Surface acoustic wave device, surface acoustic wave filter and antenna duplexer using the same, and electronic equipment using the same

A surface acoustic wave device includes a substrate including lithium niobate; a IDT being provided on an upper surface of the substrate and including a plurality of electrode fingers; and a protective film covering the IDT and having an uneven shape on an upper surface thereof. When a pitch width of one pitch of the IDT is p, a width of one of the electrode fingers is p1, a width between the electrode fingers is p2, and a thickness of the IDT is h, following relations are satisfied, p1+p2=p, and h/(2×p)≧4.5%. With this configuration, an appropriate reflection characteristic is realized, and the surface acoustic wave device having excellent temperature coefficient of frequency and electrical characteristic can be obtained.

This application is a U.S. national phase application of PCT international application PCT/JP2007/052631, filed Feb. 14, 2007.

TECHNICAL FIELD

The present invention relates to a surface acoustic wave device used as a resonator or a band-pass filter, and a surface acoustic wave filter and an antenna duplexer using the same, as well as electronic equipment using the same.

BACKGROUND ART

As to a conventional technology, a surface acoustic wave device (hereinafter, referred to as a “SAW device”) is described hereinafter as an example.

Recently, a large number of small and light SAW devices have been used in electronic equipment such as various types of mobile communication terminal devices. In particular, in a radio circuit part of a mobile phone system within a band of 800 MHz to 2 GHz, a surface acoustic wave filter formed by using a lithium tantalate (hereinafter, referred to as “LT”) substrate has been widely used. However, an LT substrate has a large thermal expansion coefficient of a substrate in the direction in which a surface acoustic wave propagates. Furthermore, the elastic constant itself varies according to temperatures. Therefore, there is a problem in terms of the temperature characteristics that the frequency characteristic of a filter is also greatly shifted according to the change in temperatures.

In such circumstances, for example, Japanese Patent Unexamined Publication No. 2004-254291 (patent document 1) discloses a method of obtaining a SAW device in which the temperature characteristics is improved. The SAW device described in patent document 1 includes a piezoelectric substrate, an electrode film and an insulating film. The electrode film is formed on the piezoelectric substrate and constitutes at least one IDT. The insulating film is formed by sputtering on the piezoelectric substrate so as to cover the electrode film. In addition, the insulating film has unevenness on the upper surface thereof. Furthermore, when the film thickness of the electrode film is in the range from 1-3% of the wavelength of the surface wave to be excited, excellent electrical characteristics can be obtained.[Patent Document 1] Japanese Patent Unexamined Publication No. 2004-254291

SUMMARY OF THE INVENTION

The present invention obtains an electronic component having excellent temperature characteristics and electrical characteristics.

A surface acoustic wave device of the present invention includes a substrate including lithium niobate, a IDT, and a protective film. The IDT is provided on an upper surface of the substrate and includes a plurality of electrode fingers. The protective film covers the IDT and has an uneven shape on an upper surface thereof. When a pitch width of one pitch of the IDT is p, a width of one of the electrode fingers that form the IDT is p1, a width between the electrode fingers is p2, and a thickness of the IDT is h, following relations are satisfied, p1+p2=p, and h/(2×p)≧4.5%. With this configuration, an appropriate reflection characteristic is realized, and a surface acoustic wave device having excellent temperature characteristics and electrical characteristics can be obtained.

REFERENCE MARKS IN THE DRAWINGS

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an electronic component of exemplary embodiments of the present invention is described with reference to the drawings.

In the exemplary embodiments, a surface acoustic wave device (hereinafter, referred to as a “SAW device”) is described as an example of an electronic component. Note here that a SAW device has a function as a resonator.

First Exemplary Embodiment

FIG. 1is a top view showing a SAW device as an electronic component in accordance with a first exemplary embodiment of the present invention.FIG. 2is a sectional view showing part23of the SAW device taken along line2-2ofFIG. 1.

As shown inFIGS. 1 and 2, surface acoustic wave device10(hereinafter, referred to as “SAW device10”) in accordance with the first exemplary embodiment includes substrate1, IDT22, reflector electrode3, and protective film4. IDT22is weighted by apodization on an upper surface of substrate1, and is provided with predetermined frequency characteristics. Reflector electrodes3are provided on both sides of IDT22. Protective film4covers at least IDT22and reflector electrode3. Furthermore, IDT22has pad5that is electrically connected to IDT22. IDT22takes out an electric signal via pad5. Thus, SAW device10is configured.

Substrate1is made of lithium niobate (LiNbO3, hereinafter, referred to as “LN”). A substrate made of lithium niobate is generally called an LN substrate. Furthermore, substrate1includes lithium niobate cut out from a Y-plate rotated by D degree around the X-axis in the Z-axis direction. Note here that a 5° Y-LN substrate, in which rotation angle D of the rotation around the X axis in the Z axis direction is 5 degree, is used.

