JP2014502809A - Electroacoustic resonator - Google Patents

Abstract

An electroacoustic resonator (10) having two electrodes (11, 12) is provided,
Each of these two electrodes includes a bus bar piece (21, 22) and a plurality of electrode fingers (1, 2).
The electrode fingers (1, 2) are arranged along the first direction and are connected to the bus bar pieces (21, 22) of the respective electrodes (11, 12) so as to be electrically connected; Extending along a second direction which is transverse to the direction of
The resonator (10) is a resonator weighted by superposition, in which the width of the superposition region (20) measured along the second direction is along the first direction; The electrode fingers (1, 2) of both electrodes (11, 12) are engaged with each other in this overlapping region,
The resonator (10) is provided with a conductive bridge (3) between the electrode fingers (1, 2) of each said electrode (11, 12), this conductive bridge being separated from the busbar piece (21, 22), respectively; A plurality of electrode fingers of the same electrode are connected so as to be electrically connected to each other.
[Selection] Figure 3A

Description

The present invention relates to an electroacoustic resonator.

  The electroacoustic resonator has one piezoelectric layer and two electrodes, and the two electrodes are disposed on the surface of the piezoelectric layer, for example. Each of these two electrodes has a plurality of electrode fingers, which are connected to electrode bus bar pieces (Sammelelektrodenabschnitt), through which time-dependent electrical potentials are applied to the electrode fingers. Is done. The electrode fingers of the two electrodes mesh with each other in a comb shape. A reflector is bounded on each side of the outer sides of the interdigitated electrodes, and these reflectors have a plurality of (but connected on both sides) similar, with a common connection. It is formed from electrode fingers. The electrode fingers of one electrode, however, are electrically connected only at one end and the other end is surrounded by the electrode fingers of the other electrode.

  The electroacoustic resonator having such a structure is called an interdigital transducer (IDT). A high-frequency AC voltage (approximately in the range of 100 MHz to several GHz) forms a high-frequency standing wave in the piezoelectric layer, and most of this standing wave is the surface as in the case of a SAW (surface acoustic wave) element. It is formed in the form of a wave or in the form of a volume wave, as in the case of a BAW (bulk acoustic wave) element or a GBAW (guided bulk acoustic wave) element.

  The present application relates to weighted resonators, and in particular to superposition weighted resonators. That is, the electrode fingers are engaged with each other at different depths rather than being introduced into the gap between adjacent electrode fingers of each other electrode over the entire length (and not exceeding a certain portion of its length). . Looking at a portion of the total resonance area between the bus bar pieces of both electrodes, each electrode has a short electrode finger and a long electrode finger that are locally alternated. The short electrode fingers are only extended to the outer edge or start of the overlap region. Between the short electrode fingers, long electrode fingers protrude toward the overlapping region and pass through this overlapping region. The overlap area of the weighted resonator is at the outer edge of the resonator when measured along the extending electrode fingers. That is, it is closest to both reflectors and has a small portion near the center between the bus bar pieces of both electrodes. On the other hand, in the central portion between the two reflectors, the overlapping region is the largest, and substantially occupies the entire distance between both bus bar pieces. Thus, the overlapping region is expanded toward the center of the resonator.

  A drawback of the resonator weighted in this way is that the conductive path length gradually increases along the electrode fingers to the overlap region toward the outer edge. Through these conductive path lengths, the charge to the connected electrodes must be transported before reaching the superposed region that contributes to the generation of standing waves in the solid anyway. The above point is not only applied to the short electrode fingers when viewed locally, but also applies to the long electrode fingers passing through the overlapping region. An electrode finger to which 2 GHz, for example, is applied as an excitation frequency has, for example, a width of 500 nm and a height of 100 to 200 nm. A loss occurs in the resonator due to the electrical resistance of the electrode finger, and this loss is added to other losses (such as elastic loss in a solid) to reduce the Q value of the resonator. These losses have a wide band, i.e. a large frequency range. The loss due to such supply current increases as the cross-sectional size of the electrode fingers decreases. For this reason, it is desirable to increase the Q value of the resonator weighted by superposition.

