JPH11112281A - Oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide stable oscillation with high Q and less spurious by using single crystal whose crystal orientation of lithium niobate is specified rotary Y cut and whose transmission direction is a Y-axis projection direction for a piezoelectric substrate. SOLUTION: In an oscillator, a pair of comb-like electrodes 2 and 3 are formed on the surface of the strip-like piezoelectric substrate 1. High frequency signals are applied to a pair of comb-like electrodes 2 and 3 from a signal generation source 4. The comb teeth parts 2a, 2a,... and the comb teeth parts 3a, 3a... of the comb-like electrodes 2 and 3 are formed and arranged to be vertical to the longitudinal direction (transmission direction) of the piezoelectric substrate 1. When the high frequency signal is applied to the electrodes 2 and 3 from the signal generation source 4, the surface acoustic wave 5 is generated and it travels on the surface of the piezoelectric substrate 1 in the longitudinal direction. A bulk wave 6 travels in the thickness of the piezoelectric substrate 1. The single crystal of lithium niobate is used as the piezoelectric substrate 1 and that whose crystal orientation is 41±15 deg. rotary cut and whose transmission direction of the surface acoustic wave is the Y-axis projection direction is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a vibrator using a piezoelectric substrate made of lithium niobate (LiNbO ₃ ) single crystal.

[0002]

2. Description of the Related Art In a conventional surface acoustic wave oscillator, a pair of comb-shaped electrodes are formed on a piezoelectric substrate made of lithium niobate single crystal, and a high frequency signal is applied to these electrodes from a signal generating source. There is something. As a piezoelectric substrate used for this surface acoustic wave vibrator, LiNbO ₃ rotation Y cut, S
This is a T-cut quartz crystal or the like, which utilizes a Rayleigh wave excited on the surface. However, these piezoelectric substrates have low vibration efficiency. Therefore, in order to improve the vibration efficiency, a comb-shaped electrode such as Au, Ag, or Pt is attached to the surface of the niobate lithium niobate substrate having a rotation angle of −10 ° to + 40 ° and a rotation Y-cut to propagate the love wave in the X direction of the substrate. A vibrator has been proposed (JP-A-63-260213).

[0003]

However, in the above-mentioned conventional vibrator, as a result of experiments by the inventors of the present application, the vibration Q is low, spurious components are distributed over the entire area, and the vibrator is still improved. There was a problem that needed to be. The present invention has been made in view of the above problems, and has as its object to provide a vibrator having higher vibration efficiency and stable vibration.

[0004]

A vibrator according to claim 1 of the present specification of the present application is formed on a piezoelectric substrate made of a single crystal of lithium niobate and a surface of the piezoelectric substrate. In a vibrator comprising an excitation electrode for generating an elastic wave, the crystal orientation of the lithium niobate single crystal is rotated by 41 ± 15 ° Y-cut, and the propagation direction of the elastic wave is Y.
It is characterized by the axial projection direction.

In this vibrator, a piezoelectric substrate having a crystal orientation of lithium niobate of 41 ± 15 ° rotation Y-cut and a propagation direction of an elastic wave in a Y-axis projection direction is used. As a result of the experiment, a sample having high Q and low spurious was obtained. Further, according to a second aspect of the present invention, in the oscillator according to the first aspect, the thickness of the piezoelectric substrate is set to a value such that the bulk vibration frequency and the surface wave vibration frequency are different.

[0006] This vibrator is characterized in that the bulk vibration frequency is used for the vibration. If the vibration frequency of the bulk and the vibration frequency of the surface wave are close to each other, the oscillation frequency becomes large due to disturbance such as ambient temperature conditions. A complicated oscillation control circuit is required to move from the vibration frequency to the surface wave vibration frequency or to avoid this. On the other hand, since the vibration frequency of the bulk is correlated with the thickness of the piezoelectric substrate, by appropriately setting the thickness, the vibration frequency of the bulk and the vibration frequency of the surface wave are made different, so that the vibration can be stabilized. .

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to embodiments. FIG. 1 is a view schematically showing a vibrator according to one embodiment of the present invention. In this vibrator, a pair of comb-shaped electrodes 2 and 3 are formed on the surface of a strip-shaped piezoelectric substrate 1, and a high-frequency signal is applied to the pair of comb-shaped electrodes 2 and 3 from a signal generation source 4. .

[0008] Comb portions 2a, 2a of the comb-like electrodes 2, 3 ...
Are formed and arranged so as to be perpendicular to the longitudinal direction (propagation direction) of the piezoelectric substrate 1.
When a high frequency signal is applied to the electrodes 2 and 3 from the signal generation source 4, a surface acoustic wave 5 is generated and travels on the surface of the piezoelectric substrate 1 in the longitudinal direction. In addition, the bulk wave 6 within the thickness of the piezoelectric substrate 1
Progresses.

