MTJ Pillar Tapering for Low-Voltage OTP Memory
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Solution Overview
Problem
Magnetoresistive random access memory (MRAM) bits used in one-time programmable (OTP) memory elements require high programming voltages, leading to manufacturing challenges such as low drive current and reliability issues, and MRAM bits are larger in size, making them unsuitable for OTP applications due to their high breakdown voltage.
Innovation Solution
A memory element and method involving a magnetic tunnel junction (MTJ) pillar with a reduced breakdown voltage, achieved by forming a multilayered MTJ stack and etching it to create a pillar with a smaller bottommost portion, where metal particles from the bottom electrode redeposit on the sidewall and oxidize, interacting with the tunnel barrier to lower the programming voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If MRAM bits are used in OTP memory elements, then data can be stored using magnetic storage elements, but the high breakdown voltage leads to low drive current and reliability issues
Solution Approach 1:
The patent applies local quality by creating a tapered MTJ pillar structure where the bottommost portion has a smaller lateral dimension than the upper portions. This local dimensional variation concentrates the electric field at the narrower bottom section, reducing the breakdown voltage locally while maintaining the overall magnetic storage functionality. The oxidized metal particles are also localized at the bottommost portion to further reduce breakdown voltage in that specific region.
Solution Approach 2:
The patent changes the physical parameters of the MTJ pillar by reducing the lateral dimension of the bottommost portion compared to the upper portions. This parameter change (dimensional reduction at the base) directly reduces the breakdown voltage from typical MRAM levels to OTP-appropriate levels, enabling reliable operation with standard drive currents while maintaining data storage capability.
2Use of energy by moving object
If OTP bits are manufactured at smaller sizes to reduce breakdown voltage, then programming voltage is reduced, but manufacturing control issues arise
Solution Approach 1:
The patent segments the MTJ pillar into distinct sections with different lateral dimensions. The upper portions maintain a larger size for ease of manufacturing and magnetic storage, while the bottommost portion is segmented to be narrower for voltage reduction. This segmentation allows each section to be optimized independently, avoiding the manufacturing control issues that would result from uniformly scaling down the entire structure.
Solution Approach 2:
Instead of reducing the breakdown voltage by scaling down all dimensions uniformly (which causes manufacturing issues), the patent uses dimensional variation along the vertical axis. The tapered structure creates a gradient in lateral dimension from top to bottom, allowing voltage reduction through vertical dimensional differentiation rather than horizontal scaling, thus avoiding manufacturing precision problems.
3Adaptability or versatility
If MRAM bits are designed with high breakdown voltage for rewriting capability, then data can be rewritten multiple times, but the size is larger making them unsuitable for OTP applications
Solution Approach 1:
The patent applies local quality by creating a tapered MTJ pillar structure where the bottommost portion has a smaller lateral dimension than the upper portions. This local dimensional variation concentrates the electric field at the narrower bottom section, reducing the breakdown voltage locally while maintaining the overall magnetic storage functionality. The oxidized metal particles are also localized at the bottommost portion to further reduce breakdown voltage in that specific region.
Solution Approach 2:
The patent changes the physical parameters of the MTJ pillar by reducing the lateral dimension of the bottommost portion compared to the upper portions. This parameter change (dimensional reduction at the base) directly reduces the breakdown voltage from typical MRAM levels to OTP-appropriate levels, enabling reliable operation with standard drive currents while maintaining data storage capability.
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 reduces the programming voltage for OTP bits, allowing for efficient data writing while maintaining the reliability of MRAM bits, enabling the construction of OTP memory elements with reduced manufacturing complexity and size.
Implementation Method 1
The etching causes metal particles from the bottom electrode structure to deposit on an outermost sidewall of the MTJ pillar
Implementation Method 2
The method further includes oxidizing the deposited metal particles to form oxidized metal particles on the outermost sidewall of the MTJ pillar
Data Source
AI summary
A memory element and methods of constructing the memory element are described. The memory element may include a bottom electrode structure having an uppermost portion of a first dimension. The memory element may further include a MTJ pillar having a bottommost portion forming an interface with the uppermost portion of the bottom electrode structure. The bottommost portion of the MTJ pillar may have a second dimension that is less than the first dimension. The memory element may further include oxidized metal particles located on an outermost sidewall of the MTJ pillar. The memory element may further include a top electrode structure located in the MTJ pillar.