Hydrogen-Free Amorphous Silicon Films for Superconducting Qubit Coherence
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Solution Overview
Problem
Superconducting qubits face decoherence issues due to dielectric loss from two-level tunneling systems (TLS) in amorphous dielectric thin films used as insulating layers, which limits their coherence time and performance.
Innovation Solution
High-density hydrogen-free amorphous dielectric insulating thin films, such as amorphous silicon, are produced by electron beam deposition at high substrate temperatures and low pressures, reducing the density of TLS and minimizing decoherence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If amorphous dielectric thin films are used as insulating layers in superconducting qubits, then the qubits can be fabricated using standard integrated circuits techniques, but the two-level tunneling systems (TLS) in the amorphous films cause dielectric loss and decoherence
Solution Approach 1:
The patent changes the physical and chemical parameters of the amorphous dielectric material by eliminating hydrogen content and increasing mass density to at least 90% of the crystalline counterpart. This parameter transformation reduces TLS density while maintaining the amorphous phase, thereby resolving the contradiction between ease of manufacture and reliability.
Solution Approach 2:
The patent employs composite material strategies by creating hydrogen-free amorphous silicon with high mass density, combining the fabrication advantages of amorphous materials with the low-TLS properties achieved through compositional modification. This composite approach maintains manufacturability while improving coherence time.
2Reliability
If hydrogenated amorphous silicon is prepared by hot-wire chemical vapor deposition to reduce TLS, then TLS content is reduced, but the material is difficult to prepare and TLS content is hard to control reproducibly
Solution Approach 1:
The patent changes the deposition parameters by using electron beam evaporation instead of hot-wire CVD, and by depositing at high substrate temperatures (300-450°C). These parameter changes produce hydrogen-free amorphous silicon with high mass density and low TLS content that is reproducible and easier to manufacture.
Solution Approach 2:
The patent extracts hydrogen from the amorphous silicon structure by preparing hydrogen-free material through electron beam evaporation. This extraction of the harmful hydrogen component eliminates the source of TLS while maintaining the amorphous phase, resolving the contradiction between TLS reduction and manufacturing ease.
3Reliability
If the dielectric layer thickness is reduced to minimize TLS impact, then the relative impact of TLS is reduced, but the device size must be made larger to maintain performance
Solution Approach 1:
The patent changes the material properties by increasing mass density to at least 90% of the crystalline counterpart, which reduces TLS density within the dielectric layer. This allows maintaining thin dielectric layer thickness without requiring larger device sizes, as the high-density material inherently provides lower TLS content and reduced dielectric loss.
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 approach results in a significant reduction of TLS density, leading to improved quantum coherence times and reduced dielectric loss, making the films suitable for use in superconducting qubits without the need for hydrogen.
Implementation Method 1
The films are prepared by deposition of a dielectric material on a substrate having a high substrate temperature Tsub just below the temperature at which the material exhibits crystalline states, the deposition being in a high vacuum (low pressure) environment, e.g., about 1×10−7 to about 1×10−11 Torr, and at a low deposition rate, e.g., less than about 0.1 nm/sec
Data Source
AI summary
A hydrogen-free amorphous dielectric insulating film having a high material density and a low density of tunneling states is provided. The film is prepared by e-beam deposition of a dielectric material on a substrate having a high substrate temperature Tsub under high vacuum and at a low deposition rate. In an exemplary embodiment, the film is amorphous silicon having a density greater than about 2.18 g/cm3 and a hydrogen content of less than about 0.1%, prepared by e-beam deposition at a rate of about 0.1 nm/sec on a substrate having Tsub=400° C. under a vacuum pressure of 1×10−8 Torr.