Chapter 41
Memristance
We have seen the three basic components of analog electronics are the resistor, capacitor, and inductor. Let’s
arrange the defining equations for resistanceR, capacitanceC, and inductanceLinto a 2 2 table:
RDV=I LDˆB=IC^1 DV=Q
(We’ll use the reciprocal of capacitance (elastance) to make the pattern clear.) Notice the pattern: in
the first row the current is in the denominator, and in the first column the voltage is in the numerator. You
might guess that there could be another combination,ˆB=Q, to fill in the lower-right corner. This idea led
American electrical engineer Leon Chua to predict the existence of afourthanalog electronic component in
1971, thememristor.^1 ThememristanceMDˆB=Qcompletes the table:
RDV=I LDˆB=IC^1 DV=Q MDˆB=Q
Memristance has the same units as resistance, ohms ().
The memristor was finally discovered during experiments with molecular electronics at the Hewlett-
Packard laboratories in 2008. It behaves like a resistor with a “memory” (hence the name): when voltage is
removed from a memristor, it still “remembers” how much voltage was last applied to it, and for how long.
The resistance increases when the current flows through it in one direction, decreases when current flows in
the opposite direction, and remains unchanged when no current flows through it.
Practical applications are still being discussed, but possibilities include applications to non-volatile com-
puter memory, including computers that could remember their previous state when being powered on, thus
avoiding the usual lengthy boot-up process.
(^1) SeeIEEE Spectrum, http://spectrum.ieee.org/semiconductors/design/the-mysterious-memristor
(May 2008).