JP4096888B2 - Piezoelectric thin film filter, duplexer, communication device - Google Patents

Description

  The present invention relates to a piezoelectric thin film filter, a duplexer, and a communication device.

  2. Description of the Related Art Conventionally, there have been remarkable technological advances in recent years in reducing the size and weight of communication devices such as mobile phones. As means for realizing this, not only the reduction and miniaturization of each component of the communication device but also the development of a component combining a plurality of functions has progressed. In particular, high performance is also required for filters and duplexers used in the RF stage.

  A ladder-type piezoelectric thin film filter is used as a filter used in the RF stage or a filter constituting the duplexer as described above. As described in Patent Document 1, the ladder-type piezoelectric thin film filter includes a substrate having an opening or a recess and a thin film portion having at least one layer of piezoelectric thin film formed on the opening or the recess. A piezoelectric thin film resonator having at least a pair of upper and lower electrodes sandwiching the upper and lower surfaces of the piezoelectric thin film resonator as a series resonator and a parallel resonator is arranged in a ladder shape.

  The filter used in the RF stage and the filter constituting the duplexer are required to have a steep characteristic of attenuation on the low band side or high band side of the pass band depending on the application. In particular, a duplexer requires a transmission side filter and a reception side filter, but depending on the application, it may be required to extremely narrow the frequency interval between the transmission side and the reception side. In the above case, the transmission side filter located on the relatively low frequency side has a steepness (large attenuation) on the high frequency side in the vicinity of the outside of the passband, and the reception side filter located on the relatively high frequency side. The steepness on the low frequency side near the outside of the passband is required.

  For example, in PCS in North America, the transmission band is 1850 MHz to 1910 MHz, the reception band is 1930 MHz to 1990 MHz, and the transmission / reception interval (Guard-band) is only 20 MHz, which corresponds to only 1% of the carrier frequency. In this 20 MHz, it is necessary to contain the filter steepness (roll-off) in consideration of the amount of frequency change accompanying the temperature change and manufacturing variation, so a filter having the steepest characteristic as much as possible is required.

In the case of the reception side filter, a low insertion loss (for example, 3.0 dB) is required in the pass band, and a high attenuation amount (for example, 50 dB) is required in the frequency band on the other side (the pass band of the transmission side filter). Therefore, steepness is required to ensure attenuation from 3.0 dB to 50 dB from 1930 MHz to 1910 MHz. Actually, since it is necessary to consider the amount of frequency change accompanying the temperature change and manufacturing variations, it is desirable that the frequency width of transition from 3.0 dB to 50 dB is about 10 MHz. The same applies to the transmission side filter. FIG. 2 shows a schematic diagram of the reception-side filter characteristics.
JP 2002-359539 A (publication date: December 13, 2002)

  However, with the conventional ladder-type piezoelectric thin film filter as described in Patent Document 1, it has been difficult to realize the steepness as described above.

  In the ladder-type piezoelectric thin film filter, the steepness on the low pass band side is determined by the frequency interval between the resonance point and the antiresonance point of the parallel resonator, and the steepness on the high pass band side is the resonance point of the parallel resonator. It depends on the frequency interval of the antiresonance point. Therefore, by narrowing the frequency interval between the resonance point and the antiresonance point of the parallel resonator or series resonator, the steepness of the passband low band side or high band side can be improved.

The ladder-type piezoelectric thin film filter described in Patent Document 1 is composed of a piezoelectric thin film resonator using a fundamental wave. Since the piezoelectric thin film resonator using the fundamental wave has a large electromechanical coupling coefficient k ^2, it is difficult to narrow the frequency interval between the resonance point and the antiresonance point of the piezoelectric thin film resonator, and it is difficult to improve the steepness. The problem that it was.

In order to solve the above problems, a piezoelectric thin film filter as a basis of the present invention includes at least a pair of a substrate and upper and lower surfaces of a thin film portion having at least one piezoelectric thin film acoustically separated from the substrate. A piezoelectric thin film filter in which a plurality of piezoelectric thin film resonators having a structure in which an upper electrode and a lower electrode are opposed to each other are arranged in a ladder form as a series resonator and a parallel resonator, respectively. It is characterized in that the electromechanical coupling coefficient k ² of the series resonator and the parallel resonator are different from each other.

According to the above configuration, by making the electromechanical coupling coefficient k ² of the series resonator and the parallel resonator different from each other, that is, by reducing the electromechanical coupling coefficient k ² of the piezoelectric thin film resonator serving as the parallel resonator. The frequency interval between the resonance point and the antiresonance point of the parallel resonator can be narrowed. Thereby, the said structure can improve the steepness of the low-pass side of the vicinity outside a pass band.

Conversely, the frequency interval between the resonance point and the antiresonance point of the series resonator can be narrowed by setting the electromechanical coupling coefficient k ² of the piezoelectric thin film resonator to be the series resonator small. Thereby, the said structure can improve the steepness of the high region side of the vicinity outside a pass band.

