Self-selective ferroelectric memory realized with semimetalic graphene channel

A new concept of read-out method for ferroelectric random-access memory (FeRAM) using a graphene layer as the channel material of bottom-gated field effect transistor structure is demonstrated experimentally. The transconductance of the graphene channel is found to change its sign depending on the direction of spontaneous polarization (SP) in the underlying ferroelectric layer. This indicates that the memory state of FeRAM, specified by the SP direction of the ferroelectric layer, can be sensed unambiguously with transconductance measurements. With the proposed read-out method, it is possible to construct an array of ferroelectric memory cells in the form of a cross-point structure where the transconductance of a crossing cell can be measured selectively without any additional selector. This type of FeRAM can be a plausible solution for fabricating high speed, ultra-low power, long lifetime, and high density 3D stackable non-volatile memory

Impact of Induced Seismicity on the Housing Market: Evidence from Pohang

In this study, we analyze the case of induced seismicity in Pohang, South Korea, in 2017 to investigate the effect of seismic risk perception on the local residential property market. Based on a hedonic pricing model with a difference-in-differences method, we examine the geographic distribution of the effects of unexpected earthquake hazards. Our results indicate an overall reduction in local property values, but the magnitudes of negative externality for housing prices decrease with respect to the distance from the epicenter. In areas within 3 km of the epicenter, the asset value reduced by approximately 20% after an earthquake event, but if the distance from the epicenter was higher than 12 km, the negative effect on the price was not significant. In addition, we examine how the experience of seismic events affect the preference on the anti-seismic building structure. The results show that the market valuation on the anti-seismic system significantly escalated after the earthquake

Impact of Induced Seismicity on the Housing Market: Evidence from Pohang

In this study, we analyze the case of induced seismicity in Pohang, South Korea, in 2017 to investigate the effect of seismic risk perception on the local residential property market. Based on a hedonic pricing model with a difference-in-differences method, we examine the geographic distribution of the effects of unexpected earthquake hazards. Our results indicate an overall reduction in local property values, but the magnitudes of negative externality for housing prices decrease with respect to the distance from the epicenter. In areas within 3 km of the epicenter, the asset value reduced by approximately 20% after an earthquake event, but if the distance from the epicenter was higher than 12 km, the negative effect on the price was not significant. In addition, we examine how the experience of seismic events affect the preference on the anti-seismic building structure. The results show that the market valuation on the anti-seismic system significantly escalated after the earthquake

Schottky Barrier Lowering Induced by Ultrathin Aluminum Oxynitride interlayer in Metal/SiC Junctions

Silicon Carbide (SiC) has been considered as the most promising wide band gap semiconductor for developing high power electronic devices. The electrical characteristics of SiC Schottky diode depend strongly on the interface energy barrier (Schottky barrier) and a lower Schottky barrier is advantageous to improve the power efficiency and acquire the fast switching. We report experimentally that the Schottky barrier of metal/SiC junction is reduced significantly with an ultra-thin (down to ~1.0 nm) aluminum oxynitride (AlON) interlayer inserted at the junction interface. The AlON thin film was deposited by using the RF magnetron sputtering with the in-situ flashing for removing the native oxide on the SiC surface and the grown AlON thin film was confirmed to be amorphous from high-resolution transmission electron microscope (HR-TEM) images. The Schottky barriers of metal/AlON/SiC and metal/SiC junctions were obtained by performing current-voltage (I-V), capacitance-voltage (C-V), and internal photoemission (IPE) measurements. It was also found that the contact resistance of junction decreased with the AlON interlayer. The Schottky barrier was reduced by up to ~0.8 eV and the reduction was similar for three types of metal with different work function (Pt: 5.65 eV, Ni: 5.01 eV, Cu: 4.33 eV). The adjustment of Schottky barrier with an interlayer is normally considered to be due to the potential change driven by fixed changes in the interlayer or Fermi-level depinning associated with the supression of metal-induced gap states. In our case, the Fermi-level pinning factor remained almost unchanged, implying that the surface states of SiC is NOT the main factor of the observed Schottky barrier reduction. It seems most likely that the Schottky barrier reduction arises from the fixed positive charges in the AlON thin film

