WO2005125005A1

WO2005125005A1 - Saw device and apparatus employing it

Info

Publication number: WO2005125005A1
Application number: PCT/JP2005/011300
Authority: WO
Inventors: Yasuhide Onozawa
Original assignee: Toyo Communication Equipment Co., Ltd.
Priority date: 2004-06-22
Filing date: 2005-06-20
Publication date: 2005-12-29
Also published as: JP2006013576A

Abstract

A SAW device removing the defects of prior art that a filter satisfying the standards required for the RF SAW filter of a GPS receiver could not be realized and that the performance of a circuit or an apparatus degrades when a SAW filter not satisfying the required standards is used in an RF circuit or a communication unit. The SAW device comprises at least one IDT electrode formed along the propagating direction of a surface wave on the major surface of a lithium tantalite (LiTaO3) substrate of Eulerian angles (0°±4°, 144.1°-160.0°, 0°±4°), and grating reflectors arranged on the opposite sides of the IDT electrode, wherein the IDT electrode and the grating reflectors are formed of alminium or aluminium alloy and its standardized electrode film thickness H/λ (H is the electrode film thickness,λ is wavelength) is set in the range of 0.10-0.14.

Description

Specification

SAW device and equipment using it

Technical field

The present invention relates to a SAW device and an apparatus using the same, and more particularly to a SAW device improved so as to satisfy both required passband width and attenuation characteristics, and an apparatus using the same. .

Background art

[0002] In recent years, SAW filters (surface acoustic wave filters) have been widely used in the field of communications, and are widely used in mobile phones and the like in particular because of their excellent characteristics such as high performance, small size, and mass productivity. For example, the 1.9 GHz band mobile phone system (PCS) in the United States uses an RF filter with a 60 MHz bandwidth (approximately 3% in specific bandwidth) for both transmission and reception, and the 1.8 GHz band mobile phone system in Korea (Korea-PCS) uses a 30MHz (approximately 1.6% relative bandwidth) RF filter for both transmission and reception!

The SAW filter for mobile phone system RF uses a rotating Y-power X-propagation lithium tantalate (LiTaO) substrate with relatively good temperature characteristics, and a cut angle of 36 ° or 4 °.

Three

2. Etc. are often used. LiTaO substrates with these cut angles are used for SAW filters.

Three

As a result, a large electromechanical coupling coefficient is obtained, which can satisfy the guaranteed bandwidth (about 1.6% to about 3% in fractional bandwidth) required for mobile phone RF filters.

[0003] On the other hand, a GPS receiver that receives signal radio waves from multiple navigation satellites and calculates the position information on the ground with high accuracy based on this signal has a center frequency of 1575.42MHz and a bandwidth of However, a narrow band RF filter of 2.046MHz (about 0.13% in specific bandwidth) is required. In the vicinity of this RF band (15575.42 ± 1.023MHz, hereafter referred to as GPS band), the band used for the INMARSAT satellite communication system (1525 to 1559MHz for downlink, 1626.5-1660 for uplink) 5MHz) and the band used for iridium mobile phone systems (16 16-1626.5 MHz), and the band used for Japanese MCA business radio systems (1501-1525MHz). In order to avoid mutual interference, the RF SAW filter of the GPS receiver has a narrow band and the attenuation characteristics near the passband are sharp. Things are required. In addition, since the signal waves arriving from the GPS satellite are weak and mobile phones equipped with GPS receivers have recently become widespread, RF filters for GPS receivers are also required to have low-loss transmission characteristics. ing.

[0004] For the SAW filter for RF of the GPS receiver, a 42 ° rotation Y-cut X-propagation LiTaO substrate is used.

3 SAW filter used is often used Force 36 ° or 42 ° Rotation Y-cut X-propagation Using a LiTaO substrate, ladder type SAW filter, DMS filter (dual mode SAW filter)

Three

When the filter is configured, for example, the pass bandwidth becomes too large with respect to the required pass bandwidth. Therefore, the attenuation in the band of the Inmarsat satellite communication system or the like becomes insufficient. In particular, the DMS filter is inferior to that of the power ladder type SAW filter in the high frequency side near the passband, so that sufficient attenuation cannot be obtained in the Inmarsat uplink band or the iridium band.

[0005] Fig. 7 (a) is a schematic diagram showing the configuration of a basic section of a ladder-type SAW filter, which is composed of a parallel arm SAW resonator Xp and a series arm SAW resonator Xs. The reactance curve is set as shown in FIG. That is, when the anti-resonance frequency of the parallel arm SAW resonator Xp (broken line) and the resonance frequency of the series arm SAW resonator Xs (solid line) are set to be substantially the same, the frequency is set as the center frequency, as shown in FIG. ), A band 'pass' filter is formed as shown by F (thick solid line). Then, attenuation poles are formed at the resonance frequency of the parallel arm SAW resonator Xp and the anti-resonance frequency of the series arm SAW resonator Xs, respectively, and a filter having low loss and a steep attenuation gradient is obtained. Furthermore, if a filter with a steep attenuation gradient or a filter with a large guaranteed attenuation is required, a ladder-type basic section filter can be cascaded to match the impedance to form a higher-order filter! ,.

[0006] As is clear from Fig. 7 (b), the bandwidth of the ladder-type SAW filter depends on the difference df = fa-fs between the resonance frequency fs of the SAW resonator and the anti-resonance frequency fa. Then, the resonance frequency difference df is expressed by the following equation by the capacitance ratio γ of the SAW resonator (the ratio of the capacitance CO to the motional capacitance C1 γ = C0ZC1).

df = fs ((l + l / _y ) 1/ ² -l)

Therefore, the bandwidth of the ladder-type SAW filter is determined by the capacitance ratio γ of the SAW resonator. That is, to obtain a narrow band ladder type SAW filter, It is necessary to increase the capacity ratio γ.

