Global Shutter Sensor Layout for Low Parasitic Light Sensitivity
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Solution Overview
Problem
Global shutter sensors face challenges in minimizing parasitic light sensitivity, which affects the responsivity of memory elements compared to photodiodes, requiring effective shielding from light to enhance shutter efficiency.
Innovation Solution
The semiconductor device incorporates a deep photodiode in a second epitaxial layer with a light shield having openings for a first epitaxial layer, forming a single crystal structure, and includes in-pixel circuits and shallow photodiodes, with a vertical transfer gate and deep trench isolation to reduce leakage currents and parasitic light sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a light shield is introduced to block parasitic light from reaching memory elements, then shutter efficiency is improved, but device complexity and manufacturing difficulty increase due to the need for precise openings and single crystal formation
Solution Approach 1:
The device is segmented into multiple functional layers: a first epitaxial layer containing in-pixel circuits and shallow photodiodes, and a second epitaxial layer containing deep photodiodes. The light shield is selectively positioned with openings only where deep photodiodes are located, allowing parasitic light blocking while maintaining light access for shallow photodiodes and circuits.
Solution Approach 2:
The light shield acts as an intermediary element between the incoming light and the memory elements. It selectively blocks parasitic light paths while allowing useful light to reach the photodiodes through precisely positioned openings, thereby mediating the light interaction without completely isolating the memory elements.
2Measurement precision
If deep photodiodes are used to enhance light sensing capability, then responsivity is improved, but parasitic light sensitivity increases which degrades shutter efficiency
Solution Approach 1:
Different regions of the device have different light exposure characteristics. Shallow photodiodes are positioned to receive light directly for high responsivity, while deep photodiodes are positioned under the light shield with openings only for necessary light paths, reducing their parasitic light sensitivity. The light shield creates local quality differences in light exposure across the device.
3Reliability
If a single crystal structure is formed between first and second epitaxial layers to reduce leakage currents, then reliability is improved, but manufacturing precision requirements increase
Solution Approach 1:
The light shield is formed with precise openings before the second epitaxial layer is grown. This preliminary positioning ensures that when the second layer is epitaxially grown, it automatically aligns with the openings, reducing the need for subsequent high-precision alignment steps and lowering overall manufacturing precision requirements while still achieving the desired single crystal structure.
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 improves shutter efficiency by minimizing parasitic light sensitivity and enhancing responsivity, achieving superior performance in sensing electromagnetic radiation.
Implementation Method 1
a photodiode region is used to receive the electromagnetic radiation and convert it into a corresponding electrical signal
Implementation Method 2
The first epitaxial layer and the second epitaxial layer may form a single crystal
Data Source
AI summary
Implementations of a semiconductor device may include a photodiode included in a second epitaxial layer of a semiconductor substrate; light shield coupled over the photodiode; and a first epitaxial layer located in one or more openings in the light shield. The first epitaxial layer and the second epitaxial layer may form a single crystal.