Magnetorheological Fluid Haptic Shoes for Walking in VR

In this article, present RealWalk, a pair of haptic shoes for HMD-based VR, designed to create realistic sensations of ground surface deformation, and texture using Magnetorheological fluid (MR fluid). RealWalk offers a novel interaction scheme through the physical interaction between the shoes, and the ground surfaces while walking in VR. Each shoe consists of two MR fluid actuators, an insole pressure sensor, and a foot position tracker. The MR fluid actuators are designed in the form of multi-stacked disc structure with a long flow path to maximize the flow resistance. With changing the magnetic field intensity in MR fluid actuators based on the ground material in the virtual scene, the viscosity of MR fluid is changed accordingly. When a user steps on the ground with the shoes, the two MR fluid actuators are pressed down, creating a variety of ground material deformation such as snow, mud, and dry sand. We built an interactive VR application, and compared RealWalk with vibrotactile-based haptic shoes in four different VR scenes: grass, sand, mud, and snow. We report that, compared to vibrotactile-haptic shoes, RealWalk provides higher ratings in all scenes for discrimination, realism, and satisfaction. We also report qualitative user feedback for their experiences

Self-Selective Non-Destructive Read-Out for Ferroelectric Memory Based on Field Effect Transistor with Graphene Channel

Ferroelectric graphene field effect transistor (FeGFET) has been studied by several research groups as one way for overcoming the destructive read-out process of ferroelectric random-access memory (FeRAM). In the FeGFET structure, the conductance of graphene channel can vary depending on the direction of spontaneous polarization (SP) in the ferroelectric gate insulator thanks to the linear energy-momentum dispersion relation near the Dirac point [1] and the memory state then can be sensed by measuring the channel conductance. Although the FeGFET structure resolves the problem associated with the destructive read-out process, the low on/off ratio due to the minimal conductance of graphene channel itself brings about the necessity of attaching an additional cell selector (transistor or diode) to each memory cell for realizing the random accessibility [2]. In this work, we experimentally demonstrate a new concept of non-destructive read-out process using transconductance measurement for FeGFET. It is found that the memory state of FeGFET, specified by the SP direction of ferroelectric layer, can be sensed unambiguously by measuring the transconductance of graphene channel. With the proposed read-out method, it is possible to construct an array of ferroelectric memory cells in the form of a cross-point structure where the transconductance of a crossing cell can be measured selectively without any additional selector, which is a main limiting factor in terms of circuit scaling [3]. This read-out process with the FeGFET structure can be a plausible solution for fabricating high speed, ultra-low power, long lifetime, and high-density 3D stackable non-volatile memory. [1] A. K. Geim, and K. S. Novoselov, Nature Materials, 6, 183-191 (2007). [2] X. Zhang, et al, IEEE International Conference on Solid-State and Integrated Circuit Technology (ICSICT), 1-3 (2014). [3] H. S. P. Wong, et al, Proceedings of the IEEE, 98, 2201-2227 (2010)

Schottky Barrier Lowering Induced by Ultrathin Aluminum Oxynitride Interlayer in Metal/SiC Junctions

It is known that the electrical characteristics of SiC Schottky diode depend strongly on the interface energy barrier (Schottky barrier) and lower Schottky barriers bring essential advantages of improving the power efficiency and obtaining the fast switching. In this work, the Schottky barrier of metal/SiC junction is reported experimentally to be reduced significantly with an ultra-thin (down to ~1.0 nm) aluminum oxynitride (AlON) interlayer inserted at the junction interface. It was also found that the contact resistance of junction decreased with the AlON interlayer. The barrier height was lowered by up to 0.8 eV and the reduction was similar for three types of metal with different work function (Pt: 5.65 eV, Ni: 5.01 eV, Cu: 4.33 eV). The adjustment of Schottky barrier with an interlayer is generally considered due to the potential change driven by fixed changes in the interlayer or Fermi-level depinning associated with the suppression of metal-induced gap states. In our case, the Fermi-level pinning factor remained almost unchanged (Fig. 1), implying that the surface states of SiC is NOT the main factor of the observed Schottky barrier reduction. It seems most likely that the Schottky barrier reduction arises from the fixed positive charges in the AlON thin film