Stacked Photodiode Image Sensor Layout for Color Separation
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Solution Overview
Problem
In longitudinal spectroscopic image sensors, color mixture occurs due to light leakage into implantation plugs, leading to decreased sensitivity and aperture ratio, which hinders the utilization of superior light use efficiency and color separation.
Innovation Solution
A solid-state imaging device with stacked photoelectric conversion units and a longitudinal transistor, where one photoelectric conversion unit is formed over the gate electrode embedded in the semiconductor layer, allowing charge readout without forming a channel during charge accumulation, thus preventing color mixture and increasing aperture ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a light shielding film is formed on the implantation plug to prevent color mixture, then color separation is improved, but the aperture ratio decreases and sensitivity decreases
Solution Approach 1:
The patent extracts and removes the implantation plug structure from the pixel configuration. Instead of using an implantation plug to transfer charge from deep photodiodes, the invention uses a transfer gate and floating diffusion structure that eliminates the need for implantation plugs, thereby removing the source of color mixture while preserving aperture ratio
Solution Approach 2:
The patent introduces a transfer gate as an intermediary element between the deep photodiode and the readout circuit. This transfer gate mediates the charge transfer process without requiring a light-blocking implantation plug, allowing charge to be transferred through electrical control rather than physical conduction through a light-blocking structure
2Ease of operation
If an implantation plug is formed to read charge from deep photodiode, then charge readout is enabled, but light leakage into the plug causes color mixture
Solution Approach 1:
The patent extracts and removes the implantation plug structure from the pixel configuration. Instead of using an implantation plug to transfer charge from deep photodiodes, the invention uses a transfer gate and floating diffusion structure that eliminates the need for implantation plugs, thereby removing the source of color mixture
Solution Approach 2:
The patent replaces the physical conduction mechanism of the implantation plug with an electrically controlled transfer gate mechanism. The transfer gate uses voltage control to enable or disable charge transfer, replacing the need for a physical light-blocking conduction path
3Use of energy by moving object
If the aperture ratio is increased to improve sensitivity, then more light reaches the photodiode, but color mixture occurs due to light leakage into the implantation plug
Solution Approach 1:
The patent extracts and removes the implantation plug structure that causes color mixture, allowing the aperture to be maximized without the need for light-blocking structures. The transfer gate mechanism enables charge readout without requiring light-blocking implantation plugs
Solution Approach 2:
The patent moves the charge transfer function from a vertical conduction path through the implantation plug to a lateral transfer path using the transfer gate and floating diffusion. This dimensional change allows the vertical column to be fully utilized for light reception without light-blocking structures
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 achieves superior color separation and high sensitivity by preventing color mixture and enhancing the area of photoelectric conversion units, improving image quality and sensitivity.
Implementation Method 1
the photodiodes are stacked at different depths in silicon to perform a color separation using that an absorption wavelength of light is different depending on a depth of the silicon substrate
Implementation Method 2
the charge is transferred to a surface of the silicon substrate through a charge transfer path (hereinafter, referred to as an 'implantation plug') formed by impurity implantation and having a charge gradient
Data Source
AI summary
The present technique relates to a solid-state imaging device and an imaging apparatus that enable provision of a solid-state imaging device having superior color separation and high sensitivity. The solid-state imaging device includes a semiconductor layer in which a surface side becomes a circuit formation surface, photoelectric conversion units PD1 and PD2 of two layers or more that are stacked and formed in the semiconductor layer, and a longitudinal transistor Tr1 in which a gate electrode is formed to be embedded in the semiconductor layer from a surface of the semiconductor layer. The photoelectric conversion unit PD1 of one layer in the photoelectric conversion units of the two layers or more is formed over a portion of the gate electrode of the longitudinal transistor Tr1 embedded in the semiconductor substrate and is connected to a channel formed by the longitudinal transistor Tr1.