SOI Device-Over-Photodetector Pixel Structure for Low Cross-Talk
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Solution Overview
Problem
BSI CMOS image sensors face limitations in optical and electrical isolation, leading to high cross-talk, low full well capacity, and noise due to limited silicon surface area and parasitic capacitance, which affect their performance and scalability.
Innovation Solution
A semiconductor-on-insulator (SOI) device-over-photodetector (DoP) image sensor design with a full-depth backside deep trench isolation structure, featuring independent readout transistors and transfer transistors, enhances optical and electrical isolation, reduces noise, and increases silicon surface area for improved scalability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If BSI CMOS image sensor structure is used, then sensitivity and angular response are improved, but optical and electrical isolation deteriorates leading to high cross-talk
Solution Approach 1:
The patent introduces an intermediary deep trench isolation structure filled with dielectric material between adjacent photodetectors. This isolation structure acts as a mediator that blocks optical leakage and electrical interference between neighboring pixels, thereby reducing cross-talk while preserving the back-side illuminated sensor's sensitivity and angular response characteristics.
2Ease of manufacture
If conventional BSI CMOS structure is used, then manufacturing flexibility is improved, but full well capacity decreases due to limited silicon surface area
Solution Approach 1:
The patent transitions from a planar surface structure to a three-dimensional structure by etching deep trenches into the silicon substrate and filling them with dielectric material. This dimensional change allows the photodetector active area to extend deeper into the substrate, increasing the available silicon surface area for charge collection and thereby increasing full well capacity while maintaining manufacturing flexibility.
3Productivity
If photodetectors are placed closer together to increase pixel density, then productivity is improved, but parasitic capacitance increases leading to noise
Solution Approach 1:
The patent extracts and removes the harmful parasitic capacitance effects by introducing deep trench isolation structures between adjacent photodetectors. These isolation trenches physically separate the photodetector regions, eliminating the parasitic capacitance coupling between neighboring pixels and thereby reducing noise even when pixel density is increased.
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 SOI DoP image sensor achieves low cross-talk, high full well capacity, and reduced noise, enabling enhanced design flexibility and high modulation transfer function with improved sensitivity and anti-blooming capabilities.
Implementation Method 1
a photodetector in the semiconductor substrate
Data Source
AI summary
Various embodiments of the present application are directed towards a semiconductor-on-insulator (SOI) DoP image sensor and a method for forming the SOI DoP image sensor. In some embodiments, a semiconductor substrate comprises a floating node and a collector region. A photodetector is in the semiconductor substrate and is defined in part by a collector region. A transfer transistor is over the semiconductor substrate. The collector region and the floating node respectively define source/drain regions of the transfer transistor. A semiconductor mesa is over and spaced from the semiconductor substrate. A readout transistor is on and partially defined by the semiconductor mesa. The semiconductor mesa is between the readout transistor and the semiconductor substrate. A via extends from the floating node to a gate electrode of the readout transistor.