MTJ Sensor ESD Protection via High-Resistance Shunt
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Solution Overview
Problem
MTJ junction cells used in current sensors are highly susceptible to damage from electrostatic discharge (ESD), leading to malfunction, as they have a low breakdown voltage and existing ESD protection methods are not effective for current sensor configurations.
Innovation Solution
An array of single domain MTJ sensors with domain restoration and high resistance shunt traces are used to divert electrostatic charges safely to ground, preventing damage and ensuring reproducible measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If MTJ junction cells are used in current sensors, then magnetic field sensing capability is achieved, but susceptibility to ESD damage increases due to low breakdown voltage
Solution Approach 1:
A shunt trace is introduced as an intermediary protective element between the MTJ cell and the external environment. This shunt trace acts as a mediator that intercepts electrostatic discharge currents before they can reach and damage the MTJ junction cell, thereby protecting the sensitive sensing component while maintaining its operational integrity
Solution Approach 2:
The shunt trace is designed with predetermined characteristics (resistance, geometry, material) that enable it to absorb and dissipate ESD energy before it can affect the MTJ cell. This prior cushioning mechanism ensures that when ESD events occur, the protective shunt is already in position to handle the discharge current, preventing damage to the sensing junction
2Reliability
If existing ESD protection methods are applied to MTJ current sensors, then some protection is provided, but effectiveness is insufficient for current sensor configurations
Solution Approach 1:
The shunt trace is strategically positioned and dimensioned to provide localized protection specifically at the MTJ cell interface. Rather than using generic ESD protection, the shunt's resistance, geometry, and material properties are optimized to match the specific requirements of current sensor configuration, providing tailored protection that is both effective and adaptable to the sensing application
3Measurement precision
If MTJ cells are used for current measurement, then magnetic field strength detection is achieved, but measurement accuracy deteriorates due to hysteresis and random noise fluctuations
Solution Approach 1:
The shunt trace geometry and MTJ cell arrangement incorporate asymmetric design elements that eliminate magnetic hysteresis effects. By breaking symmetry in the magnetic circuit design, the patent ensures that the magnetic moment returns to a consistent initial state after each measurement cycle, eliminating hysteresis-induced measurement errors and improving reproducibility
Solution Approach 2:
The shunt trace design converts potentially harmful ESD events into beneficial protective actions. By providing a controlled discharge path, the shunt not only protects against ESD damage but also stabilizes the electrical environment around the MTJ cell, reducing random noise fluctuations and improving measurement precision
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 effectively protects MTJ cells from ESD, preventing static charge buildup and ensuring accurate current and magnetic field strength measurements by eliminating hysteresis and random noise fluctuations.
Implementation Method 1
MTJ junction cells used in current sensors are highly susceptible to damage from electrostatic discharge (ESD)
Implementation Method 2
The variable resistance of the MTJ device, on the other hand, does not result from spin-dependent scattering, but from spin-dependent tunneling
Implementation Method 3
Two types of small, multilayered magnetic devices that change their resistance in response to variations in an external magnetic field
Implementation Method 4
both include a pair of thin, magnetized ferromagnetic layers separated by a nonmagnetic layer
Implementation Method 5
The magnetic moments of the free and pinned layers are perpendicular to each other
Data Source
AI summary
Presented herein is a shunted MTJ sensor formed of a plurality of electrically connected MTJ cells for measuring magnetic fields and currents and its method of fabrication. To provide stable single domain magnetic moments of the MTJ cells and to ensure that the magnetic moments return to a fixed bias point in the absence of external magnetic fields, the cells are formed of sufficiently small size and with elliptical cross-section of aspect ratio greater than 1.2. To eliminate the possibility of ESD damage to the cells, they are protected by a parallel shunt, formed as a trace of sufficiently high resistance that directs accumulated charges harmlessly to ground while bypassing the cells.