Photodiode Control Electrode for CMOS Image Sensor Dark Current
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Solution Overview
Problem
Conventional CMOS image sensors face challenges in reducing dark current and improving charge transfer efficiency, which affects their performance in capturing images.
Innovation Solution
The introduction of a photodiode control electrode and a control circuit that allows for separate control of the photodiode and transfer transistor gate electrodes, enabling the creation of majority- or minority-carrier concentration regions to impede or facilitate charge transfer, thereby optimizing the potential across the photodiode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional CMOS sensor structure is used, then device complexity is low, but dark current suppression is insufficient
Solution Approach 1:
The gate electrode is segmented into two independent parts: a transfer gate electrode for controlling charge transfer and a photodiode control electrode for controlling carrier distribution in the photodiode. This segmentation allows independent optimization of each function, enabling dark current suppression through the photodiode control electrode without affecting the simplicity of the overall device structure.
Solution Approach 2:
The photodiode control electrode applies localized control to the photodiode region by creating majority-carrier concentration regions near the electrode. This local modification of carrier distribution suppresses dark current generation at the photodiode without requiring changes to the entire device structure, thus improving dark current suppression while maintaining low device complexity.
2Productivity
If conventional charge transfer control is used, then device complexity is low, but charge transfer efficiency is insufficient
Solution Approach 1:
By dividing the gate electrode into transfer gate and photodiode control electrode components, the system enables independent control of charge transfer timing and photodiode carrier distribution. The photodiode control electrode can be activated to enhance carrier availability during transfer, improving charge transfer efficiency without adding complex control circuits.
Solution Approach 2:
The photodiode control electrode performs preliminary action by creating majority-carrier concentration regions in the photodiode before charge transfer occurs. This pre-positioning of carriers ensures efficient transfer when the transfer gate is activated, improving charge transfer efficiency without requiring complex real-time control mechanisms.
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 enhances dark current suppression and charge transfer efficiency, improving the overall performance of CMOS image sensors by controlling carrier distribution and potential across the photodiode.
Implementation Method 1
a photodiode control electrode disposed on the photodiode and configured to control a carrier distribution of the photodiode responsive to a control signal applied thereto
Implementation Method 2
CMOS image sensors are used to transform incident light energy into electrical signals
Data Source
AI summary
A sensor includes a substrate, a floating diffusion node in the substrate, a photodiode in the substrate laterally spaced apart from the floating diffusion region and a transfer transistor coupling the photodiode and the floating diffusion region. The sensor further includes a photodiode control electrode disposed on the photodiode and configured to control a carrier distribution of the photodiode responsive to a control signal applied thereto. The floating diffusion region may have a first conductivity type, the photodiode may include a first semiconductor region of a second conductivity type disposed on a second semiconductor region of the first conductivity type, and the photodiode control electrode may be disposed on the first semiconductor region. The photodiode may be configured to receive incident light from a side of the substrate opposite the photodiode control electrode. The transfer transistor may include a gate electrode on a channel region in the substrate and the photodiode control electrode and the transfer transistor gate electrode may be separately controllable. In further embodiments, the photodiode control electrode comprises an extension of the transfer transistor gate electrode.