JP4816234B2 - Unbalance-balance conversion filter and duplexer using the same - Google Patents

Description

  The present invention belongs to the technical field of communication equipment and relates to an unbalance-balance conversion filter, and more particularly to an unbalance-balance conversion filter using a thin film piezoelectric resonator and a transmission / reception switch using the same. is there.

  The RF circuit part of a cellular telephone is always required to be downsized. Recently, it has been demanded to add various functions to cellular phones, and it is preferable to incorporate as many components as possible in order to realize them, while the size of cellular phones is limited. Therefore, there is a strict demand for reduction of the exclusive area (mounting area) and height in the equipment, and therefore, components constituting the RF circuit portion are required to have a small exclusive area and a low height.

  Under such circumstances, a thin film piezoelectric filter using a thin film piezoelectric resonator that is small and can be reduced in weight is used as a band pass filter used in an RF circuit. The thin film piezoelectric filter as described above forms a piezoelectric thin film such as aluminum nitride (AlN) or zinc oxide (ZnO) so as to be sandwiched between upper and lower electrodes on a semiconductor substrate as shown in the literature, and is elastic. The RF filter is formed of a thin film bulk acoustic resonator (FBAR) in which a cavity is provided immediately below so that wave energy does not leak into the semiconductor substrate.

  FIG. 6 shows an embodiment of a thin film piezoelectric resonator, FIG. 6 (a) is a schematic plan view thereof, and FIG. 6 (b) is an XX cross-sectional view of FIG. 6 (a). The thin film piezoelectric resonator of FIG. 6 includes a piezoelectric thin film, and a lower electrode 8 and an upper electrode 10 formed so as to sandwich the piezoelectric thin film. The thin film piezoelectric resonator includes a substrate 6 having an air gap 4 and a piezoelectric stack 12 in a form in which a peripheral edge is supported on an edge on the upper surface of the substrate 6 and suspended. The piezoelectric resonator stack 12 includes a piezoelectric thin film (piezoelectric layer) 2, a lower electrode (lower electrode layer) 8 and an upper electrode (upper electrode layer) 10 formed so as to sandwich the piezoelectric thin film.

FIG. 8 shows a ladder type filter which is an embodiment of a conventional thin film piezoelectric filter, and FIG. 9 shows a lattice type filter which is an embodiment of a conventional thin film piezoelectric filter. The ladder type filter shown in FIG. 8 is an unbalanced input-unbalanced output, and the lattice type filter shown in FIG. 9 is a balanced input-balanced output. In recent years, electronic components such as ICs with balanced input / output terminals have become the mainstream, so in the past, unbalanced-balanced balun circuits, etc., between the latter stage of ladder-type thin film piezoelectric filters having unbalanced input / output terminals and the electronic circuit. The circuit configuration was such that a converter was inserted. When the balun circuit is introduced, the exclusive area of the entire RF circuit section becomes large, which is not preferable. In recent years, a so-called unbalanced input-balanced output type thin film piezoelectric filter (hereinafter referred to as a balanced type thin film piezoelectric filter) in which a thin film piezoelectric filter has a function of an unbalanced-balanced converter has been put into practical use.

Patent Documents 1 and 2 propose a balanced thin film piezoelectric filter having an unbalance-balance conversion function by combining a ladder filter and a lattice filter. As shown in FIGS. 10A and 10B, the ladder filter has a steep attenuation characteristic in the vicinity of the pass band, but the attenuation characteristic deteriorates in a frequency band away from the pass band. On the other hand, the lattice filter has a feature that the attenuation characteristic in the frequency band far from the pass band is excellent, although the steepness of the attenuation characteristic in the vicinity of the pass band is inferior. For this reason, the thin film piezoelectric filters described in Patent Document 1 and Patent Document 2 exhibit intermediate filter characteristics between a ladder circuit and a lattice filter.

US Pat. No. 6,542,055 Special table 2004-519180 gazette

  Since the thin film piezoelectric filters described in Patent Document 1 and Patent Document 2 show intermediate filter characteristics between a ladder filter and a lattice filter, the steepness of the attenuation characteristics in the vicinity of the passband is not always sufficient, and the attenuation characteristics However, it has a drawback that it cannot be applied to a communication system in which the steepness of the system is important.

  The present invention has been made in view of the above circumstances, and provides a small thin-film piezoelectric filter having a function of an unbalanced-balanced converter and having a good attenuation characteristic in the vicinity of the passband. It is for the purpose.

