Stacked Phase Change Memory Cell Structure for Leakage Reduction
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Solution Overview
Problem
Conventional phase change memory cells face challenges with high leakage current and memory failure due to the reliance on a single switch and phase change material, which complicates threshold voltage reduction and retention.
Innovation Solution
The implementation of a phase change memory cell structure with at least two switches and two phase change materials arranged in series, allowing for versatile threshold voltage tuning and reduced failure rates by tailoring materials and thicknesses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single switch and phase change material are used in conventional phase change memory cells, then the device structure is simple, but the leakage current is high and memory failure rate increases
Solution Approach 1:
The patent divides the memory cell into multiple functional segments by stacking at least two switches and two phase change materials in series. Each switch-PCM pair forms an independent operational unit, allowing the system to achieve higher reliability through modular redundancy while maintaining manageable structural complexity through standardized stacking patterns.
Solution Approach 2:
The patent applies different material compositions and thicknesses to different regions of the stacked structure. Specifically, the first and second phase change materials have different compositions (e.g., GeSbTe vs. AgInSbTe) and thicknesses (e.g., 50-200 nm vs. 30-150 nm), allowing each layer to be optimized for its specific functional requirements in terms of switching characteristics and retention properties.
2Adaptability or versatility
If multiple phase change materials or ovonic threshold switches are combined at different layers with oxide layers spacing, then material properties can be combined, but the thickness of the whole phase change structure becomes thicker
Solution Approach 1:
The patent merges multiple switches and phase change materials into a single integrated stacked structure without introducing additional oxide layer spacing between them. The switches and PCMs are directly stacked in contact or with minimal spacing, combining the functionality of multiple materials while minimizing the overall thickness compared to conventional approaches with intermediate oxide layers.
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 effectively reduces leakage current and memory cell failure rates by enabling precise control over threshold voltage and phase change properties, enhancing the reliability of phase change memory structures.
Implementation Method 1
The chalcogenide semiconductors, also called phase change materials, have a crystalline state and an amorphous state. In the crystalline state, the phase change materials have a low resistivity, while in the amorphous state they have a high resistivity.
Implementation Method 2
In a reset operation, phase change material may be heated up to a temperature higher than the melting temperature when a current passes through it.
Implementation Method 3
Region can be set back to the crystalline state by heating up the phase change material to a temperature higher than the crystallization temperature, but below the melting temperature.
Implementation Method 4
phase change material may be heated up to a temperature higher than the melting temperature when a current passes through it
Data Source
AI summary
The present disclosure provides a memory structure, including a first interlayer dielectric layer (ILD), a second ILD over the first ILD, wherein at least a portion of an interconnect structure is in the second ILD, a first switch between the first ILD and the second ILD, a second switch over the first switch, and a first phase change material stacking with the first switch and the second switch.