Source Follower Transistor RTS Noise Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Image sensors suffer from random telegraph signal (RTS) noise due to charge traps at the semiconductor material and gate oxide interface, which affects image quality by introducing noise such as white pixels and off-color pixels.
Innovation Solution
A doped layer is added under the channel of the source follower transistor, and the device is back-biased to accelerate channel well widening, reducing the interaction between traps and charge carriers, thereby minimizing signal noise output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a source follower transistor is used in image sensor pixel circuits, then signal amplification is achieved, but random telegraph signal (RTS) noise is generated due to charge traps at the semiconductor material and gate oxide interface
Solution Approach 1:
An intermediary p-type doped layer is introduced between the n-type channel and the gate oxide interface. This layer acts as a mediator that prevents charge carriers in the channel from interacting with traps at the interface, thereby reducing RTS noise while preserving the source follower's signal amplification capability
Solution Approach 2:
The harmful charge traps at the interface are not removed but rather their harmful effect is converted into a beneficial separation mechanism. By introducing the p-type layer, the traps remain at the interface but can no longer interact with channel carriers, effectively converting the trap presence into a noise-reduction mechanism through carrier separation
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
The solution effectively reduces RTS noise in image sensor pixel circuits, leading to improved image quality by minimizing signal noise output from the source follower device.
Implementation Method 1
the device is back-biased to accelerate channel well widening
Implementation Method 2
charge traps (e.g., dangling bonds, OH— groups, etc., which trap electrons or holes flowing through the channel of the device)
Data Source
AI summary
An image sensor includes a photodiode disposed in a semiconductor material to generate image charge in response to incident light, and a floating diffusion disposed in the semiconductor material proximate to the photodiode. A transfer transistor is coupled to the photodiode to transfer the image charge from the photodiode into the floating diffusion in response to a transfer signal applied to a transfer gate of the transfer transistor. A source follower transistor is coupled to the floating diffusion to amplify a charge on the floating diffusion. The source follower transistor includes a gate electrode including a semiconductor material having a first dopant type; a source electrode, having a second dopant type, disposed in the semiconductor material; a drain electrode, having the second dopant type, disposed in the semiconductor material; and a channel, having the second dopant type, disposed between the source electrode and the drain electrode.