Nonvolatile Memory Capacitor Voltage Distribution

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Solution Overview

Problem

Conventional nonvolatile semiconductor memory devices using MIM diodes as selectors face reliability issues due to high voltage requirements, leading to dielectric breakdown and difficulty in maintaining insulating properties during set and reset operations.

Innovation Solution

The implementation of a nonvolatile semiconductor memory device with a capacitor having a larger capacity than the variable resistance element, where the voltage is effectively distributed to the variable resistance element, reducing the voltage concentration on the capacitor and using high dielectric-constant films to enhance the capacitor's capacity without increasing its area, thereby preventing dielectric breakdown.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a selector with high resistance against high voltage is used, then the reliability of the selector is improved, but the device complexity increases

Engineering Contradiction:

Improveselector reliabilityVSAvoiddevice complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent changes the voltage distribution parameters by introducing a capacitor in series with the variable resistance element. This parameter change ensures that during set and reset operations, the voltage is distributed such that the selector (capacitor) does not experience excessive voltage stress, thereby improving reliability without requiring complex high-voltage-resistant selector designs

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The capacitor acts as an intermediary element between the variable resistance element and the selector diode. It mediates the voltage distribution during write operations, protecting the diode from high voltage stress while enabling effective resistance switching in the variable resistance element

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If the voltage applied to the memory cell is concentrated in the selector, then the set and reset operations are improved, but the leakage current through the selector increases

Engineering Contradiction:

Improveset and reset operation efficiencyVSAvoidleakage current

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The patent modifies the voltage distribution parameters by introducing a capacitor with specific capacitance value. This parameter change allows the voltage to be effectively concentrated across the variable resistance element during switching operations while limiting the voltage across the selector, thereby maintaining operation efficiency while reducing leakage current

Inventive Principle:

Principle #35Parameter changes

3Reliability

If the capacitor capacity is increased to distribute voltage effectively, then the voltage distribution is improved, but the area of the capacitor increases

Engineering Contradiction:

Improvevoltage distributionVSAvoidcapacitor area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent optimizes the capacitance parameter to achieve effective voltage distribution without excessive area. By carefully selecting the capacitance value range, the design achieves proper voltage distribution across the variable resistance element while maintaining a compact capacitor footprint

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs high dielectric-constant materials for the capacitor dielectric layer. This allows achieving the required capacitance value with a smaller physical area, as the higher dielectric constant enables greater capacitance density

Inventive Principle:

Principle #40Composite materials

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 distributes voltage to the variable resistance element, reducing leakage currents and preventing dielectric breakdown, thereby enhancing the reliability and durability of the memory device.

Implementation Method 1

a capacitor (CP), and a control circuit (8). The capacitor is charged by a leading edge of one of the first and second voltage pulses, and discharged at a trailing edge of one of the first and second voltage pulses

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

using high dielectric-constant films to enhance the capacitor's capacity without increasing its area

Methodology Applied

Scientific EffectDielectric permittivity: Dielectric Permittivity

Data Source

PatentUS8331137B2Nonvolatile semiconductor memory device

Publication Date: 2012.12.11 KIOXIA CORP

AI summary

According to one embodiment, a nonvolatile semiconductor memory device includes a memory cell includes a variable resistance element and a capacitor connected in series between first and second conductive lines, and a control circuit applying one of first and second voltage pulses to the memory cell. The capacitor is charged by a leading edge of one of the first and second voltage pulses, and discharged a trailing edge of one of the first and second voltage pulses. The control circuit makes waveforms of the trailing edges of the first and second voltage pulses be different, changes a resistance value of the variable resistance element from a first resistance value to a second resistance value by using the first voltage pulse, and changes the resistance value of the variable resistance element from the second resistance value to the first resistance value by using the second voltage pulse.