ZnO buffer layer for metal films on silicon substrates
Dramatic improvements in metallization integrity and electroceramic thin film performance can be achieved by the use of the ZnO buffer layer to minimize interfacial energy between metallization and adhesion layers. In particular, the invention provides a substrate metallization method utilizing a ZnO adhesion layer that has a high work of adhesion, which in turn enables processing under thermal budgets typically reserved for more exotic ceramic, single-crystal, or metal foil substrates. Embodiments of the present invention can be used in a broad range of applications beyond ferroelectric capacitors, including microelectromechanical systems, micro-printed heaters and sensors, and electrochemical energy storage, where integrity of metallized silicon to high temperatures is necessary.
1. An electroceramic thin film stack, comprising:
an oxidized silicon substrate;
a ZnO buffer layer deposited on the silicon substrate;
a metal layer deposited on the ZnO buffer layer; and
a complex oxide layer or a doped complex oxide layer deposited on the metal layer.
2. The electroceramic thin film stack of claim 1 , wherein the metal layer comprises a noble metal.
3. The electroceramic thin film stack of claim 2 , wherein the noble metal comprises platinum, gold, or palladium.
4. The electroceramic thin film stack of claim 1 , wherein the metal layer comprises copper, silver, or nickel.
5. The electroceramic thin film stack of claim 1 , wherein the metal has a contact angle of less than 120° on the ZnO.
6. The electroceramic thin film stack of claim 1 , wherein the metal has a work of adhesion value of greater than 1 J m −2 on the ZnO.
7. The electroceramic thin film stack of claim 1 , wherein the complex oxide layer or doped complex oxide layer comprises BaTiO 3 , Pb(Zr,Ti)O 3 , SrBi 2 Ta 2 O 9 , BiFeO 3 , Bi 4 Ti 3 O 12 , or (Bi,Na)TiO 3 .
8. The electroceramic thin film stack of claim 7 , wherein the BaTiO 3 is annealed to a temperature greater than 800° C.
9. The electroceramic thin film stack of claim 7 , wherein the Pb(Zr,Ti)O 3 is annealed to a temperature greater than 600° C.
10. The electroceramic thin film stack of claim 7 , wherein the doped complex oxide layer comprises BaTiO 3 doped with one or more dopants selected from the group consisting of Sr, Ca, Zr, Sn, Mn, Mg, Al, and Y.
11. The electroceramic thin film stack of claim 7 , wherein the doped complex oxide layer comprises Pb(Zr,Ti)O 3 doped with one or more dopants selected from the group consisting of La, Dy, Nd, Ta, Sn, Sr, and Ba.
12. The electroceramic thin film stack of claim 1 , wherein the complex oxide layer or doped complex oxide layer is annealed.
13. The electroceramic thin film stack of claim 12 , wherein the complex oxide layer or doped complex oxide layer that is annealed at a sufficiently high temperature to achieve bulk-like behavior of the complex oxide or doped complex oxide.
14. The electroceramic thin film stack of claim 13 , wherein the bulk-like behavior comprises a remanent ferroelectric polarization of greater than 23 μC cm −2 .
15. The electroceramic thin film stack of claim 13 , wherein the bulk-like behavior comprises a peak permittivity of greater than about 1600.
16. The electroceramic thin film stack of claim 12 , wherein the complex oxide layer or doped complex oxide layer is annealed to a temperature of greater than 700° C.
17. A method of preparing an electroceramic thin film stack, comprising:
providing a silicon substrate;
depositing a ZnO buffer layer on the silicon substrate;
depositing a metal layer on the ZnO buffer layer;
depositing a complex oxide layer on the metal layer; and
annealing the stack at a sufficiently high temperature to achieve bulk-like behavior of the complex oxide.
18. The method of claim 17 , wherein the complex oxide layer comprises Pb(Zr,Ti)O 3 and the annealing temperature is greater than 600° C.
19. The method of claim 18 , wherein the bulk-like behavior comprises a remanent ferroelectric polarization of greater than 23 μC cm 2 .
20. The method of claim 18 , wherein the bulk-like behavior comprises a peak permittivity of greater than about 1600.
21. The method of claim 17 , wherein the complex oxide layer comprises BaTiO 3 and the annealing temperature is greater than 800° C.
22. The method of claim 21 , wherein the bulk-like behavior comprises a peak permittivity of greater than about 1380.