JP4572679B2 - Piezoelectric thin film resonator - Google Patents

Description

  The present invention relates to a piezoelectric thin film resonator.

  A piezoelectric thin film resonator using acoustic resonance as a device constituting a filter used for a mobile communication terminal or a Bluetooth module is very small and useful. This device utilizes bulk longitudinal acoustic waves in a piezoelectric thin film. The simplest structure has a structure in which a piezoelectric thin film is sandwiched between two independent metal electrodes, and this structure is operated in a state of being floated in the air by a support member.

  When a voltage is applied to the two electrodes, an electric field is generated between the two electrodes, and the piezoelectric thin film becomes a device that converts part of the electrical energy into mechanical energy in the form of sound waves. The mechanical resonance frequency for a given phase velocity of sound waves traveling through the material is such that the half wavelength of the sound waves traveling vertically through the device is equal to the total thickness of the device, and this device acts as a resonator. .

  In the fundamental vibration mode of the device, there are other vibration modes different from bulk longitudinal sound waves, such as compression waves, shear waves, or Lamb waves, which are propagated perpendicular to the electrode surface. These modes move in parallel on the electrode surface and are converted into sound waves that are reflected at the end of the vibrating cavity wall or electrode layer. The fundamental frequency of these modes is considerably lower than the longitudinal vibration mode of the basic bulk longitudinal sound wave (hereinafter referred to as the fundamental longitudinal vibration mode), but the harmonics of these modes appear in the frequency band of the fundamental longitudinal vibration mode. There is a case.

  When the thickness of the piezoelectric thin film is t0, the width is W, the speed of the sound wave in the basic longitudinal vibration mode is CL, and the speed of the sound wave in the transverse propagation mode is CT, the frequency of the basic longitudinal vibration mode is CL / (2t0). On the other hand, the frequency causing the spike caused by the transverse propagation mode harmonic is a frequency centered on CTN / (2 W), where N is a natural number. Therefore, when W / N is almost equal to t0 (CT / CL) for any N, one or more spikes are generated by the transverse propagation mode in the resonance frequency range of the fundamental longitudinal vibration mode. The size of the spike is determined by N and the number of points on the outer periphery of the vibration part that may cause a transverse propagation mode at the same resonance frequency. Here, the outer periphery of the vibration part is the first of the piezoelectric thin film. It refers to a portion where two electrodes attached to the surface and the second surface overlap. In general, the coupling coefficient for a given parasitic transverse propagation mode decreases with N and increases with the number of points having the same resonant frequency.

  If a point on the outer periphery of the vibration part has the same path length of the lateral propagation mode as a point on the other outer periphery, this lateral propagation mode is degenerated, and the amplitude of the spike generated by this lateral propagation mode Will grow. Therefore, when a certain point on the outer periphery of the vibrating part has a transverse propagation mode different from other points on the outer periphery of the vibrating part, and the corresponding path length is larger than the physical dimension of the piezoelectric thin film resonator, The amplitude of this spike can be greatly reduced.

  In order to realize the above, a piezoelectric thin film resonator having an irregular polygonal shape in which opposing sides are not parallel to each other in the shape of an electrode is disclosed in Patent Document 1. FIG. 14 shows a perspective view of a piezoelectric thin film resonator according to the present invention as a conventional example.

  The dielectric film 1 having the gap 6 is formed on the substrate, and thereafter, the lower electrode 2, the piezoelectric thin film 3, and the upper electrode 4 are formed in order. A portion where the lower electrode 2 and the upper electrode 4 formed on the gap 6 are overlapped with each other through the piezoelectric thin film 3 is a vibrating portion 5 of the resonator. The lower electrode 2 and the upper electrode 4 in the vibration part 5 have an irregular polygon shape.

  The sound wave that exits a certain point on the electrode outer periphery of the vibration unit 5 is reflected on the opposing outer peripheral surface and does not return to the same point where the sound wave is emitted, and the sound wave repeats irregular reflection, The path is considerably longer than the dimensions of the electrodes of the vibration part 5. Furthermore, since the sound wave emitted from a point different from the above point is different from the above-described path, the degeneration of the transverse propagation modes is greatly reduced. As a result, the corresponding spikes are wider than those obtained with devices according to the prior art. Therefore, the parasitic transverse propagation mode spectrum is converted from individual sharp peaks to a larger number of wider peaks, and there are no spikes that can interfere with the characteristics of the piezoelectric resonant element in the operating frequency range.