For this purpose, the present application provides an electroacoustic resonator having two electrodes, each electrode comprising a bus bar piece (Sammelelektrodenabschnitt) and a plurality of electrode fingers,
The electrode fingers are arranged along a first direction, connected to each electrode bus bar piece and extending along a second direction transverse to the first direction;
The resonator is a resonator weighted by superposition, in which the width of the superposition region measured along the second direction varies along the first direction and the superposition The electrode fingers of both electrodes are engaged with each other in the region,
The resonator comprises a conductive bridge between the electrode fingers of each electrode, the conductive bridges each connecting a plurality of electrode fingers of the same electrode remote from the bus bar piece in electrical communication with each other;

  Thus, according to this resonator, the electroconductive additional connection component is provided between the electrode fingers of all the electrodes, and the electrode fingers are mutually short-circuited. These conductive bridges are preferably arranged at the outer edge of the overlap region and away from the bus bar pieces of each electrode. Therefore, the position of the conductive bridge follows the outer edge of the overlapping region of the resonator, and is correspondingly disposed at the outer edge of the resonator (near the reflector, approximately the center between the two electrodes). On the other hand, in the central portion of the resonator, the electrodes are disposed relatively close to the bus bar pieces of both electrodes. The conductive bridge proposed here is an additional conductive strip in the direction transverse to or at least oblique to the electrode fingers, allowing a balance current to flow directly along each outer edge of the overlap region However, it is only between the electrode fingers of the same electrode. These balance currents reduce losses that increase rapidly in the vicinity of the reflector due to the supply current, thereby improving the Q value of the resonator. The conductive bridge proposed here may be arranged with these electrode fingers themselves, preferably on the same plane as the electrodes, and thus may already be considered as part of the pattern of patterning of the metal layers of both electrodes. However (regardless of the conductive bridge proposed here), a finger-like structure is maintained in the resonator plane. This is because this conductive bridge shorts them together with each other only locally, that is, at a very small length of the electrode fingers.

Several example embodiments are described below with reference to the figures.
It is the upper surface schematic of the conventional piezoelectric resonator. FIG. 4 is an enlarged detail view of an embodiment of a resonator having a conductive bridge. FIG. 4 is an enlarged detail view of an embodiment of a resonator having a conductive bridge. FIG. 4 is an enlarged detail view of an embodiment of a resonator having a conductive bridge. FIG. 4 is an enlarged detail view of an embodiment of a resonator having a conductive bridge. FIG. 4 is an enlarged detail view of an embodiment of a resonator having a conductive bridge. FIG. 4 is an enlarged detail view of an embodiment of a resonator having a conductive bridge. 2B is an overall view of a resonator based on the embodiment of FIGS. 2B is an overall view of a resonator based on the embodiment of FIGS. 2B is an overall view of a resonator based on the embodiment of FIGS. 2B is an overall view of a resonator based on the embodiment of FIGS. It is a schematic sectional drawing of a piezoelectric resonator. It is a schematic sectional drawing of the piezoelectric resonator which has an additional layer. It is a figure which shows the dependence to the frequency f of the wave which generate | occur | produced with the resonator of the admittance Y of the resonator. It is a figure which shows the behavior of the reflection coefficient S. FIG. 6 shows a resonator Q value in a tabular list of parameters measured to show the resonator Q value for resonators with or without conductive bridges.

  FIG. 1 shows a schematic top view of a conductive path surface 25 of a conventional piezoelectric resonator 10, but only a half (left side) is displayed because of a symmetrical structure. Between the two reflectors 23 and 24 (see FIGS. 4A and 4B), an array of two electrodes 11 and 12 extends, and these electrodes are connected to the bus bar portion 21 or 22, respectively. A plurality of electrode fingers 1 and 2 are provided. The resonator is weighted by superposition. That is, in the overlapping region 20, the electrode fingers 1 and 2 of both electrodes mesh with each other in a comb shape, that is, overlap each other, and this overlapping region 20 extends only between the two outer edge portions R. The outer edge gradually approaches the reflectors 23 and 24. In the central portion of the resonator (on the right side of the partial view shown in FIG. 1), the width 20 of the overlapping region 20 is the maximum. Only inside the overlapping region, the electrode fingers 1 and 2 of the first electrode 11 and the second electrode 12 are engaged with each other from the opposite sides. However, on either side of the overlap region, however, only one of the electrode fingers of both electrodes 11, 12 is arranged.

