Abstract: An acoustic wave element includes: a substrate; a bonding structure on the substrate; a support layer on the bonding structure; a first electrode including a lower surface on the support layer; a cavity positioned between the support layer and the first electrode and exposing a lower surface of the first electrode; a piezoelectric layer on the first electrode; and a second electrode on the piezoelectric layer, wherein at least one of the first electrode and the second electrode includes a first layer and a second layer that the first layer has a first acoustic impedance and a first electrical impedance, the second layer has a second acoustic impedance and a second electrical impedance, wherein the first acoustic impedance is higher than the second acoustic impedance, and the second electrical impedance is lower than the first electrical impedance.

Abstract: A method for forming an acoustic wave device, including steps of: forming an acoustic wave sensing part and an acoustic wave reflecting part, wherein the step of forming the acoustic wave sensing part includes: providing a first substrate, forming a sensing layer on the first substrate, forming a bottom electrode on a side of the sensing layer, and forming a filling layer on the sensing layer and the bottom electrode; and wherein the step of forming the acoustic wave reflecting part includes: providing a second substrate, forming a reflecting element on the second substrate, and forming a cover layer on the reflecting element; joining the acoustic wave sensing part and the acoustic wave reflecting part; removing the first substrate; and forming a top electrode on another side of the sensing layer, wherein the bottom electrode, the top electrode and the reflecting element are arranged correspondingly to each other.

Abstract: An acoustic wave element includes: a substrate; a bonding structure on the substrate; a support layer on the bonding structure; a first electrode including a lower surface on the support layer; a cavity positioned between the support layer and the first electrode and exposing a lower surface of the first electrode; a piezoelectric layer on the first electrode; and a second electrode on the piezoelectric layer, wherein at least one of the first electrode and the second electrode includes a first layer and a second layer that the first layer has a first acoustic impedance and a first electrical impedance, the second layer has a second acoustic impedance and a second electrical impedance, wherein the first acoustic impedance is higher than the second acoustic impedance, and the second electrical impedance is lower than the first electrical impedance.