VCMA MRAM Storage State Determination via Virtual Array
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Solution Overview
Problem
Voltage-controlled magnetic anisotropic magnetic random access memory (VCMA MRAM) faces challenges in determining the storage state of memory cells due to smaller resistance value differences and higher precision requirements, as well as resistance deviations during the fabrication process, which can lead to read errors.
Innovation Solution
The introduction of a virtual array and a data sampling-decision-output circuit with differential transistors' width/length ratio adjustments in the sensitive amplifier circuit allows for effective determination of storage states without additional reference resistances, improving the reliability of the sensitive amplifier and reducing resistance offset risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If VCMA effect is used to program MTJ with voltage pulse, then programming time is reduced and operating speed is increased, but the resistance value difference between states becomes smaller requiring higher precision peripheral circuits
Solution Approach 1:
The patent creates a copy of the MTJ device called a 'shadow MTJ' that has identical structure and electrical characteristics to the original MTJ. This shadow MTJ is programmed simultaneously with the original MTJ using the same voltage pulse, ensuring both cells have the same resistance characteristics. The shadow MTJ serves as a reference for comparison during read operations, eliminating the need for high-precision absolute resistance measurement.
Solution Approach 2:
The patent introduces a differential amplifier as an intermediary component that compares the resistance values of the original MTJ and shadow MTJ. Instead of directly measuring the small resistance difference of a single MTJ (which requires high precision), the differential amplifier measures the difference between two matched MTJs, where the shadow MTJ compensates for process variations and resistance offsets.
2Measurement precision
If peripheral circuit precision is increased to detect smaller resistance differences, then storage state determination accuracy is improved, but manufacturing complexity and cost increase
Solution Approach 1:
By creating a shadow MTJ that is a precise copy of the original MTJ, the system transforms the problem from measuring small absolute resistance differences (requiring high-precision circuits) to measuring relative differences between matched devices (achievable with standard precision circuits). The shadow MTJ acts as a built-in reference that eliminates the need for complex high-precision measurement circuitry.
Solution Approach 2:
The shadow MTJ serves the dual purpose of being both a memory cell (storing data) and a reference device for comparison. This self-service approach allows the memory cell itself to provide the reference signal needed for accurate read operations, eliminating the need for separate external reference resistors or complex calibration circuits.
3Reliability
If process precision is improved to reduce resistance deviation, then read error rate is reduced, but manufacturing cost and complexity increase
Solution Approach 1:
The shadow MTJ is fabricated using the exact same process conditions as the original MTJ, ensuring both devices experience identical process variations. This copying approach transforms random process deviations into common-mode signals that affect both devices equally, which can then be rejected by the differential comparison, eliminating the need for ultra-precise process control.
Solution Approach 2:
Instead of trying to eliminate process variations through higher manufacturing precision, the patent embraces these variations by creating matched pairs of MTJs. The process deviations that would normally cause read errors are converted into a beneficial feature where both original and shadow MTJs are equally affected, allowing the differential amplifier to reject these common-mode signals and achieve high reliability despite manufacturing imperfections.
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 enables accurate determination of initial memory cell values and reduces the risk of read errors by using a virtual array to compare with memory cells, ensuring reliable operation and precision in VCMA MRAM systems.
Implementation Method 1
it uses the pulse of the MTJ voltage rather than the polarity to change the resistance characteristics of the MTJ
Implementation Method 2
Magnetic Random Access Memory (MRAM) is a non-volatile Memory that utilizes electromagnetic characteristics to store data
Data Source
AI summary
The disclosure provides a voltage-controlled magnetic anisotropic magnetic random access memory. The memory comprises a virtual array, a memory array and a peripheral circuit, wherein the memory array comprises memory cells with X rows and Y columns; the virtual array comprises virtual cells with X rows and one column; the peripheral circuit comprises at least one data sampling-decision-output circuit, the data sampling-decision-output circuit comprises a sensitive amplifier circuit and a logic circuit in series, and are simultaneously connected to the data sampling-decision-output circuit in the peripheral circuit at the same time. By changing the width-length ratio of a differential circuit in the sensitive amplifier circuit and adding the virtual array, the problem that the storage state of the voltage-controlled magnetic anisotropy magnetic random access memory cannot be determined is effectively solved, and the risk of resistance deviation under different process conditions also can be avoided.