STT-MRAM MTJ with Pre-heated Reference Layer for Write Error Reduction
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Solution Overview
Problem
Thermally-assisted Spin Transfer Torque Magnetic Recording (STT-MRAM) technologies face challenges in reducing the bit error rate (BER) due to initial delays in generating spin torque electrons during the write operation, leading to increased write error rates.
Innovation Solution
The configuration of a magnetic tunnel junction (MTJ) with a top and bottom reference layer, where the top reference layer is set to generate spin torque electrons from the start of the write pulse, and the bottom reference layer takes over after a handoff time, ensuring continuous spin torque generation throughout the write process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If thermally-assisted STT is used to reduce switching current, then energy consumption is reduced, but write error rate increases due to initial delays in generating spin torque electrons
Solution Approach 1:
The patent applies preliminary action by pre-heating the MTJ to a temperature below the Curie temperature before the write operation begins. This preliminary thermal preparation ensures that spin torque electrons are generated immediately when the write current is applied, eliminating the initial delay that causes write errors. The free layer is pre-heated to enhance thermal fluctuations and facilitate faster magnetization switching while maintaining the energy benefits of thermally-assisted STT.
Solution Approach 2:
The patent implements beforehand cushioning by maintaining the free layer temperature below the Curie temperature throughout the write operation. This temperature control acts as a cushion that prevents thermal runaway and ensures stable operation. By carefully managing the thermal state before and during writing, the system achieves reliable switching without the write errors that occur when spin torque generation is delayed.
2Use of energy by stationary object
If thermally-assisted STT is used to reduce switching current, then power consumption is reduced, but write speed decreases due to delayed spin torque electron generation
Solution Approach 1:
The patent applies preliminary action by pre-heating the free layer to a temperature below the Curie temperature before the write operation. This preliminary thermal preparation reduces the time required for spin torque electron generation during the actual write operation, thereby increasing write speed while maintaining the power consumption benefits of thermally-assisted STT.
Solution Approach 2:
The patent utilizes parameter changes by dynamically controlling the temperature of the free layer. The temperature is maintained below the Curie temperature during normal operation to reduce power consumption, but is temporarily increased during the write operation to accelerate spin torque electron generation and improve write speed. This dynamic parameter adjustment resolves the contradiction between power efficiency and writing speed.
3Speed
If conventional STT writing is used, then write speed is maintained, but switching current is too high for scalable density
Solution Approach 1:
The patent applies parameter changes by utilizing temperature as a control parameter to reduce the switching current. By heating the free layer to a temperature below the Curie temperature, the thermal fluctuations enhance the spin torque effect, allowing switching to occur at lower current densities. This enables scalable density while maintaining acceptable write speeds through the temporary thermal assistance during the write operation.
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 approach significantly reduces the likelihood of write errors by providing spin torque electrons from the beginning of the write pulse, improving the write error rate performance of STT-MRAM configurations.
Implementation Method 1
spin-transfer-torque (WP-STT) start time... generate spin torque electrons... initiating a process of switching the switchable magnetization direction
Implementation Method 2
imparting Joule heating to the MTJ storage element when the write pulse is applied
Implementation Method 3
The term 'magnetoresistance' describes the effect whereby a change to certain magnetic states of the MTJ storage element (or 'bit') results in a change to the MTJ resistance
Data Source
AI summary
Embodiments of the invention are directed to a magnetic tunnel junction (MTJ) storage element having a reference layer formed from a reference layer material having a fixed magnetization direction, along with a free layer formed from a free layer material having a switchable magnetization direction. The MTJ is configured to receive a write pulse having a write-pulse and spin-transfer-torque (WP-STT) start time, a WP-STT start segment duration and a write pulse duration. The WP-STT start segment duration is less than the write pulse duration. The fixed magnetization direction is configured to form an angle between the fixed magnetization direction and the switchable magnetization direction. The angle is sufficient to generate spin torque electrons in the reference layer material at the WP-STT start time. The spin torque electrons generated in the reference layer material is sufficient to initiate switching of the switchable magnetization direction at the WP-STT start time.