JP2004260402A - Surface acoustic wave device and communication device having it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave device in which spurious waves caused by bulk waves are reduced. <P>SOLUTION: The surface acoustic wave device A has, on a piezoelectric substrate, vertically connected resonator type surface acoustic wave filters 100, 200 having IDTs 101-103, 201-203 along the propagation direction of a surface acoustic wave. When resonance frequency values of two adjacent resonance modes on frequency axes of the surface acoustic wave filters 100, 200 are set as f<SB>1</SB>and f<SB>2</SB>, respectively, and the frequency of ripples caused by oscillations of bulk waves in the surface acoustic wave filters 100, 200 is set as f<SB>SSBW</SB>, f<SB>SSBW</SB>≠(f<SB>1</SB>+f<SB>2</SB>)/2 is satisfied. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a surface acoustic wave device used for a communication device such as a mobile phone, and a communication device having the same.
[0002]
[Prior art]
In recent years, there have been remarkable technological advances in miniaturization, weight reduction, power saving, higher frequency, and the like of communication devices such as mobile phones. Against this background, a surface acoustic wave filter (surface acoustic wave device) used in the RF stage of a communication device such as a mobile phone is required to have a small size, a low loss, a low price, a stable quality and the like. It has been demanded. In particular, in mobile phones, it is important to reduce the loss in the surface acoustic wave device in order to suppress power consumption.
[0003]
For example, in Patent Document 1, in the surface acoustic wave resonator, in order to reduce the transverse mode spurious, the ratio of the cross width of the electrode finger to the opening length of the electrode finger in the comb-shaped electrode portion is set to a ratio of 65 to 75%. It is disclosed that the cross width is constant in the comb-shaped electrode portion.
[0004]
Further, in Patent Document 2, in a resonator-type surface acoustic wave device using a piezoelectric substrate, particularly a quartz substrate, among the modes distributed in a direction perpendicular to the propagation direction of the surface acoustic wave (hereinafter referred to as a transverse mode), a spurious component is used. In order to suppress the transverse secondary mode, the ratio of the cross width of the electrode finger to the opening length of the electrode finger in the comb-shaped electrode portion is set in a range of 0.75 to 0.85 (excluding 0.75). Is disclosed.
[0005]
Further, in Patent Document 3, in a surface acoustic wave resonator or a resonator-type surface acoustic wave filter, lithium tantalate (LiTaO₃) Or lithium niobate (LiNbO)₃) Generated by using a piezoelectric substrate composed of a piezoelectric substrate (Leaky Surface Acoustic Wave: hereinafter referred to as LSAW) and a bulk wave (Surface Skimming Bulk Wave: hereinafter referred to as SSBW). It is disclosed that the ratio of the opening length W1 of the comb-shaped electrode portion to the non-intersection portion W2 of the electrode finger is set to 14 or more (W1 / W2 ≧ 14) in order to reduce unnecessary spurious.
[0006]
[Patent Document 1]
Japanese Patent Publication No. 6-85492 (release date: October 26, 1994)
[0007]
[Patent Document 2]
JP-A-9-260996 (Published date: October 3, 1997)
[0008]
[Patent Document 3]
JP-A-6-232682 (publication date: August 19, 1994)
[0009]
[Patent Document 4]
JP-A-11-191720 (publication date: July 13, 1999)
[0010]
[Problems to be solved by the invention]
In many surface acoustic wave devices, a quasi (leakage) surface acoustic wave can be used as a piezoelectric substrate, and lithium tantalate (LiTaO) can be used.₃) Or lithium niobate (LiNbO)₃) Etc. are used. However, in these piezoelectric substrates, in addition to the excitation of the pseudo-surface acoustic wave, a bulk wave (hereinafter, referred to as SSBW) is excited, and a ripple occurs in a pass band, and an insertion loss occurs. Was causing the increase.
[0011]
In particular, in a surface acoustic wave device including a longitudinally coupled resonator type surface acoustic wave filter, the resonance frequencies of two resonance modes adjacent to each other on the frequency axis are respectively represented by f₁, F₂And the center of the resonance frequency ((f₁+ F₂) / 2) and the ripple frequency f due to the excitation of SSBW_SSBWWhen they almost coincide with each other, there remains a problem that the insertion loss increases due to the ripple caused by the excitation of the SSBW.
[0012]
However, as disclosed in Patent Literature 3, when the distance between the tip of the electrode finger and the bus bar is too close, the capacity at the portion between the tip of the electrode finger and the bus bar increases, and conversely, the characteristics are reduced. There is a problem that it gets worse.
[0013]
SUMMARY An advantage of some aspects of the invention is to provide a surface acoustic wave device in which spurious due to SSBW is reduced without deteriorating characteristics.
[0014]
[Means for Solving the Problems]
In order to solve the above-described problems, the surface acoustic wave device of the present invention has a comb-shaped electrode portion having a comb-shaped electrode composed of a bus bar and a plurality of electrode fingers on a piezoelectric substrate along a propagation direction of the surface acoustic wave. In a surface acoustic wave device having one or more formed longitudinally coupled resonator type surface acoustic wave filters, the resonance frequencies of two resonance modes adjacent to each other on the frequency axis of the longitudinally coupled resonator type surface acoustic wave filter are respectively determined. f₁, F₂The frequency of a ripple caused by excitation of a bulk wave (Surface Skimming Bulk Wave: SSBW) in the longitudinally coupled resonator type surface acoustic wave filter is represented by f_SSBWAnd when
f_SSBW≠ (f₁+ F₂) / 2
It is characterized by satisfying.
[0015]
In the case where three or more resonance modes are present, the surface acoustic wave device has resonance frequencies of two resonance modes having the widest frequency interval and being adjacent to each other on the frequency axis.₁, F₂It is preferable that
[0016]
Further, in the surface acoustic wave device, the resonance frequency of at least one of two resonance modes adjacent to each other on the frequency axis is within a pass band, or the resonance mode of a resonance mode having a higher frequency is used. Preferably, the frequency is in the passband.
