Magnetic Memory Cell With Differential Spin Devices
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Solution Overview
Problem
Magnetic memories face an insufficient effective signal window due to variations in resistance values of spin device elements and interconnection resistances, leading to read errors caused by overlapping distributions of read and reference signal levels.
Innovation Solution
The magnetic memory design incorporates multiple spin device elements with reversible magnetizations, connected in specific configurations to enhance the signal window by applying bias voltages and utilizing resistor elements to generate differential signals, allowing data identification based on voltage polarity or differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single spin device element is used in each memory cell, then the device structure is simple, but the effective signal window is insufficient due to variations in resistance values
Solution Approach 1:
The memory cell is segmented into multiple spin device elements (first and second spin device elements) connected in series. Each element contributes to the overall resistance, and the differential configuration allows the signal window to be determined by the difference in resistance changes between the two elements, thereby amplifying the effective signal while suppressing common-mode variations.
Solution Approach 2:
The patent applies different magnetic states to different spin device elements within the same memory cell. The first spin device element and the second spin device element are configured to have opposite magnetization directions, creating local quality differences that enable differential signaling and improve the effective signal window.
2Reliability
If the MR ratio of spin device elements is increased to improve signal window, then the effective signal window increases, but the manufacturing precision requirements become more stringent
Solution Approach 1:
The patent extracts and eliminates the common-mode variations affecting both spin device elements by using a differential configuration. The effective signal window is determined by the difference in resistance changes between the two elements, which cancels out common manufacturing variations and focuses only on the differential signal.
Solution Approach 2:
The memory cell uses an asymmetric configuration where the first and second spin device elements have opposite magnetization directions. This asymmetry in magnetic state configuration creates differential resistance changes that amplify the effective signal window while being insensitive to common manufacturing variations.
3Reliability
If bias voltages are applied to multiple spin device elements, then the signal window is enhanced through differential signaling, but the device complexity increases
Solution Approach 1:
The patent merges the functionality of multiple spin device elements into a single memory cell unit. The first and second spin device elements are combined in series, sharing common connection nodes and bias voltage applications, which achieves differential signaling without proportionally increasing the overall device complexity.
Solution Approach 2:
The memory cell structure serves multiple functions simultaneously: it provides differential signaling for enhanced signal window, stores data through magnetization states, and suppresses common-mode variations. The same spin device elements used for data storage also contribute to signal amplification through their differential configuration.
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 configuration effectively increases the effective signal window, improving data reading reliability even when MR ratios are not high, by suppressing variations in spin device element properties and manufacturing process variations.
Implementation Method 1
An element including two magnetic layers and a spacer layer disposed therebetween (hereinafter, referred to as 'spin device element') exhibits a resistance depending on the relative direction of the magnetizations of the two magnetic layers due to the magnetoresistance effect
Implementation Method 2
Most typically, a magnetic memory is configured to achieve data reading by using a magnetoresistance effect, such as a tunnel magnetoresistance effect (TMR effect)
Implementation Method 3
Most typically, a magnetic memory is configured to achieve data reading by using a magnetoresistance effect, such as a tunnel magnetoresistance effect (TMR effect) and a giant magnetoresistance effect (GMR)
Data Source
AI summary
A magnetic memory includes a plurality of memory cells and a data identification circuit. Each of the memory cells includes: a first bias node to which a first voltage is applied in data reading, the first voltage being a positive voltage; a second bias node to which a second voltage is applied in the data reading, the second voltage being a negative voltage having substantially the same absolute value as the first voltage; a connection node; a first spin device element connected between the first bias node and the connection node; and a second spin device element connected between the connection node and the second bias node. The first and second spin device elements operate differentially. The data identification circuit identifies data stored in each of the memory cells based on a polarity of a voltage generated on the connection node.