UC Berkeley

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) cut-off frequency, ft ~ 1 GHz and maximum frequency of oscillation, fmax ~ 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 CdSxSe1-x (0 < x < 1) parallel NW arrays, and 3) carrier mobility of ~ 20 cm2/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 (Ion/Ioff ~ 104) from SWNT network TFTs.

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.