CMOS Time-of-Flight Sensor Stabilization via Hydrogen-Enriched Dielectric
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Solution Overview
Problem
CMOS time-of-flight image sensors face instability due to interface traps and fixed charges, which cause undesired induced electric fields, leading to variable and unreliable performance, especially in designs with low doped epitaxial layers.
Innovation Solution
The implementation of a hydrogen-enriched dielectric material above the oxide layer, combined with ultraviolet light or plasma treatments, and the addition of a shallow doping region as an electric field shield, to reduce and eliminate the effects of interface traps and fixed charges, thereby stabilizing the sensor's operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a standard CMOS fabrication process is used, then manufacturing efficiency is maintained, but interface traps and fixed charges are generated causing sensor instability
Solution Approach 1:
A hydrogen-enriched dielectric material is deposited on top of the oxide layer before final sensor assembly. This preliminary action introduces hydrogen that will later be used to passivate interface traps during thermal processing, preventing sensor instability without requiring changes to the standard CMOS fabrication process
Solution Approach 2:
The hydrogen-enriched dielectric material acts as an intermediary layer between the oxide layer and the external environment. It serves as a reservoir of hydrogen that can be thermally processed to deliver hydrogen atoms to the silicon-oxide interface, passivating traps without disrupting the standard fabrication workflow
2Reliability
If interface traps are reduced by adding hydrogen-enriched dielectric material, then sensor stability improves, but device structure becomes more complex
Solution Approach 1:
The hydrogen-enriched dielectric material serves multiple functions simultaneously: it acts as a protective passivation layer, a hydrogen reservoir for trap passivation, and a standard dielectric for electrical isolation. This multi-functionality reduces the need for additional specialized components, minimizing structural complexity while improving stability
3Object-affected harmful factors
If a shallow doping region is added as electric field shield, then induced electric field effects are reduced, but manufacturing process complexity increases
Solution Approach 1:
A shallow doping region is created only in specific areas where interface traps and fixed charges are most problematic, rather than uniformly throughout the entire sensor. This localized approach provides targeted protection against induced electric fields while minimizing the impact on overall device structure and manufacturing 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
These techniques result in a robust and reliable CMOS time-of-flight image sensor with improved performance by minimizing induced electric fields, ensuring stable operation without significant changes in detector performance or power consumption.
Implementation Method 1
The deposition of this dielectric material in the fabrication process generates hydrogen that passivates and reduces the interface traps
Implementation Method 2
an ultraviolet light treatment is performed to further passivate the interface traps and charges
Implementation Method 3
a plasma treatment is performed
Implementation Method 4
a shallow doping region or passivation layer which acts also as a protection electric shield to any induced electric field, e.g., by strongly attenuating or completely canceling the induced electric field due to traps and charges
Data Source
AI summary
A CMOS time-of-flight image sensor must be robust to interface traps and fixed charges which may be present due to fabrication and which may cause an undesired induced electric field in the silicon substrate. This undesired induced electrical field is reduced by introducing a hydrogen-enriched dielectric material. Further remedial techniques can include applying ultraviolet light and/or performing a plasma treatment. Another possible approach adds a passivation doping layer at a top of the detector as a shield against the undesired induced electric field. One or more of the above techniques can be used to prevent any unstable behavior of the time-of-flight sensor.