[0017]
Further, the surface acoustic wave device is characterized in that two resonance modes adjacent on the frequency axis are a resonance mode in which the zeroth-order mode and the second-order mode are degenerated, and a comb-shaped electrode portion and a comb-shaped electrode portion. It is preferable that the resonance mode be the excitation mode.
[0018]
According to the above configuration, usually, the center frequency (f) between the resonance points where the insertion loss becomes large₁+ F₂) / 2 is different from the frequency of the ripple generated by the excitation of the SSBW, so that the ripple becomes larger and the insertion loss can be suppressed from increasing. Thereby, the spurious generated due to the excitation of the SSBW can be reduced, and a surface acoustic wave device with reduced insertion loss can be provided.
[0019]
The level of the ripple caused by the excitation of the SSBW increases as the frequency increases. for that reason,
f_SSBW<(F₁+ F₂) / 2
Is satisfied, and f is smaller than the lowest resonance mode existing in the pass band._SSBWIs preferably low.
[0020]
Furthermore, in addition to the above-described configuration, the surface acoustic wave device according to the present invention further includes: It is preferable that the frequency of the ripple due to the excitation of the bulk wave is adjusted by the distance of.
[0021]
Further, the surface acoustic wave device according to the present invention is characterized in that a distance between a tip of an electrode finger through which a surface acoustic wave propagates and a bus bar for electrically connecting an electrode finger facing the electrode finger is increased by the surface acoustic wave. It is preferably 0.55 times or less the wavelength of the wave.
[0022]
Further, the distance between the tip of the electrode finger through which the surface acoustic wave propagates and the bus bar for electrically connecting the electrode finger facing the electrode finger is preferably 0.10 μm or more. Thereby, insertion loss due to a parasitic capacitance that increases between the electrode finger and the bus bar can be suppressed.
[0023]
Also, the distance between the tip of the electrode finger through which the surface acoustic wave propagates and the bus bar for electrically connecting the electrode finger facing the electrode finger may be made substantially equal to the minimum gap between the electrode fingers. preferable. According to the above configuration, the distance between the electrode finger and the bus bar and the minimum gap between the electrode fingers are almost the same, so that the narrow gap portion is not localized. Therefore, stable electric characteristics can be obtained, and further, surge resistance and power resistance can be improved. In addition, since the distance between the electrode finger and the bus bar and the minimum gap between the electrode fingers are almost the same, the manufacture thereof becomes easier.
[0024]
In the surface acoustic wave device according to the present invention, it is preferable that the longitudinally coupled resonator type surface acoustic wave filter has three comb-shaped electrode portions. Further, the piezoelectric substrate is provided with a lithium tantalate (LiTaO) for exciting a bulk wave or a pseudo-surface acoustic wave.₃) Or lithium niobate (LiNbO)₃) Is preferable.
[0025]
A communication device according to the present invention includes any one of the above surface acoustic wave devices. According to the above configuration, the spurious due to the SSBW in the pass band is reduced, and the transmission characteristics can be improved by having the surface acoustic wave device in which the insertion loss is improved.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
[Embodiment 1]
The first embodiment of the present invention will be described below with reference to FIGS. Note that the present invention is not limited to this.
[0027]
In the present embodiment, a PCS (Personal communication system) receiving filter having a balanced-unbalanced conversion function composed of a longitudinally coupled resonator type surface acoustic wave filter will be described as an example.
[0028]
As shown in FIG. 1, a surface acoustic wave device A according to the present embodiment includes a first surface acoustic wave filter 100 and a first surface acoustic wave filter 100 on a piezoelectric substrate (not shown). Includes a second surface acoustic wave device 200 having a phase difference of 180 degrees, and surface acoustic wave resonators 300, 400, 500, and 600.
[0029]
The first surface acoustic wave filter 100 has a comb-shaped electrode (Inter-Digital Transducer, hereinafter referred to as IDT) 101 as a center, and has IDTs 102 and 103 on the left and right of the IDT 101. Further, the first surface acoustic wave filter 100 includes a reflector 104 and a reflector 105 so as to sandwich the IDTs 101 to 103 therebetween. That is, the first surface acoustic wave filter 100 is a longitudinally coupled resonator type surface acoustic wave filter having three IDTs.
[0030]
The IDT has two comb-shaped electrodes (IDT electrodes) each including a strip-shaped bus bar (base end) and a plurality of mutually parallel electrode fingers extending in a direction perpendicular to one side of the bus bar. Have. That is, the bus bar electrically connects the electrode fingers. In addition, the IDT electrodes are provided in a state of being interposed between the electrode fingers such that the side portions of the electrode fingers of the IDT electrodes face each other. In the following, a portion where the electrode fingers cross each other in the IDT electrodes of the IDT is W, and distances between the tip of each electrode finger and the bus bar of the other IDT electrode are G1 and G2, respectively.
[0031]
The second surface acoustic wave filter 200 has an IDT 201 at the center, and has an IDT 202 and an IDT 203 on the left and right of the IDT 201. Further, the second surface acoustic wave filter 200 includes a reflector 204 and a reflector 205 so as to sandwich the IDTs 201 to 203. That is, the second surface acoustic wave filter 200 is a longitudinally coupled resonator type surface acoustic wave filter having three IDTs.
[0032]
In the second surface acoustic wave filter 200, the polarity of the central IDT 201 is opposite to the polarity of the central IDT 101 in the first surface acoustic wave filter 100. Thus, the phase of the second surface acoustic wave filter 200 is different from that of the first surface acoustic wave filter 100 by 180 degrees.
[0033]
Further, in the second surface acoustic wave filter 200, in order to increase the degree of balance in the surface acoustic wave device A, the electrode fingers near the boundary between IDT201 and IDT202 and the electrode fingers near the boundary between IDT201 and IDT203 include: About 1/2 series weighting is applied.
