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Simultaneous diffusion of Si and B in thermally grown SiO2 is modeled taking into account the effect of SiO molecules generated at the Si∕SiO2 interface and diffusing into SiO2 to enhance both Si and B diffusion. Based on the model, we simulated experimental profiles of coimplanted Si30 and B in SiO228, which showed increasing diffusivities with decreasing distance from the interface. The simulation results show that the SiO diffusion is so slow that the SiO concentration at the near-surface region critically depends on the distance from the interface. In addition, the simulation explains that the diffusivities of both Si and B increase with longer annealing times because more SiO molecules arrive from the interface. Furthermore, we examined the effect of high-concentration B on the diffusivities of Si and B in SiO2, both of which increase with higher B concentration. The experimental results were simulated assuming that the diffusivity of SiO, which enhances the diffusivities of Si and B, increases with ...

Si-based single-electron tunneling (SET) devices have of late become an important alternative to the metal-based ones, both for ultralarge scale integration (ULSI) electronics and for electrical metrology. We have very recently been designing, fabricating, and measuring SET turnstiles, pumps, and charge-coupled devices using tunable barriers in silicon. Having shown the potential of these devices, we wish to understand the error mechanisms which may manifest themselves, and to predict the level of these errors, in order to decide how feasible these devices will be. In this paper, we devote a substantial amount of analysis to the consideration of the “dynamical” error mechanism. This particular error considers how electrons split up as the barrier is raised, or alternatively how the Coulomb blockade is formed. We then consider a wide variety of other errors, including thermal, frequency, leakage, and heating errors. We show the dependence of the error rate on each of those mechanisms, and predict maxima or...

We propose a simple method to evaluate the triple quantum dots (TQDs) coupled in series with the compact device structure. Compact coupled quantum dots, each with an attached control gate, offer promising applications as quantum computing and single-electron transfer devices. However, device reduction required in practical applications creates a capacitive cross-talk between a control gate and its neighboring dots making it difficult to determine the charge transition boundaries in each dot. To properly evaluate the electron-transfer characteristics of TQDs, a method is proposed whereby the three gate voltages are simultaneously swept. We studied the charge stability diagram of the compact TQDs using Monte Carlo simulations, and confirmed the effectiveness of the method. Compact Si-TQDs were actually fabricated by the use of pattern-dependent oxidation and additional oxidation method for this study. The method was then applied to the stability diagrams obtained from the devices. The nine measurements of t...

Conductance measurements are reported for quantum dots fabricated by pattern-dependent oxidation in silicon; the small size of these devices allows observation of single electron behavior to temperatures as high as 200 K. At temperatures above 6 K the zero-bias conductance peaks, periodic in gate voltage, are asymmetric, with heights that increase rapidly with increasing temperature. These features suggest that the dominant conductance mechanism in this temperature range is thermal activation over one of the potential barriers that localize electrons in the quantum dot. Quantitative comparisons are made between the data and the theory of Matveev and Glazman, including fits of the asymmetric line shapes. However, from these fits we find a potential barrier height that is much smaller than the charging energy, indicating that our data cannot be fully explained by this theory. At lower temperatures, the conductance peaks become much less periodic, and the data in this regime suggest the presence of several q...

To investigate the electron tunneling from the nanometer‐scale Si, we fabricated tunnel devices with an extremely thin Si‐on‐insulator layer as a cathode. The devices consisted of a 5‐nm‐thick Si layer sandwiched between thick SiO2 films, a thin (≊2 nm) SiO2 film (an edge oxide) terminating the Si layer on one side, and a polycrystalline Si (poly‐Si) electrode covering the edge oxide. Using this Si/edge‐oxide/poly‐Si tunnel device, we measured the tunneling current and found that when the poly‐Si electrode was positively biased with respect to the Si layer, the current versus voltage characteristics exhibited a steplike feature at 42 K. The current decreased with increasing edge‐oxide thickness, indicating that the tunneling at the edge limited the current. The step structure was never observed in the current directly flowing into the poly‐Si electrode for devices without the edge oxide. These results indicate that the observed steps reflect the electronic nature of the electron system at the edge of the ...