[0007] Japanese Patent Application Laid-Open No. 9-167936 discloses that rotation with a cut angle of 38 ° to 46 ° Υcut X-propagation LiTaO

(3) An electrode pattern mainly composed of aluminum (A1) is formed on the substrate, and the thickness H of the electrode pattern is normalized by the wavelength of the surface wave. Fifteen SAW devices have been disclosed. Then, using these parameters, a plurality of SAW resonators are formed on the same piezoelectric substrate, and the SAW resonators are connected to each other in a ladder type. .

Also, in US Pat. No. 6,556,104, an aluminum (A1) electrode pattern is formed on a Euler angle (0, μ, 0) rotation Υ cut X propagation

3 A SAW device in which ΗΖλ is set in the range of about 0.05 to about 0.15, wherein the SAW resonator has a Euler angle force S 44 ° <≤36 ° and a ladder using the SAW resonator. Type S AW filters are disclosed!

Based on these prior arts, we decided to simulate the filter characteristics of a ladder-type SAW filter for RF in a GPS receiver. Rotation Y cut X propagation Cut of LiTaO substrate

The three angles were set to 42 ° and 46.5 °, and an aluminum alloy containing 1. Owt% of copper (Cu) was used as an electrode pattern formed on the piezoelectric substrate. Fig. 8 shows the circuit configuration of a ladder type 1 SAW filter used in the simulation.The SAW resonator Xs with four series arms and the SAW resonator Xp with three parallel arms are connected in a ladder-like fashion. This is a circuit configured by: This circuit configuration is slightly different from the circuit configuration in which ladder-type basic section filters are connected in cascade so that the impedance is matched.All SAW resonators Xs in the series arm are the same, and all SAW resonators Xp in the parallel arm are all identical. The configuration is the same. With such a circuit configuration, only the center portion of the pass band of the filter characteristic becomes flat, and the ripple increases near the end of the pass band.

FIGS. 9 and 10 are diagrams showing the electrode pattern configuration of the serial arm and parallel arm SAW resonators Xs and Xp used in the ladder-type SAW filter shown in FIG. 8, respectively. As shown in Fig. 9, the series arm SAW resonator Xs is a so-called regular IDT electrode in which the cross width W of the IDT electrode is uniform for all electrode fingers, and the line occupancy (electrode By providing a dummy electrode with a large finger line width Z (electrode finger line width + space width), a SAW waveguide structure is created. ing. The parameters of the series arm SAW resonator Xs are: wavelength Lt = λ = 2.44 μm, IDT electrode logarithm N = 50, reflector number M = 100, cross width W = 14. Ί λ electrode finger gap GO 0.20, dark electrode length DO is 2.00, dark electrode line occupancy is 60.0%, LtZLr (Lr is twice the distance between electrode fingers of the reflector) is 0.98, Ltr (IDT The distance between the electrode and the nearest electrode finger between the grating reflector (hereinafter, referred to as a reflector) was 0.45X. Note that an insulating film (such as a SiO film) does not adhere to the IDT electrode.

2

The electrode configuration of the parallel arm SAW resonator Xp is also a SAW waveguide structure with dummy electrodes provided as shown in FIG. 10, but the IDT electrode is configured to have an elliptical apodized weight. Other parameters are wavelength Lt = λ 2.m, IDT electrode pairs N 100 pairs, number of reflectors M 150 each, cross width W 39.3λ, electrode finger tip gap GO 0.20λ. The dummy electrode length DO is 0.75 λ, the dummy electrode line occupancy is 60.0%, LtZLr (Lr is twice the distance between the electrode fingers of the reflector) is 0.98, Ltr (IDT electrode and reflector The distance between the nearest electrode fingers of the above) was 0.45 mm. No insulating film (such as a SiO film) is provided on the IDT electrode.

2

The electrode thickness H was 0.24 m for both the serial arm and the parallel arm SAW resonator. In addition, the line occupancy of the IDT electrode is made slightly different depending on the cut angle of the piezoelectric substrate.When the cut angular force is 2 °, the SAW resonators of the series arm and the parallel arm are 48.7% and the cut angular force is 6.5 °. Was set to 50.0% for both SAW resonators.

FIG. 11 is a schematic diagram showing a cross-sectional view of a ladder-type SAW filter, which employs a so-called chip-size 'package (CSP) structure. A ladder-type SAW filter element (SAW chip) having an IDT electrode 32 and a connection pad electrode 33 formed on the main surface of a piezoelectric substrate 31 is composed of a connection electrode 35 formed on an alumina ceramic substrate 34 and a gold bump. The flip chip is mounted via 36. Then, a sealing resin 37 is applied thereon and cured, whereby the SAW chip T is sealed, and a chip size 'package (CSP) having a space 38 therein is formed. The alumina ceramic substrate 34 has a multilayer structure, and the inner electrode 35 and the outer electrode 39 of the package are connected by the internal wiring 40 of the alumina ceramic substrate 34.

As shown in the circuit diagram of FIG. 8, the ladder-type SAW filter includes three parallel arm SAW resonators Xp, but the ground bonding pads of each parallel arm SAW resonator Xp are independent on the SAW chip T. ing. By the internal wiring of the alumina ceramic substrate 34, 3 One parallel arm SAW resonator Xp has a structure in which the ground of the center SAW resonator is connected to the ground of another parallel arm SAW resonator. With such a structure, as shown in FIG. 8, a ladder-type SAW filter in which GND1 and GND2 are separated at high frequencies is configured, and the attenuation outside the band is improved.

