CN111342801A - Grooved BAW resonators, filters and electronics - Google Patents

Abstract

Grooved BAW resonators, filters and electronics. The invention relates to a bulk acoustic wave resonator, comprising: a substrate; an acoustic mirror; a bottom electrode, arranged on the upper side of the substrate; a top electrode; and a piezoelectric layer, arranged above the bottom electrode and between the bottom electrode and the top electrode, wherein: The area where the acoustic mirror, the bottom electrode, the piezoelectric layer, and the top electrode overlap in the thickness direction of the substrate is an effective area of the resonator; the resonator further includes at least one groove extending around the effective area. The trenches may be provided on the lower side or the upper side of the piezoelectric layer; or the trenches may be provided on the upper side or the lower side of the bottom electrode. The present invention also relates to a filter having the resonator, and an electronic device having the above-mentioned filter or resonator.

Description

Grooved BAW resonators, filters and electronics

technical field

Embodiments of the present invention relate to the field of semiconductors, and in particular, to a bulk acoustic wave resonator, a filter having the resonator, an electronic device having the filter, and a method for increasing the parallel impedance of the resonator.

Background technique

At present, RF front-end filters composed of bulk acoustic wave resonators are widely used in RF communication systems. Such filters usually have superior electrical properties, such as low insertion loss, steep transition band, large power capacity, relatively Strong anti-static discharge ability, and the processing technology can be compatible with IC technology, so it is suitable for large-scale low-cost manufacturing. The quality of the filter is closely related to the performance indicators of the resonator.

BAW resonators generally have two resonant frequencies. The frequency point with the smallest impedance is defined as the series resonant frequency fs, the corresponding impedance is the series impedance Rs, the frequency point with the largest impedance is the parallel resonant frequency fp, and the corresponding impedance is the parallel impedance Rp. The electromechanical coupling coefficient measures the piezoelectric conversion efficiency in the resonator. Generally, the series resonant frequency of the resonator determines the center frequency of the filter, while the effective electromechanical coupling coefficient of the resonator determines the maximum bandwidth that the filter can achieve, and the series and parallel impedances of the resonator determine the passband insertion loss and return wave loss. In general, the higher the parallel impedance Rp of the resonator and the lower the series impedance Rs, the better the passband insertion loss of the corresponding filter. Therefore, how to improve the performance of the resonator, especially the parallel impedance Rp of the resonator, is an important and fundamental problem in filter design.

SUMMARY OF THE INVENTION

The invention proposes a technical solution for improving the parallel impedance of a bulk acoustic wave resonator by arranging grooves.

According to an aspect of an embodiment of the present invention, a bulk acoustic wave resonator is proposed, including: a substrate; an acoustic mirror; a bottom electrode, disposed on the upper side of the substrate; a top electrode; and a piezoelectric layer, disposed on the upper side of the bottom electrode and between the bottom electrode and the top electrode, wherein: the area where the acoustic mirror, the bottom electrode, the piezoelectric layer, and the top electrode overlap in the thickness direction of the substrate is the effective area of the resonator; the resonator further includes at least one groove, the The grooves extend around the edge of the active area.

Optionally, the groove is an annular groove.

Optionally, the lateral distance between the groove and the acoustic mirror remains unchanged.

Optionally, the at least one groove includes one groove.

Optionally, the groove is disposed on the upper side of the substrate and completely covers the bottom electrode. Optionally, the depth H of the groove satisfies: 0.1 μm≤H≤0.6 μm; and the distance from the groove to the acoustic mirror is D, and the width of the groove is W, where: 1 μm≤D ≤1.8 μm, and 1.2 μm≤W≤2.5 μm.

Optionally, the groove is disposed on the upper side of the substrate and partially covers the bottom electrode. Or alternatively, the groove is disposed on the upper side of the substrate and is spaced apart from the bottom electrode. Further, the depth H of the trench satisfies the condition: 0.6 μm≦H≦1.1 μm, or 1.7 μm≦H≦2.3 μm. Further, 0.7 μm≦H≦0.8 μm, or 1.9 μm≦H≦2.1 μm.

Optionally, the at least one groove includes two grooves.

Further, the two grooves are arranged on the upper side of the substrate and are completely covered by the bottom electrode.

Optionally, the two grooves are disposed on the upper side of the substrate and are spaced apart from the bottom electrode.

