JP2010074224A - Saw resonator and saw oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a SAW resonator with an improved Q value and a SAW oscillator with the SAW resonator. <P>SOLUTION: The SAW resonator 1 includes a crystal substrate 10, two adjacent IDT electrodes 20 and 21 provided on the main surface 11 of the crystal substrate 10, and reflectors 30 and 31 provided on both sides of the two IDT electrodes 20 and 21. When a gap between the two IDT electrodes 20 and 21 is defined as D, the pitch of the electrode fingers 20a, 21a, 21a and 21b of the IDT electrodes 20 and 21 is defined as Lt, and the pitch of the electrode fingers 30a and 31a of the reflectors 30 and 31 is defined as Lr, two relation expressions, which are (1): n×(Lt/2)<D<0.045×Lt+n×(Lt/2) (provided that n is an integer ≥0) and (2):-0.02667×D+0.9992≤Lt/Lr≤-0.00667×D+0.9996, are satisfied. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a SAW resonator and a SAW oscillator including the SAW resonator, and more particularly to a Q value of the SAW resonator.

Conventionally, a plurality of grating reflectors (hereinafter referred to as reflectors), at least one excitation cross-finger electrode and reception cross-finger electrode (hereinafter referred to as IDT electrode) disposed between the reflectors, Is formed on a piezoelectric substrate (hereinafter referred to as a quartz substrate), and the distance l1 between two IDT electrodes is (2n + 1) L / 4 <l1 <(n + 1) L / 2: n = 0, 1, 2,...) Is known (for example, see Patent Document 1).
In the surface acoustic wave device, the distance l1 between the two IDT electrodes is set as described above, so that a plurality of resonance modes exist, and when used in a SAW filter as a surface acoustic wave device, the passband is widened. Is possible.

JP-A-61-192112

However, the surface acoustic wave device has a lower Q value in exchange for a wider passband. As a result, when the configuration of the surface acoustic wave device is applied to a SAW resonator as a surface acoustic wave device, for example, it is more than 2000 which is a required specification when used for a high-accuracy SAW oscillator in the GHz band. Q value cannot be obtained.
For this reason, the SAW oscillator using the SAW resonator has a problem that the phase noise characteristic that greatly depends on the Q value of the SAW resonator is not improved, and the desired performance cannot be satisfied.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

  Application Example 1 A SAW resonator according to this application example includes a quartz substrate, two adjacent IDT electrodes provided on the main surface of the quartz substrate, and reflectors provided on both sides of the two IDT electrodes. When the gap between the two IDT electrodes is D, the pitch of the electrode fingers of the two IDT electrodes is Lt, and the pitch of the electrode fingers of the reflector is Lr, (1): n * (Lt / 2) <D <0.045 * Lt + n * (Lt / 2) (where n is an integer of 0 or more) (2): -0.02667 * D + 0.9999≤Lt / Lr≤-0. It satisfies the following two relational expressions: 00667 × D + 0.9996.

  According to this, the SAW resonator has (1): n × (Lt / 2) <D <0.045 × Lt + n × (Lt / 2) (where n is an integer of 0 or more), (2): -0.02667 × D + 0.9999 ≦ Lt / Lr ≦ −0.00667 × D + 0.9996 is satisfied.

  By satisfying these two relational expressions, the SAW resonator can have, for example, an insertion loss of 9 dB or less, a spurious level of 10 dBc or more, and a Q value of 2000 or more.

  Application Example 2 In the SAW resonator according to the above application example, it is preferable that the Euler angles of the quartz crystal substrate are (0 °, 113 ° to 135 °, ± (40 ° to 49 °)).

According to this, since the Euler angles of the quartz substrate are (0 °, 113 ° to 135 °, ± (40 ° to 49 °)), the SAW resonator reduces the secondary temperature coefficient of the quartz substrate. can do.
For this reason, the SAW resonator can obtain excellent frequency temperature characteristics with less frequency fluctuation accompanying ambient temperature change.

  Application Example 3 A SAW oscillator according to this application example includes the SAW resonator according to Application Example 1 or 2, and an oscillation circuit that excites the SAW resonator.

  According to this, since the SAW oscillator includes the SAW resonator described in Application Example 1 or 2, and the oscillation circuit that excites the SAW resonator, the phase noise characteristic during oscillation is improved, and a desired The performance can be satisfied.

  Hereinafter, embodiments of the SAW resonator and the SAW oscillator will be described with reference to the drawings.