In determining the filter characteristics of the ladder-type SAW filter by simulation, the electrical characteristics of the SAW resonator were measured using force. The electrical characteristics of the wiring of the SAW chip T and the alumina ceramic substrate 34 were analyzed by electromagnetic field analysis simulation. The one obtained by the following was used. Then, by combining the measured data of the SAW resonator and the electromagnetic field analysis of the wiring, the filter characteristics of the ladder-type SAW filter were obtained.

FIGS. 12 (a) and 12 (b) show the filter characteristics obtained from the simulation, FIG. 12 (a) shows the filter attenuation characteristics, and FIG. 12 (b) is an enlarged view of the passband. The solid line in the figure shows the transmission characteristics using a 42 ° rotation Y-cut X-propagation LiTaO substrate, and the broken line shows the 46.5 ° rotation Y-cut X-propagation LiT.

Three

This is the transmission characteristics of the aO substrate. Figures 12 (a) and (b) show the requirements for RF filter for GPS receiver

Three

An example of the standard to be used is entered. Symbols A, B, C, D, and E in FIG. 12 are an MCA band, an iridium band, an Inmarsat uplink band, an Inmarsat downlink band, and a GPS band, respectively, and these are called guaranteed bands. Symbols A, BC ', D', and E 'indicate the room temperature set by the ladder-type SAW filter so that the guaranteed bands A, B, C, D, and E meet the following conditions of the standard. It is a standard and is set considerably wider than each guaranteed bandwidth.

In other words, frequency fluctuations due to temperature changes, frequency fluctuations due to reflow when the SAW filter element is soldered to the circuit board, frequency fluctuations after the SAW filter has passed high or low temperatures, and thermal and mechanical shocks to the SAW filter In consideration of various frequency fluctuations such as frequency fluctuations after the addition, the frequency range obtained by adding a margin to the frequency fluctuations due to these fluctuations is added to the guaranteed bandwidth as an inspection standard. If this inspection standard is satisfied, it is possible to guarantee various performances within the operating temperature range of the SAW filter and reliability under the above environmental conditions only by inspection at room temperature. The test bands A ', BC', D ', and E' shown in Fig. 12 are 4.76 MHz for the lower band and 5.03 MHz for the higher band for each of the guaranteed bands A, B, C, D, and E. The frequency range is included. For example, the inspection band (Ε ') of the GPS band is 1569.637 MHz to 158.1.473 MHz, and the inspection band (Α,) of the MCA band is 1496.24 to 1530.03 MHz. Inspection zone of GPS band The standard of the maximum insertion loss in the area (Ε ') is 2.2dB or less, and the minimum attenuation of each test band in the MCA band (Α'), iridium band and Inmarsat uplink band (BC,) is 45dB or more, and Inmarsat The specification of the minimum attenuation of the downlink band test band (D ') is 2.4 dB or more.

[0011] The filter characteristics of Figs. 12 (a) and 12 (b) also show that the maximum insertion loss in the test band (E,) in the GPS band meets the test standards at both the cut angles of 42 ° and 46.5 °, but the attenuation characteristics With regard to V, both the cut angle of deviation and the inspection standard are satisfied. As shown in Fig. 8, the ladder-type SAW filter was able to obtain a large amount of attenuation due to the attenuation poles formed in the lower and higher passbands of the parallel arm SAW resonator due to the ground wiring of the parallel arm SAW resonator. The attenuation characteristics near the passband are inadequate because the bandwidth is too wide.

As described above, the ladder-type SAW filter using the rotating Y-cut X-propagation LiTaO substrate disclosed in Japanese Patent Application Laid-Open No. 9-167936 and US Pat.

Three

It turned out that the bandwidth was too wide for the RF filter, and it could not meet the required standard for GPS receivers.

To improve this, means for narrowing the ladder type SAW filter is required. To narrow the ladder type SAW filter in a narrow band, means for increasing the capacitance ratio γ of the SAW resonators arranged in the parallel arm and the serial arm is required. Other methods include reducing the impedance of the parallel arm to increase the impedance of the series arm, and increasing the number of connection stages of the ladder-type basic section filter consisting of the parallel arm and the series arm. In the latter case, the insertion loss is deteriorated, and in the latter case, the ladder-type SAW filter is disadvantageously enlarged in addition to the insertion loss. For these reasons, the best way to satisfy both the low loss in the pass band and the high attenuation characteristics near the pass band is to increase the capacitance γ of the SAW resonator constituting the ladder-type SAW filter.

JP-A-8-65089 discloses an invention of a ladder-type SAW filter in which a capacitor is provided with a capacity in series or in parallel with a SAW resonator. It is described that by connecting the additional capacitors in series or in parallel, the capacitance ratio γ of the SAW resonator can be increased to realize a narrow band ladder-type SAW filter.

Japanese Patent Application Laid-Open No. 9-167937 discloses that a capacitor is connected to a SAW resonator in series or in parallel. An invention of a ladder-type SAW filter of the following type is disclosed. In another embodiment of the publication, a ladder-type SAW filter in which an inductor is connected in parallel to a series arm SAW resonator is also described. According to this, a ladder-type SAW filter in which an inductor is connected in parallel to a series-arm SAW resonator can steeply reduce the attenuation gradient on the high-passband side while maintaining the passband bandwidth.

The ladder type SAW filter described in JP-A-8-65089 and JP-A-9-167937 describes a reactance pattern (comb type capacitor, parallel plate, parallel plate) for connecting a reactance to a SAW resonator in series or parallel. Capacitors, microstrip inductors, etc.) and connection wiring patterns for connecting them to the SAW resonator must be provided on the piezoelectric substrate, which complicates wiring on the piezoelectric substrate and reduces the degree of freedom in wiring. Further, it has the disadvantage that the number of possible SAW resonators on the piezoelectric substrate is reduced.

