Electroacoustic component and crystal cuts for electroacoustic components

Abstract

An electroacoustic component is disclosed. In an embodiment, the electroacoustic component includes a piezoelectric substrate comprising a rare earth metal and calcium oxoborates (RE-COB) and component structures arranged on the substrate, the component structures being suitable for converting between RF signals and acoustic waves, wherein the waves are capable of propagation in a direction x, and wherein the direction x is determined by Euler angles (, , ), the Euler angles being selected from angle ranges (20-90, 95-160, 15-55), (20-85, 95-160, 95-125) and (15-25, 85-100, 0-175).

Claims

1. An electroacoustic component comprising: a piezoelectric substrate comprising a rare earth metal and calcium oxoborates (RE-COB); and component structures arranged on the substrate, the component structures being suitable for converting between RF signals and acoustic waves, wherein the acoustic waves are capable of propagation in a direction x, and wherein the direction x is determined by Euler angles (, , ), the Euler angles being selected from angle ranges (20-90, 95-160, 15-55), (20-85, 95-160, 95-125) and (15-25, 85-100, 0-175).

2. The electroacoustic component according to the preceding claim 1, wherein the direction x is determined by the Euler angles (30-64, 98-138, 104-124).

3. The electroacoustic component according to claim 1, wherein the piezoelectric substrate comprises neodymium (Nd)COB or consists of NdCOB.

4. The electroacoustic component according to claim 1, wherein the component structures comprise electrode fingers having a height h and a width b, wherein the electrode fingers are spaced apart such that an acoustic wave having a wavelength is capable of propagation, wherein a ratio h/ is between 1% and 15%, wherein the electrode fingers comprise a metal, wherein a metallization ratio =b/ is between 0.2 and 0.8, wherein the acoustic wave is a Rayleigh wave and/or a horizontally and/or vertically polarized shear wave and/or a mixed-polarized wave.

5. An electroacoustic component comprising: a piezoelectric substrate comprising a rare earth metal and calcium oxoborates (RE-COB); and component structures arranged on the substrate, the component structures being suitable for converting between RF signals and acoustic waves, wherein the acoustic waves are capable of propagation in a direction x, and wherein the direction x is determined by Euler angles (, , ), the Euler angles being selected from angle ranges (15-90, 100-165, 10-50), (15-90, 100-165, 120-135), (15-30, 100-110, 10-10) and (60-75, 135-155, 93-97).

6. The electroacoustic component according to claim 5, wherein the direction x is determined by the Euler angles (50 . . . 62, 112 . . . 116, 32 . . . 40).

7. The electroacoustic component according to claim 6, wherein the direction x is determined by the Euler angles (66-90, 122-138, 12-50).

8. The electroacoustic component according to claim 7, wherein the direction x is determined by the Euler angles (60-75, 135-155, 95).

9. The electroacoustic component according to claim 5, wherein the component structures comprise electrode fingers having a height h and a width b, wherein the electrode fingers are spaced apart such that an acoustic wave having a wavelength is capable of propagation, wherein a ratio h/ is between 1% and 15%, wherein the electrode fingers comprise a metal, wherein a metallization ratio =b/ is between 0.2 and 0.8, and wherein the acoustic wave is a Rayleigh wave and/or a horizontally and/or vertically polarized shear wave and/or a mixed-polarized wave.

10. The electroacoustic component according to claim 5, wherein the piezoelectric substrate comprises neodymium (Nd)COB or consists of NdCOB.

11. An electroacoustic component comprising: a piezoelectric substrate comprising a rare earth metal and calcium oxoborates (RE-COB); and component structures arranged on the substrate, the component structures being suitable for converting between RF signals and acoustic waves, wherein the acoustic waves are capable of propagation in a direction x, and wherein the direction x is determined by Euler angles (, , ), the Euler angles being selected from angle ranges (80-100, 120-170, 10-10).

12. The electroacoustic component according to claim 11, wherein the component structures comprise electrode fingers having a height h and a width b, wherein the electrode fingers are spaced apart such that an acoustic wave having a wavelength is capable of propagation, wherein a ratio h/ is between 1% and 15%, wherein the electrode fingers comprise a metal, wherein a metallization ratio =b/ is between 0.2 and 0.8, and wherein the acoustic wave is a Rayleigh wave and/or a horizontally and/or vertically polarized shear wave and/or a mixed-polarized wave.

13. The electroacoustic component according to claim 11, wherein the piezoelectric substrate comprises neodymium (Nd)COB or consists of NdCOB.

14. An electroacoustic component comprising: a piezoelectric substrate comprising a rare earth metal and calcium oxoborates (RE-COB); and component structures arranged on the substrate, the component structures being suitable for converting between RF signals and acoustic waves, wherein the acoustic waves are capable of propagation in a direction x, and wherein the direction x is determined by Euler angles (, , ), the Euler angles being selected from angle ranges (15-90, 95-165, 95-135), (60-75, 135-155, 85-95), (15-90, 95-165, 10-55).

15. The electroacoustic component according to claim 14, wherein the directions x is determined by the Euler angles (15-60, 95-109, 10-18) are excluded.

16. The electroacoustic component according to claim 14, wherein the component structures comprise electrode fingers having a height h and a width b, wherein the electrode fingers are spaced apart such that an acoustic wave having a wavelength is capable of propagation, wherein a ratio h/ is between 1% and 15%, wherein the electrode fingers comprise a metal, wherein a metallization ratio =b/ is between 0.2 and 0.8, wherein the acoustic wave is a Rayleigh wave and/or a horizontally and/or vertically polarized shear wave and/or a mixed-polarized wave.

