Phase Change Memory Pillar Structure for Contact Area Control
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Solution Overview
Problem
Conventional phase change memory devices face challenges in reducing dimension and ensuring uniformity and endurance due to limitations in photolithography for contact area between electrodes and phase change layers, affecting performance.
Innovation Solution
A method is developed to form a phase change memory device with a pillar structure comprising a first electrode layer, a dielectric layer, and a second electrode layer, where the phase change layer surrounds the pillar structure, allowing for a larger contact area without lithography limitations, reducing variations, and maintaining the phase change layer's integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If photolithography is used to define the contact area between heating electrode and phase change layer, then the contact area can be precisely controlled, but the dimension reduction is limited by lithography resolution
Solution Approach 1:
The patent transitions from planar lithography-defined contacts to three-dimensional self-aligned contacts. The heating electrode extends vertically through the phase change layer, creating contact areas at multiple heights rather than relying solely on lateral lithography definition. This dimensional transition allows contact areas to be defined by vertical etching profiles rather than lateral photolithography resolution.
Solution Approach 2:
The patent employs self-aligned fabrication where the heating electrode structure automatically defines the contact area boundaries through its own geometry and position. The contact areas are formed by etching around the heating electrode, using the electrode itself as the alignment reference, eliminating the need for separate lithography steps to define contact boundaries.
2Ease of manufacture
If planar heating electrode is used with lithography patterning, then fabrication is simplified, but the contact area size is constrained by lithography limits
Solution Approach 1:
The heating electrode is transformed from a planar structure to a three-dimensional structure that extends vertically through the phase change layer. This allows the contact area to be determined by the vertical extent and lateral dimensions of the electrode structure rather than being constrained by lithography pattern size, effectively decoupling contact area from lithography resolution limits.
3Stability of the object's composition
If phase change layer is formed by gap filling, then complete coverage is achieved, but endurance and contact uniformity are negatively affected
Solution Approach 1:
The patent replaces the mechanical gap-filling process with a conformal deposition process. The phase change layer is deposited conformally over the three-dimensional heating electrode structure, ensuring uniform thickness and complete coverage without the defects associated with gap filling. This conformal deposition maintains structural integrity and contact uniformity while achieving complete coverage.
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 enables reduced variations and improved endurance by allowing a larger contact area between the heating electrode and the phase change layer, enhancing the memory device's performance and fabrication ease, while minimizing the need for additional lithography steps.
Implementation Method 1
Phase change memory devices write, read or erase according to different resistance of a phase change material between crystal state and non-crystal state
Implementation Method 2
a phase change layer is applied with a relative high current and short pulse, such as 1 mA with 50 ns, to change from a crystal state to a non-crystal state
Implementation Method 3
When erasing, the phase change layer is applied with a low current, such as 0.2 mA, for a longer duration, such as 100 ns, to change from a non-crystal state to a crystal state
Data Source
AI summary
A memory device is disclosed. A pillar structure comprises a first electrode layer, a dielectric layer overlying the first electrode layer, and a second electrode layer overlying the dielectric layer. A phase change layer covers a surrounding of the pillar structure. A bottom electrode electrically connects the first electrode layer of the pillar structure. A top electrode electrically connects the second electrode layer of the pillar structure.