Backside Image Sensor Anti-Reflection Structure for Leakage Control
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Solution Overview
Problem
Image sensors face challenges in achieving clear image quality due to leakage currents and operation errors caused by connection issues between conductive layers and adjacent back contacts or vias, leading to suboptimal dark characteristics and quantum efficiency, particularly in blue pixel detection.
Innovation Solution
The implementation of an anti-reflection structure with a titanium oxide conductive layer, which is strategically positioned to reduce reflectivity across all colors and specifically blue light, and the application of a voltage to the conductive layer to improve dark current characteristics, while removing the conductive layer from the edge area to prevent leakage currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conductive layer is continuously disposed across the entire second surface including the edge area, then the anti-reflection performance is improved, but leakage currents occur between the conductive layer and adjacent back contacts or vias
Solution Approach 1:
The conductive layer is segmented into two distinct regions: a first conductive layer disposed in the pixel array area and a second conductive layer disposed in the edge area. This segmentation allows the patent to maintain continuous anti-reflection coverage while preventing leakage currents by electrically isolating the edge area conductive layer from back contacts and vias through insulating layers.
Solution Approach 2:
Different regions of the second surface are assigned different conductive layer configurations tailored to their specific functional requirements. The pixel array area receives a conductive layer optimized for anti-reflection, while the edge area receives a conductive layer configured to prevent leakage currents, demonstrating local quality optimization.
2Reliability
If the conductive layer is removed from the edge area to prevent leakage currents, then operation errors are reduced, but the anti-reflection performance is compromised
Solution Approach 1:
The anti-reflection structure is segmented into multiple conductive layers positioned at different locations. The first conductive layer in the pixel array area provides anti-reflection performance, while the second conductive layer in the edge area maintains anti-reflection coverage without causing leakage currents, as it is isolated from back contacts and vias by insulating layers.
Solution Approach 2:
Insulating layers are introduced as intermediary elements between the second conductive layer in the edge area and the back contacts or vias. This intermediary structure prevents direct electrical connection that would cause leakage currents while maintaining the anti-reflection function of the conductive layer.
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 solution enhances image sensor performance by reducing reflectivity, increasing quantum efficiency, particularly for blue pixels, and preventing operation errors, resulting in improved dark current characteristics and clearer image quality.
Implementation Method 1
an anti-reflection structure with a titanium oxide conductive layer, which is strategically positioned to reduce reflectivity across all colors and specifically blue light
Implementation Method 2
Each of the pixels includes a photodiode (PD). The photodiode serves to convert incident light into an electrical signal.
Data Source
AI summary
Provided is an image sensor, which includes a first substrate that has a first surface and a second surface opposite to the first surface, and includes a pixel array area and an edge area, the edge area including a first conductive pad; an anti-reflection structure on the second surface; a pixel isolator in the first substrate and defining and separating pixels; and a micro lens array that is disposed on the anti-reflection structure, in which the anti-reflection structure includes a first insulating layer, a conductive layer, a second insulating layer, and a third insulating layer sequentially stacked, the conductive layer is on the pixel array area, and is not at least in a portion of the edge area where the first conductive pad is arranged, and a voltage is configured to be applied to the conductive layer.