Optionally, one of the two trenches is completely covered by the bottom electrode, and the other trench is partially covered by the bottom electrode or is spaced apart from the bottom electrode. Optionally, one of the two trenches is partially covered by the bottom electrode, and the other trench is spaced apart from the bottom electrode.

Optionally, the groove is provided on the lower side or the upper side of the piezoelectric layer; or the groove is provided on the upper side or the lower side of the bottom electrode.

Optionally, the at least one groove includes a plurality of groove segments, and the plurality of groove segment grooves are spaced apart from each other and disposed along the active area.

According to another aspect of the embodiments of the present invention, a filter is proposed, comprising the above-mentioned bulk acoustic wave resonator.

According to yet another aspect of the embodiments of the present invention, an electronic device is provided, including the above-mentioned filter or the above-mentioned resonator.

The present invention also relates to a method for increasing the parallel impedance of a bulk acoustic wave resonator, comprising the step of forming at least one annular groove on the upper side of the base of the resonator around the effective area of the resonator.

Description of drawings

These and other features and advantages of the various disclosed embodiments of the present invention may be better understood by the following description and accompanying drawings, in which like reference numerals refer to like parts throughout, wherein:

1A is a schematic top view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention, wherein only one annular groove is provided;

FIG. 1B is a cross-sectional view of the bulk acoustic wave resonator in FIG. 1A along the direction A-A' according to an exemplary embodiment of the present invention;

FIG. 1C is an exemplary graph of the depth of the trench (ie, the annular pool height H) versus the parallel impedance of the resonator for the bulk acoustic wave resonator of FIG. 1B ;

1D is a cross-sectional view of a bulk acoustic wave resonator according to another exemplary embodiment of the present invention;

FIG. 1E is an exemplary graph of the depth of the trench (ie, the annular pool height H) versus the parallel impedance of the resonator for the bulk acoustic wave resonator of FIG. ID;

1F is a cross-sectional view of a bulk acoustic wave resonator according to yet another exemplary embodiment of the present invention;

FIG. 1G is an exemplary graph of the depth of the trench (ie, the annular pool height H) versus the parallel impedance of the resonator for the bulk acoustic wave resonator of FIG. 1F ;

2A is a schematic top view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention, wherein only two annular grooves are provided;

2B is a cross-sectional view of the bulk acoustic wave resonator in FIG. 2A along the direction B-B' according to an exemplary embodiment of the present invention;

2C is a cross-sectional view of a bulk acoustic wave resonator according to yet another exemplary embodiment of the present invention;

2D is a cross-sectional view of a bulk acoustic wave resonator according to yet another exemplary embodiment of the present invention.

Detailed ways

The technical solutions of the present invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings. In the specification, the same or similar reference numerals refer to the same or similar parts. The following description of the embodiments of the present invention with reference to the accompanying drawings is intended to explain the general inventive concept of the present invention, and should not be construed as a limitation of the present invention.

A bulk acoustic wave resonator according to an embodiment of the present invention will be described below with reference to the accompanying drawings.

1A is a schematic top view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention; FIG. 1B is a cross-section of the bulk acoustic wave resonator in FIG. 1A along the AA' direction according to an exemplary embodiment of the present invention picture.

Referring to FIGS. 1A and 1B , the BAW resonator includes a bottom electrode 120 , a piezoelectric layer 130 , a top electrode 140 , and a first annular groove 150 . The BAW resonator includes a substrate 100 and an acoustic mirror 110. The acoustic mirror is located on the upper surface of the substrate or embedded in the interior of the substrate. In FIG. 1B, the acoustic mirror is formed by a cavity embedded in the substrate, but any other acoustic mirror structure For example, the Bragg reflector is also suitable.

The BAW resonator further includes a bottom electrode 120 , a piezoelectric layer 130 , and a top electrode 140 . The bottom electrode is deposited on the upper surface of the acoustic mirror and covers the acoustic mirror. The end portions on both sides of the bottom electrode 120 can be etched into inclined planes, and the inclined planes are located outside the acoustic mirror, and can also be stepped, vertical, or other similar structures. The piezoelectric layer 130 has a first end, a corresponding second end and a middle portion, and is located on the bottom electrode, and the two end portions extend to the substrate in opposite directions respectively. The top electrode 140 is deposited over the piezoelectric layer 130 . The annular grooves 150 are located on both sides of the acoustic mirror 110, with a certain interval from the acoustic mirror, and in the non-slope region at the bottom of the bottom electrode.

