Multilayer Optical Filter Buried in IC Interconnection
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Solution Overview
Problem
Existing multilayer optical filters used in imaging devices have insufficient transmission for desired wavelengths and inadequate rejection of unwanted wavelengths, particularly in the infrared range, due to limited thickness and optical characteristics.
Innovation Solution
A multilayer optical filter is formed within an integrated circuit by burying part of the filter in the interconnection part, increasing the total thickness and resonant cavity, with two parts separated by thick layers of the interconnection part, and using materials like copper and silicon nitride, optimizing interference by maintaining parallel interfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multilayer optical filters are formed above the interconnecting section with limited thickness, then the filter can be manufactured within standard integrated circuit constraints, but the transmission near the desired wavelength is insufficient and rejection of unwanted wavelengths is inadequate
Solution Approach 1:
The filter is divided into two separate parts: a first filter part formed within the interconnecting section and a second filter part formed above it. This segmentation allows each part to contribute to the overall optical performance while managing the total thickness constraint. The first filter part provides initial filtering within the limited space of the interconnecting section, while the second filter part enhances the optical properties without exceeding manufacturing constraints.
Solution Approach 2:
The invention utilizes the vertical dimension by extending the filter structure from the interconnecting section upward. By forming the first filter part within the interconnecting section and the second filter part above it, the design effectively uses the vertical space to achieve greater total thickness and improved optical performance while maintaining compatibility with standard integrated circuit manufacturing processes.
2Reliability
If the thickness of the dielectric layer between metallic layers is increased to improve optical properties, then transmission and rejection performance improve, but the filter occupies more space above the interconnecting section
Solution Approach 1:
The filter structure is segmented into two parts located at different vertical positions. The first filter part is embedded within the interconnecting section, utilizing the available space there, while the second filter part is positioned above it. This segmentation allows the total filter thickness to be distributed optimally, improving optical performance without concentrating all thickness requirements in one location that would exceed manufacturing constraints.
Solution Approach 2:
The first filter part is nested within the interconnecting section structure, effectively using the existing vertical space allocated for interconnections. This nesting approach allows the filter to achieve greater total thickness by utilizing space that would otherwise be occupied by interconnecting structures, thereby improving optical performance without requiring additional space above the standard interconnecting section height.
3Ease of manufacture
If pigmented resin filters are used for color filtering, then the manufacturing process is simple, but the filters are not robust enough and lack sufficient selectivity particularly for infrared radiation
Solution Approach 1:
The filter employs a composite structure combining metallic layers and dielectric materials in a multilayer configuration. This composite material approach provides superior optical performance, robustness, and selectivity compared to pigmented resins, particularly for infrared radiation filtering. The metallic layers offer strong reflection and absorption properties, while the dielectric layers provide precise wavelength selection through interference effects, creating a filter that is both manufacturable and highly effective.
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 optical properties of the filter, improving transmission for desired wavelengths and significantly increasing rejection of unwanted wavelengths, achieving up to 10% increase in transmission and a few percent drop in transmission near 800 nanometers.
Implementation Method 1
optimizing interference by maintaining parallel interfaces
Data Source
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AI summary
A method for implementing a multilayer optical filter within an integrated circuit, comprising a substrate, an interconnection section (ITCI, ITCS), and the optical filter itself, comprising a first filter element (FL1) within the interconnection section above a photosensitive area located in the substrate, and a second filter element (FL2) above the first filter element and the interconnection section. The invention also relates to an integrated circuit comprising an optical filter.