## 3 Results
### Devices Featuring Ni-ALD Dielectric-Ni Junctions
#### 3.2.1 SET Devices with Ni-SiO\({}_{2}\)-Ni Tunnel Junctions
Figure 9: Scanning electron micrograph of a Ni-SiO\({}_{2}\)-Ni device where strong agglomeration occurs after a forming gas anneal (FGA) at 400 \({}^{\circ}\)C for 30 min leading to the breaks in the source and drain electrodes (nearly horizontal broken lines). Because of the detrimental effects on device performance associated with FGA, hydrogen plasma treatment has been investigated as an alternative way to reduce NiO [43; 44]. This technique has the advantages of using a lower temperature and less time than FGA, and simultaneously passivating the defects residing in the tunnel barrier dielectric [45]. With plasma, various hydrogen species (H\({}^{+}\), H, H\({}_{2}\)\({}^{-}\)) capable of reacting with NiO are introduced into the process. The remote radio frequency hydrogen plasma (RHP) source in the chamber of the Oxford FlexAl PEALD reactor enables this in-situ treatment of the as-prepared dielectric film. To investigate this technique, following fabrication of the island and 12 cycles of PEALD SiO\({}_{2}\) (\(\sim\)1.1 nm), the sample was subjected to RHP (pressure of 10 mTorr, plasma power of 100 W at 300 \({}^{\circ}\)C) for 5 min, followed by definition of the source and drain electrodes using EBL as described above. The resulting average room temperature differential conductance (0.1 \(\upmu\)S) was higher than any of the devices prepared with _two_ FGA reduction steps and it had a broader distribution of conductance values within a batch. Despite larger conductance values at 300 K, at low temperature (\(<\)10 K) devices in which the ALD dielectric was exposed to RHP exhibit a monotonic increase of conductance with applied bias at \(\mid V_{ds}\mid>\)\(E_{C}/e\) and a conductance \(G(V_{ds}\) = 0 mV) \(<<G_{0}/2\) significantly lower than expected at the peaks of CBOs (Figure 11a). Once again, this behavior is indicative of residual NiO at the interface of the oxide and top metal where thermal activation may become a limiting factor in conductance, as mentioned previously. Similar to the previously discussed devices (Figures 7b and 10b), a high level of RTS noise was also observed in CBO characteristics of these devices (Figure 11b). To achieve a more complete reduction of residual NiO in the tunnel junctions, a second RHP treatment was performed on the completed devices for 5 min under identical conditions. This treatment increased the conductance further, from an average \(\sim\)0.1 \(\upmu\)S to \(\sim\)3 \(\upmu\)S at 300 K, the highest average conductance among all fabricated batches. We attribute this relatively high conductance, observed both before and after the final RHP treatment, to hydrogen-plasma induced thinning of the PEALD dielectric during the time when the uncovered tunnel barrier is subjected to the first RHP step [46]. At low temperature the majority of devices subjected to two consecutive RHP exhibit significantly improved SET characteristics (Figure 12a), most notably, with a very strong suppression of RTS noise at \(V_{ds}\sim\)0, as compared to the single RHP treated devices in Figure 11, or FGA treated devices (Figures 7 and 10). However, in the peaks of the CBOs, the conductance still remains noticeably lower than expected (\(G<<G_{0}/2\)) and the \(G(V_{ds})\) characteristic still exhibits signs of non-linearity even at \(\mid V_{ds}\mid>>E_{C}/e\) evidently due to incomplete reduction of NiO (Figure 12a). Figure 10: (a) Typical \(G(V_{ds})\) dependence observed in samples fabricated with two FGA steps; \(T\) = 0.4 K. The metal is Ni and the barrier composition is six cycles of ALD SiO\({}_{2}\) (\(\sim\)0.7 nm) and four cycles of ALD Al\({}_{2}\)O\({}_{3}\) (\(\sim\)0.4 nm) so the total barrier thickness is \(\sim\)1.1 nm; (b) \(G(V_{g})\) dependence for the same SET, showing the excess switching noise. Furthermore, above a certain voltage threshold \(V_{Th}\)\(\sim\)5\(E_{C}/e\), a very large noise \"floods\" the measurement bandwidth to the point that it exceeds the ability of a lock-in amplifier to reject the incoherent signals (Figure 13a).