A-axis Josephson junctions with improved smoothness
According to various implementations of the invention, high quality a-axis XBCO may be grown with low surface roughness. According to various implementations of the invention, low surface roughness may be obtained by: 1) adequate substrate preparation; 2) calibration of flux rates for constituent atoms; and/or 3) appropriate control of temperature during crystal growth. According to various implementions of the invention, a wafer comprises a smoothing layer of c-axis XBCO; a first conducting layer of a-axis XBCO formed on the smoothing layer; an insulating layer formed on the first conducting layer; and a second conducting layer of a-axis XBCO formed on the insulating layer, where, for a same surface roughness, a thickness of the smoothing layer and the first conducting layer combined is greater than a thickness of the first conducting layer without the smoothing layer. According to various implementations of the invention, a Josephson Junction is etched out of the XBCO/insulating layer/XBCO trilayer by: ion mill etching the top XBCO layer and some of the insulating layer to intentionally leave some of the insulating layer on the bottom XBCO layer; and/or ion mill etching at least the insulating layer at an off angle to reduce or minimize ion damage to the bottom XBCO layer otherwise introduced by the ion mill.
1 . A method of etching a trilayer having a top YBCO layer, a PBCO layer, and a bottom YBCO layer, each layer having its own thickness, the method comprising:
etching a portion of the top YBCO layer of the trilayer via ion milling to substantially remove the thickness of the portion of the top YBCO layer; and
etching the PBCO layer of the trilayer underlying the etched portion of the top YBCO layer via ion milling to remove any remaining thickness of the etched portion of the top YBCO layer and to remove some but not all of the thickness of the underlying PBCO layer,
wherein the etching of the PBCO layer is at an ion mill etching angle less than that for the etching of the top YBCO layer.
2 . The method of claim 1 , wherein etching a portion of the top YBCO layer via ion milling to substantially remove the thickness of the portion of the top YBCO layer comprises etching the thickness of the portion of the top YBCO layer via ion milling at an ion mill etch angle of 90° to substantially remove the thickness of the portion of the top YBCO layer.
3 . The method of claim 1 , wherein etching the PBCO layer of the trilayer underlying the etched portion of the top YBCO layer via ion milling to remove any remaining thickness of the etched portion of the top YBCO layer and to remove some but not all of the thickness of the underlying PBCO layer comprises etching the underlying portion of the PBCO layer via ion milling without introducing additional ion damage to the bottom YBCO layer of the trilayer.
4 . The method of claim 1 , wherein etching the PBCO layer of the trilayer underlying the etched portion of the top YBCO layer via ion milling to remove any remaining thickness of the etched portion of the top YBCO layer and to remove some but not all of the thickness of the underlying PBCO layer comprises etching the underlying PBCO layer via ion milling at an ion mill etch angle less than 90°.
5 . The method of claim 4 , wherein etching the underlying PBCO layer via ion milling at an ion mill etch angle less than 90° comprises etching the underlying PBCO layer via ion milling at an ion mill etch angle between 30° and 70°.
6 . The method of claim 4 , wherein etching the underlying PBCO layer via ion milling at an ion mill etch angle less than 90° comprises etching the underlying PBCO layer via ion milling at an ion mill etch angle between 40° and 60°.
7 . The method of claim 1 , wherein etching the PBCO layer of the trilayer underlying the etched portion of the top YBCO layer via ion milling to remove any remaining thickness of the etched portion of the top YBCO layer and to remove some but not all of the thickness of the underlying PBCO layer comprises etching the underlying PBCO layer via ion milling at an off angle.
8 . The method of claim 1 , wherein the top YBCO layer comprises a-axis YBCO and the bottom YBCO layer comprises a-axis YBCO.
9 . A method for fabricating a Josephson Junction out of a trilayer having a top YBCO layer, a PBCO layer, and a bottom YBCO layer, each layer having its own thickness, the method comprising:
etching a portion of the top YBCO layer of the trilayer via ion milling to substantially remove the thickness of the portion of the top YBCO layer; and
etching the PBCO layer of the trilayer underlying the etched portion of the top YBCO layer via ion milling to remove any remaining thickness of the etched portion of the top YBCO layer and to remove some but not all of the thickness of the underlying PBCO layer,
wherein the etching of the PBCO layer is at an ion mill etching angle less than that for the etching of the top YBCO layer.
10 . The method of claim 9 , wherein etching a portion of the top YBCO layer via ion milling to substantially remove the thickness of the portion of the top YBCO layer comprises etching the thickness of the portion of the top YBCO layer via ion milling at an ion mill etch angle of 90° to substantially remove the thickness of the portion of the top YBCO layer.
11 . The method of claim 9 , wherein etching the PBCO layer of the trilayer underlying the etched portion of the top YBCO layer via ion milling to remove any remaining thickness of the etched portion of the top YBCO layer and to remove some but not all of the thickness of the underlying PBCO layer comprises etching the underlying portion of the PBCO layer via ion milling without introducing additional ion damage to the bottom YBCO layer of the trilayer.
12 . The method of claim 9 , wherein etching the PBCO layer of the trilayer underlying the etched portion of the top YBCO layer via ion milling to remove any remaining thickness of the etched portion of the top YBCO layer and to remove some but not all of the thickness of the underlying PBCO layer comprises etching the underlying PBCO layer via ion milling at an off angle.
13 . The method of claim 9 , wherein etching the PBCO layer of the trilayer underlying the etched portion of the top YBCO layer via ion milling to remove any remaining thickness of the etched portion of the top YBCO layer and to remove some but not all of the thickness of the underlying PBCO layer comprises etching the underlying PBCO layer via ion milling at an ion mill etch angle less than 90°.
14 . The method of claim 13 , wherein etching the underlying PBCO layer via ion milling at an ion mill etch angle less than 90° comprises etching the underlying PBCO layer via ion milling at an ion mill etch angle between 30° and 70°.
15 . The method of claim 13 , wherein etching the underlying PBCO layer via ion milling at an ion mill etch angle less than 90° comprises etching the underlying PBCO layer via ion milling at an ion mill etch angle between 40° and 60°.
16 . The method of claim 9 , wherein the top YBCO layer comprises a-axis YBCO and the bottom YBCO layer comprises a-axis YBCO.
17 . A method for fabricating a Josephson Junction out of a trilayer having a top YBCO layer, a PBCO layer, and a bottom YBCO layer, each layer having its own thickness, the method comprising:
etching a portion of the top YBCO layer of the trilayer via ion milling at an ion mill etch angle of 90° to substantially remove the thickness of the portion of the top YBCO layer; and
etching the PBCO layer of the trilayer underlying the etched portion of the top YBCO layer via ion milling at an ion mill etch angle of less than 90° to remove any remaining thickness of the etched portion of the top YBCO layer and to remove some but not all of the thickness of the underlying PBCO layer.
18 . The method of claim 17 , wherein etching the underlying PBCO layer via ion milling at an ion mill etch angle less than 90° comprises etching the underlying PBCO layer via ion milling at an ion mill etch angle between 30° and 70°.
19 . The method of claim 17 , wherein etching the underlying PBCO layer via ion milling at an ion mill etch angle less than 90° comprises etching the underlying PBCO layer via ion milling at an ion mill etch angle between 40° and 60°.
20 . The method of claim 17 , wherein the top YBCO layer comprises a-axis YBCO and the bottom YBCO layer comprises a-axis YBCO.