[0034]
The surface acoustic wave resonators 300, 400, 500, and 600 are added to secure attenuation outside the pass band. The surface acoustic wave resonator 300 is connected in series to the center IDT 101 of the surface acoustic wave filter 100. The surface acoustic wave resonator 400 is connected in series to the central IDT 201 of the surface acoustic wave filter 200. The surface acoustic wave resonator 500 is connected in series with the left and right IDTs 102 and 103 of the surface acoustic wave filter 100. The surface acoustic wave resonator 600 is connected in series with the left and right IDTs 202 and 203 of the surface acoustic wave filter 200.
[0035]
The electric terminals of the surface acoustic wave resonator 300 not connected in series to the surface acoustic wave filter 100 and the electric terminals of the surface acoustic wave resonator 400 not connected in series to the surface acoustic wave filter 200 are connected in parallel. , Unbalanced signal terminal A1. The electric terminals of the surface acoustic wave resonator 500 that are not connected in series to the surface acoustic wave filter 100 are connected to the balanced signal terminal A2. The electric terminals of the surface acoustic wave resonator 600 that are not connected in series to the surface acoustic wave filter 200 are connected to the balanced signal terminal A3.
[0036]
With the above configuration, the surface acoustic wave device A according to the present embodiment has a balance-unbalance conversion function.
[0037]
Here, the energy distribution of the surface acoustic wave (SAW) in the surface acoustic wave device will be briefly described with reference to FIG. 2 using one IDT.
[0038]
As shown in FIG. 2, the energy of the surface acoustic wave distributed in a direction perpendicular to the propagation direction of the surface acoustic wave is not only at the portion W where the electrode finger crosses, but also slightly with the tip of the electrode finger. It is also distributed in areas separated by the distances G1 and G2 from the bus bar and in the bus bar portion. Therefore, the electrical characteristics of the surface acoustic wave device change depending on the distance between the tip of the electrode finger and the bus bar. That is, in the portion W where the electrode fingers of the IDT intersect, pseudo surface acoustic waves (LSAW) are predominantly excited, but are separated by the distances G1 and G2 between the tip of the electrode fingers and the bus bar. In the region, bulk waves (SSBW) are predominantly excited. For this reason, the bulk wave (SSBW) becomes an unnecessary ripple and adversely affects the electrical characteristics of the surface acoustic wave device, particularly, the transmission characteristics in the pass band.
[0039]
Next, the energy distribution of the surface acoustic wave distributed in the propagation direction of the surface acoustic wave in the longitudinally coupled resonator type surface acoustic wave filter will be described using the surface acoustic wave filter 100 having three IDTs shown in FIG. 3 and FIG.
[0040]
As shown in FIG. 2, the energy of the surface acoustic wave in the longitudinally coupled resonator type surface acoustic wave filter is, in addition to the standing wave (transverse mode) perpendicular to the propagation direction of the surface acoustic wave, There are a plurality of standing waves (longitudinal modes) confined in the propagation direction of the surface acoustic wave, in other words, between the reflectors 104 and 105. The longitudinally coupled resonator type surface acoustic wave filter is a surface acoustic wave filter in which a plurality of longitudinal modes are acoustically coupled to broaden the band. In the surface acoustic wave filter 100 having the above three IDTs, among a plurality of longitudinal modes, a longitudinal zero-order mode, a longitudinal secondary mode, and a mode of exciting between IDTs (hereinafter, an IDT-IDT mode) ) Are acoustically coupled. FIG. 3 shows the energy distribution of the surface acoustic wave in each mode. As shown in FIG. 4, the relationship between the frequencies in these three modes is, in order from the lower frequency side, the vertical second-order mode, the vertical zero-order mode, and the IDT-IDT mode. However, FIG. 4 shows the transmission characteristics when the matching impedance is removed so that the mode arrangement on the frequency axis can be easily understood.
[0041]
Here, an example (Example 1) of design parameters in the surface acoustic wave device A according to the present embodiment will be described.
[0042]
Other design parameters of the first surface acoustic wave filter 100 and the second surface acoustic wave filter 200 are as follows.
[0043]
The first surface acoustic wave filter 100 and the second surface acoustic wave filter 200 have the same design except for the polarities of the central IDTs 101 and 201, series weighting, and the number of reflectors. Further, the electrode finger (wavelength: λ2) located near the boundary between IDTs has a shorter wavelength (λ1> λ2) than the electrode finger (wavelength: λ1) of the other part of the IDT.
Cross width W: 60 μm (29.3λ1)
Number of IDTs (in order of IDT102, IDT101, IDT103, and in order of IDT202, IDT201, IDT203): 29 (4) / (4) 55 (4) / (4) 29
The number in parentheses is the number of electrode fingers (λ2) with a short wavelength.
IDT wavelength λ1: 2.05 μm
IDT wavelength λ2: 1.86 μm
Reflector wavelength λR: 2.06 μm
Number of reflectors: first surface acoustic wave filter 100: 120
Second surface acoustic wave filter 200: 80 filters
IDT (λ1) -IDT (λ2) interval: 0.25λ1 + 0.25λ2
IDT (λ2) -IDT (λ2) interval: 0.50λ2
IDT (λ1) -reflector spacing: 0.47λ1
IDT (λ1) duty: 0.70
IDT (λ2) duty: 0.67
Reflector duty: 0.56
Electrode thickness: 0.080λ1
The detailed design of the surface acoustic wave resonators 300 and 400 is as follows.
Intersection width W_T1: 35 μm (17.7λ)_T1)
Log IDT: 140
IDT wavelength λ_T1: 1.98 μm
Reflector wavelength λ_RT1: 1.98 μm
Number of reflectors: 30
Electrode thickness: 0.083λ_T1
The detailed design of the surface acoustic wave resonators 500 and 600 is as follows.