  2A-2F show enlarged detail views of embodiments of the resonator in which conductive bridges are provided that extend transversely to the electrode fingers. The enlarged partial view shown is the region of the lower outer edge R, on which the overlapping region 20 is started. 2A and 2C illustrate a portion of the bus bar piece (Sammelelektrodenabschnitt) 21 of the lower first electrode 11. These electrode fingers 1 a to 1 d extend to the outer edge R of the overlapping region 20, and every other electrode finger 1 a, 1 c of the first electrode 11 is introduced into the overlapping region 20. The terminal ends of the other short electrode fingers 1 b and 1 d of the first electrode 11 are outside the overlapping region 20. Corresponding to these, electrode fingers 2b and 2d of the second electrode 12 are provided in the overlapping region 20. 2A to 2F, the electrode fingers of the second electrode 12 are indicated by hatching. According to FIG. 2A, a conductive bridge 3 (or short jumper conductor) is provided along the outer edge R of the overlap region 20 and is connected to each other so that adjacent electrode fingers of the first electrode are conductive, preferably It extends perpendicular to the electrode fingers. Such a conductive bridge is provided along both outer edge portions R of the overlapping region 20. A conductive bridge that connects the electrode fingers of the corresponding second electrodes 12 to each other (not shown) is provided along the other outer edge R above the overlapping region.

  According to the embodiment of FIG. 2A, each conductive bridge 3 connects two adjacent electrode fingers (identical electrodes). FIG. 2B shows one embodiment, which is further illustrated in FIG. 3A. Here, each conductive bridge 3 connects two (long) conductive bridges adjacent to every other one of the respective electrodes. Specifically, in FIG. 2B, electrode fingers 1a and 1c are connected, and 1c and 1e are connected. In this way, the conductive bridge 3 separates the short electrode fingers 1b and 1d arranged therebetween from the long electrode fingers 2b and 2d of the corresponding second electrode 12 and crosses the overlap region 20. The conductive bridge 3 extending in the horizontal direction is provided only up to the vertical position of the electrodes 11 and 12, but is not provided in the regions of the reflectors 23 and 24 (see FIGS. 3A and 4).

  In the embodiment according to FIG. 2C, each conductive bridge 3 further connects the middle short electrode fingers 1b and 1d to the adjacent long electrode fingers. For other portions, the structure and path of the conductive pattern in the conductive path surface 25 are the same as those in FIG. 2B. FIG. 2D shows one embodiment, but FIG. 3B further shows this overall view. Here, in addition to the conductive bridge 3, a conductive path piece 5 is further provided, and this conductive path piece is not connected to the first electrode or the second electrode. Thereby, the electrical application peak at the end of the electrode finger, that is, the maximum voltage value is reduced. However, the conductive bridge 3 (as in FIG. 2B) connects two long electrode fingers adjacent to every other electrode of each other. As shown in FIG. 3B, the conductive path piece 5 is disposed along both outer edge portions R of the overlapping region 20.

  FIG. 2E shows one embodiment, which is further illustrated in FIG. 3C. Here, in contrast to FIG. 2D, the pattern corresponding to the conductive path piece 5 is connected to the conductive bridge 3 so as to be conductive. In this way, the electrode finger extending portion 7 (that is, an additional small intermediate finger) is configured and arranged at the longitudinal position of the short electrode fingers 1b and 1d. Each conductive bridge 3 extends further beyond these. FIG. 2F shows one example embodiment, which is further illustrated in FIG. 3D. Here, the conductive bridge 3 not only connects every other long electrode finger 1a and 1c and the respective electrode finger extension 7 but also has a short electrode finger 1b (in contrast to FIG. 2E). Connected.