On the other hand, in Patent Document 2, two independent input electrode portions and output electrode portions are provided on the first surface of the crystal plate, and at least a part of both the input electrode and the output electrode is crystal on the second surface. There is disclosed a shape in which a common electrode having an overlapping portion through a plate is formed. In this case, the quartz plate operates as a piezoelectric body and can be called a piezoelectric resonator filter. In this patent document, a method of improving the spurious characteristics by disposing the energy distribution of the anharmonic overtone mode by providing a weight addition unit or a weight reduction unit on the outer periphery of the input electrode, the output electrode, or the common electrode is shown. . In particular, with regard to the weight reducing portion, the method of providing a notch in the outer peripheral portion of the electrode is described in the claims. However, all the embodiments relating to the notch are linear on the electrode, and the plane of the device. In the figure, it is shown symmetrically with respect to the central axis in the X direction or the central axis in the Y direction. Such a notch cannot suppress the occurrence of spikes due to transverse propagation mode resonance.
JP 2000-332568 A JP-A-10-98351

  Since the rectangular electrode, which is the simplest electrode shape, has a large effective area, the resistance of the electrode itself can be reduced. However, in this case, unnecessary resonance spikes due to the transverse propagation mode cannot be suppressed. If an irregular polygonal shape as described in the background is used in order to suppress such unwanted resonance due to the transverse propagation mode, there is a problem that the effective area of the electrode is reduced and the resistance of the electrode is increased.

  In addition, there is a problem that the circular electrode having the best resonance and anti-resonance Q in constituting the piezoelectric thin film resonator cannot be used because it generates a strong transverse propagation mode. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-described problems and to suppress unnecessary resonance spikes due to transverse propagation mode resonance while maintaining good Q by a simple method.

  In order to solve the above problem, the invention according to claim 1 is directed to a piezoelectric thin film having a first surface and a second surface, a first electrode formed on the first surface, and the second electrode. A second electrode formed on the surface of the piezoelectric thin film resonator, wherein the first electrode is a piezoelectric thin film resonator having a portion overlapping the second electrode via the piezoelectric thin film. In the plane of at least one of the overlapping portions of the second electrode and the second electrode, the slit portion has one irregularly-shaped slit portion, and the slit has one independent start point and end point 1 Provided is a piezoelectric thin film resonator characterized in that it has a continuous line shape, does not have a portion that intersects itself in the middle, and both the start point and the end point do not reach the end face of the electrode. .

The invention according to claim 2 is the piezoelectric thin film resonator according to claim 1, wherein the shape of the slit is an arbitrary point on the outer peripheral portion of the electrode where the slit is formed and a virtual point at the arbitrary point. The first distance groups obtained between the points where the perpendicular intersects the slit are different, and between any point on the slit and the point where the virtual perpendicular at the arbitrary point intersects the slit again Provided is a piezoelectric thin film resonator characterized in that the obtained second distance groups are different from each other and the first distance group and the second distance group are different from each other.

  According to a third aspect of the present invention, there is provided a piezoelectric thin film having a first surface and a second surface, a first electrode formed on the first surface, and a first electrode formed on the second surface. The first electrode is a piezoelectric thin film resonator having a portion overlapping with the second electrode via the piezoelectric thin film, the first electrode and the second electrode A plurality of irregularly-shaped slit portions in the plane of at least one of the overlapping portions, each of the slits having a single continuous line shape having one independent start point and end point And there is no part that intersects itself in the middle, and both the start point and the end point do not reach the end face of the electrode, and the electrode surface in which the plurality of slits are present is surrounded by the plurality of slits. Have an independent face To provide a piezoelectric thin-film resonator, characterized in that.

  The invention according to claim 4 is the piezoelectric thin film resonator according to claim 3, wherein the plurality of slits are formed at any point on the outer periphery of the electrode where the plurality of slits are formed, and The first distance groups obtained between the virtual perpendiculars at the points intersecting the plurality of slits are different from each other, and any point on each of the slits, and the virtual perpendicular at the arbitrary point is the slit. The second distance groups obtained between the points that intersect again and the points that intersect with other slits are different from each other, and the first distance group and the second distance group are different from each other. A piezoelectric thin film resonator is provided.

  The invention according to claim 5 is characterized in that at least one of the overlapping portions of the first electrode and the second electrode is circular, and the piezoelectric thin film resonance according to claim 1, 2, 3 or 4 Offer a child.

  The invention according to claim 6 is characterized in that at least one of the overlapping portions of the first electrode and the second electrode is elliptical, according to claim 1, 2, 3 or 4. Resonator.

In the invention according to claim 7, the slit is formed in both the first electrode and the second electrode, and the shape of the slit is symmetrical with respect to the virtual center plane with respect to the thickness of the piezoelectric thin film. The piezoelectric thin film resonator according to claim 1, wherein the piezoelectric thin film resonator is provided.

