Photodiode Inversion Layer Electrode for Low-Dark-Current Imaging
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Solution Overview
Problem
Solid-state imaging devices face challenges in improving dynamic range while maintaining yield, as steepening the PN junction leads to increased dark current and image quality deterioration due to defects and impurities near the PN junction.
Innovation Solution
A solid-state imaging device is designed with a photodiode having a first conductivity type semiconductor area and a transfer gate electrode on a semiconductor substrate, along with an inversion layer induction electrode with a higher work function to induce an inversion layer, which improves the dynamic range and suppresses yield deterioration by reducing defects and dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If shallow and dense ion implantation is performed to steepen the PN junction gradient, then the charge accumulation capacity is improved, but implantation defects remain in the vicinity of the PN junction causing increased dark current
Solution Approach 1:
A dummy pixel area is introduced as an intermediary region between the effective pixel area and the optical black area. This dummy pixel area includes a photodiode and pixel transistor that absorb excess charges and defects generated during ion implantation, preventing these harmful elements from reaching the optical black area and causing dark current increases.
Solution Approach 2:
The dummy pixel area extracts and isolates the harmful defects and excess charges from the main imaging area. By placing this sacrificial region between the effective pixels and optical black area, the defects are captured and removed from the charge transmission path, preventing them from causing dark current in the optical black area.
2Manufacturing precision
If pixel refinement is performed to increase pixel density, then the imaging resolution is improved, but the surface area of the photodiode becomes smaller reducing charge accumulation capacity
Solution Approach 1:
The dummy pixel area is strategically positioned in a specific location between the effective pixel area and optical black area, where it locally handles charge management without affecting the overall pixel density of the imaging region. This localized structure allows high pixel density in the effective area while providing sufficient charge accumulation and defect absorption capacity.
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 effectively enhances the dynamic range of the imaging device while minimizing yield loss and dark current, resulting in improved image quality by inducing an inversion layer through the inversion layer induction electrode, thus addressing the limitations of steepening the PN junction.
Implementation Method 1
an inversion layer induction electrode formed on the semiconductor substrate via a gate insulating layer in an area covering a portion or the whole of the photodiode, and composed of a conductor or a semiconductor having a work function that is larger than that of the transfer gate electrode; wherein an inversion layer is induced, which is formed by accumulating a second conductivity type carrier on a surface of the inversion layer induction electrode side of the semiconductor area through the inversion layer induction electrode
Implementation Method 2
a photodiode having photodiodes are arranged on a light sensing surface in the form of a matrix
Data Source
AI summary
A solid-state imaging device is provided, which includes a photodiode having a first conductivity type semiconductor area that is dividedly formed for each pixel; a first conductivity type transfer gate electrode formed on the semiconductor substrate via a gate insulating layer in an area neighboring the photodiode, and transmitting signal charges generated and accumulated in the photodiode; a signal reading unit reading a voltage which corresponds to the signal charge or the signal charge; and an inversion layer induction electrode formed on the semiconductor substrate via the gate insulating layer in an area covering a portion or the whole of the photodiode, and composed of a conductor or a semiconductor having a work function. An inversion layer is induced, which is formed by accumulating a second conductivity type carrier on a surface of the inversion layer induction electrode side of the semiconductor area through the inversion layer induction electrode.