Epitaxial growth of high quality vanadium dioxide films with template engineering
Layered oxide structures comprising an overlayer of high quality VO 2 and methods of fabricating the layered oxide structures are provided. Also provided are high-speed switches comprising the layered structures and methods of operating the high-speed switches. The layered oxide structures include high quality VO 2 epitaxial films on isostructural SnO 2 growth templates.
1. A layered oxide structure comprising:
a substrate comprising single-crystalline TiO 2 ;
an intervening layer comprising columnar, crystalline domains of rutile SnO 2 on the substrate, wherein the columnar, crystalline domains of SnO 2 have an epitaxial relationship with the single-crystalline TiO 2 ; and
an overlayer comprising crystalline domains of VO 2 on the intervening layer, wherein the crystalline domains of VO 2 have an epitaxial relationship with the columnar, crystalline domains of rutile SnO 2 ;
wherein the VO 2 has a metal-insulator phase transition critical temperature, below which the VO 2 has a monoclinic crystal structure and above which the VO 2 has a rutile crystal structure.
2. The structure of claim 1 , wherein the metal-insulator phase transition critical temperature is in the range from 339 to 343 K.
3. The structure of claim 1 , characterized in that, when the overlayer is heated from a temperature below its metal-insulator phase transition critical temperature to a temperature above its metal-insulator phase transition critical temperature, the VO 2 undergoes a phase transition from monoclinic to rutile with a transition sharpness of no greater than 2 K.
4. The structure of claim 3 , characterized in that, when the overlayer is heated from a temperature below its metal-insulator phase transition critical temperature to a temperature above its metal-insulator phase transition critical temperature, the VO 2 undergoes a phase transition from monoclinic to rutile and the electrical resistance of the overlayer decreases by at least four orders of magnitude.
5. The structure of claim 1 , characterized in that, when the overlayer is heated from a temperature below its metal-insulator phase transition critical temperature to a temperature above its metal-insulator phase transition critical temperature, the VO 2 undergoes a phase transition from monoclinic to rutile with a transition sharpness of no greater than 1 K.
6. The structure of claim 5 , characterized in that, when the overlayer is heated from a temperature below its metal-insulator phase transition critical temperature to a temperature above its metal-insulator phase transition critical temperature, the VO 2 undergoes a phase transition from monoclinic to rutile and the electrical resistance of the overlayer decreases by at least four orders of magnitude.
7. The structure of claim 1 , characterized in that, when the overlayer is heated from a temperature below its metal-insulator phase transition critical temperature to a temperature above its metal-insulator phase transition critical temperature, the VO 2 undergoes a phase transition from monoclinic to rutile and the electrical resistance of the overlayer decreases by at least four orders of magnitude.
8. The structure of claim 1 , wherein the overlayer has a thickness in the range from 100 to 500 nm.
9. The structure of claim 8 , wherein the overlayer has a thickness in the range from 200 to 400 nm.
10. A switch comprising:
a body comprising: a substrate comprising single-crystalline TiO 2 ; an intervening layer comprising columnar, crystalline domains of rutile SnO 2 , wherein the columnar, crystalline domains of SnO 2 have an epitaxial relationship with the single-crystalline TiO 2 ; and a channel layer comprising crystalline domains of VO 2 on the intervening layer, wherein the crystalline domains of VO 2 have an epitaxial relationship with the columnar, crystalline domains of rutile SnO 2 , and further wherein the VO 2 has a metal-insulator phase transition critical temperature, below which the VO 2 has a monoclinic crystal structure and above which the VO 2 has a rutile crystal structure;
a first electrically conducting contact in electrical communication with a first area of the channel layer;
a second electrically conducting contact in electrical communication with a second area of the channel layer; and
an external stimulus source configured to apply a metal-insulator phase transition-inducing external stimulus to the channel layer.
11. The switch of claim 10 , wherein the external stimulus source configured to apply a metal-insulator phase transition-inducing external stimulus to the channel layer is an external voltage source configured to apply an external voltage to the first electrically conducting contact.
12. A method of switching using the switch of claim 11 , the method comprising applying an external voltage from the external voltage source to the first electrically conducting contact, wherein the external voltage induces the VO 2 to undergo a phase transition from the electrically insulating monoclinic crystal structure to the electrically conducting rutile crystal structure.
13. A field effect switch comprising:
a body comprising: a substrate comprising single-crystalline TiO 2 ; an intervening layer comprising columnar, crystalline domains of rutile SnO 2 , wherein the columnar, crystalline domains of SnO 2 have an epitaxial relationship with the single-crystalline TiO 2 ; and a channel layer comprising crystalline domains of VO 2 on the intervening layer, wherein the crystalline domains of VO 2 have an epitaxial relationship with the columnar, crystalline domains of rutile SnO 2 , and further wherein the VO 2 has a metal-insulator phase transition critical temperature, below which the VO 2 has a monoclinic crystal structure and above which the VO 2 has a rutile crystal structure;
a source;
a drain, wherein the source and drain are connected by the channel layer;
a gate stack comprising: a gate oxide on the channel and a gate contact on the gate oxide; and
an external voltage source configured to apply a metal-insulator phase transition-inducing external voltage to the gate contact.
14. A method of switching using the switch of claim 13 , the method comprising:
applying a gate voltage from the external voltage source to the gate contact, wherein the external voltage induces the VO 2 to undergo a phase transition from the electrically insulating monoclinic crystal structure to the electrically conducting rutile crystal structure.
15. A method of making a layered oxide structure, the method comprising:
epitaxially growing a layer of columnar, crystalline domains of rutile SnO 2 , on a substrate comprising single-crystalline TiO 2 ; and
epitaxially growing an overlayer comprising crystalline domains of VO 2 on the layer of columnar, crystalline domains of rutile SnO 2 .