JP2006352854A - Thin film piezo-electric resonator and thin film piezo-electric filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily provide a thin film piezo-electric resonator filter having outstanding characteristics while offering a thin film piezo-electric resonator having high Q value that suppresses a generation of unnecessary horizontal acoustic mode. <P>SOLUTION: The thin film piezo-electric resonator of this invention is a thin film piezo-electric resonator which has a piezo-electric layer, an upper electrode and a lower electrode formed so as to counter each other with this piezo-electric layer sandwiched. It characterizes the invention that the outline of the portion where the upper electrode and lower electrode overlap mutually in the thickness direction is circular, and the upper electrode is not formed in the domain which includes straight lines passing along the center of this circular shape while having the length of 1/50 of the diameter. Moreover, it characterizes the invention in another configuration that the outline of the portion where the upper electrode and lower electrode overlap mutually in the thickness direction is rectangular, and the upper electrode is not formed in the domain which contains 1/10 of at least one of diagonal lines while including the intersection of two diagonal lines of this rectangle. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention belongs to the technical field of communication equipment, and relates to a thin-film piezoelectric resonator and a thin-film piezoelectric filter using the same, and more particularly to a resonator structure in which noise due to a spurious mode is suppressed.

  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. 24 shows an embodiment of a conventional thin film piezoelectric resonator, FIG. 24 (a) is a schematic plan view thereof, and FIG. 24 (b) is an XX sectional view of FIG. 24 (a). is there. The thin film piezoelectric resonator of FIG. 24 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.

A piezoelectric resonator stack 12 composed of a laminate of the piezoelectric layer 2 and the electrode layers 8 and 10 is suspended at the peripheral edge thereof, and both main surfaces thereof are in contact with air or other surrounding gas or vacuum. Yes. In this case, the piezoelectric resonator stack 12 forms an acoustic resonator having a high Q. The AC signal applied to the electrode layers 8 and 10 has a frequency equal to a value obtained by dividing the speed of sound in the piezoelectric resonator stack 12 by twice the weighted thickness of the stack 12. That is, in the case of fr = v / 2t ₀ (where fr is the resonance frequency, v is the speed of sound in the stack 12, and t ₀ is the weighted thickness of the stack 12), The piezoelectric resonator stack 12 resonates. Since the sound velocity in the layers constituting the stack 12 differs depending on the material constituting each layer, the resonance frequency of the piezoelectric resonator stack 12 is not the physical thickness but the sound velocity in the piezoelectric layer 2 and the electrode layers 8 and 10. It is determined by the weighted thickness considering their physical thickness. In the form of FIG. 24, the outer shape of the portion where the upper electrode 10 and the lower electrode 8 overlap each other in the thickness direction is a quadrangle (hereinafter, this form of piezoelectric thin film resonator is referred to as a square piezoelectric thin film resonator).

  FIG. 25 is a schematic plan view of a conventional thin film piezoelectric resonator that is different from the thin film piezoelectric resonator of FIG. 24 only in the shapes of the upper electrode, the lower electrode, and the piezoelectric thin film. In the embodiment of FIG. 25, the outer shape of the portion where the upper electrode 10 and the lower electrode 8 overlap each other in the thickness direction is circular (hereinafter, the piezoelectric thin film resonator of this embodiment is referred to as a circular piezoelectric thin film resonator).

  FIG. 26 is a schematic cross-sectional view showing an embodiment of a conventional thin film piezoelectric resonator having a substrate structure different from that of the thin film piezoelectric resonator shown in FIGS. This example is the same as that shown in FIGS. 24 and 25 except that the air gap 4 is formed not from the front side but from the back side.

  FIG. 27 is a schematic cross-sectional view showing an embodiment of a structure of a conventional thin film piezoelectric resonator different from the structure of the thin film piezoelectric resonator shown in FIG. The thin film piezoelectric resonator having this structure is the same as that shown in FIGS. 24 and 26 except that the acoustic impedance converter 22 is used instead of the air gap 4.

  In the conventional rectangular and circular thin film piezoelectric resonators as shown in FIGS. 24 to 27, it is known that the characteristic deterioration occurs due to the transverse acoustic mode. FIG. 28 schematically shows how the elastic waves propagating in the lateral direction generated from one side are reflected on the other side and overlap each other in the rectangular and circular thin film piezoelectric resonators shown in FIGS. . When the elastic wave propagating in the lateral direction is amplified in this way, even an extremely small amplitude elastic wave affects the vibration characteristics of the thickness vibration wave. Similarly, it is known that characteristic deterioration due to the transverse acoustic mode occurs also in some other shapes of thin film piezoelectric resonators.

  The FBAR is a resonator using an elastic wave (longitudinal acoustic mode) propagating in the thickness direction. However, there is also an elastic wave (transverse acoustic mode) propagating in a direction parallel to the electrode. This transverse acoustic mode interferes with the longitudinal acoustic mode, causing an increase in filter insertion loss and deterioration of phase characteristics. Degradation of these characteristics has hindered the application of FBAR as an RF device.