  All these example embodiments, which are merely exemplary, allow the conductive bridge to provide a low loss potential balance along the outer edge R of the overlap region 20. This is because loss due to the conduction resistance is reduced, and the Q value of the resonator is improved. Particularly in the vicinity of both reflectors, the distance of the outer edge R of the overlapping region 20 from the bus bar pieces 21 and 22 is maximized, and the conductive bridge 3 can effectively accelerate the potential injection into the overlapping region 20. And

  3A to 3D have already been described with reference to FIGS. In FIG. 3D, however, additional features and elements are illustrated. These are described below.

  FIG. 3D shows the schematic shape of the bus bar pieces 21 and 22 of the electrodes at the transition portions of the electrodes 11 and 12 to the electrode fingers 1 and 2 more accurately. Here, each electrode finger starts from the bus bar pieces 21 and 22 related thereto, that is, the bus bar pieces, and is directly connected to the bus bar pieces. The bus bar (Sammelelektrode) and the electrode fingers connected thereto are continuous comb-like patterns (for example, patterned metal layers, alloy layers or laminated metal layers on the conductive path surface 25) that are not cut in this way. These top views are shown in FIG. 3D). 1, 2A-2F and 3A-3E, the transition between the bus bar and electrode fingers (shown schematically) is configured similarly to FIG. 3D. In FIG. 3D, the connection terminals 8 and 9 of both electrodes are shown for completeness. These connection terminals are introduced in any other place and may have other shapes. FIG. 3D simply shows the existence of both connection terminals 8 and 9. Further, FIG. 3D shows coordinate axes, and the electrode fingers 1 and 2 are aligned along the first direction x (similar to the other already described figures) and are transverse to the first direction x. It extends | stretches along the 2nd direction y used as a direction.

  The conductive bridge does not necessarily extend into the conductive path surface 25 and may be disposed above or below the conductive path surface 25. Vias or other contacts are led from the electrode fingers to higher or deeper surfaces, where conductive bridges are placed. 3D further shows that the overlapping region 20 extending between the two outer edges R along the second direction y is more than the resonator face F, that is, more than the distance between the bus bar pieces 21 and 22 of both electrodes. It shows narrowing. The spread or width of the overlap region 20 measured along the y direction decreases, especially near the reflectors 23,24. The proposed path bridge or intermediate connection between the electrode fingers improves the resonator characteristics. In the embodiment of the present application, a plurality of conductive bridges may be provided in place of the illustrated one conductive bridge, and in particular, one set of two conductive bridges arranged close to each other may be provided.

  FIG. 4A merely schematically shows a cross section of the piezoelectric resonator 10, and this conductive path surface 25 is shown in the top views of FIGS. 1, 2A to 2F and 3A to 3D. A piezoelectric layer is disposed below the conductive path surface 25, and both electrodes 11 and 12 and both reflectors 23 and 24 are patterned on the upper surface.

  FIG. 4B merely schematically shows a cross section of the piezoelectric resonator 10, and the conductive path surface 25 is shown in the top views of FIGS. 1, 2A to 2F and 3A to 3D. This resonator is shown schematically as in FIG. 4A, except that one or more dielectric layers 26 and / or 27 are further mounted on the conductive path surface. Layers 26 and / or 27 are later removed / trimmed for the purpose of temperature compensation and / or correction of frequency state variations during manufacturing. Again, the dimensions are not always accurate.

  A material suitable for the dielectric layer 26 for temperature compensation covering the conductive path surface is, for example, SiO 2 because of its thermal characteristics. As a material of the trimming layer 27 disposed thereon, for example, Si3N4 is used because of its large bending strength.

  FIG. 5 shows the admittance Y, ie the complex conductance of the resonator, depending on the frequency of the wave (preferably a surface wave, alternatively a volume wave) generated in the resonator. The real part, the imaginary part, and the admittance are superimposed and shown in FIG. Resonance occurs at a frequency of about 1970 MHz, and anti-resonance occurs at about 2110 MHz.

In FIG. 5, there is a further subpeak on the upper side, which relates to other undesirable effects. However, this is outside the available wavelength region between resonance and anti-resonance. FIG. 5 shows the admittance of a conventional resonator without a conductive bridge (curve I) and the admittance of a resonator according to the invention with an additional conductive path bridge 3 (curve II), respectively. The vertical axis is logarithmically displayed, and the magnitudes of the real part, the imaginary part and the admittance Y (f) are logarithmically displayed [dB] with respect to the frequency [MHz].

