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Solution-processed Al<sub>2</sub>O<sub>3</sub>gate dielectrics for graphene field-effect transistors
Park, Goon-Ho,Kim, Kwan-Soo,Fukidome, Hirokazu,Suemitsu, Tetsuya,Otsuji, Taiichi,Cho, Won-Ju,Suemitsu, Maki Institute of Pure and Applied Physics 2016 Japanese Journal of Applied Physics Vol.55 No.9
<P>The performance of actual graphene FETs suffers significant degradation from that expected for pristine graphene, which can be partly attributed to the onset of defects and the doping of the graphene induced during the fabrication of gate dielectric layers. These effects are mainly due to high-temperature processes such as postdeposition annealing. Here, we propose a novel low-temperature method for the fabrication of gate dielectrics, which consists of the natural oxidation of an ultrathin Al layer and a sol-gel process with oxygen plasma treatment to form an Al2O3 layer. The method results in a significant reduction of defects and doping in graphene, and devices fabricated by this method show an intrinsic carrier mobility as high as 9100 cm(2) V-1 s(-1). (C) 2016 The Japan Society of Applied Physics</P>
Decay Rate Estimation of Continuous Time Series Using Instantaneous Lyapunov Exponent
Yusuke Totoki,Haruo Suemitsu,Takami Matsuo 제어로봇시스템학회 2009 제어로봇시스템학회 국제학술대회 논문집 Vol.2009 No.8
The Lyapunov exponent give same a sure of the mean decay/divergence rates of the flows of nonlinear systems. However, the Lyapunov exponent needs an infinite time interval of flows and the Jacobi an matrix of system dynamics. In this paper, we propose an instantaneous decay that is a kind of generalized Lyapunov exponent and call the instantaneous Lyapunov exponent(ILE) with respect to adecay function. The instantaneous Lyapunov exponent is one of the measures that estimate the decay rates of flows of nonlinear systems by assign inga comparison functon and can apply as table system whose decay rate is slower than an exponential function.
Adaptive Backstepping Control of Wheeled Inverted Pendulum with Velocity Estimator
Yuji Maruki,Kohei Kawano,Haruo Suemitsu,Takami Matsuo 제어·로봇·시스템학회 2014 International Journal of Control, Automation, and Vol.12 No.5
In this paper, we introduce a backstepping control design of a wheeled inverted pendulum. Based on a second-order motion equation of the body angle, an adaptive integral backstepping controller is designed to stabilize the body angle. It is shown that the σ-modification rule in the adaptive update law guarantees the boundedness of the errors in estimating the time-varying signal that is an output of a linear system with every bounded input signal. Then, the stabilizing controller for the wheel angle is constructed by a PD-type positive feedback. The derived controller requires the full-state measurements. In the output feedback case, the K filter or the observer backstepping is needed. How-ever, the structure of the controller becomes complicated. We propose a non-model-based differentiator based on the adaptive update law. Since the non-model-based differentiator does not require any knowledge of the dynamic structure of the signal, we can use it as a velocity estimator for unknown nonlinear systems. Therefore, we replaced the velocity measurement with the estimates by the non-model-based differentiator. Finally, simulation results for the proposed controller are presented.
Nonlinear Control for Rotational Movement of Cart-pendulum System Using Homoclinic Orbit
Hiroya Oka,Yuji Maruki,Haruo Suemitsu,Takami Matsuo 제어·로봇·시스템학회 2016 International Journal of Control, Automation, and Vol.14 No.5
In this paper, we deal with the control method for rotational movements of a pendulum using a separatrix. We design a controller that attains a homoclinic motion or a heteroclinic motion of the pendulum and the asymptoticstability of the cart by using a kind of forwarding control design. First, we derive a controller that converges toa homoclinic orbit via a Lyapunov function of the pendulum subsystem. Next, we give a nonlinear stabilizingcontroller via another Lyapunov function of the cart subsystem. Moreover, using the third Lyapunov function andadding a complementary control input, we guarantee that the pendulum converges to the homoclinic orbit and thecart is stabilized. Finally, the simulation and the experiment using the rapid controller prototyping system based onMATLAB/Simulink are performed to demonstrate the forward upward circling and the giant swing of the pendulum.
Venugopal, Gunasekaran,Jung, Myung-Ho,Suemitsu, Maki,Kim, Sang-Jae Elsevier 2011 Carbon Vol.49 No.8
<P><B>Abstract</B></P><P>We report on the fabrication and transport characteristics of nanoscale stacked-junctions of thin graphite flake. The stacked-junctions were fabricated using a three-dimensional focused-ion-beam milling. By varying the effective in-plane area down to submicron scale, the stacked-junctions with in-plane area <I>A</I> (from 2 down to 0.25μm<SUP>2</SUP>) and stack height–length (from 300 to 100nm) along <I>c</I>-axis were fabricated. The nano-stack shows perfect <I>c</I>-axis transport characteristics in which we observed a semiconducting behavior for <I>T</I>>65K and metallic behavior for <I>T</I><65K. The obtained results were well fitted with the <I>c</I>-axis electrical conduction mechanism. The stack with in-plane area <I>A</I> of 0.25μm<SUP>2</SUP> showed nonlinear concave-like <I>I</I>–<I>V</I> characteristics even at 300K; however the stack with <I>A⩾</I>1μm<SUP>2</SUP> were shown an ohmic-like <I>I</I>–<I>V</I> characteristic at 300K for both low and high-current biasing. It turned into nonlinear characteristics when the temperature goes down. The observation of this anomalous transport characteristics were discussed in detail with stack capacitance calculations. The nonlinear characteristics observed at 300K for the stack with <I>A</I> of 0.25μm<SUP>2</SUP> were shown best fit with Fowler–Nordheim tunneling model.</P>