A pair of IDT22and a pair of reflector electrodes3are formed on the upper surface of substrate1, respectively, and are made of aluminum (hereinafter, referred to as “Al”) or an Al alloy including Al as a main component. IDT22includes electrode fingers22afacing each other with a gap provided between neighboring electrode fingers22a.

Preferably, protective film4is made of silicon oxide such as silicon dioxide (hereinafter, referred to as SiO2). As shown inFIGS. 1 and 2, protective film4has an uneven shape on an upper surface thereof. Convex portion4aof protective film4is provided above a portion having IDT22and reflector electrode3on the upper surface of substrate1. Concave portion4bof protective film4is provided in a portion between convex portions4a, in which IDT22and reflector electrode3are not present on the upper surface of substrate1and their vicinities.

Hereafter, one convex portion4aand one concave portion4bof protective film4is defined as one pitch, respectively, the pitch width of this one pitch is L, the width of convex portion4aof protective film4is L1, and the width of concave portion4bof protective film4is L2. That is to say, the relation: L=L1+L2is satisfied.

Furthermore, similar to the one pitch of protective film4, a distance between one electrode finger22aof one IDT22and a portion in which another electrode finger22athat is adjacent to the one electrode finer22aat one end is located is defined as one pitch width p of IDT22. In addition, the width of one electrode finger22ais p1, and the width of a gap between the neighboring electrode fingers is p2. That is to say, p=p1+p2is satisfied. Note here that pitch width L of one pitch of protective film4and pitch width p of IDT22satisfy the relation: L≈p. Furthermore, the wavelength of an operation center frequency of the surface acoustic wave in SAW device10is λ=2×p.

The height from the surface of substrate1that is in contact with protective film4to concave portion4bof protective film4is defined as t. Thickness h of IDT22is defined as equivalent film thickness h of aluminum, which is converted from height h0from the surface of substrate1to an upper surface of IDT22. That is to say, when the material of IDT22is Al, the height from the surface of substrate1to the upper surface of IDT22is defined as a thickness of IDT22. That is to say, h0=h is satisfied. However, when the material of IDT22is a material other than Al, the equivalent film thickness h of aluminum is defined as h=h0×(ρM/ρAl) by calculating from height h0from the surface of substrate1to the upper surface of IDT22by using density ρAlof Al and density ρMof the material used for IDT22. Note here thatFIG. 2shows only two electrode fingers22a.

Hereinafter, a method of manufacturing SAW device10configured as mentioned above is described with reference to drawings.

FIGS. 3A to 3Hare schematic sectional views to illustrate a method of manufacturing SAW device10in accordance with the first exemplary embodiment of the present invention. Firstly, as shown inFIG. 3A, a film of Al or an Al alloy is formed on an upper surface of LN substrate31by a method such as vapor deposition and sputtering. Thus, electrode film32is formed. Note here that electrode film32is formed into electrode finger22aof IDT22or reflector electrode3or pad5by way of following manufacturing steps. LN substrate31is shown only partially. However, LN substrate31is patterned so that plurality of SAW devices10are formed on LN substrate31.

Next, as shown inFIG. 3B, first resist film33is formed on an upper surface of electrode film32.

Next, as shown inFIG. 3C, first resist film33is processed into predetermined shapes by using an exposure-development technique or the like.

Next, as shown inFIG. 3D, electrode film32is processed into predetermined shapes of electrode finger22aof IDT22, reflector electrode3, or the like, by using a dry-etching technique or the like. Thereafter, first resist film33is removed.

Next, as shown inFIG. 3E, a film of SiO2is formed so as to cover electrode film32by a method such as vapor deposition or sputtering. Thus, protective film34is formed.

Next, as shown inFIG. 3F, second resist film35is formed on the surface of protective film34.

Next, as shown inFIG. 3G, second resist film35is processed into predetermined shapes by using the exposure-development technique or the like. In addition, unnecessary portions of protective film34is removed by using the dry-etching technique or the like, and protective film4having opening for pad5or the like is formed.

Finally, although not shown, a plurality of SAW devices10formed on LN substrate31are divided into individual SAW devices10by a method, for example, dicing. Thereafter, SAW device10is mounted on a ceramic package by a method, for example, die bonding. Then, SAW device10is subjected to wire bonding, and then, a lid is welded to carry out hermetic sealing.

In SAW device10manufactured as mentioned above in accordance with the first exemplary embodiment of the present invention, the shapes and the dimensions of IDT22and protective film4satisfy the relations: L1≦p1and L2≧p2. As a method of obtaining the shapes of IDT22and protective film4satisfying these relations, a bias sputtering method is used. The bias sputtering method is a method of forming a film by sputtering while applying a bias voltage to electrode film32on the side of the substrate in the formation of SiO2protective film34inFIG. 3E. When protective film34is formed, the shape of SiO2protective film34is controlled by allowing the ratio of the bias voltage applied to electrode film32and sputtering electric power to be variable.

