2MTJ-2Tr MRAM Cell for Accurate Data Reading
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing MRAM technology faces challenges in accurately reading data from Magnetic Tunnel Junction (MTJ) elements due to a small resistance change ratio between the low-resistance and high-resistance states, making it difficult to correctly interpret data stored in these memory cells.
Innovation Solution
The semiconductor memory device employs a 2MTJ-2Tr structure with two MTJ elements and two select transistors, where the MTJ elements are connected to bit lines and source lines, allowing for complementary data storage and read operations without the need for a reference cell, thereby increasing the sense margin and enabling accurate data retrieval even with a small resistance change ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional single MTJ element structure is used, then the device complexity is low, but the measurement precision of resistance change is insufficient due to small MR ratio
Solution Approach 1:
The memory cell is segmented into two MTJ elements (first MTJ and second MTJ) with different resistance change ratios. The first MTJ element has a larger MR ratio and is connected to a bit line, while the second MTJ element has a smaller MR ratio and is connected to a source line. This segmentation allows the system to utilize the complementary characteristics of the two MTJ elements to improve data reading accuracy even when individual MTJ elements have small resistance changes.
Solution Approach 2:
Different MTJ elements are assigned different local qualities - specifically, different resistance change ratios (MR ratios). The first MTJ element is designed with a larger MR ratio while the second MTJ element has a smaller MR ratio. This local differentiation in resistance characteristics enables the memory cell to maintain accurate data reading capability through complementary operation, addressing the measurement precision problem without requiring uniform high-performance MTJ elements throughout.
2Measurement precision
If a reference cell is added to improve data reading accuracy, then the measurement precision increases, but the area of the memory device increases
Solution Approach 1:
The first MTJ element serves multiple functions: it acts as both a storage element and a reference element for the second MTJ element. By designing the first MTJ with a larger MR ratio, it can reliably indicate the logical state while also providing a reference for comparison. This multi-functionality eliminates the need for separate dedicated reference cells, thereby improving data reading accuracy without increasing the memory cell area.
Solution Approach 2:
The memory cell uses a complementary structure where the first MTJ element effectively serves as a reference copy for the second MTJ element. Instead of requiring separate reference cells that are exact copies of storage cells, the invention creates a functional copy through the complementary MTJ pair, where the first MTJ's larger MR ratio provides the necessary reference signal for accurate data reading from the second MTJ.
3Productivity
If the size of magnetic material is decreased to increase integration density, then the productivity increases, but the reliability of data reading decreases due to insufficient resistance change
Solution Approach 1:
The invention changes the parameter of resistance change ratio (MR ratio) distribution across different MTJ elements. By designing the first MTJ element with a larger MR ratio and the second MTJ element with a smaller MR ratio, the system can tolerate smaller absolute resistance changes in the second MTJ (which corresponds to smaller magnetic material size) while maintaining overall reading reliability. The complementary operation amplifies the detectable signal, allowing high integration density with small magnetic materials without sacrificing data reading reliability.
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 allows for reliable data reading and storage with improved sense margin, reducing the need for a reference cell and minimizing area requirements, resulting in a high-reliability MRAM with reduced cell size and increased integration density.
Implementation Method 1
An MTJ (Magnetic Tunnel Junction) element as a memory element of the MRAM has a laminated structure including two ferromagnetic layers and a non-magnetic barrier layer sandwiched therebetween and stores digital data based on change of magnetic resistance due to a spin polarization tunnel effect
Implementation Method 2
A resistance change type memory is known as a kind of semiconductor memory device. Also, as a kind of the resistance change type memory, an MRAM (magnetoresistive random access memory) is known. The MRAM is a memory device using a magnetic element having a magnetoresistive effect
Data Source
AI summary
According to one embodiment, a semiconductor memory device includes: a first active area provided in a semiconductor substrate; a second active area provided in the semiconductor substrate and intersecting with the first active area; a first select transistor comprising a first drain region provided in the first active area and a source region provided in an intersection region of the first and second active areas; a second select transistor comprising a second drain region provided in the second active area and sharing the source region; a word line coupled to gates of the first and second select transistors; and first and second variable resistance elements coupled to the first and second drain regions, respectively.