Non-volatile SRAM Cell with MTJ Backup for Leakage Reduction
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Solution Overview
Problem
Static Random Access Memory (SRAM) arrays face significant power consumption due to increasing leakage currents with aggressive scaling of MOSFETs, making it challenging to power down portions of the chip without losing stored memory contents.
Innovation Solution
Implementing a non-volatile SRAM design that transfers data from static storage nodes to non-volatile storage nodes, such as magnetic tunnel junction (MTJ) devices, during standby mode, allowing the SRAM to be powered down without data loss, and restoring data when powered back up.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If MOSFETs are aggressively scaled to increase memory density, then memory capacity is improved, but leakage currents increase causing higher power consumption
Solution Approach 1:
The SRAM cell is segmented into two distinct storage systems: volatile storage nodes (first storage node) for active data and non-volatile storage nodes (second storage node) for backup. This segmentation allows the cell to operate in different modes - fully powered for active use and partially powered for standby, thereby reducing overall power consumption while maintaining memory density benefits from scaled MOSFETs
Solution Approach 2:
The patent changes the operational parameters of the SRAM cell by introducing dual storage nodes with different volatility characteristics. The first storage node operates with standard voltage levels during active mode, while the second storage node maintains data through its non-volatile properties during standby mode, enabling dynamic parameter adjustment based on operational state
2Loss of energy
If portions of the SRAM chip are powered down to reduce leakage currents, then power consumption is reduced, but stored memory contents are lost
Solution Approach 1:
Before powering down the SRAM cell to standby mode, the data is preliminarily transferred from the volatile first storage node to the non-volatile second storage node. This preliminary action ensures data preservation before the power reduction occurs, allowing the cell to enter low-power state without losing stored information
Solution Approach 2:
The second storage node acts as an intermediary backup storage mechanism. When the first storage node is powered down, the second storage node maintains the data through its non-volatile properties, serving as a mediator that prevents information loss during the power transition
3Reliability
If a non-volatile storage node is added to each SRAM cell, then data retention during power down is improved, but device complexity increases
Solution Approach 1:
The second storage node serves multiple functions: it acts as backup storage during standby mode, enables data retention without external power, and allows the SRAM cell to operate in both volatile and non-volatile modes. This multi-functionality justifies the additional component by providing versatile operational capabilities beyond simple data storage
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 reduces power consumption during standby mode while maintaining data integrity, enabling efficient memory management and scaling in memory density.
Implementation Method 1
the second storage node comprises a two terminal magnetic tunnel junction (MTJ) device
Implementation Method 2
the first ferromagnetic layer is coupled to the first storage node and is unpinned such that a polarization of an associated spin value can rotate. The second ferromagnetic layer is in contact with an anti-ferromagnetic layer coupled to a control line and is pinned such that a polarization of an associated spin value is fixed in one direction
Data Source
AI summary
Methods, devices and systems for non-volatile static random access memory (SRAM) are provided. One method embodiment for operating an SRAM includes transferring data from a pair of static storage nodes of the SRAM to a pair of non-volatile storage nodes when the SRAM is placed in a standby mode. The method further includes transferring data from the pair of non-volatile storage nodes to the pair of static storage nodes when the SRAM exits the standby mode.