Back-Side Illuminated Image Sensor with Localized Substrate Thickness
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Solution Overview
Problem
Conventional back side illuminated (BSI) image sensors face issues with non-uniform absorption of light across different wavelengths due to the silicon substrate, leading to reduced quantum efficiency and increased pixel crosstalk, which affects image quality and resolution.
Innovation Solution
The solution involves a BSI image sensor configuration with varying depths of absorption compensation material over photo detectors, allowing for equal attenuation of light across colors, and a packaging method that integrates front-end and back-end processes for cost-effective and reliable mechanical support and electrical connectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a uniform thickness silicon substrate is used in BSI image sensors, then the structure is simple and manufacturing is easy, but the quantum efficiency varies for different colors due to non-uniform light absorption
Solution Approach 1:
The patent applies local quality by creating regions of different substrate thicknesses corresponding to different color photo-detectors. The silicon substrate is thinned to different extents in different areas: thinner regions for blue photo-detectors, medium thickness for green, and thicker regions for red photo-detectors. This ensures that each color receives approximately equal amounts of light energy, achieving uniform quantum efficiency across all colors while maintaining manufacturing feasibility through selective thinning processes.
2Productivity
If pixel size is reduced to increase the number of pixels and decrease chip size, then the sensor becomes more compact and has higher resolution, but the aperture size for each pixel decreases reducing quantum efficiency
Solution Approach 1:
The patent applies parameter changes by modifying the substrate thickness parameter to compensate for the reduced aperture size in smaller pixels. By adjusting the local substrate thickness according to the photo-detector color and size, the patent ensures that even smaller pixels receive adequate light energy. This parameter adjustment maintains quantum efficiency despite the reduced pixel dimensions and smaller apertures.
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 configuration ensures uniform light absorption across wavelengths, enhancing quantum efficiency and reducing pixel crosstalk, thereby improving image quality and resolution while providing a low-profile, cost-effective packaging solution.
Implementation Method 1
the quantum efficiency of different colors of light passing through the silicon substrate varies because the amount of the light absorbed (i.e. attenuated) by the silicon varies based upon wavelength
Implementation Method 2
image sensors, which are IC devices that include photo-detectors which transform incident light into electrical signals
Data Source
AI summary
An image sensor device that includes a substrate and a plurality of color filters. The substrate includes a plurality of photo detectors (wherein a first portion of the plurality of photo detectors each has a lateral size that is smaller than that of each of a second portion of the plurality of photo detectors) and a plurality of contact pads which are electrically coupled to the photo detectors. The plurality of color filters are each disposed over one of the photo detectors. The plurality of photo detectors are configured to produce electronic signals in response to light incident through the color filters. A third portion of the plurality of photo detectors are laterally disposed between the first and second portions of the photo detectors, and each having a lateral size between those of the first and second portions of the photo detectors.