As a means of increasing the capacitance ratio γ of the SAW resonator without connecting the reactance to the SAW resonator, there is a method of weighting the IDT electrode of the SAW resonator by thinning. This method is disclosed in detail in JP-A-11-163664 and JP-A-2002-353769. Japanese Patent Application Laid-Open No. 11-163664 discloses thinning-out weighting in which a portion where an electrode finger is not arranged is periodically provided in an IDT electrode. The thinning-out weighting belongs to excitation and reflection thinning-out.

The thinning weighting in Japanese Patent Application Laid-Open No. 2002-353769 is excitation thinning (reflection is not thinned out), and the thinning weight in the IDT electrode is made different for the left and right with respect to the SAW propagation direction.

However, although the capacitance ratio γ of the SAW resonator with the IDT electrode thinned out is large, the loss of the SAW resonator is large, so the insertion loss in the pass band of the ladder-type SAW filter increases. However, there are drawbacks in that the transmission characteristics in the passband become single-peak, and the cutoff attenuation gradient decreases. There is also a problem that spurious noise occurs due to the thinning, and the transmission characteristics of the ladder-type SAW filter deteriorate.

On the other hand, Japanese Patent Application Laid-Open No. 2001-77662 discloses that the cutting angle of a LiTaO substrate, that is, the Euler angle is limited.

Three

By using gold (Au), chromium (Cr), and other materials with high specific gravity and electrode materials for the IDT electrodes formed on the substrate, and appropriately selecting the film thickness, SAW devices with low propagation loss can be manufactured. It is described as having been obtained. The Euler angle of LiTaO depends on the electrode material of the IDT electrode.

Three

I have. For example, when the electrode material is gold (Au), the Euler angles are (0 °, 125 ° to 146 °, 0 ° ± 5 °), and the reference film thickness Η / λ is 0.001 to 0.05. Of the range. When the electrode material is chromium (Cr), the Euler angles are (0 °, 125 ° to 147 °, 0 ° ± 5 °), and H / λ is in the range of 0.003 to 0.05! / .

As described in Japanese Patent Application Laid-Open No. 2001-77662, when a metal having a large specific gravity is used as an electrode material for forming an IDT electrode, the electromechanical coupling coefficient is smaller than that when using a metal, such as aluminum (A1). Becomes larger. Therefore, the means disclosed in the above publication goes against the demand for increasing the capacitance ratio γ of the SAW resonator. When the capacitance ratio γ of the SAW resonator is increased based on the means disclosed in the publication, a reactance is connected to the SAW resonator as described above, and a certain weight is applied to the IDT electrode of the SAW resonator. In this case, the method of applying the method must be used in combination, and the disadvantages of the prior art remain unresolved. A common material for the IDT electrode is aluminum (A1) as a main component. When a metal containing gold (Au) or chromium (Cr) as a main component is used as an electrode material, it is necessary to prepare equipment different from a manufacturing process and manufacturing equipment for forming an A1 alloy electrode. When the manufacturing equipment is used in common, an electrode material switching operation newly occurs, which is not desirable in terms of simplification and simplification of the manufacturing equipment and manufacturing process. As a result, the production cost of SAW devices may decrease and the production costs may increase due to the increase in equipment costs.

Japanese Patent Application Laid-Open No. 2003-188679 discloses a 25 ° to 55 ° rotation Y-cut X-propagation LiTaO substrate.

3 An IDT electrode made of aluminum (A1) with a higher density than that of aluminum (A1) is formed on the top, and a SAW device in which a SiO film is formed on the IDT electrode to improve frequency temperature characteristics is formed to improve frequency temperature characteristics.

2

A chair is disclosed. In addition, the same publication discloses that an adhesion layer having an A1 equivalent force is provided on the upper surface of the IDT electrode in order to increase the adhesion strength of the SiO film to the metal IDT electrode having a high density of AU.

2

A digitized SAW device is also described. It is described that the thickness of the adhesive layer made of A1 or the like is preferably 1% or less of the wavelength of the surface wave. According to the same publication, the IDT electrode can be made thinner by using a metal with a higher density than A1 for the IDT electrode, and can be made thinner than when using A1. Classification of SiO film

2

It is described that the lock can be suppressed. [0015] The IDT electrode disclosed in JP-A-2003-188679 uses the same electrode material as that described in JP-A-2001-77662 described above as an electrode material, and is the same as that in JP-A-2001-77662. The problem is that using a metal with a high specific gravity for the IDT electrode results in a larger electromechanical coupling coefficient than using a metal with a low specific gravity, such as A1, and goes against the need to increase the capacitance ratio γ of the SAW resonator. I do. In addition, there is a drawback that simplification of manufacturing equipment and manufacturing processes goes against the simplification, and that a decrease in productivity of SAW devices and an increase in equipment costs lead to an increase in manufacturing costs! You.

Also, JP-A-2003-188679 assumes that an SiO film is deposited on the IDT electrode.

2

However, this method requires an additional manufacturing process to deposit the SiO film.

2

However, there is a concern that productivity may decrease. In order to improve the frequency temperature characteristics, it is necessary to form a considerably thick SiO on the IDT electrode, and the LiTaO

2 2 3 C may be damaged, and LiTaO

(3) There is a problem that it is difficult to make the wafer thinner. JP-A-2003-188679 discloses that the standardized electrode thickness HZ λ of the IDT electrode composed of A1 is reduced to 0.04 to obtain an electromechanical coupling coefficient. Is described as becoming smaller. Based on this, a SAW resonator with a waveguide structure as shown in Fig. 9 was prototyped. The piezoelectric substrate uses a rotating Y-cut X-propagating LiTaO at 38 .The electrode material is A1 alloy containing 1.0 wt% Cu.