As can be seen from the upper side in FIG. 5, the real part of the admittance is lowered with respect to the conventional resonator (that is, with respect to the curve I) in the range of about 2030 to 2110 MHz, and the Q value of the resonator is improved. In addition, as can be seen from the magnitude of admittance Y on the lower side of FIG. 5, the minimum value of 2110 MHz is further reduced. Here, both sides of the anti-resonance drop rapidly and reach a minimum value smaller than the curve I. Here again, an improved Q value (curve II) of a resonator with a conductive bridge is observed. Corresponding to the imaginary part of the admittance Y, the anti-resonance frequency is slightly lowered, but only slightly.

FIG. 6 shows the dispersion parameter (S parameter) calculated from the resonator admittance Y (f) and the standard admittance Z0 = 50 ohms of the measurement port on the Smith chart.

S (f) = (1−Z0 * Y (f)) / (1 + Z0 * Y (f))

Is shown as a function of frequency. Corresponding to the admittance function Y (f) shown in FIG. 5 from 1900 MHz to 2300 MHz, the S parameter I shown in FIG.
Or II passes the Smith chart clockwise. The intersection with the left real axis corresponds to the resonance frequency, and the intersection with the right real axis corresponds to the anti-resonance frequency. Here, the useful region between resonance and anti-resonance (the upper half of the imaginary axis in FIG. 6) is an improved resonator (curve II).
), The substantially semicircular orbit in FIG. 6 has a radius larger than that of the curve I (or a distance from the center point of the circle indicated by the radius 1). In the resonator of the present invention, the dispersion parameter S (f) exists in a far outer region, that is, in the vicinity of the unit circle, and therefore the loss is smaller. In particular, the conductive bridge between the electrode fingers reduces losses in the frequency region from the resonance frequency to more than the anti-resonance frequency. The additional conductive path piece 5 that does not have the contact terminal or the electrode finger extending portion 7 (FIGS. 2D to 2F) can further prevent a decrease in frequency at which anti-resonance occurs. On the lower half of the imaginary axis (ie outside the technically useful frequency range), for example, parasitic effects and volume radiation (ie volume wave formation) at the upper band edge of the finger stop (Fingergitter) acoustic stopband Abnormalities resulting from increased use of

Thus, the present application provides an electro-acoustic weighted and improved Q-value interdigital converter (IDT). In FIG. 7, parameters for indicating the resonator Q values are tabulated for each of the four resonators (1 to 4) having no conductive bridge and the four resonators (5 to 8) having the conductive bridge. Is summarized in The resonance Q value Qs in the case of resonance (short circuit Q value, quality short) and the resonance Q value and average Q value Qt = 0.5 (Qo + Qs) in the case of anti-resonance (open Q value, quality open) are described. . Furthermore, the resonance frequency (fs) and the anti-resonance frequency (fo) are displayed in MHz. Numerical values for resonators 5-8 (these are curves II in FIGS. 5 and 6).
Corresponding to ) And the values of resonators 1-4 (which correspond to curve I in FIGS. 5 and 6), the anti-resonance Q value Qo is increased by about 20 percent due to the conductive bridge between the electrode fingers. I understand that. In the second column from the end of FIG. 7, the pole zero distance PZD (pole-zero-distance) is

PZD = (fo−fs) / (0.5 × (fo + fs))

This is reduced only slightly from about 7 percent to about 6.8 percent by the conductive bridge. As a further indicator of the resonator Q value, the figure of merit as a further Q value parameter is listed in the last column of FIG. 7 on the basis of (FoM = PZD × Qt). Here, in the case of resonators 5-8, an increase of about 10 percent and an improvement thereby is shown.

  In addition, the width and / or length of the conductive bridge 3, the conductive path piece 5 and / or the electrode finger extending portion 7 may be changed. May be.

  In this way, the conductive bridge 3 reduces the loss that occurs in the frequency range from series resonance to anti-resonance. In this way, the improved resonator can be used, for example, in a piezoelectric filter or duplexer element.

