Low Sensing Current Non-Volatile Flip-Flop Circuit
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Solution Overview
Problem
Conventional magnetic tunnel junction (MTJ) sensing circuitry in non-volatile flip-flops experiences read disturbance due to large sensing currents, which can write unwanted data to the MTJs, compromising data integrity.
Innovation Solution
A two-stage sensing circuitry configuration is introduced, featuring low current sense paths and a secondary current path to reduce the peak sensing current and prevent direct current paths from VDD to GND during sensing operations, utilizing NMOS and PMOS transistors to manage the sensing currents effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional sensing circuitry is used in MTJ flip-flop structures, then the sensing operation can be performed, but large sensing currents cause read disturbance that writes unwanted data to the MTJs
Solution Approach 1:
The sensing operation is divided into two distinct stages: a first stage that senses the MTJ state with minimal current, and a second stage that amplifies the signal. This segmentation allows the sensing current to be separated from the signal amplification current, preventing the harmful read disturbance effect while maintaining reliable detection.
Solution Approach 2:
A sense amplifier is introduced as an intermediary component between the MTJ and the output. The amplifier takes the weak signal from the first stage and produces a strong output signal in the second stage, acting as a mediator that isolates the MTJ from large current flows while still enabling reliable sensing.
2Device complexity
If a single-stage sensing amplifier is used, then the circuit complexity is low, but the sensing current duration is long causing increased read disturbance
Solution Approach 1:
The sensing amplifier is segmented into two stages with distinct functions. The first stage performs initial sensing with short duration, while the second stage performs signal amplification. This segmentation reduces the total sensing current duration by separating the sensing function from the amplification function, thereby reducing read disturbance while maintaining acceptable circuit complexity.
Solution Approach 2:
The sensing operation uses periodic action through controlled transistor switching. The first stage transistors are activated briefly to sense the MTJ state, then turned off before the second stage activates. This periodic activation pattern minimizes the total time sensing current flows through the MTJ, reducing read disturbance effects.
3Ease of operation
If direct current paths from VDD to GND are used during sensing, then the sensing operation is simple, but large sensing currents are generated causing read disturbance
Solution Approach 1:
The current path is segmented into two stages with different current characteristics. The first stage uses a controlled current path through transistors that limits current magnitude, while the second stage uses a different current path for signal amplification. This segmentation allows simple sensing operation while preventing large currents from directly flowing through the MTJ.
Solution Approach 2:
Transistors are introduced as intermediary components that control and limit the current flowing through the MTJ during sensing. These intermediaries prevent direct large current paths from VDD to GND while still enabling the sensing operation to proceed with acceptable simplicity.
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 significantly reduces read disturbance failure probability by minimizing the sensing current duration through MTJs, enhancing data stability and integrity in MTJ flip-flop structures.
Implementation Method 1
To write data in STT MRAM, a write current with a specific direction of write '1' or '0', which exceeds a critical switching current, is applied through an MTJ. The write current exceeding the critical switching current is sufficient to change the magnetization direction of the free layer.
Implementation Method 2
The electrical resistance of an MTJ depends on whether the free layer magnetization and fixed layer magnetization are parallel or anti-parallel with each other.
Implementation Method 3
In STT MRAM, two distinct states are defined be two different resistances of an MTJ in a bitcell of the MRAM. The two different resistances represent a logic '0' and a logic '1' value stored by the MTJ.
Data Source
AI summary
A low sensing current non volatile flip flop includes a first stage to sense a resistance difference between two magnetic tunnel junctions (MTJs) and a second stage having circuitry to amplify the output of the first stage. The output of the first stage is initially pre-charged and determined by the resistance difference of the two MTJs when the sensing operation starts. The first stage does not have a pull-up path to a source voltage (VDD), and therefore does not have a DC path from VDD to ground during the sensing operation. A slow sense enable (SE) signal slope reduces peak sensing current in the first stage. A secondary current path reduces the sensing current duration of the first stage.