  Conventionally, in order to prevent characteristic deterioration due to the above-described unnecessary lateral acoustic mode, in Patent Document 1, a frame is formed around the upper electrode, and in Patent Document 2, a polygonal resonance having no parallel sides is disclosed. A vessel is shown.

  FIG. 29 shows a thin film piezoelectric resonator described in Patent Document 1. As shown in FIG. 29, the generation of noise due to the transverse acoustic mode is suppressed by providing a frame at the end of the upper electrode.

  FIG. 30 shows a thin film piezoelectric resonator described in Patent Document 2. As shown in FIG. 30, since the piezoelectric layer sandwiched between the upper electrode and the lower electrode is a polygon having no parallel sides, the generation of noise due to the transverse acoustic mode is suppressed.

US Pat. No. 6,788,170 US Pat. No. 6,215,375

  The technique described in Patent Document 1 requires a step of forming the frame and requires a line width in the order of μm, so that it is very high considering the positional accuracy with the upper electrode and the like. Processing accuracy is required, and its manufacture becomes very difficult. Therefore, the manufacturing cost is increased.

  In the polygonal resonator having no parallel sides described in Patent Document 2, when a filter is configured by arranging a large number of resonators, it is difficult to regularly arrange the resonators, and the filter cannot be downsized. There is a problem. Further, the Q value is lowered at the anti-resonance frequency, and the characteristics are deteriorated. As a resonator that solves these problems, there is a circular or quadrangular thin film piezoelectric resonator. However, these characteristics deteriorate due to an unnecessary transverse acoustic mode.

  The present invention has been made in view of the above circumstances, and provides a thin film piezoelectric resonator having a high Q value that suppresses generation of an unnecessary transverse acoustic mode in a circular or square thin film piezoelectric resonator, and is excellent. It is an object to easily provide a thin film piezoelectric resonator filter having characteristics.

  The present invention is a thin film piezoelectric resonator having a piezoelectric layer, and an upper electrode and a lower electrode formed so as to face each other with the piezoelectric layer interposed therebetween, and the upper electrode and the lower electrode overlap each other in the thickness direction. The thin film piezoelectric resonator is characterized in that the outer shape of the portion is circular, and the upper electrode is not formed in a region including a straight line having a length of 1/50 passing through the center of the circular shape.

  The present invention is also a thin film piezoelectric resonator having a piezoelectric layer, and an upper electrode and a lower electrode formed so as to face each other with the piezoelectric layer interposed therebetween, wherein the upper electrode and the lower electrode are arranged in the thickness direction. The outer shape of the overlapping portions is a quadrangle, and the upper electrode is not formed in a region including the intersection of two diagonal lines of the quadrangle and including at least 1/10 of one of the diagonal lines. The present invention relates to a thin film piezoelectric resonator.

  The present invention is also a thin film piezoelectric resonator having a piezoelectric layer, and an upper electrode and a lower electrode formed so as to face each other with the piezoelectric layer interposed therebetween, wherein the upper electrode and the lower electrode are arranged in the thickness direction. The outer shape of the overlapping parts is elliptical, and the upper electrode is not formed in a region that includes a straight line that is 1/10 of the diameter of the circle passing through the center of the circle inscribed in the elliptical shape. The present invention relates to a thin film piezoelectric resonator.

  As an embodiment of the thin film piezoelectric resonator, the ellipse is a ratio of the length a of the major axis diameter to the length b of the minor axis diameter, and a / b is 1 <a / b <1.9. B> 40 t / n, where t is the thickness of the vibrating portion where the upper electrode and the lower electrode overlap each other in the thickness direction, and n is the order of the thickness vibration mode of the vibrating portion. The present invention relates to the thin film piezoelectric resonator.

  The present invention also relates to a thin film piezoelectric filter using the thin film piezoelectric resonator.

  According to the thin film piezoelectric resonator of the present invention, the thin film piezoelectric resonator includes a piezoelectric layer, and an upper electrode and a lower electrode formed so as to face each other with the piezoelectric layer interposed therebetween. The outer shape of the portions overlapping each other in the thickness direction is circular, and the upper electrode is not formed in a region including a straight line that passes through the center of the circle and whose length is 1/50 of the diameter. A thin film piezoelectric resonator having a high Q value can be realized without causing characteristic deterioration due to the acoustic mode. In addition, a thin film piezoelectric filter using these thin film piezoelectric resonators and having excellent characteristics can be provided.

  According to the thin film piezoelectric resonator of the present invention, the thin film piezoelectric resonator includes a piezoelectric layer, and an upper electrode and a lower electrode formed so as to face each other with the piezoelectric layer interposed therebetween. The upper electrode is formed in a region including a quadrangular outer shape of a portion where the lower electrode and the lower electrode overlap each other in a thickness direction, including an intersection of two diagonal lines of the quadrangle, and including at least 1/10 of one diagonal line. Therefore, it is possible to realize a thin film piezoelectric resonator having a high Q value without causing deterioration of characteristics due to the transverse acoustic mode.

