Characterizing Charged Defects in Oxide-on-Silicon using Kelvin Probe Force Microscopy

While silicon-based quantum dot qubits are a promising platform for quantum computing, charge noise from oxide layers below and in between the gate electrodes hinders critical improvements in qubit operations. To characterize the microscopic origin of charge noise in the gate oxide, we perform Kelvin Probe Force Microscopy (KPFM) measurements on an aluminum oxide layer grown by ALD atop bulk silicon. These experiments reveal defects in the oxide that exchange charges with the AFM tip when the tip-backgate bias voltage is swept. We repeat such scans while rastering the tip over the sample and varying the tip-sample separation. By comparing measurements with electrostatic simulations of the tip and sample system, we are able to use the measured charging voltages to extract defect energies relative to aluminum oxide’s valence band. These results will be useful for understanding a major source of charge noise in our devices and potentially improving qubit gate operations.