Opposite-Face Electrostatic Gates for Spin Qubit Potential Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing quantum devices face challenges in accurately controlling the height of tunnel barriers and minimum potential of quantum dots due to material degradation from residual dopants and high defect densities at interfaces, and capacitive coupling issues with conventional electrostatic control gates, which are not suitable for cryogenic environments.
Innovation Solution
The arrangement of electrostatic control gates on opposite sides of a semiconductor portion allows for independent modulation of maximum and minimum potential energy levels, using separate gate dielectrics made by thermal oxidation, reducing material degradation and capacitive coupling, and enabling precise control with dimensions compatible with quantum devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If control gates are positioned directly above each quantum dot and tunnel barrier with pitch between 40 nm and 160 nm, then independent control of quantum dot potential and tunnel barrier height is achieved, but material degradation from residual dopants and high interface defect densities occur
Solution Approach 1:
The patent positions control gates on both the front and back faces of the semiconductor substrate, utilizing the third dimension (depth/thickness) to resolve the contradiction. Front-facing gates control quantum dot potentials while back-facing gates control tunnel barrier heights, enabling independent control without requiring high-density lateral gate arrangements that cause material degradation.
Solution Approach 2:
The control function is segmented between front and back gates. Front gates are dedicated to controlling quantum dot minimum potentials, while back gates are dedicated to controlling tunnel barrier maximum potentials. This functional segmentation eliminates the need for gates to be positioned in close proximity, reducing material degradation from residual dopants and interface defects.
2Measurement precision
If conventional electrostatic control gates are used with small pitch (40-160 nm), then accurate control of quantum dot and barrier potentials is achieved, but capacitive coupling between adjacent gates increases
Solution Approach 1:
By moving some control gates to the back face of the substrate, the patent increases the physical separation between gates that control different functions (quantum dot potential vs. tunnel barrier height). This spatial separation in the third dimension reduces capacitive coupling between gates while maintaining accurate potential control through the electrostatic field penetrating the substrate.
3Reliability
If thermal oxidation is used to make gate dielectrics, then defect density is reduced to 10^10 defects/eV/cm^2, but manufacturing complexity increases compared to plasma oxidation
Solution Approach 1:
The patent extracts the gate dielectric formation process from the conventional plasma oxidation method and replaces it with thermal oxidation. This extraction allows the use of a simpler, more reliable thermal oxidation process that produces lower defect densities at the silicon-dielectric interface, improving device reliability despite the need for separate front and back gate processing.
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
This configuration enables accurate control of tunnel barriers and quantum dot potentials with 100 μV precision, minimizing material degradation and capacitive coupling, suitable for quantum devices operating at any temperature, including cryogenic conditions.
Implementation Method 1
a first electrostatic control gate disposed in direct contact with the first region of the semiconductor portion, configured to control a minimum potential energy level in the first region
Implementation Method 2
second electrostatic control gates, each disposed in direct contact with one of the second regions of the semiconductor portion and configured to control a maximum potential energy level in one of the second regions
Implementation Method 3
at least one first gate dielectric disposed in direct contact with a first face of the semiconductor portion, between the first face and the first portion of electrically conductive material
Data Source
AI summary
A spin qubit quantum device includes a semiconductor portion having a first region disposed between two second regions; a first control gate disposed in direct contact with the first region and configured to control a minimum potential energy level in the first region, and disposed in direct contact with a first face of the semiconductor portion; and second electrostatic control gates, each disposed in direct contact with one of the second regions and configured to control a maximum potential energy level in one of the second regions, and disposed in direct contact with a second face, opposite to the first face, of the semiconductor portion, The first gate is not aligned with the second gates.