# US 2022/0034833 A1 · Methods and structure to probe the metal-metal interface for superconducting circuits > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2022/0034833 A1 - Document ID: US20220034833A1 - Status: Published application - Kind: A1 - Application number: 16/945,549 - Filed: 2020-07-31 - Published: 2022-02-03 - Earliest claimed: 2020-07-31 - Assignees: International Business Machines Corporation - Applicants: International Business Machines Corporation - Inventors: Christian Lavoie; Markus Brink; Benjamin Wymore; Jeng-Bang Yau - Web page: https://patentgrep.com/patent/US20220034833A1 ## CPC - G01N 27/041: {of a solid body} - G06N 10/40: Physical realisations or architectures of quantum processors or components for manipulating qubits, e.g. qubit coupling or qubit control - G01R 27/205: {Measuring contact resistance of connections, e.g. of earth connections} - G06N 10/00: Quantum computing, i.e. information processing based on quantum-mechanical phenomena - H10N 60/83: Element shape - H10N 60/80: Constructional details - G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q) - G06N: COMPUTING ARRANGEMENTS BASED ON SPECIFIC COMPUTATIONAL MODELS - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) - H10N: ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR ## Abstract A method of measuring contact resistance at an interface for superconducting circuits is provided. The method includes using a chain structure of superconductors to measure a contact resistance at a contact between contacting superconductor. The method further includes eliminating ohmic resistance from wire lengths in the chain structure by operating below the lowest superconducting transition temperature of all the superconductors in the chain structure. The measurement is dominated by contact resistances of the contacts between contacting superconductors in the chain. ## Claims ### Claim 1 A method of measuring contact resistance at an interface for electronic circuits comprising: providing a chain structure of conducting elements, the conducting elements arranged in series to contact adjacent conducting elements at respective contacts having respective contact resistances; measuring a serial resistance of the chain structure at cryogenic temperatures; and determining a contact resistance based on the measured serial resistance. ### Claim 2 A method of measuring contact resistance at an interface for superconducting circuits comprising: using a chain structure of superconductors to measure a contact resistance at a contact between contacting superconductors; eliminating ohmic resistance from wire lengths in the chain structure by operating below the lowest superconducting transition temperature of all the superconductors in the chain structure, wherein the measurement is dominated by contact resistances of the contacts between contacting superconductors in the chain. ### Claim 3 (depends on 2) The method of claim 2, wherein the superconductors of the chain structure of superconductors are made of a first superconducting material and a second superconducting material different from the first superconducting material. ### Claim 4 (depends on 3) The method of claim 3, wherein the superconductors of the chain structure of superconductors are alternately arranged between superconductors of the first superconducting material and superconductors of the second superconducting material. ### Claim 5 (depends on 2) The method of claim 2, wherein the superconducting elements of the chain structure are shaped as wires. ### Claim 6 A method of measuring contact resistance at an interface for superconducting circuits comprising: providing a chain structure of superconducting elements, the superconducting elements arranged in series to contact adjacent superconducting elements at respective contacts having respective contact resistances; operating the chain structure such that all of the superconducting elements are in a superconducting state; and measuring a serial resistance of the chain structure while all of the superconducting elements are in a superconducting state. ### Claim 7 (depends on 6) The method of claim 6, wherein a number of contacts in the chain structure depends on the resistance per contact and the measurement noise. ### Claim 8 (depends on 6) The method of claim 6, wherein the operating of the chain structure such that all of the superconducting elements are in a superconducting state comprises cooling the chain structure to a temperature below a superconducting transition temperature of all of the superconducting elements. ### Claim 9 (depends on 6) The method of claim 6, wherein the superconducting elements of the chain structure of superconducting elements are made of a first superconducting material and a second superconducting material different from the first superconducting material. ### Claim 10 (depends on 9) The method of claim 9, wherein the superconducting elements of the chain structure of superconductors are alternately arranged between superconducting elements of the first superconducting material and superconducting elements of the second superconducting material. ### Claim 11 (depends on 6) The method of claim 6, wherein the superconducting elements of the chain structure are shaped as wires. ### Claim 12 (depends on 6) The method of claim 6, wherein the number of superconducting elements of the chain structure is more than 10000. ### Claim 13 A contact resistance measuring device comprising: a chain structure of superconducting elements, the superconducting elements arranged in series to contact adjacent superconducting elements at respective contacts having respective contact resistances; and a serial resistance measuring device arranged to measure a serial resistance of the chain structure while all of the superconducting elements in the chain structure are in a superconducting state. ### Claim 14 (depends on 13) The contact resistance measuring device of claim 13, further comprising a cryostat arranged to cool the chain structure such that all of the superconducting elements are in a superconducting state. ### Claim 15 (depends on 13) The contact resistance measuring device of claim 13, wherein the chain structure further comprises a first conduction pad electrically connected to a first of the superconducting elements arranged in series and a last conduction pad electrically connected to a last of the superconducting elements arranged in series. ### Claim 16 (depends on 15) The contact resistance measuring device of claim 15, wherein the chain structure further includes a first intermediate conduction pad electrically connected to a first intermediate of the superconducting elements arranged in series and a second intermediate conduction pad electrically connected to a second intermediate of the superconducting elements arranged in series. ### Claim 17 (depends on 16) The contact resistance measuring device of claim 16, wherein the first intermediate conduction pad and the second intermediate conduction pad are adjacent to each other. ### Claim 18 (depends on 13) The contact resistance measuring device of claim 13, wherein the superconducting elements are arranged in a first group and a second group. ### Claim 19 (depends on 18) The contact resistance measuring device of claim 18, wherein each superconducting element of the first group contacts at least one superconducting element of the second group. ### Claim 20 (depends on 18) The contact resistance measuring device of claim 18, wherein the superconducting elements of the first group are alternately arranged with superconducting elements of the second group. ### Claim 21 (depends on 18) The contact resistance measuring device of claim 18, wherein the superconducting elements of at least one of the first group or the second group are all of a same length. ### Claim 22 (depends on 18) The contact resistance measuring device of claim 18, wherein the superconducting elements of the first group are arranged in a direction perpendicular to a direction the superconducting elements of the second group are arranged. ### Claim 23 (depends on 18) The contact resistance measuring device of claim 18, wherein the superconducting elements of the first group and the superconducting elements of the second group are shaped as wires, each wire having a first wire width of a first portion of the wire and a contact wire width of a second portion of the wire, the second portion of the wire contacting an adjacent wire. ### Claim 24 (depends on 23) The contact resistance measuring device of claim 23, wherein the first wire width is greater than the contact wire width for at least one of the first group or the second group. ### Claim 25 (depends on 18) The contact resistance measuring device of claim 18, further comprising a dielectric material arranged between the superconducting elements of the first group and the superconducting elements of the second group, the first group of superconducting elements contacting the second group of superconducting elements through respective holes in the dielectric material.