Solid-State Sensor Charge Draining Region Design
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Miniaturization of solid-state sensors is hindered by the width of lateral overflow drains (LODs) required to prevent blooming, leading to decreased sensitivity and storage capacity due to the barrier role of p-type regions around n-type regions acting as drains.
Innovation Solution
A semiconductor substrate design where a second region of the second conductivity type is formed below the junction surface to drain excess charge, allowing the pixel separating region to be minimized, thereby improving sensitivity and storage capacity without the need for conventional LODs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lateral overflow drains (LODs) with p-type regions around n-type drain regions are used to prevent blooming, then charge overflow is effectively drained, but the pixel separating region width increases, decreasing sensitivity and storage capacity
Solution Approach 1:
The patent extracts the charge draining function from the lateral overflow drain structure at the pixel separating region and relocates it to a dedicated charge draining region positioned below the photodiode. This separation allows the pixel separating region to be minimized while the charge draining region handles excess charge below the junction surface, thereby resolving the contradiction between blooming prevention and sensitivity.
Solution Approach 2:
The patent transitions the charge draining function from a lateral (in-plane) structure to a vertical (depth) structure by positioning the charge draining region below the junction surface. This dimensional change allows charge draining to occur in the depth direction rather than requiring wide lateral separating regions, thus improving sensitivity while maintaining blooming prevention.
2Quantity of substance
If lateral overflow drains with p-type barrier regions are used to drain excess charge, then charge storage capacity is protected, but the device complexity and manufacturing difficulty increase due to multiple doped regions
Solution Approach 1:
The patent extracts the charge draining function from the complex lateral LOD structure with multiple doped regions (p-type barriers around n-type drains) and relocates it to a simpler charge draining region below the junction surface. This reduces the number of doped regions needed in the pixel separating area while maintaining charge storage capacity protection.
Solution Approach 2:
The charge draining region below the junction surface serves multiple functions: it drains excess charge to prevent blooming, maintains charge storage capacity, and eliminates the need for complex lateral barrier structures. This multi-functional design simplifies the overall device structure while achieving the same protective effects.
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 design enhances the sensitivity and storage capacity of photodiodes by allowing the pixel separating region to be set to the smallest required width, with a 20% increase in both sensitivity and charge storage capacity compared to conventional LODs, and improved sensitivity on the long wavelength side.
Implementation Method 1
A photodiode is a diode that generates electric current upon receiving light. When the pn junction is reverse-biased and a high electric field is applied, the depletion layer widens. Incident light is absorbed mainly in the depletion layer and generates electron-hole pairs.
Implementation Method 2
a pixel separating region of the first conductivity type formed to penetrate through the first region to separate the adjacent regions of the photodiodes
Implementation Method 3
a second region of the second conductivity type that is separated from the junction surface between the semiconductor substrate and the first region and is formed in the semiconductor substrate below the junction surface and is used to drain excess charge
Data Source
AI summary
A sensor having photodiodes whose sensitivity and storage capacity can be increased is provided. The sensor is formed by arranging the photodiodes in an array with first region of second conductivity type is formed on the principal surface of a substrate of a first conductivity type. A pixel separating region of the first conductivity type is formed to penetrate through the first semiconductor region to separate the regions of the adjacent photodiodes. A second region of the second conductivity type used to drain excess charge is formed in substrate at a position away from the junction surface between substrate and the first region and below the junction surface.