Memristor

The Mysterious Memristor Revolution

Anyone familiar with electronics knows the trinity of fundamental components: the resistor, the capacitor and the inductor. In 1971, a University of California, Berkeley, engineer predicted that there should be a fourth element: a memory resistor, or memristor. But no one knew how to build one. Now, 37 years later, electronics have finally gotten small enough to reveal the secrets of that fourth element “The memristor”. A memristor (a portmanteau of "memory resistor") is a passive two-terminal circuit element in which the resistance is a function of the time history of the current and voltage through the device.

The memristor's story starts nearly four decades ago with a flash of insight by IEEE Fellow and nonlinear-circuit-theory pioneer Leon Chua. Examining the relationships between charge and flux in resistors, capacitors, and inductors in a 1971 paper, Chua postulated the existence of a fourth element called the memory resistor. Such a device, he figured, would provide a similar relationship between magnetic flux and charge that a resistor gives between voltage and current. In practice, that would mean it acted like a resistor whose value could vary according to the current passing through it and which would remember that value even after the current disappeared. But the hypothetical device was mostly written off as a mathematical dalliance. Thirty years later, HP senior fellow Stanley Williams and his group were working on molecular electronics when they started to notice strange behaviour in their devices. ”They were doing really funky things, and we couldn't figure out what [was going on],” Williams says. Then his HP collaborator Greg Snider rediscovered Chua's work from 1971. ”He said, ’Hey guys, I don't know what we've got, but this is what we want ,' ” Williams remembers. Williams spent several years reading and rereading Chua's papers. ”It was several years of scratching my head and thinking about it.” Then...