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Hiroshi Ishiwara, Hiroshi Ishiwara 한국재료학회 1995 Fabrication and Characterization of Advanced Mater Vol.2 No.e3
Adaptive-learning neuron circuits are proposed, in which a pulse frequency modulation (PFM) system is used and the interval of output pulses is continuously changed through the learning process. Kdy components of the circuits are MISFETs in which the gate insulator film is composed of a ferroelectric material and the source-drain resistance of the FETs is gradually changed by applying input pulses to the gates. Then, the curent status of the basic research for realizing these circuits are reviewed. In order to fabricate FETs with a ferroelectirc gate insulator, BaMg$F_4$ films are formed on Si and GaAs substrates using a molecular beam epitaxy method. It has been shown that BaMg$F_4$ films grow epitaxially on both substrates and the polarization vs. electric field characteristics of the capactiors formed on Si(III) and GaAs(100) subsrates show ferroelectric hystersis loops.
Current Status and Prospects of FET-type Ferroelectric Memories
Ishiwara, Hiroshi The Institute of Electronics and Information Engin 2001 Journal of semiconductor technology and science Vol.1 No.1
Current status and prospects of FET-type FeRAMs (ferroelectric random access memories) are reviewed. First, it is described that the most important issue for realizing FET-type FeRAMs is to improve the data retention characteristics of ferroelectric-gate FETs. Then, necessary conditions to prolong the retention time are discussed from viewpoints of materials, device structure, and circuit configuration. Finally, recent experimental results related to the FET-type memories are introduced, which include optimization of a buffer layer that is inserted between the ferroelectric film and a Si substrate, development of a new ferroelectric film with a small remnant polarization value, proposal and fabrication of a 1T2C-type memory cell with good retention characteristics, and so on.
Hiroshi Ishiwara 한국물리학회 2009 Current Applied Physics Vol.9 No.11
Current status of ferroelectric-gate FETs (field effect transistors) is reviewed. First, characteristics of Si FETs with MFIS (metal–ferroelectric–insulator–semiconductor) gate structures are discussed. It has been shown that the data retention characteristics of ferroelectric-gate FETs are much improved by use of HfO2-based buffer layers which are inserted between the ferroelectric-gate film and Si substrate for preventing inter-diffusion of constituent elements. Then, usefulness of organic ferroelectrics such as copolymers of vinyliden fluoride and trifluoroethylene (P(VDF–TrFE)) in fabrication of MFIS devices is demonstrated. In an Au/P(VDF–TrFE)/Ta2O5/Si MFIS diode, a memory window as wide as 2.9 V has been obtained with a voltage sweep of ±4 V. Finally, operation mechanisms in ferroelectric-gate CNT (carbon nano-tube) transistors are discussed, assuming Schottky barrier conduction at the source and drain contacts. Current status of ferroelectric-gate FETs (field effect transistors) is reviewed. First, characteristics of Si FETs with MFIS (metal–ferroelectric–insulator–semiconductor) gate structures are discussed. It has been shown that the data retention characteristics of ferroelectric-gate FETs are much improved by use of HfO2-based buffer layers which are inserted between the ferroelectric-gate film and Si substrate for preventing inter-diffusion of constituent elements. Then, usefulness of organic ferroelectrics such as copolymers of vinyliden fluoride and trifluoroethylene (P(VDF–TrFE)) in fabrication of MFIS devices is demonstrated. In an Au/P(VDF–TrFE)/Ta2O5/Si MFIS diode, a memory window as wide as 2.9 V has been obtained with a voltage sweep of ±4 V. Finally, operation mechanisms in ferroelectric-gate CNT (carbon nano-tube) transistors are discussed, assuming Schottky barrier conduction at the source and drain contacts.
Impurity substitution effects in BiFeO<sub>3</sub> thin films-From a viewpoint of FeRAM applications
Elsevier 2012 Current Applied Physics Vol.12 No.3
Impurity substitution effects in BiFeO<SUB>3</SUB> thin films are reviewed from a viewpoint of FeRAM (ferroelectric random access memory) applications, in which such characteristics as a large remanent polarization, a low coercive voltage, and excellent fatigue endurance are most important. First, it is described that substitution experiments for Bi and Fe atoms in the films have already been conducted using almost all rare earth and transition metal elements. A list of the published paper is given in a form of the periodic table of elements. Then, two typical cases, La substitution for the Bi site and Mn substitution for the Fe site, are reviewed in detail. Particular attention is paid to the role of these impurity atoms by which the ferroelectric and insulating properties of BiFeO<SUB>3</SUB> films are significantly improved. Finally, impurity effects due to substitution or co-substitution of other elements are reviewed.
Min Liao,Ishiwara, H.,Ohmi, S. IEEE 2011 IEEE electron device letters Vol.32 No.11
<P>Low-voltage operating pentacene-based organic field-effect transistors (OFETs) with a HfON gate insulator have been fabricated with a fully room-temperature process. Despite its thin capacitance equivalent thickness of 3.3 nm, the room-temperature-processed HfON gate insulator shows a low leakage current density of 7 × 10<SUP>-7</SUP> A/cm<SUP>2</SUP> at a gate voltage of -2 V. Moreover, the fully room-temperature-fabricated OFET (channel <I>W</I>/<I>L</I> = 1650/100 μm) shows a low subthreshold swing of 0.12 V/decade, a large on/off-current ratio of 6.8 × 10<SUP>4</SUP>, a threshold voltage of -0.5 V, and a hole mobility of 0.25 cm<SUP>2</SUP>/V·s at an operating voltage of -2 V.</P>