Pressure conductive thin film filter of the present invention, in order to solve the above problems, a substrate and are acoustically separated from the substrate, at least one pair of upper and lower surfaces of the thin film portion having a piezoelectric thin film of at least one or more layers A piezoelectric thin film filter in which a plurality of piezoelectric thin film resonators having a structure in which an electrode and a lower electrode are opposed to each other are arranged in a ladder shape as a series resonator and a parallel resonator. One of the resonator and the parallel resonator has a piezoelectric thin film resonator having an n-th harmonic (n is a positive integer) as a main vibration, and the other of the series resonator and the parallel resonator (an integer of (n + 1) or more) a harmonic. It is characterized by using a piezoelectric thin film resonator whose main vibration is.

  According to the above configuration, the piezoelectric thin film resonator having the nth harmonic as the main vibration is used as the series resonator, and the piezoelectric thin film resonator having the (twisted (n + 1) or more) harmonic as the main vibration is used as the parallel resonator. As an example, a piezoelectric thin film resonator having a fundamental wave as a main vibration is used as a series resonator, and a piezoelectric thin film resonator having a second harmonic as a main vibration is used as a parallel resonator.

Therefore, in the above configuration, the piezoelectric thin film resonator having a harmonic as the main vibration (an integer greater than (n + 1)) has an electromechanical coupling coefficient k ² as compared with the piezoelectric thin film resonator having the n harmonic as the main vibration. The frequency interval between the resonance point and the antiresonance point of the parallel resonator can be reduced. Thereby, the said structure can improve the steepness of the low-pass side outside a pass band.

  In the above-described piezoelectric thin film filter, the piezoelectric thin film resonator whose main vibration is an ((n + 1) or more integer) harmonic wave has an insulating film between the substrate and the lower electrode, and the insulating film is a piezoelectric thin film. It is preferable to have different frequency temperature coefficients.

  According to the above configuration, the temperature characteristics can be improved by using a combination of films having different frequency temperature coefficients.

  In the piezoelectric thin film filter, an upper insulating film made of the same material may be provided on the upper electrodes of the series resonator and the parallel resonator. The piezoelectric thin film filter may have upper insulating films made of different materials on the upper electrodes of the series resonator and the parallel resonator.

  In the above-described piezoelectric thin film filter, the piezoelectric thin film resonator whose main vibration is the (multiple of (n + 1) or more) harmonics may have an insulating film on the upper electrode. In the piezoelectric thin film filter, the insulating film preferably has a frequency temperature coefficient different from that of the piezoelectric thin film.

  In the piezoelectric thin film filter, an intermediate insulating film may be provided between the insulating film on the upper electrode and the upper electrode. In the piezoelectric thin film filter, the intermediate insulating film may also be formed on an upper electrode of a piezoelectric thin film resonator having an n-th harmonic as a main vibration.

  In the piezoelectric thin film filter, the piezoelectric thin film resonance having an insulating film made of the same material on each of the upper electrodes of the series resonator and the parallel resonator and having the ((n + 1) or more) harmonic as a main vibration. The insulating film on the upper electrode of the child is preferably thicker than the insulating film on the upper electrode of the piezoelectric thin film resonator whose main vibration is n-th harmonic.

  The duplexer of the present invention is characterized by using any of the piezoelectric thin film filters described above in order to solve the above-described problems.

  In order to solve the above-mentioned problems, a communication device of the present invention is characterized by using any one of the above-described piezoelectric thin film filters or the above branching filter.

The piezoelectric thin-film filter having a basic of the invention, as described above, the series resonator and the parallel resonator which is arranged in ladder, the electromechanical coupling coefficient k ² of the series resonator and the parallel resonator is different configurations It is.

Therefore, in the above configuration, the frequency interval between the resonance point and the antiresonance point of the resonator is controlled by making the electromechanical coupling coefficient k ² different from each other, so that the high band or the low band side near the outside of the pass band is steep. Therefore, when used in a duplexer, the isolation characteristics between the receiving side and the receiving side can be improved, and the transmission characteristics when the duplexer is used in a communication device can be improved.

Pressure conductive thin film filter of the present invention, as described above, (n is a positive integer) one to n harmonic of the series resonator and the parallel resonator of the piezoelectric thin-film resonator that the the principal vibration, the other ((n + 1 It is a configuration using a piezoelectric thin film resonator whose main vibration is an integer above)).

  Therefore, the above configuration controls the frequency interval between the resonance point and the anti-resonance point of the resonator by making the main vibration different between the series resonator and the parallel resonator, so that Since it can improve the steepness of the high band or low band side, when used in a duplexer, it can improve the isolation characteristics between the receiving side and the receiving side, and when the duplexer is used in a communication device Transmission characteristics can be improved.

  Each embodiment of the present invention will be described with reference to FIGS. 1 to 15 as follows.

(First embodiment)
FIG. 1 shows a ladder-type piezoelectric thin film filter according to a first embodiment of the piezoelectric thin film filter of the present invention. In the present embodiment, the ladder-type piezoelectric thin film filter constitutes a PCS reception filter having a passband of 1930 MHz to 1990 MHz.

