Po-Yuan Lo

Novel method of converting metallic-type carbon nanotubes to semiconducting-type carbon nanotube field-effect transistors

Depending on the chirality, single-walled carbon nanotubes (SWNTs) can be either metallic or semiconducting. Thus far, the production of SWNTs, irrespective of synthesis methods, still yields a mixture of both types, with the metallic type being prevalent. However, semiconducting-type SWNTs are needed for carbon nanotube field-effect transistors (CNT-FETs) as well as many sensors. This is because only the semiconducting-type SWNTs can be effectively modulated by the gate voltage. In contrast, the lack of field effect in metallic-type SWNTs adversely impacts their applications in high-performance electronic devices. In this study, we demonstrate for the first time a novel plasma treatment method that allows us to convert metallic-type carbon nanotubes to semiconducting-type CNT-FETs. On the basis of our experimental results, we believe that the ion bombardment during Ar plasma treatment attacks both metallic- and semiconducting-type nanotubes; however, the metallic-type carbon nanotubes are more vulnerable to the attack than those of the semiconducting type, and are subsequently transformed into the latter type.

Enhanced P3HT OTFT Transport Performance Using Double Gate Modulation Scheme

Electrical properties of single-gated (bottom-gated or top-gated) and double-gated (DG) organic thin-film transistors (OTFTs) are systematically investigated in terms of threshold voltage (V th), subthreshold slope, and I ON/OFF. We found that the device structure has significant impacts on the aforementioned electrical properties and the operation modes in a poly-3-hexyl thiophene DG OTFT. An empirical electrostatic potential model is employed to describe well V th behaviors of DG OTFTs in different modulation schemes. In addition, selective active-area coating in OTFTs is realized using an inkjet printing process, and consequently, parasitic leakage is much suppressed.

Study of Carrier Transport by Pentacene Thin-Film Transistors at High Temperatures

In this study, the interface properties of pentacene organic thin-film transistors (OTFTs) were analyzed at elevated temperatures. The pentacene layers were deposited on the poly(α-methyl styrene) (PMS)-treated SiO2 dielectric layers. The threshold voltages (Vt) were varied drastically in the temperature range from 100 to 200 °C due to the phase transition of the PMS layer after the Tg point (TgPMS=76 °C). After high temperature electric measurements, the deformation of pentacene was observed using atomic force microscopy and the oxidation of pentacene was also observed in the fourier transform infrared spectroscopy (FTIR) (about 80 °C) by the appearance of C=O bonds. The drastic decrease in mobility of pentacene OTFTs about 100 °C was attributed to the distortion of the pentacene conjugate structure.

Stability Improvement of Organic Thin-Film Transistors Using Stacked Gate Dielectrics

Poly-3-hexylthiophene organic thin-film transistors (OTFTs) were fabricated with different kinds of stacked gate dielectrics, which exhibit an individual effective trap behavior. The transistor fabricated with a stacked gate dielectric in a donor-like trap behavior exhibits a significant current hysteresis loop, a large threshold voltage shift, and subthreshold swing changes during operation in the dark and under illumination. The device performance is improved using a stacked gate dielectric with acceptor-like traps. The mechanisms of OTFTs with an acceptor-like trap dielectric and a donor-like dielectric are discussed.

Stable Polymer Dielectric Film for Polythiophene Thin Film Transistor on Modified Poly(vinyl phenol) with Polar Functional Group

In this work, a modified poly(vinyl phenol) (MPVP) polymer dielectric solution with high permittivity and resistant to moisture was used. The MPVP was synthesized by replacing the hydroxyl group in PVP with a polar amino functional group. The material properties of polymer films were characterized by nuclear magnetic resonance (NMR) analysis, gel permeation chromatography (GPC), and thermogravimetric analysis (TGA). Dielectric layers properties were analyzed by current–voltage and capacitance–voltage measurement of a metal–dielectric–metal capacitor and a polythiophene (P3HT) polymer transistor. The stable leakage current, permittivity and output characteristic indicate that MPVP is suitable for a large-area continues-printing process.

Prospect of cobalt-mix-tetraethoxysilane method on localized lateral growth of carbon nanotubes for both p- and n-type field effect transistors

To apply carbon nanotubes (CNTs) to nanoelectronics, researchers must effectively control the placement and manipulation of massive numbers of CNTs. In this work, we demonstrate a precise growth of single-walled carbon nanotubes (SWNT) on preassigned locations with only cobalt as catalyst. This is in contrast to the laborious and time-consuming physical manipulation of numerous nanotubes one at a time used in the conventional approach. Laterally grown CNTs were accomplished in preassigned areas using an integrated circuit compatible process in this study. In order to synthesize SWNT as the channel of a field effect transistor (FET), the cobalt-mix-tetraethoxysilane (CMT) solution and catalytic chemical vapor deposition were used. The CMT solution has the unique property of well dispersing the cobalt catalyst and uniformly embedding it in predetermined locations after the CMT solution has solidified. Our results show that laterally grown bundled-CNTs could be formed in atmospheric chemical vapor deposition...

A novel method to convert metallic-type CNTs to semiconducting-type CNT-FETs

Bae-Horng Chen, Jeng-Hua Wei, Po-Yuan Lo, Ming-Jinn Tsai, Tien-Sheng Chao, Horng-Chih Lin,and Tiao-Yuan Huang Electronics Research & Service Organization (ERSO), ITRI W3100, Build., 11, 195 Sec4.Chung Hsing Rd., Chutung, Hsinchu, Taiwan, 310 Phone: +886-3-5913271 E-mail: cbh@itri.org.tw Institute of Electronics, National Chiao Tung University 1001 Ta-Hsueh Road, Hsinchu, Taiwan 30050, R.O.C Department of Electronic Engineering, Ching Yun University, Jung-Li 229, Taiwan Institute and Department of Electrophysics, National Chiao Tung University