Bulk acoustic wave resonators having low atomic weight metal electrodes

A bulk acoustic wave (BAW) resonator, comprising:

• an acoustic stack, comprising:
• a substrate comprising an acoustic reflector;
• a first beryllium electrode disposed over the acoustic reflector, the first beryllium electrode being a thickness in a range of 3,000 angstroms to 5,000 angstroms;
• a piezoelectric layer disposed over the first beryllium electrode;
• a second beryllium electrode disposed over the piezoelectric layer, the second beryllium electrode being the thickness in the range of 3,000 angstroms to 5,000 angstroms;
• a first barrier layer disposed between the first beryllium electrode and the piezoelectric layer;
• and
• a second barrier layer disposed between the piezoelectric layer and the second beryllium electrode;
• wherein the first barrier layer is made of the same material as the first beryllium electrode, and the second barrier layer is made of the same material as the second beryllium electrode.

A bulk acoustic wave (BAW) resonator, comprising:

• a substrate comprising an acoustic reflector;
• an acoustic stack, comprising:
• a first piezoelectric layer disposed over the substrate;
• a first electrode disposed over the first piezoelectric layer and the acoustic reflector, and comprising a first layer comprising a comparatively high acoustic impedance material, and a second layer comprising a comparatively low acoustic impedance material;
• a piezoelectric layer disposed over the second layer;
• a first barrier layer disposed between the second layer and the piezoelectric layer;
• a second electrode disposed over the piezoelectric layer, and comprising a third layer comprising the comparatively low acoustic impedance material, and a fourth layer comprising the comparatively high acoustic impedance material;
• and
• a second barrier layer disposed between the piezoelectric layer and the third layer;
• wherein the second layer and the third layer are each a Beryllium layer of a thickness in a range of 3,000 angstroms to 5,000 angstroms;
• wherein the first barrier layer is made of the same material as the first layer, and the second barrier layer is made of the same material as the fourth layer.