Two-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 two-terminal switch, comprising:
 a first electrode;   a second electrode; and   a memory element positioned between the first and second electrodes and 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 first electrode is physically connected with the mixed valence oxide, and   wherein the second electrode is physically connected with the electrolyte.   
     
     
         2 . The two-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 two-terminal switch of  claim 1 , wherein the electrolyte includes a thickness that is approximately 50 Å or less. 
     
     
         4 . The two-terminal switch of  claim 1 , wherein the mixed valence oxide includes a thickness that is approximately 500 Å or less. 
     
     
         5 . The two-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 two-terminal switch of  claim 5 , wherein the mobile ions comprise cations or anions. 
     
     
         7 . The two-terminal switch of  claim 6 , wherein the anions comprise oxygen ions. 
     
     
         8 . The two-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 two-terminal switch of  claim 1 , wherein the electrolyte comprises a metal oxide. 
     
     
         10 . The two-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 two-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 two-terminal switch of  claim 1 , wherein the memory element and the first and second electrodes are positioned in a cross-point array. 
     
     
         13 . The two-terminal switch of  claim 1 , wherein the mixed valence oxide comprises a conductive oxide. 
     
     
         14 . The two-terminal switch of  claim 13 , wherein the conductive oxide comprise a material having a form of an ABX 3  structure. 
     
     
         15 . The two-terminal switch of  claim 13 , wherein the ABX 3  structure comprises a perovskite. 
     
     
         16 . The two-terminal switch of  claim 1 , wherein a selected one or both of the first electrode or the second electrode comprises platinum. 
     
     
         17 . The two-terminal switch of  claim 1  and further comprising:
 a reservoir physically in contact with the electrolyte and positioned between the second electrode and the electrolyte, the reservoir operative as a repository for the mobile ions.   
     
     
         18 . The two-terminal switch of  claim 17 , wherein the reservoir comprises IrO x . 
     
     
         19 . The two-terminal switch of  claim 18 , wherein the mobile ions are oxygen ions. 
     
     
         20 . A method of operating a two-terminal switch, comprising:
 providing a memory element including a mixed valence oxide having mobile ions and physically connected with a first 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 second electrode;   applying a first write voltage across the first and second 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 first and second 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.   
     
     
         21 . The method of operating a two-terminal switch of  claim 20 , wherein the first conductivity and the second conductivity are indicative of stored data. 
     
     
         22 . The method of operating a two-terminal switch of  claim 21 , wherein the stored data is retained in the absence of power. 
     
     
         23 . The method of operating a two-terminal switch of  claim 20  and further comprising:
 applying a read voltage across the across the first and second 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.   
     
     
         24 . The method of operating a two-terminal switch of  claim 23 , wherein the read voltage is applied as a voltage pulse. 
     
     
         25 . The method of operating a two-terminal switch of  claim 20 , wherein the first conductivity is lower than the second conductivity. 
     
     
         26 . The method of operating a two-terminal switch of  claim 20 , wherein the first write voltage has a magnitude and/or a polarity that is different than the second write voltage. 
     
     
         27 . The method of operating a two-terminal switch of  claim 20 , wherein the first write voltage and the second write voltage are applied as voltage pulses. 
     
     
         28 . A reversibly switchable two-terminal switch, comprising:
 a first electrode;   a second electrode; and   a memory element positioned between the first and second electrodes and 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 first electrode is physically connected with the mixed valence oxide,   wherein the second electrode is physically connected with the electrolyte, and   wherein the memory element is configured to reversibly switch between a second conductivity and a first conductivity by applying a first voltage across the first and second electrodes operative to transport a portion of the mobile ions from the mixed valence oxide and into the electrolyte and is configured to reversibly switch between the first conductivity and the second conductivity by applying a second voltage across the first and second electrodes operative to transport the portion of mobile ions from the electrolyte and back into the mixed valence oxide.   
     
     
         29 . The reversibly switchable two-terminal switch of  claim 28 , wherein the first conductivity and the second conductivity are indicative of stored data. 
     
     
         30 . The reversibly switchable two-terminal switch of  claim 28  and further comprising:
 a reservoir physically in contact with the electrolyte and positioned between the second electrode and the electrolyte, the reservoir operative as a repository for the mobile ions.   
     
     
         31 . A method for reversibly switching a two-terminal switch, comprising:
 providing a memory element positioned between a first electrode and a second electrode, the 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, the first electrode is physically connected with the mixed valence oxide, and the second electrode is physically connected with the electrolyte;   applying a first voltage across the first and second 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 voltage is applied, the transport operative to change a conductivity of the memory element to a first conductivity;   applying a second voltage across the first and second 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 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;   optionally repeating the applying the first voltage to switch the memory element from the second conductivity to the first conductivity; and   optionally repeating the applying the second voltage to switch the memory element from the first conductivity to the second conductivity.   
     
     
         32 . A variable conductivity reversibly switchable two-terminal switch, comprising:
 a first electrode;   a second electrode; and   a memory element positioned between the first and second electrodes and 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 first electrode is physically connected with the mixed valence oxide,   wherein the second electrode is physically connected with the electrolyte, and   wherein the memory element includes a variable conductivity that is a function of a quantity of the mobile ions that are transported into the electrolyte or transported out of the electrolyte under the influence of the voltage.   
     
     
         33 . The variable conductivity reversibly switchable two-terminal switch of  claim 32 , wherein the variable conductivity is indicative of multiple resistive states. 
     
     
         34 . The variable conductivity reversibly switchable two-terminal switch of  claim 33 , wherein the multiple resistive states are indicative of at least two bits of stored data. 
     
     
         35 . The variable conductivity reversibly switchable two-terminal switch of  claim 32  and further comprising:
 a reservoir physically in contact with the electrolyte and positioned between the second electrode and the electrolyte, the reservoir operative as a repository for the mobile ions.