Phase Change Memory Access Capacitor Current Source

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Solution Overview

Problem

Phase change memory devices require significant currents for programming, leading to large and costly current sources that occupy substantial chip area, limiting their compatibility with existing technologies like CMOS and increasing power consumption.

Innovation Solution

A low-level current source is used to charge an access capacitor, which supplies current to the phase change memory cell, allowing for reduced current source capacity and size by utilizing a combination of access and supplemental capacitance to extend the discharge time, enabling efficient SET and RESET operations with lower power consumption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a high-capacity current source is used to provide sufficient programming current to the phase change memory cell, then reliable SET and RESET operations are achieved, but the current source occupies substantial chip area and increases power consumption

Engineering Contradiction:

Improveprogramming operation reliabilityVSAvoidcurrent source chip area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The access capacitor is pre-charged to a voltage level that stores the necessary charge for programming operations. This preliminary charging action allows the memory cell to receive sufficient programming current when needed, without requiring the current source to continuously provide high current, thereby reducing the current source size while maintaining reliable SET and RESET operations

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The access capacitor acts as an intermediary energy storage element between the current source and the phase change memory cell. It decouples the current source from the high-current demand of programming operations, allowing the current source to be smaller while the capacitor provides the additional current surge needed for reliable programming

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If a high-capacity current source is used to provide sufficient programming current, then programming operations are reliable, but power consumption increases

Engineering Contradiction:

Improveprogramming operation reliabilityVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The access capacitor is pre-charged during non-critical periods to store energy that will be used during programming operations. This preliminary energy storage reduces the instantaneous power demand on the current source, lowering overall power consumption while ensuring reliable programming when the capacitor discharges its stored energy

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system uses periodic charging of the access capacitor followed by discharge during programming operations. This periodic action pattern allows the current source to operate at lower average power levels, reducing energy loss while still providing the high current pulses needed for reliable SET and RESET operations when the capacitor is discharged

Inventive Principle:

Principle #19Periodic action

3Area of stationary object

If the access capacitor discharge time is extended to allow low-level current sources to suffice, then current source capacity can be reduced, but the charging time increases

Engineering Contradiction:

Improvecurrent source sizeVSAvoidcapacitor charging time

Core Design Contradiction:

Area of stationary objectVSLoss of time

Solution Approach 1:

The access capacitor is charged to a voltage level that provides more charge than the minimum required for a single programming operation. This excessive charging allows the capacitor to supply current for extended periods or multiple operations, enabling smaller current sources while the extended charging time is acceptable because it occurs during non-critical periods

Inventive Principle:

Principle #16Partial or excessive 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 reduces the size and cost of current sources, enhances compatibility with CMOS technologies, and minimizes power consumption while maintaining reliable operation of phase change memory devices.

Implementation Method 1

A low-level current source charges an access capacitor in order to store sufficient charge for an ensuing access

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

heats the chalcogenic material by the Joule effect

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Implementation Method 3

Phase change may be induced by increasing the temperature locally. Below 150° C., both of the phases are relatively stable. Above 200° C. and at temperatures less than those necessary for reset, there is an increase in nucleation of the crystallites and, if the material is kept at the crystallization temperature for a sufficiently long time, it undergoes a phase change and becomes crystalline

Methodology Applied

Scientific EffectPhase change: Phase Change

Data Source

PatentUS7778064B2Accessing a phase change memory

Publication Date: 2010.08.17 OVONYX MEMORY TECHNOLOGY LLC

AI summary

A memory employs a low-level current source to access a phase change memory cell. The current source charges an access capacitor in order to store sufficient charge for an ensuing access. When a memory cell is accessed, charge stored on the capacitor is discharged through the phase change memory, supplying a current to the phase change memory cell that is sufficient for the intended access operation and greater than that provided directly by the current source.