(Embodiment)
FIG. 1 is a schematic plan view showing the main configuration of the SAW resonator of the present embodiment.
As shown in FIG. 1, the SAW resonator 1 includes a flat crystal substrate 10 having a substantially rectangular planar shape, and two adjacent IDT electrodes 20 and 21 provided on the main surface 11 of the crystal substrate 10. The reflectors 30 and 31 provided on both sides of the two IDT electrodes 20 and 21 are provided.

The quartz substrate 10 is formed from a quartz wafer or the like polished to a predetermined thickness so that the Euler angles are (0 °, 127 °, 45 °). The Euler angles of the quartz substrate 10 do not need to be limited to (0 °, 127 °, 45 °), and are selected from the range of (0 °, 113 ° to 135 °, ± (40 ° to 49 °)). it can. Within this range, the SAW resonator 1 having a good frequency temperature characteristic with a small secondary temperature coefficient can be obtained.
The IDT electrodes 20 and 21 and the reflectors 30 and 31 are formed using a photolithography technique or the like after a conductive metal is formed into a thin film on the main surface 11 of the quartz substrate 10 by vapor deposition or sputtering. In addition, metals such as aluminum and aluminum alloys are used as the conductor metal, but other metals such as gold, silver, copper, tantalum, and tungsten, and alloys based on any of these metals should be used. Is possible.
The IDT electrodes 20 and 21 and the reflectors 30 and 31 are formed so that t / λ (wavelength of SAW (surface acoustic wave)) = 0.05, where t is a thickness not shown. . Note that t / λ = 0.05 is an example, and t / λ may be a value other than 0.05.

The IDT electrodes 20 and 21 are composed of a plurality of pairs of comb-like electrode fingers 20a, 20b, 21a, and 21b that mesh with each other, and the electrode fingers 20a, 20b, 21a, and 21b each have one end in the extending direction (longitudinal direction). Commonly connected.
The reflectors 30 and 31 include a plurality of electrode fingers 30a and 31a, and the electrode fingers 30a and 31a are commonly connected at both ends in the extending direction. However, the common connection location may not be at both ends in the extending direction of the electrode fingers 30a and 31a. For example, it may be at either one end in the extending direction, or is commonly connected at the center in the extending direction. May be.

Here, in the SAW resonator 1, the gap between the two IDT electrodes 20, 21 is D, the pitch of the electrode fingers 20a, 20b, 21a, 21b of the IDT electrodes 20, 21 is Lt, and the reflectors 30, 31 When the pitch of the electrode fingers 30a and 31a is Lr,
(1): n × (Lt / 2) <D <0.045 × Lt + n × (Lt / 2) (where n is an integer of 0 or more),
(2): −0.02667 × D + 0.9999 ≦ Lt / Lr ≦ −0.00667 × D + 0.9996,
It is the structure which satisfy | fills these two relational expressions.
Note that the gap D is a distance obtained by subtracting a total of Lt / 2 by Lt / 4 on one side from the distance L1 between the center lines along the extending direction of the electrode fingers 20b, 21a adjacent to the IDT electrodes 20, 21. It is.

  Further, the distance L2 between the center lines along the extending direction of the electrode fingers 20a, 30a adjacent to the IDT electrode 20 and the reflector 30, and the electrode fingers 21b adjacent to the IDT electrode 21 and the reflector 31, The distance L3 between the respective centerlines along the extending direction of 31a is (Lt + Lr) / 4.

Here, the setting process of the gaps D and Lt / Lr will be described with reference to the drawings.
The inventors set the gaps D and Lt / Lr by the following procedures using methods such as simulation and confirmation of prototype samples. In the simulation, n in the relational expression (1) was set to 0.

The required specifications for the SAW resonator used in, for example, a high-accuracy SAW oscillator in the GHz band, which is a precondition for setting, are as follows.
-Q value: 2000 or more.
-Insertion loss: 9 dB or less.
-Spurious level: 10 dBc or more.

First, Lt / Lr was fixed at 0.999, and the relationship between the gap D, the insertion loss, and the spurious level was grasped by simulation.
FIG. 2 is a graph showing the relationship between the gap D, the insertion loss, and the spurious level. FIG. 2A is a graph showing the relationship between the gap D and the insertion loss, and FIG. 2B is a graph showing the relationship between the gap D and the spurious level.

  As shown in FIG. 2A, the value of the gap D that satisfies the insertion loss of 9 dB or less is −0.1 Lt to +0.06 Lt. Further, as shown in FIG. 2B, the value of the gap D that satisfies the spurious level of 10 dBc or more is −0.1 Lt to +0.12 Lt.

