Electron Mobility and Magneto Transport Study of Ultra-Thin Channel Double-Gate Si MOSFETs

We report on detailed room temperature and low temperature transport properties of double-gate Si MOSFETs with the Si well thickness in the range 7-17 nm. The devices were fabricated on silicon-on-insulator wafers utilizing wafer bonding, which enabled us to use heavily doped metallic back gate. We observe mobility enhancement effects at symmetric gate bias at room temperature, which is the finger print of the volume inversion/accumulation effect. An asymmetry in the mobility is detected at 300 K and at 1.6 K between the top and back interfaces of the Si well, which is interpreted to arise from different surface roughnesses of the interfaces. Low temperature peak mobilities of the reported devices scale monotonically with Si well thickness and the maximum low temperature mobility was 1.9 m2/Vs, which was measured from a 16.5 nm thick device. In the magneto transport data we observe single and two sub-band Landau level filling factor behavior depending on the well thickness and gate biasing

Determination of |V_us| from hadronic tau decays

The recent update of the strange spectral function and the moments of the invariant mass distribution by the OPAL collaboration from hadronic tau decay data are employed to determine |V_us| as well as m_s. Our result, |V_us|=0.2208\pm0.0034, is competitive to the standard extraction of |V_us| from K_e3 decays and to the new proposals to determine it. Furthermore, the error associated to our determination of |V_us| can be reduced in the future since it is dominated by the experimental uncertainty that will be eventually much improved by the B-factories hadronic tau data. Another improvement that can be performed is the simultaneous fit of both |V_us| and m_s to a set of moments of the hadronic tau decays invariant mass distribution, which will provide even a more accurate determination of both parameters.Comment: 6 pages. Invited talk given by E.G. at the XXXXth Rencontres de Moriond on Electroweak Interactions and Unified Theories, La Thuile, Italy, 5-12 Mar 200

2D-TCAD Simulation on Retention Time of Z2FET for DRAM Application

Traditional memory devices are facing more challenges due to continuous down-scaling. 6T-SRAM suffers from variability [1-2] and reliability [3-4] issues, which introduce cell stability problems. DRAM cells with one transistor, one capacitor (1T1C) struggle to maintain refresh time [5-6]. Efforts have been made to find new memory solutions, such as one transistor (1T) solutions [7-9]. Floating body based memory structures are among the potential candidates, but impact ionization or band-to-band tunnelling (B2BT) limits their refresh time [10]. A recently proposed zero impact ionization and zero subthreshold swing device named Z2FET [9, 11-12] has been demonstrated and is a promising candidate for 1T DRAM memory cell due to technology advantages such as CMOS technology compatibility, novel capacitor-less structure and sharp switching characteristics. In the Z2FET memory operation, refresh frequency is determined by data retention time. Previous research [11-12] is lacking systematic simulation analysis and understanding on the underlying mechanisms. In this paper, we propose a new simulation methodology to accurately extract retention time in Z2FET devices and understand its dependency on applied biases, temperatures and relevant physical mechanisms. Since the stored ‘1’ state in Z2FET is an equilibrium state [9, 11-12] and there is no need to refresh, we will concentrate on state ‘0’ retention. Two types of ‘0’ retention time: HOLD ‘0’ and READ ‘0’ retention time will be discussed separately

Determination of m_s and |V_us| from hadronic tau decays

The mass of the strange quark is determined from SU(3)-breaking effects in the tau hadronic width. Compared to previous analyses, the contributions from scalar and pseudoscalar spectral functions, which suffer from large perturbative corrections, are replaced by phenomenological parametrisations. This leads to a sizeable reduction of the uncertainties in the strange mass from tau decays. Nevertheless, the resulting m_s value is still rather sensitive to the moment of the invariant mass distribution which is used for the determination, as well as the size of the quark-mixing matrix element |V_us|. Imposing the unitarity fit for the CKM matrix, we obtain m_s(2 GeV)=117+-17 MeV, whereas for the present Particle Data Group average for |V_us|, we find m_s(2 GeV)=103+-17 MeV. On the other hand, using an average of m_s from other sources as an input, we are able to calculate the quark-mixing matrix element |V_us|, and we demonstrate that if the present measurement of the hadronic decay of the tau into strange particles is improved by a factor of two, the determination of |V_us| is more precise than the current world average.Comment: 25 pages, 1 eps figur

MS-EMC vs. NEGF: A comparative study accounting for transport quantum corrections