  As shown in FIG. 1A, the ladder-type piezoelectric thin film filter of the present embodiment has a plurality of piezoelectric resonators arranged in, for example, a π-type ladder type, and is arranged on a signal path. It has a series resonator 12 and a parallel resonator 11 arranged between the signal path and the ground side.

The ladder-type piezoelectric thin film filter has the following structure shown in FIG. The parallel resonator 11 includes, in a Si substrate 1 having an opening 1a, an insulating film 2 made of SiO ₂ formed on the opening 1a, a lower electrode 3 made of Al on the insulating film 2, and a piezoelectric made of AlN. The piezoelectric thin film resonator has a structure in which a thin film 4 and an upper electrode 5a made of Al are sequentially formed, and a second harmonic wave is a main vibration.

  On the other hand, the series resonator 12 includes, in the Si substrate 1 having the opening 1a, the lower electrode 3 made of Al, the piezoelectric thin film 4 made of AlN, and the upper electrode 5b made of Al formed in order on the opening 1a. A piezoelectric thin film resonator having a formed structure and having a fundamental wave as a main vibration. In the parallel resonator 11 and the series resonator 12, the portions of the lower electrode 3 and the upper electrodes 5a and 5b sandwiching the piezoelectric thin film 4 on the opening 1a form a vibrating portion (diaphragm). By forming the vibration part on such an opening 1 a or a concave part to be described later, the vibration part is acoustically separated from the Si substrate 1.

  In the structure of the present embodiment, the resonance frequency difference between the series resonator 12 and the parallel resonator 11 can be realized by the insulating film 2. Therefore, since the film thicknesses of the lower electrode 3, the upper electrodes 5 a and 5 b, and the piezoelectric thin film 4 can all be set to be the same, they can be manufactured in the same process, so that manufacturing is easy.

The insulating film 2 made of SiO _{2 of the} parallel resonator 11 may be formed by oxidizing the Si substrate 1 by thermal oxidation or the like, or may be formed by film formation by sputtering. Further, instead of the insulating film 2 made of SiO _2, SiO ₂ and AlN laminate film, a multilayer film of SiO ₂ and Al ₂ O ₃ may be used as the insulating film 2.

  In the present embodiment, the piezoelectric thin film 4 made of AlN is used. However, the present invention is not limited to this, and a piezoelectric thin film made of ZnO may be used. Furthermore, in the present embodiment, the electrodes 3, 5a, 5b made of Al are used, but the present invention is not limited to this, and Cu, Mo, Pt, Ir, Ta, W, Au, Ag, or theirs An alloy may be used.

Further, in FIG. 1 (b), the insulating film 2 made of SiO ₂ is formed only on the parallel resonator 11 may be formed similar insulating film even in the series resonator 12.

  In addition, in the structure of FIG. 1B, an upper insulating film made of the same material may be further formed on the upper electrodes 5a and 5b of the parallel resonator 11 and the series resonator 12, respectively. By etching this upper insulating film, the frequency of the series resonator and the parallel resonator, that is, the frequency of the ladder type piezoelectric thin film filter can be adjusted.

  In the structure of FIG. 1B, an upper insulating film made of a material having a different etching rate may be further formed on the upper electrodes 5a and 5b of the parallel resonator 11 and the series resonator 12, respectively. By etching the upper insulating film made of this different material, the frequency of only one of the series resonator 12 and the parallel resonator 11 can be adjusted.

  The ladder-type piezoelectric thin film filter according to the first embodiment of the present invention is characterized in that the parallel resonator 11 has a piezoelectric thin film resonator whose main vibration is a double wave having a relatively narrow frequency interval between the resonance point and the antiresonance point. The series resonator 12 is a piezoelectric thin film resonator whose main vibration is a fundamental wave having a relatively wide frequency interval between the resonance point and the antiresonance point.

In the present embodiment, since the parallel resonator 11 is a piezoelectric thin film resonator whose main vibration is a second harmonic, vibration energy is transmitted to the outside of the piezoelectric thin film 4 (here, the insulating film 2), and thus parallel resonance. The electromechanical coupling coefficient k ^{2 of the} child 11 is reduced, and the frequency interval between the resonance point and the antiresonance point can be narrowed. Thereby, the attenuation amount on the low pass band side can be made steep.

  In addition, in the parallel resonator 11 which is a piezoelectric thin film resonator having a second harmonic as the main vibration, the fundamental wave is also oscillated together with the second harmonic, but the frequency is higher than the frequency of the second harmonic which is the main vibration. Since the frequency is much lower, there is no problem in the frequency characteristics of the ladder-type piezoelectric thin film filter.

In the present embodiment, the parallel resonator 11 has a frequency temperature coefficient such as the piezoelectric thin film 4 made of AlN having a negative frequency temperature coefficient and the insulating film 2 made of SiO ₂ having a positive frequency temperature coefficient. However, the frequency change amount due to temperature change can be reduced, and in particular, the temperature characteristics on the low pass band side can be improved.

