Image Sensor Shield Device for Carrier Cross-Talk Reduction
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Solution Overview
Problem
Conventional image sensors, such as POAP, suffer from carrier cross-talk between adjacent pixels, leading to resolution and uniformity degradation, as well as poor color fidelity due to dark leakage currents caused by potential differences between pixel electrodes.
Innovation Solution
A shield device is introduced between adjacent pixel electrodes, comprising a shield electrode and an isolation structure, which is grounded to prevent current flow and create a potential barrier, thereby isolating adjacent pixels and reducing cross-talk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a POAP image sensor with stacked p-i-n layer structure is used to achieve high fill factor and quantum efficiency, then photo sensing performance is improved, but carrier cross-talk between adjacent pixels occurs causing resolution and uniformity degradation
Solution Approach 1:
A shield electrode is introduced as an intermediary element positioned between adjacent pixel electrodes. This shield electrode acts as a mediator to block the direct electrical interaction and carrier diffusion between neighboring pixels, thereby preventing cross-talk while preserving the high fill factor structure of the POAP sensor.
Solution Approach 2:
The harmful electric field and potential difference between adjacent pixels are extracted or removed by introducing the shield electrode. The shield electrode isolates the electrical environments of adjacent pixels, taking out the cross-talk mechanism from the system while maintaining the original photo sensing structure.
2Area of stationary object
If pixel electrodes are positioned close to each other to maximize fill factor, then photo sensing area is increased, but dark leakage current flows between adjacent pixels due to potential difference
Solution Approach 1:
The shield electrode serves as a physical and electrical intermediary between adjacent pixel electrodes. It blocks the direct current path that would otherwise allow dark leakage current to flow between pixels with different potentials, while maintaining minimal spacing between pixels to preserve fill factor.
Solution Approach 2:
The potential difference between adjacent pixels, which originally caused harmful dark leakage current, is converted into a beneficial effect by using the shield electrode to create controlled isolation. The shield electrode leverages the electrical environment to establish a barrier that prevents unwanted current flow while maintaining the electrical functionality of each pixel.
3Reliability
If adjacent pixels are isolated to prevent cross-talk, then image fidelity is improved, but device structure becomes more complex
Solution Approach 1:
The shield electrode is merged with the existing pixel electrode structure and fabrication process. It is formed using the same conductive layer materials and deposition techniques as the pixel electrodes, integrating the isolation function into the existing device architecture rather than adding completely separate isolation structures.
Solution Approach 2:
The shield electrode performs multiple functions: it acts as an electrical barrier to prevent cross-talk, serves as a structural element in the stacked p-i-n layer configuration, and can be integrated with the transparent conductive oxide layer system. This multi-functionality reduces the need for additional dedicated isolation components.
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 shield device effectively prevents carrier cross-talk, enhancing image sensor performance and sensitivity by maintaining a high potential barrier between adjacent pixels, thus improving image fidelity and accuracy.
Implementation Method 1
the different pixel electrodes 18a, 18b of the prior-art image sensor 10 may have various voltages under illumination, resulted in an electric filed with potential difference between the adjacent pixels 14a, 14b
Implementation Method 2
The shield device comprises a shield electrode and an isolation structure surrounding the shield electrode to isolate the shield electrode from the pixel electrodes and the photo conductive layer
Implementation Method 3
The image sensor such as complementary metal oxide semiconductor (CMOS) or charge coupled device (CCD) is a silicon semiconductor device designed to capture photons and convert them into electrons
Data Source
AI summary
An image sensor contains a semiconductor substrate, a plurality of pixels defined on the semiconductor substrate, a photo conductive layer and a transparent conductive layer formed on the pixel electrodes of the pixels in order, and a shield device positioned between any two adjacent pixel electrodes. The shield device has a shield electrode and an isolation structure surrounding the shield electrode so that the shield electrode is isolated from the pixel electrodes and the photo conductive layer by the isolation structure.