Oxide Semiconductor Photodiode Stacking for Low Power Imaging
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Solution Overview
Problem
Miniaturization of pixels in solid-state image sensing devices makes it difficult to secure the area occupied by photodiodes, and existing transistors with single crystal silicon do not have ideal electrical characteristics, leading to high off-state current and inadequate charge retention.
Innovation Solution
A semiconductor device is designed with a driver circuit, a transistor including an oxide semiconductor layer in the channel formation region, and a photodiode stacked over the semiconductor substrate, where the photodiode partly overlaps the transistor, allowing for lower power consumption and improved electrical characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If pixels are miniaturized to increase integration density, then the overall device area is reduced, but the area occupied by photodiodes becomes insufficient
Solution Approach 1:
The patent transitions from a planar arrangement to a three-dimensional stacked structure, placing the photodiode layer above the transistor layer. This vertical stacking enables the photodiode to occupy the area above the transistor rather than competing for the same planar space, effectively resolving the area conflict through dimensional change.
Solution Approach 2:
The photodiode structure is positioned to overlap with and partially enclose the transistor structure in the vertical direction. The photodiode's active area is configured to extend over the transistor region, creating a nested spatial relationship where the photodiode utilizes the space above the transistor without interfering with its operation.
2Ease of manufacture
If transistors with single crystal silicon are used, then manufacturing is straightforward, but off-state current is too high for adequate charge retention
Solution Approach 1:
The patent changes the material parameter of the transistor channel from single crystal silicon to oxide semiconductor. This material substitution fundamentally alters the electrical characteristics, achieving ultra-low off-state current (10^-21 to 10^-24 A) while maintaining compatibility with existing semiconductor manufacturing processes through sputtering deposition.
Solution Approach 2:
The transistor structure employs a composite material approach by combining oxide semiconductor layers with conventional semiconductor materials. The channel formation region uses oxide semiconductor (such as In-Ga-Zn-O) which provides superior electrical characteristics, while integrating with standard silicon-based device structures for manufacturability.
3Device complexity
If more area is allocated to transistors, then device functionality is improved, but the percentage of photodiode area in the pixel decreases
Solution Approach 1:
By stacking the photodiode above the transistor in the vertical dimension, the patent enables both components to occupy their full required areas without reducing the photodiode's area percentage in the planar view. The photodiode layer is positioned at a higher elevation, allowing simultaneous optimization of both transistor functionality and photodiode area.
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 configuration ensures sufficient area for the photodiode, increases the amount of saturation signal charge, enhances dynamic range, and reduces power consumption while maintaining stable electrical characteristics with low off-state current.
Implementation Method 1
a photoelectric conversion element such as a photodiode
Implementation Method 2
a transistor including an oxide semiconductor layer in a channel formation region... having lower off-state current
Data Source
AI summary
A solid-state image sensing element including a transistor with stable electrical characteristics (e.g., significantly low off-state current) is provided. Two different element layers (an element layer including an oxide semiconductor layer and an element layer including a photodiode) are stacked over a semiconductor substrate provided with a driver circuit such as an amplifier circuit, so that the area occupied by a photodiode is secured. A transistor including an oxide semiconductor layer in a channel formation region is used as a transistor electrically connected to the photodiode, which leads to lower power consumption of a semiconductor device.