It has been experimentally found that the frequency temperature coefficient of the SiO ₂ film obtained by oxidizing the Si substrate 1 is about five times the frequency temperature coefficient of SiO _{2 formed} by sputtering. In order to cancel out the negative frequency temperature coefficient of AlN and to improve the temperature characteristics, SiO ₂ formed by sputtering may be insufficient. Therefore, SiO ₂ formed by thermal oxidation or sputtering in it it is preferable to use the formed SiO ₂ of a laminated film formed of SiO ₂ and the thermal oxide was.

  The ladder-type piezoelectric thin film filter having good steepness and temperature characteristics on the low pass band side as described above should be used as a reception side filter (a filter having a relatively high frequency) in the duplexer. Is preferred.

  FIG. 3 shows frequency characteristics on the low pass band side in the ladder-type piezoelectric thin film filter of the present embodiment. In the ladder type piezoelectric thin film filter of the present embodiment, the frequency interval between the resonance point and the antiresonance point of the parallel resonator 11 is 32 MHz, and the frequency interval between the resonance point and the antiresonance point of the series resonator 12 is 52 MHz.

  In FIG. 3, as Comparative Example 1, the series resonator and the parallel resonator, both of which are conventional structures, are piezoelectric thin film resonators having a fundamental wave as the main vibration, and the resonance points of the series resonator and the parallel resonator. The frequency interval of the antiresonance points is 52 MHz, and the characteristics of the ladder-type piezoelectric thin film filter having a pass band of 1930 MHz to 1990 MHz are also shown in the same manner as in this embodiment.

  The ladder-type piezoelectric thin film filter of Comparative Example 1 is a substrate in which both series resonators and parallel resonators have openings. A lower electrode made of Al, a piezoelectric thin film made of AlN, formed on the openings, Al The upper electrode is formed in order.

  Here, the roll-off of the filter was measured as a characteristic showing steepness. Here, roll-off is defined as the width of the frequency (freq.) Necessary for the insertion loss to transition from 3.0 dB to 50 dB, and the steeper characteristics become as the roll-off is smaller.

  As is clear from FIG. 3, in Comparative Example 1, the roll-off is 18 MHz, whereas in the present embodiment, the roll-off is 15 MHz, and the roll-off is small. That is, it can be seen that the frequency characteristics on the low pass band side are steep.

  FIG. 4 shows the frequency characteristics of the pass band in the ladder type piezoelectric thin film filter of the present embodiment. As in the case of FIG. 3, the ladder-type piezoelectric thin film filter of the present embodiment has a frequency interval between the resonance point of the parallel resonator 11 and the antiresonance point of 32 MHz, and the frequency between the resonance point of the series resonator 12 and the antiresonance point. The interval is 52 MHz.

  In FIG. 4, as a comparative example 2, both the series resonator and the parallel resonator are piezoelectric thin film resonators whose main vibration is a second harmonic, and the resonance points and antiresonance points of the series resonators and the parallel resonators. The characteristics of a ladder-type piezoelectric thin film filter whose frequency interval is 32 MHz are also shown.

In the ladder-type piezoelectric thin film filter of Comparative Example 2, both a series resonator and a parallel resonator are formed on a substrate having an opening, an insulating film made of SiO ₂ formed on the opening, and Al on the insulating film. A lower electrode, a piezoelectric thin film made of AlN, and an upper electrode made of Al are sequentially formed. In Comparative Example 2, as in Comparative Example 1, the pass band is 1930 MHz to 1990 MHz.

As is apparent from FIG. 4, in Comparative Example 2, good steepness can be obtained on both the low band side and the high band side of the pass band, but the insertion loss is deteriorated and the dent is generated in the central part in the pass band. And the characteristics are getting worse. In order to improve the steepness, in both the series resonator and the parallel resonance, the electromechanical coupling coefficient k ² of the resonator becomes small, and the frequency interval between the resonance point and the antiresonance point is narrow. This is because a piezoelectric thin film resonator is used. The principle of the dent will be described with reference to FIGS. 3 and 4 together with factors due to the difference in structure between the present embodiment and Comparative Examples 1 and 2.

  Normally, in a ladder filter, the parallel resonator's anti-resonance point and the series resonator's resonance point coincide with each other, and the parallel resonator's resonance point passes the attenuation pole on the low passband side. A resonance point forms an attenuation pole on the high side of the passband, and a bandpass filter is formed.

In Comparative Example 1, since the fundamental wave is the main vibration, a piezoelectric thin film resonator having a large electromechanical coupling coefficient k ² and a wide frequency interval between the resonance point and the antiresonance point is used for the series resonator and the parallel resonator. Yes. Therefore, the ladder type filter is configured by matching the antiresonance point of the parallel resonator and the resonance point of the series resonator. Therefore, there is no problem with the passband width and the insertion loss within the passband, but the steepness on both the low band side and the high band side of the pass band is insufficient.

