Multi-Mesa Optical Subassembly Layout for Stable SMSR Yield
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Solution Overview
Problem
The integration of multiple light emitting devices in optical semiconductor devices leads to increased manufacturing costs and reduced yield due to side mode suppression ratio (SMSR) failures, which are inherent when diffraction gratings extend to the back end surface and are coated with reflective films, causing phase control difficulties.
Innovation Solution
The optical semiconductor device features a semiconductor substrate with mesa stripes having diffraction gratings extending to the back end surface, a reflective film with 30% or more reflectivity, and a center-to-center distance of 150 μm or less between mesa stripes, allowing at least two mesa stripes to be driven simultaneously, thereby reducing phase differences and enhancing yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If multiple light emitting devices are integrated on one semiconductor substrate, then manufacturing cost is reduced, but yield is reduced due to SMSR failures
Solution Approach 1:
The semiconductor substrate is divided into multiple mesa stripes, each containing a light emitting device. This segmentation allows independent control and optimization of each device while maintaining cost benefits of integration. The diffraction grating is also segmented to extend only to specific positions rather than the back end surface, reducing SMSR failures.
Solution Approach 2:
The diffraction grating is designed with non-uniform extension, reaching the back end surface only in specific mesa stripes (first and second light emitting devices) but not in others (third and fourth light emitting devices). This local quality differentiation reduces SMSR failures in devices where the grating does not extend to the back surface, thereby improving overall yield while maintaining cost efficiency.
2Reliability
If center-to-center distance between mesa stripes is reduced, then phase difference is reduced and yield is improved, but manufacturing precision requirements increase
Solution Approach 1:
The center-to-center distance between adjacent mesa stripes is specifically set to 150 μm or less, which is a critical parameter change that reduces phase differences between adjacent light emitting devices. This parameter optimization improves yield by minimizing interference effects, while the relatively large absolute distance (150 μm) maintains reasonable manufacturing precision requirements.
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 stabilizes the side mode suppression ratio, increases the yield of the optical semiconductor device, and reduces the likelihood of SMSR failures, making the device more cost-effective by minimizing defects.
Implementation Method 1
each of which includes an active layer and a diffraction grating, the diffraction grating extending up to a back end surface of each of the plurality of mesa stripes
Implementation Method 2
a reflective film provided at back end surfaces of the plurality of mesa stripes and having a reflectivity of 30% or more
Data Source
AI summary
An optical semiconductor device includes a semiconductor substrate; a plurality of mesa stripes, which are arranged side by side on the semiconductor substrate, and each of which includes an active layer and a diffraction grating, the diffraction grating extending up to a back end surface of each of the plurality of mesa stripes; a plurality of electrodes, each of which is electrically connected to an upper surface of a corresponding one of the plurality of mesa stripes, having a pad portion for wire bonding; a plurality of waveguides, each of which is optically connected to the active layer of a corresponding one of the plurality of mesa stripes; and a reflective film provided at back end surfaces of the plurality of mesa stripes, and wherein at least two mesa stripes, of the plurality of mesa stripes, are configured to be driven at the same time.