Preservation Circuit And Methods To Maintain Values Representing Data In One Or More Layers Of Memory

Abstract

Circuitry and methods for restoring data in memory are disclosed. The memory may include at least one layer of a non-volatile two-terminal cross-point array that includes a plurality of two-terminal memory elements that store data as a plurality of conductivity profiles and retain stored data in the absence of power. Over a period of time, logic values indicative of the stored data may drift such that if the logic values are not restored, the stored data may become corrupted. At least a portion of each memory may have data rewritten or restored by circuitry electrically coupled with the memory. Other circuitry may be used to determine a schedule for performing restore operations to the memory and the restore operations may be triggered by an internal or an external signal or event. The circuitry may be positioned in a logic layer and the memory may be fabricated over the logic layer.

1 . A memory device, comprising:
 a plurality of re-writeable non-volatile two-terminal memory devices in electrical communication with a memory bus, each memory device including   at least one memory layer including a plurality of memory elements having exactly two terminals and configured in at least one two-terminal cross-point array, each memory element is configured to store data associated with resistance values and includes a tunnel barrier electrically in series with an ion reservoir, and   a silicon substrate including circuitry fabricated on a logic layer of the silicon substrate and at least a portion Of the circuitry electrically coupled with the at least one two-terminal cross-point array and configured to perform data operations on one or more of the plurality of memory elements, wherein the at least one memory layer is in contact with and is fabricated directly above the silicon substrate;   at least one preservation circuit in electrical communication with the at least one two-terminal cross-point array and operative to perform preservation operations on one or more of the plurality of memory elements and configured to, in response to a trigger signal, restore the resistance values to represent the data; and   at least one trigger circuit electrically coupled with the at least one preservation circuit and configured to detect a triggering event and generate the trigger signal.   
     
     
         2 . The memory device of  claim 1 , wherein the at least one preservation circuit is in electrical communication with the memory bus. 
     
     
         3 . The memory device of  claim 1 , wherein the at least one trigger circuit is in electrical communication with the memory bus. 
     
     
         4 . The memory device of  claim 1 , wherein the trigger circuit is configured to detect a change in power as a triggering event and generate the trigger signal to initiate a preservation operation. 
     
     
         5 . The memory device of  claim 1 , wherein the trigger signal comprises a signal selected from the group consisting of a power-on signal and a power-down signal. 
     
     
         6 . The memory device of  claim 1 , wherein the preservation circuit comprises at least one nonvolatile register configured to store information associated with restoring the resistance values to represent the data. 
     
     
         7 . The memory device of  claim 1 , wherein the trigger signal is generated at least 500 milliseconds apart from a previous trigger signal. 
     
     
         8 . The memory device of  claim 1 , wherein the trigger signal and one or more previous trigger signals are aperiodic. 
     
     
         9 . The memory device of  claim 1 , wherein the preservation circuit is further configured to preserve the resistance values of a subset of the memory elements. 
     
     
         10 . The memory device of  claim 1 , wherein the two terminals of each memory element includes a first terminal and a second terminal, a magnitude and a polarity of a write voltage applied across the first and second terminals is operative to move a portion of mobile ions between the ion reservoir and the tunnel barrier, and the resistance values of the data are determined by the mobile ions positioned in the ion reservoir and the tunnel barrier after the write voltage is removed from the first and second terminals, and wherein the data is retained in an absence of electrical power. 
     
     
         11 . The memory device of  claim 10 , wherein each memory element stores non-volatile data as at least two distinct logic states. 
     
     
         12 . The memory device of  claim 11 , wherein the preservation circuit is further configured to restore parametric values representing the distinct logic states. 
     
     
         13 . The memory device of  claim 12 , wherein the preservation circuit is operative to restore the distinct logic states by applying a voltage across the first and second terminals of at least one of the memory elements. 
     
     
         14 . The memory device of  claim 13 , wherein the application of the voltage is operative to increase a resistance value of the at least one of the memory elements and the resistance value is indicative of the logic values. 
     
     
         15 . The memory device of  claim 13 , wherein the application of the voltage is operative to decrease a resistance value of the at least one of the memory elements and the resistance value is indicative of the logic values. 
     
     
         16 . The memory device of  claim 10 , wherein the mobile ions comprise oxygen ions. 
     
     
         17 . The memory device of  claim 1 , wherein the at least one memory layer comprises a plurality of vertically stacked memory layers that are in contact with one another and are integrally fabricated directly over the silicon substrate. 
     
     
         18 . The memory device of  claim 1 , wherein the at least one preservation circuit is included in the circuitry of the logic layer of at least one of the plurality of re-writeable non-volatile two-terminal memory devices. 
     
     
         19 . The memory device of  claim 1 , wherein the at least one trigger circuit is included in the circuitry of the logic layer of at least one of the plurality of re-writeable non-volatile two-terminal memory devices. 
     
     
         20 . The memory device of  claim 1  and further comprising: a host device included in the circuitry of the logic layer of at least one of the plurality of re-writeable non-volatile two-terminal memory devices, the host device in electrical communication with the memory bus.