Tapered Transfer Gate Pixel Unit for Imaging Devices
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Related-art solid-state imaging devices have a structure with an extended transfer gate that reduces the PD region size, leading to insufficient light input and uneven electric potential, resulting in degraded transfer characteristics.
Innovation Solution
A pixel unit with a transfer transistor having a first gate portion and a second gate portion of different widths, where the second gate portion tapers from a wider to a narrower width, ensuring a constant distance between the photodiode and the floating diffusion region, improving the transfer electric field and characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an extended transfer gate is used to improve transfer characteristics, then the transfer gate can reach the PD region, but the PD region size is reduced leading to insufficient light input
Solution Approach 1:
The transfer gate is designed with a tapered structure where the gate width varies along the gate length direction. The gate width is wider at the PD region side and narrower at the FD region side, allowing the gate to extend to the PD region without uniformly reducing the PD area. This local variation in gate width enables the gate to reach the PD region for improved transfer characteristics while preserving sufficient PD region area for light input.
2Reliability
If an extended transfer gate is used to improve transfer characteristics, then the transfer gate can reach the PD region, but uneven electric potential is generated resulting in degraded transfer characteristics
Solution Approach 1:
The tapered gate structure creates a non-uniform electric field distribution that compensates for the uneven potential. By making the gate wider at the PD region side, the electric field is strengthened in that region, balancing the potential distribution across the PD region and preventing the uneven potential that would otherwise degrade transfer characteristics.
3Stability of the object's composition
If the transfer gate width is reduced to maintain constant distance, then the electric potential becomes consistent, but the transfer gate cannot effectively reach the PD region
Solution Approach 1:
Rather than uniformly reducing the gate width, the invention applies local quality variation by tapering the gate width from wider at the PD side to narrower at the FD side. This allows the gate to maintain effective width at the PD region for good transfer characteristics while gradually reducing width toward the FD region to maintain consistent electric potential distribution.
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 enhances light input, maintains a consistent electric potential, and improves transfer characteristics by maintaining a positive electric field, reducing the likelihood of insufficient transfer and enhancing the imaging device's performance.
Implementation Method 1
Each pixel includes a photoelectric conversion element (PD) such as a photodiode, pixel transistors of various types, and a floating diffusion (FD) region for converting electric charge obtained through photoelectric conversion into voltage
Implementation Method 2
A transfer transistor (TX) included in the pixel transistors has a transfer gate (TG) for transferring electric charge from the PD region to the FD region for read-out
Data Source
AI summary
An pixel unit includes a photoelectric conversion element, a transfer transistor having a transfer gate abutting on the photoelectric conversion element, and a floating diffusion region on which the transfer gate abuts, wherein the transfer gate includes a first gate portion having a first gate width in a gate width direction, the first gate portion abutting on the floating diffusion region and extending away from the floating diffusion region in a gate length direction, and a second gate portion having a second gate width narrower than the first gate width in the gate width direction, the second gate portion extending continuously from the first gate portion in the gate length direction, and wherein a width of the second gate portion gradually decreases from the first gate width to the second gate width toward a direction away from the first gate portion.