Semiconductor Light-Receiving Element Bridge Electrode Parasitic Capacitance
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Solution Overview
Problem
The existing semiconductor light-receiving elements face an increase in parasitic capacitance due to the deformation of resist overhang portions during metal film deposition, leading to wider bridge electrodes and increased capacitance between the semiconductor layer and the bridge electrode, which hampers the response speed in optical communication systems.
Innovation Solution
The solution involves forming the bridge electrode in a separate layer from the light-receiving and pad electrodes, using a resist with an opening and overhang portion specifically for the bridge electrode, which prevents deformation and maintains the desired width, thereby reducing parasitic capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the bridge electrode is formed using a resist with an overhang portion during vapor deposition, then the metal film can be deposited over level differences, but the overhang portion deforms due to heat and stress causing the bridge electrode to be wider than desired, increasing parasitic capacitance
Solution Approach 1:
The electrode formation process is segmented into two separate operations: first forming the light-receiving portion electrode and pad electrode in one layer, then forming the bridge electrode in a separate subsequent layer. This segmentation allows each electrode to be independently optimized and formed without the deformation issues that occur when using a single resist pattern with overhang portions for all electrodes.
Solution Approach 2:
The bridge electrode is formed in a different layer dimension separate from the light-receiving portion electrode and pad electrode layers. This dimensional separation enables the bridge electrode to be formed with precise width control without being constrained by the resist overhang deformation that affects electrodes formed in the same layer.
2Speed
If the bridge electrode width is reduced to decrease parasitic capacitance, then the response speed improves, but the ease of manufacture decreases due to the complexity of forming narrow electrodes over level differences
Solution Approach 1:
By segmenting the electrode formation into separate operations for the light-receiving portion electrode/pad electrode and the bridge electrode, the process enables precise control of the narrow bridge electrode width without requiring complex single-step resist patterning with overhang portions.
Solution Approach 2:
Forming the bridge electrode in a separate layer dimension allows for precise width control to minimize parasitic capacitance while maintaining manufacturing feasibility, as the separate layer formation avoids the deformations that occur in single-layer formation with overhang portions.
3Device complexity
If the bridge electrode is formed in the same layer as the light-receiving portion electrode and pad electrode, then the manufacturing process is simpler, but the parasitic capacitance increases due to electrode width enlargement from resist deformation
Solution Approach 1:
The electrode system is segmented into two formation operations: the light-receiving portion electrode and pad electrode formed first, then the bridge electrode formed separately in a subsequent layer. This segmentation eliminates the parasitic capacitance issue caused by resist overhang deformation while maintaining reasonable process complexity.
Solution Approach 2:
The bridge electrode is positioned in a separate layer dimension from the light-receiving portion electrode and pad electrode. This dimensional separation prevents the parasitic capacitance generated by resist deformation in single-layer formation, while the added layer complexity is offset by the elimination of subsequent capacitance problems.
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 approach effectively suppresses the generation of parasitic capacitance between the bridge electrode and the semiconductor layer, enhancing the response speed and adaptability of semiconductor light-receiving elements for high-speed optical communication.
Implementation Method 1
forming a metal film by vapor deposition on a top surface of the resist and in the region in which the bridge electrode is to be formed
Data Source
AI summary
A semiconductor light-receiving element includes a substrate; a light-receiving mesa portion, formed on top of the substrate, including a first semiconductor layer of a first conductivity type, an absorption layer, and a second semiconductor layer of a second conductivity type; a light-receiving portion electrode, formed above the light-receiving mesa portion, connected to the first semiconductor layer; a pad electrode formed on top of the substrate; and a bridge electrode, placed so that an insulating gap is interposed between the bridge electrode and the second semiconductor layer, configured to connect the light-receiving portion electrode and the pad electrode on top of the substrate, the bridge electrode being formed in a layer separate from layers of the light-receiving portion electrode and the pad electrode.