## 3 Results
### Devices Faturing Pt-ALD Dielectric-Pt Junctions
#### 3.1.2 O\({}_{3}\)-Based vs. H\({}_{2}\)O-Based ALD of Al\({}_{2}\)O\({}_{3}\) in SETs
Figure 7 shows the Coulomb diamond plot measured at 0.35 K for O\({}_{3}\)-based devices treated with forming gas at 90 \({}^{\circ}\)C in a single post-fabrication step. The performance of these devices, however, was hampered by unusually high levels of excess noise far exceeding Johnson and shot noise levels typical for MIM SETs [26]. This noise is identified as random telegraph signal (RTS) noise [27], a topic that will be discussed below. Figure 7b shows a series of \(G(V_{ds})\) characteristics measured in the peak of CBO at several temperatures for an O\({}_{3}\)-based device treated in forming gas. It is clear that the conductance in the peaks of CBOs, instead of saturating at a level of \(G_{0}/2\) (~55 nS in Figure 7b) as expected for MIM SETs, continues to drop with the lowering of temperature. An estimation of activation energy in the peak of blockade gives a value of less than 0.05 meV, typical for granular metals [28; 29]. This observation suggests that a thin layer of platinum oxide survived the forming gas treatment and its presence in series with the Al\({}_{2}\)O\({}_{3}\) tunnel barrier results in the weak activation behavior in the peaks of CBO at \(V_{ds}\) = 0 mV [29]. A comparison of experimental results obtained for two batches of devices featuring Pt-Al\({}_{2}\)O\({}_{3}\)-Pt junctions (Figures 3 and 7) with the exact same number of ALD cycles (nine) and similar overlap areas for the junctions shows a significant difference in charging energy. Namely, the charging energy for the H\({}_{2}\)O-based device of Figure 3 (\(E_{C}\approx\) 0.185 meV) as compared to the O\({}_{3}\)-based device of Figure 7 (\(E_{C}\approx\) 0.37 meV) was about two times smaller, while its conductance was about two orders of magnitude larger. This difference in charging energy is evidently caused by a difference in the junction capacitances and for the same area of the junctions a doubling of the dielectric thickness would result in half the capacitance and exponentially larger resistance, in reasonable agreement with the experiments. (This is admittedly just an \"order of magnitude\" estimate, because in both cases (Figures 3 and 7) the shape of the diamonds also indicates a significant difference in junction capacitances in each device, most likely caused by non-uniformities in the dielectric thickness and uncertainty in the junction area.) This observation suggests that the actual thickness of a dielectric is  
Figure 7: Electrical characteristics for O\({}_{3}\)-based Pt-Al\({}_{2}\)O\({}_{3}\)-Pt SET after anneal in forming gas at 90 \({}^{\circ}\)C for 1 h: (**a**) diamond plot at 0.3 K with \(V_{g}\) (\(V_{ds}\) = 0 mV, blue) and \(V_{ds}\) (\(V_{g}\) = 5.4 mV, red) cross sections; and (**b**) \(G(V_{ds})\) dependence of SET conductance measured in the peak of Coulomb blockade at several temperatures. The peaks of CBOs are below \(G_{0}/2\) (black dashed line), contrary to Coulomb blockade theory for metal-insulator-metal SETs. different for the two different oxidant precursors with the same number of deposition cycles. Namely, the actual thickness of the dielectric in the water-based devices was about half of what was expected from the number of deposition cycles. The likely cause for this is the different effects of H\({}_{2}\)O and O\({}_{3}\) oxidizing pulses on the nucleation delay and metal surface oxidation. This again provides evidence for the more aggressive action of O\({}_{3}\) in forming PtO\({}_{x}\) (and potentially more uniform coverage) compared to H\({}_{2}\)O. Note that in both cases values of junction capacitances are consistent with a reduced dielectric constant, \(\varepsilon<5\), compared to the bulk value (\(\varepsilon\approx 9\)) [21; 30]. The above experiments also provide evidence that the formation of native oxide and interfacial layers, even on noble metals, can drastically change the properties of the MIM junctions. PEALD of SiO\({}_{2}\) using O\({}_{2}\) plasma and Bis(diethylamino)silane was also attempted on platinum.