Next, the gap D was fixed at +0.03 Lt, and the relationship between Lt / Lr, insertion loss, and Q value was grasped by simulation.
FIG. 3 is a graph showing the relationship between Lt / Lr, insertion loss, and Q value. FIG. 3A is a graph showing a relationship between Lt / Lr and insertion loss, and FIG. 3B is a graph showing a relationship between Lt / Lr and Q value.

As shown in FIG. 3A, the insertion loss increases as Lt / Lr approaches 1, and when Lt / Lr exceeds 0.9995, it becomes 9 dB or more.
Further, as shown in FIG. 3B, the Q value increases as Lt / Lr approaches 1, and becomes 2000 or more in the vicinity.

Next, the relationship between Lt / Lr, insertion loss, and Q value when the gap D was changed from 0 Lt to +0.09 Lt was grasped by simulation.
FIG. 4 is a graph showing the relationship between Lt / Lr of each gap D, insertion loss, and Q value. FIG. 4A is a graph showing the relationship between Lt / Lr and insertion loss of each gap D, and FIG. 4B shows the relationship between Lt / Lr and Q value of each gap D. It is a graph.

As shown in FIG. 4A, the insertion loss is 9 dB or more when Lt / Lr exceeds 0.9996 when the gap D is 0 Lt, and Lt / Lr is 0 when the gap D is +0.015 Lt. Over 99.99, when the gap D is +0.03 Lt, over 90.995 when Lt / Lr exceeds 0.9995.
Furthermore, when the gap D is + 0.045Lt, the insertion loss becomes 9 dB or more when Lt / Lr exceeds 0.9993, and when the gap D is + 0.06Lt, when Lt / Lr exceeds 0.9999, 9 dB or more.

As shown in FIG. 4B, when the gap D is 0 Lt, the Q value is 2000 or more when the Lt / Lr exceeds 0.9992, and when the gap D is +0.015 Lt, the Lt / Lr is 0. When .9988 is exceeded, it is 2000 or more. When the gap D is +0.03 Lt, when Lt / Lr exceeds 0.9982, it is 2000 or more.
Further, when the gap D is +0.045 Lt or more, the Q value is 0.9980, which is 0.9980, which exceeds 2000.

Next, based on the above-described contents, the gap D and the range of Lt / Lr satisfying the above required specifications in the SAW resonator 1 were set.
FIG. 5 is an explanatory diagram showing the relationship between the gap D and Lt / Lr based on FIG. FIG. 5A is a graph showing the relationship between the gap D and Lt / Lr, and FIG. 5B is a reference for setting the ranges of the gap D and Lt / Lr in FIG. It is the table | surface which showed the value of the gap D and Lt / Lr of each point A, B, C, and E which become.

As shown in FIG. 5 (a), when the gap D is in the range of 0Lt to + 0.06Lt, the region sandwiched between the polygonal line F and the polygonal line G has gaps D and Lt / Lr satisfying the above required specifications. It becomes a range.
The area surrounded by the broken lines connecting the points A, B, C, E (hatched) is a range that satisfies the two relational expressions (1) and (2). .
Here, the broken line H is represented by Lt / Lr = −0.00667 × D + 0.9996, and the broken line I is represented by Lt / Lr = −0.02667 × D + 0.9999.

As a result, the SAW resonator 1 has the gap D and Lt / Lr within the region surrounded by the broken line.
-Q value: 2000 or more.
-Insertion loss: 9 dB or less.
-Spurious level: 10 dBc or more.
The simulation result was obtained that the required specifications were sufficiently satisfied.

Next, as support for setting the ranges of the gap D and Lt / Lr, the SAW resonator prototype sample using the conventional technique and the SAW resonator 1 prototype sample (gap D and Lt / Lr of this embodiment) are used. Was compared with a sample having a value indicated by a point J in FIG.
Hereinafter, the comparative test results will be described with reference to the drawings.

FIG. 6 is an explanatory diagram of a comparison test result of a prototype sample of the SAW resonator according to the related art and the present embodiment. 6A is a frequency characteristic diagram, FIG. 6B is an enlarged view of a portion K in FIG. 6A, and FIG. 6C is a performance comparison table. In FIG. 6A, the solid line represents the prototype sample of this embodiment, and the broken line represents the prototype sample of the prior art.
The two prototype samples have common specifications except for the gap D and Lt / Lr.

As shown in FIG. 6, the prototype sample of this embodiment sufficiently satisfies the required specifications, with a Q value of 2230, an insertion loss of 7.7 dB, and a spurious level of 20 dBc.
In contrast, the prototype of the prior art satisfies the required specifications for the insertion loss and spurious level, with an insertion loss of 6.1 dB and a spurious level of 22 dBc, but the Q value is 900 and the required specifications. , There is a big gap and the required specifications are not satisfied.

