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

We aim to map the strain around spin CMOS compatible spin qubits at cryogenic temperature by Scanning Xray Diffraction Microscopy (SXDM). The qubits are housed in an epitaxial Si/SiGe quantum well with lithograpically fabricated TiN electrodes on top. Spin qubits qubits are operated at temperatures T close to 0 K, while the local strains in the device will vary with T due to the different coefficients of thermal expansions of TiN compared to Si and SiGe. Strain fluctuations are expected to cause variations in the local electromagnetic potential in the QW, which will strongly influence the qubit performance. Thus SXDM measurements at low T, which are performed on a sample in a He-flow cryostat are necessary to determine the strain distribution during qubit operation. We will compare the experimental results with Finite Element (FEM) simulations based on an edge-force model, which will provide valuable insight for designing large qubit arrays with uniform properties.