SAW component having an improved temperature coefficient
View Patent ↗An apparatus including a piezoelectric substrate having at least one transducer electrode structure. The structure having a metallization formed by one or more metals with a mean specific density that is at least 50% higher than that of aluminum. The structure having a compensation layer that is applied fully or partially over the metallization. The compensation layer is of a material having a temperature dependence of elastic constants that counteracts the temperature coefficient of frequency of the substrate. The compensation layer has a thickness that is less than 15% of an acoustic wavelength of a wave capable of propagation in the structure.
1. An apparatus comprising:
a piezoelectric substrate comprising at least one transducer electrode structure comprising:
a metallization formed by one or more metals, the one or more metals having a mean specific density that is at least 50% higher than that of aluminum;
a compensation layer applied fully or partially over the metallization, the compensation layer being of a material having a temperature dependence of elastic constants that substantially counteracts a temperature coefficient of frequency of the substrate, the compensation layer having a thickness that is less than 15% of an acoustic wavelength of a wave capable of propagation in the structure; and
a passivation layer that is thinner than the compensation layer, the passivation layer being beneath the compensation layer.
2. The apparatus of claim 1 , wherein the elastic constants of the metallization have less temperature dependency than elastic constants of aluminum.
3. The apparatus of claim 1 , wherein the metallization comprises one or more of the following: copper, molybdenum, tungsten, gold, silver and platinum.
4. The apparatus of claim 1 , wherein the compensation layer comprises SiO 2 .
5. The apparatus of claim 1 , wherein the metallization comprises copper or a copper alloy and has a thickness of 6 to 14% h/λ, where h is the thickness of the compensation layer and λ is the acoustic wavelength of a wave capable of propagation in the structure.
6. The apparatus of claim 1 , wherein the compensation layer has a thickness of 4 to 10% h/λ, where h is the thickness of the compensation layer and λ is the acoustic wavelength of a wave capable of propagation in the structure.
7. The apparatus of claim 1 , wherein the substrate comprises lithium tantalate with a rotated cut.
8. The apparatus of claim 1 , wherein the substrate comprises lithium tantalate with a rotated cut and an angle of intersection of between 30 and 480°.
9. The apparatus of claim 1 , wherein the substrate comprises lithium niobate.
10. The apparatus of claim 1 , wherein the substrate comprises quartz.
11. The apparatus of claim 1 , further comprising an adhesive layer beneath the metallization.
12. The apparatus of claim 11 , wherein the adhesive layer comprises one or more of the following: aluminum, molybdenum, titanium, tungsten, chromium, and nickel.
13. The apparatus of claim 11 , wherein the adhesive layer has a thickness of 1 to 7 nm.
14. The apparatus of claim 1 , wherein the compensation layer comprises SiO 2 with a refractive index of between 1.43 and 1.49.
15. The apparatus of claim 1 , wherein the temperature coefficient of frequency is less than 20 ppm/k.
16. The apparatus of claim 1 , wherein the apparatus comprises a multiport filter.
17. The apparatus of claim 1 , wherein the apparatus comprises a reactance filter.
18. The apparatus of claim 1 , wherein the apparatus comprises a dual mode surface acoustic wave filter.
19. The apparatus of claim 1 , wherein the apparatus comprises a single phase uni-directional transducer filter.
20. The apparatus of claim 1 , wherein the apparatus comprises a duplexer.
21. The apparatus of claim 1 , wherein the apparatus comprises a diplexer.
22. The apparatus of claim 1 , wherein the apparatus comprises a 2-in-1 filter.