Well thermalized microstrip formation for flexible cryogenic microwave lines in quantum applications
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Solution Overview
Problem
Current microstrips are not suitable for quantum computing applications due to poor thermalization, high crosstalk, and limited operational frequency and temperature range, which are critical issues for reliable operation of superconducting qubits at cryogenic temperatures.
Innovation Solution
A well-thermalized microstrip (q-microstrip) is developed using a polyimide film with a conductor that provides high thermal and electrical conductivity, along with a flexible structure to prevent crosstalk, and is fabricated using a copper-nickel alloy to ensure reliable bonding at cryogenic temperatures, maintaining impedance and reducing microwave interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional microstrip structures are used, then fabrication is simple, but thermalization is poor and crosstalk is high
Solution Approach 1:
The patent employs a composite structure consisting of a copper-nickel alloy conductor layer deposited on a polyimide substrate. This composite material approach enables simultaneous achievement of high thermal conductivity (from copper-nickel alloy) and high breakdown voltage (from polyimide), resolving the contradiction between simple fabrication and reliable thermalization while maintaining structural integrity at cryogenic temperatures.
Solution Approach 2:
The patent utilizes a thin polyimide film as the substrate for the microstrip conductor. This thin film structure provides mechanical flexibility and thermal isolation while maintaining electrical insulation, enabling effective thermalization of the microstrip line to the substrate without requiring complex multi-layer constructions.
2Temperature
If standard conductor materials are used, then electrical conductivity is adequate, but thermal conductivity is insufficient at cryogenic temperatures
Solution Approach 1:
The patent changes the material parameters by selecting a copper-nickel alloy with optimized composition (e.g., 70/30 or 80/20 ratio) that maintains high electrical conductivity while achieving superior thermal conductivity at cryogenic temperatures. This parameter optimization resolves the contradiction between electrical and thermal performance in the conductor material.
3Area of stationary object
If microstrip lines are placed close together, then space is efficient, but crosstalk increases above acceptable levels
Solution Approach 1:
The patent introduces the polyimide substrate as an intermediary layer between adjacent microstrip lines. This substrate material with high breakdown voltage and appropriate dielectric properties acts as an effective barrier that reduces electromagnetic coupling and crosstalk between closely-spaced lines, enabling compact layouts without sacrificing signal integrity.
4Reliability
If bonding is performed at room temperature, then fabrication is easier, but bonding reliability fails at cryogenic temperatures
Solution Approach 1:
The patent performs bonding operations at room temperature before cryogenic cooling, when materials are more ductile and bonding is easier to achieve. The copper-nickel alloy and polyimide substrate are bonded in the warm state, and this preliminary bonding action ensures reliable mechanical and thermal contact that persists through subsequent thermal cycling to cryogenic temperatures.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The q-microstrip achieves effective thermalization and electrical conductivity, reducing crosstalk to acceptable levels, enabling reliable operation at cryogenic temperatures and frequencies above 1 GHz, thus supporting the requirements of quantum computing environments.
Implementation Method 1
a material of the conductor provides greater than a threshold thermal conductivity (TH) with a structure of a dilution fridge stage
Implementation Method 2
a material of the conductor provides greater than a threshold electrical conductivity (TC) with an electrical component in the stage
Implementation Method 3
A well-thermalized microstrip (q-microstrip) is developed using a polyimide film with a conductor
Data Source
AI summary
A microstrip that is usable in a quantum application (q-microstrip) includes a ground plane, a polyimide film disposed over the ground plane at a first surface of the polyimide film, and a conductor formed on a second side of the polyimide film such that the first surface is substantially opposite to the second surface. A material of the conductor provides greater than a threshold thermal conductivity (TH) with a structure of a dilution fridge stage (stage). The stage is maintained at a cryogenic temperature, and the material of the conductor bonds at the cryogenic temperature with a second material of a part of a connector of a microwave line.