BULK ACOUSTIC WAVE RESONATOR AND FILTER

Abstract

A bulk acoustic wave resonator includes an acoustically active area where an acoustic wave is excitable, and a transition area adjacent to an outside edge of the acoustically active area. A critical frequency of the acoustic wave in the transition area differs from a critical frequency of the acoustic wave in the active area. The transition area includes an additional layer. The bulk acoustic wave resonator includes electrodes for electrically connecting to electrical supply lines. The additional layer is irregular in areas adjacent to junction areas between the electrical supply lines and the resonator.

Description

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-section of a bulk acoustic wave resonator.

FIG. 2A shows a plan view of a bulk acoustic wave resonator with an additional layer having a reduced width in junction areas to electrical supply lines.

FIG. 2B shows the bulk acoustic wave resonator of FIG. 2A in cross section.

FIG. 3A shows a plan view of a bulk acoustic wave resonator with an additional layer having a reduced thickness injunction areas to electrical supply lines.

FIG. 3B shows the bulk acoustic wave resonator of FIG. 3A in cross section.

FIGS. 4A and 4B show filter arrangements that include hulk acoustic wave resonators.

DETAILED DESCRIPTION

FIG. 1 shows a resonator which comprises a resonator area 1 and an acoustic mirror 2. The resonator is located on a carrier substrate 3. Acoustic mirror 2 is arranged between resonator area 1 and carrier substrate 3.

Resonator area 1 comprises electrodes 11, 12 and a piezoelectric layer 10 arranged between them. The resonator area is divided into an acoustically active area 100, in which a bulk acoustic wave is excited, and a transition area 101 adjacent to the active area. Active area 100 may occupy only a (centrally arranged) region of the surface area of the resonator. The boundary region of this surface area comprises transition area 101.

Transition area 101 differs from active area 100 with respect to structure in that transition area 101 comprises an additional layer 4. Layer 4 is located in the boundary region of resonator area 1, e.g., on upper electrode 12. Additional layer 4 may be limited to transition area 101. For example, active area 100 may be free of the additional layer.

Additional layer 4 may be constructed in the form of a frame. A layer sequence with the additional layer is distinguished from a layer sequence without the additional layer by a lower critical frequency.

At least one supply line 5, 6 is connected to each electrode 11, 12 of the resonator, as shown in FIG. 2A.

FIGS. 2A and 2B show different views of parts of a resonator with an additional layer 4. The width of additional layer 4 is reduced in areas 41 adjoining junction areas of supply lines 5, 6. In FIG. 2B, a cross section along line AA. (of FIG. 2A) is shown.

FIGS. 3A and 3B show different views of a resonator with an additional layer 4. The thickness of additional layer 4 is reduced in areas 42 adjoining junction areas of supply lines 5, 6. FIG. 3B shows a cross-section along line AA of the resonator shown in FIG. 3A.

Different thickness ranges of additional layer 4 can be obtained by applying a second sublayer to the first sublayer outside of areas 42. Alternatively, it is possible to etch additional layer 4 in areas 42 to a predetermined depth.

In area 42, the width of the additional layer 4 can be also changed along with the thickness.

There is the possibility of increasing the thickness and/or the width of additional layer 4 in areas 41, 42.

FIG. 4A shows a filter having a ladder-type arrangement. The filter comprises a series arm connecting an input IN and an output Out. At least one series resonator RS is arranged in the series arm.

A parallel resonator RP is arranged in a branch transverse to the series arm, which connects the series arm to a reference potential, which is ground GND in this example. The filter may comprise additional series resonators arranged in the series arm and additional transverse branches, which is/are indicated by the broken line.

FIG. 4B shows another ladder-type arrangement which is useful for symmetric signals and balanced operation. There are two series arms connecting symmetric inputs IN1sym, IN2sym to symmetric outputs Out1sym, OUT2sym. A transverse branch interconnects the two series arms. There may be additional series resonators in the series arms and additional transversal branches interconnecting the series arms.

Components of different embodiments described herein may be combined to form other embodiments not specifically set forth above. Other embodiments not specifically described herein are also within the scope of the following claims.

