ReRAM Forming Current Limiting Circuit
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional resistance change memory devices face challenges with a small margin between setting and resetting voltages, leading to potential false operations and high power consumption due to excessively low resistance values after the forming operation.
Innovation Solution
A nonvolatile semiconductor memory device with a memory cell array incorporating a variable resistor and a current limiting circuit that applies a forming voltage while limiting current to prevent excessive resistance reduction, allowing for controlled transitions between high and low resistance states, thereby maintaining a stable resistance margin and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a forming operation is applied to bring the memory cell structure to a usable state, then the memory cell can change between high-resistance state and low-resistance state, but the resistance value becomes too low causing excessively high current and high power consumption
Solution Approach 1:
The patent applies a forming operation with limited current before normal operation to preliminarily establish the conductive filament without creating excessive low resistance. This preliminary action prepares the memory cell for usable operation while controlling the resistance to remain within acceptable ranges, preventing the excessive current and power consumption that would occur with uncontrolled forming operations.
2Ease of operation
If a small margin is provided between setting voltage and resetting voltage, then the memory cell can operate, but false operations such as false resetting operations may occur
Solution Approach 1:
The patent modifies the resistance characteristics of the variable resistor through controlled forming operations, which changes the voltage-current relationship and enables a larger margin between setting and resetting voltages. By adjusting the resistance parameters during forming, the memory cell achieves both operational feasibility and reliability with reduced risk of false operations.
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
The solution ensures accurate data storage by maintaining a sufficient voltage margin between setting and resetting operations and reduces power consumption by preventing excessive current flow during the forming process.
Implementation Method 1
there is known a resistance change memory (ReRAM: Resistive RAM) that has a transition metal oxide as a recording layer and is configured to store a resistance state in a nonvolatile manner. Write of data to a memory cell is implemented by applying for a short time to a variable resistor a certain setting voltage Vset. As a result, the variable resistor changes from a high-resistance state to a low-resistance state.
Implementation Method 2
erase of data in the memory cell MC is implemented by applying for a long time to the variable resistor in the low-resistance state subsequent to the setting operation a resetting voltage Vreset which is lower than the setting voltage Vset of a time of the setting operation. As a result, the variable resistor changes from the low-resistance state to the high-resistance state.
Data Source
AI summary
A nonvolatile semiconductor memory device according to an embodiment herein includes a memory cell array. The memory cell array includes memory cells each provided between a first line and a second line and each including a variable resistor. A control circuit applies through the first and second lines a voltage necessary for a forming operation of the memory cell. A current limiting circuit limits a value of a current flowing across the memory cell during the forming operation to a certain limit value. The control circuit repeats an operation of applying the voltage by setting the limit value to a certain value and an operation of changing the limit value from the certain value, until forming of the memory cell is achieved.