Superconductor thermal filter
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Solution Overview
Problem
Current NIS coolers have limited temperature throw due to non-equilibrium quasi-particles in superconducting leads, leading to overheating, and lack effective methods to prevent phonon heat migration back to superconducting electrodes.
Innovation Solution
A superconductor thermal filter with a multilayer structure of superconductors having decreasing energy band gaps and a normal metal quasiparticle trap, combined with a bias voltage to remove hot electrons and prevent quasi-particle backflow, utilizing thermal boundary resistance mismatch to block phonon heat flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a normal metal quasiparticle trap is used to remove hot electrons, then cooling efficiency is improved, but phonon heat migration back to superconducting electrodes increases
Solution Approach 1:
The superconductor is divided into multiple layers with decreasing energy band gaps from cold side to hot side. This segmentation creates a gradient structure that allows hot electrons to be systematically removed through each layer while phonons are blocked at each interface due to thermal boundary resistance mismatch, thus resolving the contradiction between cooling efficiency and phonon heat migration.
Solution Approach 2:
Different regions of the superconductor are given different energy band gap properties. The cold side has larger band gap superconductors while the hot side has smaller band gap superconductors, creating local variations in electronic and thermal properties that enable selective transport of hot electrons while blocking phonons.
2Power
If high current is used to enhance cooling, then cooling power is improved, but non-equilibrium quasi-particles accumulate causing overheating
Solution Approach 1:
Hot electrons (non-equilibrium quasi-particles) are extracted from the superconducting electrode through the multilayer structure with decreasing energy band gaps. By providing a pathway for these hot carriers to leave the superconductor and enter the normal metal trap, the accumulation of hot quasi-particles is prevented, allowing high current operation without overheating.
Solution Approach 2:
The multilayer superconductor structure acts as an intermediary between the cold superconducting electrode and the hot normal metal trap. This intermediate structure with gradient energy band gaps facilitates the controlled removal of hot electrons while maintaining the integrity of the superconducting state, enabling high power operation without temperature runaway.
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
Enhances temperature difference between hot and cold sides by effectively removing hot electrons and phonons, reducing overheating and improving cooling efficiency in cryogenic applications.
Implementation Method 1
Solid-state electron cooling by the tunneling of 'hot' electrons across a normal metal - insulator -superconductor (NIS) junction
Implementation Method 2
a multilayer superconductor structure comprises a plurality of superconductor layers with each superconductor layer having a smaller superconducting energy band gap than the preceding superconductor
Implementation Method 3
phonon heat generated in the quasiparticle trap can migrate back to the superconducting electrodes also limiting the temperature difference
Implementation Method 4
utilizing thermal boundary resistance mismatch to block phonon heat flow
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A superconductor thermal filter (10 is disclosed that includes a normal metal layer (12) having a first side, an insulating layer (14) overlying the first side of the normal metal layer, and a multilayer superconductor structure (15) having a first side overlying a side of the insulting layer opposite the side that overlies the normal metal layer. The multilayer superconductor structure is comprised of a plurality of superconductor layers (16, 18, 20) with each superconductor layer having a smaller superconducting energy band gap than the preceding superconductor as the superconductor layers extend away from the normal metal layer. The thermal filter further includes a normal metal layer quasiparticle trap (22) having a first side and a second side with the first side being disposed on a second side of the multilayer superconductor. A bias voltage is applied between the normal metal layer and the normal metal layer quasiparticle trap to remove hot electrons from the normal metal layer.