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
1Reliability
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 dark current issue without affecting the quantum efficiency enhancement provided by the alternative semiconductor material, allowing both goals to be achieved simultaneously
2Ease of manufacture
If silicon-based CMOS image sensors are used, then manufacturing cost and power consumption are reduced, but quantum efficiency for NIR and IR radiation deteriorates
Solution Approach 1:
The patent employs a composite structure combining silicon-based CMOS technology with alternative semiconductor materials having smaller bandgaps. This composite approach maintains the manufacturing advantages of silicon while adding the optical detection capabilities of alternative materials, achieving both cost-effectiveness and high quantum efficiency for NIR and IR radiation
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 PIN diodes, thus improving the performance of sensors using 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
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.