On the other hand, in Comparative Example 2, since the second harmonic is the main vibration, the piezoelectric thin film resonator having a small electromechanical coupling coefficient k ² and a narrow frequency interval between the resonance point and the antiresonance point is used as the series resonator and the parallel resonator. Used for. In such a configuration, in order to achieve the same passband width as in Comparative Example 1, the antiresonance point of the parallel resonator and the resonance point of the series resonator are not matched, It is necessary to increase the frequency difference from the resonance point of the series resonator.

  As a result, the insertion loss is deteriorated at the center portion of the pass band, a dent is generated, and the characteristics are deteriorated. In the configuration as in Comparative Example 2, in order to prevent the insertion loss in the passband from deteriorating, when the antiresonance point of the parallel resonator is matched with the resonance point of the series resonator, the resonance point of the piezoelectric thin film resonator is Since the frequency interval between the anti-resonance points is narrow, the passband width becomes very narrow.

  Therefore, in Comparative Examples 1 and 2, sufficient characteristics cannot be realized in all of the desired passband width, insertion loss in the passband, and steepness of attenuation outside the passband.

On the other hand, in the present embodiment, in order to improve the steepness of the low frequency side of the pass band, the second harmonic is used as the main vibration, so the electromechanical coupling coefficient k ² is small, and the resonance point and anti-resonance A piezoelectric thin film resonator having a narrow frequency interval between points is used as a parallel resonator 11 and a fundamental wave is a main vibration. Therefore, a piezoelectric thin film resonator having a large electromechanical coupling coefficient k ² and a wide frequency interval between a resonance point and an antiresonance point. Is used for the series resonator 12.

  With such a configuration, in order to achieve the same passband width as in Comparative Example 1, the antiresonance point of the parallel resonator 11 is slightly shifted to the lower frequency side than the resonance point of the series resonator 12. . As a result, in the present embodiment, although the insertion loss slightly falls in the central portion in the passband to such an extent that it does not cause a problem, the steepness on the low band side of the passband is maintained while maintaining the desired passband width. A good piezoelectric thin film filter can be realized.

Hereinafter, modifications of the present embodiment will be shown. 5, in the parallel resonator 11, without forming the insulating film 2 made of SiO ₂ on the opening portion 1a, forming the upper insulating film 6 made of SiO ₂ on the upper electrode 5a, is a piezoelectric thin-film filter . In this structure, since the insulating film 2 made of SiO ₂ is not formed on the opening 1a, no step occurs in the piezoelectric thin film 4 and the lower electrode 3. Therefore, the diaphragm is not easily broken, and the manufacturing yield is improved. In this structure, a thin insulating film (not shown) made of any one of SiO ₂ , SiN, ZnO, and AlN is provided on the opening 1 a so as to extend over both the parallel resonator 11 and the series resonator 12. It may be formed.

  FIG. 6 shows a modification shown in FIG. 5 in which a protective film 7 is formed under the upper insulating film 6. With this structure, when the upper insulating film 6 is formed by etching after being formed on the entire surface, the protective film 7 made of a material that is not affected by the etching of the upper insulating film 6 is used. It is possible to prevent the piezoelectric thin film 4 and the upper electrode 5b from being damaged by etching. Further, by forming the protective film 7 on both the series resonator 12 and the parallel resonator 11, the difference between the etching rates of the upper insulating film 6 and the protective film 7 is used to make the series resonator 12 and the parallel resonator. 11 can be separately adjusted in frequency.

  FIG. 7 shows a modification shown in FIG. 5 in which a protective film 8 is formed over the entire surface of the upper insulating film 6. With this structure, by etching the protective film 8 from the upper surface, the frequency of the series resonator 12 and the parallel resonator 11 can be adjusted simultaneously, and the frequency of the entire filter can be adjusted to a desired value. .

  In the present embodiment, in order to obtain good steepness on the low pass band side, the parallel resonator 11 receives a double wave having a relatively narrow frequency interval between the resonance point and the antiresonance point as a main vibration. A piezoelectric thin film filter is constructed using a piezoelectric thin film resonator whose main vibration is a fundamental wave having a relatively wide frequency interval between the resonance point and the antiresonance point. However, the present invention is not limited to this. In order to obtain good steepness on the high passband side, a piezoelectric thin film resonator having a fundamental wave having a relatively wide frequency interval between the resonance point and the antiresonance point as a main vibration is used as the parallel resonator 11. A piezoelectric thin film filter may be configured by using a piezoelectric thin film resonator whose main vibration is a double wave whose frequency interval between the resonance point and the antiresonance point is relatively narrow as the series resonator 12.

  The ladder-type piezoelectric thin film filter having good steepness on the high pass band side as described above is preferably used as a transmission-side filter (a filter having a relatively low frequency) in a duplexer. .

