Solid-State Imaging Device Inversion Layer Induction Electrode
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Solution Overview
Problem
Solid-state imaging devices face challenges in improving dynamic range while maintaining yield due to issues with PN junction steepening, which leads to increased dark current and image quality deterioration, especially in back-illuminated designs where the semiconductor substrate does not function effectively as an overflow drain.
Innovation Solution
A solid-state imaging device is designed with a photodiode having a first conductivity type semiconductor area divided for each pixel, a transfer gate electrode, and an inversion layer induction electrode with a larger work function than the transfer gate electrode, inducing an inversion layer to improve dynamic range and suppress yield deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If shallow and dense ion implantation is performed to steepen the PN junction, 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 surface inversion layer is introduced as an intermediary between the photodiode and the external environment. This inversion layer, formed by applying a negative potential to a conductive layer on the light-receiving surface, acts as a protective barrier that prevents harmful effects from reaching the PN junction while allowing the steepened junction to maintain its high charge accumulation capacity.
Solution Approach 2:
The surface inversion layer is formed in advance before the device operates, creating a pre-established protective barrier. This beforehand cushioning prevents external harmful factors (such as those causing increased dark current) from directly affecting the PN junction, allowing the steepened junction to function at full capacity without suffering from the usual detrimental effects.
2Object-generated harmful factors
If heat treatment is increased to remove implantation defects, then the dark current is reduced, but thermal diffusion occurs compromising the steep PN junction
Solution Approach 1:
The surface inversion layer serves as a mediator that decouples the relationship between defect removal and junction preservation. By providing this protective barrier, the system can tolerate higher heat treatment levels that would otherwise damage the steep junction, as the inversion layer protects the junction while the heat treatment removes defects.
Solution Approach 2:
The invention changes the operational parameters by applying a negative potential to create the surface inversion layer. This parameter change (applying voltage to form inversion layer) allows the system to achieve defect removal through heat treatment without compromising junction steepness, as the inversion layer formation compensates for any thermal diffusion that occurs.
3Productivity
If pixel refinement is performed to increase pixel density, then the imaging resolution is improved, but the photodiode area becomes smaller reducing charge accumulation capacity
Solution Approach 1:
The invention changes the electrical parameters at the surface by forming an inversion layer, which fundamentally alters the charge distribution and accumulation characteristics. This parameter change allows small photodiodes to achieve high charge accumulation capacity through the enhanced electric field and charge confinement provided by the surface inversion layer, effectively decoupling pixel size from charge accumulation capability.
Solution Approach 2:
The surface inversion layer creates a localized region with different electrical properties at the light-receiving surface. This local quality change (creating an inversion layer with high carrier concentration) concentrates the charge accumulation function in a specific region, allowing the entire photodiode structure to achieve high charge capacity even when the overall photodiode area is small.
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 by steepening the PN junction without increasing dark current, thereby improving image quality and maintaining yield by inducing an inversion layer through the inversion layer induction electrode, which aids in charge accumulation and overflow management.
Implementation Method 1
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 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 a first conductivity type semiconductor area that is dividedly formed for each pixel arranged on a light sensing surface of a semiconductor substrate 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.