The area where the top electrode, the piezoelectric layer, the bottom electrode, and the cavity overlap in the thickness direction is the effective area of the resonator, that is, the area d2 in the figure. When the sound wave leaks from the effective area, it propagates in the surrounding medium in the form of traveling waves. When the annular groove 150 is added, the acoustic impedance of the air is 0 due to the introduction of the air interface, and the corresponding areas are d1 and d3 in the figure. The equivalent acoustic impedance of the area will be lower than the acoustic impedance of the adjacent two sides, thus forming two impedance mismatch interfaces, so that the sound wave can be reflected at these two interfaces, so that a part of the leaked sound wave energy can return to the resonant cavity d2 , thereby increasing the parallel impedance Rp.

The depth of the annular groove may or may not be the same as the depth of the cavity 110 . Referring to FIG. 1B , define H as the depth of the annular groove, W as the width of the annular groove, D as the distance between the inner edge of the annular groove and the cavity edge, and the distance E from the bottom electrode beyond the cavity. A two-dimensional simulation of the above structure was carried out using the finite element method, and the simulation results are shown in Figure 1C. In the simulation, E is set to 5um, and four cases of W=1um, D=1um; W=1um, D=2um; W=2um, D=1um and W=2um, D=1um are calculated respectively. In FIG. 1C, the abscissa is the depth H of the annular groove, and the ordinate is the parallel resistance Rp. The case of H=0 is the case of no groove; it can be seen from Figure 1C that in the case of W=2um, D=1um, when H=0.3um, the parallel impedance Rp can reach 2477, an increase of about 250 ( about 11.2%).

Correspondingly, in the exemplary embodiment according to the present invention, for the case where the trench is completely covered by the bottom electrode, the depth H of the trench satisfies: 0.1 μm≤H≤0.6 μm; The distance of the acoustic mirror is D, and the width of the groove is W, wherein: 1 μm≤D≤1.8 μm, and 1.2 μm≤W≤2.5 μm. In a further embodiment, 0.1 μm≦H≦0.6 μm. Further, 1 μm≦D≦1.2 μm, and 1.8 μm≦W≦2.0 μm.

The annular groove 150 may also be disposed outside the bottom electrode 120, as shown in FIG. 1D. The structure of Fig. 1D is simulated, and the simulation result is shown in Fig. 1E. In the simulation, E is set to 5um, and three cases of W=1um, D=5um; W=1um, D=7um; W=1um, D=9um are calculated respectively. The abscissa in the figure is the depth H of the annular groove, and the ordinate is the parallel resistance Rp. The case of H=0 is the case of no annular groove; in the case of W=1um and D=7um, when H=0.7um, the parallel impedance Rp reaches 2929, an increase of about 700 (about 31.5%). In the case of W=1um, D=9um, when H=2um, the parallel impedance Rp reaches 2977, an increase of about 750 (33.7%).

Optionally, the end of the bottom electrode 120 is located above the annular groove 150, but does not completely cover the annular groove 150, as shown in FIG. 1F. The structure of Fig. 1F is simulated, and the simulation result is shown in Fig. 1G. In the simulation, E is set to 5um, and three cases of W=1um, D=4.25um; W=1um, D=4.5um; W=1um, D=4.75um are calculated respectively. The abscissa in the figure is the depth H of the annular groove, and the ordinate is the parallel resistance Rp. The case of H=0 is the case of no annular groove; in the case of W=1um and D=4.5um, when H=0.8um, the parallel impedance Rp reaches 3015, which is increased by about 790 (about 35.6%). Comparing the simulation results of Figures 1C, 1E, and 1G, it can be seen that when the groove width is fixed, such as W=1um, when the annular groove spans the end of the bottom electrode (the third structural case), the best performance can be achieved Improve the effect of parallel impedance Rp.

Correspondingly, in the exemplary embodiment according to the present invention, for the case where the trench is not covered by the bottom electrode or is not completely covered by the bottom electrode, the depth H of the trench satisfies the condition: 0.6 μm≤H≤1.1 μm, Or 1.7μm≤H≤2.3μm. Further, 0.7 μm≦H≦0.8 μm, or 1.9 μm≦H≦2.1 μm.