In the present embodiment, in order to obtain a good steepness on the low pass band side, the parallel resonator 11 receives a double wave having a relatively narrow frequency interval between the resonance point and the antiresonance point as a main vibration. A piezoelectric thin film filter is constructed using a piezoelectric thin film resonator whose main vibration is a fundamental wave having a relatively wide frequency interval between the resonance point and the antiresonance point. However, the present invention is not limited to this, and the parallel resonator 11 uses a piezoelectric thin film resonator whose main vibration is a high-order mode of (n + 1) order or higher (n is a positive integer), and a series resonator. A piezoelectric thin film filter may be configured in 12 using a piezoelectric thin film resonator having an n-order mode as a main vibration. By using, as the parallel resonator 11, a piezoelectric thin film resonator whose main vibration is a higher mode than the series resonator 12, that is, a piezoelectric thin film resonator having a small electromechanical coupling coefficient k ² , the low pass band side. Therefore, good steepness can be obtained.

Further, in order to obtain a good steepness on the high side of the pass band, a piezoelectric thin film resonator having an n-order mode as a main vibration is used for the parallel resonator 11, and the (n + 1) th order or more is used for the series resonator 12. A piezoelectric thin film filter may be configured using a piezoelectric thin film resonator whose main vibration is the higher order mode. By using a piezoelectric thin film resonator whose main vibration is a higher mode than that of the parallel resonator 11, that is, a piezoelectric thin film resonator having a small electromechanical coupling coefficient k ² for the series resonator 12, Therefore, good steepness can be obtained.

  In the above embodiment, an example of the π type is given as the ladder type piezoelectric thin film filter. However, the ladder type piezoelectric thin film filter is not limited to the above example, and may be, for example, T type or L type as shown in FIG. Or more than one may be combined.

  In the ladder-type piezoelectric thin film filter, an example in which the opening 1a penetrating the Si substrate 1 in the thickness direction is provided. However, it may be any as long as it does not inhibit the vibration of the vibration part, and instead of the opening 1a. Then, a recess may be formed in the Si substrate 1 at a position facing the vibration part.

(Second embodiment)
As shown in FIG. 9, the duplexer according to the second embodiment of the present invention includes an antenna (Ant) terminal 33, a matching circuit 22, a transmission side filter 25, a reception side filter 26, and a transmission side. In this embodiment, which has a (Tx) terminal 31 and a receiving side (Rx) terminal 32, the pass band of the reception side filter 26 is 1930 MHz to 1990 MHz, and the pass band of the transmission side filter 25 is 1850 MHz to 1910 MHz. A certain PCS duplexer is configured.

  As shown in FIG. 10, the receiving-side filter 26 in the duplexer of the present embodiment is a piezoelectric thin film resonator having a second harmonic as a main vibration, as in the first embodiment shown in FIG. This is a ladder-type piezoelectric thin film filter formed by combining a certain parallel resonator 11 and a series resonator 12 that is a piezoelectric thin film resonator having a fundamental wave as a main vibration.

  On the other hand, the transmission-side filter 25 in the duplexer of the present embodiment, contrary to FIG. 1, includes a parallel resonator 11 a that is a piezoelectric thin film resonator having a fundamental wave as a main vibration, and a double wave as a main vibration. This is a ladder type piezoelectric thin film filter formed by combining series resonators 12a which are piezoelectric thin film resonators.

  A capacitance 21 is inserted in series between the transmission filter 25 and the antenna terminal 33. The capacitance 21 is for adjusting the shift amount to the capacitive characteristic in the pass band (1930 MHz to 1990 MHz) of the reception side filter 26.

  A matching circuit 22 including an inductance 22 a and capacitances 22 b and 22 c is inserted between the reception filter 26 and the antenna terminal 33. The matching circuit 22 may have a configuration other than the above. Further, inductances 23 and 24 are provided between the parallel resonators 11a of the transmission filter 25 and the ground side, respectively. With the inductances 23 and 24, the pass band of the transmission filter 25 can be extended particularly to the low frequency side.

  In such a duplexer, the reception-side filter 26 uses a piezoelectric thin-film resonator whose main vibration is a double wave whose frequency interval between the resonance point and the antiresonance point is relatively narrow as the parallel resonator 11. The resonator 12 is a ladder-type piezoelectric thin film filter using a piezoelectric thin film resonator whose main vibration is a fundamental wave having a relatively wide frequency interval between the resonance point and the antiresonance point. As a result, the steepness on the low frequency side outside the passband is good.

  On the other hand, the transmission filter 25 uses a piezoelectric thin film resonator whose main vibration is a fundamental wave having a relatively large frequency interval between the resonance point and the antiresonance point for the parallel resonator 11a, and a relative resonator for the series resonator 12a. In particular, this is a ladder type piezoelectric thin film filter using a piezoelectric thin film resonator whose main vibration is a double wave having a narrow frequency interval between a resonance point and an antiresonance point. As a result, the steepness on the high frequency side outside the pass band is good.

  Therefore, the duplexer can secure a large amount of attenuation in the transmission band of the other party in the transmission filter 25 and the reception filter 26, can suppress mutual interference, and realizes a duplexer having good characteristics. can do.

