Acoustic resonators

An acoustic resonator comprising:

• a substrate;
• at least one generally crystalline primer layer provided on said substrate either directly or on top of one or more intermediate layers;
• a generally smooth and generally crystalline electrode layer provided on said primer layer;
• and
• a piezoelectric layer provided on said electrode layer, wherein:
• (iv) the primer layer, or at least one of the primer layers, has a crystallographic structure belonging to a first crystal system, and
• (v) said electrode layer has a crystallographic structure belonging to a second crystal system which is different to said first system;
• and
• (vi) the atomic spacing, in at least one orientation, of said primer layer, or at least the primer layer which interface with the electrode, and that of said electrode matches to within about 15%.

A method of forming an acoustic resonator which comprises:

• depositing at least one primer layer,
• depositing an electrode layer containing Molybdenum on the upper surface of the primer layer;
• and,
• depositing a layer of piezoelectric material on the uppermost electrode layer, wherein the primer layer comprises a generally crystalline material the upper surface of which has an atomic spacing that matches the atomic spacing of said electrode layer to within about 15% and is not of cubic crystalline form.

A method of forming an acoustic resonator which comprises:

• depositing at least one primer layer,
• depositing an electrode layer containing Molybdenum or Tungsten on the upper surface of the primer layer;
• and
• depositing a layer of piezoelectric material on the uppermost electrode layer, wherein the primer layer, or at least one primer layer, comprises a generally crystalline material the upper surface of which has an atomic spacing that matches the atomic spacing in at least one orientation of said electrode layer to within about 15% and is not of cubic crystalline form.

An acoustic resonator comprising:

• a substrate,
• an electrode layer comprising Molybdenum or Tungsten provided directly on said substrate or indirectly on one or more intermediate layers on said substrate;
• and
• a layer of piezoelectric material provided on said electrode layer,
• wherein said electrode layer is deposited by a predominately Neon sputtering process and said electrode layer is treated with a hydrogen plasma.

A method of forming an acoustic resonator that comprises:

• using a predominately Neon sputtering process and a Molybdenum or Tungsten target to provide an electrode layer comprising Molybdenum or Tungsten directly on a substrate or indirectly on one or more intermediate layers on a substrate;
• treating said electrode layer with a hydrogen plasma;
• and
• providing a layer of piezoelectric material on said electrode layer.