Voltage-Controlled Nonvolatile Magnetic Element for Low Power MRAM
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Solution Overview
Problem
Current nonvolatile magnetic random access memory (MRAM) technologies face challenges in reducing write current, which leads to increased power consumption and larger cell sizes, and struggle with retaining magnetization direction changes made by voltage.
Innovation Solution
A nonvolatile magnetic element comprising a first insulating layer, a ferromagnetic free layer, a charged layer with lower resistivity, and an injection layer, where the charged layer accumulates electric charges to change the magnetization direction using voltage, allowing for low power consumption and retention of the changed state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the Oersted magnetic field method is used for writing, then the magnetization can be switched, but the write current becomes several milliamperes which increases power consumption and cell size
Solution Approach 1:
The patent replaces the conventional current-based Oersted magnetic field method with a voltage-based magnetization switching mechanism. By applying voltage to the ferromagnetic substance, the magnetization direction is controlled through voltage-induced magnetic anisotropy changes, eliminating the need for large write currents and reducing power consumption significantly.
Solution Approach 2:
The patent changes the fundamental parameter for magnetization control from current (amperes) to voltage (volts). By utilizing voltage-controlled magnetic anisotropy in the ferromagnetic substance, the system achieves magnetization switching without requiring the large currents needed for Oersted field generation, thereby reducing power consumption while maintaining switching capability.
2Use of energy by moving object
If spin-transfer torque is used to reduce write current, then the write current becomes scalable with miniaturization, but the method still uses current rather than voltage for writing
Solution Approach 1:
The patent replaces the spin-transfer torque current-based mechanism with a voltage-based mechanism. Instead of introducing current directly into the magnetic substance to generate spin torque, the invention applies voltage to the ferromagnetic substance to control magnetization through voltage-induced changes in magnetic anisotropy, simplifying the writing operation.
3Use of energy by moving object
If voltage is used for writing instead of current, then power consumption is remarkably suppressed, but the magnetization direction change cannot be retained after the voltage is removed
Solution Approach 1:
The patent applies voltage in advance to change the magnetic anisotropy of the ferromagnetic substance before the actual magnetization switching occurs. This preliminary voltage application creates a state where the magnetization can be switched and retained without requiring continuous voltage application, enabling both low power consumption during writing and reliable retention of the written state.
Solution Approach 2:
The patent utilizes dynamic changes in magnetic anisotropy induced by voltage application. The ferromagnetic substance transitions between different magnetic anisotropy states based on applied voltage, allowing the magnetization direction to be controlled and retained. The system dynamically adjusts the magnetic properties during writing operations while maintaining stable retention when voltage is removed.
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 enables writing with vanishingly small current consumption, maintaining low power usage while achieving fast random access times and excellent retention characteristics, similar to conventional MRAMs.
Implementation Method 1
a charged layer for accumulating an electric charge, the charged layer being formed on another side of the first insulating layer and opposed to the first free layer
Data Source
AI summary
Provided is a nonvolatile magnetic device that is capable of realizing low power consumption by performing writing with a voltage and is also excellent in retention characteristics. The nonvolatile magnetic device includes a nonvolatile magnetic element. The nonvolatile magnetic element includes: a first free layer made of a ferromagnetic substance; a first insulating layer made of an insulator, the first insulating layer being provided to be connected to the first free layer; a charged layer provided adjacent to the first insulating layer; a second insulating layer made of an insulator, the second insulating layer being provided adjacent to the charged layer; and an injection layer provided adjacent to the second insulating layer. The charged layer is smaller in electric resistivity than both of the first insulating layer and the second insulating layer. The injection layer is smaller in electric resistivity than the second insulating layer.