NIS Cooler With Aluminum Oxide Insulators for Quasi-Particle Overheating
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Solution Overview
Problem
Current NIS coolers have a limited temperature throw due to the accumulation of non-equilibrium quasi-particles in superconducting leads, leading to severe overheating, which is not effectively addressed by existing methods.
Innovation Solution
A solid-state cooler device is developed using a normal metal-insulator-superconductor (NIS) junction with thin aluminum oxide layers as insulators, where a bias voltage is applied to remove hot electrons across the junctions, facilitating efficient heat removal and preventing heat return to the normal metal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a bias voltage is applied to remove hot electrons across the NIS junction, then cooling efficiency is improved, but severe overheating occurs in the superconducting electrodes due to accumulated non-equilibrium quasi-particles
Solution Approach 1:
A normal metal layer is introduced as an intermediary between the superconducting electrode and the NIS junction. This normal metal layer acts as a quasi-particle trap, accepting non-equilibrium quasi-particles from the superconductor and allowing them to relax their energy through electron-electron and electron-phonon interactions. This mediator prevents the accumulation of hot quasi-particles in the superconducting electrode, thereby preventing severe overheating while maintaining the cooling function of the NIS junction.
Solution Approach 2:
The invention changes the physical state and properties of the superconducting electrode by introducing a normal metal layer with different electronic properties. This layer has a normal metal density of states rather than a superconducting gap, fundamentally changing how quasi-particles behave at the interface. The parameter change from superconducting to normal metal state creates an effective sink for hot quasi-particles, resolving the overheating problem.
2Temperature
If NIS coolers are used for solid-state electron cooling, then cooling function is achieved below 1K, but the temperature throw is limited to maximum 150 mK
Solution Approach 1:
The normal metal layer serves as a mediator that enables more efficient heat removal from the superconducting electrode. By trapping quasi-particles and facilitating their energy relaxation, the normal metal layer prevents the buildup of thermal energy that limits temperature throw. This intermediary mechanism allows the NIS cooler to achieve larger temperature differences between hot and cold sides, extending the temperature throw beyond the conventional 150 mK limit.
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 device achieves enhanced cooling efficiency by effectively removing heat from the cold side and preventing heat return, allowing for cooling down to milliKelvin temperatures with improved temperature difference across the refrigeration stages.
Implementation Method 1
Solid-state electron cooling by the tunneling of 'hot' electrons across a normal metal-insulator-superconductor (NIS) junction
Implementation Method 2
Solid-state electron cooling by the tunneling of 'hot' electrons across a normal metal-insulator-superconductor (NIS) junction, using a bias voltage
Implementation Method 3
performing an oxidization process on the aluminum layer to form an aluminum oxide layer overlying the aluminum layer
Data Source
AI summary
A solid state cooler device is disclosed that comprises a first normal metal pad, a first aluminum layer and a second aluminum layer disposed on the first normal metal pad and separated from one another by a gap, a first aluminum oxide layer formed on the first aluminum layer, and a second aluminum oxide layer formed on the second aluminum layer, and a first superconductor pad disposed on the first aluminum oxide layer and a second superconductor pad disposed on the second aluminum oxide layer. The device further comprises a first conductive pad coupled to the first superconductor pad, and a second conductive pad coupled to the second superconductor pad, wherein hot electrons are removed from the first normal metal pad when a bias voltage is applied between the first conductive pad and the second conductive pad.