2H/1T phase contact engineering for high performance transition metal dichalcogenide chemical vapor sensors
Inventors
Friedman, Adam L. • Perkins, F. Keith • Culbertson, James C. • Hanbicki, Aubrey T. • Campbell, Paul M.
Assignees
Publication Number
US-10436744-B2
Publication Date
2019-10-08
Expiration Date
2037-04-04
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Abstract
A method of making a low dimensional material chemical vapor sensor comprising providing a monolayer of a transition metal dichalcogenide, applying the monolayer to a substrate, applying a PMMA film, defining trenches, and placing the device in a n-butyl lithium (nbl) bath. A low dimensional material chemical vapor sensor comprising a monolayer of a transition metal dichalcogenide, the monolayer applied to a substrate, a region or regions of the transition metal dichalcogenide that have been treated with n-butyl lithium, the region or regions of the transition metal dichalcogenide that have been treated with n-butyl lithium have transitioned from a semiconducting to metallic phase, metal contacts on the region or regions of the transition metal dichalcogenide that have been treated with the n-butyl lithium.
Core Innovation
This invention discloses 2H/1T phase contact engineering for high performance transition metal dichalcogenide (TMD) chemical vapor sensors. It addresses the problem of poor contacts in TMD devices, which are mostly dominated by Schottky contacts when Au or Ti/Au are used, limiting current in the channel and resulting in uncontrollable and variable sensitivity to polar molecules. The invention selectively transitions the contacts in a TMD field effect transistor (FET)-based chemical vapor sensor from a semiconducting to metallic phase, thereby improving sensor performance.
The invention demonstrates that by using selective phase engineering, several enhancements are obtained: Ohmic contacts result in behavior no longer dominated by Schottky barrier effects; the sensor shows complete spontaneous recovery after chemical exposure; band-bending effects at the contacts are removed, eliminating environmentally variable responses to polar molecules; and there is increased selectivity to labile nitrogen-containing electron donor analyte species. The invention further presents a process to create phase engineered contacts on monolayer and few-layer MoS2, which can be applied to other semiconducting TMD thin films, enabling a range of selective, sensitive, robust, flexible, and inexpensive chemical vapor sensors.
Claims Coverage
The patent includes two independent claims covering a method for making the sensor and the low dimensional material chemical vapor sensor itself, presenting five main inventive features.
Method of fabricating a phase-engineered chemical vapor sensor
The method involves providing a monolayer of a transition metal dichalcogenide, applying it onto a SiO2/n+ Si substrate, coating with polymethyl-methacrylate (PMMA), defining trenches for patterned metal contacts via electron-beam lithography, and placing the device in an n-butyl lithium (nbl) bath to enable selective phase transition in contact regions.
Selective phase transition to create metallic contacts
Treating the accessible regions of the transition metal dichalcogenide with n-butyl lithium induces a phase transition from the semiconducting 2H phase to the metallic 1T phase in those regions, while maintaining the 2H phase elsewhere by masking with PMMA film.
Use of specific materials and processing steps for enhanced contacts
Utilizing a 1.6 M n-butyl lithium bath in an argon glove box, rinsing in hexane and deionized water, followed by deposition of Ti/Au metal contacts (5 nm Ti and 35 nm Au) by electron-beam evaporation and lift-off to form improved Ohmic contacts on the metallic regions.
Low dimensional material chemical vapor sensor structure
A sensor comprising a monolayer of transition metal dichalcogenide on a SiO2/n+ Si substrate, with specific regions treated with n-butyl lithium transitioned to the 1T metallic phase, and metal contacts applied on these treated regions.
Sensor with spontaneous recovery after chemical exposure
The sensor is characterized by the ability to spontaneously recover its baseline electrical state following chemical exposure, improving reusability without additional cleaning steps.
Together, these inventive features detail a method and device structure that creates improved Ohmic contacts via selective phase engineering, thereby enhancing chemical vapor sensor performance including sensitivity, selectivity, and spontaneous recovery.
Stated Advantages
Ohmic contacts eliminate Schottky barrier effects, improving electrical behavior and sensor reliability.
Complete spontaneous recovery of the sensor after chemical exposure, allowing repeated use without additional cleaning.
Removal of band-bending effects at contacts, eliminating environmentally variable responses to polar molecules.
Enhanced selectivity toward labile nitrogen-containing electron donor analytes, relevant for detection of explosives and nerve agents.
The sensor devices are flexible, inexpensive, mechanically robust, selective, highly sensitive, and low power, benefiting from the low dimensional TMD materials and phase-engineered contacts.
Documented Applications
Chemical vapor sensing for detection of strong electron donor species such as triethylamine (TEA), relevant to identification of explosives and nerve agents.
Use in sensor suites combining multiple TMDs to analyze mixtures of compounds, effectively serving as a synthetic nose.
Low-power, selective chemical vapor sensors operational over wide temperature ranges and environmental conditions.
Applicable in devices requiring flexibility, robustness, and low fabrication expense for trace chemical detection.
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