Optical Waveguide Insulating Film Refractive Index Gradient
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Solution Overview
Problem
Semiconductor devices with optical waveguides face reliability issues due to leaked light causing noise from metal wiring and heater metal wires, which affects signal integrity and chip area efficiency.
Innovation Solution
The solution involves forming an optical waveguide with a refractive index n1 and a second insulating film with refractive index n2 over a first insulating film, with a third insulating film having a refractive index n3, where n1 > n2 and n3 > n2, and the shortest distance between the waveguide and the third insulating film is smaller than the first insulating film's thickness, using silicon nitride or silicon oxynitride to suppress return light and improve signal reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If metal wiring and heater metal wires are placed close to the optical waveguide to reduce chip area, then chip size is reduced, but noise from return light increases and signal reliability deteriorates
Solution Approach 1:
A third insulating film with refractive index n3 (where n3 > n2) is introduced between the second insulating film and the metal wiring/heater metal wire. This intermediary layer suppresses the generation of return light by creating a refractive index gradient that prevents light reflection back into the optical waveguide, thereby reducing noise while allowing close placement of wiring for compact chip design
Solution Approach 2:
The refractive index parameter is strategically manipulated by selecting materials for the third insulating film with n3 > n2 (higher than the second insulating film). This parameter change creates an optimal refractive index profile (n1 > n2 and n3 > n2) that suppresses return light generation, enabling close wiring placement without compromising signal reliability
2Reliability
If metal wiring is placed farther from the optical waveguide to reduce noise, then signal reliability is improved, but chip area increases and wiring efficiency decreases
Solution Approach 1:
The third insulating film acts as a mediator that enables close wiring placement by suppressing return light generation through its specific refractive index property (n3 > n2). This eliminates the need for large spacing between wiring and optical waveguide, maintaining compact chip area while ensuring signal reliability
3Area of stationary object
If the shortest distance between the optical waveguide and the third insulating film is made smaller than the first insulating film thickness to improve wiring efficiency, then chip area is reduced, but manufacturing precision requirements increase
Solution Approach 1:
By changing the refractive index parameter of the third insulating film to be higher than the second insulating film (n3 > n2), the design achieves return light suppression with a compact structure where the shortest distance from the optical waveguide to the third insulating film can be smaller than the first insulating film thickness, optimizing chip area while maintaining manufacturability
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 effectively reduces noise from return light, enhances signal reliability, and allows for more efficient wiring arrangements, reducing chip size and parasitic resistance while maintaining control over the refractive index of the optical waveguide.
Implementation Method 1
the refractive indices n1, n2, and n3 satisfy the relationship of n1>n2 and n3>n2
Data Source
AI summary
Two optical waveguides and an insulating film provided to cover the optical waveguides are formed over an insulating layer. Two wirings and a heater metal wire are formed over the insulating film via an insulating film different from the above insulating film. The latter insulating film is thinner than the former insulating film, and has a higher refractive index than the former insulating film. The leaked light from either of the two optical waveguides can be suppressed or prevented from being reflected by any one of the two wirings, the heater metal wire, and the like to travel again toward the two optical waveguides by utilizing the difference between the refractive indices of the two insulating films.