  According to the thin film piezoelectric resonator of the present invention, the thin film piezoelectric resonator includes a piezoelectric layer, and an upper electrode and a lower electrode formed so as to face each other with the piezoelectric layer interposed therebetween. The region where the lower electrode and the lower electrode overlap with each other in the thickness direction is an ellipse, and passes through the center of the circle inscribed in the ellipse and includes a straight line whose length is 1/10 of the diameter of the circle. By not forming the upper electrode, it is possible to realize a thin film piezoelectric resonator having a high Q value without causing characteristic deterioration due to the transverse acoustic mode. Moreover, the effect is remarkable in a specific ellipse shape.

  Furthermore, the present invention can provide a thin film piezoelectric filter having excellent characteristics using these thin film piezoelectric resonators.

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

  The present invention provides a thin film piezoelectric resonator that suppresses the deterioration of the characteristics of a resonator due to an unnecessary transverse acoustic mode, has a high Q value, and facilitates the arrangement of the resonator when a filter is configured. It is an object.

  A thin film piezoelectric resonator of the present invention is a thin film piezoelectric resonator having a piezoelectric layer, and an upper electrode and a lower electrode formed so as to face each other with the piezoelectric layer interposed therebetween, and the upper electrode and the lower electrode are The outer shape of the portions overlapping each other in the thickness direction is circular, and the upper electrode is not formed in a region including a straight line having a length of 1/50 of the diameter passing through the center of the circular shape.

  FIG. 1 shows an embodiment of the thin film piezoelectric resonator of the present invention, FIG. 1 (a) is a schematic plan view thereof, and FIG. 1 (b) is a sectional view taken along line XX of FIG. 1 (a). . The thin film piezoelectric resonator of the present invention includes a piezoelectric thin film (piezoelectric layer) 2 and a lower electrode 8 and an upper electrode 10 formed so as to sandwich the piezoelectric thin film. The outer shape of the portion of the piezoelectric thin film 2 sandwiched between the lower electrode 8 and the upper electrode 10 is circular. However, a conductive thin film (referred to as a connection conductor) formed to connect the upper electrode and the lower electrode to an external circuit is not included in these shapes. Further, the boundary between the connection conductor and the upper electrode or the lower electrode is obtained by extending a line of the outer shape of another part of the upper electrode or the lower electrode.

  In the thin film piezoelectric resonator of the present invention, in particular, the upper electrode is not formed in a region 40 that passes through the center of the circle and includes a straight line whose length is 1/50 of the diameter. FIG. 2 shows several embodiments of a region 40 that includes a straight line that passes through the center of the circle and is 1/50 of the diameter in diameter. In FIG. 2, the length of the straight line and the size of the region 40 are schematically shown for easy understanding, and do not indicate the actual length or size. The straight line 50 passes through the center of a circle which is the outer shape of the portion sandwiched between the lower electrode 8 and the upper electrode 10 of the piezoelectric thin film 2, and the length is 1/50 of the diameter. The region 40 is a region including the straight line 50 and can be arbitrarily determined. The size and shape of the region 40 are not particularly limited. However, if this region 40 is too large, the vibration region is narrowed and affects the impedance of the thin film piezoelectric resonator. When a filter is configured using a piezoelectric resonator, an optimum impedance exists in the resonator due to matching with a connected system. However, when the vibration region is narrowed, the resonator impedance increases, and in order to obtain the desired impedance, the external dimensions of the resonator must be increased. Therefore, the size of the region 40 is appropriate depending on the design. The size should be large. Further, the shape of the region 40 is not particularly limited. Various shapes can be used as shown in FIG.

  As the configuration and material of the thin film piezoelectric resonator of the present invention, the same configuration and material as those of a 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).

  In the present invention, by forming the region 40 inside the upper electrode as described above, an excellent thin film piezoelectric resonator that suppresses the generation of noise due to the transverse acoustic mode without impairing the high Q value can be obtained.

  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, the through hole 30 reaching from the upper surface of the substrate to the sacrificial layer is formed using the patterning technique, and then the sacrificial layer is removed with an etching solution. Thereby, the pit portion becomes the air gap 4.

  Further, in the present invention, the outer shape of the portion where the upper electrode and the lower electrode overlap with each other in the thickness direction is circular, and the upper portion is located in the region 40 including a straight line passing through the center of the circle and having a length of 1/50 of the diameter. As a form in which the electrode is not formed, there is an embodiment as shown in FIG. 3 in addition to the embodiment shown in FIG. FIG. 3 is a cross-sectional view of a thin film piezoelectric resonator showing another embodiment of the present invention. In the embodiment of FIG. 1B, the upper electrode is not partially formed, but in the embodiment of FIG. 3, the piezoelectric layer corresponding to the region 40 is further removed or formed. It is a form that does not. There is also an embodiment shown in FIG. In the embodiment of FIG. 4, the lower electrode corresponding to the region 40 is not removed or formed. In the embodiment of FIGS. 3 and 4 as well, an excellent thin film piezoelectric resonator that suppresses the generation of noise due to the transverse acoustic mode without impairing the high Q value can be obtained.

  The thin film piezoelectric resonator shown in FIG. 3 can be manufactured, for example, as follows. After each layer is formed by the same method as that of the thin film piezoelectric resonator shown in FIG. 1, the through hole 30, the upper electrode, and the piezoelectric material reaching from the upper electrode to the sacrificial layer from the upper surface of the substrate using a patterning technique such as RIE. A region 42 from which the layer has been removed is formed. Thereafter, the sacrificial layer is removed with an etching solution.