The present invention is an unbalanced-balanced conversion filter including an unbalanced circuit in which a series resonator and a parallel resonator are connected in a ladder form, and a balanced circuit, wherein the unbalanced circuit includes a first input terminal, A two-terminal pair network including a second input terminal, a first output terminal, and a second output terminal, wherein the balanced circuit includes a third input terminal, a fourth input terminal, and a third output terminal. And a fourth output terminal, wherein the first output terminal is connected to the third input terminal, and the second output terminal is connected to the fourth input terminal. The second input terminal and the second output terminal are connected to a ground terminal, and an inductor is provided between the fourth input terminal and the ground terminal. The present invention relates to an unbalanced-balanced conversion filter.

  The present invention also relates to the unbalanced-balanced conversion filter, wherein the series resonator and the parallel resonator constituting the unbalanced circuit and the balanced circuit are thin film piezoelectric resonators.

  The present invention also relates to the unbalanced-balanced conversion filter, characterized in that an inductor is provided between the parallel resonator constituting the unbalanced circuit and the ground terminal.

  The present invention also relates to a transmission / reception switch using the unbalance-balance conversion filter as a reception filter.

According to the present invention, there is provided an unbalanced-balanced conversion filter including an unbalanced circuit and a balanced circuit in which a series resonator and a parallel resonator are connected in a ladder shape, and the unbalanced circuit has a first input. A two-terminal pair network including a terminal, a second input terminal, a first output terminal, and a second output terminal, wherein the balanced circuit includes a third input terminal, a fourth input terminal, and a third input terminal. A two-terminal network including an output terminal and a fourth output terminal, wherein the first output terminal is connected to the third input terminal, and the second output terminal is the fourth input terminal. The second input terminal and the second output terminal are connected to a ground terminal, and there is an unbalance having an inductor between the fourth input terminal and the ground terminal. -By using a balanced conversion filter, it has the function of an unbalanced-balanced converter. It can steepness of attenuation characteristics near the passband to provide a good balanced film piezoelectric filter.

  According to the present invention, the series resonator and the parallel resonator constituting the unbalanced circuit and the balanced circuit are the unbalanced-balanced conversion filter that is a thin film piezoelectric resonator, so that the unbalanced-balanced conversion is achieved. It is possible to provide a balanced thin-film piezoelectric filter that has a function of a vessel and has a good steepness in the attenuation characteristic in the vicinity of the passband.

  Further, according to the present invention, the unbalanced-balanced conversion filter having an inductor between the parallel resonator constituting the unbalanced circuit and the ground terminal makes the steepness of the attenuation characteristic near the passband. Can provide a good balance type thin film piezoelectric filter

  According to the present invention, the unbalance-balance conversion filter is used as a transmission / reception switch for the reception filter, so that the reception output side has the function of an unbalance-balance conversion and has an attenuation near the passband. It is possible to provide a transmission / reception switch with good characteristics steepness.

  Embodiments of the present invention will be described below with reference to the drawings.

  An object of the present invention is to provide a small-sized thin film piezoelectric filter having a function of an unbalanced-balanced converter and having a good steepness of attenuation characteristics in the vicinity of the pass band.

The balanced thin film piezoelectric filter of the present invention is an unbalanced-balanced conversion filter including an unbalanced circuit and a balanced circuit in which a series resonator and a parallel resonator are connected in a ladder shape, and the unbalanced circuit includes: A two-terminal pair network including a first input terminal, a second input terminal, a first output terminal, and a second output terminal, wherein the balanced circuit includes a third input terminal and a fourth input terminal. And a third output terminal and a fourth output terminal, wherein the first output terminal is connected to the third input terminal, and the second output terminal is The second input terminal and the second output terminal are connected to a ground terminal, and an inductor is connected between the fourth input terminal and the ground terminal. imbalance characterized by having a - with equilibrium conversion filter, not衡 - has a function of balanced converter can steepness of attenuation characteristics near the passband to provide a good balanced film piezoelectric filter.

