CCD Transfer Electrode Segmentation for Capacitance Noise Reduction
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Solution Overview
Problem
Conventional CCD image sensors experience inefficiencies in charge transfer due to increased capacitance and noise caused by overlapping transfer electrodes outside the channel region, leading to reduced charge handling capacity and signal quality.
Innovation Solution
The CCD design limits the overlap of adjacent transfer electrodes outside the channel region, reducing capacity coupling and maintaining channel electric potential stability by selectively forming overlap portions within the channel width direction, thereby minimizing noise and enhancing transfer efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If transfer electrodes are extended outside the channel region to cover the entire channel length, then charge transfer coverage is improved, but capacitance between adjacent electrodes increases causing noise and potential instability
Solution Approach 1:
The transfer electrode is segmented into a first transfer electrode portion within the channel region and a second transfer electrode portion outside the channel region. This segmentation allows the electrode to fulfill its charge transfer function while reducing unwanted capacitance coupling with adjacent electrodes in the extended region.
Solution Approach 2:
Different portions of the transfer electrode are designed with different characteristics: the first portion within the channel region maintains full overlap for effective charge transfer, while the second portion outside the channel region is configured to minimize capacitance coupling. This local differentiation resolves the contradiction between transfer efficiency and noise reduction.
2Productivity
If adjacent transfer electrodes overlap extensively to improve charge transfer efficiency, then charge transfer efficiency is improved, but channel electric potential stability deteriorates due to potential drag
Solution Approach 1:
The transfer electrode is divided into functional segments: the first portion within the channel region provides necessary overlap for efficient charge transfer, while the second portion outside the channel region is minimized to reduce capacitive coupling that causes potential drag and instability.
Solution Approach 2:
Overlap between adjacent transfer electrodes is maintained in the channel region for efficiency but reduced outside the channel region for stability. This local quality differentiation allows the system to achieve both high transfer efficiency and potential stability.
3Quantity of substance
If transfer electrodes are made longer to increase charge handling capacity, then charge handling capacity is improved, but noise increases due to extended overlap regions
Solution Approach 1:
The transfer electrode is segmented into a functional first portion within the channel region that handles charge transfer, and a minimized second portion outside the channel region. This segmentation maintains charge handling capacity while minimizing the noise-generating overlap region.
Solution Approach 2:
The electrode structure implements local quality differentiation where the channel region portion provides necessary length for charge handling, while the extended portion outside the channel is minimized to reduce noise, achieving both high capacity and low noise.
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 reduces noise and maintains charge handling capacity by limiting capacitance between electrodes, improving the overall efficiency of charge transfer and signal quality in CCD image sensors.
Implementation Method 1
CCD comprises a channel region (charge transfer channel region) formed on a surface of a semiconductor substrate, and a plurality of transfer electrodes arranged in the channel region along a direction of charge transfer. Adjacent transfer electrodes are formed by using, for example, two layers of polysilicon to enable boundaries thereof to overlap each other whereby a fringe electric field is preferably generated below the boundaries of the transfer electrodes
Implementation Method 2
Adjacent transfer electrodes are formed by using, for example, two layers of polysilicon to enable boundaries thereof to overlap each other whereby a fringe electric field is preferably generated below the boundaries of the transfer electrodes and an improvement in charge transfer efficiency is achieved
Data Source
AI summary
When capacity coupling between an output gate electrode (OG) and a last-stage transfer electrode is large at an output end of a CCD shift register, an electric potential of the OG is varied according to transfer clocks with the result that noise is liable to generate in an output signal. As measures for this, convex portions projecting horizontally are formed in those positions of the last-stage transfer electrode and the OG, which correspond to a channel region, and overlap between the electrodes is caused only on the convex portions. A clearance is formed between the OG and the transfer electrode except those locations, in which the convex portions are provided. In that location, in which the OG and the transfer electrode, respectively, are extended relatively lengthily toward wirings, the electrodes do not overlap each other. In this manner, capacity coupling between the electrodes is reduced.