Single Bit Line SMT MRAM Array Architecture for Scalable Programming
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Solution Overview
Problem
Conventional spin moment transfer (SMT) MRAM cells require two bit lines for programming, which increases complexity and reduces scalability, whereas conventional MRAMs rely on external magnetic fields for programming, limiting their scalability further.
Innovation Solution
A single bit line architecture is implemented for SMT MRAM cells, utilizing out-of-phase and in-phase data signals, along with column and source line select signals, to program cells bi-directionally, eliminating the need for two bit lines by using a precharge circuit to charge or discharge the bit lines based on logic states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If two bit lines are used for programming SMT MRAM cells, then programming capability is achieved, but device complexity and area increase
Solution Approach 1:
The patent combines the functions of two separate bit lines into a single shared bit line. The single bit line is used for both writing data to and reading data from MRAM cells, eliminating the need for separate bit lines and reducing overall device complexity while maintaining full programming capability.
Solution Approach 2:
The single bit line is designed to serve multiple functions: it acts as both a write bit line and a read bit line, and can be connected to multiple MRAM cells through word lines. This multi-functional design reduces the total number of bit lines needed while preserving all necessary programming and reading operations.
2Ease of operation
If two bit lines are used for programming SMT MRAM cells, then programming capability is achieved, but area increases
Solution Approach 1:
By merging two bit lines into one shared bit line, the physical area required for bit line routing is reduced. The single bit line can be shared across multiple word lines and MRAM cells, decreasing the overall area occupied by the memory array while maintaining programming functionality.
Solution Approach 2:
The patent implements a three-dimensional crossbar architecture where bit lines and word lines intersect in space, allowing a single bit line to serve multiple cells through different word lines. This spatial arrangement enables efficient area utilization compared to planar two-bit-line designs.
3Reliability
If conventional MRAM uses external magnetic fields for programming, then magnetic moment reversal is achieved, but scalability is limited
Solution Approach 1:
The patent replaces the external magnetic field mechanism with a spin transfer torque mechanism. Instead of using external magnets or field coils to reverse magnetic moments, the invention uses spin-polarized current flowing through the MRAM cells to directly transfer angular momentum and reverse magnetization, enabling better scalability and integration.
Solution Approach 2:
The invention changes the fundamental programming parameter from external magnetic field strength to spin-polarized current density. This parameter change enables more efficient and scalable programming, as current can be precisely controlled and localized to individual cells through the crossbar architecture, unlike external magnetic fields that affect larger areas.
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 solution allows for efficient programming of SMT MRAM cells with a single bit line, enhancing scalability and reducing complexity by enabling bi-directional current flow through the magnetic layers, similar to conventional MRAMs but without the need for external magnetic fields.
Implementation Method 1
A spin-torque MTJ element has two ferromagnetic layers, F1 10 and F2 15, and a spacer layer 20 between the ferromagnetic layers, F1 10 and F2 15. When a spin polarized electron 40 flows through the ferromagnetic layers, F1 10 and F2 15, the spin direction 42 rotates according to the directions of magnetic moment M2 55 and M1 50 respectively to the directions 43 and 44. The rotation of spin direction of the electrons in the ferromagnetic layers, F1 10 and F2 15 are the origin of a spin-torque, dM1/dt 47 and dM2/dt 45, to the magnetic moment M1 50 and M2 55. If the given torque is large enough, magnetization of ferromagnetic layer F2 15 and thus the magnetic moment M2 55 is reversed.
Data Source
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AI summary
An SMT MRAM device includes a plurality of SMT MRAM cells arranged in an array of rows and columns. Single bit lines connect the columns of the SMT MRAM cells for receiving an in-phase data signal. Source lines connect pairs of rows of the SMT MRAM cells for receiving an out-of-phase data signal. Out-of-phase switching devices are connected to the source lines for selectively transferring the out-of-phase signal to the at least one source lines. Column select transistors are connected to the single bit lines for transferring an in-phase data signal to a selected column of the SMT MRAM cells. A precharge circuit selectively charges or discharges the single bit lines. Ground switching devices selectively connect to the source lines to a ground reference voltage source. A method for programming a selected SMT MRAM cell within a provided SMT MRAM device is described.