In this regard, as shown in FIG. 6B, in the prototype sample of the present embodiment, the gap portion and the Lt / Lr are set within the above ranges, so that the peak portion can be compared with the prototype sample of the prior art. Since the frequency band is narrowed, the Q value is about 2.5 times that of the prototype sample of the prior art, which is remarkably improved.
The above comparative test results confirmed the validity of setting the gap D and Lt / Lr ranges in the SAW resonator 1.

As described above, in the SAW resonator 1 of the present embodiment, the gap between the two IDT electrodes 20 and 21 is D, the pitch of the electrode fingers 20a, 20b, 21a, and 21b of the IDT electrodes 20, 21 is Lt, When the pitch of the electrode fingers 30a and 31a of the reflectors 30 and 31 is Lr, (1): n × (Lt / 2) <D <0.045 × Lt + n × (Lt / 2) (where n is An integer greater than or equal to 0),
(2): −0.02667 × D + 0.9999 ≦ Lt / Lr ≦ −0.00667 × D + 0.9996,
It is the structure which satisfy | fills these two relational expressions.

  Accordingly, the SAW resonator 1 can have an insertion loss of 9 dB or less, a spurious level of 10 dBc or more, and a Q value of 2000 or more. The SAW resonator 1 can exhibit the same effect due to the characteristics of the surface acoustic wave even when n in the relational expression (1) is 1 or more.

Further, since the Euler angle of the quartz substrate 10 is within the range of (0 °, 113 ° to 135 °, ± (40 ° to 49 °)), the SAW resonator 1 has a secondary temperature of the quartz substrate 10. The coefficient can be reduced.
From this, the SAW resonator 1 can obtain excellent frequency temperature characteristics with less frequency fluctuation accompanying ambient temperature change.

(SAW oscillator)
By providing the above-described SAW resonator 1 and an oscillation circuit for exciting the SAW resonator 1, a SAW oscillator can be configured. Note that the oscillation circuit may use a known technique.

According to this, since the SAW oscillator includes the SAW resonator 1 having an insertion loss of 9 dB or less, a spurious level of 10 dBc or more, and a Q value of 2000 or more, the oscillation greatly depends on the Q value of the SAW resonator 1. The phase noise characteristics at the time are greatly improved. In addition, the SAW oscillator can reduce jitter by improving the Q value of the SAW resonator 1.
For these reasons, the SAW oscillator can satisfy desired performance as a high-accuracy SAW oscillator in the GHz band, for example.

FIG. 2 is a schematic plan view showing a main configuration of a SAW resonator according to the present embodiment. The graph which showed the relationship between the gap D, insertion loss, and a spurious level. The graph which showed the relationship between Lt / Lr, insertion loss, and Q value. The graph which showed the relationship between Lt / Lr of each gap D, insertion loss, and Q value. Explanatory drawing which showed the relationship between the gap D and Lt / Lr based on FIG. Explanatory drawing about the comparative test result of the trial sample of the prior art and the SAW resonator of this embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... SAW resonator, 10 ... Quartz substrate, 11 ... Main surface of quartz substrate, 20, 21 ... IDT electrode, 20a, 20b, 21a, 21b ... Electrode finger of IDT electrode, 30, 31 ... Reflector, 30a, 31a ... electrode fingers of reflectors, D ... gaps between IDT electrodes, Lt ... pitch of electrode fingers of IDT electrodes, Lr ... pitch of electrode fingers of reflectors.

Claims (3)

A quartz substrate, two adjacent IDT electrodes provided on the main surface of the quartz substrate, and reflectors provided on both sides of the two IDT electrodes,
When the gap between the two IDT electrodes is D, the pitch of the electrode fingers of the two IDT electrodes is Lt, and the pitch of the electrode fingers of the reflector is Lr,
(1): n × (Lt / 2) <D <0.045 × Lt + n × (Lt / 2) (where n is an integer of 0 or more)
(2): −0.02667 × D + 0.9999 ≦ Lt / Lr ≦ −0.00667 × D + 0.9996
A SAW resonator that satisfies the following two relational expressions.   2. The SAW resonator according to claim 1, wherein an Euler angle of the quartz crystal substrate is (0 °, 113 ° to 135 °, ± (40 ° to 49 °)). 3.   3. A SAW oscillator comprising the SAW resonator according to claim 1 and an oscillation circuit for exciting the SAW resonator.

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