Imaging Device Pixel Cell Capacitance Ratio for Dynamic Range
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Solution Overview
Problem
There is a demand in the field of image sensors for a wider dynamic range, which existing technologies have not adequately addressed, particularly in the context of optical detection elements and photoelectric converters.
Innovation Solution
The proposed imaging device includes a configuration of pixel cells with photoelectric converters and field effect transistors, where the capacitance ratios between the photoelectric converters and their respective nodes are optimized to produce different sensitivity levels, allowing for a wider dynamic range by adjusting the capacitance of the gate insulating layers and the photoelectric conversion layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single photoelectric converter with fixed capacitance is used, then the device structure is simple, but the dynamic range is limited
Solution Approach 1:
The photoelectric conversion system is segmented into multiple pixel cells (first pixel cell and second pixel cell), each with different capacitance ratios. This segmentation allows different regions to capture different intensity ranges, thereby expanding the overall dynamic range without requiring complex adjustable mechanisms in each individual pixel.
Solution Approach 2:
Different pixel cells are designed with different local capacitance characteristics (Cpd1/Cn1 vs Cpd2/Cn2). The first pixel cell uses one capacitance ratio optimized for certain light intensities, while the second pixel cell uses another capacitance ratio optimized for different light intensities. This local quality differentiation enables the system to handle a wider dynamic range.
2Measurement precision
If the photoelectric conversion layer has high sensitivity, then signal detection is improved, but halation occurs
Solution Approach 1:
Different pixel cells are assigned different sensitivity levels through different capacitance ratios. Some pixel cells are optimized for high sensitivity to detect weak signals, while others are optimized to reduce halation effects. This local quality differentiation allows the system to capture both faint and bright regions without mutual interference.
3Measurement precision
If the photoelectric conversion layer has high sensitivity, then weak signals are detected, but black-out occurs in bright regions
Solution Approach 1:
The image sensor is segmented into multiple pixel cells with different sensitivity characteristics. High-sensitivity pixel cells capture weak signals effectively, while low-sensitivity pixel cells prevent black-out in bright regions. The combination of these segmented regions produces an image with both detailed shadows and highlights.
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 enables the imaging device to capture images with both high and low sensitivity, effectively expanding the dynamic range and suppressing halation and black-out, thereby improving image quality.
Implementation Method 1
light can be detected by detecting a photocurrent that is generated in the photoelectric converter with irradiation of the light
Implementation Method 2
the dielectric constant of the gate insulating film is changed with irradiation of light to the gate insulating film. Accordingly, a current flowing between a source and a drain is changed with the irradiation of the light to the gate insulating film
Data Source
AI summary
An imaging device including: pixel cells each comprising: a photoelectric converter including two electrodes and a photoelectric conversion layer therebetween; a field effect transistor having a gate and a channel region; and a node between the photoelectric converter and the field effect transistor. The field effect transistor outputs an electric signal corresponding to change in dielectric constant between the electrodes, the change being caused by incident light on the photoelectric conversion layer. Cpd1, Cn1, Cpd2 and Cn2 satisfy a relation of Cpd1/Cn1<Cpd2/Cn2 where a capacitance value of a first photoelectric converter in a state of receiving no incident light is Cpd1, a capacitance value between a first node and a first channel region is Cn1, a capacitance value of a second photoelectric converter in a state of receiving no incident light is Cpd2, and a capacitance value between a second node and a second channel region is Cn2.