Optical Encoder Dummy Light Receiving Device Side Light Noise
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Solution Overview
Problem
Existing reflective type optical encoders face manufacturing cost increases and noise issues due to side light interference, which is not effectively blocked by conventional light blocking members.
Innovation Solution
An optical module with a sensor substrate featuring a dummy light receiving device made of the same conductive type impurity diffusion layer as the light receiving devices, positioned deeper around the through-hole to absorb side light, eliminating the need for additional manufacturing processes and enhancing light blocking without reflective interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a light blocking member is provided on the side wall of the through-hole using a thin metal film, then side light blocking is improved, but manufacturing cost increases due to additional manufacturing processes
Solution Approach 1:
The dummy light receiving device is integrated into the sensor substrate using the same impurity diffusion process as the light receiving devices, merging the light blocking function with the existing semiconductor manufacturing process. This eliminates the need for separate light blocking member fabrication and reduces manufacturing steps while effectively absorbing side light.
Solution Approach 2:
The mechanical/light blocking approach using thin metal films is replaced with a semiconductor-based impurity diffusion layer that absorbs side light through its material properties. This substitution uses the inherent light-absorbing characteristics of the doped semiconductor region rather than relying on physical blocking by metal layers.
2Object-affected harmful factors
If a light blocking member is provided on the side wall of the through-hole, then side light blocking is improved, but device complexity increases
Solution Approach 1:
The light blocking function is merged with the light receiving device structure by forming the dummy light receiving device as an integral part of the sensor substrate. This integration reduces the number of discrete components and simplifies the overall device structure while maintaining effective side light blocking.
Solution Approach 2:
The dummy light receiving device serves multiple functions: it blocks side light from entering the active sensing region, absorbs stray light to reduce noise, and is fabricated using the same process as the light receiving devices. This multi-functionality reduces the need for separate dedicated light blocking structures.
3Object-affected harmful factors
If the light receiving device is made deeper to block side light, then side light blocking is improved, but manufacturing precision requirements increase
Solution Approach 1:
The dummy light receiving device is positioned at a specific depth location around the through-hole where it can effectively intercept side light without requiring excessive depth. The local placement strategy allows side light blocking at a controlled depth that is achievable with standard manufacturing tolerances.
Solution Approach 2:
The dummy light receiving device uses the same impurity diffusion layer structure and fabrication process as the light receiving devices, copying the proven manufacturing methodology. This ensures consistent depth control and manufacturing precision without requiring new deep etching or doping processes.
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 noise current generation by effectively blocking side light, simplifies manufacturing, and improves signal-to-noise ratio while maintaining the same manufacturing process for light receiving devices.
Implementation Method 1
A dummy light receiving device is formed between the light receiving device and the through-hole, around the through-hole, and in the sensor substrate... effectively blocking side light... reduces noise current generation
Implementation Method 2
Light sources such as LEDs emit light not only from the top surface but also from the side surface
Data Source
AI summary
An optical module includes a fixed substrate, and a sensor substrate secured to the fixed substrate and having a through-hole formed therein. A light emitting device is secured to the fixed substrate at a position in the through-hole. A light receiving device is provided in the sensor substrate. A dummy light receiving device is formed between the light receiving device and the through-hole, around the through-hole, and in the sensor substrate. The light receiving device and the dummy light receiving device are made of an impurity diffusion layer having a same conductive type as a conductive type of a surface layer of the sensor substrate. The dummy light receiving device is deeper than the light receiving device.