Light Receiving Element with Reflection Suppressing Structure
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Solution Overview
Problem
CAPD sensors of the surface irradiation type face limitations in securing a sufficient photoelectric conversion region due to the necessity of wiring and control lines on the light receiving surface, which reduces pixel sensitivity and aperture ratio.
Innovation Solution
A light receiving element with an on-chip lens, a wiring layer, and a semiconductor layer that includes voltage applying units and charge detection units, featuring a reflection suppressing structure in the wiring layer to minimize light reflection and enhance charge detection efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If wiring and control lines are disposed on the light receiving surface side of the PD, then charge extraction and control functions are enabled, but the photoelectric conversion region is limited and pixel sensitivity is reduced
Solution Approach 1:
The patent transitions from a surface-irradiation type structure to a transmission type structure, changing the dimension of light incidence from surface to through-substrate. This allows wiring to be disposed on the rear surface while light enters from the front surface, resolving the conflict between wiring placement and photoelectric conversion region.
Solution Approach 2:
The patent inverts the conventional structure by placing wiring and control lines on the rear surface opposite to the light receiving surface. Instead of having wiring on the light receiving side, the wiring is now on the opposite side, allowing light to pass through the semiconductor layer without being blocked by wiring.
2Ease of operation
If wiring is disposed on the light receiving surface, then charge extraction is enabled, but aperture ratio is reduced
Solution Approach 1:
The patent changes the spatial arrangement by moving wiring from the front surface to the rear surface, allowing the front surface to be fully dedicated to light reception. This dimensional reorganization maximizes the aperture ratio while maintaining charge extraction functionality through the rear-surface wiring.
3Measurement precision
If a reflection suppressing structure is added to reduce light reflection, then charge detection accuracy is improved, but device complexity increases
Solution Approach 1:
The patent converts the harmful effect of light reflection at the semiconductor-substrate interface into a beneficial effect by introducing a reflection suppressing structure. The reflection that would otherwise cause charge detection errors is now suppressed, improving measurement precision. The structure uses a simple refractive index mismatch approach rather than complex multi-layer coatings.
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
Improves pixel sensitivity and distance measurement characteristics by maximizing quantum efficiency and aperture ratio, while reducing charge detection errors and enhancing high-speed driving capabilities.
Implementation Method 1
a sensor that is able to distribute a signal charge obtained by receiving light due to reflection of active light radiated
Implementation Method 2
a reflection suppressing structure that suppresses reflection of light in a plane region corresponding to the first charge detection unit and the second charge detection unit
Data Source
AI summary
There is provided a light receiving element including; an on-chip lens; a wiring layer; and a semiconductor layer disposed between the on-chip lens and the wiring layer. The semiconductor layer includes a first voltage applying unit to which a first voltage is applied, a second voltage applying unit to which a second voltage different from the first voltage is applied, a first charge detection unit disposed in a vicinity of the first voltage applying unit, and a second charge detection unit disposed in a vicinity of the second voltage applying unit, and the wiring layer includes a reflection suppressing structure that suppresses reflection of light in a plane region corresponding to the first charge detection unit and the second charge detection unit.