Photodiode Window Stack for Better Blue Light Response
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Solution Overview
Problem
The detection of blue light in photodiodes within light sensors is challenging due to its short wavelength and increased reflectivity, making it difficult to detect, especially when photodiodes are placed behind other components in integrated circuits.
Innovation Solution
The method involves forming a photodiode structure with a reduced thickness oxide window and a nitride layer, where the oxide window and nitride layer directly contact each other, reducing the overall thickness to improve blue light response, and using existing masks to minimize additional costs and prevent photoresist pollution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple layers are present between the photodiode and substrate, then structural integrity and component protection are improved, but blue light detection capability deteriorates due to increased reflectivity and absorption
Solution Approach 1:
The patent changes the optical parameters of the layers by reducing their thickness to specific ranges (oxide window: 50-200 nm, nitride layer: 100-300 nm) to optimize blue light transmission while preserving structural integrity. This parameter optimization resolves the contradiction between protection and detection capability.
Solution Approach 2:
The patent converts the harmful effect of layer reflectivity into a beneficial anti-reflective effect by carefully controlling layer thicknesses to create optical interference that reduces overall reflectivity. The layers that originally caused reflection are transformed into an anti-reflective structure through precise thickness control.
2Area of stationary object
If photodiodes are placed behind other components to save space, then device integration density is improved, but light signal detection deteriorates due to increased path length through interfering layers
Solution Approach 1:
The patent changes the thickness parameters of the oxide and nitride layers to minimize optical absorption and maximize transmission in the blue light range (450-485 nm). This allows photodiodes positioned behind components to still receive sufficient light signal intensity.
Solution Approach 2:
The oxide window and nitride layer act as optical intermediaries that facilitate light transmission from the incident surface through to the photodiode. By optimizing their thickness, they serve as effective mediators that enable space-efficient positioning while maintaining detection capability.
3Productivity
If layer thickness is reduced to improve blue light transmission, then light detection efficiency is improved, but layer fabrication precision requirements increase
Solution Approach 1:
The patent identifies specific thickness ranges (oxide: 50-200 nm, nitride: 100-300 nm) that optimize blue light transmission while being manufacturable with standard precision capabilities. These parameter specifications balance detection efficiency with fabrication feasibility.
Solution Approach 2:
Rather than reducing thickness to extreme minimal values, the patent uses moderate thickness reductions within practical manufacturing ranges. This partial action approach achieves significant improvement in light transmission without demanding excessive fabrication precision that would be difficult to maintain consistently.
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 enhances the detection of blue light by allowing more light to pass through, improving the photodiode's spectrum response and enabling a reduction in the total area required for each photodiode while maintaining performance, without incurring additional mask costs.
Implementation Method 1
A method involves the formation of an oxide window and a nitride layer with controlled thickness to enhance the light response, particularly for blue light, by reducing the number of layers between the photodiode and the substrate
Implementation Method 2
blue light (about 450 nm to about 485 nm wavelength) is made up of short wavelengths, and thus is more difficult to detect due to reflectivity
Implementation Method 3
the photodiode(s) of a light sensor are placed behind other components
Data Source
AI summary
A photodiode with improved response, particular in the blue light portion of the spectrum, is disclosed. An oxide window is formed adjacent a silicide junction. An etch stop layer is applied over the silicide junction, and the oxide window is then etched to form a thin film. A nitride layer is then applied. The resulting photodiode has increased transmission of blue light.