Vertical Signal Storage for Solid-State Imaging Resolution
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Solution Overview
Problem
Solid-state imaging devices face challenges in achieving a wide dynamic range and high resolution due to reduced pixel size, leading to increased noise, reduced charge storage capacity, and color mixing, which limits image quality and color reproducibility.
Innovation Solution
A solid-state imaging device with a vertical signal storage portion and deep trench isolation (DTI) element isolation structure, where the signal storage portion is configured to increase the P-N junction interface area and capacitance, and the element isolation portion effectively separates pixels to prevent light leakage and noise, allowing for improved charge storage and reduced noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the area of each pixel is reduced to increase resolution, then the number of pixels increases, but the charge storage capacity of the photodiode is reduced
Solution Approach 1:
The patent extends the photodiode structure in the depth direction (vertical dimension) by forming a deep well region that penetrates through the substrate thickness. This vertical extension compensates for the reduced horizontal area, maintaining charge storage capacity while enabling smaller pixel pitch for higher resolution.
Solution Approach 2:
The patent forms a stacked structure where the photodiode region is nested within the substrate, with the deep well penetrating through the substrate thickness. This nesting approach maximizes the use of available space in the vertical dimension to compensate for reduced horizontal area.
2Measurement precision
If the area of each pixel is reduced to increase resolution, then the number of pixels increases, but noise increases and S/N ratio decreases
Solution Approach 1:
By extending the photodiode depth vertically through the substrate, the patent increases the photoelectric conversion volume without increasing horizontal area. This maintains signal strength while reducing the relative impact of noise sources associated with smaller transistor dimensions.
Solution Approach 2:
The patent replaces reliance on horizontal photodiode area with vertical depth for charge storage. This substitution allows the use of larger transistors for readout circuits (reducing noise) while maintaining adequate charge storage capacity through the deep vertical well structure.
3Measurement precision
If the area of each pixel is reduced to increase resolution, then the number of pixels increases, but color mixing increases and color reproducibility deteriorates
Solution Approach 1:
The patent uses vertical depth separation to isolate photodiodes from adjacent pixels. The deep well structure extends through the substrate thickness, creating physical separation that prevents lateral diffusion of charge carriers between adjacent pixels, thereby reducing color mixing.
Solution Approach 2:
The patent introduces a pinned photodiode structure with specific doping profiles that act as an intermediary barrier between adjacent pixels. The pinned region with controlled impurity concentration prevents charge carrier diffusion across pixel boundaries while allowing vertical charge collection.
4Measurement precision
If the area of each pixel is reduced to increase resolution, then the number of pixels increases, but the dynamic range is reduced
Solution Approach 1:
The patent compensates for reduced horizontal photodiode area by extending the vertical depth of the photodiode well through the substrate. This increases the charge storage volume, allowing the pixel to handle both dim and bright scenes simultaneously, thereby maintaining wide dynamic range in high-resolution images.
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 enhances the charge storage capacity and reduces noise, enabling the capture of images with improved dynamic range and color reproducibility, even at smaller pixel sizes, while maintaining high sensitivity and suppressing random noise.
Implementation Method 1
a photodiode that accumulates signal charge generated by photoelectric conversion in the pixel
Data Source
AI summary
According to one embodiment, in a solid-state imaging device, a signal storage portion in each of a plurality of pixels includes a first semiconductor region and a second semiconductor region. The first semiconductor region is of a first conductive type. The first semiconductor region coveres a side wall of an element isolation portion on a side of the signal storage portion. The second semiconductor region is of a second conductive type. The second conductive type is an opposite conductive type to the first conductive type. The second semiconductor region is arranged vertically in a depth direction from a deeper position than a front surface in a semiconductor substrate and extending in a plate shape along the first semiconductor region.