric axis is 37@<lθ1.
By setting the angle within the range of ≦45°, it is possible to confine vibrational energy within the region between opposing electrodes.

[For production]

In the piezoelectric vibrator having the above configuration, the angle is 37° and 1θ
The phase velocity Vp of the rotating Y plate or rotating X plate of Li1B40 within the range l≦45° is 742°≦Vp≦7540
Since the speed is as high as m/s, it is possible to manufacture a vibrator having a fundamental mode vibration wave within the VHF band.

Also, l, 1 within the range of 37@<101≦45°
The frequency constant FH of the rotating Y plate or rotating X plate of gB4O is 3
Since 630≦FH<3710Hz・-, the frequency F
When the frequency is 30 to 150 MHz, the thickness H of the vibrator satisfies 24.2≦H<124 μm. Since this value is sufficient to allow polishing, a VHF band vibrator can be easily manufactured.

Moreover, by setting 1θl>37″, it becomes possible to confine vibrational energy within the region between the central opposing electrodes.

In addition, by setting it within the range of 37@<101≦45°, Δfr/frl within the temperature range of 0 to 100°C.
The target value of ≦5oopp- can be met,
A thickness longitudinal vibrator with good temperature characteristics can be realized.

Furthermore, Li1 within the range of 37°<1θ1≦45°
Ba0y - Electromechanical coupling coefficient of rotating Y plate or rotating X plate''
Since 4%<K155%, a highly coupled thick longitudinal oscillator can be realized.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

Lithium borate (L i t Ba 0?) single crystal was developed as a SAW material with a high degree of bonding (K"mtt ' 1%), but the present inventor has developed Li z Ba 0?
Focusing on the low density of a single crystal of 2435 kg/m'', and using a Li2840w single crystal as a thickness oscillator of a rotating Y plate or a rotating Focusing on the fact that it can be piezoelectrically excited by an electric field, we considered realizing a VHF band vibrator using thickness longitudinal vibration with a high propagation velocity (phase velocity).

Figure 1 shows L i z Ba 0? This figure shows a single-crystal rotating Y plate (hereinafter referred to as L i * Ba Ot rotating Y plate) and its coordinate system. Electrical and mechanical coupling coefficients of thickness longitudinal vibration waves! , which shows the rotation angle dependence of the phase velocity Vp, the frequency temperature coefficient, and the frequency constant FH. Here, the direction of rotation in the counterclockwise direction around the X axis, that is, the electric axis is defined as positive (+). But L l x Ba
0? Since the single crystal has a square symmetry (4+++m), even when it is rotated clockwise (negative (-) direction), the same characteristics can be obtained as when it is rotated counterclockwise. In other words, +〇 and -θ give the same result, so θ
The absolute value 1θ of is significant.

From FIG. 2, it can be seen that as the rotation angle 1θ1 increases, the coupling coefficient increases rapidly by 2, and there is a rotation angle θ where K2>1%. The Li2B4O7 rotating Y-plate resonator can be used as a high-coupling resonator, considering that the crystal resonator (using thickness-shear waves), which is known as a highly stable resonator, has a ratio of about 2#0.5%. It turns out that.

In addition, as can be seen from Fig. 3, the phase velocity Vp of the Li 1 B409 rotating Y plate is 5500≦Vp≦7600m/
s, it is clear that it is possible to manufacture a vibrator having a fundamental mode vibration wave within the VHF band.

In order to realize a vibrator with good temperature characteristics, the rotation angle θ at which the primary frequency temperature coefficient becomes zero is required. oscillator is required. From Figure 4, the rotation angle 1θI that gives zero temperature coefficient is 32°.
It is. The frequency constant FH at this time is approximately 3740Hz-
m (see Figure 5), so the frequency F is set to 1, for example.
00 MHz, the thickness H of the vibrator is 37 μm. This value is sufficient for polishing, so 10
It can be seen that a 0 MHz Ji mover can be easily manufactured.

However, as shown in Figure 6, the dispersion characteristics of thickness longitudinal oscillation waves generally have a high-frequency cut-off type, making it impossible to realize energy confinement using the mass addition of the central electrode and piezoelectric reaction. In many cases, the above 32° rotation Y
Li, B using a plate.

0, the thickness longitudinal oscillator is no exception, and the thickness longitudinal fundamental wave (TE
The phase velocity of the thickness-shear wave (I mode) is the second mode of the thickness-shear wave (T
S2 mode). Therefore, in the case of thickness-shear waves, the energy can be confined within the central interelectrode region within the vibrator, as shown in Figure 7, but in the case of thickness-longitudinal vibration, the vibration energy can be confined within the vibrator. cannot be confined within the interelectrode region.