  FIG. 1 shows an embodiment of a balanced thin film piezoelectric filter of the present invention, which includes a first input terminal 101, a second input terminal 102, a first output terminal 103, and a second output terminal 104. The ladder-type filter unit 110, which is an unbalanced circuit, and the ladder, which is a balanced circuit, includes a third input terminal 105, a fourth input terminal 106, a third output terminal 107, and a second output terminal 108. The circuit configuration is a combination of the mold filter unit 120. The first output terminal 103 of the unbalanced circuit is connected to the third input terminal 105 of the unbalanced circuit, and the second output terminal 104 of the unbalanced circuit is connected to the fourth input terminal 106 of the unbalanced circuit. ing. The second input terminal 102 and the second output terminal 104 are connected to a ground terminal. Therefore, the input terminal consisting of the input terminals 101 and 102 is an unbalanced terminal, and the output terminal consisting of the output terminals 107 and 108 is a balanced terminal, so that a balanced filter having an unbalanced-balanced conversion function is obtained.

  The ladder filter unit 110, which is an unbalanced circuit, includes series resonators 111 and 113 and parallel resonators 112 and 114, and the parallel resonators 112 and 114 are grounded. The ladder type filter unit that is an unbalanced circuit of the present invention is not limited to the circuit configuration shown in FIG. 1, and may be a ladder type filter that is an unbalanced circuit including a series resonator and a parallel resonator. Thus, the effects of the present invention can be obtained.

  The ladder-type filter unit 120 that is a balanced circuit includes series resonators 121 and 123 and parallel resonators 122 and 124. The ladder type filter unit 120 that is a balanced circuit of the present invention is not limited to the circuit configuration shown in FIG. 1, and may be any ladder type filter that is a balanced circuit composed of a series resonator and a parallel resonator. The effects of the present invention can be obtained.

  The series resonators 111, 113, 121, and 123 and the parallel resonators 112, 114, 122, and 124 that constitute the ladder filters 110 and 120 of the present invention are shown in FIGS. 6 (a) and (b), for example. Such a thin film piezoelectric resonator is preferably used. This is because the thin film piezoelectric resonator has a high quality factor Q value, and therefore, the steepness of the attenuation characteristic in the vicinity of the pass band, which is one of the objects of the present invention, is excellent.

  FIG. 2 shows an embodiment of a balanced thin film piezoelectric filter of the present invention. A ladder-type filter unit 110 that is an unbalanced circuit including a first input terminal 101, a second input terminal 102, a first output terminal 103, and a second output terminal 104; a third input terminal 105; The circuit configuration in which the ladder-type filter unit 120, which is a balanced circuit including the fourth input terminal 106, the third output terminal 107, and the fourth output terminal 108, is combined is shown in FIG. Similar to the example. In the ladder-type filter unit 110 that is an unbalanced circuit, the parallel resonators 112 and 114 are connected to the ground terminal via inductors (131, 132), and the ladder-type filter that is one balanced circuit. The unit 120 is different from the embodiment of FIG. 1 in that the connection node between the series resonator 123 and the parallel resonator 122 is connected to the second output terminal 104 via the inductor 133. By connecting to the ground terminal via the inductors (131, 132, 133), the attenuation pole appearing outside the passband can be controlled.

  As in the embodiment shown in FIG. 1, the configuration of the ladder filter units 110 and 120 of the present invention is not limited to the circuit configuration shown in FIG. 2, and the ladder filter unit 110, which is an unbalanced circuit, is provided. When at least one of the constituting parallel resonators is grounded via an inductor, it is an embodiment of the present invention. In addition, an output terminal (FIG. 5) is connected to a ground terminal of the ladder type filter unit 110 via a inductor at a connection node between the series resonator and the parallel resonator constituting the ladder type filter unit 120 which is a balanced circuit. 2 is equivalent to the output terminal 104)).

  FIG. 3 shows an embodiment of the balanced thin film piezoelectric filter of the present invention. A ladder-type filter unit 110 that is an unbalanced circuit including a first input terminal 101, a second input terminal 102, a first output terminal 103, and a second output terminal 104; a third input terminal 105; 1 and FIG. 2 show that the circuit configuration is a combination of a ladder-type filter unit 120 that is a balanced circuit including a fourth input terminal 106, a third output terminal 107, and a fourth output terminal 108. This is the same as the second embodiment. Further, the parallel resonator constituting the ladder filter 110 which is an unbalanced circuit is connected to the ground terminal via the inductor, as in FIG. 2, but in the embodiment of FIG. 2 is different from the embodiment of FIG. 2 in that one parallel resonator (parallel resonators 112 and 114) is connected to the ground terminal via an inductor 141. Thus, by grounding a plurality of parallel resonators via a single inductor, it is possible to cause an attenuation pole to appear on the high frequency side in the vicinity of the passband with a relatively small inductance, thereby reducing the size of the filter. Very advantageous.