Three

Gold, wavelength Lt = λ 4 / zm, number of electrode pairs N 50, number of reflectors M 100 each, intersection width W 20, IDT electrode line occupancy 46.1%, electrode finger tip gap G0 the 0. 15 lambda, the dummy electrode lengths DO 0. 75 lambda, the dummy electrode line occupancy 60 ^_0/0, Lt / Lr to 1. 0, L tr a 0. 5 lambda, the normalized electrode thickness Itazeta lambda Is set to 0.04, and the SiO film on the IDT electrode is

2 No.

FIG. 13 is a diagram showing the frequency characteristic of the absolute value of the impedance of a SAW resonator prototyped using the above parameters. From this figure, it can be seen that a large spur occurs near the high frequency side of the anti-resonance frequency. When such a SAW resonator is used in a parallel arm of a ladder-type SAW filter, a large spur is generated in the pass band or near the high side of the pass band. As a technique to keep this spurious away from the anti-resonant frequency force, it is known that an insulating film such as SiO is formed on the IDT electrode. It is necessary to form an SiO film, which is accompanied by the above-mentioned disadvantages associated with the formation of the SiO film.

twenty two

In addition, it is not preferable to reduce the thickness of the IDT electrode because power resistance and electrostatic withstand voltage are deteriorated and filter characteristics may be deteriorated due to an increase in electric resistance of the electrode. Also, JP-A-2003-188679 discloses a SiO film ZAu electrode / rotated Y cut.

2

The relationship between the cut angle Li of the LiTaO substrate in the X-propagation LiTaO structure and the electromechanical coupling coefficient

3 3

This indicates that the larger the cut angle 0, the smaller the electromechanical coupling coefficient tends to be. This tendency is the same even when the SiO film thickness is 0, that is, when there is no SiO film.

twenty two

However, Au as an electrode material has the above-mentioned disadvantages, and has poor quality and reliability such as Au being an expensive electrode material and weak adhesion to metal oxides such as LiTaO.

Three

There are also disadvantages such as a decrease.

Japanese Patent Application Laid-Open No. 2003-218664 discloses that an IDT electrode made of silver (Ag) is formed on a LiTaO substrate having an Euler angle (0 ° ± 3 °, 110 ° to 150 °, 0 ° ± 3 °), and a frequency-temperature characteristic is obtained. Improvement

Three

For this purpose, a SAW device in which a SiO film is formed on an IDT electrode is disclosed. This means

2

Also has the same drawbacks as JP-A-2003-188679 mentioned above. In other words, it is said that Ag is an expensive electrode material and its adhesion to metal oxides such as LiTaO is weak.

Three

It has disadvantages.

Patent Document 1 JP-A-9167936

Patent Document 2 U.S. Pat.No. 6,556,104

Patent Document 3 JP-A-8-65089

Patent Document 4 JP 9 167937 A

Patent Document 5 Japanese Patent Laid-Open No. 11-163163

Patent Document 6 JP 2002-353769A

Patent Document 7 JP 2001-77662 Gazette

Patent Document 8 JP 2003-188679

Patent Document 9 JP 2003-218664 Gazette

Patent Document 10: JP-A-11 92147

Patent Document 11: Japanese Patent Application Laid-Open No. 2004-35396

Special Reference 1: http://www.cdmatech.com/solutions/pdf/msm6275_chipset.pdf Disclosure of the invention

Problems to be solved by the invention

[0017] The present invention solves the disadvantages of the prior art in which a filter satisfying the standard required for an RF SAW filter of a GPS receiver cannot be realized.

Further, the present invention solves the drawback of the prior art in that the use of a SAW filter that does not satisfy the required standards in an RF circuit or a communication device deteriorates the performance of the circuit or device.

Means for solving the problem

The invention according to claim 1 is a tantalum having Euler angles (0 ° ± 4, 144.1 ° to 160.0 °, 0 ° ± 4) in order to satisfy the RF filter standard of the GPS receiver. Lithium oxide (LiTaO

3) A SAW device including at least one IDT electrode formed on a main surface of a substrate along a propagation direction of a surface wave, and grating reflectors disposed on both sides of the IDT electrode, wherein The electrodes and grating reflector are made of aluminum or aluminum alloy, and the standardized electrode film thickness λ λ (H is the electrode film thickness, λ is the wavelength) is set in the range of 0.10 to 0.14. It is characterized by comprising.

The invention of claim 2 provides a lithium tantalate substrate having an Euler angle (0 ° ± 4 °, 144.1 ° to 160.0 °, 0 ° ± 4 °), and a surface on the main surface of the lithium tantalate substrate. A SAW device comprising at least one IDT electrode formed along the wave propagation direction, wherein the IDT electrode is formed of aluminum or an aluminum alloy, and a standardized electrode film thickness ΗΖλ (H is The feature is that the electrode film thickness and λ are set in the range of 0.10 to 0.14.

A third aspect of the present invention is characterized in that, in the first or second aspect, the SAW device is a negative terminal-pair SAW resonator.

[0019] The invention of claim 4 is the ladder type according to claim 1 or 2, wherein the SAW device is connected to a serial arm and a parallel arm sequentially in a ladder shape with a lead electrode formed on the lithium tantalate substrate. A SAW filter is configured.

According to a fifth aspect of the present invention, a duplexer is configured using the SAW device according to the fourth aspect. A sixth aspect of the present invention is characterized in that, in any one of the first to fifth aspects, the lithium tantalate substrate has a higher Balta conductivity.

