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The memristor (; a portmanteau of ''memory resistor'') was a term coined in 1971 by circuit theorist Leon Chua as a missing non-linear passive two-terminal electrical component relating electric charge and magnetic flux linkage. The operation of RRAM devices was recently connected to the memristor concept.〔D. B. Strukov, G. S. Snide, D. R. Stewart, and R. S. Williams, “The missing memristor found”, Nature 453, 80-83, 2008〕 According to the characterizing mathematical relations, the memristor would hypothetically operate in the following way. The memristor's electrical resistance is not constant but depends on the history of current that had previously flowed through the device, i.e., its present resistance depends on how much electric charge has flowed in what direction through it in the past. The device remembers its history—the so-called ''non-volatility property''.〔 When the electric power supply is turned off, the memristor remembers its most recent resistance until it is turned on again. Leon Chua has more recently argued that the definition could be generalized to cover all forms of two-terminal non-volatile memory devices based on resistance switching effects. However, some experimental evidence contradicts this claim since a non-passive nanobattery effect is observable in resistance switching memory. Chua also argued that the memristor is the oldest known circuit element, with its effects predating the resistor, capacitor and inductor. In 2008, a team at HP Labs claimed to have found Chua's missing memristor based on an analysis of a thin film of titanium dioxide; the HP result was published in ''Nature''.〔 The memristor is currently under development by various teams including Hewlett-Packard, SK Hynix and HRL Laboratories. These devices are intended for applications in nanoelectronic memories, computer logic and neuromorphic/neuromemristive computer architectures. In October 2011, the HP team announced the commercial availability of memristor technology within 18 months, as a replacement for Flash, SSD, DRAM and SRAM. Commercial availability of new memory was more recently estimated as 2018. In March 2012, a team of researchers from HRL Laboratories and the University of Michigan announced the first functioning memristor array built on a CMOS chip. ==Background== In his 1971 paper, Chua extrapolated a conceptual symmetry between the nonlinear resistor (voltage vs. current), nonlinear capacitor (voltage vs. charge) and nonlinear inductor (magnetic flux linkage vs. current). He then inferred the possibility of a memristor as another fundamental nonlinear circuit element linking magnetic flux and charge. In contrast to a linear (or nonlinear) resistor the memristor has a dynamic relationship between current and voltage including a memory of past voltages or currents. Other scientists had proposed dynamic memory resistors such as the memistor of Bernard Widrow, but Chua attempted to introduce mathematical generality. Memristor resistance depends on the integral of the input applied to the terminals (rather than on the instantaneous value of the input as in a varistor).〔 Since the element "remembers" the amount of current that last passed through, it was tagged by Chua with the name "memristor". Another way of describing a memristor is as any passive two-terminal circuit element that maintains a functional relationship between the time integral of current (called charge) and the time integral of voltage (often called flux, as it is related to magnetic flux). The slope of this function is called the ''memristance'' ''M'' and is similar to variable resistance. The memristor definition is based solely on the fundamental circuit variables of current and voltage and their time-integrals, just like the resistor, capacitor and inductor. Unlike those three elements however, which are allowed in linear time-invariant or LTI system theory, memristors of interest have a dynamic function with memory and may be described as some function of net charge. There is no such thing as a standard memristor. Instead, each device implements a particular function, wherein the integral of voltage determines the integral of current, and vice versa. A linear time-invariant memristor, with a constant value for ''M'', is simply a conventional resistor.〔 Manufactured devices are never purely memristors (''ideal memristor''), but also exhibit some capacitance and resistance. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「memristor」の詳細全文を読む スポンサード リンク
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