In the first exemplary embodiment, firstly, in order to examine what shape the SiO2protective film is formed into leads to obtaining excellent characteristics when protective film4is formed, the following four kinds of SAW devices (an example 1 and comparative examples 1 to 4) are formed. Note here that h/(2×p)=h/λ is defined as an electrode normalized film thickness, and t/(2×p)=t/λ is defined as an SiO2normalized film thickness.

A SAW device of the comparative example 1 has the electrode normalized film thickness of 4% and is not provided with the SiO2protective film. A SAW device of the comparative example 2 has the electrode normalized film thickness of 4.5% and is not provided with the SiO2protective film. A SAW device of the comparative example 3 has the electrode normalized film thickness of 4% and is provided with the SiO2protective film whose shape satisfies the relations: L1>p1and L2<p2. A SAW device of the comparative example 4 has the electrode normalized film thickness of 4.5% and is provided with the SiO2protective film whose shape satisfies the relations: L1>p1and L2<p2. Furthermore, SAW device10of the example 1 has the electrode normalized film thickness of 4.5% and is provided with the SiO2protective film whose shape satisfies the relations: L1≦p1and L2≧p2.

Note here that the SiO2normalized film thickness: t/(2×p) in SAW device10of the example 1 and the SAW devices of the comparative examples 3 and 4 as mentioned above are all 20%.

Furthermore,FIG. 4shows a sectional shape of the SAW device of the comparative example 3;FIG. 5shows a sectional shape of the SAW device of the comparative example 4; andFIG. 6shows a sectional shape of SAW device10of the example 1. In addition,FIG. 7is a graph showing the electrical characteristics of the SAW devices, respectively. Segment line41shows the characteristic of the example 1. Segment lines51,52,53and54show the characteristics of the comparative examples 1, 2, 3, and 4, respectively. Furthermore, the sectional shape of each SAW device is identified from the results of observation in which the surface of the SAW device is coated with metal and carbon, the electrode is cut by FIB (Focused Ion Beam) in the direction in which the surface acoustic wave propagates, and then observation by the use of an electron microscope is carried out.

As shown inFIG. 7, in the comparative examples 1 and 2 in which the SiO2protective film is not provided, spurious caused by Rayleigh wave is generated and an anti-resonant frequency is divided, showing very bad characteristics. In the comparative examples 3 and 4, the shapes of the SiO2protective films satisfy the relations: L1>p1and L2<p2. In the comparative example 3, spurious around the resonance frequency is not observed. However, in the comparative example 4, spurious is generated at the side of frequency lower than the resonance frequency and the insertion loss in the resonance frequency is extremely bad. Furthermore, in the example 1 in which the shape of the SiO2protective film satisfies the relations: L1≦p1and L2≧p2, spurious around the resonance frequency is not observed. Furthermore, the insertion loss in the example 1 is remarkably improved as compared with the insertion loss in the comparative examples 3 and 4.

Next, for comparison, SAW devices of a comparative example 5 and an example 2 are produced. A SAW device of the comparative example 5 has the electrode normalized film thickness of 3%≦h/(2×p)≦9% and the shape of the SiO2protective film satisfying the relations: L1>p1and L2<p2. SAW device10of the example 2 has the electrode normalized film thickness of 4.5% h/(2×p)≦9% and the shape of the SiO2protective film satisfying the relations: L1≦p1and L2≧p2. In the electrode normalized film thickness, 4.5% h/(2×p)≦9% means 0.045≦h/(2×p) 0.09. The same is true in the condition relations mentioned below.

The SAW device satisfying the conditions of the example 2 is produced as shown inFIG. 8Aas an L-type filter in which SAW devices10shown inFIG. 1are connected in serial-parallel arrangement. Similarly, the SAW device satisfying the conditions of the comparative example 5 is produced as shown inFIG. 8Aas an L-type filter. As shown inFIG. 8A, surface acoustic wave filter80(hereinafter, referred to as “filter80”) is formed on substrate81made of the LN substrate and includes serially connected surface acoustic wave device83(hereinafter, referred to as “SAW device83”) and parallel connected surface acoustic wave device84(hereinafter, referred to as “SAW device84”). Furthermore, by using SAW device10for at least one of SAW device83and SAW device84, the effect and advantage of the present invention can be obtained.

Furthermore, when filter80shown inFIG. 8Ais produced by using SAW device10, pitch p between the electrodes shown inFIG. 2is adjusted so that the resonance frequency of SAW device83coincides with the anti-resonance frequency of SAW device84.