The invention according to claim 7 is the method according to any one of claims 1 to 6, wherein the lithium tantalate substrate is left in a combination of heat and an atmosphere in which the substrate is chemically reduced to enhance the conductivity of the substrate. Characterized in that:

The invention according to claim 8 is the method according to any one of claims 1 to 6, wherein the lithium tantalate substrate is heated in an atmosphere containing metal vapor at a temperature lower than the Curie temperature in order to increase the conductivity of the substrate. It is characterized by the following.

The invention of claim 9 is characterized in that the SAW device according to any one of claims 1 to 8 is mounted on a circuit of a GPS receiver.

The invention's effect

[0020] If a SAW device is configured using the lithium tantalate substrate having a cut angle according to the present invention and the standardized electrode film thickness, all the standards required for the RF filter of the GPS receiver can be satisfied. This has the effect. Further, when the SAW device of the present invention is used for an RF circuit or device, there is an effect that the performance of the circuit or device is improved.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1A is a circuit diagram showing an embodiment of a ladder-type SAW filter according to the present invention, in which a plurality of SAW resonances are provided on a main surface of a piezoelectric substrate 11 along a propagation direction of a surface acoustic wave. And a parallel arm SAW resonator Xs, a parallel arm SAW resonator Xp, a serial arm SAW resonator Xs, and a parallel arm SAW resonator Xp are formed by a lead electrode on which the SAW resonator is formed on the same piezoelectric substrate 11. And a ladder-type SAW filter element 12 are sequentially connected. Then, as shown in the cross-sectional view of FIG. 1B, the pad electrode 13 formed on the ladder-type SAW filter element 12 (SAW chip) and the connection electrode 15 formed on the alumina ceramic substrate 14 are connected to the gold bumps 16. Through flip chip mounting. Then, if a sealing resin 17 is applied on this and cured, the SAW chip is sealed and a chip size package (CSP) having a space 18 therein is formed. The alumina ceramic substrate 14 has a multilayer structure, and the electrodes 15 on the inner side of the package and the external electrodes 19 are connected by the internal wiring 20 of the alumina ceramic substrate 14 to form a ladder type SAW filter. The RF filter of the GPS receiver has an insertion loss of 2.2 dB or less in the GPS band, an attenuation of 45 dB or more in the MCA band, iridium band, and Inmarsat uplink band, and an attenuation of 2.4 dB in the Inmarsat downlink band. It is necessary to meet the above standards. Rotation Y cut X propagation Ladder type SAW filter using LiTaO

Three

We examined what value the capacitance ratio γ of each SAW resonator should take. As a result, it was necessary to make it necessary that the capacitance ratio γ of the series arm and the parallel arm SAW resonator both take a value within the range of 14.6-23.6. When the capacity ratio γ is smaller than 14.6, the standard of the attenuation band near the GPS band cannot be satisfied, and when the capacity ratio γ is larger than 23.6, the standard of the insertion loss in the GPS band cannot be satisfied. Can not.

Therefore, when A1 is used as the electrode material, the rotation angle Υ cut X propagation

Three

Using the standardized electrode film thickness ΗΖλ as a parameter, a simulation was performed on the capacitance ratio γ of a SAW resonator having a waveguide structure as shown in Fig. 9. The design parameters of the SAW resonator are: wavelength Lt = λ = 2.5 m, IDT electrode pairs N = 50, number of reflectors M = 100, cross width W = 20 λ, IDT electrode line occupancy 50% The electrode finger tip gap GO is 0.15, the dummy electrode length DO is 0.75, the dummy electrode line occupancy is 60%, Lt / Lr = 1.0, Ltr = 0.5, and the SiO film is Does not adhere on IDT electrodes.

2

Figure 2 shows the capacitance ratio γ of the SAW resonator obtained for the cut angle and the standardized electrode thickness HZλ. According to Fig. 2, the cut angle is 54.1 ° to 70. When the value of Η / λ is in the range of 0.10 to 0.14, the capacitance ratio γ is found to be in the range of 14.6 to 23.6. On the other hand, when the cut angular force was ^ 42 ° and 46.5 °, the capacitance ratio γ was smaller than 14.6 even when Η / λ was changed from 0.10 to 0.14. . That is, when the cut angles are 42 ° and 46.5 °, the attenuation characteristics in the vicinity of the GPS band cannot be satisfied, and this is consistent with the simulation result of the filter characteristics in FIG.

When the cut angle is 75 °, if λλ is set to a value smaller than 0.12, the capacity ratio γ becomes larger than 23.6, and the GPS band insertion loss standard of 2.2 dB or less cannot be satisfied. When the cut angle is 75 ° and ΗΖ λ is set to a value in the range of 0.12 to 0.14, the force ratio γ becomes a value in the range of 14.6 to 23.6. When the cut angle increases, the frequency temperature coefficient (TCF) deteriorates, so setting the cut angle larger than 70 ° is not desirable. Also, the leaky wave propagation loss becomes large and impractical when the cut angle is 70 ° or more, so the cut angle range is preferably 54.1 ° to 70 °.

If the cut angle is larger than the conventionally used cut angles of 42 ° and 46.5 °, the frequency temperature coefficient generally deteriorates.However, the frequency temperature coefficient can be reduced by setting the standardized electrode film thickness HZλ to be large.される λ should be set to 0.10 or more when the cut angle is in the range of 54.1 ° to 70 °.

[0023] Fig. 4 shows a prototype SAW resonator made using 55 ° rotation Υ cut X-propagation LiTaO.

