Memory Cell TMR Ratio Enhancement via Series TMRE Element
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Solution Overview
Problem
As magnetic tunnel junctions (MTJs) in memory devices are scaled to smaller dimensions, their tunneling magnetoresistance (TMR) ratio decreases, leading to performance issues due to reduced differences in resistance states, making them unsuitable for certain memory applications, despite optimizations of the free, fixed, and dielectric layers which are inherently limited.
Innovation Solution
Incorporating a tunneling magnetoresistance enhancement (TMRE) element in series with the MTJ, which is a variable resistor that switches between high and low resistance states in response to a voltage, enhancing the overall TMR ratio by maintaining a stable low resistance state when the MTJ is in its low resistance state and remaining in a high resistance state when the MTJ is in its high resistance state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If magnetic tunnel junctions are scaled to smaller dimensions to increase memory capacity, then the number of memory cells per chip area increases, but the tunneling magnetoresistance ratio decreases leading to performance degradation
Solution Approach 1:
The patent divides the memory cell into multiple functional segments: the original MTJ element and an additional enhancement element coupled in series. This segmentation allows each component to perform a specific function - the MTJ provides the basic magnetic storage while the enhancement element specifically addresses the TMR ratio degradation, thereby resolving the contradiction between scaling and performance maintenance
Solution Approach 2:
The patent employs a composite structure combining different material systems - the magnetic tunnel junction (with its ferromagnetic layers and tunnel barrier) and the enhancement element (with its own resistive materials). This composite approach allows the system to leverage the advantages of each material system: the MTJ's non-volatile magnetic storage and the enhancement element's ability to compensate for TMR loss at scaled dimensions
2Area of stationary object
If the size of MTJ elements is reduced to increase device density, then more memory cells fit in given area, but the difference between high and low resistance states diminishes
Solution Approach 1:
The enhancement element acts as an intermediary component that amplifies the resistance state difference. It couples in series with the MTJ and provides an additional resistance modulation effect, thereby enhancing the overall TMR ratio and improving the differentiation between high and low resistance states in scaled-down devices
Solution Approach 2:
The enhancement element introduces dynamic resistance control to the memory cell. By applying voltages to the enhancement element, the overall resistance of the memory cell can be dynamically adjusted to optimize the TMR ratio, allowing the system to maintain performance across different operating conditions and scaled dimensions
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 TMRE element significantly increases the collective TMR ratio of the memory cell, achieving enhancements of up to 200% or more over the intrinsic TMR of the MTJ, improving the memory cell's performance by maintaining a stable voltage drop and ensuring accurate state determination during read and write operations.
Implementation Method 1
a tunneling magnetoresistance enhancement (TMRE) element in series with the MTJ, which is a variable resistor that switches between high and low resistance states in response to a voltage
Implementation Method 2
The electrical resistance of an MTJ such as an STTM element may be impacted by the orientation of the magnetization of the free magnetic layer relative to the orientation of the magnetization of the fixed magnetic layer
Implementation Method 3
When a current is passed through a magnetization layer of such devices, called the fixed magnetic layer, the current will come out spin polarized. With the passing of each electron in the current through the fixed magnetic layer, the resulting spin (angular momentum) may be transferred to the magnetization of another magnetic layer in the device, called the free magnetic layer, resulting in a small change in the magnetization of the free magnetic layer
Data Source
AI summary
Memory cells with improved tunneling magnetoresistance ratio (TMR) are disclosed. In some embodiments such devices may include a magnetoresistive tunnel junction (MTJ) element coupled in series with a tunneling magnetoresistance enhancement element (TMRE). The MTJ element and TMRE may each be configured to transition between high and low resistance states, e.g., in response to a voltage. In some embodiments, the MTJ and TMRE are configure such that when a read voltage is applied to the cell while the MTJ is in its low resistance state the TMRE is driven to is low resistance state, and when such voltage is applied while the MTJ is in its high resistance state, the TMRE remains in its high resistance state. Devices and systems including such memory cells are also disclosed.