Vertical Transfer Gate Layout to Reduce Image Sensor GIDL
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Solution Overview
Problem
The integration of image sensors leads to increased leakage current due to gate-induced drain leakage (GIDL) between the floating diffusion region and the dual vertical transfer gate, degrading image quality and reliability.
Innovation Solution
Incorporating a concave portion in the electrode pad portion of the vertical transfer gate to create a sufficient distance from the floating diffusion region, reducing GIDL and read noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the electrode pad portion is positioned close to the floating diffusion region to reduce device area, then area is reduced, but gate-induced drain leakage current increases
Solution Approach 1:
The electrode pad portion is extended in the vertical direction (depth dimension) to form a recessed structure. This dimensional change allows the pad to maintain sufficient horizontal distance from the floating diffusion region while occupying minimal planar area, thus reducing GIDL without increasing device footprint.
Solution Approach 2:
The electrode pad portion is nested within the vertical transfer gate structure, forming a recessed region. This nesting arrangement allows the pad to be positioned close to the floating diffusion region in the planar view while maintaining vertical separation, effectively reducing both area and leakage current.
2Productivity
If the vertical transfer gate is positioned close to the floating diffusion region to improve charge transfer efficiency, then transfer efficiency is improved, but gate-induced drain leakage current increases
Solution Approach 1:
The vertical transfer gate is extended in the vertical direction to form a deeper structure that reaches closer to the photoelectric conversion region. This dimensional extension improves charge transfer efficiency by reducing the transfer distance while the recessed electrode pad portion maintains sufficient horizontal separation from the floating diffusion region to minimize GIDL.
3Reliability
If the electrode pad portion is extended horizontally to reduce contact resistance, then electrical connection is improved, but distance to floating diffusion region decreases increasing leakage
Solution Approach 1:
Instead of extending the electrode pad horizontally, the pad is extended in the vertical direction to form a recessed structure. This allows the pad to maintain good electrical contact with the vertical transfer gate through the recessed region while keeping sufficient horizontal distance from the floating diffusion region, thus reducing leakage current while maintaining low contact resistance.
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 effectively minimizes leakage current and enhances the reliability and quality of the image sensor by securing a gap between the vertical transfer gate and the floating diffusion region.
Implementation Method 1
a photoelectric conversion region (e.g., photodiode) receiving incident light and converting the light into an electrical signal
Data Source
AI summary
An image sensor, comprising a semiconductor substrate having first and second surfaces opposed to each other, a photoelectric conversion region in the semiconductor substrate, a floating diffusion region adjacent to the first surface in the semiconductor substrate, and a vertical transfer gate on the first surface of the semiconductor substrate, and extending in a direction perpendicular to the first surface and connected to the photoelectric conversion region. The vertical transfer gate may transfer photocharges collected in the photoelectric conversion region to the floating diffusion region. The vertical transfer gate includes a first vertical electrode portion and a second vertical electrode portion extending from the first surface of the semiconductor substrate in the vertical direction, and connected to the photoelectric conversion region, respectively.