Stable Al-based SETs for Si-based Spin Qubit Readout

Using a novel plasma oxidation technique, we have overcome the instability problem in metal-based single electron transistors (SETs) and are fabricating stable AlOx-based SETs with the goal of improved output current and ease of measurement. While metal-based SETs were extensively studied more than 20 years ago, they were not feasible as qubit charge sensors due to instability issues. By minimizing defects in the tunnel junction through plasma oxidation, we have achieved a remarkable reduction in charge offset drift (∆Q0 = 0.13 e ± 0.01 e over 7 days), a significant improvement compared to previous literature. Therefore, we are seeking to produce aluminum-based SETs using plasma oxidation that can be coupled to Si-based quantum dots for precise charge-sensing purposes. The main deficiency in these SETs now is the limited output current at ~4 pA level, which we are aiming to increase to ~100 pA. To achieve this, we are varying the AlOx tunnel junction oxidation time from our nominal 7 s, expecting reduced time will decrease the resistance. We expect to report the results from the SET devices with varying oxidation times as well as show their long-term stability in this talk.