The above description takes a single trench as an example, and the following describes the resonator according to the present invention by taking two trenches as an example with reference to FIGS. 2A-2D .

As shown in FIGS. 2A-2D , the BAW resonator includes a bottom electrode 220 , a piezoelectric layer 230 , a top electrode 240 , a first annular groove 250 and a second annular groove 260 .

In the embodiment shown in FIG. 2B, it is a cross-sectional view of the bulk acoustic wave resonator taken along the top view B-B' of FIG. 2A. The BAW resonator includes a substrate 200 and an acoustic mirror 210. The acoustic mirror is located on the upper surface of the substrate or embedded in the interior of the substrate. In FIG. 2B, the acoustic mirror is formed by a cavity embedded in the substrate, but any other acoustic mirror structure For example, the Bragg reflector is also suitable.

The BAW resonator further includes a bottom electrode 220 , a piezoelectric layer 230 , and a top electrode 240 . The bottom electrode is deposited on the upper surface of the acoustic mirror and covers the acoustic mirror. The end portions on both sides of the bottom electrode 220 can be etched into inclined planes, and the inclined planes are located outside the acoustic mirror, and can also be stepped, vertical, or other similar structures. The piezoelectric layer 230 has a first end and a corresponding second end and a middle portion, and is located on the bottom electrode, and the two end portions respectively extend to the substrate in opposite directions. Top electrode 240 is deposited over piezoelectric layer 230 . The first annular groove 250 and the second annular groove 260 are located on both sides of the acoustic mirror 210, with a certain interval from the acoustic mirror, and in the non-slope region at the bottom of the bottom electrode.

By arranging multiple annular grooves, more acoustic impedance mismatch interfaces can be formed than the embodiment shown in FIG. 1A , thereby reflecting the leaked acoustic waves back to the effective area multiple times to enhance the parallel impedance Rp of the resonator.

The first annular trench 250 and the second annular trench 260 may not all be disposed in the non-slope region at the bottom of the bottom electrode. For example, the first annular groove 250 is disposed on the outer side of the bottom electrode 220, and the second annular groove 260 is disposed in the slope area at the bottom of the bottom electrode, as shown in FIG. 2C .

Optionally, the end of the bottom electrode 220 is located above the first annular trench 250 but does not cover the first annular trench 250, and the second annular trench 260 is disposed under the bottom electrode 220, as shown in FIG. 2D .

Although only two grooves are shown in FIGS. 2A-2D, three or more grooves may be provided as required, which are all within the protection scope of the present invention.

Based on the above, the present invention proposes a bulk acoustic wave resonator, comprising:

base 100 or 200;

Acoustic mirror 110 or 210;

The bottom electrode 120 or 220 is arranged on the upper side of the substrate 100 or 200;

top electrode 140 or 240; and

The piezoelectric layer 130 or 230 is disposed on the upper side of the bottom electrode and between the bottom electrode and the top electrode,

in:

The area where the acoustic mirror, the bottom electrode, the piezoelectric layer, and the top electrode overlap in the thickness direction of the substrate is the effective area of the resonator;

The resonator further includes a trench 150 or 250 or 260 extending around the edge of the active area (in FIG. 1A , which can be considered to correspond to the boundary area d2 of the top electrode 140 , by way of example).

In the present invention, a groove structure is processed on, for example, a substrate at one or multiple edges of the effective area of the resonator. In practice, by selecting an appropriate groove size, the acoustic waves leaking into the substrate can be effectively reflected, thereby Effectively improve the parallel impedance Rp value of the resonator.

The groove is a micro-groove structure. In the drawings of the present invention, the grooves are annular grooves. However, the grooves may also be a plurality of groove segments spaced apart from each other and arranged along the active area. For example, the groove segment may be one or more groove segments disposed on one or more sides of the active area of the polygon shown in FIG. 1A .

In the present invention, as shown in the accompanying drawings, in an optional embodiment, the lateral distance between the groove and the acoustic mirror remains unchanged.

In an exemplary embodiment of the present invention, the trenches are all formed on the substrate. However, the present invention is not limited thereto, and the groove may be formed at the lower surface of the piezoelectric layer opposite to the substrate, or provided at the upper surface of the piezoelectric layer. Alternatively, the trench is disposed on the upper side or the lower side of the bottom electrode.

