Automated calibration of logarithmic current-to-voltage amplifiers for wide-dynamic-range scanning tunneling microscopy measurements

Logarithmic current-to-voltage amplifiers are widely used in scanning tunneling microscopy and break-junction measurements to accommodate the large and rapidly varying current range of nanoscale junctions, but their practical input–output conversion functions deviate from ideal logarithmic behavior and drift with temperature and time, requiring accurate calibration. Manual calibration procedures based on resistor switching are slow, sparse, and prone to systematic error. We present a fully automated calibration framework based on a relay-controlled precision resistor array and real-time data acquisition, which generates dense current–voltage datasets spanning 0.1 pA to 100 mA and extracts the conversion function using an iterative residual-controlled fitting procedure. A sixth-order polynomial model combined with a linear ultra-low-current correction provides a continuous and accurate description of the amplifier response over the dynamic range. Systematic optimization of scan rate, fitting order, and blending parameters yields a robust balance between calibration accuracy and efficiency. Compared with manual calibration, the automated approach suppresses switching-induced artifacts, improves reproducibility, and significantly reduces fitting residuals. Validation using scanning tunneling microscopy break-junction measurements and current–voltage characteristics shows accurate reproduction of the Au–Au atomic contact conductance and symmetric conductance–voltage characteristics. A software-based recalibration and parameter-sharing scheme further enables long-term stability under environmental drift.