Variable Resistance Memory Device Using Middle Admittance Reference Current
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Solution Overview
Problem
Existing semiconductor memory devices, such as MRAM, face challenges in generating a reference signal for data reading, which requires extra space and power consumption, and are prone to read disturbance errors due to frequent access of the reference cell during read operations.
Innovation Solution
A semiconductor memory device that includes a variable resistance element, a current generator to produce a reference current with middle admittance between the resistance values of '0' and '1' states, and a sense amplifier to compare currents, using dummy cells to generate a stable reference current without reversing magnetization, thus reducing read errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a reference cell is used to generate reference signal during read operation, then data reading can be performed, but read disturbance errors occur frequently due to repeated access of the reference cell
Solution Approach 1:
The patent pre-establishes multiple reference cells with different resistance values (Rmin, Rmax, and Rmid) before the read operation. The Rmid reference cell is specifically designed to provide a reference signal without causing read disturbance, as it is accessed only once during initialization rather than repeatedly during data reading operations.
Solution Approach 2:
The patent creates a copy of the TMR element structure (the Rmid reference cell) that replicates the necessary resistance characteristics without requiring repeated access. This copied reference cell provides the needed reference signal while avoiding the read disturbance problem that affects the main memory cells.
2Ease of operation
If middle resistance Rmid is used to generate reference current, then reference signal can be obtained from TMR element, but the reference current is not at the correct amperage level resulting in decreased sense margin
Solution Approach 1:
The patent changes the resistance parameter of the reference cell to match the desired reference current level. By carefully selecting and designing the Rmid reference cell with specific resistance characteristics, the patent achieves the correct amperage level for the reference current while maintaining the ability to generate the reference signal from the TMR element structure.
3Ease of operation
If external circuit is used to form reference signal, then reference signal can be generated, but extra space and extra power consumption are required
Solution Approach 1:
The patent designs the Rmid reference cell to serve multiple functions: it acts as both a reference signal generator and a memory element with the same TMR structure. This eliminates the need for separate external reference circuits, as the reference function is integrated within the memory array using the same technological process and structural elements.
Solution Approach 2:
The patent enables the memory device to generate its own reference signal using the TMR element structure itself, rather than requiring external circuits. The Rmid reference cell is formed using the same fabrication process and material layers as the main memory cells, allowing the device to self-produce the reference signal without additional external components or infrastructure.
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
The solution increases the sense margin and reduces read errors by generating a reference current at an appropriate amplitude level, preventing magnetization reversal and maintaining high accuracy and stability during read operations.
Implementation Method 1
a magnetic random access memory (MRAM) using a variable resistance element as a memory element is attracting attention and being developed. The MRAM uses, as a memory element, a magnetic tunnel junction (MTJ) element using the magnetoresistive effect by which the resistance value changes in accordance with the magnetization direction
Implementation Method 2
a large resistance change is obtained by a tunneling magnetoresistive (TMR) element using the TMR effect. The TMR effect is a phenomenon in which the resistance of the TMR element changes depending on the relative relationship (parallel/antiparallel) between the two magnetization directions
Data Source
AI summary
According to one embodiment, a semiconductor memory device includes a variable resistance element configured to store data “0” and data “1” in accordance with a change in resistance value, a current generator configured to generate a reference current for determining data of the variable resistance element, and having an admittance middleat a level in between an admittance of a variable resistance element storing data “0” and an admittance of a variable resistance element storing data “1”, and a sense amplifier includes a first input terminal connected to the variable resistance element and a second input terminal connected to the current generator, and configured to compare currents of the first input terminal and the second input terminal.