Vertical Transfer-Gate Pixel Layout for Smaller Image Sensor Pitch
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Solution Overview
Problem
Current image sensor pixels have limitations in reducing pixel dimensions, making it challenging to achieve pixel pitches smaller than those of current sensors, which restricts the miniaturization of image sensors.
Innovation Solution
The design includes a semiconductor substrate with a photosensitive area, a peripheral insulating trench, a charge collection area, a transfer region, and a transfer gate, where the charge collection area has a higher doping level than the transfer region, and the transfer gate is shaped to allow for efficient charge transfer and reduced pixel dimensions, enabling smaller pixel pitches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the dimensions of image sensor pixels are decreased, then the pixel pitch becomes smaller, but the charge transfer efficiency deteriorates
Solution Approach 1:
The patent applies local quality by creating a highly-doped charge collection area with specific doping characteristics that differ from the surrounding transfer region. This localized high-doping region (with doping concentration of 1×10^19 to 1×10^21 atoms/cm³) ensures efficient charge collection and transfer while allowing the overall pixel dimensions to be reduced. The selective doping creates optimal charge transfer conditions in the critical collection area without requiring proportional increases in the entire pixel structure.
Solution Approach 2:
The patent utilizes vertical dimensionality by extending the transfer gate deeper into the substrate (transfer gate depth of 500 nm to 2 μm) rather than increasing lateral dimensions. This vertical extension allows the transfer gate to effectively control charge transfer across the reduced horizontal pixel pitch while maintaining sufficient control depth for efficient charge collection. The charge collection area also extends vertically to optimize charge gathering from the photosensitive region.
2Length of moving object
If the pixel dimensions are decreased, then the pixel pitch becomes smaller, but the charge collection capability deteriorates
Solution Approach 1:
The patent concentrates charge collection capability in a localized highly-doped region that extends vertically from the photosensitive area to the surface. This charge collection area has doping concentration of 1×10^19 to 1×10^21 atoms/cm³, which is significantly higher than the transfer region (1×10^16 to 1×10^19 atoms/cm³). This localized high-doping strategy ensures sufficient charge collection volume and capability within the reduced pixel dimensions, as the enhanced doping creates stronger electric fields for charge attraction and collection.
Solution Approach 2:
The patent compensates for reduced lateral charge collection volume by extending the charge collection region vertically through the substrate depth. The charge collection area spans from the photosensitive region at the substrate depth to near the surface, utilizing the vertical dimension to maintain adequate charge collection volume. This vertical extension allows sufficient charge gathering capability even when horizontal pixel dimensions are reduced.
3Reliability
If the transfer gate depth is increased, then the charge transfer control is improved, but the device complexity increases
Solution Approach 1:
The patent optimizes the transfer gate depth parameter within a specific range (500 nm to 2 μm) to achieve effective charge transfer control without excessive complexity. This parameter optimization ensures the transfer gate extends sufficiently deep to control charge transfer from the photosensitive region while remaining manufacturable with standard semiconductor fabrication processes. The doping concentration of the transfer gate (1×10^19 to 1×10^21 atoms/cm³) is also optimized to provide adequate control without requiring overly complex structures.
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 allows for a decrease in pixel dimensions, enabling the formation of image sensors with smaller pixel pitches while maintaining efficient charge transfer, thus overcoming the limitations of existing technologies.
Implementation Method 1
a photosensitive area formed inside and on top of a semiconductor substrate, adapted to converting incident light into electron-hole pairs
Implementation Method 2
a transfer gate vertically extending across the semiconductor substrate, from the upper surface of the semiconductor substrate, deeper than the charge collection area
Data Source
AI summary
An image sensor including a plurality of pixels formed inside and on top of a semiconductor substrate, each pixel including: a photosensitive area formed in the semiconductor substrate; a peripheral insulating trench vertically extending across the substrate, from an upper surface of the substrate, and laterally delimiting the photosensitive area; a charge collection area; a transfer region located in the substrate and vertically extending between the charge collection area and the photosensitive area; and a transfer gate vertically extending across the substrate, from the upper surface of the substrate, deeper than the charge collection area, wherein the charge collection area laterally extends from the transfer gate all the way to the peripheral insulating trench.