According to the present invention, spikes due to unnecessary transverse propagation mode resonance can be reduced even when rectangular electrodes are used. Furthermore, even if a circular electrode, which is considered to be the best mode for producing a piezoelectric thin film resonator, is used, a resonator with reduced unnecessary transverse propagation mode resonance can be produced.

  1 and 2 show a first embodiment of the present invention. FIG. 1A is a perspective view of a piezoelectric thin film resonator, FIG. 1B is a central sectional view thereof, and FIG. 2 is a plan view thereof. Originally, there is a substrate under the dielectric thin film 1, but the drawing is omitted in this figure.

  The dielectric film 1 is formed so as to continuously cover the surface of the sacrificial layer and the substrate surface after forming a sacrificial layer for forming the gap 6 on the substrate. Although the sacrificial layer is not shown, the lower electrode 2, the piezoelectric thin film 3, and the upper electrode 4 are formed and then removed to form the gap 6.

  As shown in FIG. 1A, the layer on the dielectric film 1 is formed in the order of the lower electrode 2, the piezoelectric thin film 3, and the upper electrode 4. A portion where the lower electrode 2 and the upper electrode 4 formed on the gap 6 are overlapped with each other through the piezoelectric thin film 3 is a vibrating portion 5 of the resonator. The slit 7 is a removed portion of the electrode formed on the upper electrode 4 in the vibrating portion 5.

  In FIG. 2, reference numeral 5 denotes a vibrating portion of this resonator, which is a portion where the upper electrode 4 overlaps the lower electrode 2 through the piezoelectric thin film 3. A slit 7a is formed in the upper electrode 4 in the region indicated by the vibration part 5a by photoetching or laser processing. The slit 7a may reach the piezoelectric thin film, and the electrode may be completely cut off at that portion, or may be a recess having a depth that is more than half the thickness of the upper electrode 4.

  The transverse propagation mode sound wave excited from a certain point at the end of the upper electrode 4 of the vibration part 5 is reflected by the slit 7a, but the slit 7a is not parallel to the end of the electrode, so that the upper electrode 4 is the same. A different point is reached without returning to the end point. Further, the sound wave is reflected at this point and reaches a different point at the end on the upper electrode 4 or a point different from the previous reflection point of the slit 7a, and thereafter the same reflection is repeated. When the slit 7a is processed by a laser, the resonance frequency in the basic longitudinal vibration mode can be finely adjusted by changing the length, width, or depth.

  As described above, each point on the outer periphery of the electrode of the vibrating portion has a transverse propagation mode different from any other point on the outer periphery. Similarly, the path length of the corresponding transverse propagation mode is larger than the physical dimension of the vibration part because irregular reflection is repeated by the irregularly shaped slit and the end of the electrode. Unnecessary spikes due to can be greatly reduced.

  FIG. 3 shows a modification of the first embodiment, in which one of the start point and the end point of the slit 7b reaches the end of the electrode.

  Similarly, FIG. 4 is a modification of the first embodiment, and the slit 7c has an irregular polygonal shape. In this case, the arbitrary vertex of the polygon may be a rounded vertex instead of the corner, and the line segment from the arbitrary vertex to the adjacent vertex may be a curved line.

  FIG. 5 shows a second embodiment in which two independent slits 7d and 7e are formed in the region indicated by the vibration part 5. FIG. The effect is the same as in the first embodiment. In this figure, two slits 7d and 7e are drawn, but a larger number of slits may exist.

  FIG. 6 shows a modification of the second embodiment, in which two slits 7f and 7g having one intersecting point are formed in the region indicated by the vibrating portion 5. In FIG.

  Similarly, FIG. 7 shows a modification of the second embodiment, in which three slits 7 h, 7 i, 7 j are formed in the region indicated by the vibration part 5. 7i has an intersection with 7h, and 7j also has an intersection with 7h. Each of these slits has a linear shape, but has an irregular shape as a whole, and the effect is the same as that of the first embodiment.

  FIG. 8 shows a third embodiment, and the electrodes in the vibrating portion 5a are circular. In this case, the piezoelectric thin film resonator using the basic longitudinal vibration mode is in an ideal state in which Q is maximum for both resonance and anti-resonance. However, when a slit is not formed and a simple circular electrode is used, the transverse propagation mode is very strong. Is done. The “Whispering Gallery” resonator utilizes these modes. By providing the circular electrode with the slit 7k, an effect similar to that of the embodiment described with reference to FIG. 2 is produced, and the piezoelectric thin film resonator using the ideal fundamental longitudinal vibration mode can be realized while the transverse propagation mode is suppressed. .

