Photo-Sensitive Device Charge Transport Layer Dark Current Reduction
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Solution Overview
Problem
Photo-sensitive devices using silicon have limitations in wavelength detection and suffer from high reset noise, defective contact regions leading to high dark current, and low conversion gain, resulting in poor noise characteristics and image quality.
Innovation Solution
A photo-sensitive device with a layer structure comprising an active layer, a charge transport layer, and a gate separated by a dielectric material, where the charge transport layer is configured to control charge transfer between portions, enabling accurate charge generation and read-out, and integrated with a read-out integrated circuit for compact and efficient signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a photodiode area is directly connected to a pixel circuit below the photodiode area, then the device structure is simplified, but defective contact regions generate high dark current
Solution Approach 1:
The patent transitions from a planar direct connection structure to a three-dimensional stacked structure where the charge transport layer is positioned in a second plane separate and parallel to the active layer in the first plane. This vertical stacking arrangement eliminates direct lateral contact between the photodiode area and pixel circuit, preventing defective contact regions from generating dark current while maintaining structural integration.
Solution Approach 2:
The charge transport layer acts as an intermediary between the active layer and the pixel circuit. It transports accumulated charges from the active layer to the pixel circuit through controlled charge transfer, eliminating the need for direct contact between the photodiode area and pixel circuit, thereby preventing dark current generation from defective contacts.
2Measurement precision
If a photodiode capacitance is added to a floating diffusion node for charge-to-voltage conversion, then the conversion process is completed, but conversion gain becomes low resulting in poor noise characteristics
Solution Approach 1:
The patent segments the charge transport path into distinct portions: the active layer in the first plane for charge generation, and the charge transport layer in the second plane for charge accumulation and transfer. This segmentation allows the charge transport layer to be laterally displaced relative to the active layer, enabling controlled charge transfer to the pixel circuit without adding photodiode capacitance to the floating diffusion node, thereby maintaining high conversion gain and good noise characteristics.
3Adaptability or versatility
If silicon is used in light detection, then the device can be formed with standard semiconductor materials, but the wavelengths that may be detected are limited
Solution Approach 1:
The patent employs a composite material structure where the active layer is formed of a material suitable for detecting a broader range of wavelengths (including infrared), while the charge transport layer is formed of a semiconductor material that can be integrated with standard silicon-based pixel circuits. This composite approach enables extended wavelength detection capability while maintaining compatibility with standard semiconductor manufacturing processes.
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
The solution provides good noise characteristics, limits reset noise, reduces dark current, and achieves high conversion gain, enhancing image quality and enabling detection of a broader range of wavelengths, including infrared.
Implementation Method 1
an active layer, being arranged in a first plane, wherein the active layer is configured to generate charges in response to incident light on the active layer
Implementation Method 2
a gate separated by a dielectric material from the charge transport layer, wherein said gate and said charge transport layer are arranged such that the first portion of the charge transport layer is between the gate and the active layer and wherein the gate is configured to control a potential of the first portion of the charge transport layer
Implementation Method 3
a transfer gate, which is arranged to be separated by a dielectric material from a transfer portion of the charge transport layer between the first portion and the second portion, wherein the transfer gate is configured to control transfer of accumulated charges in the first portion to the second portion
Data Source
Figure 1~2B
Figure 3~4
Figure 5A~5B
AI summary
A photo-sensitive device comprises: an active layer (116) configured to generate charges in response to incident light; a charge transport layer (114) arranged below the active layer (116), wherein the charge transport layer (114) comprises a first portion (114a) and a second portion (114b) being laterally displaced in relation to the first portion (114a); a gate (110) separated by a dielectric material (112) from the charge transport layer (114), wherein said gate (110) is arranged below the first portion (114a) and configured to control a potential thereof; and a transfer gate (122), which is separated by a dielectric material (112; 124) from a transfer portion (114b) of the charge transport layer (114) between the first portion (114a) and the second portion (114b), wherein the transfer gate (122) is configured to control transfer of accumulated charges in the first portion (114a) to the second portion (114b) for read-out of detected light.