Yoshifumi Nishi

Comprehensive Study on Injection Velocity Enhancement in Dopant-Segregated Schottky MOSFETs

The carrier transport in dopant-segregated Schottky (DSS) and conventional MOSFETs was thoroughly investigated in terms of carrier injection velocity, vinj. It was found that vinj enhancement associated with the velocity overshoot enhances the current drivability in DSS, in addition to the reduction of parasitic resistance. A physical-based model was newly developed to explain the velocity overshoot behavior and reproduced the experimental data very well. Moreover, a novel type of DSS FinFET to take full advantage of the velocity overshoot was proposed and demonstrated as a primary study

Novel doping technology for a 1nm NiSi/Si junction with dipoles comforting Schottky (DCS) barrier

This paper studies the Schottky barrier height (SBH) modulation effect induced by dipoles, which several types of impurity atoms generate at the nickel silicide (NiSi)/silicon (Si) interface, through both first-principles calculations and experimental methods. Based on these understandings, we discuss their applicability to the DCS junction, leading to a principle for choosing dopants.

Simulation of TaO x -based complementary resistive switches by a physics-based memristive model

Highly predictive memristive models of resistive switches are required to simulate the behavior of anti-serially connected resistive switches, so called complementary resistive switches (CRSs). As an emerging non-volatile device suited for ultra-dense memory architectures, CRS cells offer great potential also as content addressable memories. Here, we introduce a circuit model for TaOx-based resistive switches which we implemented in VerilogA. This model is capable of predicting CRS behavior correctly.

Experimental Study on Performance Improvement in Dopant-Segregated Schottky Metal–Oxide–Semiconductor Field-Effect Transistors

Factors that underlie the performance improvement of dopant-segregated Schottky (DSS) metal–oxide–semicondutor field-effect transistors (MOSFETs) compared with conventional (Conv.) MOSFETs are examined experimentally. Three factors are compared for DSS and Conv. MOSFETs; namely, effective junction depth, the hot carrier effect, and parasitic resistance. We found that all the following factors are associated with performance improvement in DSS MOSFETs: shallower junction depth, higher impact ionization rate, and lower parasitic resistance. It is considered that the shallower junction depth and lower parasitic resistance respectively contribute to the better short-channel-effect immunity and higher drive current of the DSS MOSFETs. The higher impact ionization rate is consistent with the higher carrier injection velocity, which is another factor of the drive current enhancement. We focus on the reduction of parasitic resistance and compare the components of the parasitic resistances of DSS and Conv. MOSFETs to analyze the factors of the reduction of parasitic resistance. We also speculate on the effectiveness of the parasitic resistance reduction in DSS FETs as high-performance devices for future LSIs.

Interfacial Segregation of Metal at NiSi/Si Junction for Novel Dual Silicide Technology

It is demonstrated that Schottky barrier height (PhiB) for NiSi/Si junction can be modulated by interfacial segregation of metals. Thin films of rare earth (RE) metals and platinum (Pt) are deposited on NiSi/Si Schottky diodes and annealed. The metals diffuse into NiSi and segregate at NiSi/Si interface, which leads to PhiB modulation by 0.1 eV. Similar technique can be applied to PtSi/Si junction as well for advanced dual silicide process.

Impact of platinum incorporation on thermal stability and interface resistance in NiSi/Si junctions based on first-principles calculation

We studied extremely low interface resistance and thermal stability of the interface of NiSi/Si junctions with Pt (Ni(Pt)Si/Si junctions) based on first-principles calculation. The physical origin of thermal stability of NiSi enhanced by Pt is clarified by the calculations. Our calculations show clear difference of energies for dopant atoms of As and B between PtSi/Si and NiSi/Si. The results obtained theoretically and experimentally in this study demonstrate the dipole comforting Schottky junctions enhanced by PtSi at the interface for extremely low resistance.

Fano-Kondo effect in a two-level system with triple quantum dots

We theoretically study the Fano-Kondo effect in a triple quantum dot (QD) system where two QDs constitute a two-level system and the other QD works in a detector with electrodes. We found that the Fano dip is clearly modulated by strongly coupled QDs in a two-level system and a slow detector with no interacting QD. This setup suggests a new method of reading out qubit states.

Weibull analysis of the kinetics of resistive switches based on tantalum oxide thin films

We study the kinetics of bipolar resistive switches in tantalum oxide thin films having different thicknesses. The time to switch from the high resistance state to the low resistance state (SET) is measured repeatedly in a single cell of each sample and analyzed based on a Weibull distribution. In the thin film device the Weibull parameter fJ> 1 is observed in the short time region, followed by a distribution with ß <; 1 in the long time region. This indicates that a progressing phenomenon induces the SET action in the short time region, while it is saturated in the long time region, where the SET is triggered by a sporadic event. In the thick film sample a distribution with ß<; 1 is dominant almost in the whole time range. Further analysis revealed that the heat generated before the switch-on can be responsible for the SET in the fJ> 1 mode.

Noise characteristics of the Fano effect and the Fano?Kondo effect in triple quantum dots

We theoretically compare transport properties of the Fano-Kondo effect with those of the Fano effect, focusing on the effect of a two-level state in a triple quantum dot (QD) system. We analyze shot noise characteristics in the Fano-Kondo region at zero temperature, and discuss the effect of strong electronic correlation in QDs. We found that the modulation of the Fano dip is strongly affected by the on-site Coulomb interaction in QDs, and stronger Coulomb interaction (Fano-Kondo case) induces larger noise.Quantum dot (QD) systems have attracted a lot of interest over many years because of their variety of controllability of small number of electrons in order to understand many-body effects in electronic systems. Quantum correlation between localized states in QDs and free electrons in electrodes induces interesting phenomena such as the Fano effect and the Kondo effect. A number of important experiments have been carried out and many theories have been proposed. The Fano effect occurs as a result of quantum interference between a discrete energy state and a continuum state. The Kondo effect is observed as a result of many-body correlations where internal spin degrees of freedom play an important role. The Fano-Kondo effect, which is a combination of the Fano effect and the Kondo effect, can be observed when on-site Coulomb interaction in a QD is strong. A T-shaped QD is considered to be suitable for discussing the Fano-Kondo effect.

Successful enhancement of metal segregation at NiSi/Si junction through pre-amorphization technique

A new technique to enhance the metal segregation at NiSi/Si interface for reducing contact resistance in source/drain electrodes is proposed. It is demonstrated that metal segregation at the junction of pre-amorphized NiSi/Si using ion-implantation leads to reduction of Schottky barrier height by > 0.2 eV. This modulation width is far beyond the previous metal segregation technique [1] and allows 90% reduction of contact resistance in source/drain junctions.