Intersection width W_T2: 100 μm (49.1λ)_T2)
Log IDT: 120
IDT wavelength λ_T2: 2.04 μm
Reflector wavelength λ_RT2: 2.04 μm
Number of reflectors: 30
Electrode thickness: 0.081λ_T2
Next, in each IDT of the surface acoustic wave filter 100, when the distances G1 and G2 between the electrode fingers and the bus bar are set to 1.0 μm, the relationship between the ripple caused by the SSBW excitation and the frequency in each resonance mode is described. Shown in FIG. In FIG. 5, the transmission characteristics in the vicinity of the pass band in the surface acoustic wave filter 100 of the surface acoustic wave device A shown in FIG. 1, and the relationship between the frequency of the ripple due to the excitation of the SSBW and the resonance frequency of each resonance mode are clear. As can be seen from FIG. 2, the transmission characteristics are shown with the matching impedance set to about 1/1000. Here, the peak of the transmission characteristic appearing when the matching impedance is set to about 1/1000 is defined as the resonance frequency of each mode. Note that the resonance frequencies of two adjacent resonance modes on the frequency axis are respectively represented by f₁, F₂And the frequency of the ripple caused by the SSBW excitation is f_SSBWAnd When there are three or more resonance modes, two resonance modes that are adjacent to each other on the frequency axis and have the widest frequency interval are respectively represented by f₁, F₂And it is sufficient.
[0044]
Excitation of the SSBW is caused by various factors, but is mainly caused by the distance between the electrode finger and the bus bar.
[0045]
In the surface acoustic wave device A of the present embodiment, of the three modes described above, the zeroth-order mode and the second-order mode are located very close on the frequency axis. Therefore, the vertical zero-order mode and the vertical secondary mode are degenerated without being separated. Therefore, in FIG. 5, a resonance point in the mode in which the vertical zeroth-order mode and the vertical second-order mode are degenerated and a resonance point in the IDT-IDT mode can be confirmed as two peaks.
[0046]
As is clear from FIG. 5, the ripple (approximately 1948 MHz) caused by the excitation of the SSBW is substantially at the center between the resonance point in the mode in which the longitudinal zero-order mode and the longitudinal secondary mode are degenerated and the resonance point in the IDT-IDT mode. Located in the department. The insertion loss between the resonance points (especially at the center between the resonance points) increases, but in that region, the ripple occurs due to the excitation of the SSBW, so that the above ripple increases and the insertion loss increases. You can see that it is doing.
[0047]
Next, in the surface acoustic wave device A, when only the distances G1 and G2 between the electrode finger and the bus bar in the first surface acoustic wave filter 100 and the second surface acoustic wave filter 200 are changed, FIG. 6 shows changes in the transmission characteristics.
[0048]
According to FIG. 6, when the distances G1 and G2 between the tip of the electrode finger and the bus bar are changed from 1.0 μm to 0.30 μm, the insertion loss near 1945 MHz is reduced by about 0.2 dB and improved. You can see that. That is, by reducing the distances G1 and G2 between the electrode fingers and the bus bar, the ripple caused by the excitation of the bulk wave (SSBW) is reduced, and the ripple frequency (f_SSBW) Moves to the low frequency side, and the resonance frequency (f₁Or f₂) And the resonance frequency of the IDT-IDT mode (f₂Or f₁) And the center ((f₁+ F₂It is considered that the insertion loss was improved by moving to the lower side than the vicinity of () / 2). The improvement of the insertion loss is not only in the vicinity of 1945 MHz where the SSBW ripple exists, but also the insertion loss is reduced as a whole. This means that the excitation by SSBW has a wide influence not only near 1945 MHz but also in the pass band. Reducing the excitation of SSBW is suitable for improving the overall insertion loss. Is shown.
[0049]
When there are a plurality of ripples caused by the SSBW excitation, the frequency of the largest ripple is represented by f_SSBWAnd
[0050]
[Comparative Example 1]
The following will describe Comparative Example 1 of the present invention with reference to FIGS. 7 to 9. For the sake of convenience, members having the same functions as those described in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.
[0051]
Also in Comparative Example 1, as in Embodiment 1, a PCS receiving filter having a balanced-unbalanced conversion function composed of a longitudinally coupled resonator type surface acoustic wave filter will be described as an example. The surface acoustic wave device of Comparative Example 1 has the same basic structure as that of the first embodiment, but differs from the first embodiment in the method of connecting the IDT.
[0052]
As shown in FIG. 7, a surface acoustic wave device B of Comparative Example 1 has a first surface acoustic wave filter 700 and a first surface acoustic wave filter 700 on a piezoelectric substrate (not shown). A second surface acoustic wave device 800 having a phase difference of 180 degrees is provided, and surface acoustic wave resonators 900, 1000, 1100, and 1200 are provided.
[0053]
The first surface acoustic wave filter 700 has a comb-shaped electrode (Inter-Digital Transducer, hereinafter referred to as IDT) 701 as a center, and has IDTs 702 and 703 on the left and right of the IDT 701. Further, the first surface acoustic wave filter 700 includes a reflector 704 and a reflector 705 so as to sandwich the IDTs 701 to 703. That is, the first surface acoustic wave filter 700 is a longitudinally coupled resonator type surface acoustic wave filter having three IDTs.
[0054]
The second surface acoustic wave filter 800 has an IDT 801 at the center, and has an IDT 802 and an IDT 803 on the left and right of the IDT 801. Further, the second surface acoustic wave filter 800 includes a reflector 804 and a reflector 805 so as to sandwich the IDTs 801 to 803. That is, the second surface acoustic wave filter 800 is a longitudinally coupled resonator type surface acoustic wave filter having three IDTs.
[0055]
In the second surface acoustic wave filter 800, the polarities of the left and right IDTs 802 and 803 are opposite to the polarities of the left and right IDTs 702 and 703 in the first surface acoustic wave filter 700. Thus, the second surface acoustic wave filter 800 is different in phase from the first surface acoustic wave filter 700 by 180 degrees.
[0056]
Further, in the second surface acoustic wave filter 800, in order to increase the degree of balance in the surface acoustic wave device B, the electrode fingers near the boundary between IDT 801 and IDT 802 and the electrode fingers near the boundary between IDT 801 and IDT 803 include: About 1/2 series weighting is applied.
