Method of forming an acoustic resonator

1. 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.

2. 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.

3. A method as claimed in claim 1 or claim 2 wherein the primer layer is deposited at between 20° C. and 100° C.

4. A method as claimed in claim 3 wherein the primer layer is deposited at about 40° C.

5. A method as claimed in claim 3 , wherein there is no vacuum break between the deposition of the primer layer and the electrode.

6. 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, wherein said hydrogen plasma treating is carried out using a parallel plate type reactor; and

providing a layer of piezoelectric material on said electrode layer.

7. A method according to claim 6 , wherein said piezoelectric material comprises Aluminium Nitride (AlN).

8. A method according to claim 6 , wherein said hydrogen plasma treating is carried out in a hydrogen pressure above about 0.5 Torr.

9. A method according to claim 6 , wherein said hydrogen plasma treating is carried out using a high frequency.

10. A method according to claim 6 , wherein said hydrogen plasma treating is carried out at a power above about 0.5 KW for a 200 mm diameter substrate (1.6 watts/cm 2 ).

11. A method according to claim 6 , wherein, prior to provision of said electrode layer of Molybdenum or Tungsten, a primer layer is provided on said substrate, wherein said primer layer comprises a generally crystalline material having a atomic spacing parameter which matches the atomic spacing parameter of said electrode layer to within about 15% and is not of cubic crystalline form.

12. A method of selecting a primer layer for a lower electrode layer in an acoustic resonator comprising selecting a layer of different crystallography to the electrode layer and with an atomic spacing, in at least one orientation, that matches the atomic spacing of the electrode layer to within about 15%.

13. A method as claimed in claim 12 wherein the primer layer comprises more than one layer and a lower layer has the different crystallography.

14. A method as claimed in claim 12 wherein the electrode layer is deposited using a long throw sputter chamber.

15. A method as claimed in claim 14 wherein the target to substrate distance is between 400 and 450 mm.

16. A method as claimed in claim 14 wherein the chamber includes a magnetic confinement coil to enhance ionisation.

17. A method as claimed in claim 14 wherein more than 20% of the sputtered target material is ionised.