Al-Al₂O₃-Al Tunnel-Junction-Array Coulomb Blockade Thermometers

Reliable electron thermometry is essential for millikelvin quantum-transport experiments, where weak electron-phonon coupling makes the electron temperature highly susceptible to residual heat loads. We report Al-Al₂O₃-Al tunnel-junction-array Coulomb blockade thermometers (CBTs) that enable wide-range, on-chip electron thermometry compatible with high magnetic fields. The fabricated multi-junction devices exhibit well-defined Coulomb-blockade conductance dips, an enhanced operating voltage range, and robust performance in magnetic fields up to 10 T after the Al electrodes are driven into the normal state. By combining measurements from distinct CBT devices optimized with different charging energies and thermalization structures, we demonstrate reliable electron thermometry over a broad temperature range from approximately 30 mK to 3 K. The observed saturation of the electron temperature at the lowest temperatures indicates residual electron overheating, highlighting thermalization and parasitic-heat control as the key constraints for millikelvin thermometry. These results demonstrate that Al-Al₂O₃-Al CBT arrays constitute a practical and reliable platform for wide-range, magnetic-field-compatible on-chip electron thermometry, with broad applications in mesoscopic physics, quantum-material research, and cryogenic metrology.