Three

This is the frequency characteristic of the absolute value of the impedance. The electrode material is A1 alloy containing 1.Owt% Cu, wavelength Lt = λ 2.5 m, IDT electrode pairs N 50 pairs, reflector number M 100 each, cross width W 14 IDT electrode line occupancy 50%, electrode finger tip gap GO 0.20, dummy electrode length DO 1.00, dummy electrode line occupancy 60%, LtZLr 0.98, Ltr 0.45 No SiO film is provided on the IDT electrode. Thick solid line is standardized electrode film thickness

2

When λ λ is 0.128, the thin solid line is the frequency characteristic of the impedance absolute value when ΗΖ λ is 0.064, and the thin broken line is the frequency characteristic of the absolute value when λ λ is 0.16. If the standardized electrode film thickness λλ is out of the range of 0.10 to 0.14, the loss of the resonator increases, so ΗΖλ is preferably set in the range of 0.10 to 0.14.

Rotation Υcut X propagation Euler angle corresponding to a cut angle of 54.1 ° to 70 ° in LiTaO is (0

Three

°, 144.1 ° to 160.0 °, 0 °), and other than the cut angle, according to the results of the experiment, it may be within the range of ± 4 °. In other words, on a LiTaO substrate with Euler angle notation (0 ° ± 4 °, 144.1 ° to 160.0 °, 0 ° ± 4 °), A

Three

If a ladder-type SAW filter is formed using a SAW resonator with a standardized electrode thickness λλ of 0.10 to 0.14, the RF filter of the GPS receiver is required. It is assumed that the required standards can be satisfied.

[0024] Figs. 5 (a) and 5 (b) show the simulation results of the filter characteristics of the RF ladder-type SAW filter of the GPS receiver. Fig. 5 (a) shows the filter characteristics in the attenuation region. b) is a characteristic with an expanded passband. The simulation used actual measurement data only for the SAW resonator, and the others used the results of electromagnetic field analysis. 55 ° rotation on piezoelectric substrate Y-cut X-propagation LiTaO

Using ID3, the IDT electrode was an A1 alloy containing 1.0% Cu, the electrode thickness H was 0.31 μm, The series arm SAW resonator Xs has a wavelength Lt = λ = 2.36 m, the dummy electrode length DO is 1.00 λ, the IDT electrode line occupancy is 49.6%, and the parallel arm SAW resonator Χρ is the wavelength Lt = λ = 2.43 m, dummy electrode length DO was 0.75 λ, IDT electrode line occupancy was 49.6%, and the other parameters were the same as those shown in Fig. 12. Further, 直列 λ of the serial arm and the parallel arm SAW resonator is 0.131 and 0.127, respectively.

The thick and solid lines in the filter characteristics shown in FIG. 5 indicate a ladder-type SAW filter according to the present invention. For comparison, a ladder-type SAW filter using 42 ° and 46.5 ° rotation Y-cut X-propagation LiTaO was used.

Three

The filter characteristics of the filter are also overwritten. The former filter characteristic is a thin solid line, and the latter is a thin broken line.

As is clear from Fig. 5, it was found that all the standards required for GPS receiver RF filters were satisfied.

The ladder type SAW filter of the present invention has an IDT electrode finger caused by the pyroelectric effect of LiTaO.

Three

The use of a rotating Y-cut X-propagation LiTaO, which has increased the balta conductivity of the piezoelectric substrate, to prevent the destruction of the piezoelectric substrate and to prevent charging of the sealing resin in the filter with the CSP structure as shown in Fig. 1 (b).

Three

The cut angle is 55 °. The means for increasing the bulk conductivity of LiTaO is disclosed in

Three

No. 2147—disclosed in JP-A-2004-35396. As a result of the experiment, there is a difference in the SAW resonator characteristics between the LiTaO with increased Balta conductivity and the normal one.

Three

I couldn't.

As is apparent from FIG. 5, the ladder-type SAW filter according to the present invention can satisfy all the required standards that cannot be satisfied by the conventional ladder-type SAW filter. Even in the pass band, the filter characteristics do not deteriorate, but rather occur in the conventional ladder-type SAW filter, and the ripple power is suppressed in the ladder-type SAW filter of the present invention. The insertion loss and the maximum deviation were improved over the conventional ladder type 1 SAW filter.

It is presumed that ripples occur in the passband in the conventional ladder-type filter using a cut angle because the sidelobe characteristics of the reflection characteristics of the reflector, which weaken the energy confinement inside the IDT electrode, are superimposed near the resonance frequency. You.

Rotational Y-cut X-propagation LiTaO substrate according to the present invention Since the substrate was used and the standardized electrode film thickness HZλ was also increased (increased), the larger the value of / λ, the greater the reflection of each electrode finger force, and the larger the reflection coefficient as a whole. As a result, the SAW resonator according to the present invention has a high energy confinement inside the IDT electrode, so that the reflector can be omitted.

Therefore, in the ladder-type SAW filter according to the present invention, the reflectors provided on both sides of the IDT electrode can be omitted, and the size of the ladder-type SAW filter can be reduced.

[0026] The main object of the present invention is to obtain a means for realizing a ladder-type SAW filter narrower than the conventional one. To reduce the impedance of the series arm by increasing the number of cascade stages of the basic section filter consisting of the parallel arm and the series arm, and to reduce the frequency difference between the parallel arm SAW resonator and the series arm S AW resonator. By using a method to increase the passband, it is possible to guarantee a pass band width of about 3.5% (such as RF filter for PCS in the United States).

Further, the present invention can be applied to a DMS filter that is not limited to a ladder-type SAW filter, and can also be applied to a filter in which one of input and output is balanced. However, the SAW resonator according to the present invention reduces the logarithm of each IDT electrode in a DMS filter that utilizes acoustic coupling between a plurality of adjacent IDT electrodes that have strong energy confinement inside the IDT electrode. Therefore, means for strengthening the acoustic coupling between the IDT electrodes is required.

Furthermore, a SAW duplexer can be configured using the SAW filter according to the present invention.