  As in the embodiment shown in FIGS. 1 and 2, the configuration of the ladder filter units 110 and 120 of the present invention is not limited to the circuit configuration shown in FIG. 3, but a ladder filter that is an unbalanced circuit. When at least two of the parallel resonators constituting the unit 110 are grounded via the same inductor, this is an embodiment of the present invention.

  FIG. 4 shows an embodiment of the duplexer according to the present invention. The reception filter 100 includes a first input terminal 101, a second input terminal 102 (not shown), a first output terminal 103 (not shown), and a second output terminal 104 (not shown). A ladder filter unit 110, which is an unbalanced circuit, a third input terminal 105 (not shown), a fourth input terminal 106 (not shown), a third output terminal 107, and a fourth output terminal 108. The ladder-type filter unit 120, which is a balanced circuit including the circuit configuration, is combined. In addition, by installing a phase shifter between the antenna and the reception filter, it is possible to suppress deterioration in characteristics of the transmission filter 200. The transmission filter 200 is a ladder type filter 200 that is an unbalanced circuit composed of a conventional ladder type circuit, and the transmission input port is an unbalanced input. Thus, in the transmission / reception switching device of the present invention, the reception port can be a balanced terminal and the transmission port can be a transmission / reception switching device having an unbalanced terminal.

  In the present invention, as a reception filter, a ladder filter unit 110 that is an unbalanced circuit including a first input terminal 101, a second input terminal, a first output terminal, and a second output terminal; The ladder-type filter unit 120, which is a balanced circuit having an input terminal, a fourth input terminal, a third output terminal 107, and a fourth output terminal 108, is combined. Since a ladder-type filter is used as the filter, a transmission / reception switch with good attenuation characteristics in the vicinity of the passband can be obtained.

  Similar to the embodiment shown in FIGS. 1 to 3, the configuration of the ladder filter units 110 and 120 of the reception filter constituting the transmission / reception switch of the present invention is not limited to the circuit configuration shown in FIG. The ladder-type filter unit 110 that is an unbalanced circuit is a ladder-type filter that is an unbalanced circuit including a series resonator and a parallel resonator, and the ladder-type filter unit 120 that is a balanced circuit is a series resonator 121, 123. And the parallel resonators 122 and 124 is an embodiment of the present invention. In addition, the case where a balanced filter in which a parallel resonator is grounded via an inductor as shown in FIGS. 2 to 3 is used as a reception filter is also included in the embodiment of the present invention.

  The series resonator and the parallel resonator constituting the transmission / reception switching device of the present invention are preferably formed of a thin film piezoelectric resonator. As an example of the thin film piezoelectric resonator, for example, a form as shown in FIG. This is because the thin film piezoelectric resonator has a high quality factor Q value, and therefore, the steepness of the attenuation characteristic in the vicinity of the pass band, which is one of the objects of the present invention, is excellent.

  As the configuration and material of the thin film piezoelectric resonator constituting the thin film piezoelectric filter of the present invention, the same configuration and material as those of the conventional thin film piezoelectric resonator can be applied. For example, the substrate 6 may be made of a silicon substrate, a gallium arsenide substrate, a glass substrate, or the like, and the air gap 4 can be formed by a conventional technique such as anisotropic wet etching or RIE (Reactive Ion Etching). The piezoelectric thin film (piezoelectric layer) 2 may be made of a piezoelectric material that can be manufactured as a thin film such as zinc oxide (ZnO) or aluminum nitride (AlN).

  The thin film piezoelectric resonator as described above can be manufactured as follows. After a pit portion is formed on a substrate 6 such as a silicon wafer by a technique such as wet etching, a sacrificial layer is formed by a film forming technique such as a CVD method. Thereafter, the surface of the substrate is planarized by a planarization technique such as a CMP method to obtain a substrate on which a sacrificial layer is deposited only inside the pits. The lower electrode 8, the piezoelectric layer 2, and the upper electrode 10 are formed by a film forming method such as sputtering or vapor deposition, and each layer is patterned using a patterning technique such as wet etching, RIE, or lift-off. At this time, a region 40 where the upper electrode is not formed is formed at the center of the upper electrode. Further, after forming the through hole 30 reaching from the upper surface of the substrate to the sacrificial layer using the patterning technique, the sacrificial layer is removed with an etching solution. Thereby, the pit portion becomes the air gap 4.