In the present embodiment, the reception-side filter 26 uses a piezoelectric thin film resonator whose main vibration is a second harmonic with a narrow frequency interval between the resonance point and the antiresonance point, as the parallel resonator 11. The series resonator 12 is a ladder-type piezoelectric thin film filter using a piezoelectric thin film resonator whose main vibration is a fundamental wave having a relatively wide frequency interval between the resonance point and the anti-resonance point. It is not limited. The parallel resonator 11 uses a piezoelectric thin film resonator whose main vibration is an (n + 1) -order or higher order mode, and the series resonator 12 uses a piezoelectric thin film resonator whose main vibration is an n-order mode. A thin film filter may be configured. By using a piezoelectric thin film resonator whose main vibration is a higher mode than that of the series resonator 12, that is, a piezoelectric thin film resonator having a small electromechanical coupling coefficient k ^{2 as the} parallel resonator 11, a low out-of-pass band is obtained. Good steepness can be obtained on the band side.

  In the present embodiment, the transmission-side filter 25 uses a piezoelectric thin film resonator whose main vibration is a fundamental wave having a relatively wide frequency interval between the resonance point and the antiresonance point for the parallel resonator 11a. The resonator 12a is a ladder-type piezoelectric thin film filter that uses a piezoelectric thin film resonator whose main vibration is a double wave whose frequency interval between the resonance point and the antiresonance point is relatively narrow. It is not limited to.

For example, a piezoelectric thin film resonator whose main vibration is an nth order mode is used for the parallel resonator 11a, and a piezoelectric thin film resonator whose main vibration is a higher order mode of (n + 1) th order or higher is used for the series resonator 12a. A piezoelectric thin film filter may be configured. By using a piezoelectric thin film resonator whose main vibration is a higher-order mode than the parallel resonator, that is, a piezoelectric thin film resonator having a small electromechanical coupling coefficient k ² , a high frequency side outside the passband is used for the series resonator. Therefore, good steepness can be obtained.

  In the above description, the duplexer is shown in FIG. 10, but is not limited to FIG. 10. For example, each duplexer shown in the circuit block diagrams shown in FIGS. 11 to 13 may be used. In FIG. 12, another matching circuit 22 including inductances 22d and 22e and a capacitance 22f is provided.

  The duplexer of the present invention using the ladder type filter of the present invention, particularly for the reception filter 26, has good attenuation characteristics in the vicinity of the pass band outside the pass band. It has an excellent characteristic that it is large and has a wide passband.

(Third embodiment)
A piezoelectric thin film filter according to a third embodiment of the present invention, instead of the opening 1a and the recess described in the first embodiment, as shown in FIG. An acoustic reflecting portion 43 is inserted between the vibrating portion formed on the Si substrate 44. The vibration part is a part in which the piezoelectric thin film 4 is sandwiched between the lower electrode 3 and the upper electrode 5 as in the first embodiment. An upper insulating film 6 may be further formed on the vibration part.

  The acoustic reflection unit 43 has different acoustic impedances, for example, AlN layers 43a and 43c and SiO2 layers 43b and 43d, which are alternately stacked, and has an increased acoustic reflectivity. In order to increase the acoustic reflectivity, it is desirable that the materials having different acoustic impedances that are alternately laminated have a larger difference in acoustic impedance.

  By adopting a configuration in which such an acoustic reflecting portion 43 is provided, a state in which the vibrating portion is acoustically separated from the Si substrate 44 can be formed as in the first embodiment. In addition, since the vibration part is formed in contact with the upper surface of the acoustic reflection part 43 in the above configuration, the vibration part strength is improved as compared with the case where the vibration part is formed on the opening 1a or the recess. In addition to improving yield and reliability, power durability can also be improved.

  Therefore, it is possible to configure a duplexer by combining a plurality of such piezoelectric thin film filters, for example, a ladder type, and also in the obtained duplexer, yield and reliability can be improved, and power durability can also be improved. .

(Fourth embodiment)
Next, a communication device according to a fourth embodiment of the present invention is one in which any one of the piezoelectric thin film filters described in the first and third embodiments or the above-described duplexer is mounted. The said communication apparatus is demonstrated based on FIG. The communication device 600 includes an antenna 601, an antenna sharing unit / RFTop filter 602, an amplifier 603, an Rx interstage filter 604, a mixer 605, a 1st IF filter 606, a mixer 607, and a 2nd IF filter 608 as a receiver side (Rx side) that performs reception. 1st + 2nd local synthesizer 611, TCXO (temperature compensated crystal oscillator) 612, divider 613, and local filter 614.

  It is preferable to transmit from the Rx interstage filter 604 to the mixer 605 using each balanced signal in order to ensure balance, as indicated by the double line in FIG.

  The communication device 600 shares the antenna 601 and the antenna sharing unit / RFTop filter 602 as a transmitter side (Tx side) that performs transmission, and also includes a TxIF filter 621, a mixer 622, a Tx interstage filter 623, an amplifier. 624, a coupler 625, an isolator 626, and an APC (automatic power control) 627.

