Variably Biased Tungsten Isolation for Global Shutter Pixel Storage
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Solution Overview
Problem
Global shutter image sensors face inefficiencies due to parasitic light and electrical crosstalk, leading to image distortion and lag in capturing fast-moving objects, as existing technologies struggle to effectively isolate storage transistors from stray light and charge.
Innovation Solution
The implementation of variably biased isolation structures filled with tungsten, which block parasitic stray light and charge, improving global shutter efficiency by reducing electron-hole pair generation and deep silicon electrical crosstalk, and controlling bias to minimize dark current and lag during image charge transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If storage transistors are isolated from parasitic light and electrical crosstalk, then global shutter efficiency is improved, but device complexity increases due to additional isolation structures
Solution Approach 1:
The patent introduces an isolation structure filled with tungsten as an intermediary element between the storage transistor and surrounding structures. This tungsten-filled isolation structure acts as a mediator to block parasitic light and electrical crosstalk from reaching the storage transistor, thereby improving global shutter efficiency while managing the added complexity through a targeted isolation approach.
2Manufacturing precision
If tungsten isolation structures are used to block parasitic light, then image distortion is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent specifies that the isolation structure be filled with tungsten, changing the material parameter to achieve optimal light blocking properties. This material selection addresses the need to reduce image distortion from parasitic light while the tungsten filling process integrates with existing semiconductor manufacturing techniques, balancing manufacturing feasibility with image quality requirements.
3Reliability
If bias is applied to isolation structures to control dark current, then image lag is reduced, but energy consumption increases
Solution Approach 1:
The patent implements periodic biasing of the isolation structure to control dark current during specific operational phases. By applying bias voltage to the isolation structure at appropriate times during the image capture and transfer cycle, the system minimizes dark current and image lag while avoiding continuous energy consumption, thus balancing reliability improvement with energy efficiency.
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 solution enhances global shutter efficiency, reduces image distortion, and minimizes lag in image charge transfer, enabling better capture of fast-moving objects without perceptible elongation distortion.
Implementation Method 1
isolation structures that are optically opaque and that block parasitic stray light from entering the storage transistor
Implementation Method 2
The isolation structures are coupled to receive a variable bias signal to control a bias of the isolation structure during operation
Data Source
AI summary
A pixel cell includes a photodiode disposed in a semiconductor material to accumulate image charge in response to incident light and a global shutter gate transistor coupled to the photodiode to selectively deplete the image charge from the photodiode. A storage transistor is disposed in the semiconductor material to store the image charge. An isolation structure is disposed in the semiconductor material proximate to the storage transistor to isolate a sidewall of the storage transistor from stray light and stray charge. The isolation structure is filled with tungsten and is coupled to receive a variable bias signal to control a bias of the isolation structure. The variable bias signal is set to a first bias value during a transfer of the image charge to the storage transistor. The variable bias signal is set to a second bias value during a transfer of the image charge from the storage transistor.