Stepped Light-Incident Surface for UV Imaging Quantum Efficiency
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Solution Overview
Problem
Existing solid-state imaging devices, such as CMOS and CCD, face limitations in improving performance for light with short to middle wavelengths, particularly UV light, due to high light absorption by silicon, leading to reflection losses and reduced quantum efficiency.
Innovation Solution
The development of a solid-state imaging device with a semiconductor substrate featuring a recessed light incident surface and an on-chip lens, where the recess dimensions and lens parameters are optimized to enhance light absorption, including specific expressions for the difference in height between recess steps and the width of the light incident surface, to improve light absorption and reduce reflection losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional flat light incident surface is used, then the device structure is simple, but reflection losses occur and quantum efficiency is reduced for UV light
Solution Approach 1:
The patent applies curvature by forming a recessed surface with multiple steps on the light incident surface of the semiconductor substrate. This stepped recessed structure modifies the optical path of incident UV light, enabling multiple internal reflections that increase light absorption probability while reducing reflection losses. The curved/stepped geometry transforms the conventional flat surface into an optimized optical interface.
Solution Approach 2:
The patent introduces vertical dimensionality by creating a recessed surface with multiple steps at different height levels. This multi-level stepped structure adds depth to the light incident surface, allowing light to undergo multiple reflections between steps before exiting or being absorbed. This dimensional transformation increases the effective optical path length and improves quantum efficiency for UV wavelengths.
2Loss of energy
If the light incident surface area is increased to improve UV light absorption, then quantum efficiency improves, but the device area increases
Solution Approach 1:
The patent resolves this contradiction by utilizing the vertical dimension through stepped recesses. Instead of expanding the horizontal device area, the invention creates multiple reflection surfaces at different vertical levels within a compact footprint. This allows increased light absorption efficiency by extending the optical path length vertically rather than horizontally, maintaining small device area while improving UV light capture.
Solution Approach 2:
The stepped recessed structure enables continuous light interaction through multiple reflections between steps. Light that would otherwise reflect away from a flat surface is instead guided through multiple bounces between the stepped surfaces, increasing the probability of absorption. This continuous interaction within a compact area improves light absorption efficiency without requiring larger device area.
3Loss of energy
If an on-chip lens is added to focus light, then light absorption is enhanced, but device complexity increases
Solution Approach 1:
The patent merges the light focusing function with the light incident surface structure itself. Instead of adding a separate on-chip lens component, the refractive focusing element is integrated directly into the recessed surface geometry. This combination of the recessed stepped structure and on-chip lens creates a unified optical interface that focuses UV light while maintaining compact design and reducing overall device complexity.
Solution Approach 2:
The on-chip lens integrated into the recessed surface performs multiple functions: it focuses incident UV light onto the photoelectric conversion region, defines the optical aperture, and works in conjunction with the stepped structure to enhance light trapping. This multi-functional integration improves light absorption efficiency while avoiding the need for separate components, thereby managing device complexity effectively.
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 significantly enhances the quantum efficiency and reduces reflection losses for UV light, improving the overall performance of the solid-state imaging device by increasing the surface area for light absorption and optimizing light handling.
Implementation Method 1
an on-chip lens may be provided on the light incident surface of the semiconductor substrate
Implementation Method 2
a photoelectric conversion unit provided in the first pixel
Data Source
AI summary
Provided is a solid-state imaging device including a semiconductor substrate, a photoelectric conversion unit on the semiconductor substrate, and a recess of two or more steps formed on a surface on a light incident side of the semiconductor substrate, and further provided is a solid-state imaging device including a semiconductor substrate, a photoelectric conversion unit provided on the semiconductor substrate, and a light-shielding wall above the light incident side of the semiconductor substrate, in which the light-shielding wall includes a first portion having a first width extending in a direction substantially parallel to a light incident surface of the semiconductor substrate, and a second portion having a second width extending in a direction substantially perpendicular to the light incident surface, the second width being smaller than the first width, and the second portion is provided between the first portion and the semiconductor substrate.