17. The electroacoustic component according to claim 14, wherein the piezoelectric substrate comprises neodymium (Nd)COB or consists of NdCOB.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The features underlying the present invention are explained in greater detail below with reference to schematic drawings.

(2) In the figures:

(3) FIG. 1 shows a listing sorted in accordance with the sets of Euler angles and advantageous normalized heights of the component structures and metallization ratios;

(4) FIG. 2 shows the essential constituents of an electroacoustic transducer and the direction of propagation of the acoustic waves X;

(5) FIG. 3 shows a schematic diagram visually representing the definition used for the Euler angles;

(6) FIG. 4 shows calculated values of the electroacoustic coupling coefficient .sup.2 as a function of the Euler angles and ; and

(7) FIG. 5 shows calculated temperature dependencies.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(8) FIG. 1 shows a sorted representation of expedient Euler angles for crystal cuts or directions of propagation of acoustic waves in electroacoustic components. Expedient Euler angles are in this case substantially divided into four groups (A, B, C, D).

(9) Group A in this case comprises the subsets A1, A2 and A3. The subset A1 for example demands a value of between 20 and 90 for the first Euler angle. The second Euler angle is between 95 and 160. The third Euler angle is between 15 and 55.

(10) The subset A2, in particular, includes a sub-subset A2* having the Euler angles (30-64, 98-138, 104-124). In the sub-subset A2*, the electroacoustic coupling coefficient .sup.2 is approximately 0.8% virtually independently of the metallization ratio.

(11) Correspondingly, the set of Euler angles B comprises the subsets B1, B2, B3 and B4. In this case, the subset B1 comprises the further sub-subsets B1* and B1. The sub-subset B1, in particular, enables quadratic temperature coefficients TCF.sub.2<40 ppb/K.sup.2.

(12) The set of Euler angles C substantially consists of the subset C1, the Euler angles of which are characterized in that the third Euler angle is chosen to be between 10 and 10. The symmetry of the piezoelectric material here may be such that the third Euler angle also corresponds to an interval of between 170 and 190.

(13) The set D comprises the subsets D.sub.1, D.sub.22 and D.sub.3. The subset D.sub.1 here comprises the combinations of Euler angles (15-90, 95-165, 10-55), wherein the intervals for the Euler angles (, , ) (15-60, 95-109, 10-18) are excluded. The set of remaining Euler angles is thus substantially the set of Euler angles (]60-90, 95-165, 10-55)+(15-60, ]109-165, 10-55)+(15-90, 95-109, ]18-55), wherein the numerical value 60, for the Euler angle in the first case, the value of 109 in the second case and the value of 18 in the third case are theoretically excluded. However, since the number of atoms in a crystal is quantized and cutting planes intersect atoms of the crystal, the number of possible cut angles is finite, in principle, and the possible values for , , cannot be arbitrarily close together. Whether or not the critical values 60 for , 109 for and 18 for are thus advantageously chosen in combination with the respectively corresponding other values of the subset D.sub.1 can thus be left open.

(14) FIG. 2 shows an electroacoustic transducer W comprising interdigital structures IDS flanked by reflector fingers RF. In this case, the interdigital structure IDS comprises electrode fingers EFI interconnected in each case with a busbar. An RF signal can be applied to respectively adjacent electrode fingers. Then the piezoelectric effect is utilized and an acoustic wave is excited in the piezoelectric substrate PSu. Conversely, it is also possible to convert an acoustic wave in the piezoelectric substrate PSu into an RF signal by means of the transducer structure. In this case, a component can comprise a plurality of transducers that are acoustically coupled e.g. in an acoustic track. In this case, the direction of propagation of the acoustic waves is specified by X. In this case, the electrode fingers EFI extend in the direction Y.

(15) FIG. 3 graphically shows the definition of the Euler angles. In this case, denotes the first Euler angle, by which the original X-axis and the original Y-axis are rotated about the original Z-axis. A rotation about the axis x by the angle subsequently follows. Finally, a rotation about the axis Z by the angle specifies how the resulting X-axis (X) must have been rotated in order that the direction of propagation of the acoustic waves relative to the crystallographic axes, represented by the original axes x, y, z, is obtained.

(16) FIG. 4 shows calculated values for the electroacoustic coupling coefficient .sup.2 as a function of the Euler angles and in the case of a constant Euler angle of 80 in a so-called contour plot. The values of constant coupling coefficients are identified here by dotted lines. A center around which closed contour lines pass here indicates a maximum or a minimum of the coupling coefficient.

(17) FIG. 5 shows calculated temperature coefficients. In this case, the values approximately at 80 C. have a horizontal tangent, i.e. a vanishing gradient, such that a parabolic temperature response in a development around a temperature T.sub.o=80 C. is obtained. For advantageous Euler angles, metallization ratios and normalized heights of the component structures, the temperature minimum of the parabola may be shifted here to significantly higher temperatures, such that a rise or a fall in temperature during the operation of a mobile communication device at customary room temperatures does not entail excessively great effects on the transmission behavior of the corresponding front-end modules.

(18) The invention described is not restricted here to the schematic exemplary embodiments and figures. Electroacoustic components which comprise further component parts such as piezoelectric materials, layer systems in the component structures, temperature condensation layers and strain layers, compositions of the component structures, etc., are therefore likewise part of the invention.