Towards improved spin qubit quality: Low temperature determination of strain fluctuations in Si/SiGe induced by metal surface electrodes

We aim to investigate the strain fluctuations induced by TiN electrodes in epitaxial Si/SiGe quantum well (QW) heterostructures for housing of spin qubits. For this, we employ Scanning Xray Diffraction Microscopy (SXDM) at low temperature. Strain fluctuations are expected to cause variations in the local electromagnetic potential in the QW, which will strongly influence the qubit performance. Qubits are operated at cryogenic temperatures, while the strain is dependent on temperature due to the different coefficients of thermal expansion. Thus measurements at low temperature are necessary to determine the strain distribution which will affect the qubit. We will compare the experimental results with Finite Element (FEM) simulations based on an edge-force model. We have chosen TiN as an electrode material because it is commonly used in CMOS processes, which are suitable due to their technological maturity to fabricate large arrays of qubits with homogenous properties.