## 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  
Initial experiments described above indicated that H\({}_{2}\)O-based ALD of tunnel barriers resulted in functional devices, but these suffered from intrinsic barrier instabilities resulting in irreversible detrimental changes in the device performance. An alternative method for forming Al\({}_{2}\)O\({}_{3}\) in the Cambridge Savannah ALD reactor is to use a different oxidizer by replacing H\({}_{2}\)O with O\({}_{3}\) from a dedicated ozone generator. To investigate the difference between H\({}_{2}\)O-based ALD and O\({}_{3}\)-based ALD, two batches of Pt-Al\({}_{2}\)O\({}_{3}\)-Pt SET devices were fabricated with an equal number of ALD cycles using ozone and water [14]. It was discovered that SETs that used H\({}_{2}\)O-based ALD showed much lower resistance than SETs fabricated with O\({}_{3}\)-based ALD for a given number of ALD cycles. For both batches, nine cycles of ALD (-1 nm in thickness) were used as this was found to be an optimal balance between complete coverage of the barrier over the electrodes and measureable tunneling currents. Structures fabricated using H\({}_{2}\)O showed an average resistance of around 1 M\(\Omega\) with a very significant spread of resistances ranging from tens of k\(\Omega\) to several M\(\Omega\). Again, after a few weeks at ambient conditions, the resistance of these devices dropped to about 10 k\(\Omega\). In contrast, the as-prepared, O\({}_{3}\)-based devices showed an average resistance of almost 1 G\(\Omega\). Low temperature (-5 K) testing of both O\({}_{3}\)- and H\({}_{2}\)O-based devices revealed, in addition to a \"dip\" near \(V_{ds}\) = 0 mV related to Coulomb blockade, a temperature dependent monotonic increase of conductance with increasing bias outside of the Coulomb gap (\(\mid V_{ds}\mid>2E_{c}/e\)) contrary to orthodox Coulomb blockade theory [16]. This indicates the presence of a parasitic non-metallic component in series with the tunnel barrier in the junctions. One technique frequently used to improve the quality of thin films is annealing, which can passivate fabrication defects [23]. However, the results of annealing the SETs after fabrication (375 \({}^{\circ}\)C for 3 min in an Ar environment) differed drastically depending on the oxidant used in the ALD process for devices fabricated with the same number of deposition cycles. Namely, most of the H\({}_{2}\)O-based devices developed electrical shorts after annealing. In contrast, the resistance of devices fabricated with O\({}_{3}\)-based ALD dropped by approximately two orders of magnitude after annealing under the same conditions, yet they did not develop any shorts. Instead, the resistance became quite  
Figure 3: Electrical characterization of Pt-Al\({}_{2}\)O\({}_{3}\)-Pt SET prepared using nine ALD cycles of Al\({}_{2}\)O\({}_{3}\) (\(\sim\)1 nm) with no post fabrication treatments: (**a**) Coulomb diamond plot and \(G(V_{ds})\) dependence for \(V_{g}\) = 2.3 mV (a peak of Coulomb blockade oscillation). Note that zero bias conductance \(G(V_{ds}\) = 0 mV) is just slightly below the \(G_{0}/2\) value (indicated by the dashed line) expected from orthodox theory; (**b**) Coulomb Blockade Oscillations (CBOs) for \(V_{ds}\) = 0 mV. \(T\) = 0.3 K, measurements were performed immediately after fabrication. uniformly reduced to a few M\(\Omega\)s and remained stable over time (for at least six months, the longest observation time available). When tested again at \(\sim\)5 K with \(\mid\!V_{ds}\!\mid\!>2E_{C}/e\) applied, the annealed O\({}_{3}\)-based devices displayed almost constant differential conductance, as expected from orthodox Coulomb blockade theory. (The value of the charging energy in these experiments\(-\)as estimated above from the parallel plate model\(-\)is on the order of 5 K, precluding observation of developed Coulomb blockade at the temperature of experiment (\(\sim\)5 K).)