[0057]
The surface acoustic wave resonators 900, 1000, 1100, and 1200 are added to secure attenuation outside the pass band. The surface acoustic wave resonator 900 is connected in series with the left and right IDTs 702 and 703 of the surface acoustic wave filter 700. The surface acoustic wave resonator 1000 is connected in series with the left and right IDTs 802 and 803 of the surface acoustic wave filter 800. The surface acoustic wave resonator 1100 is connected in series to the center IDT 701 of the surface acoustic wave filter 700. The surface acoustic wave resonator 1200 is connected in series to the central IDT 801 of the surface acoustic wave filter 800.
[0058]
An electric terminal of the surface acoustic wave resonator 900 not connected to the surface acoustic wave filter 700 in series and an electric terminal of the surface acoustic wave resonator 1000 not connected to the surface acoustic wave filter 800 are connected in parallel. , Unbalanced signal terminal A1. Electrical terminals of the surface acoustic wave resonator 1100 that are not connected in series to the surface acoustic wave filter 700 are connected to the balanced signal terminal A2. The electric terminals of the surface acoustic wave resonator 1200 that are not connected in series to the surface acoustic wave filter 800 are connected to the balanced signal terminal A3.
[0059]
With the above configuration, the surface acoustic wave device B as a comparative example of the present embodiment has a balance-unbalance conversion function.
[0060]
In Comparative Example 1, in each IDT of the surface acoustic wave device B, the transmission characteristics in the vicinity of the pass band when the distances G1 and G2 between the tip of the electrode finger and the bus bar were widened contrary to the first embodiment. The change is shown.
[0061]
Here, an example (comparative example 1) of design parameters in the surface acoustic wave device B which is a comparative example of the present embodiment will be described.
[0062]
The first surface acoustic wave filter 700 and the second surface acoustic wave filter 800 have the same design except for the polarities of the left and right IDTs 702, 703, 802, 803, serial weighting, and the number of reflectors. The electrode finger (wavelength: λ4) located near the boundary between the IDTs has a shorter wavelength (λ3> λ4) than the electrode fingers (wavelength: λ3) of the other IDTs.
Cross width W: 65 μm (29.3λ3)
Number of IDTs (in the order of IDT702, IDT701, and IDT703, and in the order of IDT802, IDT801, and IDT803): 33 (4) / (4) 43 (4) / (4) 33
The number in parentheses indicates the number of electrode fingers (λ4) with a short wavelength.
IDT wavelength λ3: 2.05 μm
IDT wavelength λ4: 1.87 μm
Reflector wavelength λR: 2.06 μm
Number of reflectors: First surface acoustic wave filter 700: 120
Second surface acoustic wave filter 800: 90 filters
IDT (λ3) -IDT (λ4) interval: 0.25λ3 + 0.25λ4
IDT (λ4) -IDT (λ4) interval: 0.50λ4
IDT (λ3) -reflector spacing: 0.50λ3
IDT (λ3) duty: 0.60
IDT (λ4) duty: 0.60
Reflector duty: 0.60
Electrode thickness: 0.080λ3
The detailed design of the surface acoustic wave resonators 900 and 1000 is as follows.
Intersection width W_T1: 50 μm (24.5λ)_T1)
Log IDT: 140
IDT wavelength λ_T1: 2.04 μm
Reflector wavelength λ_RT1: 2.04 μm
Number of reflectors: 30
Electrode thickness: 0.081λ_T1
The detailed design of the surface acoustic wave resonators 1100 and 1200 is as follows.
Intersection width W_T2: 35 μm (17.7λ)_T2)
Log IDT: 140
IDT wavelength λ_T2: 1.98 μm
Reflector wavelength λ_RT2: 1.98 μm
Number of reflectors: 30
Electrode thickness: 0.083λ_T2
FIG. 8 shows transmission characteristics when the distances G1 and G2 between the tip of the electrode finger and the bus bar are 0.5 μm, 1.0 μm, and 2.0 μm in each IDT of the surface acoustic wave device B. .
[0063]
As shown in FIG. 8, as the distances G1 and G2 between the tips of the electrode fingers and the bus bar are increased, the ripple caused by the excitation of the SSBW increases, contrary to the first embodiment (see FIG. 6). You can see that. Further, it can be seen that this ripple has moved further to the higher frequency side.
[0064]
Here, in Example 1 and Comparative Example 1, the distance between the tip of the electrode finger and the bus bar and the frequency of the ripple (f_SSBW) And the resonance frequency (f) of a mode in which the zeroth-order mode and the second-order mode are degenerated₁Or f₂) And the IDT-IDT mode resonance frequency (f₂Or f₁) Center ((f₁+ F₂) / 2) will be described. Here, a value (horizontal axis) normalized by the wavelength of the surface acoustic wave propagating along the distance between the tip of the electrode finger and the bus bar, and 2 × f_SSBW/ (F₁+ F₂9) (vertical axis). Note that 2 × f_SSBW/ (F₁+ F₂) Is the frequency of the ripple (f_SSBW) And the resonance frequency (f) of a mode in which the zeroth-order mode and the second-order mode are degenerated₁Or f₂) And the IDT-IDT mode resonance frequency (f₂Or f₁) Center ((f₁+ F₂) / 2).
[0065]
FIG. 9 shows that the frequency of the ripple (f) caused by the excitation of the SSBW is achieved by setting the distance between the tip of the electrode finger and the bus bar to 0.55 times or less the wavelength of the surface acoustic wave._SSBW) Is the resonance frequency (f) of the mode in which the zeroth-order mode and the second-order mode are degenerated.₁Or f₂) And the IDT-IDT mode resonance frequency (f₂Or f₁) Center ((f₁+ F₂) / 2).
[0066]
As described above, the resonance frequencies of two adjacent resonance modes on the frequency axis are respectively represented by f₁, F₂And the center of the two resonance frequencies ((f₁+ F₂) / 2) and the frequency of the ripple (f_SSBW) Can improve the insertion loss in the pass band of the surface acoustic wave device. As a method for this, it is effective to change the distance between the tip of the electrode finger of one IDT electrode and the bus bar of the other IDT electrode in one IDT.