  The thin film piezoelectric resonator shown in FIG. 4 can be manufactured, for example, as follows. After each layer is formed by the same method as that of the thin film piezoelectric resonator shown in FIG. 1, through holes 30, the upper electrode, and the lower electrode reaching from the upper surface of the substrate to the sacrificial layer using a patterning technique such as RIE. A region 44 from which the electrodes and the piezoelectric layer are removed is formed. Thereafter, the sacrificial layer is removed with an etching solution.

  FIG. 5 shows another embodiment of the thin film piezoelectric resonator of the present invention. The thin film piezoelectric resonator shown in FIG. 5 differs from the thin film piezoelectric resonator shown in FIGS. 1 to 4 in that the air gap 4 is formed from the back surface of the substrate 6. As shown in FIG. 6, the thin film piezoelectric resonator of the present invention may have a configuration in which an acoustic reflection layer 22 is provided instead of the air gap 4.

  As shown in FIG. 7, the thin film piezoelectric resonator according to the present invention is a thin film piezoelectric resonator having a dielectric layer 18 below the lower electrode and a dielectric layer 20 on the upper surface of the upper electrode. Similarly to the thin film piezoelectric resonator shown in FIGS. 1 to 6, a thin film piezoelectric resonator having a high Q value can be obtained without causing characteristic deterioration due to the transverse acoustic mode. FIG. 8 schematically shows the state of the elastic wave propagating in the lateral direction in the thin film piezoelectric resonance of the present invention. Most of the elastic waves propagating in the lateral direction are reflected by the region 40 where the upper electrode provided at the center is not formed and do not overlap. Therefore, the generation of noise due to the transverse acoustic mode is suppressed.

  Another thin film piezoelectric resonator of the present invention is a thin film piezoelectric resonator having a piezoelectric layer, and an upper electrode and a lower electrode formed so as to face each other with the piezoelectric layer interposed therebetween. The upper electrode is formed in a region including a quadrangular outer shape of a portion where the lower electrode and the lower electrode overlap each other in a thickness direction, including an intersection of two diagonal lines of the quadrangle, and including at least 1/10 of one diagonal line. It is characterized by not.

  FIG. 9 shows an embodiment of the thin film piezoelectric resonator of the present invention. The thin film piezoelectric resonator includes a piezoelectric thin film (piezoelectric layer) 2 and a lower electrode 8 and an upper electrode 10 formed so as to sandwich the piezoelectric thin film. The outer shape of the region between the lower electrode 8 and the upper electrode 10 of the piezoelectric thin film 2 is a quadrangle. However, a conductive thin film (referred to as a connection conductor) formed to connect the upper electrode and the lower electrode to an external circuit is not included in these shapes. Further, the boundary between the connection conductor and the upper electrode or the lower electrode can be obtained by extending the outline of the upper electrode or the lower electrode.

  The thin film piezoelectric resonator of the present invention includes an intersection of two diagonals of a square of the piezoelectric thin film sandwiched between the lower electrode 8 and the upper electrode 10 and a region including 1/10 on at least one diagonal 40, the upper electrode 8 is not formed. FIG. 10 illustrates some embodiments of a region 40 that includes the intersection of two diagonals of a square and includes 1/10 straight lines 60 on at least one diagonal. In FIG. 10, the length of the straight line and the size of the region 40 are schematically shown for easy understanding, and do not indicate the actual length or size. The region 40 is a region including the straight line 60 and can be arbitrarily determined. The size and shape are not particularly limited. However, if this region 40 is too large, the vibration region is narrowed and affects the impedance of the thin film piezoelectric resonator. When a filter is configured using a piezoelectric resonator, an optimum impedance exists in the resonator due to matching with a connected system. However, when the vibration region is narrowed, the resonator impedance increases, and in order to obtain the desired impedance, the external dimensions of the resonator must be increased. Therefore, the size of the region 40 is appropriate depending on the design. The size should be large. Further, the shape of the region 40 is not particularly limited. Various shapes can be used as shown in FIG.

  As the configuration and material of the thin film piezoelectric resonator of the present invention, the same configuration and material as those of a 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).

  In the thin film piezoelectric resonator of the present invention, by forming the region 40 inside the upper electrode in this way, an excellent thin film piezoelectric resonator that suppresses the generation of noise due to the transverse acoustic mode without impairing the high Q value. Is obtained. Furthermore, a thin film piezoelectric resonator having a large load Q value at the antiresonance frequency can be obtained, which is preferable.

  The thin film piezoelectric resonator as described above can be manufactured by the same method as the thin film piezoelectric resonator shown in FIG.