The most distinctive feature of this embodiment is that a single crystal of lithium niobate is used as the piezoelectric substrate 1, its crystal orientation is 41 ° rotated Y-cut, and the propagation direction of the elastic wave is in the Y-axis projection direction. That is, we used something. As shown in FIG. 2, this piezoelectric substrate 1 has a piezoelectric body 1 in which a piezoelectric crystal is grown in an ingot at an angle of 131 ° on the Y axis.
1 and a strip-shaped piezoelectric substrate 12 is cut out from the piezoelectric body 11. The piezoelectric substrate 12 has a 41 ° rotation Y cut having an angle of 41 ° with respect to the Y axis, and its longitudinal direction is the Y axis projection direction. That is, the propagation direction of the bulk wave and the surface wave is the Y-axis projection direction.

Here, propagation of a bulk wave in the piezoelectric substrate 1 will be described with reference to FIG. The bulk wave 6 is applied to the piezoelectric substrate 1
Assuming that the normal direction of the isophase surface of the bulk wave 6 excited and propagated obliquely to the direction is θ, as shown in the figure, θ is given by the following equation, and the direction changes according to the frequency. I do. θ = sin (Vb / P · f) where Vb is the phase velocity of the bulk wave, P is the pitch of the comb-shaped electrode, and f is the frequency.

In this piezoelectric substrate 1, the vibration source of the piezoelectric substrate 1 is a comb-toothed portion 2 of alternately formed comb-shaped electrodes 2, 3.
a and 3a, and the generated vibration waves are a surface wave 5 and a bulk wave 6. The bulk wave 6 propagates while reflecting on the boundary surface of the piezoelectric substrate 1. The vibration frequency of the surface wave 5 excited by the comb-shaped electrodes 2 and 3 is mainly determined by the sound velocity and the electrode pitch on the surface.
Is determined by the thickness t. Specifically, the pitch P between the same poles of the comb-shaped electrode is desirably about 0.2 to 1.5 mm, and the thickness t of the piezoelectric substrate 1 is, for example, 0.1 mm.
A thickness of 5 to 1.5 mm is desirable.

When the vibration frequency of the surface wave 5 and the bulk wave vibration frequency are close to each other, the operation at the surface wave vibration frequency, the operation at the bulk wave vibration frequency, or the unstable frequency due to a slight change in the vibration load. In order to prevent this, the configuration of the oscillation circuit may be complicated. To avoid this, the thickness t of the piezoelectric substrate 1 is selected so that the bulk vibration frequency differs from the surface wave vibration frequency. As a specific difference between the bulk vibration frequency and the surface vibration frequency, if there is a difference of about 2 MHz from the experimental results, a stable vibration can be obtained as the frequency.

In an experiment, the impedance was measured while changing the signal frequency of the signal source 1 from 5 MHz to 9 MHz on a piezoelectric substrate having a Y-cut of 41 ° rotation and a propagation direction of the X-axis projection direction. Obtained. In the characteristics of FIG. 5, Q is low and spurious is generated in a considerable wave range. On the other hand, when the same measurement was performed using the piezoelectric substrate used in the above-described embodiment, that is, the piezoelectric element in which the Y direction was 41 ° rotated and the propagation direction was the Y-axis projection direction, 7.57 MHZ was obtained as shown in FIG. (Shown by ○), a high Q resonance characteristic is obtained, and almost no spurious is generated in other wave ranges.

In the above embodiment, the rotation Y-cut angle is set to 41 °. However, the angle of rotation is within a range of 41 ° ± 15 °, and the propagation direction of the elastic wave is within a range of ± 10 ° from the Y-axis projection direction. A sufficiently practical vibrator can be obtained even with the deviation.

[0015]

According to the present invention, since a piezoelectric substrate having a crystal orientation of lithium niobate of 41 ± 15 ° rotation Y-cut and a propagation orientation in the Y-axis projection direction is used for the piezoelectric substrate,
Stable vibration with high Q and little spurious can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a vibrator according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a crystal orientation cut and a propagation direction of a piezoelectric substrate used in the resonator according to the embodiment.

FIG. 3 is a diagram for explaining propagation of a bulk wave as a surface wave of the resonator according to the embodiment.

FIG. 4 is a diagram showing frequency-impedance characteristics of the resonator according to the embodiment.

FIG. 5 shows that the crystal orientation is rotated by 41 ° Y on the piezoelectric substrate of the vibrator.
It is a figure which shows the frequency-impedance characteristic at the time of cutting and the propagation direction using an X-axis projection direction.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric substrate 2, 3 Comb electrode 4 Signal generator 5 Surface wave 6 Bulk wave

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kei Asai 24, Yamanouchi Yamanoshitamachi, Ukyo-ku, Kyoto-shi Inside Omron Life Science Laboratory Co., Ltd. Science Institute

Claims (2)

[Claims] 1. A vibrator comprising a piezoelectric substrate made of a lithium niobate single crystal and an excitation electrode for generating an elastic wave formed on a surface of the piezoelectric substrate, wherein the crystal orientation of the lithium niobate single crystal is 41. ± 15
A vibrator characterized in that the rotation Y-cut and the propagation direction of the elastic wave are set to the Y-axis projection direction. 2. The vibrator according to claim 1, wherein said piezoelectric substrate has a thickness set such that a bulk vibration frequency and a surface wave vibration frequency are different from each other.