Multibit Ferroelectric Memory Cells Using Segmented Layer Coercive Fields
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Solution Overview
Problem
Current three-dimensional memory devices face challenges in achieving high-density storage with multibit ferroelectric memory cells, as existing technologies struggle to efficiently integrate and differentiate ferroelectric material layers for enhanced memory capacity and performance.
Innovation Solution
A three-dimensional memory device is developed with an alternating stack of insulating and conductive layers, featuring vertically stacked ferroelectric memory elements composed of distinct ferroelectric material portions differing in composition and lateral thickness, formed through a method involving sacrificial material layers and isotropic recessing processes to create toroidal ferroelectric memory elements surrounding semiconductor channels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If single-bit memory cells are used in three-dimensional vertical NAND strings, then device simplicity is maintained, but storage density is limited
Solution Approach 1:
The memory cell is segmented into multiple ferroelectric material layers (first ferroelectric material layer and second ferroelectric material layer with different coercive fields), where each layer can be independently controlled to store one bit of data. This segmentation enables multibit storage per cell without requiring multiple separate memory cells, thereby increasing storage density while maintaining manageable structural complexity.
Solution Approach 2:
Different regions of the memory cell employ ferroelectric materials with different local properties (different coercive fields). The first ferroelectric material layer has a first coercive field and the second ferroelectric material layer has a second coercive field, allowing selective switching of each layer by applying voltages within specific ranges. This local quality differentiation enables independent control of multiple storage elements within a single cell structure.
2Quantity of substance
If multibit ferroelectric memory cells are implemented, then storage capacity is enhanced, but differentiation and control of multiple ferroelectric layers becomes difficult
Solution Approach 1:
The patent utilizes parameter changes in the ferroelectric materials, specifically different coercive field values, to enable differentiation and independent control of multiple ferroelectric layers. By selecting ferroelectric materials with distinct coercive fields, each layer responds to voltage stimuli differently, allowing selective switching and independent data storage in each layer without interference from other layers.
3Manufacturing precision
If isotropic recessing processes are used to form toroidal ferroelectric elements, then manufacturing precision is improved, but process complexity increases
Solution Approach 1:
Sacrificial material layers are deposited and patterned beforehand to define the precise geometry of the toroidal ferroelectric elements. The sacrificial materials serve as templates that guide the subsequent formation of ferroelectric layers. After the ferroelectric layers are formed around the sacrificial materials, the sacrificial materials are removed, leaving behind precisely formed toroidal structures with controlled dimensions and shapes.
Data Source
AI summary
A three-dimensional memory device includes an alternating stack of insulating layers and electrically conductive layers and memory stack structures vertically extending through the alternating stack. Each of the memory stack structures includes a vertical semiconductor channel and a vertical stack of ferroelectric memory elements surrounding the vertical semiconductor channel and located at levels of the electrically conductive layers. Each of the ferroelectric memory elements includes a respective vertical stack of a first ferroelectric material portion and a second ferroelectric material portion that differs from the first ferroelectric material portion by at least one of a material composition and a lateral thickness.