In addition,FIG. 9shows the temperature coefficient of frequency (TCF) measured in the center frequency in the filter properties of the SAW devices satisfying the conditions of the comparative example 5 and the example 2. InFIG. 9, line segment42shows the temperature coefficient of frequency of the example 2 and line segment55shows the temperature coefficient of frequency of the comparative example 5. Note here that the temperature coefficient of frequency (TCF) is one of the physical properties determined by the temperature coefficient and the thermal expansion coefficient of the dielectric constant with respect to the surrounding temperature and expressed by the rate of change per K (ppm/K). It is shown that as the value of temperature coefficient of frequency (TCF) is smaller, the SAW device can be stably used in the wider temperature range.

As shown inFIG. 9, in the SAW device of the comparative example 5 in which the shape of the SiO2protective film satisfies the relations: L1>p1and L2<p2, when the electrode normalized film thickness is increased, the temperature coefficient of frequency is deteriorated. However, in SAW device10of the example 2 in which the shape of SiO2protective film4satisfies the relations: L1≦p1and L2≧p2, even if the electrode normalized film thickness is increased, the temperature coefficient of frequency is still excellent. In particular, the higher the electrode normalized film thickness is, the larger the effect becomes.

Furthermore,FIG. 8Bis a top view showing a ladder type surface acoustic filter as another electronic component in accordance with the first exemplary embodiment. As shown inFIG. 8B, ladder type surface acoustic wave filter80includes a plurality of serially connected surface acoustic wave devices83and a plurality of parallel connected surface acoustic wave devices84on substrate81. Furthermore, filter80includes input terminal85, output terminal86, ground terminal87and line88on substrate81. The plurality of SAW devices83are disposed between input terminal85and output terminal86. Line88connects input terminal85to SAW device83, connects SAW device83to output terminal86, and connects between SAW devices83. Furthermore, branch portion89is provided between input terminal85and output terminal86. The plurality of SAW devices84are disposed between branch point89and ground terminal87. Then, line88connects branch point89to SAW device84, connects SAW device84to ground terminal87, and connects between SAW devices84. SAW devices83and SAW devices84connected in this way are called serial connection and parallel connection, respectively. Furthermore, SAW devices83and SAW devices84are covered with protective film82. Pitch p between electrodes is adjusted so that the resonance frequency of SAW device83coincides with the anti-resonance frequency of SAW device84. Furthermore, by using SAW device10for at least one of the plurality of SAW devices83and the plurality of SAW devices84, the effect and advantage of the present invention can be obtained. Filter80shown inFIG. 8Bincludes four SAW devices83, two SAW devices84and one branch point89. However, filter80is not limited to this configuration. The combination of SAW device83, SAW device84and branch point89may be determined depending upon characteristics required by filter80.

Furthermore,FIG. 8Cis a schematic configuration view showing a longitudinal mode binding type surface acoustic wave filter as another electronic component in accordance with the first exemplary embodiment. As shown inFIG. 8C, longitudinal mode binding type surface acoustic wave filter90(hereinafter, referred to as “filter90”) includes a plurality of surface acoustic wave devices10a(hereinafter, referred to as “SAW devices10a”) disposed along the direction in which the surface acoustic wave propagates (in the direction shown by an arrow91). In addition, IDTs22constituting neighboring SAW devices10aare in adjacent to each other. Furthermore, SAW device10aincludes a pair of IDTs22facing each other. The difference between SAW device10aand SAW device10is in that individual SAW device10adoes not include a pair of reflector electrodes3respectively but filter90as a whole includes a pair of reflector electrodes3. Therefore, similar to SAW device10, SAW device10ahas a configuration in which the shape of SiO2protective film4satisfies the relations: L1≦p1and L2≧p2. In addition, SAW device10ahas the same configuration as SAW device10in terms of the conditions such as the electrode normalized film thickness. Thus, also in the configuration of filter90, the same effect and advantage as those of SAW device10can be exhibited. Note here that filter90shown inFIG. 8Cincludes three SAW devices10a. However, filter90is not necessarily limited to this configuration. A plurality of SAW devices10amay be disposed along the direction in which a surface acoustic wave propagates (in the direction shown by arrow91). Furthermore, it is not necessary that SAW device10ais used in all the surface acoustic wave devices. At least one surface acoustic wave device may be SAW device10a.

As mentioned above, when protective film4is formed so that the electrode normalized film thickness is h/(2×p)≧4.5% and the shape of SiO2protective film4satisfies the relations: L1≦p1and L2≧p2, it is possible to obtain SAW devices10and10ahaving an excellent temperature characteristics and an excellent electrical characteristic.

