Backside Illuminated Image Sensor Diffracting Element
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Solution Overview
Problem
The quantum efficiency of image sensors with backside illumination for near-infrared wavelengths is low due to low silicon absorption, and existing methods to improve it are insufficient, particularly in compact sensors with small silicon thicknesses.
Innovation Solution
Incorporating a diffracting element with a refractive index different from the active region, such as an oxide, in the central zone of the active region, combined with metallization levels that reflect diffracted rays, to increase the optical path and absorption of near-infrared light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the optical path is increased by reflection on metallization levels or insulating trenches, then quantum efficiency is improved, but the silicon thickness must be increased which reduces sensor compactness
Solution Approach 1:
The patent introduces a diffracting element that operates in the optical dimension rather than relying on physical thickness increase. By using diffraction gratings or similar structures, the optical path is extended through multiple internal reflections and diffractions within a thin silicon layer, achieving high quantum efficiency without increasing sensor thickness.
Solution Approach 2:
The patent modifies the refractive index parameters by introducing oxide layers and metallization structures with specific optical properties. These parameter changes create enhanced light-matter interaction through controlled refraction and reflection, improving absorption efficiency in near-infrared wavelengths without requiring thicker silicon.
2Reliability
If silicon thickness is increased to improve near-infrared absorption, then quantum efficiency is improved, but device compactness is reduced
Solution Approach 1:
Instead of solving the absorption problem by increasing the vertical dimension (thickness), the patent uses diffracting elements to create complex optical paths within the existing thin silicon layer. This approach extends the effective optical path length through multiple bounces and diffractions without adding vertical space.
Solution Approach 2:
The patent embeds diffracting elements and metallization structures within the existing sensor architecture. These elements are integrated into the thin silicon substrate, creating a nested configuration where multiple functional layers coexist in a compact vertical arrangement, maintaining sensor compactness while enhancing near-infrared absorption.
3Volume of moving object
If conventional backside illumination is used with thin silicon, then sensor compactness is maintained, but quantum efficiency for infrared light is insufficient
Solution Approach 1:
The patent changes the optical parameters of the thin silicon structure by introducing materials with different refractive indices (oxide layers, metallization). These parameter changes enhance the interaction between infrared light and the silicon substrate through controlled refraction, reflection, and diffraction, improving quantum efficiency without sacrificing compactness.
Solution Approach 2:
The patent introduces diffracting elements and metallization structures as intermediary components that mediate the interaction between infrared light and the thin silicon substrate. These intermediaries trap and redirect light multiple times through the active region, enhancing absorption efficiency in near-infrared wavelengths while maintaining the thin silicon profile.
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 enhances the absorption of infrared radiation by up to three times compared to similar sensors without a diffracting element, significantly improving quantum efficiency.
Implementation Method 1
the active region comprises at least one diffracting element which has a refractive index different from the refractive index of the active region (for example, an oxide) and lies at least partly in the central zone, on one of the faces of the active region. Thus, by forming a specific diffracting element at least partly in the central zone, the optical path travelled by the light rays in the silicon is increased even further because of the numerous diffractions resulting from the positioning of this diffracting element.
Implementation Method 2
The sensor may furthermore comprise at least one metallization level which lies in front of the second face of the active region, is encapsulated in an insulating region and is optically coupled to the diffracting element. Thus, the effect of the diffracting element is increased even further by the presence of at least one metallization level, which reflects the rays diffracted by the diffracting element.
Implementation Method 3
a converging lens which lies in front of the first face of the active region and is configured in order to direct the light rays arriving on the lens towards a central zone of the active region
Data Source
AI summary
An integrated image sensor with backside illumination includes a pixel. The pixel is formed by a photodiode within an active semiconductor region having a first face and a second face. A converging lens, lying in front of the first face of the active region, directs received light rays towards a central zone of the active region. At least one diffracting element, having a refractive index different from a refractive index of the active region, is provided at least partly aligned with the central zone at one of the first and second faces.