Integrated Optical Filter in Photosensitive Cell Interconnection

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Solution Overview

Problem

Conventional photosensitive cells with filters positioned on top face challenges such as high aspect ratio, increased fabrication complexity, and reduced optical performance due to the distance of filters from the sensitive element and sensitivity to high illumination, leading to color overlap and high production costs.

Innovation Solution

Integrating an optical filter within the interconnection part of the photosensitive cell, between the photosensitive element and the metallization layers, using dielectric layers and metal oxide glass or doped transparent materials to maintain optical properties and reduce the stack height, allowing for closer proximity to the photosensitive element and reduced aspect ratio.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If filters are positioned on top of the photosensitive cells, then optical filtering is achieved, but the aspect ratio increases and color overlap occurs

Engineering Contradiction:

Improveoptical filtering performanceVSAvoidaspect ratio

Core Design Contradiction:

ReliabilityVSLength of stationary object

Solution Approach 1:

The filter is moved from a horizontal position on top of the cell to a vertical position within the interconnection part, changing the spatial dimension of filter placement. This integration within the interconnection stack reduces the horizontal footprint while maintaining filtering functionality, thereby reducing the aspect ratio without compromising optical performance

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Reliability

If filters are positioned on top of the interconnection part, then filtering is achieved, but the distance from the photosensitive element increases causing color overlap

Engineering Contradiction:

Improvecolor discriminationVSAvoiddistance from photosensitive element

Core Design Contradiction:

ReliabilityVSLength of moving object

Solution Approach 1:

The filter is nested within the interconnection part structure, specifically integrated into the metallization layers or dielectric layers. This nesting approach places the filter in close proximity to the photosensitive element while utilizing the existing interconnection stack space, thereby minimizing the distance between filter and photosensitive element and preventing color overlap

Inventive Principle:

Principle #7Nested doll (Nesting)

3Reliability

If photoresist filters are used, then filtering is achieved, but they cannot withstand high temperatures above 300°C

Engineering Contradiction:

Improvefiltering functionVSAvoidthermal resistance

Core Design Contradiction:

ReliabilityVSTemperature

Solution Approach 1:

The filter material is changed from photoresist to a high-temperature resistant material such as metal oxide glass or doped transparent material. This parameter change in material composition enables the filter to withstand the high temperatures (around 400°C) required for anneal steps during metallization fabrication while maintaining its optical filtering properties

Inventive Principle:

Principle #35Parameter changes

4Reliability

If filters are placed on top of the stack, then filtering is achieved, but light reflections from metallization levels cause color overlap

Engineering Contradiction:

Improvecolor discriminationVSAvoidlight reflection

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The filter is positioned as an intermediary element between the input face and the photosensitive element, specifically within the interconnection part. This intermediate placement ensures that light passes through the filter before reaching the metallization levels, preventing reflections from causing color overlap. The filter acts as a mediator that controls light wavelength content before it interacts with other structures

Inventive Principle:

Principle #24Intermediary (Mediator)

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 optical performance by minimizing color overlap, reducing the stack height, and maintaining filter integrity under high temperatures, resulting in a compact, reliable, and cost-effective photosensitive cell with improved fabrication efficiency.

Implementation Method 1

Filters are chosen to decompose any given light signal into a reduced number of wavelengths. This may, for example, be three primary colours such as blue, green and red.

Methodology Applied

Scientific EffectOptical filtering: Filter (optical)

Implementation Method 2

Many optical components integrate photosensitive cells that deliver an electrical signal representative of the received light intensity.

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS7880253B2Integrated optical filter

Publication Date: 2011.02.01 STMICROELECTRONICS FRANCE

AI summary

The disclosure relates to an integrated circuit comprising at least one photosensitive cell. The cell includes a photosensitive element, an input face associated with the said photosensitive element, an optical filter situated in at least one optical path leading to the photosensitive element and an interconnection part situated between the photosensitive element and the input face. The optical filter is disposed between the photosensitive element and the surface of the interconnection part closest to the input face. In particular, the optical filter can be disposed within the interconnection part. The disclosure also proposes that the filter be formed using a glass comprising cerium sulphide or at least one metal oxide.