  FIG. 9 shows a fourth embodiment in which the lower electrode 2 is formed larger than the upper electrode 4 in the vibrating portion 5b. In such a form, a problem that the overlapping portion of the electrode is partially lost in the vibrating portion 5c due to the positional deviation of the electrode that occurs during manufacture is prevented, and the characteristics are stabilized. Although a circular electrode is taken as an example here, the electrode shape may be a rectangle, a polygon, an ellipse, or the like.

  FIG. 10 shows a fifth embodiment. In the vibrating portion 5c, the electrode has an elliptical shape and is provided with a slit 7l. In this case, it is possible to obtain an intermediate effect between the effect of reducing the electrode resistance by increasing the effective area of the electrode by making the electrode rectangular and the effect of maximizing the resonance and anti-resonance Q in the basic longitudinal vibration mode by making the electrode circular. it can.

  FIG. 11 shows a sixth embodiment. In the vibrating part 5d, slits 7m and 7n are formed in the lower electrode 2 and the upper electrode 4 facing each other with the piezoelectric thin film 3 interposed therebetween, and the slits 7m and 7n are piezoelectric. It has a symmetrical shape with respect to a virtual center plane in the thickness direction of the body thin film. According to this embodiment, since the upper electrode 4 is provided with the slit 7m and the lower electrode 2 with the slit 7n, the lateral propagation mode is suppressed on both the upper and lower surfaces, and the occurrence of spikes is more effectively suppressed. Since the slits 7m and 7n have a symmetrical shape with respect to the virtual center plane in the thickness direction of the piezoelectric thin film, the factor that disturbs the fundamental longitudinal vibration mode is reduced, and the characteristics of the main mode are kept good.

  FIGS. 12A and 12B show a seventh embodiment, which is an enlarged view of the vicinity of the vibrating portion 5e of the piezoelectric thin film resonator. In FIG. 12A, the distance between the intersection of an arbitrary point on the outer peripheral portion of the vibrating portion 5e of the electrode 4 and the slit 7o recognized by the virtual perpendiculars 8a, 8b, 8c, and 8d at the arbitrary point is The slits 7o are configured so that they all have different distances. Although the distances are indicated by four perpendicular lines 8a, 8b, 8c and 8d in the drawing, these distances are determined at arbitrary points on the outer peripheral portion of the vibrating portion 5e of the electrode 4, and the distance is determined. There are an infinite number of positions. Ideally, all of these distances are different, but it is desirable that these distances differ with a probability of 90% or greater.

  Similarly, in FIG. 12B, the distances between the arbitrary points in the slit 7o and the intersections between the arbitrary points on the virtual perpendicular lines 9a, 9b, and 9c and the slit 7o itself are all different distances. Thus, the slit 7o is configured. Although the distances are indicated by three perpendicular lines 9a, 9b, and 9c in the drawing, these distances are determined at arbitrary points on the slit 7o, and there are infinite positions where the distance is determined. Ideally, all of these distances are different, and the distance between the slit 7o described with reference to FIG. 12A and the outer periphery of the electrode 4 is ideal, but these distances differ with a probability of 90% or more. It is desirable that

  FIG. 13 shows a modification of the seventh embodiment, in which a slit 7p is added to the same structure as in FIGS. 12 (a) and 12 (b). The slits 7o and 7p are configured such that the distances between the arbitrary points in the slit 7o and the intersections of the slits 7p recognized by the virtual perpendiculars 10a, 10b, and 10c at the arbitrary points are all different. Yes. Although the distances are indicated by three perpendicular lines 10a, 10b, and 10c in the drawing, these distances are determined at arbitrary points on the slit 7o, and there are infinite positions for determining the distances. All of these distances are different and are different from the distance group between the slit 7o described with reference to FIG. 12A and the outer periphery of the electrode 4, and the slit 7o and the electrode 4 described with reference to FIG. Different from the distance group between the slit 7p obtained by the same method as the distance to the outer peripheral portion and the outer peripheral portion of the electrode 4, and different from the distance between the slit 7o described with reference to FIG. It is ideal that the distance between the slit 7p and the slit 7p obtained by the same method as the distance between the slit 7o and itself described with reference to FIG. It is desirable that the distances be different.

