Monthly Archives: December 2014

Effects of low-temperature (120 °C) annealing on the carrier concentration and trap density in amorphous indium gallium zinc oxide thin film transistors

We report an investigation of the effects of low-temperature annealing on the electrical properties of amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs). X-ray photoelectron spectroscopy was used to characterize the charge carrier concentration, which is related to the density of oxygen vacancies. The field-effect mobility was found to decrease as a function of the charge carrier concentration, owing to the presence of band-tail states. By employing the transmission line method, we show that the contact resistance did not significantly contribute to the changes in device performance after annealing. In addition, using low-frequency noise analyses, we found that the trap density decreased by a factor of 10 following annealing at 120 °C. The switching operation and on/off ratio of the a-IGZO TFTs improved considerably after low-temperature annealing.

High-performance thin-film-transistors based on semiconducting-enriched single-walled carbon nanotubes processed by electrical-breakdown strategy

Publication date: 15 February 2015 Source:Applied Surface Science, Volume 328 Author(s): B. Aïssa , M. Nedil , M.A. Habib , E.H. Abdul-Hafidh , F. Rosei Over the past two decades, among remarkable variety of nanomaterials, single-walled carbon nanotubes (SWCNTs) remain the most intriguing and uniquely well suited materials for applications in high-performance electronics. The most advanced technologies require the ability to form purely semiconducting SWCNTs. Here, we report on our strategy based on the well known progressive electrical breakdown process that offer this capability and serves as highly efficient means for selectively removing metallic carbon nanotubes from electronically heterogeneous random networks, deposited on silicon substrates in a thin film transistor (TFT) configuration. We demonstrate the successful achievement of semiconducting enriched-SWCNT networks in TFT scheme that reach On/Off switching ratios of ∼100,000, on-conductance of 20μS, and a subthreshold swing of less than 165mV/decades. The obtained TFT devices were then protected with thin film poly(methyl methacrylate) (PMMA) to keep the percolation level of the SWCNTs network spatially and temporally stable, while protecting it from atmosphere exchanges. TFT devices were found to be air-stable and maintained their excellent characteristics in ambient atmosphere for more than 4 months. This approach could work as a platform for future nanotube-based nanoelectronics.

Electrical properties of ultrathin titanium dioxide films on silicon

Ultrathin (2) films are being widely investigated as high-k dielectrics for future metal oxide semiconductor (MOS) technology. In this paper, ultrathin TiO2 films (∼20 nm) were deposited on silicon substrates by sputtering technique and subsequently annealed at 800 °C in oxygen environment for different durations (15–60 min). The annealed films were polycrystalline in nature with rutile phase. The value of dielectric constant was found to be 32–60 at 1 kHz measurement frequency. Threshold voltages of the MOS structures were found to vary from −0.1 to −0.5 V with the duration of annealing. Leakage current density (1 × 10−2–1 × 10−8 A/cm2 at 1 V) and dielectric breakdown fields (8.15–9.8 MV/cm) were observed to improve with annealing time.

Effects of low-temperature (120 °C) annealing on the carrier concentration and trap density in amorphous indium gallium zinc oxide thin film transistors

We report an investigation of the effects of low-temperature annealing on the electrical properties of amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs). X-ray photoelectron spectroscopy was used to characterize the charge carrier concentration, which is related to the density of oxygen vacancies. The field-effect mobility was found to decrease as a function of the charge carrier concentration, owing to the presence of band-tail states. By employing the transmission line method, we show that the contact resistance did not significantly contribute to the changes in device performance after annealing. In addition, using low-frequency noise analyses, we found that the trap density decreased by a factor of 10 following annealing at 120 °C. The switching operation and on/off ratio of the a-IGZO TFTs improved considerably after low-temperature annealing.

Atomic layer deposition grown MOx thin films for solar water splitting: Prospects and challenges

The magnitude of energy challenge not only calls for efficient devices but also for abundant, inexpensive, and stable photoactive materials that can enable efficient light harvesting, charge separation and collection, as well as chemical transformations. Photoelectrochemical systems based on semiconductor materials have the possibility to transform solar energy directly into chemical energy the so-called “solar hydrogen.” The current challenge lies in the harvesting of a larger fraction of electromagnetic spectrum by enhancing the absorbance of electrode materials. In this context, atomically precise thin films of metal oxide semiconductors and their multilayered junctions are promising candidates to integrate high surface areas with well-defined electrode–substrate interface. Given its self-limited growth mechanism, the atomic layer deposition (ALD) technique offers a wide range of capabilities to deposit and modify materials at the nanoscale. In addition, it opens new frontiers for developing precursor chemistry that is inevitable to design new processes. Herein, the authors review the properties and potential of metal oxide thin films deposited by ALD for their application in photoelectrochemical water splitting application. The first part of the review covers the basics of ALD processes followed by a brief discussion on the electrochemistry of water splitting reaction. The second part focuses on different MOx films deposited by atomic layer deposition for water splitting applications; in this section, The authors discuss the most explored MOx semiconductors, namely, Fe2O3, TiO2, WO3, and ZnO, as active materials and refer to their application as protective coatings, conductive scaffolds, or in heterojunctions. The third part deals with the current challenges and future prospects of ALD processed MOx thin films for water splitting reactions.