  In the thin film piezoelectric resonator of the present invention, the upper electrode 8 is not formed in a region 40 including an intersection of two diagonal lines of a quadrangle and including 1/10 on at least one diagonal line. In addition to the embodiment shown in FIG. 9B, there is an embodiment having a cross-sectional view similar to FIG. FIG. 3 is also a cross-sectional view of a thin film piezoelectric resonator showing another embodiment of the present invention. In the embodiment of FIG. 9 (b), the upper electrode is not partially formed. However, in the embodiment of the present invention having the cross-sectional view shown in FIG. The piezoelectric layer is also removed or not formed. Further, there is an embodiment having a cross-sectional view as shown in FIG. In the embodiment having the cross-sectional view of FIG. 4, the lower electrode corresponding to the region 40 is not removed or formed. Even in the embodiments having the cross-sectional views of FIGS. 3 and 4, an excellent thin film piezoelectric resonator in which the generation of noise due to the transverse acoustic mode is suppressed without impairing the high Q value can be obtained.

  FIG. 11 schematically shows the state of elastic waves propagating in the lateral direction in the thin film piezoelectric resonator of the present invention. Most of the elastic waves propagating in the lateral direction are reflected by the region 40 where the upper electrode provided at the center is not formed and do not overlap. Therefore, the generation of noise due to the transverse acoustic mode is suppressed. It is preferable that the contour line of the portion sandwiched between the lower electrode and the upper electrode of the piezoelectric thin film is not parallel to the contour line of the region 40 where the upper electrode is not formed because the effect of suppressing the transverse acoustic mode is large.

  FIG. 12 shows another embodiment of the thin film piezoelectric resonator of the present invention, FIG. 12 (a) is a schematic plan view thereof, and FIG. 12 (b) is an XX sectional view of FIG. 12 (a). . The thin film piezoelectric resonator shown in FIG. 12 includes a piezoelectric thin film (piezoelectric layer) 2 and a lower electrode 8 and an upper electrode 10 formed so as to sandwich the piezoelectric thin film. A portion of the piezoelectric thin film 2 sandwiched between the lower electrode 8 and the upper electrode 10 is a parallelogram. As described above, even when the portion where the lower electrode and the upper electrode overlap each other in the thickness direction is a parallelogram, two diagonal lines of the parallelogram are formed as in the present embodiment shown in FIGS. 9 and 10. The generation of noise due to the transverse acoustic mode is suppressed without impairing the high Q value by providing a region that does not form the upper electrode in a region that includes 1/10 on at least one of the diagonal lines. An excellent thin film piezoelectric resonator can be obtained.

  According to the thin film piezoelectric resonator of the present invention, the quadrangle that is the outer shape of the portion where the upper electrode and the lower electrode overlap with each other in the thickness direction is not particularly limited, but in particular, the square, rectangular, trapezoidal A parallelogram or the like is preferable because it has a great effect of suppressing the generation of noise due to the transverse acoustic mode. Furthermore, a square and a rectangle are preferable because a thin film piezoelectric resonator having a large load Q value at the antiresonance frequency can be obtained.

  FIG. 13 shows another embodiment of the thin film piezoelectric resonator of the present invention, FIG. 13 (a) is a schematic plan view thereof, and FIG. 13 (b) is a sectional view taken along line XX of FIG. 13 (a). . The thin film piezoelectric resonator shown in FIG. 13 includes a piezoelectric thin film (piezoelectric layer) 2 and a lower electrode 8 and an upper electrode 10 formed so as to sandwich the piezoelectric thin film. The outer shape of the portion where the upper electrode 10 and the lower electrode 8 overlap each other in the thickness direction is elliptical. However, a conductive thin film (referred to as a connection conductor) formed to connect the upper electrode and the lower electrode to an external circuit is not included in these shapes. Further, the boundary between the connection conductor and the upper electrode or the lower electrode can be obtained by extending the outline of the upper electrode or the lower electrode.

  In the thin film piezoelectric resonator of the present invention, the upper electrode is not formed in a region that passes through the center of the circle inscribed in the ellipse and includes a straight line whose length is 1/50 of the diameter of the circle. FIG. 14 shows some embodiments of a region 40 that includes a straight line 50 that passes through the center of a circle inscribed in the ellipse and is 1/50 of the diameter of the circle.

  In FIG. 14, the length of the straight line and the size of the region 40 are schematically shown for easy understanding, and do not indicate the actual length or size. The region 40 is a region including the straight line 60 and can be arbitrarily determined. The size and shape are not particularly limited. However, if this region 40 is too large, the vibration region is narrowed and affects the impedance of the thin film piezoelectric resonator. When a filter is configured using a piezoelectric resonator, an optimum impedance exists in the resonator due to matching with a connected system. However, when the vibration region is narrowed, the resonator impedance increases, and in order to obtain the desired impedance, the external dimensions of the resonator must be increased. Therefore, the size of the region 40 is appropriate depending on the design. The size should be large. Further, the shape of the region 40 is not particularly limited. Various shapes can be used as shown in FIG.

  The ellipse is preferably an ellipse having a ratio of the major axis diameter a to the minor axis diameter b, a / b of 1 <a / b <1.9, It is preferable that b> 40 t / n, where t is the thickness of the vibrating portion where the lower electrode and the lower electrode overlap each other in the thickness direction, and n is the order of the thickness vibration mode of the vibrating portion. The ratio of the length a of the major axis diameter to the length b of the minor axis diameter in which the region 40 where the electrode of the present invention is not formed is not formed, a / b is 1 <a / b <1.9. In the thin-film piezoelectric resonator having the elliptical vibration part, the generation of noise due to the transverse acoustic mode is particularly large. Under the above conditions, the noise suppression effect by not forming an electrode in the region 40 of the present invention is remarkably remarkable. is there.

