Optical Waveguide Electrode Layers for Low-Loss High-Frequency Modulation
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Solution Overview
Problem
Existing optical waveguide devices face issues with increased conductor loss due to high surface roughness of electrodes, which deteriorate high-frequency characteristics, and difficulty in forming resin patterns and securing sufficient bonding connections due to the surface roughness of electrodes.
Innovation Solution
The optical waveguide device features a signal and ground electrode formed with multiple tiers of electrode layers, where at least two layers have different surface roughness, with the narrowest part between the electrodes having lower surface roughness than other layers, and specific surface roughness ranges are defined for different parts of the electrodes to minimize conductor loss and ensure strong bonding connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of the electrode layer is increased above several μm using the plating method, then the electrode can provide sufficient conductivity and structural integrity, but the surface roughness of the electrode layer is increased compared to other methods
Solution Approach 1:
The electrode is divided into multiple layers with different thicknesses and surface roughness characteristics. The lower layer has greater thickness for conductivity, while the upper layer has smaller thickness for smooth surface, resolving the contradiction between structural integrity and surface precision.
Solution Approach 2:
Different parts of the electrode structure have different surface roughness properties. The lower layer near the substrate has higher roughness for bonding, while the upper layer has lower roughness for signal transmission, addressing both conductivity requirements and surface precision requirements in different locations.
2Strength
If the surface roughness of the electrode layer is increased to secure sufficient bonding connection strength for wire bonding or flip-chip bonding, then bonding strength is improved, but conductor loss is increased during propagation of the modulation signal
Solution Approach 1:
The electrode is segmented into multiple functional layers: the lower layer provides rough surface for strong bonding, while the upper layer provides smooth surface for low conductor loss during signal propagation, thus resolving the contradiction between bonding strength and energy loss.
Solution Approach 2:
Different surface roughness properties are assigned to different layers of the electrode structure. The lower layer has high surface roughness optimized for bonding strength, while the upper layer has low surface roughness optimized for minimizing conductor loss in the signal transmission region.
3Reliability
If a photosensitive resin is used to cover the optical waveguide and a electrode layer protrudes to the side closer to the optical waveguide, then the resin layer can provide protection and insulation, but air bubbles enter the boundary surface between the resin and electrode due to high surface roughness of the electrode layer
Solution Approach 1:
The electrode structure is segmented into multiple layers where the upper layer provides a smooth surface that prevents air bubble entrapment during resin coating, while the lower layer maintains the necessary structural properties, thus enabling both protection/insulation and precise pattern formation.
Solution Approach 2:
The electrode layers are designed with different surface roughness characteristics at different locations and depths. The upper surface has low roughness for good resin adhesion and bubble-free pattern formation, while deeper layers have appropriate roughness for bonding, resolving the contradiction between protection function and manufacturing precision.
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 reduces conductor loss, prevents air bubbles in resin layers, and enhances bonding strength, thereby improving high-frequency characteristics and enabling effective pattern formation and connection with feeding lines.
Implementation Method 1
an optical waveguide is formed on a substrate of lithium niobate (LN) or the like having an electro-optic effect, and an electrode that applies an electric field to the optical waveguide is formed on the substrate
Data Source
AI summary
An object of the present invention is to provide an optical waveguide device that has an excellent high-frequency characteristic and that is also favorable for forming a pattern of a resin layer covering an optical waveguide and bonding a feeding line to an electrode. An optical waveguide device of the present invention includes an optical waveguide (10) formed on a substrate (1), and a signal electrode(S) and a ground electrode (G) disposed on the substrate (1), in which each electrode of the signal electrode(S) and the ground electrode (G) is formed with a plurality of tiers of electrode layers (30, 31) excluding an underlayer, and at least two electrode layers among the plurality of tiers of electrode layers have different surface roughness.