[0067]
In particular, as shown in the first embodiment, in one IDT, by reducing the distance between the tip of the electrode finger of one IDT electrode and the bus bar of the other IDT electrode, the ripple due to the excitation of the SSBW is reduced. Frequency (f_SSBW) Is the resonance frequency (f) of the mode in which the zeroth-order mode and the second-order mode are degenerated.₁Or f₂) And the IDT-IDT mode resonance frequency (f₂Or f₁) Center ((f₁+ F₂) / 2), that is, f_SSBW<(F₁+ F₂In the case of () / 2), the ripple level is also small, which means that it is effective in improving the insertion loss. However, as shown in Comparative Example 1, conversely f_SSBW> (F₁+ F₂In the case of) / 2, the level of the ripple itself becomes large, so that it can be seen that the insertion loss is worse than when both frequencies are almost the same.
[0068]
Further, f_SSBW<(F₁+ F₂In order to realize () / 2), it is particularly effective to set the distance between the tip of the electrode finger and the bus bar to 0.55 times or less the wavelength of the propagating surface acoustic wave.
[0069]
Here, in the same filter configuration as in Comparative Example 1, the distances G1 and G2 between the tip of the electrode finger and the bus bar, and the frequency of the ripple (f_SSBWFIG. 10 shows the relationship with the insertion loss in ()). From FIG. 10, it can be understood that ripples caused by SSBW excitation are effective in improving insertion loss by reducing the distances G1 and G2 between the tip of the electrode finger and the bus bar.
[0070]
However, by reducing the distances G1 and G2 between the tip of the electrode finger and the bus bar, the parasitic capacitance between the tip of the electrode finger and the bus bar may increase. There is a possibility that the insertion loss is deteriorated by the parasitic capacitance. Therefore, in FIG. 11, in a configuration similar to that of Comparative Example 1, the capacitance change caused by changing the distances G1 and G2 between the tip of the electrode finger and the bus bar is obtained by the finite element method, and the insertion loss due to the capacitance change is determined. Indicates a change. From FIG. 11, when the distances G1 and G2 between the tip of the electrode finger and the bus bar become 0.10 μm or less, the parasitic capacitance at the portion between the tip of the electrode finger and the bus bar sharply increases. It is clear that the insertion loss gets worse.
[0071]
FIG. 12 shows the change in the insertion loss when both the change in the insertion loss due to the ripple due to the excitation of the SSBW shown in FIG. 10 and the insertion loss due to the parasitic capacitance shown in FIG. 11 are considered. By setting the distances G1 and G2 between the tip of the electrode finger and the bus bar to be narrow, particularly 0.55 times or less the wavelength of the surface acoustic wave to be propagated, the ripple caused by the excitation of the SSBW is reduced. As is apparent, when the distances G1 and G2 between the tip of the electrode finger and the bus bar are 0.10 μm or less, the insertion due to the increase in the parasitic capacitance is more effective than the effect of the reduction in the insertion loss due to the smaller ripple of the SSBW. The worse the loss, the greater. As a result, the overall insertion loss will be worse. Therefore, the distances G1 and G2 between the tip of the electrode finger and the bus bar are preferably 0.55 times or less the wavelength of the propagating surface acoustic wave, and more preferably 0.10 μm or more.
[0072]
As described above, when the distances G1 and G2 between the tip of the electrode finger and the bus bar change, the excitation of the SSBW and the parasitic capacitance change. For this reason, when an IDT made of a metal thin film is actually formed on a piezoelectric substrate, it is necessary to control the film thickness of the IDT and the line width of the electrode finger with high precision, as in the related art, in a surface acoustic wave device. Without obtaining stable electrical characteristics, the distance between the tip of the electrode finger and the bus bar also needs to be controlled with high precision.
[0073]
Here, a photolithography method is generally used for forming the IDT, and the wavelength of the exposure light source is about 0.2 μm to 0.4 μm. Therefore, when the dimension of the gap portion of the IDT electrode is about 0.5 μm or less, it becomes difficult to control the gap width of the IDT electrode with high accuracy due to a light diffraction effect. However, the size of the IDT electrode has been reduced from the viewpoint of characteristics, and in the present invention, the distance between the tip of the electrode finger and the bus bar, the minimum gap between the electrode fingers, and the wavelength of the exposure light source The effect is obtained by making it about the same as above. Therefore, by making the distance between the tip of the electrode finger and the bus bar almost equal to the minimum gap between the electrode fingers, the distance between the tip of the electrode finger and the bus bar also becomes the minimum gap between the electrode fingers. In both cases, control can be performed with high precision, and more stable electrical characteristics can be obtained in the surface acoustic wave device. Also, since the distance between the tip of the electrode finger and the bus bar and the minimum gap between the electrode fingers are the same, the narrow portion is not localized, and as a result, the surge resistance and the A further effect of improving power performance can be obtained.
[0074]
In the first embodiment, the rotation YcutX propagation LiTaO₃Although a substrate was used, the present invention is not limited to this substrate.₃Substrate, 41 degree rotation YcutX propagation LiNbO₃The same effect can be obtained with a piezoelectric substrate such as a substrate.
[0075]
In the above description, a surface acoustic wave device having a balanced-unbalanced conversion function using two longitudinally coupled resonator type filters of the 3IDT type and four surface acoustic wave elements is described as an example. The above effect is due to the relationship between the resonance frequency of the mode and the frequency of the ripple in the excitation of the SSBW. Therefore, in order to obtain desired frequency characteristics, each design parameter in the surface acoustic wave device is arbitrarily changed in the crossover width, the number of IDTs, the interval between electrode fingers, and the number of traps is increased or decreased as necessary. , The same effects can be obtained. Furthermore, the number of IDTs and the number of filters are not particularly limited.
[0076]
Therefore, Embodiments 2 to 7 will be described below with reference to FIGS.
[0077]
As shown in FIG. 13, the surface acoustic wave filter according to the second embodiment includes three IDTs formed on the piezoelectric substrate along the propagation direction of the surface acoustic wave and does not have a balance-unbalance conversion function. This is a coupled resonator type surface acoustic wave filter.
