ReRAM Over-Programming Prevention via Feedback Passgate Control

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Solution Overview

Problem

Resistive random-access memory (ReRAM) cells tend to be over-programmed to an on resistance (Ron) level that is too low, making it difficult to re-erase them, as the programming speed is dependent on the power applied and can result in unacceptably low Ron values, leading to challenges in later re-programming.

Innovation Solution

The implementation of negative feedback-passgate-devices between pull-up and pull-down devices and bit-lines, in parallel with erase-mode-bypass-devices, which sense and limit the programming current based on IR drops across bit-lines, ensuring the ReRAM cells are programmed to a higher Ron level by controlling the feedback-passgate resistance and using MOS transistor voltage threshold drops or buffers to manage the programming current.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If programming voltage is applied to decrease ReRAM resistance to achieve faster programming speed, then programming speed is improved, but ReRAM resistance becomes too low (over-programming) making re-erasing difficult

Engineering Contradiction:

Improveprogramming speedVSAvoidre-erasing capability

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The patent implements a feedback mechanism using passgate devices that sense the programming current and dynamically adjust the programming voltage. When the ReRAM cell resistance reaches a predetermined threshold indicating sufficient programming, the feedback circuit automatically reduces or terminates the programming voltage, preventing over-programming while maintaining fast programming speeds throughout the effective programming range.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent employs dynamic control of the programming voltage through passgate devices whose resistance changes based on the programming state. The passgate resistance increases as programming progresses, naturally limiting the current and voltage applied to the ReRAM cell, thereby preventing over-programming while allowing fast initial programming.

Inventive Principle:

Principle #15Dynamics

2Productivity

If programming current is increased to improve programming speed, then programming speed is improved, but power consumption increases and causes IR drops affecting voltage control

Engineering Contradiction:

Improveprogramming throughputVSAvoidpower consumption

Core Design Contradiction:

ProductivityVSUse of energy by moving object

Solution Approach 1:

The feedback mechanism monitors the actual current flowing through the ReRAM cell and adjusts the programming voltage accordingly. This ensures optimal power utilization - applying sufficient voltage to achieve fast programming without excessive current that would waste power and cause problematic IR drops in the bit lines and access transistors.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent dynamically changes the programming voltage parameter during the programming operation. The voltage starts at a higher level for fast initial programming and automatically decreases as the ReRAM cell approaches the target resistance state, optimizing the balance between programming speed and power consumption throughout the process.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If programming voltage is continuously applied to ensure complete programming, then programming completeness is improved, but ReRAM resistance drops below acceptable levels causing over-programming

Engineering Contradiction:

Improveprogramming completenessVSAvoidresistance control precision

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The feedback circuit continuously monitors the programming progress and automatically terminates or reduces the programming voltage when the ReRAM cell resistance reaches the predetermined threshold. This ensures complete programming without over-programming, maintaining precise control over the final resistance value and preserving re-erasing capability.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent sets a predetermined resistance threshold before programming begins, which serves as the stopping criterion. The feedback mechanism ensures programming stops precisely at this pre-determined point, preventing the resistance from dropping below acceptable levels while guaranteeing sufficient programming completeness.

Inventive Principle:

Principle #10Preliminary action

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach effectively prevents over-programming by terminating the programming operation at a higher Ron value, allowing for easier re-erase of ReRAM cells by shifting and sharpening power peaks, ensuring the cells remain at a stable resistance within the desired range.

Implementation Method 1

limit the programming current as a function of a rise in programming current... sensing programming current drawn by the ReRAM cell... based on IR drops across bit-lines

Methodology Applied

Scientific EffectIR drop: Ohm's Law

Data Source

PatentUS10147485B2Circuits and methods for preventing over-programming of ReRAM-based memory cells

Publication Date: 2018.12.04 MICROSEMI SOC CORP

AI summary

A method for preventing over-programming of resistive random access (ReRAM) based memory cells in a ReRAM memory array includes applying a programming voltage in a programming circuit path including a ReRAM memory cell to be programmed, sensing programming current drawn by the ReRAM cell while the programming voltage is applied across the memory cell, and decreasing the programming current as a function of a rise in programming current.