MRAM Ternary CAM Cell Design for High-Speed Lookup
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Solution Overview
Problem
Current MRAM-based TCAM cells struggle with storing more than two resistance states and achieving compact size due to their design, leading to limitations in search speed and capacity in high-speed lookup-intensive applications.
Innovation Solution
A self-referenced MRAM-based TCAM cell design featuring two magnetic tunnel junctions with freely variable search magnetization, a storage layer that can switch between stable directions, and a tunnel barrier layer, along with specific current lines for writing and heating, allowing for the storage of three distinct logic states by generating magnetic fields and heating currents to switch magnetization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional MRAM-based TCAM cell design is used, then the cell structure is simple, but the cell cannot store more than two resistance states
Solution Approach 1:
The TCAM cell is segmented into two separate magnetic tunnel junctions (MTJs) connected in series, where each MTJ independently stores one bit of information. This segmentation allows the cell to store three distinct resistance states (0, 1, and X) by combining the states of individual MTJs, thereby increasing storage versatility without excessive complexity
Solution Approach 2:
The patent implements multi-functionality by enabling the TCAM cell to perform both standard binary storage and ternary storage operations using the same physical structure. The two MTJs can be configured to achieve three resistance states, allowing the cell to function as either binary or ternary storage depending on the application requirements
2Speed
If separate match logic per memory row is implemented, then search speed is improved, but device area increases
Solution Approach 1:
The patent merges the storage function and match logic function into a single integrated structure. The two MTJs per cell serve dual purposes: storing data and performing match operations through their combined resistance states. This eliminates the need for separate match logic circuits, thereby reducing device area while maintaining high search speed through parallel operation across all cells
3Speed
If SRAM-based TCAM cell is used, then search operation is fast, but power dissipation is high due to volatility
Solution Approach 1:
The patent replaces the volatile SRAM-based mechanical switching system with a non-volatile magnetic tunnel junction system. The MTJs use magnetic tunneling effects rather than charge-based switching, providing non-volatile storage that maintains data without continuous power, thereby reducing power dissipation while maintaining fast search operation capabilities
4Adaptability or versatility
If two perpendicular field lines are used for writing, then write capability is improved, but cell compactness deteriorates
Solution Approach 1:
The patent transitions from using two perpendicular field lines in the plane to using a single field line combined with thermal activation. By heating the MTJ above the blocking temperature and then applying a field pulse, the system achieves enhanced write capability through thermal assistance without requiring additional perpendicular field lines, thereby maintaining cell compactness
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
Enables high-speed write and search operations while enabling the storage of three distinct cell logic states, improving search speed and capacity without compromising compactness.
Implementation Method 1
registered data is written by setting a magnetic orientation of the first magnetic layer in the magnetic tunnel junction via current pulses in one or more current lines
Implementation Method 2
The data sense is performed by measuring cell resistance, which depends upon the relative magnetic orientation of the magnetic layers
Implementation Method 3
a heating current for heating the magnetic tunnel junction above a blocking temperature
Data Source
Figure 1
Figure 2
Figure 3(a)~3(d)
AI summary
The present disclosure concerns a self-referenced magnetic random access memory-based ternary content addressable memory (MRAM-based TCAM) cell (1) comprising a first and second magnetic tunnel junction (2, 2'); a first and second conducting strap (7, 7') adapted to pass a heating current (31) in the first and second magnetic tunnel junction (2, 2'), respectively; a conductive line (3) electrically connecting the first and second magnetic tunnel junctions (2, 2') in series; a first current line (4) for passing a first field current (41) to selectively write a first write data to the first magnetic tunnel junction (2); and a second current line (4') for passing a write current (31, 41') to selectively write a second write data to the second magnetic tunnel junction (2'), such that three distinct cell logic states can be written in the MRAM-based TCAM cell (1).