Buried electrode geometry for lowering surface losses in superconducting microwave circuits

Patent metadata

Field	Value
Publication number	US-10546992-B2
Application number	US-201816021202-A
Country	US
Kind code	B2
Filing date	Jun 28, 2018
Priority date	Jun 28, 2018
Publication date	Jan 28, 2020
Grant date	Jan 28, 2020

Abstract

Embodiments are directed to a superconducting microwave circuit. The circuit includes a substrate and two electrodes. The latter form an electrode pair dimensioned so as to support an electromagnetic field, which allows the circuit to be operated in the microwave domain. The substrate exhibits a raised portion, which includes a top surface and two lateral surfaces. The top surface connects the two lateral surfaces, which show respective undercuts (on the lateral sides of the raised portions). Each of the electrodes includes a structure that includes a potentially superconducting material. Two protruding structures are accordingly formed, which are shaped complementarily to the respective undercuts. This way, the shaped structure of each of the electrodes protrudes toward the other one of the electrodes of the pair.

First claim

What is claimed is:

1. A superconducting microwave circuit comprising:
a substrate having a raised portion, which includes a top surface and two lateral surfaces, wherein the top surface connects the two lateral surfaces, the two lateral surfaces comprising respective undercuts; and
two electrodes forming an electrode pair, wherein:
each of the two electrodes comprises a structure that includes a potentially superconducting material and is shaped complementarily to a respective one of the undercuts, so as to protrude toward another one of the two electrodes, thereby forming two protruding structures,
the electrode pair is dimensioned so as to support an electromagnetic field that allows the circuit to be operated in the microwave domain,
a maximal extension of the two protruding structures is between 200 nm and 100 μm, wherein the maximal extension is measured perpendicularly to the top surface.

2. The superconducting microwave circuit according to claim 1 , wherein the undercuts extend parallel to each other along the two lateral surfaces of the raised portion and extend parallel to the top surface of the raised portion.

3. The superconducting microwave circuit according to claim 1 , wherein the substrate comprises n raised portions, n≥2, each of the n raised portions structured as the raised portion, so as to form n electrode pairs.

4. The superconducting microwave circuit according to claim 1 , wherein the raised portion has one or more bifurcations in-plane with the substrate, the bifurcations give rise to at least three raised portions in a cross-sectional plane perpendicular to each of the top surface and the lateral surfaces.

5. The superconducting microwave circuit according to claim 4 , wherein:
the circuit is a quantum processing device that comprises a superconducting qubit that includes a pair of capacitor plates coupled via a Josephson junction,
the raised portion of the substrate is structured so as for the two electrodes thereof to couple with the capacitor plates, the raised portion exhibiting undercut portions extending along the capacitor plates, and
the Josephson junction is formed in a layer of potentially superconducting material extending between the capacitor plates, from one of the undercut portions to an opposite one of the undercut portions.

6. The superconducting microwave circuit according to claim 5 , wherein the Josephson junction is formed in a layer portion of the layer of potentially superconducting material, in which the layer portion extends flat from the one of the undercut portions to the opposite one of the undercut portions, such that the Josephson junction is recessed with respect to the top surface of the raised portion.

7. The superconducting microwave circuit according to claim 1 , wherein the protruding structure of each of the two electrodes is a convex structure.

8. The superconducting microwave circuit according to claim 7 , wherein each of the two electrodes is structured so as to form a single convex structure.

9. The superconducting microwave circuit according to claim 7 , wherein the convex structure has a rounded shape.

10. The superconducting microwave circuit according to claim 7 , wherein:
the two electrodes comprise opposite portions, which are substantially symmetric under reflection through a bisecting plane of the opposite portions,
the opposite portions include, each, a respective one of the protruding structures, and
the bisecting plane is perpendicular to the top surface.

11. The superconducting microwave circuit according to claim 7 , wherein the undercuts are, each, offset from the top surface, so as to define, for each of the electrodes, a spacing portion that extends from the top surface, the convex structure of each of the electrode being at an end of the spacing portion, so as to be distinctly offset from the top surface.

12. The superconducting microwave circuit according to claim 11 , wherein a tip of each of the convex structures is offset from said top surface by a distance that is between 200 nm and 100 μm.

13. A superconducting microwave circuit comprising:
a substrate having a raised portion, which includes a top surface and two lateral surfaces, wherein the top surface connects the two lateral surfaces, the two lateral surfaces comprising respective undercuts; and
two electrodes forming an electrode pair, wherein:
each of the two electrodes comprises a structure that includes a potentially superconducting material and is shaped complementarily to a respective one of the undercuts, so as to protrude toward another one of the two electrodes, thereby forming two protruding structures,
the electrode pair is dimensioned so as to support an electromagnetic field that allows the circuit to be operated in the microwave domain,
the substrate comprises n raised portions, n≥2, each of the n raised portions structured as the raise portion, so as to form n electrode pairs, and
n=2, the circuit further comprising a coplanar waveguide that comprises a conducting track and a pair of return conductors on either side of the track, wherein the return conductors are separated from the conducting track by respective gaps that are filled by respective ones of the n=2 raised portions, such that opposite pairs of the undercuts of the raised portions extend longitudinally along a respective one of the gaps.

14. The superconducting microwave circuit according to claim 13 , wherein the coplanar waveguide is configured in the circuit as a coplanar waveguide resonator.

15. A method of fabricating a superconducting microwave circuit, the method comprising:
providing a substrate;
patterning the substrate to obtain a raised portion, which includes a top surface and two lateral surfaces, wherein the top surface connects the two lateral surfaces, the two lateral surfaces comprising respective undercuts; and
complementarily patterning two electrodes to form an electrode pair, wherein
each of the two electrodes comprises a structure that includes a potentially superconducting material and is shaped complementarily to a respective one of the undercuts, so as to protrude toward another one of the two electrodes, thereby forming two protruding structures,
the electrode pair is dimensioned so as to support an electromagnetic field that allows the superconducting microwave circuit to be operated in the microwave domain, and
patterning the substrate comprises forming opposite, concave undercuts, so as to form the protruding structures subsequently patterned to form convex structures.

16. The method according to claim 15 , wherein forming the opposite, concave undercuts is carried out by etching an oxide mask deposited on the substrate and subsequently etching, isotropically, the substrate with the etched oxide mask.

17. The method according to claim 15 , wherein patterning the substrate further comprises, after forming the opposite undercuts, partly coating the patterned substrate with a layer of the potentially superconducting material.

18. The method according to claim 17 , wherein patterning the substrate further comprises, after partly coating the patterned substrate, depositing an electrically conducting material on top of the layer of potentially superconducting material.

Assignees

• IBM

Inventors

• Fuhrer Andreas
• Kuhlmann Andreas
• Drechsler Ute
• Deshpande Veeresh V
• FILIPP Stefan
• Ganzhorn Marc

Classifications

• H01P3/08

  Microstrips; Strip lines · CPC title

• H01L39/025 Primary

  Electricity · mapped topic

• H01L39/223

  Electricity · mapped topic

• G06N10/00

  Quantum computing, i.e. information processing based on quantum-mechanical phenomena · CPC title

• H01L39/2493

  Electricity · mapped topic