1, 1a, 1b. . . : Electrode fingers of the first electrode 2, 2a, 2b. . . : Electrode finger of second electrode 3: Conductive bridge 5: Conductive path piece 7: Electrode finger extending portion 8 and 9: Contact terminal 10: Resonator 11: First electrode 12: Second electrode 20: Overlapping region 21, 22: Bus bar pieces 23, 24: Reflector 25: Conductive path surface F: Resonator surface fo: Anti-resonance frequency fs: Resonance frequency PZD: Resonance-anti-resonance distance R: Outer edge portion Qo: Anti-resonance Q value Qs: Resonance Q value Qt: Average Q value x: First direction y: Second direction

Claims (10)

An electroacoustic resonator (10) having two electrodes (11, 12),
Each of the two electrodes includes a bus bar piece (21, 22) and a plurality of electrode fingers (1, 2).
The electrode fingers (1, 2) are arranged along the first direction (x) and are electrically connected to the electrode bus bar pieces (21, 22) of the respective electrodes (11, 12); Connected and extending along a second direction (y) that is transverse to the first direction (x),
The resonator (10) is a resonator weighted by superposition, in which the width of the superposition region (20) measured along the second direction (y) is the first 1 and the electrode fingers (1, 2) of both electrodes (11, 12) are engaged with each other in the overlapping region,
The resonator (10) comprises a conductive bridge (3) between the electrode fingers (1, 2) of each of the electrodes (11, 12), said conductive bridges being respectively connected to the bus bar pieces (21, 22); A plurality of electrode fingers of the same electrode separated from each other are connected so as to be electrically connected to each other. The resonator according to claim 1, wherein
The conductive bridges (3) of the electrodes (1, 2) are connected to the bus bar pieces (21, 21) of the outer edge (R) facing the electrodes (1, 2) of the overlapping region (20). 22) A resonator characterized by being arranged along the line. The resonator according to claim 1 or 2,
The conductive bridge (3) of each of the electrodes (1, 2) is disposed at a distance from the bus bar piece (21, 22), and the distance is determined between the conductive bridge (3) and the bus bar. Resonator changing in the first direction (x) between the pieces (21, 22). The resonator according to any one of claims 1 to 3,
Each conductive bridge (3) shorts two adjacent electrode fingers (1a, 1b, 1c, 1d, 1e; 2a, 2b, 2c ...) of the same electrode (1, 2) to each other. A resonator characterized by. The resonator according to any one of claims 1 to 4,
Each conductive bridge (3) shorts two adjacent electrode fingers (1a, 1c, 1e; 2b, 2d ...) to every other one of the same electrodes (1; 2). Resonator. The resonator according to any one of claims 1 to 5,
Each of the conductive bridges (3) shorts the electrode fingers (1a, 1c) of the same electrode (1) to each other, and the intermediate electrode fingers (1b) of the same electrode (1) provided therebetween. ) To pass through. The resonator according to any one of claims 1 to 6,
Between the conductive bridges (3), a conductive path piece (5) is provided at a vertical position of the electrode finger (2b) of the other electrode (12) reaching the intermediate electrode (1b), and the first A resonator characterized in that it is not connected to one electrode (11) or to the second electrode (12). The resonator according to any one of claims 1 to 7,
An electrode finger extension (7) is connected to each conductive bridge (3), and the electrode finger extension extends from the conductive bridge (3) at the longitudinal position of the intermediate electrode finger (1b). Resonator, starting and extending towards the other electrode (2). The resonator according to claim 7 or 8,
The conductive path piece (5) and / or the electrode finger extension (7) has a length, and the length is set to be constant or the conductive path piece (F) in the resonator plane (F). 5) and / or a resonator that varies along the first direction (x) at the position of the electrode finger extension (7). The resonator according to any one of claims 1 to 9,
One or more conductive bridges (3) are provided between the electrode fingers (1, 2), respectively, and the conductive bridges (3) are sized and / or crossed along the second direction (y). And a width equal to or greater than the width of the electrode fingers (1, 2) along the first direction (x).

Images