Transparent Conductive Layer for Backside Illuminated Image Sensor Charge Transfer
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Solution Overview
Problem
As backside illuminated (BSI) image sensor devices continue to scale down, existing technologies face challenges in maintaining satisfactory quantum efficiency and reducing defects, such as dark current and white pixel generation, which affect their performance.
Innovation Solution
Incorporating a transparent conductive layer over the back surface of the substrate, capacitively coupled to the sensor element, which enhances the electric field and improves charge transfer ability, potentially replacing the need for a pinned layer and reducing defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If device geometry is scaled down to achieve lower fabrication costs and higher integration density, then fabrication costs decrease and integration density increases, but quantum efficiency deteriorates and defects increase
Solution Approach 1:
The patent changes the electrical parameters at the back surface by introducing a transparent conductive layer with specific work function characteristics. This layer creates a Schottky barrier that modifies the charge carrier behavior, allowing efficient charge collection even in scaled-down devices where traditional pinned layers become less effective. The parameter change in surface electrical properties directly addresses the quantum efficiency deterioration caused by scaling.
Solution Approach 2:
The transparent conductive layer acts as an intermediary between the semiconductor substrate and the external environment. It mediates the interaction between incident light and the semiconductor material while simultaneously managing charge carrier extraction. This intermediary layer provides both optical transparency for light sensing and electrical functionality for charge collection, resolving the conflicts arising from device scaling.
2Reliability
If a pinned layer is used to improve charge transfer, then charge transfer ability improves, but device complexity and fabrication difficulty increase
Solution Approach 1:
The patent extracts the charge transfer enhancement function from the traditional pinned layer structure and implements it through a transparent conductive layer. By removing the need for a separate pinned layer and its associated complex fabrication steps (such as precise doping profiles and multiple processing stages), the solution simplifies device structure while maintaining or improving charge transfer ability through the conductive layer's work function characteristics.
Solution Approach 2:
The transparent conductive layer performs multiple functions simultaneously: it provides charge transfer enhancement, maintains optical transparency for light detection, and serves as an electrode contact. This multi-functionality eliminates the need for separate pinned layer structures and reduces overall device complexity while achieving the desired charge transfer performance.
3Illumination intensity
If the substrate is made thinner to improve light transmission in BSI devices, then fill factor increases and destructive interference reduces, but charge transfer ability deteriorates
Solution Approach 1:
The patent changes the electrical parameter at the back surface (where light enters in BSI devices) by introducing the transparent conductive layer. This creates a Schottky barrier that enhances the electric field strength, compensating for the reduced substrate thickness. The parameter change in surface electrical properties ensures sufficient charge transfer ability even when the substrate is made thinner to improve light transmission.
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 transparent conductive layer enhances charge transfer and quantum efficiency, improving the performance of BSI image sensor devices by reducing dark current and white pixel generation, while maintaining high transparency and conductivity.
Implementation Method 1
a transparent conductive layer over the back surface of the substrate, capacitively coupled to the sensor element, which enhances the electric field and improves charge transfer ability
Data Source
AI summary
The present disclosure provides an image sensor device and a method of forming the image sensor device. In an example, an image sensor device includes a substrate having a front surface and a back surface; a sensor element disposed at the front surface of the substrate, the sensor element being operable to sense radiation projected toward the back surface of the substrate; and a transparent conductive layer disposed over the back surface of the substrate, the transparent conductive layer at least partially overlying the sensor element. The transparent conductive layer is configured for being electrically coupled to a bottom portion of the sensor element.