If a vibrator that cannot realize energy confinement is used, it will be difficult to support the peripheral portion, and the support will cause deterioration of vibration characteristics.

On the other hand, FIG. 8 shows the rotation angle dependence of the phase velocity Vp of the thickness shear wave (fast mode and slow mode) in the Li, B, 7-rotation Y plate. Here, when we compare and examine the phase velocity characteristics of the thickness longitudinal oscillation wave in Figure 3 and the thickness shear wave in Figure 8, we find that in the latter slow mode, the phase velocity Vp is approximately 3920 when 1θ = 32°.
m/s, but as iθI increases, the phase velocity Vp becomes
The phase velocity decreases rapidly, and when 50°≦Iθ1≦559, the phase velocity decreases by about 600a+/s to about 3350 m/s.

On the other hand, in the case of the former thickness longitudinal vibration, the change in the phase velocity Vp is small, and the phase velocity difference between 1θ1=32° and 1θ1=50' is about 300 m/s, about half of the latter.

Therefore, within a limited range of 1θ1 from around 35°C to around 60°, the dispersion characteristics of the fundamental wave mode (TEI mode) of thickness longitudinal vibration shift from high-speed profile characteristics to low-frequency cutoff characteristics. is possible. In view of these points,
The present inventor attempted a theoretical analysis of the dispersion characteristics of the thickness longitudinal vibration wave in a rotating Y plate for the 12B40, and found an appropriate rotation angle to reverse the high-speed profile characteristic to the low-frequency cut-off type characteristic.

Figure 9 shows a model for analyzing thickness longitudinal vibration. Here, it is assumed that the waves vibrate in the thickness direction (Y' force direction and propagate in the Z' force direction. The mass of the electrode is ignored, and it is assumed that it is uniform in the X direction.

The displacement in the y and z directions and the electric potential are expressed as U y=
A ei tl y eI (βtot)Uz=Be”
αY eth βt) ψ = CeIαy e i (Set β wing −wt+, substitute the above equation into the equation of the piezoelectric base, and y=0°) A solution that satisfies the mechanical and electrical boundary conditions at l = H seek. Here, α and β represent complex number propagation constants in the X direction and two directions, respectively. The analysis results are shown in FIGS. 10 to 12.

Figure 10 shows the dispersion characteristics when there is no electrode in the local mode and TS2 mode when 1θ1 is 35'' and 45°.Here, Ω on the vertical axis represents the angular frequency ω (2π/2H ) M ρ, indicates the angular frequency standardized by ρ, C++(0) indicates the elastic constant C0 value when the rotation angle lθ1 is 06, and ρ is the density.In other words, the horizontal axis is the wave number The real part of the product βH of β and thickness H (Re
) and the imaginary part (1m) are shown. From Figure 10, θI=35
”, the normalized angular frequency or cutoff frequency at βH=0 of each mode is Ω”Tll+Ω’? ! ! +
Then, Ω'tst > Ω07□,
This is a high-speed profile dispersion characteristic that is commonly seen in thickness longitudinal vibrations. On the other hand, when 1θ=45°, Ω0
T□〉Ω・1,2, which is reversed, and has a low-speed profile dispersion characteristic.

FIG. 11 shows the results of a more detailed analysis of the case of 1θ1-40°. In FIG. 11, the solid line shows the dispersion characteristic when there is no electrode (electrode non-short circuit state B), and the broken line shows the dispersion characteristic when the electrode is added on the surface (electrode short circuit state).

In the resonant state, it is considered that the electrodes are short-circuited, so the angular frequency Ω decreases due to piezoelectric reaction. Near the cutoff frequency (βH=0), TE
In I mode, the angular frequency Ω decreases significantly (approximately 1.008
However, in the case of TS2 mode, the angular frequency Ω is hardly affected (Ω#0.9
67), it is possible to confine the vibrational energy of the TEI mode within the interelectrode region in the low-velocity profile dispersion characteristic as shown in FIG. That is, when using the vicinity of βH-0, the wave number β becomes a real number (Re) in the interelectrode region.
On the other hand, since it becomes an imaginary number (In) in the electrodeless part,
Waves decay exponentially as they propagate.

Figure 12 is l, iz Ba O? This figure shows the dependence of the cut-off frequency ΩO of the TEI mode and TS2 mode of the thickness longitudinal vibration wave in the rotating Y plate on the rotation angle 1θ1. From FIG. 12, when there are no electrodes, the following will occur.

1θ1≦35.4”j Ω0!32≧Ω0Ttl(
High frequency cutoff type) θ l>35.4': Ω6te sz< Ω
0TE1 (Low cutoff type) On the other hand, when the electrodes are short-circuited, the following occurs.

