VERIFY SCHEME FOR ReRAM

Abstract

Circuitry coupled to a programmable element comprising metal oxide is configured to execute a program-verify operation including: an initial cycle of a program operation and a verify operation, and subsequent cycles. The initial cycle includes an initial instance of the program operation to establish a cell resistance of the programmable element, and an initial instance of the verify operation to determine whether the cell resistance of the memory cell is within the target resistance range. At least one of the subsequent cycles includes an additional pulse having a second polarity to the programmable element, and a subsequent instance of the verify operation. The first polarity of the initial program pulse and the second polarity of the additional pulse have opposite polarities. A subsequent instance of the program operation includes applying a subsequent program pulse having the first polarity to the programmable element.

Description

PRIORITY APPLICATION[0001]This application claims the benefit of U.S. Provisional Patent Application No. 62 / 161,112 filed 13 May 2015. The application is incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention relates to high density memory arrays based on RRAM devices, and particularly relates to a verify scheme for such devices.[0004]2. Description of Related Art[0005]Resistive random access memory (RRAM) is a type of nonvolatile memory that includes metal oxide material which changes resistance between two or more stable resistance ranges by application of electrical pulses at levels suitable for implementation in integrated circuits. The resistance can be read and written via random access. The access lines coupled to the memory cells are connected to circuitry to perform operations, such as SET and RESET operations, which change the state of the memory element in order to store or erase data.[0006]If the data is not...

AI Technical Summary

Benefits of technology

[0008]In various embodiments of the technology, after a program verify operation fails, follow-on pulses do not have to increase in amplitude for successful programming. Because the amplitude does not have to increase, the memory devices undergo less stress and are more reliable. In various embodiments of the technology, after a program verify operation fails, a pulse with a polarity opposite to the polarity of the program pulse is applied after the failed program verify operation and prior to the subsequent program pulse.

Problems solved by technology

Such stronger operation conditions, however, stress and damage the memory element, which makes the device less reliable over repeated use.

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