1T2R RRAM Cell with Reactive Electrode for Crossbar Array Power Reduction

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Solution Overview

Problem

Crossbar array circuits with traditional one-transistor-one-memristor (1T1R) structures face limitations in power consumption, manufacturing cost, and transistor utilization due to high conductance in Low-Resistance State (LRS) during vector-matrix multiplication operations, and significant area overhead from Digital-to-Analog Converter (DAC) and Analog-to-Digital Converter (ADC) circuits.

Innovation Solution

The implementation of a one-transistor-two-memristor (1T2R) crossbar array circuit with a reactive top electrode creating oxygen vacancies and a second RRAM stack acting as a current limiter, reducing LRS conductance, and utilizing a single set of DAC and ADC to support two crossbar arrays, effectively doubling computing memory capacity and reducing power consumption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a traditional 1T1R crossbar array circuit is used, then the structure is simple and manufacturing is easier, but the LRS conductance is high causing high power consumption during vector-matrix multiplication

Engineering Contradiction:

Improvestructure simplicityVSAvoidpower consumption

Core Design Contradiction:

Ease of manufactureVSLoss of energy

Solution Approach 1:

The patent merges two RRAM stacks into a single 1T2R cell structure, where the first RRAM stack provides high conductance for analog computing while the second RRAM stack limits the LRS conductance. This combination allows the circuit to achieve low power consumption through the current-limiting effect of the second stack, while maintaining the manufacturing simplicity of standard crossbar array processes.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent changes the conductance parameter of the LRS state by introducing the second RRAM stack with higher resistance. This parameter modification reduces the LRS conductance by at least one order, directly addressing the high power consumption issue while preserving the essential crossbar array functionality.

Inventive Principle:

Principle #35Parameter changes

2Productivity

If more DAC and ADC circuits are added to support more crossbar arrays, then the computing memory capacity increases, but the area overhead and manufacturing cost increase

Engineering Contradiction:

Improvecomputing memory capacityVSAvoidarea overhead

Core Design Contradiction:

ProductivityVSArea of stationary object

Solution Approach 1:

The patent makes a single set of DAC and ADC circuits universal by enabling them to support multiple crossbar arrays through the 1T2R structure. The second RRAM stack acts as a current limiter that allows the same I/O circuitry to be shared across multiple arrays, effectively doubling the computing memory capacity supported by each DAC-ADC pair and reducing the area overhead per unit of computing capacity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Productivity

If traditional 1T1R structures are used, then transistor utilization is lower, but the device complexity is reduced

Engineering Contradiction:

Improvetransistor utilizationVSAvoidstructure complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent combines two RRAM stacks with a single transistor to form a 1T2R structure, thereby doubling the transistor utilization compared to traditional 1T1R designs. Each transistor now controls two memory devices, effectively increasing productivity while the added complexity is confined to the memory stack rather than the control circuitry.

Inventive Principle:

Principle #5Merging (Combining)

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 configuration reduces operation current by at least one order, lowers power consumption, enhances reliability and uniformity during vector-matrix multiplication, and halves the manufacturing cost by allowing a single set of DAC and ADC to support two crossbar arrays, while doubling transistor utilization and reducing area overhead.

Implementation Method 1

a top electrode formed on the first RRAM stack... the top electrode is a reactive electrode which is configured to provide the first RRAM stack and the second RRAM stack with oxygen vacancies near the reactive electrode

Methodology Applied

Scientific EffectOxygen diffusion: Diffusion

Data Source

PatentUS10804324B11T2R RRAM cell and common reactive electrode in crossbar array circuits

Publication Date: 2020.10.13 TETRAMEM INC

AI summary

Technologies relating to a crossbar array circuit with a one-transistor-two-memristor (1T2R) Resistive Random-Access Memory (RRAM) and a common reactive electrode in the applications of the crossbar array circuit are disclosed. An example crossbar array circuit includes: a two-memristor structure, wherein the two-memristor structure includes: a first bottom electrode; a first RRAM stack formed on the first bottom electrode; a top electrode formed on the first RRAM stack; a second RRAM stack formed on the top electrode; and a second bottom electrode formed on the second RRAM stack, wherein the top electrode is a reactive or scavenging electrode which is configured to provide the first RRAM stack and the second RRAM stack with oxygen vacancies near the reactive electrode; and a one-transistor structure, wherein the one-transistor structure includes: a source electrode; a gate electrode; and a drain electrode, wherein the source electrode is connected to the top electrode.