[0078]
Further, as shown in FIG. 14, the surface acoustic wave filter according to the third embodiment has a balanced-unbalanced conversion composed of an IDT having two IDTs formed on a piezoelectric substrate along the propagation direction of the surface acoustic wave. This is a longitudinally coupled resonator type surface acoustic wave filter having no function.
[0079]
As shown in FIG. 15, the surface acoustic wave filter according to the fourth embodiment has a balanced-unbalanced conversion function including five IDTs formed on the piezoelectric substrate along the propagation direction of the surface acoustic wave. This is not a longitudinally coupled resonator type surface acoustic wave filter.
[0080]
As shown in FIG. 16, the surface acoustic wave filter according to the fifth embodiment is the same as the surface acoustic wave filter according to the third embodiment, except that the tip of the electrode finger of one IDT electrode and the bus bar of the other IDT electrode in the IDT are different from each other. And a vertical coupling resonator type surface acoustic wave filter having no balance-unbalance conversion function, in which small electrode fingers protruding from the bus bar are added.
[0081]
As shown in FIG. 17, the surface acoustic wave filter according to the sixth embodiment is a longitudinally coupled resonator having no balanced-unbalanced conversion function in which two longitudinally coupled resonator type surface acoustic wave filters are cascaded. Type surface acoustic wave filter.
[0082]
As shown in FIG. 18, the surface acoustic wave filter according to the seventh embodiment includes three IDTs arranged along the propagation direction of the surface acoustic wave, and one of the three IDTs at the center IDT. Is a longitudinally coupled resonator type surface acoustic wave filter having a balanced-unbalanced conversion function in which the IDT electrode is divided in the propagation direction of the surface acoustic wave. In the surface acoustic wave filter according to the present embodiment, the left and right IDTs of the central IDT are connected to unbalanced signal terminals. The divided IDT electrodes in the center IDT are connected to balanced signal terminals, respectively. The bus bar of the IDT electrode not connected to the balanced signal terminal of the central IDT may or may not be grounded.
[0083]
In the surface acoustic wave filters according to the second to seventh embodiments, the same effect can be obtained by using the surface acoustic wave filter alone, as the principle of the effect described in the first embodiment indicates. The surface acoustic wave filter alone can be called a surface acoustic wave device. Further, even in the case of a surface acoustic wave device including a plurality of the above surface acoustic wave filters, the effects described in the first embodiment can be similarly obtained.
[0084]
Next, a communication device using the surface acoustic wave device described in the above embodiment will be described with reference to FIG. The communication device 1300 includes an antenna 1301, an antenna common unit / RFTop filter 1302, an amplifier 1303, an Rx interstage filter 1304, a mixer 1305, a first IF filter 1306, a mixer 1307, and a second IF filter 1308 on the receiver side (Rx side) that performs reception. It comprises a 1st + 2nd local synthesizer 1311, a TCXO (temperature compensated crystal oscillator) 1312, a divider 1313, and a local filter 1314.
[0085]
As shown by two lines in FIG. 19, it is preferable to transmit each balanced signal from the Rx inter-stage filter 1304 to the mixer 1305 in order to ensure balance.
[0086]
In addition, the communication device 1300 shares the antenna 1301 and the antenna common unit / RFTop filter 1302 as a transceiver side (Tx side) that performs transmission, and also includes a TxIF filter 1321, a mixer 1322, a Tx interstage filter 1323, and an amplifier. 1324, a coupler 1325, an isolator 1326, and an APC (automatic power control) 1327.
[0087]
The surface acoustic wave device described in the present embodiment can be suitably used for the Rx interstage filter 1304, the first IF filter 1306, the TxIF filter 1321, and the Tx interstage filter 1323.
[0088]
The surface acoustic wave device according to the present invention has excellent characteristics such that spurious due to SSBW in the pass band is reduced and insertion loss is improved. Therefore, the communication device of the present invention having the surface acoustic wave device can improve transmission characteristics.
[0089]
The present invention is not limited to the above embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining the technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.
[0090]
【The invention's effect】
As described above, the surface acoustic wave device according to the present invention relates to a surface acoustic wave device having one or more longitudinally coupled resonator-type surface acoustic wave filters. A surface acoustic wave device having at least one longitudinally coupled resonator type surface acoustic wave filter in which a plurality of comb-shaped electrode portions each having a plurality of electrode fingers formed of a plurality of electrode fingers are formed. The resonance frequencies of two resonance modes adjacent on the frequency axis in the filter are represented by f₁, F₂In the longitudinally coupled resonator type surface acoustic wave filter, the ripple frequency due to the SSBW excitation is represented by f_SSBWAnd when
f_SSBW≠ (f₁+ F₂) / 2
It is the structure which satisfies.
[0091]
According to the above configuration, it is possible to provide a surface acoustic wave device in which spurious due to SSBW is reduced and insertion loss in a pass band is reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of a surface acoustic wave device according to Embodiment 1 of the present invention.
FIG. 2 is a diagram illustrating an energy distribution of surface acoustic waves distributed in a cross width direction in one surface acoustic wave filter of the surface acoustic wave device.
FIG. 3 is a diagram illustrating the energy distribution of surface acoustic waves distributed in the surface acoustic wave direction in each mode of the surface acoustic wave filter.
FIG. 4 is a graph showing transmission characteristics for explaining the position of each mode on the frequency axis in the surface acoustic wave filter.
FIG. 5 is a graph showing transmission characteristics for explaining the resonance frequency of each mode, the frequency and arrangement of ripples caused by SSBW excitation in the surface acoustic wave filter according to the first embodiment of the present invention;
FIG. 6 is a graph showing transmission characteristics when the distance between the tip of the electrode finger and the bus bar in the surface acoustic wave filter of Example 1 is changed.
FIG. 7 is a diagram showing a schematic configuration of a surface acoustic wave device according to Comparative Example 1 of the present invention.
FIG. 8 is a graph showing transmission characteristics when the distance between the tip of the electrode finger and the bus bar is changed in the surface acoustic wave filter of Example 2 according to Comparative Example 1.
