Stabilization and Circuit Strategies for Enhanced Vapor Sensing with Polymer Semiconductors

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Non-technical: Sensing of gas-phase compounds is essential for monitoring industrial processes, detecting military and security threats, ensuring air quality, and, most recently, aids medical diagnosis. Small, unobtrusive, and low-cost sensors can be deployed throughout an area or a building and incorporated into wearable electronics. Organic semiconductors (OSCs) are attractive for use in vapor sensors as they can be incorporated into simple devices such as resistors or transistors and are compatible with mechanically flexible substrates and low-cost fabrication processes. The chemical properties of OSCs can be tuned to optimize the response to target gases and control the electronic responses of sensors. One major drawback of OSC-based sensors is the tendency of the output current or voltage to drift over time due to environmental effects such as temperature and humidity or in response to non-target gases (interferents). This project will use chemically stable OSCs and employ them in circuit layouts that minimize the influence of interferents and environmental effects. Progress will be made by combining material synthesis with device fabrication and simulation of devices and circuits. Circuits will be developed that preserve sensitivity while minimizing environmental drift; arrays of these circuits will provide increased selectivity. The project will include multiple outreach efforts. Computer modeling opportunities will be offered to undergraduate and high school students from the underserved Appalachian region anchored by Frostburg State University. A related class will be developed and a summer camp for high school students will be held at Frostburg State University. High school interns will be recruited to Johns Hopkins University from a local high school that serves an underrepresented community. Technical: Sensing of gas-phase compounds is essential for monitoring industrial processes, detecting military and security threats, ensuring air quality, and most recently as a tool in medical diagnosis. The smallest, least intrusive, and lowest cost options can be used for widespread deployment throughout a building or geographic zone or incorporated into wearable electronics. Organic semiconductors (OSCs), including molecules and polymers, have multiple advantages for vapor sensors, as they are compatible with simple sensing circuitry, mechanically flexible substrates, and low-cost fabrication processes. They also have well understood chemical tunability and interactions with gaseous analytes for optimal design and control of the electronic responses to the analytes. They may be incorporated into simple resistive devices, or organic field-effect transistors for cascading in logic circuits. One major drawback of OSC-based sensors is the tendency of the output current or voltage to drift over time, related to their responsiveness to interferents and environmental perturbations, such as humidity and temperature change. This proposal will demonstrate the advantages to be gained by using OSCs with greater chemical stability and employing them in circuit layouts that minimize the influence of interferents and make the responses to analytes more pronounced. Progress will be made by combined efforts in material and device fabrication and in simulation of devices and circuits. The combined material sensitivity to analytes and stability against environmental influences will be optimized. Circuits will be developed that preserve analyte signaling while minimizing the environmental drift. Arrays of these circuits will provide increased selectivity. This work will provide an enabling solution to performance requirements for the adoption of OSC-based sensors in commercial technologies. Electronic device simulation opportunities will be offered to undergraduate and high school students from the underserved Appalachian region anchored by Frostburg State University. Undergraduate students will learn semiconductor device physics, develop computer programming skills, and learn modern device simulation software. High school interns will be recruited to Johns Hopkins University from predominantly female-minority Western High School in Baltimore City.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.