  As the configuration and material of the thin film piezoelectric resonator of the present invention, the same configuration and material as those of a 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).

  In the thin film piezoelectric resonator of the present invention, by forming the region 40 inside the upper electrode in this way, an excellent thin film piezoelectric resonator that suppresses the generation of noise due to the transverse acoustic mode without impairing the high Q value. Is obtained. Furthermore, a thin film piezoelectric resonator having a large load Q value at the antiresonance frequency can be obtained, which is preferable.

  The thin film piezoelectric resonator as described above can be manufactured by the same method as the thin film piezoelectric resonator shown in FIG.

  In the thin film piezoelectric resonator of the present invention, the upper electrode 8 is formed in a region 40 that passes through the center of the circle inscribed in the ellipse and includes a straight line whose length is 1/50 of the diameter of the circle. There is also an embodiment having a cross-sectional view similar to that of FIG. 3 in addition to the embodiment shown in FIG. FIG. 3 is also a cross-sectional view of a thin film piezoelectric resonator showing another embodiment of the present invention. In the embodiment of FIG. 9 (b), the upper electrode is not partially formed. However, in the embodiment of the present invention having the cross-sectional view shown in FIG. The piezoelectric layer is also removed or not formed. Further, there is an embodiment having a cross-sectional view as shown in FIG. In the embodiment having the cross-sectional view of FIG. 4, the lower electrode corresponding to the region 40 is not removed or formed. Even in the embodiments having the cross-sectional views of FIGS. 3 and 4, an excellent thin film piezoelectric resonator in which the generation of noise due to the transverse acoustic mode is suppressed without impairing the high Q value can be obtained.

  By using a plurality of thin film piezoelectric resonators of the present invention, it is possible to configure a thin film piezoelectric filter that suppresses the occurrence of noise due to the transverse acoustic mode. As an embodiment of the thin film piezoelectric filter, there is a filter in which thin film piezoelectric resonators are arranged in a ladder shape as shown in FIG. 15, but the present invention is not limited to this.

Example 1
The thin film piezoelectric resonator shown in FIG. 1 was manufactured, in which the upper electrode had a circular shape with a radius of 100 μm and a square portion in which the upper electrode with a side of 10 μm was removed at the center. The thickness of each constituent layer in this example was set as follows. The lower electrode was made of Mo with a thickness of 300 nm, the piezoelectric layer was made of AlN with a thickness of 1700 nm, and the upper electrode was made of Mo with a thickness of 200 nm.
FIG. 16A shows the impedance and phase characteristics of the resonator formed as described above. Generation of noise due to the transverse acoustic mode is suppressed, and a good thin film piezoelectric resonator is obtained. Further, the load Q value at the antiresonance frequency of the obtained thin film piezoelectric resonator was 550, which was a high value. Further, FIG. 16B shows pass characteristics of the filter formed by the ladder type circuit shown in FIG. It can be seen that the generation of spike noise in and out of the band is suppressed compared with the pass characteristic of the filter formed by the thin film piezoelectric resonator manufactured by the conventional technique shown in FIG.

(Comparative Example 1)
The same thin film piezoelectric resonator as that of Example 1 was manufactured except that the upper electrode was formed up to the center without forming a square portion at the center of the upper electrode. That is, the process of removing a part of the upper electrode, the piezoelectric layer, and the lower electrode is not performed. FIG. 17A shows the impedance and phase characteristics of the obtained thin film piezoelectric resonator. As apparent from FIG. 17A, noise due to the transverse acoustic mode is generated, and it can be seen that the noise is suppressed in the first embodiment. FIG. 17B shows the pass characteristics of the filter formed by the ladder type circuit shown in FIG. It can be seen that many noises are generated in the passband and outside the passband, and the filter characteristics are deteriorated due to the transverse acoustic mode.

(Example 2)
A thin film piezoelectric resonator in which the upper electrode has a circular shape with a radius of 100 μm and a cross section in which a square portion in which the upper electrode, the lower electrode, and the piezoelectric layer with a side of 10 μm are removed at the same location exists in the center is formed as shown in FIG. . The thickness of each constituent layer in this example was the same as that in Example 1.
FIG. 18A shows the impedance and phase characteristics of the resonator formed as described above. Compared with the characteristics of the thin film piezoelectric resonator manufactured by the conventional technique shown in FIG. 17A, the generation of noise due to the transverse acoustic mode is greatly suppressed, and a good thin film piezoelectric resonator is obtained. Further, the load Q value at the antiresonance frequency of the obtained thin film piezoelectric resonator was 520, which was a high value. Further, FIG. 18B shows pass characteristics of the band pass filter formed by the ladder type circuit shown in FIG. Compared to the pass characteristic of the filter formed by the thin film piezoelectric resonator manufactured by the conventional technique shown in FIG. 17B, the generation of spike noise in and out of the band is suppressed, and it can be seen that the filter characteristic is good. .

