MRAM Cell Area Reduction via Segmented MTJ and Pulse Control
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Solution Overview
Problem
The spin transfer torque writing type MRAM requires a smaller cell area to reduce chip fabrication costs, but existing methods for decreasing the cell area are not applicable due to the need for bidirectional electric currents, necessitating a new configuration for the spin transfer torque writing method.
Innovation Solution
A semiconductor memory device with n resistance change elements connected in series or parallel, where a write circuit applies pulse currents with varying current values or pulse widths to change between low- and high-resistance states, allowing for different data to be written in each MTJ element by controlling the current amount or pulse time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the cell area is decreased to reduce chip fabrication cost, then the manufacturing cost is reduced, but the ability to apply bidirectional currents for spin transfer torque writing becomes difficult
Solution Approach 1:
The memory cell is segmented into multiple resistance change elements (first, second, third, and fourth MTJ elements) with different resistance values, allowing selective writing to each element through controlled current application. This segmentation enables the use of a simplified current path configuration while maintaining the ability to write different data to multiple elements within the same cell area.
Solution Approach 2:
Each resistance change element is designed with different resistance values (R1 > R2 > R3 > R4) to create local quality differences. This allows the write circuit to apply a single polarity current that selectively affects different elements based on their resistance characteristics, eliminating the need for bidirectional current paths while enabling multi-data storage in a compact cell.
2Area of stationary object
If multiple resistance change elements are arranged in one cell, then the cell area per bit is reduced, but the writing control complexity increases
Solution Approach 1:
The write circuit controls the writing process by changing current parameters (amplitude and pulse width) rather than requiring complex switching of current directions. By applying a single polarity current with controlled amplitude and duration, the circuit can selectively write to different resistance change elements based on their resistance values, simplifying the control logic while achieving multi-data storage in a reduced cell area.
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 enables efficient writing of different data in multiple MTJ elements within a single cell, reducing the cell area per bit and facilitating the development of a low-cost, high-capacity spin transfer torque MRAM.
Implementation Method 1
a spin transfer torque writing type magnetic random access memory (MRAM)
Implementation Method 2
The MRAM is a device that stores information by using the magnetoresistive effect
Data Source
AI summary
A semiconductor memory device includes n resistance change elements which are arranged in one cell, have a low-resistance state and a high resistance state, are connected in series or parallel, have different resistance values in the same resistance state, and change between the low-resistance state and the high-resistance state under different conditions, and a write circuit which is connected to one end of the n resistance change elements, and applies a pulse current m (1≦m≦n) times to the n resistance change elements during a write operation. Letting Im be a current value of an mth pulse current, condition I1>I2> . . . >Im holds.