Image Sensor Passivation Layer for Dark Current Reduction
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Solution Overview
Problem
CMOS image sensors based on silicon have poor quantum efficiency for near-infrared (NIR) and infrared (IR) radiation due to their large bandgap, leading to inaccuracies in time-of-flight imaging due to high dark current, which is exacerbated by the use of alternative semiconductor materials with smaller bandgaps that enhance quantum efficiency but increase dark current.
Innovation Solution
Incorporating a high k dielectric passivation layer that induces a dipole moment along the top surface of the cap layer, drawing mobile charge carriers away from PIN diodes and reducing dark current, thereby improving the accuracy of distance measurements in time-of-flight imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If alternative semiconductor materials with smaller bandgaps are used, then quantum efficiency for NIR and IR radiation is improved, but dark current increases
Solution Approach 1:
A passivation layer is introduced as an intermediary between the alternative semiconductor material and the environment. This passivation layer specifically targets and mitigates the harmful dark current effect without interfering with the beneficial quantum efficiency enhancement provided by the alternative semiconductor material, thus resolving the contradiction between improved measurement precision and reduced harmful factors
Solution Approach 2:
The electrical properties at the semiconductor surface are modified by introducing the passivation layer, which changes the surface potential and carrier concentration parameters. This parameter change reduces the generation of mobile charge carriers that cause dark current, while maintaining the optical absorption properties that provide high quantum efficiency
2Measurement precision
If passivation layer is added to reduce dark current, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The harmful effect of dark current is extracted and isolated from the main photodetector structure by introducing a dedicated passivation layer. This separate functional layer addresses the measurement accuracy issue without fundamentally redesigning the core photodetector architecture, thus limiting the increase in device complexity
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 solution effectively reduces dark current impact on measurements, enhancing the accuracy of distance determination in CMOS image sensors by neutralizing mobile electrons at the PIN diodes, thus improving the performance of sensors operating with alternative semiconductor materials.
Implementation Method 1
Incorporating a high k dielectric passivation layer that induces a dipole moment along the top surface of the cap layer
Implementation Method 2
Incorporating a high k dielectric passivation layer that induces a dipole moment
Implementation Method 3
drawing mobile charge carriers away from PIN diodes and reducing dark current, thereby improving the accuracy of distance measurements
Data Source
AI summary
Various embodiments of the present disclosure are directed towards an image sensor with a passivation layer for dark current reduction. A device layer overlies a substrate. Further, a cap layer overlies the device layer. The cap and device layers and the substrate are semiconductor materials, and the device layer has a smaller bandgap than the cap layer and the substrate. For example, the cap layer and the substrate may be silicon, whereas the device layer may be or comprise germanium. A photodetector is in the device and cap layers, and the passivation layer overlies the cap layer. The passivation layer comprises a high k dielectric material and induces formation of a dipole moment along a top surface of the cap layer.