Spin Transistor With Piezoelectric Layer for Low-Power MRAM
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Solution Overview
Problem
Conventional magnetic tunnel junctions (MTJs) used in memory applications, such as MRAM, consume power when switching between states, which is a concern for reducing power consumption in portable electronics and other devices.
Innovation Solution
A spin transistor is created using two magnetic tunnel junctions with a shared multiferroic layer, where a piezoelectric thin film over a ferromagnetic thin film with a metal electrode induces stress to control the spin state, allowing for low-power switching between parallel and anti-parallel orientations by applying a small voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional magnetic tunnel junctions (MTJs) are used for switching between states, then non-volatile data storage capability is achieved, but power consumption increases
Solution Approach 1:
The patent changes the physical mechanism from charge-based switching to strain-based magnetic anisotropy control. By applying mechanical strain through the piezoelectric layer, the magnetic anisotropy energy barrier is modified, enabling state transitions with minimal current. This parameter change from electrical to mechanical control resolves the contradiction by achieving non-volatile storage without the high power consumption of conventional MTJ switching.
Solution Approach 2:
The patent replaces the conventional electrical switching mechanism with a piezoelectric mechanical strain mechanism. The piezoelectric layer converts electrical voltage to mechanical strain, which then modifies the magnetic anisotropy of the ferromagnetic layer. This substitution allows state changes with much lower current requirements while maintaining non-volatile storage capability.
2Ease of operation
If charge based switches (CMOS or MOSFET) are used, then circuit switching function is achieved, but power consumption remains high
Solution Approach 1:
The patent replaces charge-based electrical switching with strain-based magnetic switching. The piezoelectric layer applies mechanical strain to control the magnetic state, eliminating the need for continuous charge flow. This mechanical substitution achieves the switching function with dramatically reduced power consumption, as the strain field can be applied and maintained without continuous energy input.
Solution Approach 2:
The piezoelectric layer acts as an intermediary between the electrical control signal and the magnetic state. Instead of directly switching current through the magnetic junction, the piezoelectric material converts voltage to strain, which then modulates the magnetic anisotropy. This intermediary mechanism enables efficient switching by decoupling the electrical control from the magnetic state change, reducing direct current consumption.
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 the current required for state changes, minimizing power consumption and extending battery life in mobile devices while maintaining non-volatile data storage capabilities.
Implementation Method 1
a piezoelectric thin film over a ferromagnetic thin film (FM channel) with a metal electrode (metal) induces stress to control the spin state
Implementation Method 2
The free and pinned layers 12, 14 can store information even when the magnetic H-field is '0' due to the hysteresis loop 18 of the MTJ 10
Implementation Method 3
The tunneling current depends on the relative orientation of the free and pinned layers 12, 14. When using a spin-torque-transfer (STT) MTJ, the difference in the tunneling current as the spin alignment of the free and pinned layers 12, 14 is switched between parallel (P) and anti-parallel (AP) is known as the tunnel magnetoresistance ratio (TMR)
Data Source
AI summary
Spin transistors and related memory, memory systems, and methods are disclosed. A spin transistor is provided by at least two magnetic tunnel junctions (MTJs) with a shared multiferroic layer. The multiferroic layer is formed from a piezoelectric (PE) thin film over a ferromagnetic thin film (FM channel) with a metal electrode (metal). The ferromagnetic layer functions as the spin channel and the piezoelectric layer is used for transferring piezoelectric stress to control the spin state of the channel. The MTJ on one side of the shared layer forms a source and the MTJ on the other side is a drain for the spin transistor.