Nanomaterials processing toward large-scale flexible/stretchable electronics

Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission. Abstract Nanomaterials processing toward large-scale flexible/stretchable electronics In recent years, there has been tremendous progress in large-scale mechanically flexible electronics, where electrical components are fabricated on non-crystalline substrates such as plastics and glass. These devices are currently serving as the basis for various applications such as flat-panel displays, smart cards, and wearable electronics. In this thesis, a promising approach using chemically synthesized nanomaterials is explored to overcome various obstacles current technology faces in this field. Here, we use chemically synthesized semiconducting nanowires (NWs) including group IV (Si, Ge), III-V (InAs) and II-IV (CdS, CdSe) NWs, and semiconductor-enriched SWNTs (99 % purity), and developed reliable, controllable, and more importantly uniform assembly methods on 4-inch wafer-scale flexible substrates in the form of either parallel NW arrays or SWNT random networks, which act as the active components in thin film transistors (TFTs). Thusly obtained TFTs composed of nanomaterials show respectable electrical and optical properties such as 1) cutoff frequency, f t ~ 1 GHz and maximum frequency of oscillation, f max ~ 1.8 GHz from InAs parallel NW array TFTs with channel length of ~ 1.5 µm, 2) photodetectors covering visible wavelengths (500-700 nm) using compositionally graded CdS x Se 1-x (0 < x < 1) parallel NW arrays, and 3) carrier mobility of ~ 20 cm 2 /Vs, which is an order of magnitude larger than conventional TFT materials such as a-Si and organic semiconductors, without sacrificing current on/off ratio (I on /I off ~ 10 4) from SWNT network TFTs. 2 The capability to uniformly assemble nanomaterials over large-scale flexible substrates enables us to use them for more sophisticated applications. Artificial electronic skin (e-skin) is demonstrated by laminating pressure sensitive rubber on top of nanomaterial-based active matrix backplanes. Furthermore, an x-ray imaging device is also achieved by combining organic photodiodes with this backplane technology. i To my family and everyone else whom I've had the privilege of running into from birth to present day.