CBE Seminar - Xiaoxue Wang

A Synergistic Approach to Soft Materials and Soft Electronics

Abstract

In the last decade, the rapid development of the flexible and stretchable (soft) electronics has been largely fueled by the fundamental breakthrough in soft materials synthesis and new fabrication technologies. Among the soft electronic materials, polymers stand out due to their merits of high stretchability, biocompatibility, light weight, scalability and cost-efficiency. However, despite the great prospects of electronic polymers, several critical challenges still need to be addressed: (1) Key electrical properties, such as electrical conductivity (σ) and carrier mobility (μ) of polymers are still relatively low compared with conventional rigid semiconductors, and result in higher power consumption and lower operation speed; (2) Low thermal conductivity (κ) makes heat dissipation a critical issue; (3) Conventional solution-based processing technologies may pose wettability and compatibility issues for device fabrication on flexible substrates. Here I present a synergistic approach to combat these challenges by using Chemical Vapor Deposition (CVD) technology as an effective tool. First, I demonstrate record high electrical conductivity (σ) and charge carrier mobility (μ) achieved in poly(3,4-ethylenedioxythiophene) (PEDOT), with engineered crystallization and morphology implemented by CVD. We also build wafer-scale PEDOT-Si rectifier arrays operating at 13.56 MHz for RFID readers by direct CVD synthesis. Second, I demonstrate record high cross-plane thermal conductivity (>10x common polymers) in intrinsic poly(3-hexylthiophene) (P3HT) thin films by using a self-assembling CVD growth method. This method generates an extended chain structure with π- π stacking, and thereby significantly facilitates the thermal transport. Lastly, I will present CVD’s powerful capability in device application, with gas sensors as an example. In summary, this work establishes an innovative method to effectively tune the key physical properties of polymers by CVD-based structure-property engineering on the molecular level. In addition, this work also has the potential to facilitate novel device fabrication technologies and applications in artificial skin, bio-degradable sensors, stretchable photovoltaics and light emitting diodes (LEDs).

Bio

Xiaoxue Wang is a Ph.D. candidate in the Department of Chemical Engineering under the supervision of Prof. Karen K. Gleason at Massachusetts Institute of Technology, with a minor in Electrical Engineering. She received her B.S. in Chemical Engineering from Tsinghua University in 2012. Her research interests mainly focus on the structure-property engineering of polymers synthesized by Chemical Vapor Deposition (CVD) method, as well as the electronic device fabrication based on CVD polymers.