(Example 3)
The thin film piezoelectric resonator shown in FIG. 9 was manufactured, in which the upper electrode was a rectangle having a side of 180 μm, and a rectangular portion having a rectangular shape with a side of 10 μm and a side of 30 μm was removed. The thickness of each constituent layer in this example was the same as that in Example 1. FIG. 19 shows the impedance and phase characteristics of the resonator formed as described above. The generation of noise due to the transverse acoustic mode is suppressed, and it can be seen that a good thin film piezoelectric resonator is obtained. Further, the load Q value at the antiresonance frequency of the obtained thin film piezoelectric resonator was 470, which was a high value.

(Comparative Example 2)
Except for not performing the process of removing a part of the upper electrode, the piezoelectric layer, and the lower electrode, the upper electrode is formed up to the central part without the rectangular part in the central part of the upper electrode in the same manner as in Example 3. The same thin film piezoelectric resonator as in Example 3 was manufactured except for the above. FIG. 20 shows the impedance and phase characteristics of the obtained thin film piezoelectric resonator. As apparent from FIG. 20, noise due to the lateral acoustic mode is generated, and it can be seen that in Example 3, the generation of noise due to the lateral acoustic mode is suppressed.

Example 4
FIG. 4 shows a cross section in which one side of the upper electrode has a rectangular shape of 180 μm, and a rectangular portion in which the upper electrode, the lower electrode, and the piezoelectric layer are removed at the same place in a rectangular shape with a side of 10 μm and a side of 30 μm. A thin film piezoelectric resonator was fabricated. The thickness of each constituent layer in this example was the same as that in Example 1.

  FIG. 21 shows the impedance and phase characteristics of the resonator formed as described above. Compared with the characteristics of the thin film piezoelectric resonator manufactured by the conventional technique shown in FIG. 20, the generation of noise due to the transverse acoustic mode is suppressed, and a good thin film piezoelectric resonator is obtained. Further, the load Q value at the antiresonance frequency of the obtained thin film piezoelectric resonator was 440, which was a high value.

(Comparative Example 3)
A thin film piezoelectric resonator having a polygonal shape having no parallel sides as shown in Patent Document 2 and having the same resonator area as that of Example 1 was manufactured. Although the noise due to the transverse acoustic mode of the obtained thin film piezoelectric resonator was suppressed, the load Q at the antiresonance frequency was as low as 320. It can be seen that the electrode shape is preferably a circle or a rectangle rather than a polygon having no parallel sides.

(Example 5)
The outer shape of the portion where the upper electrode and the lower electrode overlap each other in the thickness direction is an elliptical resonator, the upper electrode is an elliptical shape having a short axis diameter of 100 μm and a long axis diameter of 140 μm, and an upper electrode having a side of 10 μm at the center, A thin film piezoelectric resonator having a cross section in which a square portion where the electrode and the piezoelectric layer were removed at the same location exists was manufactured as shown in FIG. The thickness of each constituent layer in this example was the same as that in Example 1.
FIG. 22 shows the impedance and phase characteristics of the resonator formed as described above. Compared with the characteristics of the thin film piezoelectric resonator manufactured by the conventional technique shown in FIG. 17A, the generation of noise due to the transverse acoustic mode is greatly suppressed, and a good thin film piezoelectric resonator is obtained. Further, the load Q value at the antiresonance frequency of the obtained thin film piezoelectric resonator was 500, which was a high value.

(Comparative Example 4)
Except for not performing the process of removing a part of the upper electrode, the piezoelectric layer, and the lower electrode, the upper electrode is formed up to the central part without the rectangular part in the central part of the upper electrode in the same manner as in Example 5. The same thin film piezoelectric resonator as in Example 3 was manufactured except for the above. FIG. 23 shows the impedance and phase characteristics of the obtained thin film piezoelectric resonator. As is apparent from FIG. 22, noise due to the transverse acoustic mode is generated, and it can be seen that in Example 5, the occurrence of noise due to the transverse acoustic mode is suppressed.

