Single-electron charge sensor self-aligned to a quantum dot array by double-gate patterning process

The high sensitivity of a single electron transistor (SET) is essential to faithfully identify the number of electrons in a quantum dot (QD) towards a silicon-based quantum computer. The sensitivity depends on the critical dimension between the SET and the QD, which is limited by the resolution of the electron beam lithography and the layer-to-layer alignment accuracy. Here, we report integration of an SET charge sensor with a QD array by repeating the self-aligned double-gate patterning processes. This fabrication technique allowed us to place the SET adjacent to the QD array beyond the lithography resolution, enabling sensitive charge sensing. We confirm that our device can detect single electrons in the QD and demonstrate real-time detections of electron tunneling by monitoring the SET current.