In the first exemplary embodiment, Al or an Al alloy is used for electrode film32. However, materials of electrode film32, that is, electrode finger22aof IDT22and reflector electrode3are not limited to these materials. For example, a heavy metal having a higher density than Al, for example, Ti, Cu, W, Ag, Au, or the like, may be used. In addition, an ally including a metal having a higher density than Al as a main component may be used.

Furthermore, as shown inFIG. 10, electrode film32may be formed by laminating first electrode film32aand second electrode film32b. For example, Al or an Al alloy may be used for first electrode film32a, and a material having a higher density than Al, for example, Ti, Cu, W, Ag, Au, or the like, or an alloy including such materials as a main component may be used for second electrode film32b. Furthermore, alternatively, a material having a higher density than Al, for example, Ti, Cu, W, Ag, Au, or the like, or an alloy including such materials as a main component may be used for first electrode film32a, and Al or an Al alloy may be used for second electrode film32b. When a metal having a higher density than Al is used for first electrode film32aor second electrode film32b, or electrode film32, actual thickness h0of electrode film32for obtaining the predetermined electrode normalized film thickness h is reduced.

Furthermore, as protective film4, the SiO2material is used. However, a material of protective film4is not limited to the SiO2material. For example, other dielectric materials such as SiN, SiON, Ta2O5, and TeO2may be used. In addition, combinations of such dielectric materials may be used. That is to say, as long as the shape of protective film4made of a dielectric material satisfies the conditions of L1≦p1and L2≧p2, the same effects can be obtained.

In the first exemplary embodiment, IDT22is weighted by apodization. However, as to the weighting ratio by apodization is not limited to the configuration shown inFIG. 1. When the weighting ratio is 0, that is to say, when the weighting is not carried out at all, SAW device10is a normal type resonator. Furthermore, the number of pairs of IDTs22and the number of reflector electrodes3disposed on both sides of IDT22are not limited to those shown inFIG. 1. Note here that the ratio of weighting by apodization means a ratio of a region of IDT22in which the crossing width of electrode finger22ais different from the width of SAW device10.

Furthermore, as the method of forming protective film4, the bias sputtering method is used. However, the method of forming protective film4is not limited to the bias sputtering method. Other methods of forming protective film4may be used.

Second Exemplary Embodiment

A SAW device as an electronic component in accordance with a second exemplary embodiment of the present invention is described with reference to drawings.

The same reference numerals are given to the same configurations of the second exemplary embodiment as those of the first exemplary embodiment, and the detailed description thereof is omitted.

FIG. 11is a top view showing a main part of a SAW device as an electronic component in accordance with the second exemplary embodiment of the present invention.FIG. 12is a sectional view of the SAW device taken along line12-12ofFIG. 11. Similar toFIG. 12,FIG. 13is a sectional view showing the SAW device. InFIGS. 11 and 12, SAW device10includes substrate1, IDT22, reflector electrode3and protective film4. IDT22and reflector electrode3are provided on the upper surface of substrate1and includes Al or an Al alloy. Protective film4is made of SiO2and covers IDT22and reflector electrode3. Also, protective film4has the uneven shape on the surface thereof.

Furthermore, the equivalent film thickness of aluminum of IDT22is h. Furthermore, a value of an electrode normalized film thickness: h/(2×p)=h/λ is 7.8%≦h/(2×p)≦9.8%. Note here that wavelength: λ=2×p is a wavelength in the operation center frequency of the surface acoustic wave in SAW device10.

Furthermore, substrate1is made of lithium niobate cut out from a Y-plate rotated by D degree around the X-axis in the Z-axis direction. Rotation angle D satisfies −25 degree≦D≦+25 degree, and further preferably, 0 degree≦D≦+25 degree.

Similar to SAW device10in accordance with the first exemplary embodiment, SAW device10in accordance with the second exemplary embodiment satisfies the relations: L1≦p1and L2≧p2.

A method of manufacturing SAW device10in accordance with the second exemplary embodiment is the same as the method of manufacturing SAW device10in accordance with the first exemplary embodiment described with reference toFIGS. 3A to 3H. Therefore, the detailed description is omitted.

Next,FIG. 14shows a relation between the electrode normalized film thickness and normalized Qs as a Q value of a resonance point of SAW device10in accordance with the second exemplary embodiment of the present invention.FIG. 15shows a relation between the electrode normalized film thickness of SAW device10and normalized Qp as a Q value of an anti-resonance point.FIGS. 16 and 17show a passing property of SAW device10.FIG. 18shows a relation between the electrode normalized film thickness of SAW device10and an attenuation. Herein, normalized Qs and normalized Qp are normalized by using Qs and Qp when the electrode normalized film thickness is 5.8%.

Note here that protective film4uses SiO2. In film thickness t of SiO2protective film4, the SiO2normalized film thickness: t/(2×p)=t/λ is 20%.