It is (a) typical top view and (b) sectional view showing one embodiment of a thin film piezoelectric resonator of the present invention. It is a schematic diagram which shows other embodiment of the area | region 40 which does not form the upper electrode of the thin film piezoelectric resonator of this invention. It is a typical sectional view showing other embodiments of the field which does not form the upper electrode of the thin film piezoelectric resonator of the present invention. It is a typical sectional view showing other embodiments of the field which does not form the upper electrode of the thin film piezoelectric resonator of the present invention. It is (a) typical top view and (b) sectional view showing other embodiments of the thin film piezoelectric resonator of the present invention. It is (a) typical top view and (b) sectional view showing other embodiments of the thin film piezoelectric resonator of the present invention. It is (a) typical top view and (b) sectional view showing other embodiments of the thin film piezoelectric resonator of the present invention. It is typical explanatory drawing which shows the effect | action which suppresses a transverse acoustic mode with the thin film piezoelectric resonator of this invention. It is (a) typical top view and (b) sectional view showing one embodiment of a thin film piezoelectric resonator of the present invention. It is a schematic diagram which shows other embodiment of the area | region which does not form the upper electrode of the thin film piezoelectric resonator of this invention. It is typical explanatory drawing which shows the effect | action which suppresses a transverse acoustic mode with the thin film piezoelectric resonator of this invention. It is (a) typical top view and (b) sectional view showing other embodiments of the thin film piezoelectric resonator of the present invention. It is (a) typical top view and (b) sectional view showing other embodiments of the thin film piezoelectric resonator of the present invention. It is a schematic diagram which shows other embodiment of the area | region which does not form the upper electrode of the thin film piezoelectric resonator of this invention. It is a figure which shows the ladder type circuit which is one Embodiment of the filter using the thin film piezoelectric resonator of this invention. It is a figure which shows the filter characteristic of the filter using (a) thin film piezoelectric resonator of this invention obtained in Example 1, and (b) the filter using a thin film piezoelectric resonator. It is a figure which shows the filter characteristic of the filter using (a) the thin film piezoelectric resonator obtained in Comparative Example 1, and (b) the filter using the thin film piezoelectric resonator. It is a figure which shows the filter characteristic of the filter using the (a) thin film piezoelectric resonator of this invention obtained in Example 2, and (b) the filter using a thin film piezoelectric resonator. It is a figure which shows the impedance characteristic of the thin film piezoelectric resonator of this invention obtained in Example 3. FIG. 6 is a diagram showing impedance characteristics of a thin film piezoelectric resonator obtained in Comparative Example 2. FIG. It is a figure which shows the impedance characteristic of the thin film piezoelectric resonator of this invention obtained in Example 4. FIG. It is a figure which shows the impedance characteristic of the thin film piezoelectric resonator of this invention obtained in Example 5. FIG. It is a figure which shows the impedance characteristic of the thin film piezoelectric resonator obtained by the comparative example 4. It is (a) typical top view of the conventional thin film piezoelectric resonator, and (b) sectional drawing. It is a typical top view which shows the structure of the conventional thin film piezoelectric resonator. It is typical sectional drawing which shows the structure of the conventional thin film piezoelectric resonator. It is typical sectional drawing which shows the structure of the conventional thin film piezoelectric resonator. It is a schematic diagram which shows the effect | action of transverse acoustic mode generation | occurrence | production with the conventional thin film piezoelectric resonator. It is (a) typical top view of the conventional thin film piezoelectric resonator, and (b) sectional drawing. It is a typical top view of the conventional thin film piezoelectric resonator.

Explanation of symbols

2 Piezoelectric layer 4 Air gap 6 Substrate 8 Lower electrode 10 Upper electrode 12 Piezoelectric resonator stack 14 Connection conductor 16 Frame layer 18 Lower dielectric layer 20 Upper dielectric layer 22 Acoustic impedance converter 30 Sacrificial layer etching through hole 40 Upper Region where no electrode is formed (upper electrode layer removal part)
42 Region where upper electrode is not formed (upper electrode and piezoelectric layer removing portion)
44 Region where the upper electrode is not formed (upper electrode, lower electrode and piezoelectric layer removing portion)
50 A straight line passing through the center of the outer shape 50 and having a length of 1/50 of the diameter 60 A straight line having a length of 1/10 of the diagonal passing through the intersection of two diagonal lines of the rectangular outer shape 100 Thin film piezoelectric filter 101 , 102 I / O ports 111, 113, 115 Series resonant elements of thin film piezoelectric filter 112, 114, 116 Shunt resonant elements of thin film piezoelectric filter

Claims (5)

  A thin film piezoelectric resonator having a piezoelectric layer and an upper electrode and a lower electrode formed so as to face each other with the piezoelectric layer interposed therebetween, and an outer shape of a portion where the upper electrode and the lower electrode overlap each other in the thickness direction A thin film piezoelectric resonator characterized in that the upper electrode is not formed in a region that is circular and passes through the center of the circle and includes a straight line whose length is 1/50 of the diameter.   A thin film piezoelectric resonator having a piezoelectric layer and an upper electrode and a lower electrode formed so as to face each other with the piezoelectric layer interposed therebetween, and an outer shape of a portion where the upper electrode and the lower electrode overlap each other in the thickness direction A thin film piezoelectric resonator having a quadrangular shape, wherein the upper electrode is not formed in a region including an intersection of two diagonal lines of the quadrilateral and including 1/10 of at least one diagonal line.   A thin film piezoelectric resonator having a piezoelectric layer and an upper electrode and a lower electrode formed so as to face each other with the piezoelectric layer interposed therebetween, and an outer shape of a portion where the upper electrode and the lower electrode overlap each other in the thickness direction A thin film characterized in that the upper electrode is not formed in a region that is elliptical and passes through the center of a circle inscribed in the elliptical shape and includes a straight line whose length is 1/50 of the diameter of the circle. Piezoelectric resonator.   The ellipse is an ellipse in which the ratio of the major axis diameter length a to the minor axis diameter length b is 1 / a / b <1.9, and the upper electrode and the lower electrode The thickness of the vibration part which is a part which an electrode mutually overlaps with a thickness direction is set to t, and it is b> 40t / n when the order of the thickness vibration mode of the said vibration part is set to n. Thin film piezoelectric resonator.   A thin film piezoelectric filter using the thin film piezoelectric resonator according to claim 1.

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