Graduation Year

2023

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Degree Granting Department

Electrical Engineering

Major Professor

Arash Takshi, Ph.D.

Committee Member

Ashwin Parthasarathy, Ph.D.

Committee Member

Jing Wang, Ph.D.

Keywords

Wearable electronics, conductive polymer, PEDOT:PSS, DBSA, Fabric base semiconductor

Abstract

Wearable electronics interest has attracted the attention of a few sectors because of their applicability in different areas like healthcare, military, and our daily basis. Still building circuits on fabrics to make these wearable electronics is challenging. As transistors are the building blocks of electronic circuits and most of the biosensors, recently, fiber-shaped electrochemical transistors have been studied extensively for a lot of applications including bioelectronics. Fiber-based devices are getting popular in different applications due to their low fabrication cost, lightweight, and flexibility without losing their properties. Additionally, they are potentially suitable for making sensors on garments.

In this work, we have studied various types of coating processes of PEDOT:PSS conducting polymer into different fabric types. After the coating, the conductive threads have been used to make organic electrochemical transistors (OECTs). Different studies before have shown the advantages of using dodecylbenzene sulfonic acid (DBSA) solution in PEDOT:PSS to improve conductivity. In this work, threads were tested with and without DBSA to make OECTs and the effects of conductivity change on these transistors performance have been studied. The results show the performance improvement in the treated thread with an acid. The transistor design is considered in the development for its application as a wearable pH sensor to monitor perspiration in the future wearable medical point-of-care systems.

In this work, we investigated the effect of thread materials on the performance of fiber-based OECTs made for wearable pH sensors. Three most commercially available threads were selected and tested in this research: 100% cotton, 25% cotton-75% polyester, and 32% cotton-68% polyester threads. Threads were coated with PEDOT:PSS polymer to use as the channel between the drain and source contacts. Then a silver-coated thread was used as the gate and a polyvinyl alcohol (PVA) gel electrolyte was used between the two threads. Devices were tested by applying different voltages to the transistor terminals and monitoring the current through the PEDOT:PSS channel. The best transistor was obtained with 25%cotton-75% polyester. The results obtained from the experiment show a promising approach toward wearable sensors.

Finally, we end up with the analysis of the transistor behavior when exposed to solutions of different pHs. Results showed a change in drain current after adding different solutions with different pH levels. The analysis revealed the effect of the pH on the PEDOT:PSS coating used as a semiconductor in the transistor that was made leading to results encouraging for the application of a new flexible bioelectronic device.

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