Self-diffusion coefficients of Si in thermally grown SiO2 on a semiconductor-grade silicon wafer have been determined at temperatures between 1150 and 1300 °C under equilibrium conditions using isotope heterostructures (natSiO2/28SiO2). Si self-diffusion was induced by appropriate heat treatments, and the diffusion depth profiles of 30Si isotope from natSiO2 to 28SiO2 layers were determined by secondary ion mass spectrometry (SIMS). The diffusion coefficients found in the present study for 1150–1300 °C are more than two orders of magnitude smaller than the values measured with semiconductor-grade SiO2 in the presence of excess silicon, i.e., in nonequilibrium conditions, and agree very well with previously reported values of Si self-diffusion in fused silica under equilibrium conditions.

Tunability of capacitive coupling in the Si double-quantum-dot system is discussed by changing the number of electrons in quantum dots (QDs), in which the QDs are fabricated using pattern-dependent oxidation (PADOX) of a Si nanowire and multi-fine-gate structure. A single QD formed by PADOX is divided into multiple QDs by additional oxidation through the gap between the fine gates. When the number of electrons occupying the QDs is large, the coupling capacitance increases gradually and almost monotonically with the number of electrons. This phenomenon is attributed to the gradual growth in the effective QD size due to the increase in the number of electrons in the QDs. On the other hand, when the number of electrons changes in the few-electron regime, the coupling capacitance irregularly changes. This irregularity can be observed even up to 40 electrons. This behavior is attributable the rough structure of Si nano-dots made by PADOX. This roughness is thought to induce complicated change in the electron wave function when an electron is added to or subtracted from a QD.

Clean polishing is performed by helium‐ion etching on a surface of high‐Tc YBa2Cu3O7−y. Based on a knock‐on cascade model, the decrease of surface roughness is discussed. A rate process of etching is applied for the surface roughness of the high‐Tc YBa2Cu3O7−y.

Conduction measurements with simultaneous observations by transmission electron microscopy (TEM) were performed on a thin NiO film, which is a candidate material for resistance random access memories (ReRAMs). To conduct nanoscale experiments, a piezo-controlled TEM holder was used, where a fixed NiO sample and a movable Pt-Ir counter electrode were placed. After the counter electrode was moved to make contact with NiO, I-V measurements were carried out from any selected nanoregions. By applying a voltage of 2 V, the insulating NiO film was converted to a low resistance film. This phenomenon may be the "forming process" required to initialize ReRAMs. The corresponding TEM image indicated a structural change in the NiO layer generating a conductive bridge with a width of 30-40 nm. This finding supports the "breakdown" type forming in the so-called "filament model" of operation by ReRAMs. The inhomogeneity of resistance in the NiO film was also investigated.

A common observation in metal-based (specifically, those with AlOx tunnel junctions) single-electron tunneling (SET) devices is a time-dependent instability known as the long-term charge offset drift. This drift is not seen in Si-based devices. Our aim is to understand the difference between these, and ultimately to overcome the drift in the metal-based devices. A comprehensive set of measurements shows that (1) brief measurements over short periods of time can mask the underlying drift, (2) we have not found any reproducible technique to eliminate the drift, and (3) two-level fluctuators (TLFs) in the metal-based devices are not stable. In contrast, in the Si-based devices the charge offset drifts by less than 0.01e over many days, and the TLFs are stable. We also show charge noise measurements in a SET device over four decades of temperature. We present a model for the charge offset drift based on the observation of nonequilibrium heat evolution in glassy materials, and obtain a numerical estimate in go...

The ultimate goal of future information processing might be the realization of a circuit in which one bit is represented by a single electron. Such a challenging circuit would comprise elemental devices whose tasks are to drag, transfer, and detect single electrons. In achieving these tasks, the Coulomb blockade, which occurs in tiny conducting materials, plays an important role. This paper describes the current status of research on such single-charge-control devices from the viewpoints of circuit applications.

The new Pt silicide formation method using the reaction between Pt film and SiH4 has been proposed. It has been found that Pt silicide is formed by the reaction with SiH4 at a low temperature range of 250–400 °C. Parabolic relationships of silicide growth using the reaction with SiH4 as well as the growth using the reaction between Pt and substrate Si are confirmed. Pt silicide formation with SiH4 is less influenced by oxygen contamination than the formation by the reaction between Pt and substrate Si.