Oxygen-Deficient Tantalum Oxide Memory Element for Rewritable Nonvolatile Storage
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Solution Overview
Problem
Conventional resistance variable nonvolatile memory elements using transition metal oxides face challenges such as slow switching speed, need for a forming process, and instability in resistance state retention, particularly with tantalum oxide-based memories which can only be written once and lack reversibility.
Innovation Solution
A nonvolatile memory element with a resistance variable layer comprising a layered structure of first and second oxygen-deficient tantalum oxides (TaOx and TaOy) allows reversible resistance changes without a forming process, utilizing a stacked structure where the second oxygen-deficient tantalum oxide layer is in contact with one electrode and has a thickness between 1 nm and 8 nm, enabling high-speed and stable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-layer oxygen-deficient tantalum oxide is used as the resistance variable layer, then the structure is simple, but the memory element requires a forming process and cannot be rewritten
Solution Approach 1:
The resistance variable layer is segmented into two distinct layers: a first oxygen-deficient tantalum oxide layer (TaOx, 0.5<x<2) and a second oxygen-deficient tantalum oxide layer (TaOy, 1<y≤2). This segmentation allows each layer to perform different functions - the first layer provides reversible resistance change capability while the second layer enables forming-free operation, thereby achieving both structural simplicity and rewritability
Solution Approach 2:
The patent uses a composite structure of two different oxygen-deficient tantalum oxide layers with distinct compositional ranges. The first layer (TaOx with 0.5<x<2) and second layer (TaOy with 1<y≤2) form a composite material system where each component contributes specific properties, enabling the memory element to achieve both forming-free operation and reversible resistance changes
2Ease of manufacture
If conventional transition metal oxide resistance variable layers are used, then the manufacturing process is established, but the switching speed is slow
Solution Approach 1:
The patent optimizes the oxygen content parameters of the tantalum oxide layers to achieve high-speed switching. By controlling the composition ranges (TaOx with 0.5<x<2 and TaOy with 1<y≤2) and thickness parameters, the resistance change speed is dramatically improved to 100 ns or less while maintaining compatibility with established semiconductor manufacturing processes
3Reliability
If a thick resistance variable layer is used, then the resistance change magnitude is large, but the switching speed decreases
Solution Approach 1:
The resistance variable layer is divided into two thinner layers instead of one thick layer. The first layer (TaOx) and second layer (TaOy) each have optimized thicknesses that collectively provide sufficient resistance change magnitude while reducing the switching time to 100 ns or less, thereby maintaining reliability without sacrificing speed
4Reliability
If a forming process is applied to initialize the resistance variable layer, then the layer becomes operational, but the process adds manufacturing complexity and cost
Solution Approach 1:
The second oxygen-deficient tantalum oxide layer (TaOy) is designed with specific compositional characteristics (1<y≤2) that pre-condition the resistance variable layer during manufacturing. This preliminary structural design eliminates the need for subsequent forming processes, allowing the memory element to be operational immediately after standard fabrication steps, thereby reducing manufacturing complexity and cost
5Ease of manufacture
If tantalum oxide-based resistance variable layers are used, then the material is compatible with semiconductor processes, but the memory can only be written once
Solution Approach 1:
The patent creates a composite structure using two different oxygen-deficient tantalum oxide layers with distinct compositional ranges. This composite approach maintains semiconductor process compatibility while the specific combination of TaOx (0.5<x<2) and TaOy (1<y≤2) layers enables reversible resistance changes, achieving rewritability that single-layer tantalum oxide cannot provide
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 enables high-speed, reversible, and stable resistance changes without the need for a forming process, improving manufacturing efficiency and reducing costs, while maintaining compatibility with semiconductor processes.
Implementation Method 1
a resistance variable layer (106) comprising an oxygen-deficient tantalum oxide
Implementation Method 2
a resistance variable layer (106) comprising an oxygen-deficient tantalum oxide
Data Source
AI summary
A nonvolatile memory element comprises a first electrode layer (103), a second electrode (107), and a resistance variable layer (106) which is disposed between the first electrode layer (103) and the second electrode layer (107), a resistance value of the resistance variable layer varying reversibly according to electric signals having different polarities which are applied between the electrodes (103), (107), wherein the resistance variable layer (106) has a first region comprising a first oxygen-deficient tantalum oxide having a composition represented by TaOx (0<x<2.5) and a second region comprising a second oxygen-deficient tantalum oxide having a composition represented by TaOy (x<y<2.5), the first region and the second region being arranged in a thickness direction of the resistance variable layer.