Backside Image Sensor Structure for Near-Infrared Light Absorption
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Solution Overview
Problem
Traditional back-illuminated image sensors have a lower absorption ratio for infrared light due to its longer wavelength, leading to undesired image signal quality, especially with the increasing demand for technologies using near-infrared light sources like AR/VR and 3D face recognition.
Innovation Solution
The image sensor incorporates a spherical crown structure on the substrate with a conformal dielectric layer and a reflective layer, which generates dielectric-layer and reflective-layer reflective light to increase absorption of incident light at various angles, optimizing the absorption ratio and signal quality by controlling the thickness of the conformal dielectric layer to satisfy optical resonance conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the silicon substrate is made thinner to reduce cost and improve manufacturing, then manufacturing cost decreases and manufacturing precision improves, but the absorption ratio for infrared light deteriorates because infrared light penetrates through the substrate
Solution Approach 1:
The patent converts the harmful effect of light penetration through the substrate into a beneficial reflection mechanism. By adding a reflective layer on the back surface of the substrate, the light that would otherwise be lost is reflected back into the photodiode, converting the harmful penetration effect into a beneficial double-absorption opportunity.
Solution Approach 2:
The patent introduces a new dimension (the back surface of the substrate) to solve the absorption problem. Instead of only considering front surface absorption, the reflective layer on the back surface creates a second absorption opportunity, effectively utilizing the third dimension (depth) to improve overall light absorption.
2Productivity
If the silicon substrate is made thinner to improve responsiveness and reduce manufacturing complexity, then device complexity decreases and responsiveness improves, but the absorption ratio for infrared light deteriorates
Solution Approach 1:
The reflective layer converts the harmful light penetration into a beneficial reflection mechanism, allowing thin substrates to maintain high infrared absorption by reflecting transmitted light back for secondary absorption.
3Manufacturing precision
If a reflective layer is added to increase infrared light absorption, then the absorption ratio improves, but the device complexity increases due to additional manufacturing steps
Solution Approach 1:
The reflective layer is applied locally only on the back surface of the substrate where it is most needed for reflecting light back into the photodiode, rather than making the entire device more complex. This localized approach minimizes added complexity while maximizing absorption benefit.
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 significantly enhances the absorption ratio of near-infrared light, improving the responsiveness and image signal quality of the image sensor, particularly in applications using near-infrared wavelengths.
Implementation Method 1
a photodetector arranged in the substrate, a photosensitive surface of the photodetector facing a back surface of the substrate to generate a charge upon receiving an incident light from the back surface of the substrate
Implementation Method 2
a conformal dielectric layer arranged on the spherical crown structure and used to generate a dielectric-layer reflective light when the incident light reaches the conformal dielectric layer
Implementation Method 3
a reflective layer arranged on the conformal dielectric layer and used to generate a reflective-layer reflective light when the incident light reaches the reflective layer
Implementation Method 4
optimizing the absorption ratio and signal quality by controlling the thickness of the conformal dielectric layer to satisfy optical resonance conditions
Data Source
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AI summary
Some embodiments of the present disclosure provide an image sensor and a method for manufacturing the image sensor. The image sensor includes a substrate (400) and at least one pixel unit. The pixel unit comprises a photodetector (401) arranged in the substrate, a photosensitive surface of the photodetector facing a back surface of the substrate to generate a charge upon receiving an incident light from the back surface of the substrate, a spherical crown structure (406) arranged on the substrate and located on an opposite surface of the photosensitive surface, a conformal dielectric layer (420) arranged on the spherical crown structure and used to generate a dielectric-layer reflective light when the incident light reaches the conformal dielectric layer, and a reflective layer (430) arranged on the conformal dielectric layer and used to generate a reflective-layer reflective light when the incident light reaches the reflective layer. In this way, an absorption ratio for the incident light is increased, thereby improving signal quality of an image.