Variable Pixel Area Array for Hyperspectral S/N Ratio
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Solution Overview
Problem
Hyperspectral cameras with array sensors face challenges in maintaining a consistent signal-to-noise ratio (S/N ratio) due to wavelength-dependent responsivity of the light-receiving layers, leading to variations in charge accumulation and insufficient or oversaturated capacitors, especially when using InGaAs layers with peak responsivity at 1620 nm.
Innovation Solution
The array type light-receiving device is designed with pixels having different areas determined based on their responsivity to specific wavelengths, ensuring that the product of responsivity and pixel area is constant across all pixels, allowing uniform light reception and charge output, thereby improving the S/N ratio by adjusting pixel areas according to their wavelength-dependent sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the light-receiving layer is made of InGaAs with peak responsivity at 1620 nm, then the responsivity at peak wavelength is improved, but the S/N ratio becomes variable across different wavelengths due to wavelength-dependent responsivity
Solution Approach 1:
The patent applies local quality by making each pixel have a different area according to its specific wavelength characteristics. Pixels with lower responsivity at their assigned wavelengths are given larger areas to compensate, while pixels with higher responsivity have smaller areas. This localized adjustment of pixel area based on individual wavelength-dependent responsivity characteristics resolves the contradiction by maintaining consistent S/N ratio across all wavelengths while preserving the high responsivity advantage of InGaAs material.
2Reliability
If the pixel area is increased to improve charge accumulation, then the S/N ratio is improved, but the device area and complexity increase
Solution Approach 1:
The patent changes the parameter of pixel area from a uniform value to a variable value that depends on wavelength. By adjusting the pixel area parameter according to the specific responsivity characteristics at different wavelengths, the system achieves consistent S/N ratio without requiring all pixels to have maximally large areas. This parameter change allows optimal S/N ratio while minimizing the overall device area compared to a uniform large-pixel design.
3Device complexity
If uniform pixel areas are used for all pixels, then the device structure is simplified, but the S/N ratio becomes variable across wavelengths due to wavelength-dependent responsivity
Solution Approach 1:
The patent implements local quality by assigning different areas to pixels based on their specific wavelength characteristics. Instead of uniform pixel areas that would maintain simple device structure but cause variable S/N ratio, the patent locally adjusts each pixel's area to compensate for wavelength-dependent responsivity variations, thereby achieving consistent S/N ratio across all wavelengths while accepting increased structural complexity.
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 ensures that all pixels receive uniform photocurrents even with different wavelengths, reducing variations and enhancing the S/N ratio, resulting in improved wavelength information signals with consistent and large signal quality.
Implementation Method 1
The array sensor has a responsivity having a wavelength dependence related to the semiconductor material constituting a light-receiving layer included in the pixels. When the light-receiving layer in the pixels is made of InGaAs, for example, the array sensor has a peak of responsivity at a wavelength of 1620 nm. Therefore, the photocurrent output from the pixel received a light component having a wavelength of 1620 nm is larger than the photocurrents output from the pixels received light components having wavelengths other than the wavelength of 1620 nm
Data Source
AI summary
An array type light-receiving device includes a plurality of pixels two-dimensionally arranged in a first direction and a second direction perpendicular to the first direction, each of the pixels including a light-receiving layer having a responsivity to a wavelength of light. The pixels arranged in the second direction constitute a plurality of pixel lines extending in the second direction, the plurality of pixel lines being arranged in the first direction to form an array. The pixels in each of the pixel lines have different pixel areas from each other. In addition, the pixel area of each of the pixels included in at least one of the pixel lines is determined in accordance with the responsivity to a wavelength of light received by each of the pixels.