Binary Optical Lens in CMOS Backend Stack for Light Collection
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Solution Overview
Problem
Front-illuminated optical sensors in CMOS devices suffer from optical losses due to metal-covered peripheries that obstruct incoming light, limiting the collection of light into the sensor.
Innovation Solution
Integration of a binary optical lens within the CMOS backend stack, specifically in the nitride passivation layer, which focuses incoming light onto the sensor element without requiring additional layers, using a Fresnel zone plate design optimized for specific wavelengths and formed through minimal additional photolithography and etching steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a binary optical lens is integrated into the CMOS backend stack, then the fill factor and optical power are improved, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The optical lens is merged with the CMOS backend stack structure, specifically utilizing the nitride passivation layer that already exists in the device architecture. This integration approach combines the optical focusing function with the existing structural layer, avoiding the need for separate optical components and reducing overall device complexity while maintaining optical power enhancement
Solution Approach 2:
The nitride passivation layer serves dual purposes: it provides electrical passivation for the CMOS device and simultaneously functions as the optical lens material. This multi-functionality approach allows the same structural element to fulfill both electrical and optical roles, improving fill factor without adding extra layers or components
2Illumination intensity
If additional layers are added to form the optical lens, then the optical focusing capability is improved, but the manufacturing process complexity increases
Solution Approach 1:
The existing nitride passivation layer, which is already deposited as part of the standard CMOS backend process, is repurposed to form the optical lens. This self-service approach utilizes an existing layer for a dual function, eliminating the need for additional material deposition steps and simplifying the manufacturing process while maintaining optical focusing capability
3Device complexity
If metal-covered peripheries are present in the CMOS device, then the device structure is simplified, but optical losses increase due to light obstruction
Solution Approach 1:
The optical lens is positioned locally at the sensor surface where light enters the device, creating a localized optical focusing zone. This local quality approach addresses the light obstruction problem specifically at the entry point without requiring changes to the overall device structure or removal of metal peripheries, thereby reducing optical losses while maintaining structural simplicity
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
Increases the fill factor of the sensor by effectively directing light past obstructive structures in the backend stack, enhancing optical power in the active area without adding extra layers, and is flexible across various wavelength spectra.
Implementation Method 1
an optical lens formed in a layer of the one or more layers and arranged to direct light incident upon it towards the sensor element
Implementation Method 2
Commonly, a Fresnel zone plate design is chosen to make the lens
Data Source
AI summary
An optical sensor in an integrated Complementary Metal Oxide Semiconductor, CMOS, device, the sensor including a sensor element with an optical active region and a CMOS backend stack including one or more layers. The sensor further includes an optical lens formed in a layer of the one or more layers and arranged to direct light incident upon it towards the sensor element.