We have observed a switching transition between bistable memory switching and monostable threshold switching in Pt/NiO/Pt structure. Bistable memory switching could be changed to monostable threshold switching by applying a positive electrical pulse with height of 2 V and width between 10−2 and 10−4 s. The change is reversible by applying a negative electrical pulse with the same height and width. By considering polarity- and width-dependence of the switching transition and compositional difference on electrical properties in NiOx, we have proposed a model in which the migration of oxygen ions (O2−) is responsible for the switching transition in Pt/NiO/Pt structures.
Time-dependent electroforming phenomena in NiO capacitors are investigated. Different current-voltage characteristics between dc sweep mode and pulse mode indicate that electroforming is time-dependent process. Statistical time-dependent dielectric breakdown (TDDB) measurements show the exponential dependence of electroforming time on applied voltage, confirming that forming process is not a spontaneous process at some critical voltage, but an upsurge process resulting from stress-induced defects. The statistical TDDB analysis explains not only the nature of electroforming process but also the anomalous forming and large variations in forming parameters.
We have fabricated Si(1-x)Ge(x) alloy nanowire devices with Ni and Ni/Au electrodes. The electrical transport characteristics of the alloy nanowires depended strongly on the annealing temperature and contact metals. Ni/Au-contacted devices annealed at 400 degrees C showed p-type transistor behavior as well as a resistance switching effect, while no switching was observed from Ni-contacted alloy nanowire devices. To identify the origin of such a hysteretic resistance switching effect, we constructed nanowire devices on a 40 nm Si(3)N(4) membrane. Transmission electron microscopy analysis combined with electrical transport measurements revealed that devices contacted with Ni/Au, and thereby showing resistance switching, have Au atoms right next to the alloy nanowire.
We have investigated the activation and deactivation of the 1 kV BF 3 plasma doping ͑PLAD͒ with excimer laser annealing ͑ELA͒. Half of the dopants were activated by ELA, and the deactivation was dramatically increased after the postannealing. We have confirmed that 1 kV BF 3 PLAD did not form an amorphous layer at the substrate using X-ray transmission electron microscopy ͑X-TEM͒ and that boron and fluorine segregated after annealing using secondary ion mass spectroscopy profiles and plane-view TEM. Based on the results, we proved that fluorine can suppress boron diffusion, although it retards the activation and increases the deactivation of BF 3 PLAD with ELA.As the dimensions of devices become smaller, the size and junction depths of devices must be made shallower to prevent the short channel effect. According to The International Technology Roadmap for Semiconductors, ͑ITRS͒ the junction depth of the lightly doped drain ͑LDD͒ region may be as shallow as roughly 20-30 nm in a 0.1 m metal oxide semiconductor field effect transistor ͑MOSFET͒ device. 1 Compared with the n + /p junction, it is difficult to form an untrashallow p + /n junction due to boron channeling and transientenhanced diffusion ͑TED͒ which is related to extra interstitials generated during the implantation. 2,3 Therefore, many studies have been conducted to discover alternative methods for shallower p + /n junctions. 4-6 Plasma doping ͑PLAD͒, which is a method to create a shallow junction, has been studied as a replacement for conventional ion implantation. 7 However, at a low doping energy of 1 kV or less, TED during activation annealing is inevitable. 8,9 Therefore, to reduce the enhanced diffusion and to obtain a highly activated dopant profile, excimer laser annealing ͑ELA͒ has also been studied. 10 Over the past few years there has been considerable interest in the effect of fluorine on boron diffusion in silicon to suppress boron diffusion. [11][12][13][14][15][16][17][18][19] Research on the effects of fluorine from a BF 2 + implant reveals that shallower junctions could be obtained when BF 2 + was implanted instead of boron. 11-13 Also, it has been reported that fluorine was implanted separately into the boron to characterize the effect of the fluorine on boron diffusion. This work shows that the fluorine implant reduced boron TED and increased boron activity. [14][15][16][17][18][19] In conjunction with these studies, the deactivation of dopants also should be considered because the postannealing process is accompanied with the deactivation of dopants during device fabrication. In the case of boron, Takamura et al. 20 have already shown that the deactivation of boron in laser-annealed silicon is stable.To be conclusive further studies are needed to investigate how the low energy BF 3 PLAD with ELA is effective for forming an ultrashallow junction. In this paper, we report the electrical properties of the low-energy BF 3 PLAD activated by ELA and the behavior of boron and fluorine after the annealing along with time-offlight ͑TOF͒ second...
We investigated the dynamics of reversible resistance switching of NiO nonvolatile memory devices by measuring the switching time as a function of applied voltage. A model of local switching induced by charge carrier fluence was proposed to explain the time-dependent switching behaviors. Charge carrier flow under Poole–Frenkel emission builds up local conductive paths inside NiO. The enhanced electric field at the ends of conductive clusters abruptly increases local Poole–Frenkel emission and accelerates the percolation propagation. The results of Monte Carlo calculation strongly supported the model of local switching induced by charge carrier fluence.
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