SAW COMPONENT WITH REDUCED DISTURBANCES BY TRANSVERSAL AND SH MODES AND HF FILTER WITH SAW COMPONENT

Abstract

A SAW component and an HF filter with a SAW component are specified, each with reduced disturbances by transversal modes and by SH modes. The SAW component comprises an active area with an internal area between two peripheral areas. The main mode of the SAW component has a lower velocity in the peripheral areas than in the internal area.

Claims

1. A surface acoustic wave (SAW) component (SAW-B) with reduced disturbances by transversal and sheer horizontal (SH) modes, comprising: a piezoelectric substrate (PS); and an active area (AB) with interlacing electrode fingers (EF), the active area (AB) having an internal area (IB) and two peripheral areas (RB), the internal area (AB) being arranged between the two peripheral areas (RB), wherein: a main mode is capable of propagation in the active area (AB); a thickness of the interlacing electrode fingers (EF) in the peripheral areas is less than a thickness of the interlacing electrode fingers (EF) in the internal area (IB); and one weighting strip (BS) is arranged in each of the peripheral areas (RB).

2. The SAW component according to the previous claim, wherein the peripheral areas (RB) extend along the propagation area of the main mode.

3. (canceled)

4. The SAW component according to one of the previous claims, wherein a metallization ratio in the peripheral areas (RB) deviates from a metallization ratio in the internal area (IB).

5. The SAW component according to the previous claim, wherein the weighting strips (BS) comprise a material that is selected from: copper (Cu), silver (Ag), gold (Au), tungsten (W), and titanium (Ti).

6. The SAW component according to one of the 2 previous claims, wherein the weighting strips (BS) have a thickness d in units of a pitch p, wherein d is within the range: 0.024d/p0.196, the pitch being a distance between a center of two adjacent electrodes of the interlacing electrode fingers (EF).

7. The SAW component according to one of the 3 previous claims, wherein a dielectric layer is arranged between the weighting strips (BS) and a substrate (SU).

8. The SAW component according to the previous claim, wherein the dielectric layer (DL) comprises a silicon oxide, a germanium oxide or a tellurium oxide.

9. The SAW component according to any of the previous claims, wherein the metallization ratio is within the range: 0.390.66.

10. The SAW component according to one of the 3 previous claims, further comprising an upper dielectric layer (DL2) disposed above the dielectric layer.

11. The SAW component according to the previous claim, wherein the upper dielectric layer (DL2) comprises a silicon oxide, a germanium oxide.

12. The SAW component according to one of the 2 previous claims, wherein the dielectric layer (DL) has a thickness d.sub.1, the upper dielectric layer (DL2) has the thickness d.sub.2 and (d.sub.1+d.sub.2)/p=0.65.

13. The SAW component according to one of the 3 previous claims, wherein the dielectric layer (DL) has the thickness d.sub.1, the upper dielectric layer (DL2) has the thickness d.sub.2, the weighting strip (BS) comprises Ti and has a thickness d.sub.BS and (d.sub.1+d.sub.2+d.sub.BS)/p=0.66, wherein p refers to a pitch, the pitch being a distance between a center of two adjacent electrodes of the interlacing electrode fingers (EF).

14. The SAW component according to one of the 4 previous claims, furthermore comprising a dielectric top layer (DDL) being disposed above the upper dielectric layer (DL2).

15. The SAW component according to the previous claims, wherein the dielectric top layer (DDL) comprises a silicon nitride.

16. The SAW component according to one of the 2 previous claims, wherein the dielectric top layer (DDL) has a thickness d that is within the range: 40 nmd120 nm.

17. The SAW component according to one of the previous claims, wherein the main mode is a Rayleigh mode, and wherein 3460 m/sv.sub.i3600 m/s, wherein v.sub.i is a velocity of the main mode.

18. (canceled)

19. The SAW component according to one of the previous claims, wherein the electrode fingers (EF) comprise Cu, and wherein a thickness d(EF) of electrode fingers (EF) is within the range: 0.15d(EF)/p0.19 nm, wherein p refers to a pitch, the pitch being a distance between a center of two adjacent electrodes of the interlacing electrode fingers (EF).

20. The SAW component according to one of the previous claims, wherein the electrode fingers (EF) comprise Cu, and wherein a thickness d(DL) of the dielectric layer (DL) is within the range: 0.23d(DL)/p0.42.

21. The SAW component according to one of the previous claims, wherein the electrode fingers (EF) comprise Cu, and wherein a thickness d(BS) of the weighting strip (BS) is within the range: 0.02d(BS)/p0.05, wherein p refers to a pitch, the pitch being a distance between a center of two adjacent electrodes of the interlacing electrode fingers (EF).

22. The SAW component according to one of the previous claims, wherein the electrode fingers (EF) comprise Ti, and wherein a thickness d(BS) of the weighting strip (BS) is within the range: 0.09d(BS)/p0.21, wherein p refers to a pitch, the pitch being a distance between a center of two adjacent electrodes of the interlacing electrode fingers (EF).

