Solid-State Imaging Pixel with Capacitive Multiplication Gate
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Solution Overview
Problem
Solid-state imaging devices face challenges in miniaturizing pixels while maintaining sensitivity, as existing configurations require multiple gate electrodes for avalanche multiplication, increasing pixel size and making it difficult to decrease the voltage applied to the multiplication gate electrode.
Innovation Solution
A solid-state imaging device configuration with a charge barrier portion between the charge holding portion and the insulation film, allowing for capacitively coupled multiplication gate electrodes, which reduces the voltage required for avalanche multiplication by forming a potential well and accelerating electric charges over a shorter distance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple gate electrodes are used for avalanche multiplication, then the sensitivity is improved, but the pixel size increases
Solution Approach 1:
The patent combines the charge storage function and avalanche multiplication function into a single gate electrode structure. The multiplication gate electrode is capacitively coupled to the charge holding portion, allowing the same electrode to both store charges and perform avalanche multiplication, thereby eliminating the need for separate gate electrodes and reducing pixel size while maintaining sensitivity.
Solution Approach 2:
The multiplication gate electrode serves multiple functions: it acts as a charge holding portion to store photoelectrically converted charges and simultaneously functions as a multiplication electrode to perform avalanche multiplication. This multi-functionality reduces the number of required electrodes and minimizes pixel area while preserving sensitivity.
2Reliability
If multiple gate electrodes are used for avalanche multiplication, then the sensitivity is improved, but the device complexity increases
Solution Approach 1:
The patent merges the charge holding portion and multiplication gate electrode into a single integrated structure. The multiplication gate electrode is capacitively coupled to the charge holding portion through an insulation film, combining storage and multiplication functions in one component, thereby reducing device complexity while maintaining sensitivity.
3Reliability
If the distance for charge acceleration is increased, then the avalanche multiplication is improved, but the voltage applied to the multiplication gate electrode increases
Solution Approach 1:
The patent introduces a charge barrier portion with high impurity concentration between the charge holding portion and the insulation film. This creates a localized region with a small potential difference that forms an efficient acceleration path for charges. The localized high-field region enables effective avalanche multiplication with lower applied voltage compared to uniform field distribution.
4Productivity
If the pixel size is reduced, then the number of pixels is increased, but the light receiving area per pixel decreases
Solution Approach 1:
By combining the charge holding portion and multiplication gate electrode into a single integrated structure, the patent reduces the overall area required per pixel. This space efficiency allows for increased pixel density while maintaining sufficient light receiving area for each pixel, thereby increasing the total number of pixels without sacrificing individual pixel sensitivity.
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 miniaturization of pixels, reduces the voltage needed for avalanche multiplication, and enhances the sensitivity of the imaging device by allowing the same electrode to store and multiply electric charges efficiently.
Implementation Method 1
a photoelectric conversion portion that has a second conductive type, is arranged in a surface layer portion of a surface of a semiconductor substrate having a first conductivity type, and converts light incident on the surface into an electric charge
Implementation Method 2
If a predetermined voltage is applied to the multiplication gate electrode, the potential increases toward the insulation film in the direction of arranging the insulation film, the charge barrier portion, and the charge holding portion. An electric charge present in the charge holding portion accelerates toward the insulation film and increases in the charge barrier portion due to avalanche multiplication.
Implementation Method 3
The charge barrier portion between the insulation film and the charge holding portion forms a region having a potential smaller than the interface between the semiconductor substrate and the insulation film and the charge holding portion. The charge holding portion exhibits a larger potential than the charge barrier portion and a region opposite the charge barrier portion with reference to the charge holding portion in the direction of arranging the insulation film, the charge barrier portion, and the charge holding portion. In other words, a potential well is formed.
Implementation Method 4
a multiplication gate electrode that is capacitively coupled with the charge holding portion, and is arranged on the semiconductor substrate via an insulation film
Data Source
AI summary
A solid-state imaging device includes: multiple pixels. Each pixel is arranged at a surface layer portion of a semiconductor substrate, and includes: a photoelectric conversion portion that converts light incident into an electric charge; a charge holding portion that stores the electric charge, and is arranged in the semiconductor substrate; a multiplication gate electrode that is capacitively coupled with the charge holding portion, and is arranged on the semiconductor substrate via an insulation film; and a charge barrier portion that is arranged between the charge holding portion and the insulation film, and has a higher impurity concentration than the semiconductor substrate.