As shown inFIGS. 14 and 15, when the electrode normalized film thickness satisfies 7.8%≦h/(2×p)≦9.8%, normalized Qs and normalized Qp are 1.2 or more. Thus, SAW device10having a high Q value can be obtained. In particular, when the electrode normalized film thickness satisfies 8.5%≦h/(2×p)≦9.0%, the Q value becomes highest.

Furthermore,FIGS. 16 and 17show the passing property of SAW device10.FIG. 17shows the passing property when the electrode normalized film thickness is 8.7%. Furthermore,FIG. 16shows the passing property when the electrode normalized film thickness is 5.8%. As shown inFIGS. 16 and 17, the attenuation of SAW device10when the electrode normalized film thickness is in the range of 7.8%≦h/(2×p)≦9.8% is larger by about 6 dB as compared with the attenuation of SAW device10when the electrode normalized film thickness is 5.8%. Note here that the displacement of the frequency is caused by the difference in the electrode normalized film thickness. The configurations of the SAW devices such as the number of pairs, crossing width, or the like, of IDT22have the substantially same characteristics. Furthermore, as shown inFIG. 18, when the electrode normalized film thickness is in the range of 7.8%≦h/(2×p)≦9.8%, the attenuation is larger by about 5 dB or more as compared with the case in which the electrode normalized film thickness is 5.8%. In particular, when the electrode normalized film thickness is in the range of 8.5%≦h/(2×p)≦9.0%, the most excellent property also in terms of the attenuation is exhibited.

FIGS. 19 and 20show the filter property of a ladder-type filter in which SAW devices10are connected like a ladder. An example of the ladder type filter includes a configuration of filter80having one stage of serial SAW device83and one stage of parallel SAW device84, as shown inFIG. 8A.FIG. 20is an enlarged view enlarging part903of the filter property shown inFIG. 19. Furthermore, inFIGS. 19 and 20, line segment901shows the filter property when the electrode normalized film thickness of parallel SAW device84is 7.8% and the electrode normalized film thickness of serial SAW device83is 8.3%. Furthermore, line segment902shows the filter property when the electrode normalized film thickness of parallel SAW device84is 5.8% and the electrode normalized film thickness of serial SAW device83is 6.2%. As shown inFIGS. 19 and 20, when the electrode normalized film thickness is in the range of 7.8%≦h/(2×p)≦9.8%, the insertion loss is improved by 0.1 dB. Note here that the displacement of the frequency is caused by the difference in the electrode normalized film thickness. The configurations of the SAW devices such as the number of pairs, crossing width, or the like, of IDT22have the substantially same characteristics.

Furthermore, as protective film4, the SiO2material is used. However, a material of protective film4is not limited to the SiO2material. For example, other dielectric materials such as SiN, SiON, Ta2O5, and TeO2may be used. In addition, combinations of such dielectric materials may be used.

Furthermore, when SAW device10constitutes an antenna duplexer as an SAW filter, pitch p of electrode finger22amay be different between a transmitting SAW filter and a receiving SAW filter. In this case, when electrode film thicknesses h are equal to each other, the electrode normalized film thickness h/(2×p) becomes different. Therefore, by changing the electrode film thicknesses h of the transmitting SAW filter and the receiving SAW filter, respectively, an antenna duplexer having an optimal configuration can be obtained.

Furthermore, when ladder-type filter80as shown inFIG. 8AorFIG. 8Bis configured, if the pitch of electrode finger22ais different between serial SAW device83and parallel SAW device84, the electrode normalized film thickness becomes different. In this case, by changing the electrode film thicknesses h in serial SAW device83and parallel SAW device84, a configuration capable of obtaining optimum filter properties can be realized. Furthermore, the conditions of SAW device10as shown inFIG. 8Cin the second exemplary embodiment can be applied to a SAW device used in a longitudinal mode binding type surface acoustic wave filter.

Third Exemplary Embodiment

A SAW device as an electronic component in accordance with a third exemplary embodiment of the present invention is described with reference to drawings.

In SAW device10in accordance with the third exemplary embodiment, SAW device10having the same configuration as SAW device10used in the first or second exemplary embodiment is used, and filter80shown inFIG. 8Ais produced. Therefore, since the structure and the manufacturing method of SAW device10in the third exemplary embodiment are the same as those of SAW device10respectively shown inFIGS. 1,2and3, the detail description is omitted.

In the third exemplary embodiment, in order to clarify the relation between the film thickness of SiO2protective film4and the temperature characteristics, four kinds of SAW devices having different film thicknesses of SiO2protective film4are produced.FIG. 21shows a relation between the film thickness of SiO2protective film4and the temperature coefficient of frequency. InFIG. 21, line segment40shows the relation between the film thickness of SiO2protective film4and the temperature coefficient of frequency. SAW device10in accordance with the third exemplary embodiment satisfies the relations: L1≦p1and L2≧p2. Furthermore, the electrode normalized film thickness h/(2×p) of IDT22is 4.5%.