Claims

1. A bulk acoustic wave resonator, comprising: an acoustically active area where an acoustic wave is excitable;a transition area adjacent to an outside edge of the acoustically active area, the transition area comprising an additional layer; andelectrodes to electrically connect to electrical supply lines;wherein the additional layer is irregular in areas adjacent to junction areas between the electrical supply lines and the bulk acoustic wave resonator; andwherein a critical frequency of the acoustic wave in the transition area differs from a critical frequency of the acoustic wave in the active area.

2. The bulk acoustic wave resonator of claim 1, wherein, in areas adjacent to the junction areas, the additional layer has a width that is different from a width of the additional layer in areas that are not adjacent to the junction areas; and wherein the width in the areas adjacent to junction areas is measured in a longitudinal direction of the supply lines.

3. The bulk acoustic wave resonator of claim 1, wherein, in areas adjacent to the junction areas, the additional layer has a thickness that is different from a thickness of the additional layer in areas that are not adjacent to the junction areas.

4. The bulk acoustic wave resonator of claim 3, wherein the thickness of the additional layer is between 20 nm and 80 nm.

5. The bulk acoustic wave resonator of claim 1, wherein the electrodes comprise two electrodes, each of the two electrodes comprising a conductive layer having a specific density that exceeds a specific density of Al by at least 50%; and wherein a thickness of additional layer is between 20 nm and 140 nm.

6. The bulk acoustic wave resonator of claim 1, wherein the additional layer comprises silicon dioxide.

7. The bulk acoustic wave resonator of claim 1, wherein an irregularity of the additional layer in an area adjacent to a junction area has a width that corresponds to a width of an electrical supply line.

8. The bulk acoustic wave resonator of claim 1, wherein the additional layer is frame-shaped.

9. The bulk acoustic wave resonator of claim 2, wherein, in areas adjacent to the junction areas, the additional layer has a thickness that is different from a thickness of the additional layer in areas that are not adjacent to the junction areas.

10. The hulk acoustic wave resonator of claim 9, wherein the additional layer comprises silicon dioxide.

11. The bulk acoustic wave resonator of claim 3, wherein, in areas adjacent to the junction areas, the additional layer has a width that is different from a width of the additional layer in areas that are not adjacent to the junction areas.

12. The bulk acoustic wave resonator of claim 11, wherein the additional layer comprises silicon dioxide.

13. The bulk acoustic wave resonator of claim 1, further comprising: a piezoelectric layer between the electrodes; andan acoustic mirror below the electrodes and the piezoelectric layer.

14. A filter comprising: series bulk acoustic wave resonators; andparallel bulk acoustic wave resonators;wherein each of the series bulk acoustic wave resonators and each of the parallel bulk acoustic wave resonators comprises: an acoustically active area where an acoustic wave is excitable;a transition area adjacent to an outside edge of the acoustically active area, the transition area comprising an additional layer; andelectrodes to electrically connect to electrical supply lines;wherein the additional layer is irregular in areas adjacent to junction areas between the electrical supply lines and the resonator; andwherein a critical frequency of the acoustic wave in the transition area differs from a critical frequency of the acoustic wave in the active area; andwherein a size of a first irregularity in an additional layer in a series bulk acoustic wave resonator is different than a size of a second irregularity in an additional layer in a corresponding parallel bulk acoustic wave resonator.

15. The filter of claim 14, wherein the first and second irregularities comprise same irregularities.

16. The filter of claim 14, wherein the first and second irregularities comprise thicknesses of additional layers in the series bulk acoustic wave resonator and in the parallel bulk acoustic wave resonator.

17. The filter of claim 14, wherein the first and second irregularities comprise widths of additional layers in the series bulk acoustic wave resonator and in the parallel bulk acoustic wave resonator.

18. A bulk acoustic wave resonator, comprising: an acoustically active area where an acoustic-wave is excitable;a transition area adjacent to an outside edge of the acoustically active area, the transition area comprising an additional layer and having a different acoustic property than the acoustically active area; andelectrodes to electrically connect to electrical supply lines;wherein the additional layer is irregular in an area adjacent to a junction area between an electrical supply lines and the bulk acoustic wave resonator.

19. The bulk acoustic wave resonator of claim 18, wherein, in the area adjacent to the junction area, the additional layer has a width that is different from a width of the additional layer in areas that are not adjacent to the junction area.

20. The bulk acoustic wave resonator of claim 18, wherein, in the area adjacent to the junction area, the additional layer has a thickness that is different from a thickness of the additional layer in areas that are not adjacent to the junction area.