Solid-State Imaging Device Dark Current Suppression
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Solution Overview
Problem
In multi-layer solid-state imaging devices, the use of electrons as signal charges leads to a significant dark current due to voltage differences across the accumulation diode, degrading the signal-to-noise ratio, especially in low-light conditions, while using holes as signal charges poses challenges in correctly detecting signals from a low-voltage accumulation diode.
Innovation Solution
The implementation of a solid-state imaging device with a semiconductor substrate and vertical signal lines, where the threshold voltage of the amplifying transistor is set lower than the accumulation diode's potential, and the selection transistor is strategically placed to manage voltage differences, reducing dark current by controlling the voltage applied to the p-n junction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If electrons are used as signal charges in multi-layer solid-state imaging devices, then the photoelectric conversion efficiency is improved, but a significant dark current occurs due to voltage differences across the accumulation diode, degrading the signal-to-noise ratio
Solution Approach 1:
The patent inverts the conventional approach by using holes instead of electrons as signal charges. This inversion changes the polarity of the accumulation diode voltage, allowing the anode to be at a lower potential than the cathode, thereby suppressing dark current while maintaining photoelectric conversion efficiency
Solution Approach 2:
The patent changes the voltage parameter configuration of the accumulation diode by using holes as charge carriers. The anode is set at a lower potential (e.g., 0V or -3.3V) compared to the cathode, creating a voltage difference that suppresses dark current flow while enabling effective signal accumulation
2Measurement precision
If the pixel size is reduced to achieve finer pixels, then the resolution is improved, but the optical absorption efficiency deteriorates, leading to decreased sensitivity
Solution Approach 1:
The patent employs a multi-layer structure combining different materials with complementary properties: a silicon substrate for mechanical support and circuit integration, and an amorphous silicon photoelectric conversion layer with high optical absorption coefficient. This composite structure enables fine pixel dimensions while maintaining high light absorption efficiency
Solution Approach 2:
The patent transitions from a single-layer planar structure to a multi-layer stacked configuration. The photoelectric conversion layer is positioned in a different spatial dimension above the substrate, allowing independent optimization of pixel size and light absorption path length, thereby resolving the trade-off between resolution and sensitivity
3Use of energy by moving object
If the photodiode depth is increased to improve optical absorption, then the sensitivity is improved, but oblique incident light enters adjacent photodiodes causing color mixture (cross talk)
Solution Approach 1:
The patent segments the photoelectric conversion function into a dedicated amorphous silicon layer positioned above the substrate, separated from the underlying circuit structures. This segmentation allows the photoelectric layer to be optimized for light absorption without being constrained by substrate thickness, achieving high sensitivity while preventing cross-talk through spatial separation
Solution Approach 2:
The patent introduces an insulating film as an intermediary layer between the substrate and the amorphous silicon photoelectric conversion layer. This intermediary structure provides electrical isolation and optical separation, enabling the photoelectric layer to capture oblique incident light efficiently while preventing charge leakage and cross-talk to adjacent pixels
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 effectively suppresses dark current, improving image quality by maintaining a low voltage across the accumulation diode and reducing noise components, enabling high-quality image capture even in poorly illuminated conditions.
Implementation Method 1
a photoelectric converting film 45 which is formed above the insulating film 35 and converts incident light into an electrical signal
Data Source
AI summary
A solid-state imaging device in the present disclosure includes a semiconductor substrate, pixels, and column signal lines. Each of the pixels includes an amplifying transistor, a selection transistor, a reset transistor, and a photoelectric converting unit. The photoelectric converting unit includes a photoelectric converting film, a transparent electrode, a pixel electrode, and an accumulation diode. The pixel electrode and the accumulation diode are connected to a gate of the amplifying transistor. The amplifying transistor has a source connected to the column signal line and a drain connected to a power source line. The reset transistor has a source connected to the pixel electrode. The selective transistor is provided between the source of the amplifying transistor and the column signal line. A threshold voltage of the amplifying transistor is lower than a voltage of the accumulation diode.