In FIGS. 12A, 12B, and 13, the electrode 4 of the vibrating portion 5f is circular. However, this electrode may be rectangular, polygonal, or elliptical. Moreover, although the slit 7o and the slit 7p were shown by the irregular curve shape, the slit which has a linear part partially may be sufficient. Although FIG. 13 shows an example in which there are two slits, it may have three or more slits, and in this case as well, the electrode outer periphery and the slit recognized on the perpendicular at any point on the electrode outer periphery A distance group between the slit perceived on the normal of any point on each slit and the point of intersection again with the slit per se, and another slit recognized on the vertical of any point on each slit It is desirable that the distance groups are as different as possible.

(A) It is a perspective view which shows the piezoelectric thin film resonator of this invention. (B) It is center sectional drawing of the piezoelectric thin film resonator of this invention. It is explanatory drawing explaining the 1st Example of this invention. It is explanatory drawing explaining the modification of the 1st Example of this invention. It is explanatory drawing explaining the modification of the 1st Example of this invention. It is explanatory drawing explaining the 2nd Example of this invention. It is explanatory drawing explaining the modification of the 2nd Example of this invention. It is explanatory drawing explaining the modification of the 2nd Example of this invention. It is explanatory drawing explaining the 3rd Example of this invention. It is explanatory drawing explaining the 4th Example of this invention. It is explanatory drawing explaining the 5th Example of this invention. It is explanatory drawing explaining the 6th Example of this invention. (A) It is explanatory drawing explaining the 7th Example of this invention. (B) It is explanatory drawing explaining the 7th Example of this invention. It is explanatory drawing explaining the modification of the 7th Example of this invention. It is a perspective view which shows the conventional transverse propagation mode suppression piezoelectric thin film resonator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dielectric thin film 2 Lower electrode 3 Piezoelectric thin film 4 Upper electrode 5, 5a-5e Vibrating part 6 Gap part 7a-7p Slit 8a-8d The perpendicular in the arbitrary points of the outer periphery of the upper electrode 4 in a vibrating part 9a-9c On a slit Perpendicular at any point of 10a to 10d Perpendicular at any point on the slit

Claims (7)

A piezoelectric thin film having a first surface and a second surface; a first electrode formed on the first surface; and a second electrode formed on the second surface; The first electrode is a piezoelectric thin film resonator having a portion overlapping with the second electrode via the piezoelectric thin film,
In the plane of at least one of the overlapping portions of the first electrode and the second electrode, the slit has one irregularly-shaped slit portion, and the slit has one independent start point and end point A piezoelectric thin film resonator characterized by having a continuous line shape having no part where it intersects itself in the middle, and both the start point and the end point do not reach the end face of the electrode . The piezoelectric thin film resonator according to claim 1, wherein the shape of the slit is
The first distance groups obtained between an arbitrary point on the outer peripheral portion of the electrode where the slit is formed and a point where a virtual perpendicular at the arbitrary point intersects the slit are different from each other.
And the second distance groups obtained between an arbitrary point on the slit and a point where the virtual perpendicular at the arbitrary point intersects the slit again are different from each other, and the first distance group and the second distance group are different from each other. A piezoelectric thin film resonator, wherein the distance groups are formed differently. A piezoelectric thin film having a first surface and a second surface; a first electrode formed on the first surface; and a second electrode formed on the second surface; The first electrode is a piezoelectric thin film resonator having a portion overlapping with the second electrode via the piezoelectric thin film,
In the plane of at least one of the overlapping portions of the first electrode and the second electrode, a plurality of irregularly shaped slit portions are provided, and each of the slits is an independent starting point. And one continuous line shape having an end point, no part intersecting itself in the middle, and both the start point and the end point do not reach the end face of the electrode, and the plurality of slits exist The piezoelectric thin film resonator is characterized in that the electrode surface does not have an independent surface surrounded by the plurality of slits. The piezoelectric thin film resonator according to claim 3, wherein the plurality of slits are shaped as follows:
The first distance groups obtained between an arbitrary point on the outer periphery of the electrode where the plurality of slits are formed and a point where a virtual perpendicular at the arbitrary point intersects the plurality of slits are different from each other,
And the second distance groups obtained between an arbitrary point on each of the slits, a point where a virtual perpendicular at the arbitrary point intersects the slit again, and a point where it intersects with the other slits are different from each other, and A piezoelectric thin-film resonator, wherein the first distance group and the second distance group are formed different from each other.   5. The piezoelectric thin film resonator according to claim 1, wherein at least one of the overlapping portions of the first electrode and the second electrode is circular.   5. The piezoelectric thin film resonator according to claim 1, wherein at least one of overlapping portions of the first electrode and the second electrode is elliptical.   The slit is formed in both the first electrode and the second electrode, and the shape of the slit is symmetrical with respect to a virtual center plane with respect to the thickness of the piezoelectric thin film. The piezoelectric thin film resonator according to any one of 1 to 6.

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