Buried Phase Change Memory Cell with Segmented Electrode
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Solution Overview
Problem
Manufacturing high-density memory devices with small electrodes is challenging due to poor adhesion and mechanical stability issues, which affect the yield and reliability of phase change memory cells.
Innovation Solution
A memory cell design featuring a bottom electrode with a base portion and a pillar portion, where the pillar portion has a width less than the base portion, surrounded by a dielectric with a recessed memory element, concentrating current density and improving mechanical stability through a larger contact area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If very small electrodes are used to reduce the active area and reset current, then the current density increases and reset current decreases, but the adhesion and mechanical stability of the electrodes deteriorate
Solution Approach 1:
The bottom electrode is segmented into two distinct portions: a larger base portion that provides mechanical stability and adhesion, and a smaller pillar portion that concentrates current density. This segmentation allows the electrode to simultaneously achieve low reset current and high reliability.
Solution Approach 2:
Different portions of the bottom electrode have different sizes and functions. The base portion has a larger area for mechanical support, while the pillar portion has a smaller area for current concentration. This local quality differentiation resolves the contradiction between needing small contact area for low reset current and large contact area for mechanical stability.
2Manufacturing precision
If the contact area between electrode and phase change material is reduced, then higher current densities are achieved with smaller absolute current values, but the mechanical stability during manufacturing decreases
Solution Approach 1:
The electrode structure is divided into a base portion for mechanical support and a pillar portion for precise current delivery. This segmentation enables both high current density control and mechanical stability during manufacturing.
Solution Approach 2:
The electrode transitions from a single-dimensional small contact area to a two-dimensional structure with both lateral extent (base portion) and vertical height (pillar portion), allowing mechanical stability in one dimension while maintaining small contact area in another dimension.
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 needed for phase change and enhances mechanical stability, improving manufacturing yield by focusing current density in a small active region and providing thermal isolation, thus minimizing the reset current required.
Implementation Method 1
Phase change based memory materials, like chalcogenide based materials and similar materials, can be caused to change phase between an amorphous state and a crystalline state by application of electrical current
Implementation Method 2
The change from the amorphous to the crystalline state is generally a lower current operation. The change from crystalline to amorphous, referred to as reset herein, is generally a higher current operation, which includes a short high current density pulse to melt or breakdown the crystalline structure
Implementation Method 3
The recess portion of the memory element has a width substantially equal to the width of the pillar portion of the bottom electrode, concentrating current density in the active region
Implementation Method 4
techniques are used to thermally isolate the active region in the phase change cell so that the resistive heating needed to induce the phase change is confined to the active region
Data Source
AI summary
Memory cells are described along with methods for manufacturing. A memory cell as described herein includes a bottom electrode comprising a base portion and a pillar portion on the base portion, the pillar portion having a width less than that of the base portion. A dielectric surrounds the bottom electrode and has a top surface. A memory element is overlying the bottom electrode and includes a recess portion extending from the top surface of the dielectric to contact the pillar portion of the bottom electrode, wherein the recess portion of the memory element has a width substantially equal to the width of the pillar portion of the bottom electrode. A top electrode is on the memory element.