Magnetic Tunnel Junction Gas Sensor for Multi-Gas Detection
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Solution Overview
Problem
Conventional semiconductor gas sensors face limitations in detecting multiple target gases due to high-temperature resistance measurement issues and limited accuracy in quantitatively measuring gas concentrations, particularly with chemical-reaction-type and thermal-reaction-type sensors.
Innovation Solution
The use of magnetic tunnel junction (MTJ) elements operably coupled with gas sensing elements, where MTJ elements switch resistance states in response to target gas concentrations, allowing for non-volatile memory-like functionality to capture data at high temperatures and read out at lower temperatures, and employing multiple MTJ elements with different storage blocking temperatures for higher resolution measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional semiconductor gas sensors use chemical-reaction-type or thermal-reaction-type sensing elements, then they can detect target gases, but they are limited to detecting one or a small number of target gases and have limited accuracy in quantitatively measuring gas concentrations
Solution Approach 1:
The gas sensing function is segmented across multiple MTJ elements, each configured with different storage blocking temperatures. This allows the system to detect multiple target gases with different concentrations by observing which MTJ elements switch states at different temperature thresholds, thereby achieving both multi-gas detection capability and quantitative measurement precision
Solution Approach 2:
The invention changes the parameter of storage blocking temperature across different MTJ elements to enable selective gas detection. By configuring MTJ elements with progressively higher storage blocking temperatures, the system can distinguish between different gas concentrations and types based on which elements respond at specific temperature ranges, resolving the contradiction between versatility and measurement precision
2Power
If thermal-reaction-type gas sensors operate at high temperatures to detect target gases, then they can generate sufficient reaction heat, but resistance measurement accuracy deteriorates at these high temperatures
Solution Approach 1:
The MTJ elements capture gas concentration data during the high-temperature gas sensing phase when reaction heat is generated, but the actual resistance measurement is deferred to a later low-temperature readout phase. This preliminary capture of information during high-power operation followed by accurate measurement during low-temperature operation resolves the contradiction between heat generation capability and measurement accuracy
Solution Approach 2:
The MTJ element acts as an intermediary that bridges the high-temperature sensing environment and the low-temperature measurement environment. It captures the gas concentration information at high temperatures when reaction heat is sufficient, then stores this information in a non-volatile manner for accurate readout at lower temperatures, eliminating the direct conflict between operating temperature and measurement accuracy
3Adaptability or versatility
If multiple gas sensor units with different gas sensing element materials are used to detect multiple target gases, then detection versatility improves, but device complexity and cost increase
Solution Approach 1:
A single MTJ-based gas sensor unit achieves multi-functionality by incorporating multiple MTJ elements with different storage blocking temperatures. This universal design allows one sensor unit to detect multiple target gases with different concentrations without requiring multiple separate sensor units with different sensing element materials, thereby reducing device complexity while maintaining versatility
Solution Approach 2:
The invention merges the detection functions of multiple gas sensor units into a single integrated sensor by using multiple MTJ elements with different thermal characteristics. This combining approach achieves the same multi-gas detection capability as having separate specialized sensors but with reduced complexity and lower cost
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 approach enables faster and more accurate gas concentration level measurements, avoiding high-temperature measurement challenges and providing high-resolution data, enhancing the ability to detect multiple gases effectively.
Implementation Method 1
magnetic tunnel junction (MTJ) element... a resistance state of the MTJ element switches from a known initial resistance value to an opposite resistance value
Implementation Method 2
MTJ element switching from a first magnetic orientation to a second magnetic orientation in response to a change in temperature
Implementation Method 3
a chemical reaction caused by changes in the composition or chemical structure of the gas sensing element in response to adsorption of the target gas
Implementation Method 4
a temperature change of the gas sensing element as a result of endothermic or exothermic reaction of the gas sensing element with the target gas
Implementation Method 5
MTJ elements switch resistance states in response to target gas concentrations, allowing for non-volatile memory-like functionality to capture data at high temperatures and read out at lower temperatures
Data Source
AI summary
Gas sensing using MTJ elements to capture/store gas concentration level data for readout at room temperature. In one embodiment, during reset the MTJ elements are heated above blocking temperatures of their storage layers while applying a first magnetic biasing force to set initial magnetic orientations. During gas sensing, reaction heat from a gas sensing element combines with control heat to raise each MTJ element's temperature from a work point temperature above its blocking temperature only when the target gas exceeds an associated concentration level, whereby a second magnetic biasing force causes the magnetic orientation to switch directions. During readout, read currents are measured to determine the MTJ elements' final resistance states, which indicate their switched/non-switched states, and the resistance states are correlated with stored data to determine the measured gas concentration level. The MTJ elements are cooled after reset and gas sensing to facilitate accurate CDS readout data.