Tungsten Reflective Layer for Back-Illuminated Imaging Sensors
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Solution Overview
Problem
Back-illuminated solid-state imaging devices face challenges in efficiently converting long-wavelength light into electrical signals and effectively shielding long-wavelength light, leading to reduced sensitivity and crosstalk issues due to insufficient reflection and leakage.
Innovation Solution
A reflective layer composed of a single tungsten layer or a tungsten laminate is placed on the second surface of the semiconductor layer opposite to the light-entering surface, reflecting transmitted long-wavelength light back to the photoelectric conversion section, thereby increasing light reception and preventing crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a polysilicon layer and aluminum layer are arranged on photodiodes for light reflection, then light reflection is provided, but long-wavelength light components are insufficiently shielded and light leaks from grain boundaries reducing reflectance
Solution Approach 1:
The patent changes the material parameter of the reflective layer from conventional polysilicon/aluminum to tungsten, which has different optical properties with higher density and better long-wavelength light reflection capability. This material substitution resolves the contradiction by providing both ease of manufacture and improved long-wavelength light shielding.
Solution Approach 2:
The patent employs a composite structure with multiple layers including tungsten reflective layer, polysilicon layer, and aluminum layer. This composite material approach combines the advantages of different materials to achieve both manufacturing ease and superior long-wavelength light reflection while preventing light leakage through grain boundaries.
2Measurement precision
If the silicon layer thickness is reduced to several micrometers or less, then short-wavelength light absorption is improved, but long-wavelength light is transmitted to the signal circuit section causing crosstalk
Solution Approach 1:
The patent converts the harmful transmitted long-wavelength light into a beneficial resource by using the tungsten reflective layer to reflect it back to the photodiode. This allows the thin silicon layer to maintain good short-wavelength light absorption while the reflected long-wavelength light is reused, preventing crosstalk and improving overall light utilization efficiency.
Solution Approach 2:
The reflective layer creates a feedback mechanism where long-wavelength light transmitted through the photodiode is reflected back to the same photodiode. This feedback loop ensures that long-wavelength light does not cause crosstalk in neighboring pixels but instead contributes to the signal generation in the original photodiode.
3Device complexity
If light is transmitted through the photodiode to the signal circuit section, then the structure is simple, but sensitivity to long-wavelength light is reduced and crosstalk occurs
Solution Approach 1:
The patent adds a new dimension to the device structure by introducing a reflective layer on the back surface of the substrate. This dimensional addition allows the system to maintain structural simplicity while effectively addressing long-wavelength light reflection and crosstalk prevention, achieving both simplicity and high performance.
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 sensitivity of the photoelectric conversion section to long-wavelength light, improves light absorption, and reduces crosstalk by reflecting long-wavelength light back to the intended pixels, resulting in improved dynamic range and image quality.
Implementation Method 1
The reflective layer reflects light transmitted through the photoelectric conversion section back thereto
Implementation Method 2
photodiodes 221 are arranged, and a signal circuit section 231. Light is incident on a first surface of the silicon substrate 211
Data Source
AI summary
A solid-state imaging device includes the following elements. A photoelectric conversion section is arranged in a semiconductor layer having a first surface through which light enters the photoelectric conversion section. A signal circuit section is arranged in a second surface of the semiconductor layer opposite to the first surface. The signal circuit section processes signal charge obtained by photoelectric conversion by the photoelectric conversion section. A reflective layer is arranged on the second surface of the semiconductor layer opposite to the first surface. The reflective layer reflects light transmitted through the photoelectric conversion section back thereto. The reflective layer is composed of a single tungsten layer or a laminate containing a tungsten layer.