In the present invention, the trench or the trench segment may be filled with other materials, or not filled, all within the protection scope of the present invention.

In an alternative embodiment of the invention, one of the two trenches is completely covered by the bottom electrode and the other trench is partially covered by the bottom electrode or is spaced apart from the bottom electrode. Optionally, one of the two trenches is partially covered by the bottom electrode, and the other trench is spaced apart from the bottom electrode.

In the present invention, "upper side" in the orientation means the side away from the substrate in the thickness direction of the resonator, and "lower side" means the side close to the substrate in the thickness direction of the resonator.

Based on the above, the embodiments of the present invention also relate to a filter including the above-mentioned bulk acoustic wave resonator.

Embodiments of the present invention also relate to an electronic device comprising the above-mentioned filter or resonator. It should be pointed out that the electronic equipment here includes but is not limited to intermediate products such as RF front-end, filter and amplifier modules, and terminal products such as mobile phones, WIFI, and drones.

Correspondingly, the present invention also provides a method for increasing the parallel impedance of a bulk acoustic wave resonator, comprising the step of: forming at least one annular groove on the upper side of the base of the resonator around the effective area of the resonator.

Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is determined by It is defined by the appended claims and their equivalents.

Claims (20)

1. A bulk acoustic wave resonator, comprising: base; acoustic mirror; a bottom electrode, arranged on the upper side of the substrate; top electrode; and The piezoelectric layer is arranged on the upper side of the bottom electrode and between the bottom electrode and the top electrode, in: The area where the acoustic mirror, the bottom electrode, the piezoelectric layer, and the top electrode overlap in the thickness direction of the substrate is the effective area of the resonator; The resonator also includes at least one trench extending around the edge of the active area. 2. The resonator of claim 1, wherein: The groove is an annular groove. 3. The resonator of claim 2, wherein: The lateral distance between the groove and the acoustic mirror remains constant. 4. The resonator of any one of claims 1-3, wherein: The at least one groove includes a groove. 5. The resonator of claim 4, wherein: The trench is provided on the upper side of the substrate and completely covers the bottom electrode. 6. The resonator of claim 5, wherein: The depth H of the trench satisfies: 0.1 μm≤H≤0.6 μm; and The distance from the groove to the acoustic mirror is D, and the width of the groove is W, where: 1 μm≤D≤1.8 μm, and 1.2 μm≤W≤2.5 μm. 7. The resonator of claim 4, wherein: The trench is disposed on the upper side of the substrate and partially covers the bottom electrode. 8. The resonator of claim 4, wherein: The trench is provided on the upper side of the substrate and is spaced apart from the bottom electrode. 9. The resonator of claim 7 or 8, wherein: The depth H of the trench satisfies the condition: 0.6 μm≦H≦1.1 μm, or 1.7 μm≦H≦2.3 μm. 10. The resonator of claim 9, wherein: At 0.7μm≤H≤0.8μm, or 1.9μm≤H≤2.1μm. 11. The resonator of any one of claims 1-3, wherein: The at least one groove includes two grooves. 12. The resonator of claim 11, wherein: The two trenches are provided on the upper side of the substrate and are completely covered by the bottom electrode. 13. The resonator of claim 11, wherein: The two trenches are disposed on the upper side of the substrate and are spaced apart from the bottom electrode. 14. The resonator of claim 11, wherein: One of the two trenches is completely covered by the bottom electrode and the other trench is partially covered or spaced from the bottom electrode. 15. The resonator of claim 11, wherein: One of the two trenches is partially covered by the bottom electrode and the other trench is spaced apart from the bottom electrode. 16. The resonator of any of claims 1-3, wherein: The groove is provided on the lower side or the upper side of the piezoelectric layer; or The trench is disposed on the upper side or the lower side of the bottom electrode. 17. The resonator of any of claims 1-3, wherein: The at least one trench includes a plurality of trench segments spaced apart from each other and disposed along the active area. 18. A filter comprising the bulk acoustic wave resonator of any of claims 1-17. 19. An electronic device comprising a filter according to claim 18 or a resonator according to any of claims 1-17. 20. A method of increasing the parallel impedance of a bulk acoustic wave resonator, comprising the steps of: At least one annular groove is formed on the upper side of the base of the resonator around the active area of the resonator.

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