Multi-terminal reversibly switchable memory device

Abstract

A memory using mixed valence conductive oxides is disclosed. The memory includes a mixed valence conductive oxide that is less conductive in its oxygen deficient state and a mixed electronic ionic conductor that is an electrolyte to oxygen and promotes an electric field effective to cause oxygen ionic motion.

1 . A three-terminal switch, comprising:
 a source electrode;   a drain electrode;   a gate electrode; and   a memory element including
 a mixed valence oxide that includes mobile ions, and 
 an electrolyte that promotes a first electric field operative to transport the mobile ions while under an influence of a voltage, the electrolyte is in contact with the mixed valence oxide and is operative as a repository for the mobile ions, 
   wherein the gate electrode is physically connected with the mixed valence oxide, and   wherein the source electrode and the drain electrode are physically connected with the electrolyte.   
     
     
         2 . The three-terminal switch of  claim 1 , wherein the memory element has an electrical conductivity that can be reversibly switched between a first conductivity and a second conductivity that is greater than the first conductivity as a function of mobile ions that are transported from the mixed valence oxide and into the electrolyte or transported out of the electrolyte and into the mixed valence oxide. 
     
     
         3 . The three-terminal switch of  claim 1 , wherein the electrolyte includes a thickness that is approximately 50 Å or less. 
     
     
         4 . The three-terminal switch of  claim 1 , wherein the mixed valence oxide includes a thickness that is approximately 500 Å or less. 
     
     
         5 . The three-terminal switch of  claim 1 , wherein the mobile ions in the mixed valence oxide comprise a species of ion selected to change a conductivity of the mixed valence oxide from a relatively high conductivity to a relatively low conductivity when a portion of the mobile ions are transported into the electrolyte or from a relatively low conductivity to a relatively high conductivity when the portion mobile ions are transported back into the mixed valence oxide. 
     
     
         6 . The three-terminal switch of  claim 5 , wherein the mobile ions comprise cations or anions. 
     
     
         7 . The three-terminal switch of  claim 6 , wherein the anions comprise oxygen ions. 
     
     
         8 . The three-terminal switch of  claim 1 , wherein the voltage is operative to generate the first electric field in the electrolyte and a second electric field in the mixed valence oxide, the first electric field having a greater magnitude than the second electric field and the first electric field extending into the mixed valance oxide by a distance of at least one Debye length. 
     
     
         9 . The three-terminal switch of  claim 1 , wherein the electrolyte comprises a metal oxide. 
     
     
         10 . The three-terminal switch of  claim 9 , wherein the metal oxide comprises a material selected from the group consisting of Al 2 O x , Ta 2 O x , HfO x , RuO x , CuO x , and ZrO x . 
     
     
         11 . The three-terminal switch of  claim 9 , wherein the metal oxide is stabilized with CaO, MgO, or Y 2 O x  or the metal oxide is doped with Sc. 
     
     
         12 . The three-terminal switch of  claim 1 , wherein the electrolyte is operative as a gate oxide. 
     
     
         13 . The three-terminal switch of  claim 1 , wherein the mixed valence oxide comprises a conductive oxide. 
     
     
         14 . The three-terminal switch of  claim 13 , wherein the conductive oxide comprise a material having a form of an ABX 3  structure. 
     
     
         15 . The three-terminal switch of  claim 13 , wherein the ABX 3  structure comprises a perovskite. 
     
     
         16 . The three-terminal switch of  claim 1 , wherein a selected one or more of the gate, source, or drain electrodes comprises platinum. 
     
     
         17 . A method of operating a three-terminal switch, comprising:
 providing a memory element including, a mixed valence oxide having mobile ions and physically connected with a gate electrode, and an electrolyte in contact with the mixed valence oxide and operative as a repository for the mobile ions, the electrolyte physically connected with a source electrode and a drain electrode;   applying a first write voltage across the gate electrode and a selected one or both of the source and drain electrodes, the electrolyte promotes a first electric field operative to transport a portion of the mobile ions from the mixed valence oxide and into the electrolyte while the first write voltage is applied, the transport operative to change a conductivity of the memory element to a first conductivity; and   applying a second write voltage across the gate electrode and a selected one or both of the source and drain electrodes, the electrolyte promotes a second electric field operative to transport the portion of the mobile ions from the electrolyte and back into the mixed valence oxide while the second write voltage is applied, the transport operative to change the conductivity of the memory element to a second conductivity that is different than the first conductivity.   
     
     
         18 . The method of operating a three-terminal switch of  claim 17 , wherein the first conductivity and the second conductivity are indicative of stored data. 
     
     
         19 . The method of operating a three-terminal switch of  claim 18 , wherein the stored data is retained in the absence of power. 
     
     
         20 . The method of operating a three-terminal switch of  claim 17  and further comprising: applying a read voltage across the across the gate electrode and a selected one or both of the source and drain electrodes, the read voltage operative to generate a read current having a magnitude that is indicative of the first conductivity or the second conductivity, wherein the first write voltage and the second write voltage have magnitudes that are greater than a magnitude of the read voltage, and wherein applying the read voltage is non-destructive to the first conductivity or the second conductivity. 
     
     
         21 . The method of operating a three-terminal switch of  claim 20 , wherein the read voltage is applied as a voltage pulse. 
     
     
         22 . The method of operating a three-terminal switch of  claim 17 , wherein the first conductivity is lower than the second conductivity. 
     
     
         23 . The method of operating a three-terminal switch of  claim 17 , wherein the first write voltage has a magnitude and/or a polarity that is different than the second write voltage. 
     
     
         24 . The method of operating a three-terminal switch of  claim 17 , wherein the first write voltage and the second write voltage are applied as voltage pulses.