Optical Proximity Sensor Sidewall Coating for Stray Light Blocking
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Solution Overview
Problem
Conventional proximity sensors in electronic devices often require a separate glass layer that increases their thickness, and stray reflections from sidewalls can degrade the signal-to-noise ratio of the sensor readings.
Innovation Solution
The solution involves forming a bandpass filter coating directly on the semiconductor die and covering the sidewalls with an opaque coating, eliminating the need for a separate glass layer and preventing stray light from entering through the sidewalls, thereby optimizing the signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separate glass layer is used in conventional proximity sensors, then the sensor structure is protected and optical transmission is enabled, but the overall thickness of the sensor increases
Solution Approach 1:
The patent merges the glass layer functionality directly into the semiconductor die structure by forming optical transmission layers and protective coatings as integral parts of the die itself, eliminating the need for a separate external glass layer while maintaining both protection and optical transmission functions
Solution Approach 2:
The patent embeds the optical transmission and protective functions within the internal structure of the semiconductor die, nesting these functional layers within the die itself rather than placing them as external separate components
2Ease of manufacture
If sidewalls are left exposed in the semiconductor die, then manufacturing is simpler, but stray reflections from sidewalls degrade the signal-to-noise ratio
Solution Approach 1:
The patent applies different surface properties to different regions of the semiconductor die - the sidewalls are coated with opaque or light-absorbing material to prevent stray reflections, while the top surface maintains optical transmission properties for the proximity sensor function
Solution Approach 2:
The patent converts the potentially harmful stray reflections from exposed sidewalls into beneficial controlled reflections by using reflective coatings on the sidewalls, transforming the harmful effect into a controlled optical management mechanism that improves signal-to-noise ratio
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 reduces the overall thickness of the proximity sensor and enhances the signal-to-noise ratio by blocking unwanted light, resulting in improved sensor performance.
Implementation Method 1
An opaque coating can be formed on the sidewall of the semiconductor die. The opaque coating can be a reflective coating or an absorptive coating such as black ink.
Implementation Method 2
An infrared bandpass filter coating can be formed directly on the semiconductor die.
Implementation Method 3
the light source emits light. In the presence of nearby objects, some of the emitted light is reflected back towards the proximity sensor and is detected by the light detector.
Data Source
AI summary
An electronic device may include a proximity sensor for detecting whether an external object is in the vicinity of the device. The proximity sensor may be implemented as an optical sensor module having a substrate, a light emitter die mounted on the substrate, a light detector die mounted on the substrate, and a package enclosure housing the light emitter and detector dies within the module. A infrared bandpass filter layer may be formed directly on the light detector die. The light detector die may have sidewalls at least partially covered by an opaque coating. The light detector die may include a highly doped backside reflection absorption layer interposed between an intrinsic absorption layer and an n-type layer within the light detector die. Opaque adhesive material may be used to mount the light detector die onto the surface of the substrate.