As shown inFIG. 21, as the SiO2normalized film thickness is increased, the temperature coefficient of frequency is improved. Furthermore, when the SiO2normalized film thickness t/(2×p) reaches 30%, almost zero temperature coefficient is realized. Therefore, when SAW device10is manufactured so that it satisfies the relations: L1≦p1and L2≧p2and the film thickness of SiO2protective film4satisfies the relation: t/(2×p)≦30%, SAW device10having the excellent temperature characteristics and the excellent characteristics can be obtained.

Fourth Exemplary Embodiment

A SAW device as an electronic component in accordance with a fourth exemplary embodiment of the present invention is described with reference to drawings.

SAW device10in accordance with the fourth exemplary embodiment uses SAW device10having the same configuration as SAW device10used in the first or second exemplary embodiment. Therefore, since the structure and the manufacturing method of SAW device10are the same as those of SAW device10shown inFIGS. 1,2and3, the detail description is omitted.

In the fourth exemplary embodiment, SAW device10satisfies the relations: L1≦p1and L2≧p2. Furthermore, in the fourth exemplary embodiment, the electrode normalized film thickness: h/(2×p) of IDT22used in all examples and comparative examples is 4.5%.

In the fourth exemplary embodiment, in order to show the relation between a cut-out angle D degree of substrate1and the electromechanical coupling coefficient of SAW device10in which protective film4having the shape shown in the first exemplary embodiment is formed, SAW devices using six kinds substrates having different cut-out angles are produced.FIG. 22shows the relation between the cut-out angle and the electromechanical coupling coefficient. InFIG. 22, values43,44, and45show the electromechanical coupling coefficients of examples 3, 4, 5, respectively. Furthermore, values56,57, and58show the electromechanical coupling coefficients of the comparative examples 6, 7, and 8, respectively. The examples 3, 4, and 5 show the electromechanical coupling coefficients when D is 5 degree, 15 degree, and −5 degree, respectively. Furthermore, the comparative examples 6 and 7 show the electromechanical coupling coefficients when D is 41 degree and 64 degree, respectively. Furthermore, the comparative example 8 shows the electromechanical coupling coefficient when the SiO2protective film is not provided and D is 64 degree. As shown inFIG. 22, the coupling coefficient when the cut-out angle D is 41 degree is about 11% and the coupling coefficient when the cut-out angle D is 64 degree is about 5.5%. On the contrary, in the examples 3, 4 and 5, extremely large electromechanical coupling coefficients are obtained. Furthermore, as the comparative example 8, the electromechanical coupling coefficient when the SiO2protective film is not provided and D is 64 degree is shown in the drawing. Therefore, in order to obtain an electromechanical coupling coefficient that is not smaller than the electromechanical coupling coefficient when the SiO2protective film is not provided, D satisfies at least the relation: −25 degree≦D≦25 degree.

Therefore, when SAW device10is produced so that it satisfies the relations: L1≦p1and L2≧p2and the cut-out angle D of the LN substrate satisfies the relation: −25 degree≦D≦25 degree, SAW device10having the excellent temperature characteristics and the large electromechanical coupling coefficient can be obtained. As to the cut-out angle D of the LN substrate, a rotation angle around the X-axis in the Z-axis direction is defined as D degree.

Fifth Exemplary Embodiment

A SAW device as an electronic component in accordance with a fifth exemplary embodiment of the present invention is described with reference to drawings.

SAW device10in accordance with the fifth exemplary embodiment is different from SAW device10used in the first or second exemplary embodiment in substrate1used for SAW device10. That is to say, in SAW device10in accordance with the fifth exemplary embodiment, a bonded substrate of a 5° Y-LN substrate cut out from a Y-plate rotated by D=5 degree around the X-axis in the Z-axis direction and a silicon substrate is used as substrate1. The configuration of other than substrate1is the same as in SAW device10used in the first or second exemplary embodiment. As a method of bonding the LN substrate and the silicon substrate to each other, a method such as a direct bonding technology or a bonding method using an adhesive agent can be used.

Similar to the first to fourth exemplary embodiments, SAW device10in accordance with the fifth exemplary embodiment satisfies the relations: L1≦p1and L2≧p2. In order to show the relation of the temperature characteristics depending upon the presence of lamination of the silicon substrate, two kinds of SAW devices10are produced.

FIGS. 23 and 24show the electrical characteristics of SAW device10measured in the temperature environment of −35 degree Celsius, 25 degree Celsius, and +85 degree Celsius, respectively.

