Optically Switchable Magnetic Tunnel Junctions for Radiation-Hardened Image Sensors
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Solution Overview
Problem
Conventional CMOS-based image sensors are not radiation hardened, leading to data leakage and require a large chip area due to the number of devices per pixel, which complicates efficient image capture and storage.
Innovation Solution
An image sensor array utilizing optically switchable magnetic tunnel junctions (MTJs) arranged in columns and rows, with transparent conductive and conductive lines for biasing, enabling global reset, sense, and read operations without transistors, and incorporating an on-demand radiation shield for controlled radiation exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If CMOS-based pixels with photodiodes and transistors are used, then image sensing functionality is achieved, but chip area consumption increases and radiation hardness deteriorates
Solution Approach 1:
The patent extracts and removes the transistor components from the pixel structure, retaining only the essential photodetching element. This extraction eliminates the radiation-sensitive transistor while preserving the core imaging function, thereby improving radiation hardness and reducing chip area.
Solution Approach 2:
The patent replaces the electronic transistor-based switching and readout mechanism with a magnetic field-based readout system using TMR junctions. This substitution eliminates the need for complex transistor circuits while maintaining imaging functionality, reducing chip area and improving radiation resistance.
2Ease of operation
If multiple devices per pixel (photodiode and transistors) are used, then image sensing is enabled, but device complexity and chip area increase
Solution Approach 1:
The patent extracts and removes the transistor components from each pixel, reducing the device count from multiple components to a single photodetching element per pixel. This simplification maintains imaging capability while dramatically reducing device complexity.
Solution Approach 2:
The patent merges the functions of multiple devices into a single integrated structure where the TMR junction serves both as the photodetching element and the readout mechanism, eliminating the need for separate transistors and simplifying the overall pixel architecture.
3Reliability
If transistors are used for pixel control, then pixel operation is enabled, but radiation sensitivity increases
Solution Approach 1:
The patent extracts and removes transistors from the pixel structure, eliminating the radiation-sensitive semiconductor components that are prone to data leakage under radiation exposure. This leaves only the radiation-hardened TMR junction for data storage and readout.
Solution Approach 2:
The patent replaces the expensive and radiation-sensitive transistor-based pixel structure with a simpler, more radiation-resistant TMR junction structure that can withstand radiation environments without data loss, effectively using a more robust but simpler component.
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 provides radiation-hardened, efficient image data storage with reduced chip area consumption, allowing for accurate image capture and storage without immediate data read requirements, and improves image capture accuracy through controlled radiation exposure.
Implementation Method 1
The MTJs can concurrently store image data in response to specific biasing conditions on the first lines and the second lines and concurrent exposure of the first lines to radiation
Implementation Method 2
The first lines can be made, at least in part, of a transparent conductive material... concurrent exposure of the first lines to radiation
Data Source
AI summary
An image sensor includes an array of optically switchable magnetic tunnel junctions (MTJs) arranged in columns and rows. The image sensor has first lines of transparent conductive material and second lines of conductive material. Each first line is in contact with the free layers of the MTJs in a corresponding row. Each second line is electrically connected to the fixed layers MTJs in a corresponding column. The first lines are concurrently exposable to radiation. The first and second lines are selectively biasable. In a global reset operation, biasing conditions are such that all MTJs are switched to an anti-parallel state. In a global sense operation, biasing conditions are such that, depending upon the intensity of radiation received at those portions of the first lines in contact with MTJs, the MTJs may switch to a parallel state. In selective read operations, biasing conditions are such that stored data values in the MTJs can be read.