As electronic devices approach the nanometer scale, quantum transport theories have been recognized as the best option to reproduce their performance. Other possible trend, mainly focused on reducing the computational effort, is the inclusion of quantum effects in semi-classical simulators. This work presents a comparison between a NEGF simulator and a MS-EMC tool including S/D tunneling both applied on a DGSOI transistor

Thorough understanding of retention time of Z2FET memory operation

A recently reported zero impact ionization and zero subthreshold swing device Z2FET is a promising candidate for capacitor-less dynamic random access memory (DRAM) memory cell. In the memory operation, data retention time determines refresh frequency and is one of the most important memory merits. In this paper, we have systematically investigated the Z2FET retention time based on a newly proposed characterization methodology. It is found that the degradation of HOLD ``0'' retention time originates from the gated-silicon on insulator (SOI) portion rather than the intrinsic-SOI region of the Z2FET. Electrons accumulate under front gate and finally collapse the potential barrier turning logic ``0''-``1.'' It appears that Shockley-Read-Hall (SRH) generation is the main source for electrons accumulation. Z2FET scalability has been investigated in terms of retention time. As the Z2FET is downscaled, the mechanism dominating electrons accumulation switches from SRH to parasitic injection of electrons from the cathode. The results show that the downscaling of Lg has little effect on data ``0'' retention, but Lin is limited to ~ 125 nm. An optimization method of the fabrication process is proposed based on this new understanding, and Lin can be further scaled down to 75 nm. We have demonstrated by 2-D TCAD simulation that Z2FET is a promising DRAM cells' candidate particularly for Internet-of-Things applications

Bicarbonate-controlled reduction of oxygen by the QA semiquinone in Photosystem II in membranes

Photosystem II (PSII), the water/plastoquinone photo-oxidoreductase, plays a key energy input role in the biosphere. Q∙−A, the reduced semiquinone form of the nonexchangeable quinone, is often considered capable of a side reaction with O2, forming superoxide, but this reaction has not yet been demonstrated experimentally. Here, using chlorophyll fluorescence in plant PSII membranes, we show that O2 does oxidize Q∙−A at physiological O2 concentrations with a t1/2 of 10 s. Superoxide is formed stoichiometrically, and the reaction kinetics are controlled by the accessibility of O2 to a binding site near Q∙−A, with an apparent dissociation constant of 70 ± 20 µM. Unexpectedly, Q∙−A could only reduce O2 when bicarbonate was absent from its binding site on the nonheme iron (Fe2+) and the addition of bicarbonate or formate blocked the O2-dependant decay of Q∙−A. These results, together with molecular dynamics simulations and hybrid quantum mechanics/molecular mechanics calculations, indicate that electron transfer from Q∙−A to O2 occurs when the O2 is bound to the empty bicarbonate site on Fe2+. A protective role for bicarbonate in PSII was recently reported, involving long-lived Q∙−A triggering bicarbonate dissociation from Fe2+ [Brinkert et al., Proc. Natl. Acad. Sci. U.S.A. 113, 12144–12149 (2016)]. The present findings extend this mechanism by showing that bicarbonate release allows O2 to bind to Fe2+ and to oxidize Q∙−A. This could be beneficial by oxidizing Q∙−A and by producing superoxide, a chemical signal for the overreduced state of the electron transfer chain

Experimental analysis of variability in WS2_2-based devices for hardware security

This work investigates the variability of tungsten disulfide (WS$_2$)-based devices by experimental characterization in view of possible application in the field of hardware security. To this aim, a preliminary analysis was performed by measurements across voltages and temperatures on a set of seven Si/SiO$_2$/WS$_2$ back-gated devices, also considering the effect of different stabilization conditions on their conductivity. Obtained results show appreciable variability in the conductivity, while also revealing similar dependence on bias and temperature across tested devices. Overall, our analysis demonstrates that WS$_2$-based devices can be potentially exploited to ensure adequate randomness and robustness against environmental variations and then used as building blocks for hardware security primitives

Assessment of Gate Leakage Mechanism Utilizing Multi-Subband Ensemble Monte Carlo

The inclusion in advanced device simulators of quantum effects different than standard confinement becomes mandatory to describe device behavior as technology approaches the nanometer scales. This work presents a model to include the gate leakage mechanism considering direct and trap assisted tunneling in Multi-Subband Ensemble Monte Carlo (MS-EMC) simulators. The tool is used for the study of FDSOI and FinFET devices