In addition, if the SAW filter according to the present invention is used in an RF circuit, a GPS receiver, or the like, not only the performance of the SAW filter alone, miniaturization, and price reduction, but also the performance improvement, miniaturization, and price reduction of the GPS receiver can be achieved. Also, the effects of reducing the number of parts and reducing power consumption can be exhibited.

[0027] In the above, the power of the SAW device has been described. According to the Chipset Solution Data Sheet of Qualcomm's chipset MSM62 75 ™, the RF stage of the GPS receiver circuit includes the 1st antenna between the GPS antenna and the Pre-LNA. One band 'pass' filter (hereinafter referred to as an interstage filter) between the LNA and LNA. A 'pass' filter is used. For example, a TOP filter uses a SAW filter, a multilayer ceramic LC filter, a coaxial resonator type dielectric filter, etc. A SAW filter or the like is used as a filter. In general, TOP filters require low-loss characteristics, and interstage filters require high attenuation characteristics.For example, the attenuation characteristics of SAW filters used in interstage filters are accompanied by deterioration of insertion loss in the passband. If the improvement is achieved without any problem, the attenuation required for the TOP filter can be reduced accordingly. This has various advantages.For example, when a multilayer LC filter is used for the TOP filter, the number of multilayer ceramic layers can be reduced, and the number of elements such as inductors and capacitors built into the multilayer ceramic can be reduced. For example, it can contribute to downsizing and low price. In addition, when a dielectric filter is used as the TOP filter, it is possible to reduce the number of coaxial resonators, which can contribute to downsizing and low cost. Furthermore, it is possible to omit the TOP filter itself, and it is possible to reduce power consumption by reducing the number of components used in the circuit and the number of active elements such as amplifiers.

Brief Description of Drawings

FIG. 1 (a) is a diagram showing a circuit configuration of a ladder type SAW filter according to the present invention, and FIG. 1 (b) is a schematic configuration diagram showing a cross section of a ladder type SAW filter.

FIG. 2 is a diagram showing a capacitance ratio γ when a cut angle and a standardized electrode film thickness are used as parameters.

FIG. 3 is a diagram showing a frequency temperature coefficient when a cut angle and a standardized electrode film thickness are used as parameters.

FIG. 4 is a diagram showing a frequency characteristic of an impedance absolute value of a SAW resonator.

FIG. 5 (a) shows attenuation characteristics and (b) shows passband characteristics of a ladder-type SAW filter according to the present invention.

FIG. 6 is a diagram showing a relationship between a cut angle, a maximum insertion loss, and a maximum deviation.

FIGS. 7A and 7B are diagrams showing a ladder-type basic interval filter and its filter characteristics.

FIG. 8 is a diagram showing a circuit configuration of a conventional ladder-type SAW filter.

FIG. 9 is a view showing an electrode pattern of a serial arm SAW resonator.

FIG. 10 is a view showing an electrode pattern of a parallel arm SAW resonator.

FIG. 11 is a cross-sectional view illustrating a structure of a ladder-type SAW filter.

[FIG. 12] (a) shows attenuation characteristics and (b) shows passband characteristics of a conventional ladder-type SAW filter. FIG. 13 is a diagram showing a frequency characteristic of an impedance absolute value of a conventional SAW resonator. Explanation of reference numerals

11 Piezoelectric substrate, 14 Alumina ceramic substrate, Xs series arm SAW resonator, Xp parallel arm SAW resonator, GND1, GND2 ground, 12 SAW chip, 13 pad electrode, 15 connection electrode, 16 gold bump, 17 resin, 18 space, 19 external electrode, 20 internal wiring

Claims

The scope of the claims

[1] Euler angles (0. ± 4., 144.1 ° to 160.0 °, 0 ° ± 4.) Along the propagation direction of surface waves on the main surface of a lithium tantalate (Li TaO) substrate At least one ID formed

Three

A SAW device including a T electrode and grating reflectors arranged on both sides of the IDT electrode, wherein the IDT electrode and the grating reflector are formed of aluminum or an aluminum alloy, and standardized. A SAW device characterized in that the electrode thickness λλ (Η is the electrode thickness, λ is the wavelength) is set in the range of 0.10 to 0.14.

[2] Lithium tantalate substrate with Euler angles (0. ± 4, 144.1 ° to 160.0 °, 0 ° ± 4.) And propagation of surface waves on the main surface of the lithium tantalate substrate A SAW device comprising at least one IDT electrode formed along a direction, wherein the IDT electrode is formed of aluminum or an aluminum alloy, and a standardized electrode film thickness Η / λ (Η Is an electrode film thickness, and λ is a wavelength) in the range of 0.10 to 0.14.

3. The SAW device according to claim 1, wherein the SAW device is a terminal-pair SAW resonator.

[4] The ladder-type SAW filter is configured by connecting the SAW device in series with a serial arm and a parallel arm in a ladder shape with a lead electrode formed on the lithium tantalate substrate. SAW device as described in.

[5] A SAW device comprising a duplexer using the SAW device according to claim 4.

[6] The SAW device according to any one of claims 1 to 5, wherein the lithium tantalate substrate has an increased balta conductivity.

7. The lithium tantalate substrate according to any one of claims 1 to 6, wherein the substrate is left in a combination of heat and an atmosphere in which the substrate is chemically reduced to enhance the conductivity of the substrate. SAW device as described in section.

8. The method according to claim 1, wherein the lithium tantalate substrate is heated in an atmosphere containing metal vapor at a temperature lower than the Curie temperature in order to increase the conductivity of the substrate. SAW device. An apparatus comprising the SAW device according to any one of claims 1 to 8 mounted on a circuit of a GPS receiver.