Charge offset drift in single electron devices containing aluminum oxide

Single electron devices (SEDs) suffer from a long-time instability, referred to as charge offset drift (ΔQ₀), that hampers integration of SEDs in applications such as quantum metrology and computing. Previous measurements of ΔQ₀ show SEDs containing aluminum oxide (AlOx) have been less stable than comparable SEDs containing only silicon dioxide (SiO2). Here, we have fabricated two different types of SEDs: all-metal Al/AlOx/Al tunnel junction-based devices and tunable barrier silicon metal-oxide-semiconductor (MOS) devices. The all-metal SEDs contain plasma-oxidized AlOx as the tunnel barrier. The charge offset stability measured on these devices is better than any other reported metallic SEDs, displaying a very small linear ΔQ₀ of 0.1e over 7.5 days and two times lower standard deviation. The MOS SEDs are made on a silicon-on-insulator (SOI) substrate with a thermal SiO2 gate oxide, Al gates, and thermal AlOx as an isolation oxide. Four of the five MOS SEDs measured show a linear charge offset drift of less than 0.07 e over 7 days and standard deviations less than 0.02 e. These results suggest the stability of devices made with AlOx may be significantly better than previously thought and that other factors, such as geometry, are playing as large a role as materials.