Transfer Transistor Gate Electrode Extension for CMOS Image Sensors
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Solution Overview
Problem
In solid-state imaging devices, particularly CMOS image sensors, the 'top surface irradiation type' faces challenges with light sensitivity due to circuit elements and wiring shielding or reflecting light, while the 'bottom surface irradiation type' risks photodiode damage during manufacturing and increases manufacturing steps and costs, hindering image quality improvement.
Innovation Solution
A solid-state imaging device with photoelectric conversion units and pixel transistors on opposite surfaces of a semiconductor substrate, where the transfer transistor's gate electrode extends with a gate insulating film from the channel area to the photoelectric conversion unit, using polysilicon with specific impurity types and concentrations to enhance signal transfer and reduce manufacturing complexities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a control electrode is provided to improve sensitivity and suppress dark current in bottom surface irradiation type devices, then image quality improves, but the manufacturing process becomes more complex and costly
Solution Approach 1:
The patent extracts the control function from a separate control electrode and integrates it into the pixel transistor gate electrode structure. The gate electrode of the pixel transistor serves dual purposes: controlling the pixel transistor operation and controlling the photodiode potential, thereby eliminating the need for a separate control electrode and reducing manufacturing complexity
Solution Approach 2:
The pixel transistor gate electrode is designed to perform multiple functions: it controls the pixel transistor's source and drain regions and simultaneously controls the potential of the photodiode. This multi-functionality reduces the total number of electrodes needed and simplifies the manufacturing process while maintaining image quality
2Reliability
If a control electrode is provided to improve sensitivity, then dark current suppression improves, but the section between control electrode and transfer electrode becomes narrow, increasing manufacturing steps
Solution Approach 1:
The patent removes the separate control electrode structure and integrates its functionality into the pixel transistor gate electrode, thereby eliminating the narrow section problem and reducing the number of manufacturing steps required for electrode formation and alignment
Solution Approach 2:
The control function and the pixel transistor gate function are merged into a single electrode structure. This combination eliminates the need for separate electrode formation processes and reduces alignment complexity, making the manufacturing process easier while maintaining dark current suppression capability
3Ease of manufacture
If top surface irradiation type is used, then circuit elements and wiring are accessible, but light sensitivity deteriorates due to shielding and reflection
Solution Approach 1:
The patent inverts the conventional top surface irradiation approach by using bottom surface irradiation. Light enters through the bottom surface where there are no circuit elements or wiring to cause shielding or reflection, thereby improving light sensitivity while maintaining circuit element accessibility through the top surface
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 improves image quality by reducing dark current and white spots, simplifying the manufacturing process, and enhancing transfer efficiency without increasing costs, thereby improving captured image quality.
Implementation Method 1
A photoelectric conversion unit is, for example, a photodiode, and receives light that enters through an externally provided optical system on the light-receiving surface thereof and photoelectrically converts the light, thereby generating signal charge
Data Source
AI summary
A solid-state imaging device includes a plurality of photoelectric conversion units configured to receive light and generate signal charge, the plurality of photoelectric conversion units being provided in such a manner as to correspond to a plurality of pixels in a pixel area of a semiconductor substrate; and pixel transistors configured to output the signal charge generated by the photoelectric conversion units as electrical signals. Each of the pixel transistors includes at least a transfer transistor that transfers the signal charge generated in the photoelectric conversion unit to a floating diffusion corresponding to a drain. A gate electrode of the transfer transistor is formed in such a manner as to extend with a gate insulating film in between from a channel formed area to a portion where the photoelectric conversion unit has been formed on the surface of the semiconductor substrate.