  FIG. 7 shows another embodiment of the thin film piezoelectric resonator. It is the same as the embodiment shown in FIG. 6 except that an acoustic reflection layer is provided in place of the air gap 4, and can be used as a thin film piezoelectric resonator used in the thin film piezoelectric filter of the present invention.

Example 1
A 1900 MHz band balance filter was fabricated with the circuit configuration shown in FIG. The thickness of each component layer in this example was set such that the lower electrode was made of Mo with a thickness of 300 nm, the piezoelectric layer was made of AlN with a thickness of 1300 nm, and the upper electrode was made of Mo with a thickness of 300 nm. FIG. 5 shows the amplitude characteristics of the balanced thin film piezoelectric filter formed as described above. As is clear from FIG. 5, the attenuation characteristic in the vicinity of the pass band is steep, and it can be applied to a communication system in which the pass band and the stop band are close to each other.

1 shows an embodiment of a thin film piezoelectric filter of the present invention. 1 shows an embodiment of a thin film piezoelectric filter of the present invention. 1 shows an embodiment of a thin film piezoelectric filter of the present invention. 1 shows an embodiment of a duplexer according to the present invention. The amplitude characteristic of the thin film piezoelectric filter obtained in Example 1 is shown. It is (a) typical top view and (b) sectional view showing one embodiment of a thin film piezoelectric resonator. 1 illustrates one embodiment of a thin film piezoelectric resonator. 1 shows a conventional ladder circuit filter. 1 shows a conventional lattice circuit filter. It is a figure which shows (a) narrow-band characteristic and (b) wide-band characteristic of the amplitude characteristic of the conventional ladder type circuit filter.

Explanation of symbols

2 Piezoelectric layer 4 Air gap 6 Substrate 8 Lower electrode 10 Upper electrode 12 Piezoelectric resonator stack 14 Acoustic impedance converter 30 Sacrificial layer etching through hole 100 Reception filter 101, 104 Unbalanced input terminal 103, 104 Unbalanced output terminal 105, 106 Balanced input terminals 107 and 108 Balanced output terminal 110 Ladder type filter unit 120 which is an unbalanced circuit Ladder type filter units 111 and 113 which are balanced circuits, Series resonators 112 and 114 which constitute the ladder type filter unit 110, Ladder type Parallel resonators 121 and 123 constituting the filter unit 110, series resonators 122 and 124 constituting the ladder type filter unit 120, and parallel resonators 131, 132, 133, 141, and 142 constituting the ladder type filter unit 120 Inductor 151 , 153, 155 Conventional ladder filter Series Resonators 152, 154, and 156 Parallel Resonators 161 and 163 Constructing Conventional Ladder Filters Series Resonators 162 and 164 Constructing Conventional Grating Filters Parallel Resonators 200 Constructing Conventional Grating Filters Transmission filters 211, 213, 215, 217 Series resonators 212, 214, 216, 218 constituting transmission filter 200 Parallel resonators forming transmission filter 200

Claims (4)

An unbalanced-balanced conversion filter including an unbalanced circuit and a balanced circuit in which a series resonator and a parallel resonator are connected in a ladder shape, wherein the unbalanced circuit includes a first input terminal and a second input. A two-terminal network including a terminal, a first output terminal, and a second output terminal, wherein the balanced circuit includes a third input terminal, a fourth input terminal, a third output terminal, and a fourth output terminal. A two-terminal pair network including an output terminal, wherein the first output terminal is connected to the third input terminal, and the second output terminal is connected to the fourth input terminal. The second input terminal and the second output terminal are connected to a ground terminal, and an inductor is provided between the fourth input terminal and the ground terminal. Balance conversion filter.   2. The unbalanced-balanced conversion filter according to claim 1, wherein the series resonator and the parallel resonator constituting the unbalanced circuit and the balanced circuit are thin film piezoelectric resonators.   2. The unbalanced-balanced conversion filter according to claim 1, further comprising an inductor between a parallel resonator constituting the unbalanced circuit and the ground terminal.   A transmission / reception switching device using the unbalance-balance conversion filter according to claim 1 as a reception filter.

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