MRAM Read Disturb Suppression via Shortened Current Pulse Duration
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Solution Overview
Problem
Current MRAM devices face challenges in reducing cell area and suffer from 'read disturb' and thermal instability issues due to longer current supply durations, which affect data reliability and access speed.
Innovation Solution
A nonvolatile memory device design that uses first and second current supply lines to supply write and read currents to memory cells, with the read current duration shorter than the write current duration to minimize thermal assist effects and prevent accidental data writes, and determines the read current direction based on the write current's absolute value to optimize resistance changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the read current value is increased to improve data read speed, then access speed is improved, but read disturb occurs causing data corruption
Solution Approach 1:
The patent applies periodic pulsed action by supplying read current in short pulses with duration shorter than the thermal time constant of the memory cell. This allows the read operation to complete before thermal diffusion can cause magnetization reversal, thus achieving fast read access while preventing read disturb effects
2Measurement precision
If the read current supply duration is increased to improve signal detection, then measurement precision is improved, but thermal assist effect increases causing accidental data writes
Solution Approach 1:
The patent uses partial action by applying read current for a duration that is sufficient for signal detection but intentionally shorter than the thermal time constant. This partial duration ensures adequate sense voltage for reliable reading while preventing excessive thermal accumulation that would cause magnetization reversal
Solution Approach 2:
The patent performs preliminary action by optimizing the read current pulse width beforehand to be shorter than the thermal time constant. This pre-determined timing ensures that the read operation completes before thermal diffusion can affect the stored magnetization state, preventing accidental writes
3Temperature
If the write current supply duration is decreased to reduce thermal disturbance, then thermal disturbance resistance is improved, but writing reliability may be affected
Solution Approach 1:
The patent changes the temporal parameter of write current by optimizing both the amplitude and duration of write pulses. By carefully selecting write current parameters, the patent achieves reliable magnetization reversal while limiting total energy input and subsequent thermal disturbance to the memory cell
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 design reduces cell area, suppresses read disturb, and enhances thermal disturbance resistance, allowing for faster data access and improved data reliability by controlling current supply durations and directions.
Implementation Method 1
an electric current flowing through a tunneling magneto-resistance element (TMR element) therein or an end-to-end voltage of the TMR element can be measured to indirectly measure the electric resistance value of the TMR element
Implementation Method 2
an electric current is applied directly through a TMR element to reverse the direction of magnetization of the TMR element. The electric-current flow direction is changed to switch the direction of magnetization of a free layer to the parallel or antiparallel direction with respect to a fixed layer. This method is called the spin injection technique
Implementation Method 3
the temperature of the TMR element itself increases, the free layer becomes unstable and reversal of the magnetization direction is likely to occur. This phenomenon is called 'thermal assist effect.'
Data Source
AI summary
Between the value of an electric current and the supply duration for which the electric current is supplied that cause magnetization reversal, there is the relation of monotonous decrease. This means that, as the supply duration is shortened, the threshold current value for causing the magnetization reversal is larger. Therefore, in terms of suppressing occurrence of read disturb, the read current supply duration may be shortened to increase the threshold value of the current causing the magnetization reversal and thereby ensure a sufficient read disturb margin. Therefore, the read current supply duration may be shortened relative to the write current supply duration ensure the read disturb margin and suppress occurrence of read disturb.