Re: memristors?
Posted: Wed Feb 04, 2009 2:21 pm
MrAl, Given how little we really know about these things, your motor/pot analogy is as good as any. However the output is determined by the input at all times making it more like just a non linear function. To be a memristor (by my definition) it needs some hysteresis. Maybe if you added some slop to the gear box or a band where the motor would turn but the pot was still stationary
Going back to the device described in the IEEE article. I like to think in terms of a curve trace. Imagine an X,Y graph where X is voltage and Y is current (Curve trace plot) Starting at the origin such a device would trace out a resistive characteristic going in the +, + direction (upper right quadrant) at some point the slope of this resistor would start to change (lower in this case) when the sweep voltage is reversed, the trace would proceed back to the origin at the new lower resistance slope. Operating the device below the current/voltage where it started changing would not alter the resistance. Now going in the -, - direction the slope would be for a low resistance until it reached the threshold again and then the characteristic would bend back to the higher resistance and stay that way as the voltage were reduced back to 0V again. Naturally there would be limits to how much the resistance could change. It appears they want to use this device in and out of saturation like a switch rather than as a non linear transfer function (which I described as near the point the curve bends) but that may yield interesting applications too.
Theoretically it may be possible to make one of these starting with a FET but the channel would need to trap the minority carriers (that allow conduction) and keep them there while the power was off then reject those carriers when an opposite gate voltage were applied. In practical terms it would be very hard to find a material that allows carrier mobility without having massive leakage when it was off. Remember charge carriers are holes and electrons which can move within a crystal lattice while a memristor requires that the atoms or ions become mobile. Flash memory is similar but requires several or more transistors and a very special capacitor like structure to replicate this function.
Going back to the device described in the IEEE article. I like to think in terms of a curve trace. Imagine an X,Y graph where X is voltage and Y is current (Curve trace plot) Starting at the origin such a device would trace out a resistive characteristic going in the +, + direction (upper right quadrant) at some point the slope of this resistor would start to change (lower in this case) when the sweep voltage is reversed, the trace would proceed back to the origin at the new lower resistance slope. Operating the device below the current/voltage where it started changing would not alter the resistance. Now going in the -, - direction the slope would be for a low resistance until it reached the threshold again and then the characteristic would bend back to the higher resistance and stay that way as the voltage were reduced back to 0V again. Naturally there would be limits to how much the resistance could change. It appears they want to use this device in and out of saturation like a switch rather than as a non linear transfer function (which I described as near the point the curve bends) but that may yield interesting applications too.
Theoretically it may be possible to make one of these starting with a FET but the channel would need to trap the minority carriers (that allow conduction) and keep them there while the power was off then reject those carriers when an opposite gate voltage were applied. In practical terms it would be very hard to find a material that allows carrier mobility without having massive leakage when it was off. Remember charge carriers are holes and electrons which can move within a crystal lattice while a memristor requires that the atoms or ions become mobile. Flash memory is similar but requires several or more transistors and a very special capacitor like structure to replicate this function.