θ 1 ≦ 37 @: Ω'71! ≧
Ω'? ! 1 (high-frequency cutoff type) θl>37@: Ω'ys*<Ω”ttI (low-frequency cutoff type) Therefore, when 1θI>37°, it is possible to confine vibration energy within the region between the central opposing electrodes. It turned out that.

On the other hand, it is desired that the energy confinement type resonator has good temperature characteristics. Therefore, FIG. 13' shows the analysis results of the temperature characteristics in the TRI mode when the electrodes are provided on an infinite plane.

From FIG. 13, it can be seen that within the temperature range of 0 to 100° C., the angle that can approximately satisfy the target value of Δ fr/frl ≦ 500 pp is 35° and 1θ≦45@. Here, fr is the resonance frequency (reference resonance frequency) at the reference temperature (25° C.), and Δfr is the difference between the resonance frequency at each temperature and the reference resonance frequency.

On the other hand, the electromechanical coupling coefficient! is 37°〈1θ≦45@
It can be seen that K''-4 to 5% (see Fig. 2) is obtained, and a high degree of bonding can be obtained.

From the above analysis results, it was found that by setting 1θ1 to 37@<lθ≦45°, it was possible to easily confine the energy of a highly coupled and highly stable thickness longitudinal vibration wave within the central interelectrode region. .

The above analysis was conducted for the thickness longitudinal vibration propagating in the direction of L, i z Ba Ot O-rotated Y plate Z', but L
ig Due to the symmetry of Ba Oy single crystal, Li2B4O7
It is clear that exactly the same result can be obtained for the rotating X-plate Z' direction propagation curve (see FIG. 14).

〔Effect of the invention〕

As is clear from the above description, according to the configuration of the present invention, it is possible to confine vibrational energy within the region between opposing electrodes within the vibrator, so a vibrator with a high Q value can be obtained. , high coupling degree and good temperature characteristics, fundamental frequency is VH
A vibrator having an F band can be easily obtained. Therefore, by applying the vibrator according to the present invention to a filter, an oscillator, etc., a broadband, highly stable, and compact VHF band device can be easily obtained.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the l, izB40w rotating Y plate according to the present invention and its coordinate system, Fig. 2 is a diagram showing the rotation angle dependence of the electromechanical coupling coefficient of the thickness longitudinal vibration wave in the L+zBa○1 rotating Y plate, Figure 3 is a diagram showing the rotation angle dependence of the phase velocity of the thickness longitudinal vibration wave in the L 42 Ba 07 rotating Y plate, and Figure 4 is the
Figure 5 shows the rotation angle dependence of the frequency constant of the thickness longitudinal vibration wave in the L it Ba 01 rotation Y plate. Figure 6 is a diagram showing the dispersion characteristics of a thickness longitudinal vibration wave, Figure 7 is a diagram showing a thickness shear wave excitation model, and Figure 8 is a diagram showing the thickness shear wave excitation model.
? A diagram showing the rotation angle dependence of the phase velocity of the thickness shear wave in a rotating Y plate, FIG. 9 is L L Ba 0? A diagram showing the thickness longitudinal vibration wave excitation model in the rotating Y plate, Figure 10 is Lit B40? Figure 11 is a diagram showing the dispersion characteristics of angular frequency in a rotating Y plate. Figure 11 is a diagram showing the dispersion characteristics of angular frequency in a 406 rotation Y plate. Figure 12 is a diagram showing the cutoff of longitudinal vibration waves in the Li2 Ba Oq rotating Y plate. A diagram showing the rotation angle dependence of vibration frequency, FIG. 13 is a diagram showing the temperature characteristics of TEI mode of L iz B40q rotation Y plate thickness longitudinal vibration, and FIG. 14 is a diagram showing the temperature characteristics of L iz Ba Oq rotation X according to the present invention.
It is a diagram showing a plate and its coordinate system. Fig. Thickness shear wave excitation model Fig. Thickness longitudinal vibration wave excitation model Fig. L12B4O7 Temperature characteristics of thickness longitudinal vibration TEI mode seen in rotating Y plate Fig. 13 (C axis) LI28407 rotating X plate and its coordinate system Fig. 14

Claims (1)

[Claims] 1. Rotating Y plate or rotating X of Li_2B_4O_7 single crystal
This is a thickness longitudinal vibrator using a plate, and by setting the rotation angle θ around the electric axis within the range of 37°<|θ|≦45°, vibration energy is confined within the region between opposing electrodes. A piezoelectric vibrator that is characterized by being able to.