  The Rx interstage filter 604, the 1stIF filter 606, the TxIF filter 621, and the Tx interstage filter 623 are any of the piezoelectric thin film filters described in the first and third embodiments of the present invention. The duplexer described in the second embodiment can be preferably used as the antenna sharing unit / RFTop filter 602.

  The piezoelectric thin film filter according to the present invention can have a filter function, and also has excellent characteristics such as good attenuation characteristics on both sides in the vicinity of the pass band outside the pass band and a wide pass band. Therefore, the communication device of the present invention equipped with the piezoelectric thin film filter and the duplexer using the piezoelectric thin film filter can improve the transmission characteristics.

  The piezoelectric thin film filter of the present invention, a duplexer using the same, and a communication device equipped with them have good attenuation characteristics outside the passband, near the highband side and / or lowband side of the passband, Since it has the outstanding characteristic that a pass band is wide, the transmission characteristic of a communication apparatus can be improved and it can utilize suitably for the communication field | area.

The piezoelectric thin film filter of 1st Embodiment based on this invention is shown, (a) is a circuit block diagram, (b) is principal part sectional drawing. It is a graph which shows the frequency characteristic of a receiving side filter. It is a graph which shows the attenuation amount of each piezoelectric thin film filter of the said 1st Embodiment and the comparative example 1. FIG. It is a graph which shows the frequency characteristic in the pass band of each piezoelectric thin film filter of the 1st embodiment of the above and comparative example 2. It is principal part sectional drawing which shows the modification of the said 1st Embodiment. It is principal part sectional drawing which shows the other modification in the said 1st Embodiment. It is principal part sectional drawing which shows the further another modification in the said 1st Embodiment. It is a circuit block diagram of each modification of ladder type arrangement in the 1st embodiment of the above, (a) shows T type and (b) shows L type. It is a block diagram of a duplexer as a second embodiment of the present invention. It is a circuit diagram of the said splitter. It is a circuit diagram which shows the modification of the said splitter. It is a circuit diagram which shows the other modification of the said splitter. It is a circuit diagram which shows the other modification of the said splitter. It is principal part sectional drawing of the piezoelectric thin film filter as 3rd Embodiment of this invention. It is a block diagram of the communication apparatus as 4th Embodiment of this invention.

Explanation of symbols

1: Si substrate 1a: Opening 3: Lower electrode 4: Piezoelectric thin film 5a: Upper electrode 11: Parallel resonator 12: Series resonator

Claims (11)

A plurality of vibration parts having a structure in which an upper and lower surfaces of a thin film part having at least one or more piezoelectric thin films that are acoustically separated from the substrate are sandwiched between at least a pair of upper and lower electrodes. Piezoelectric thin-film filters, in which a piezoelectric thin-film resonator is arranged in a ladder form as a series resonator and a parallel resonator,
One of the series resonator and the parallel resonator has a piezoelectric thin film resonator whose main vibration is an n-fold wave (n is a positive integer), and the other of the series resonator and the parallel resonator is an integer ((n + 1) or more). A piezoelectric thin film filter using a piezoelectric thin film resonator whose main vibration is a wave. The piezoelectric thin film resonator whose main vibration is an ((n + 1) or more) harmonic wave has an insulating film between the substrate and the lower electrode, and the insulating film has a frequency temperature coefficient different from that of the piezoelectric thin film. The piezoelectric thin film filter according to claim 1 , wherein: 3. The piezoelectric thin film filter according to claim 1, further comprising upper insulating films made of the same material on the upper electrodes of the series resonator and the parallel resonator. 3. The piezoelectric thin film filter according to claim 1, further comprising upper insulating films made of different materials on the upper electrodes of the series resonator and the parallel resonator. 2. The piezoelectric thin film filter according to claim 1 , wherein the piezoelectric thin film resonator whose main vibration is an (multiple of (n + 1) or more) harmonic has an insulating film on an upper electrode. The piezoelectric thin film filter according to claim 5 , wherein the insulating film has a frequency temperature coefficient different from that of the piezoelectric thin film. Between the insulating film and the upper electrode on the upper electrode, characterized in that an intermediate insulating film, the piezoelectric thin-film filter according to claim 5 or 6. 8. The piezoelectric thin film filter according to claim 7 , wherein the intermediate insulating film is also formed on an upper electrode of a piezoelectric thin film resonator whose main vibration is an n-th harmonic wave. On the upper electrodes of the series resonator and the parallel resonator, each has an insulating film made of the same material,
The insulating film on the upper electrode of the piezoelectric thin film resonator whose main vibration is an ((n + 1) or more) harmonic wave is more than the insulating film on the upper electrode of the piezoelectric thin film resonator whose main vibration is an n harmonic wave. The piezoelectric thin film filter according to claim 1 , wherein the piezoelectric thin film filter is thick. A duplexer using the piezoelectric thin film filter according to any one of claims 1 to 9 . A communication device using the piezoelectric thin film filter according to any one of claims 1 to 9 or the duplexer according to claim 10 .

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