Reducing orthotropic strain fluctuations in quantum dot devices by gate-layer stacking

Strain-induced fluctuations in the potential energy landscape can interfere with the electrostatic confinement of silicon quantum dots. These meV-scale variations may cause unintentional quantum dots or alter exchange interactions between neighboring qubits. More broadly, the interplay between material properties, oxide thickness, and gate-stack design can create counterintuitive strain profiles—for instance, thicker oxides between closely spaced gates can amplify short-range potential fluctuations. Understanding and mitigating these effects is therefore essential for scalability.

In this work, we present simulations showing that careful engineering can suppress such fluctuations. We study strain-induced energy variations in Si/SiGe heterostructures arising from (i) lattice mismatch, (ii) materials-dependent thermal contraction, and (iii) depositional stress in the metal gates. Simulations across a range of gate geometries show that optimizing gate and oxide thicknesses can minimize strain-induced energy fluctuations.

In this work, we model the heterostructure using an orthotropic elastic tensor rather than the commonly assumed isotropic one, finding up to 21.7% differences in strain fields, indicating the need for orthotropic models in accurate device simulations.