MRAM Cell With Series MTJs for Data State Distinction
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Solution Overview
Problem
Conventional MRAM technologies face challenges in distinguishing between data states '1' and '0' due to limited tunnel magnetoresistance ratios (TMR) and variations in resistance values during the manufacturing process, leading to degraded reliability in data writing and reading.
Innovation Solution
The proposed solution involves an MRAM cell structure that includes a pair of magnetic tunnel junctions (MTJs) with opposite states, connected in series between a bit line and a bit line bar. This configuration allows for data storage based on the relative resistance ratio between the MTJs, enhancing the ability to distinguish between data states '1' and '0'.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single MTJ is used for data storage, then the device complexity is low, but the reliability of data reading is degraded due to difficulty in distinguishing data states
Solution Approach 1:
The storage node is segmented into two separate MTJs (first MTJ and second MTJ) connected in series. Each MTJ independently stores one bit of information, creating distinct resistance states that are easier to distinguish. This segmentation resolves the contradiction by improving data reading reliability through better state differentiation while maintaining a relatively simple series connection configuration.
Solution Approach 2:
The patent inverts the conventional single-MTJ approach by using two MTJs with opposite magnetic states (one with parallel magnetization, one with anti-parallel magnetization). This inversion creates complementary resistance states that enhance distinguishability during reading operations, thereby improving reliability without significantly increasing overall system complexity.
2Measurement precision
If the TMR ratio is limited, then the manufacturing process is simple, but the ability to distinguish data states '1' and '0' is degraded
Solution Approach 1:
The series connection of two MTJs creates a feedback mechanism where the total resistance is the sum of individual MTJ resistances. This feedback structure amplifies the resistance difference between data states '1' and '0', improving measurement precision for state distinction while the self-correcting nature of the series configuration compensates for manufacturing variations.
Solution Approach 2:
The patent changes the resistance parameter by using two MTJs with opposite magnetic states, creating complementary resistance values. This parameter transformation enhances the distinguishability of data states by maximizing the resistance contrast between '1' and '0' states, effectively overcoming limitations of limited TMR ratios in individual MTJs.
3Reliability
If absolute resistance values vary during manufacturing, then the manufacturing process is simpler, but the reliability of data writing and reading is degraded
Solution Approach 1:
The patent uses opposite magnetic states in the two MTJs to create complementary resistance characteristics. This inversion approach ensures that variations in absolute resistance values during manufacturing are compensated for, as the series combination maintains a consistent total resistance profile that preserves data writing and reading reliability.
Solution Approach 2:
The series connection configuration provides inherent feedback where the total resistance measurement reflects the combined state of both MTJs. This feedback mechanism compensates for manufacturing variations in individual MTJ resistance values, maintaining reliable data operations even when absolute resistance values deviate from nominal specifications.
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 approach enhances the reliability of data writing and reading by allowing the MRAM cell to differentiate between data states without being influenced by absolute resistance values or manufacturing deformations, thereby improving data storage and access functions.
Implementation Method 1
The MRAM stores information in the MTJ based on the resistance value. For reading the stored information, the MRAM measures a resistance state of the MTJ. That is, the MRAM is a memory configured to write or read information using a magnetoresistive effect (called 'tunnel magnetoresistance (TMR)') generated at the MTJ.
Data Source
AI summary
An MRAM cell includes a switch unit configured to determine opening and closing thereof by a word line voltage and to activate a current path between a bit line and a bit line bar in an opened state thereof, first and second MTJs having opposite states, respectively, and connected in series between the bit line and the bit line bar, to constitute a storage node, and a sensing line configured to be activated in a reading mode of the MRAM cell, thereby creating data reading information based on a voltage between the first and second MTJs, wherein the first and second MTJs have different ones of a low resistance state and a high resistance state, respectively, in accordance with a voltage drop direction between the bit line and the bit line bar, thereby storing data of 0 or 1.