Back-Side Illuminated Pixel With Insulated Conductive Wall
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Solution Overview
Problem
Back-side illuminated image sensors face challenges with insulation between transistors and the substrate where photogenerated electrons are stored, leading to issues like current leakage and transistor disturbance.
Innovation Solution
A back-side illuminated pixel design featuring a semiconductor substrate with a three-layer assembly on the front side, including a heavily-doped layer, an insulating layer, and a semiconductor layer, laterally delimited by an insulated conductive wall that extends from the front to the back side, allowing for controlled charge transfer and reduced leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If transistors are formed directly on the substrate in conventional pixels, then the device complexity is reduced, but current leakage occurs and photogenerated charges disturb transistor operation
Solution Approach 1:
The pixel structure is segmented into distinct functional layers: a substrate for charge storage, an insulating layer for isolation, and a semiconductor layer for transistor formation. This segmentation physically separates the transistor from the substrate, preventing current leakage and charge disturbance while maintaining operational stability.
Solution Approach 2:
An insulating layer is introduced as an intermediary between the substrate and the transistor-containing semiconductor layer. This intermediate layer acts as a barrier that prevents harmful electrical interactions (current leakage and charge disturbance) while allowing the transistor to function properly.
2Loss of energy
If the pixel uses conventional insulation structures, then the manufacturing process is simpler, but current leakage occurs between transistors and substrate
Solution Approach 1:
The pixel is divided into a substrate portion and a semiconductor layer portion separated by an insulating layer. This segmentation eliminates the direct electrical connection causing current leakage, while the layered structure can be fabricated using standard semiconductor processing techniques.
Solution Approach 2:
The pixel employs a composite structure combining substrate material (for charge storage), insulating material (for leakage prevention), and semiconductor material (for transistor operation). This composite approach addresses current leakage while maintaining manufacturability through established multi-material processing.
3Manufacturing precision
If transistors are formed in a heavily-doped layer directly on substrate, then the manufacturing precision is improved, but photogenerated charges disturb transistor operation
Solution Approach 1:
The transistor-forming semiconductor layer is extracted from the substrate and placed on top of an insulating layer. This extraction removes the transistor from the harmful electromagnetic environment of the substrate, protecting it from photogenerated charge disturbance while preserving manufacturing precision through controlled layer deposition.
Solution Approach 2:
The insulating layer serves as a protective intermediary that shields the transistor in the semiconductor layer from photogenerated charges in the substrate. This intermediate barrier prevents charge disturbance while allowing precise transistor formation in the isolated semiconductor environment.
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 enables transistors to operate at lower voltages with reduced current leakage and smaller surface area, while minimizing disturbance from photogenerated charges, improving the overall performance and manufacturing efficiency of the image sensor pixels.
Implementation Method 1
an insulating layer, and a semiconductor layer, the three-layer assembly being interrupted in a central portion of the pixel by a transfer region
Implementation Method 2
a layer of the second conductivity type
Data Source
AI summary
A back-side illuminated pixel including a semiconductor substrate of a first conductivity type coated, on the front side of the pixel, with a three-layer assembly successively including a first layer of the second conductivity type, an insulating layer, and a second semiconductor layer. The three-layer assembly is interrupted in a central portion of the pixel by a transfer region of the first conductivity type laterally delimited by an insulated conductive wall extending from the front surface, Transistors are formed in the second semiconductor layer.