23. A HF filter with the SAW component (SAW-B) according to one of the previous claims.

Description

[0063] The functionality and examples that serve to illustrate the design of the layer stacks become apparent in the schematic figures.

[0064] Shown are:

[0065] FIG. 1: top view of a SAW component with peripheral areas in the active area,

[0066] FIG. 2: cross section through a corresponding component and the definition of the pitch p,

[0067] FIG. 3: cross section through a component with an electrode finger embedded in a dielectric layer,

[0068] FIG. 4: cross section through an additional component with weighting strips,

[0069] FIG. 5: widened electrode fingers in the peripheral area,

[0070] FIG. 6: narrower electrode fingers in the peripheral area,

[0071] FIGS. 7-21: advantageous parameters.

[0072] FIG. 1 shows a top view of the electrode structure of a SAW component SAW-B, in which electrode fingers EF are respectively arranged next to each other in longitudinal direction and themselves extend along the transversal direction. In this, the electrode fingers EF are alternately switched to one of two busbars BB respectively. The area in which the electrode fingers of opposite busbars overlap is the active area AB where the switch between HF signals of the desired frequency and acoustic waves takes place. For this, the active area AB has peripheral areas RB and an internal area IB. Substantially, the peripheral areas cover the ends of the electrode fingers that are not directly linked to a busbar, the so-called free finger ends. The internal area IB is arranged between the peripheral areas.

[0073] By reducing the velocity v.sub.r in the peripheral areas relatively to the velocity v.sub.i of the main modes in the internal area IB, the result is a transversal velocity profile that firstly suppresses a transversal mode and secondly reduces the electro-acoustic coupling for SH modes to such an extent that the component is even ideal for use in filters working in broadband mode.

[0074] FIG. 2 shows a cross section through a layer structure to illustrate the definition of the pitch p: Electrode fingers EF are arranged on the piezoelectric substrate PS. The distance from the left or right finger edges to the adjacent electrode fingers is the pitch p.

[0075] FIG. 3 shows a cross section through a layer stack in the internal area TB with electrode fingers EF that are arranged on the piezoelectric substrate PS. On the top surface of the piezoelectric substrate PS and/or the electrode finger EF, a dielectric material of the dielectric layer DL has been arranged. The material of the dielectric layer DL may have a thermal expansion coefficient that is selected in such a way that the temperature variation of the frequencies at a given expansion coefficient of the substrate and the finger material is selected in such a way that the temperature variation of the entire layer stack is reduced or decreased.

[0076] A dielectric top layer DDL is arranged on the dielectric layer DL that may serve as a passivation layer.

[0077] Silicon oxide is a possible material for the dielectric layer. Silicon nitride is a possible material for the dielectric top layer.

[0078] FIG. 4 shows a cross section through a layer stack at the level of the peripheral area RB, wherein the weighting strip BS is arranged on material of the dielectric layer DL. Thus, the material of the dielectric layer not only has the task of reducing a temperature variation of the frequencies. The material of the dielectric layer DL rather has the task preventing the material of the weighting strip BS from short-circuiting with the electrode fingers that are switched to different busbars.

[0079] An upper dielectric layer DL2 is arranged above the weighting strip, and the dielectric top layer DDL in turn is arranged on said upper dielectric layer.

[0080] FIG. 5 schematically shows that the finger widths (and thus the metallization ratio r.sub.i) in the peripheral area may be lower than the finger widths in the internal area.

[0081] FIG. 6 shows in an analogous manner that the finger widths in the internal area may be smaller than in the peripheral area.

[0082] FIGS. 7 to 21 show advantageous parameters of the SAW component. FIGS. 7 to 18 show values for a transducer with electrode fingers and weighting strips made of copper. FIGS. 19 to 21 show values for a transducer with electrode fingers made of Cu and weighting strips made of titanium.

[0083] FIGS. 7 to 11 show values for a transducer whose electrode fingers have a thickness of 335 nm. FIGS. 12 to 18 show values for a transducer whose electrode fingers have a thickness of 355 nm. FIGS. 19 to 21 show values for a transducer whose electrode fingers have a thickness of 335 nm. The indicated values for the thickness of the dielectric layer DL, the thickness of the weighting strip BS, the metallization ratio that is advantageous for a certain pitch p (e.g. p=2.050.15), the relative coupling strength k.sub.rel that is advantageous for a certain pitch p and the advantageous reduction of the velocity are summarily illustrated in the table shown.

[0084] If the pitch p deviates from 2.05, the respective optimized values can be taken from the charts.

LIST OF REFERENCE CHARACTERS

[0085] AB: active area

[0086] BB: busbar

[0087] d: thickness of the dielectric layer

[0088] DDL: dielectric top layer

[0089] DL: dielectric layer

[0090] DL2: upper dielectric layer

[0091] EF: electrode finger

[0092] IB: internal area

[0093] p: pitch

[0094] PS: piezoelectric substrate

[0095] RB: peripheral area

[0096] SAW-B: SAW component

[0097] v, v.sub.i, v.sub.r: propagation velocity

[0098] w: width of the electrode fingers

[0099] k.sup.2: coupling strength