3D Image Sensor Trench Structure for Light Sensitivity
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Solution Overview
Problem
As the number of pixels in a limited area increases, the pixel area decreases, leading to degraded light sensitivity and an increased signal-to-noise ratio (SNR) in image sensors, which deteriorates device characteristics.
Innovation Solution
The image sensor incorporates trenches in the photoelectric conversion area with controlled depth and entrance width based on the wavelength of incident light, increasing the photo-detecting area and preventing the generation of noise-causing photocharges, thereby enhancing light sensitivity and reducing SNR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of pixels is increased in a limited area, then the resolution is improved, but the pixel area is decreased leading to degraded light sensitivity
Solution Approach 1:
The patent extends the photoelectric conversion region from a two-dimensional surface to a three-dimensional structure by forming trenches in the substrate. This vertical extension increases the photo-detecting area without increasing the lateral pixel area, thereby maintaining high resolution while improving light sensitivity through increased light absorption volume.
Solution Approach 2:
The patent optimizes the trench depth and width parameters based on the wavelength of incident light. By adjusting these geometric parameters, the photoelectric conversion efficiency is maximized for different wavelengths, improving light sensitivity across the spectrum while maintaining the compact pixel structure needed for high resolution.
2Productivity
If the pixel area is decreased, then the number of pixels per area is increased, but the signal to noise ratio is degraded
Solution Approach 1:
By forming trenches that extend vertically into the substrate, the patent increases the photoelectric conversion volume within each pixel without increasing the lateral pixel area. This maintains high pixel density while improving the signal strength through increased photon absorption, thereby improving the signal-to-noise ratio.
Solution Approach 2:
The patent applies different trench depths and widths to different wavelength bands (e.g., deeper trenches for blue light, shallower for red light) based on their penetration depths. This localized optimization ensures maximum photoelectric conversion efficiency for each wavelength, improving signal strength and signal-to-noise ratio while maintaining compact pixel structures.
3Area of stationary object
If trenches are formed in the photoelectric conversion area, then the photo-detecting area is increased, but the device complexity is increased
Solution Approach 1:
The patent divides the photoelectric conversion area into multiple trenches separated by isolation regions. This segmentation increases the total photo-detecting area by utilizing the vertical dimension while the isolation regions simplify the manufacturing process by providing clear boundaries for etching and filling operations, thereby managing device complexity.
Solution Approach 2:
The trenches serve multiple functions: they increase the photo-detecting area, act as isolation structures between pixels, and provide pathways for light absorption. This multi-functionality reduces the need for additional separate structures, thereby increasing photo-detecting area while minimizing 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
This approach effectively improves light sensitivity and decreases the signal-to-noise ratio by increasing the photo-detecting area within a limited pixel area, even when the pixel area is reduced, by optimizing the trench structure in the image sensor.
Implementation Method 1
a photoelectric conversion area corresponding to the first pixel and the second pixel formed in the substrate
Implementation Method 2
the first pixel includes a first filter for filtering a visible light having a first wavelength band, and the second pixel includes a second filter for filtering a visible light having a second wavelength band
Data Source
AI summary
An image sensor includes a transfer gate formed over a substrate including front and back sides, a photoelectric conversion area formed in the substrate on one side of the transfer gate, a trench formed in the photoelectric conversion area and having a trench entrance located on the back side of the substrate, and a color filter formed over the backside of the substrate.