Semiconductor Memory Device With Light-Blocking Layers
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Solution Overview
Problem
In semiconductor memory devices using oxide semiconductors, the threshold voltage shifts and off-state current increases due to light exposure, leading to reduced data retention time and memory capacity per unit area.
Innovation Solution
A memory device with a transistor and capacitor structure where the oxide semiconductor has a wide band gap and low intrinsic carrier density, and a light-blocking layer is used to prevent light-induced degradation, ensuring low off-state current and increased memory capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the area occupied by each memory cell is decreased to increase memory capacity per unit area, then memory capacity per unit area is improved, but the area occupied by the capacitor for holding charge is decreased, making it difficult to ensure sufficient capacitance value
Solution Approach 1:
The patent transitions from planar capacitor structure to a three-dimensional stacked structure where the capacitor is formed vertically above the transistor. This vertical stacking allows the capacitor to occupy the space above the transistor rather than requiring additional lateral area, thereby maintaining sufficient capacitance value while reducing the overall memory cell footprint and increasing memory capacity per unit area.
Solution Approach 2:
The patent merges the transistor and capacitor into a tightly integrated memory cell structure where the capacitor is positioned directly above the transistor with minimal spacing. This merging approach maximizes the use of vertical space and reduces lateral area requirements, allowing both components to coexist in a compact configuration that maintains reliability while improving density.
2Reliability
If a transistor including oxide semiconductor is used to achieve high mobility and uniform characteristics, then transistor performance is improved, but light-induced degradation causes threshold voltage shifts and increased off-state current, shortening data retention period
Solution Approach 1:
The patent introduces a light-blocking layer as an intermediary component positioned between the oxide semiconductor transistor and incident light. This light-blocking layer acts as a protective mediator that prevents harmful light from reaching the oxide semiconductor, thereby preventing light-induced degradation such as threshold voltage shifts and off-state current increases, while allowing the transistor to maintain its high mobility and uniform characteristics.
3Area of stationary object
If the capacitor area is reduced to shrink memory cell size, then memory density is improved, but the capacitance value becomes insufficient to hold data for long time
Solution Approach 1:
The patent utilizes the vertical dimension to increase capacitor capacitance value without increasing lateral area. By forming the capacitor in a stacked configuration above the transistor and utilizing the full vertical space available, the capacitor achieves sufficient capacitance value for long-term data holding while the memory cell maintains a compact lateral footprint, thereby improving memory density without sacrificing data retention capability.
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 effectively prevents light-induced degradation, maintaining low off-state current and enhancing data retention time while increasing memory capacity per unit area.
Implementation Method 1
At least one of a pair of electrodes of the capacitor has a light-blocking property. Further, the memory device includes a light-blocking layer such as a light-blocking conductive film or a light-blocking insulating film
Implementation Method 2
a transistor including an oxide semiconductor in an active layer for control of accumulating, holding, and discharging charge in the memory element
Data Source
AI summary
One object is to propose a memory device in which a period in which data is held can be ensured and memory capacity per unit area can be increased. The memory device includes a memory element, a transistor including an oxide semiconductor in an active layer for control of accumulating, holding, and discharging charge in the memory element, and a capacitor connected to the memory element. At least one of a pair of electrodes of the capacitor has a light-blocking property. Further, the memory device includes a light-blocking conductive film or a light-blocking insulating film. The active layer is positioned between the electrode having a light-blocking property and the light-blocking conductive film or the light-blocking insulating film.