Single-Line MRAM Cell Design for Power and Density Optimization
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Solution Overview
Problem
Conventional thermally-assisted switching magnetic tunnel junction (TAS-MTJ) based MRAM cells have high power consumption and require multiple CMOS metal levels, leading to increased complexity and cost, as well as reduced cell density due to the need for separate lines for heating and magnetic field generation.
Innovation Solution
A single-line thermally-assisted switching MRAM cell design that uses a current line for both heating and magnetization switching, reducing the number of CMOS metal levels to two and allowing for a higher ratio of magnetic field to field current, thereby lowering power consumption and increasing cell density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If separate dedicated lines are used for magnetic field generation and heating, then the magnetic field can be generated effectively, but the device complexity and manufacturing cost increase due to requiring multiple CMOS metal levels
Solution Approach 1:
The patent combines the magnetic field generation line and heating line into a single current line. This single line performs dual functions: generating the magnetic field for magnetization switching and providing heating current for thermally-assisted switching, thereby reducing the number of required CMOS metal levels from three to two
Solution Approach 2:
The current line is designed to serve multiple purposes: it acts as both the field line for magnetic field generation and the bit line for heating and reading operations. This multi-functional design eliminates the need for a separate dedicated field line, simplifying the overall cell structure
2Power
If separate dedicated lines are used for magnetic field generation and heating, then the magnetic field can be generated effectively, but the cell density decreases due to increased spacing requirements
Solution Approach 1:
By merging the field line and heating line into a single current line, the patent eliminates the need for additional spacing between separate lines. This reduces the minimum cell dimensions and allows for higher cell density in the memory array
Solution Approach 2:
The patent repositions the current line to run above the magnetic tunnel junction rather than underneath, utilizing the vertical stacking capability of CMOS processes. This dimensional rearrangement allows the cell to be stacked on the transistor, further reducing the cell footprint
3Area of moving object
If the field line is placed above the magnetic cell at M3 level, then cell density increases, but the magnetic field strength relative to field current decreases requiring higher field current
Solution Approach 1:
The patent applies thermally-assisted switching by heating the magnetic tunnel junction before applying the magnetic field. This preliminary heating action reduces the coercivity of the storage layer, enabling magnetization switching at lower field currents and reducing overall power consumption
Solution Approach 2:
The patent changes the temperature parameter of the magnetic tunnel junction by applying heating current, which modifies the magnetic properties of the storage layer. This parameter change enables more efficient magnetic switching with reduced field current requirements
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 single-line design results in lower manufacturing complexity and cost, increased cell density, and reduced power consumption by maximizing the magnetic field strength relative to the field current, while enabling easier downsizing and higher cell packing density.
Implementation Method 1
heating the magnetic tunnel junction with a heating current that passes through the magnetic tunnel junction
Implementation Method 2
a field current is passed through the field line, producing a magnetic field capable of addressing the magnetic tunnel junction by switching the magnetization
Data Source
AI summary
Magnetic random access memory (MRAM) cell with a thermally assisted switching writing procedure and methods for manufacturing and using same. The MRAM cell includes a magnetic tunnel junction that has at least a first magnetic layer, a second magnetic layer, and an insulating layer disposed between the first and a second magnetic layers. The MRAM cell further includes a select transistor and a current line electrically connected to the junction. The current line advantageously can support a plurality of MRAM operational functions. The current line can fulfill a first function for passing a first portion of current for heating the junction and a second function for passing a second portion of current in order to switch the magnetization of the first magnetic layer.