Ring-Shaped Gate Conversion Gain Capacitor for Image Sensors
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Solution Overview
Problem
Current image sensing devices face challenges in efficiently adjusting conversion gain to accommodate both low-illuminance and high-illuminance conditions, limiting their performance in various applications.
Innovation Solution
The image sensing device incorporates a pixel array with unit pixel blocks sharing a floating diffusion region and a conversion gain capacitor, which adjusts capacitance based on a conversion gain signal, allowing the device to switch between low and high gain modes by using a ring-shaped gate MOS capacitor to surround the source/drain region, thereby enhancing its illuminance characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional conversion gain capacitor is used, then the device can adjust conversion gain, but the capacitor size increases when switching between low-illuminance and high-illuminance modes
Solution Approach 1:
The gate electrode is configured in a ring shape that surrounds the source/drain region, with the source/drain region nested within the gate structure. This nested arrangement allows the conversion gain capacitor to achieve higher capacitance values without increasing the overall footprint area, as the gate wraps around the source/drain region rather than extending linearly. The ring-shaped gate effectively utilizes vertical and radial space to maximize capacitance density.
Solution Approach 2:
The conversion gain capacitor transitions from a conventional planar structure to a three-dimensional ring-shaped structure. By configuring the gate electrode to surround the source/drain region in a ring shape, the capacitor utilizes vertical stacking and radial extension to increase capacitance without occupying additional horizontal area. This dimensional transformation allows the capacitor to provide both low-illuminance and high-illuminance characteristics within the same footprint.
2Area of stationary object
If the conversion gain capacitor size is reduced, then the device area decreases, but the ability to switch between low and high gain modes is compromised
Solution Approach 1:
The ring-shaped gate structure nests the source/drain region within its circumference, creating a compact conversion gain capacitor that maintains sufficient capacitance value for both low-gain and high-gain modes. This nested configuration allows the capacitor to achieve the required capacitance range for gain switching without increasing the overall device area, as the gate electrode efficiently utilizes the space around the source/drain region.
Solution Approach 2:
The conversion gain capacitor enables switching between different gain modes by changing the capacitance parameter through the ring-shaped gate structure. The gate electrode, configured to surround the source/drain region, can modulate the capacitance value to provide both low-illuminance and high-illuminance characteristics, allowing the device to adapt its gain parameter without requiring a larger physical structure.
3Reliability
If a ring-shaped gate MOS capacitor is used, then capacitance efficiency increases, but the manufacturing complexity increases
Solution Approach 1:
The ring-shaped gate structure with the source/drain region nested within provides high capacitance efficiency by maximizing the electric field interaction between the gate and source/drain regions. Despite the unconventional shape, the structure can be fabricated using standard semiconductor manufacturing processes, as the ring shape can be formed through conventional photolithography and etching techniques that define patterns on the substrate.
Solution Approach 2:
The ring-shaped gate MOS capacitor achieves superior capacitance efficiency by changing the geometric parameters of the capacitor structure. The gate electrode surrounds the source/drain region in a ring configuration, increasing the effective capacitance area without proportionally increasing manufacturing steps. This parameter change in geometry can be integrated into existing fabrication workflows with minimal additional complexity.
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 design enables the image sensing device to effectively switch between low-illuminance and high-illuminance modes, improving its performance across different lighting conditions without increasing the size of the conversion gain capacitor.
Implementation Method 1
at least one photoelectric conversion element configured to generate photocharges by converting incident light
Implementation Method 2
a gate structured to surround the source/drain region and coupled to the floating diffusion region to change a gain of the floating diffusion region in response to a change in the conversion gain signal
Data Source
AI summary
An image sensing device includes a pixel array including a plurality of unit pixel blocks each including a plurality of unit image sensing pixels arranged in the pixel array and structured to convert light into photocharges. Each of the unit pixel blocks includes a first sub-pixel block including a first floating diffusion region structured to hold the photocharges and a plurality of unit image sensing pixels sharing the first floating diffusion region, and a conversion gain capacitor arranged adjacent to one side of the first sub-pixel block. The conversion gain capacitor includes an impurity region coupled to an input node that receives a conversion gain signal, and a gate structured to surround the impurity region and coupled to the first floating diffusion region to change a gain of the first floating diffusion region in response to a change in the conversion gain signal.