3D Image Sensor Depth Pixel With Bidirectional Charge Drift
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Solution Overview
Problem
Three-dimensional (3D) image sensors face challenges in maintaining sensitivity and performance with reduced photo gate sizes, leading to increased power consumption and noise levels.
Innovation Solution
The design incorporates a depth pixel structure with a photo detection region, multiple photo gates, and floating diffusion regions, where the doping density decreases away from the gates, allowing photo charges to be bidirectionally drifted based on an internal electric field, enabling effective charge storage and transfer even with smaller photo gates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the photo gate size is reduced, then the sensitivity of the depth pixel is improved, but the power consumption increases and noise levels increase
Solution Approach 1:
The photo detection region is divided into multiple sub-regions, each associated with a separate photo gate and floating diffusion region. This segmentation allows independent control and optimization of each segment, enabling reduced photo gate size while maintaining sensitivity through distributed charge collection across multiple regions.
Solution Approach 2:
Different regions of the photo detection structure are assigned different doping densities, with higher doping near photo gates for efficient charge collection and lower doping in central areas for reduced noise. This local quality variation optimizes both sensitivity and power consumption characteristics in different spatial zones.
2Measurement precision
If the photo gate size is reduced, then the sensitivity of the depth pixel is improved, but the noise level increases
Solution Approach 1:
The doping density is varied spatially within the photo detection region, with higher doping concentrations near photo gates to enhance charge collection efficiency and lower doping concentrations in central areas to minimize thermal generation noise. This local quality optimization allows small photo gates to maintain sensitivity while reducing overall noise levels.
Solution Approach 2:
Floating diffusion regions are introduced as intermediary structures between photo gates and charge storage nodes. These intermediaries facilitate efficient charge transfer while providing isolation that reduces noise propagation, enabling small photo gates to achieve high sensitivity without proportionally increased noise.
3Measurement precision
If the photo gate size is reduced, then the sensitivity of the depth pixel is improved, but the demodulation contrast decreases at high modulation frequencies
Solution Approach 1:
Multiple photo gates are distributed across the photo detection region, each capable of independent operation. This segmentation provides redundancy and parallel charge collection paths that maintain demodulation contrast at high frequencies even when individual photo gate sizes are reduced, as the distributed structure preserves temporal response characteristics.
Solution Approach 2:
The doping density profile is optimized with higher concentrations near photo gates to enhance charge collection speed and reduce transit time. This parameter change in the electrical characteristics of the photo detection region maintains frequency response and demodulation contrast even with smaller photo gate dimensions.
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 approach reduces power consumption, maintains demodulation contrast at high modulation frequencies, and minimizes dark currents and noise, resulting in improved performance for 3D image sensors.
Implementation Method 1
the photo detection region collects photo charges based on light reflected by an object
Implementation Method 2
configured to direct the collected photo charges in a first direction and a second direction different from the first direction based on an internal electric field in the photo detection region
Implementation Method 3
A doping density in the photo detection region may gradually decrease as a first distance from the first photo gate or a second distance from the second photo gate increases
Data Source
AI summary
A depth pixel includes a photo detection region, first and second photo gates and first and second floating diffusion regions. The photo detection region collects photo charges based on light reflected by an object. The collected photo charges are drifted in a first direction and a second direction different from the first direction based on an internal electric field in the photo detection region. The first photo gate is activated in response to a first photo control signal. The first floating diffusion region accumulates first photo charges drifted in the first direction if the first photo gate is activated. The second photo gate is activated in response to the first photo control signal. The second floating diffusion region accumulates second photo charges drifted in the second direction if the second photo gate is activated.