FIG. 9 is a graph showing a relationship between an interval between a tip of an electrode finger and a bus bar, a frequency of a ripple caused by SSBW excitation, and resonance frequencies of two resonance modes adjacent on a frequency axis.
FIG. 10 is a graph showing a change in insertion loss due to ripple of SSBW in the surface acoustic wave filter according to the embodiment of the present invention having the same configuration as Comparative Example 1.
FIG. 11 is a graph showing a change in insertion loss due to a parasitic capacitance in the surface acoustic wave filter according to the embodiment of the present invention having the same configuration as Comparative Example 1.
FIG. 12 shows the relationship between the insertion loss due to the ripple of the SSBW and the insertion loss due to the parasitic capacitance in the surface acoustic wave filter according to the embodiment of the present invention having the same configuration as that of Comparative Example 1. It is a graph which shows a change.
FIG. 13 is a diagram illustrating a schematic configuration of a surface acoustic wave filter (surface acoustic wave device) according to a second embodiment of the present invention;
FIG. 14 is a diagram illustrating a schematic configuration of a surface acoustic wave filter (surface acoustic wave device) according to a third embodiment of the present invention;
FIG. 15 is a diagram illustrating a schematic configuration of a surface acoustic wave filter (surface acoustic wave device) according to a fourth embodiment of the present invention;
FIG. 16 is a diagram illustrating a schematic configuration of a surface acoustic wave filter (surface acoustic wave device) according to a fifth embodiment of the present invention;
FIG. 17 is a diagram illustrating a schematic configuration of a surface acoustic wave filter (surface acoustic wave device) according to a sixth embodiment of the present invention;
FIG. 18 is a diagram illustrating a schematic configuration of a surface acoustic wave filter (surface acoustic wave device) according to a seventh embodiment of the present invention;
FIG. 19 is a main part block diagram of a communication device using the surface acoustic wave device according to the above embodiment.
[Explanation of symbols]
A surface acoustic wave device
100, 200 surface acoustic wave filter
300, 400, 500, 600 surface acoustic wave resonator
101, 102, 103 Comb electrode (IDT)
201, 202, 203 Comb electrode (IDT)
104, 105 reflector
204, 205 reflector
A1 Unbalanced signal terminal
A2, A3 terminal for balanced signal
B surface acoustic wave device
700, 800 surface acoustic wave filter
900, 1000, 1100, 1200 Surface acoustic wave resonator
701, 702, 703 Comb electrode (IDT)
801, 802, 803 Comb electrode (IDT)
704, 705 reflector
804, 805 reflector

Claims (14)

One or more longitudinally-coupled resonator-type surface acoustic wave filters having a plurality of comb-shaped electrode portions each having a comb-shaped electrode composed of a bus bar and a plurality of electrode fingers formed on a piezoelectric substrate along a propagation direction of the surface acoustic wave. A surface acoustic wave device having
The resonance frequencies of two resonance modes adjacent to each other on the frequency axis in the longitudinally coupled resonator type surface acoustic wave filter are denoted by f ₁ and f ₂ , respectively, and the ripple due to excitation of a bulk wave in the vertically coupled resonator type surface acoustic wave filter is described. _Is f _SSBW ,
f _SSBW ≠ (f ₁ + f ₂ ) / 2
A surface acoustic wave device characterized by satisfying the following. When there are three or more resonance modes, the resonance frequencies of two resonance modes having the widest frequency interval and being adjacent to each other on the frequency axis are f ₁ and f ₂ , respectively. 2. The surface acoustic wave device according to claim 1. 3. The surface acoustic wave device according to claim 1, wherein a resonance frequency of at least one resonance mode among two resonance modes adjacent to each other on a frequency axis is within a pass band. The surface acoustic wave according to any one of claims 1 to 3, wherein a resonance frequency of a resonance mode having a higher frequency among two resonance modes adjacent on the frequency axis is within a pass band. apparatus. Two adjacent resonance modes on the frequency axis are a resonance mode in which the zeroth-order mode and the vertical second-order mode are degenerated, and a resonance mode in which excitation occurs between the comb-shaped electrode portion and the comb-shaped electrode portion. The surface acoustic wave device according to any one of claims 1 to 4, wherein f _SSBW <(f ₁ + f ₂ ) / 2
The surface acoustic wave device according to any one of claims 1 to 5, wherein the following condition is satisfied. The surface acoustic wave device according to any one of claims 1 to 6, wherein f _SSBW is lower than a lowest resonance mode existing in a pass band. The frequency of the ripple caused by excitation of the bulk wave is adjusted by the distance between the tip of the electrode finger through which the surface acoustic wave propagates and the bus bar for electrically connecting the electrode finger facing the electrode finger. The surface acoustic wave device according to any one of claims 1 to 7, wherein: The distance between the tip of the electrode finger through which the surface acoustic wave propagates and the bus bar for electrically connecting the electrode finger facing the electrode finger is not more than 0.55 times the wavelength of the surface acoustic wave. The surface acoustic wave device according to claim 8, wherein: 10. The distance between a tip of an electrode finger through which a surface acoustic wave propagates and a bus bar for electrically connecting the electrode finger facing the electrode finger is 0.10 μm or more. A surface acoustic wave device according to claim 1. The distance between the tip of the electrode finger through which the surface acoustic wave propagates and the bus bar for electrically connecting the electrode finger facing the electrode finger is substantially equal to the minimum gap between the electrode fingers. The surface acoustic wave device according to any one of claims 1 to 10. The surface acoustic wave device according to any one of claims 1 to 11, wherein the longitudinally coupled resonator type surface acoustic wave filter has three comb-shaped electrode portions. The piezoelectric substrate is made of lithium tantalate (LiTaO ₃ ) or lithium niobate (LiNbO ₃ ) for exciting a bulk wave or a pseudo-surface acoustic wave. Surface acoustic wave device. A communication device comprising the surface acoustic wave device according to any one of claims 1 to 13.

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