FIG. 23shows the characteristic as a comparative example 9, when the 5° Y-LN substrate is used as substrate1. Line segments59a,59band59cshow the electrical characteristics of the SAW device as the comparative example 9 measured in the temperature environment of −35 degree Celsius, 25 degree Celsius, and +85 degree Celsius, respectively. Furthermore,FIG. 24shows the characteristic as an example 6 when the bonded substrate of the 5° Y-LN substrate and the silicon substrate is used as substrate1. Similarly, line segments45a,45band45cshow the electrical characteristics of SAW device10of the example 6 measured in the temperature environment of −35 degree Celsius, 25 degree Celsius, and +85 degree Celsius, respectively. As shown inFIGS. 23 and 24, the frequency variation with respect to temperatures when the bonded substrate of the 5° Y-LN substrate and the silicon substrate is used as substrate1is smaller as compared with the frequency variation with respect to temperatures when the 5° Y-LN substrate is used as substrate1. The temperature coefficient of frequency calculated from the anti-resonant frequency in the respective characteristics is about −33 ppm/K when the 5° Y-LN substrate is used as substrate1. On the contrary, the temperature coefficient of frequency is about −10 ppm/K when the bonded substrate of the 5° Y-LN substrate and the silicon substrate is used as substrate1, showing a significant improvement. Therefore, when the bonded substrate of the LN substrate and the silicon substrate is used as substrate1, it is possible to obtain SAW device10having further excellent temperature characteristics and electrical characteristic.

Although the fifth exemplary embodiment does not refer to a thickness of the LN substrate, when the LN substrate is polished so as to be thin and then laminated with a silicon substrate, an effect of further improvement of the temperature characteristics can be obtained.

Furthermore, in the fifth exemplary embodiment, the silicon substrate is used. However, when glass, sapphire, or the like, having smaller coefficient of thermal expansion than the silicon substrate is used, the equal or higher effect can be obtained.

Sixth Exemplary Embodiment

In a sixth exemplary embodiment, a mobile phone is described as an example of electronic equipment.

FIG. 25is an overview diagram showing a mobile phone in accordance with the sixth exemplary embodiment of the present invention.FIG. 26is an electric-circuit diagram showing a main part stored inside the mobile phone shown inFIG. 25. As shown inFIG. 25, mobile phone140includes first case141and second case142, which are held around hinge part143in a way capable of opening and closing. Furthermore, mobile phone140has display part144and antenna151provided on first case141, and input part145provided on second case142. Furthermore, a circuit such as radio circuit (not shown) is stored inside first case141and second case142, respectively. As shown inFIG. 26, mobile phone140includes antenna151and antenna duplexer152connected to antenna151. Antenna duplexer152includes transmitting SAW filter153, receiving SAW filter154and phase circuit155. Transmitting SAW filter153and receiving SAW filter154are configured by connecting plural stages of SAW devices10described in the first to fifth exemplary embodiments in serial-parallel arrangement. Antenna duplexer152is an electric circuit that is electrically connected to antenna151, for example, an antenna duplexer for WCDMA.

Furthermore, transmitting SAW filter153and receiving SAW filter154constituting antenna duplexer152may have different pitches of electrode finger22a. However, by allowing transmitting SAW filter153and receiving SAW filter154to have different electrode normalized film thicknesses respectively, the frequency characteristics can be adjusted. When transmitting SAW filter153and receiving SAW filter154have different pitches of electrode finger22a, since electrode film thickness h can be changed between a filter at the transmitting side and a filter at the receiving side, an optimum configuration of antenna duplexer152can be obtained.

FIG. 27shows the electrical characteristics of antenna duplexer152using transmitting SAW filter153and receiving SAW filter154. Line segment47shows the electrical characteristic of transmitting SAW filter153and line segment48shows the electrical characteristic of receiving SAW filter154. In the passband, an excellent insertion loss of about −1.5 dB is realized. Furthermore, also in the stopband, an excellent attenuation of about −60 dB is realized. Note here that the passband means the range from 1920 MHz to 1980 MHz at the transmitting side and the range from 2110 MHz to 2170 MHz at the receiving side. Furthermore, the stopband means the range from 2110 MHz to 2170 MHz at the transmitting side and the range from 1920 MHz to 1980 MHz at the receiving side. In this way, when SAW devices10described in the first to fifth exemplary embodiments are used in the electronic equipment, it is possible to easily obtain an antenna duplexer that is excellent in the temperature characteristics and the electrical characteristics.

INDUSTRIAL APPLICABILITY

As mentioned above, according to the present invention, a protective film is formed so as to cover an electrode formed on a substrate. By setting the shape or the thickness of the protective film to a specific range, it is possible to obtain a surface acoustic wave device that is excellent in the temperature characteristics and the electrical characteristic.