MRAM Write Amplifiers for High-Speed Data Storage
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Solution Overview
Problem
Conventional magnetic random access memory (MRAM) using the spin-injection writing method faces challenges in reducing write time and increasing write speed due to the need for larger sense amplifiers, which complicates downsizing and leads to shared sense amplifiers among bit line pairs, resulting in lower write and read speeds compared to DRAM.
Innovation Solution
The implementation of write amplifiers between bit lines and source lines, allowing data to be temporarily stored and then concurrently written to memory cells, reducing the overall write time by utilizing latch circuits with MOSFETs, and optimizing the configuration of write amplifiers for each memory cell block to enhance data transfer rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the sizes of transistors in sense amplifiers are increased to reduce performance fluctuations, then the sense amplifier size increases, but this makes it difficult to arrange sense amplifiers for each bit line pair when MRAM is downscaled
Solution Approach 1:
The patent divides the sense amplifier function into two separate components: a traditional sense amplifier for reading operations and a dedicated write amplifier for writing operations. This segmentation allows each amplifier to be optimized independently, enabling the write amplifier to use larger transistors for stable performance without increasing the size of the sense amplifier used for reading, thus resolving the contradiction between reliability and area.
2Area of stationary object
If sense amplifiers are shared by multiple bit line pairs to enable further downsizing, then the number of sense amplifiers is reduced, but this reduces the page size and write/read speed
Solution Approach 1:
By separating the write function from the sense amplifier, the patent enables dedicated write amplifiers to be assigned to each bit line pair. This allows full-page writing capability to be maintained even when the memory array is downsized, as each bit line pair has its own write amplifier that can operate independently without sharing, thus maintaining high productivity.
Solution Approach 2:
The write amplifier acts as an intermediary component between the bit line pair and the memory cells, buffering and preparing write data before it is transferred to the memory cells. This intermediary structure enables efficient data transfer and maintains high write speed even when memory density is increased through downsizing.
3Use of energy by moving object
If the spin-injection writing method is used to increase integration degree and reduce power consumption, then magnetization reversal current is reduced for smaller magnetic bodies, but the read current becomes microscopic requiring larger sense amplifiers
Solution Approach 1:
The patent separates the read and write functions into distinct circuits: the spin-injection writing method is used for writing with its low power consumption characteristics, while a separate sense amplifier is dedicated to reading operations. This segmentation allows the sense amplifier to be optimized for detecting microscopic read currents without being constrained by the power consumption requirements of the write operation, thus maintaining reliable read current detection capability.
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 significantly reduces data write time and increases the effective writing transfer rate, enabling faster data write operations while maintaining or improving read speeds, thus enhancing the performance of MRAM compared to conventional methods.
Implementation Method 1
Writing methods of the MRAM include a magnetic-field writing method and a spin-injection writing method. Among these, the spin-injection writing method is advantageous in increasing the integration degree, reducing the power consumption, and enhancing the performance because it is characterized such that a spin injection current required for magnetization reversal becomes lower when a magnetic body has a smaller size.
Implementation Method 2
Writing methods of the MRAM include a magnetic-field writing method and a spin-injection writing method.
Implementation Method 3
To quickly sense a difference in these microscopic currents, sizes (current driving capabilities) of transistors included in sense amplifiers need to be increased to reduce performance fluctuations in differential amplification of the sense amplifiers.
Data Source
AI summary
A memory according to an embodiment includes bit lines, word lines, source lines, magnetic tunnel junction elements and transistors that are serially connected between the bit lines and the source lines, respectively, and a sense amplifier that detects data stored in the magnetic tunnel junction elements. The semiconductor storage device includes multiplexers between the bit lines and the sense amplifier in order to select one of the bit lines to be connected to the sense amplifier, and write amplifiers that are located corresponding to memory cell blocks each of which includes memory cells each including the magnetic tunnel junction element and the transistor and are connected to the bit lines or connected via the multiplexers to the bit lines. To write data, the sense amplifier applies a write voltage to the bit lines and then the write amplifiers hold the write voltage.