Comparison of defects in crystalline oxide semiconductor materials by electron spin resonance

Defects in crystalline InGaZnO4 (IGZO) induced by plasma were investigated using electron spin resonance (ESR). Thermal stabilities and ɡ factors of two ESR signals (A and B observed at ɡ = 1.939 and 2.003, respectively) in IGZO were different from those of the ESR signals observed in component materials such as Ga2O3 (signal observed at ɡ = 1.969), In2O3 (no signal), and ZnO (signal observed at ɡ = 1.957). Signal A in IGZO increased upon annealing at 300 °C for 1 h, but decreased when annealing was continued for more than 2 h. On the other hand, signal B decreased upon annealing at 300 °C for 1 h. The ESR signal in ZnO decayed in accordance with a second-order decay model with a rate constant of 2.1 × 10−4 s−1; however, this phenomenon was not observed in other materials. This difference might have been due to randomly formed IGZO lattices such as asymmetrical (Ga, Zn)O and In-O layers. Defects in signals A and B in IGZO were formed in trap states (at the deep level) and tail states, respectively.

Independent Chemical/Physical Role of Combustive Exothermic Heat in Solution processed Metal Oxide Semiconductors for Thin-Film Transistors

J. Mater. Chem. C, 2014, Accepted ManuscriptDOI: 10.1039/C4TC02408G, CommunicationSeong Jip Kim, Ae Ran Song, Sun Sook Lee, Sahn Nahm, Youngmin Choi, Kwun-Bum Chung, Sunho JeongThe development of high performance, soluble metal oxide semiconductors have been of paramount interest in various fields of electronic applications. Among the variety of methodologies for synthesizing soluble precursor solutions,...The content of this RSS Feed (c) The Royal Society of Chemistry

High-Responsivity and High-Sensitivity Graphene Dots/a-IGZO Thin-Film Phototransistor

An a-IGZO thin-film phototransistor incorporating graphene absorption layer was proposed to enhance the responsivity and sensitivity simultaneously for photodetection from ultraviolet to visible regime. The spin-coated graphene dots absorb incident light, transferring electrons to the underlying a-IGZO to establish a photochannel. The 5 A/W responsivity and 1000 photo-to-dark current ratio were achieved for graphene phototransistor at 500 nm. As compared with <1% absorption, the graphene phototransistor indicates a >2700 transistor gain. The highest responsivity and photo-to-dark current ratio is 897 A/W and $10^{6}$ , respectively, under 340-nm light illumination.

Oxide Semiconductor Thin Film Transistors on Thin Solution-Cast Flexible Substrates

We report ZnO thin-film transistors (TFTs) fabricated on solution-cast thin polyimide flexible substrates. Plasma-enhanced atomic layer deposition was used to deposit ZnO semiconductor and Al2O3 dielectric layers and the highest processing temperature used was 200 °C. The TFTs fabricated on thin polyimide substrates have characteristics very similar to devices fabricated on glass substrates and device characteristics changed little with release from the casting substrate. Typical TFT mobility was >12 $mathrm{cm}^{2}$/${rm V} cdot {rm s}$ for a gate electric field of 2 MV/cm. Released substrates with the TFTs were flexed between 3.5-mm radius and flat for 50000 cycles with little change in device characteristics. These results demonstrate solution casting of thin polymer layer substrates as a simple path to oxide semiconductor flexible electronics.

Benzobisthiadiazole-based conjugated donor-acceptor polymers for organic thin film transistors: effects of [small pi]-conjugated bridges on ambipolar transport

J. Mater. Chem. C, 2014, Accepted ManuscriptDOI: 10.1039/C4TC02273D, PaperYang Wang, Tomofumi Kadoya, Lei Wang, Teruaki Hayakawa, Masatoshi Tokita, Takehiko Mori, Tsuyoshi MichinobuA new series of benzobisthiadiazole (BBT)-based donor-acceptor copolymers, namely PBBT-FT, PBBT-T-FT, and PBBT-Tz-FT, with different [small pi]-conjugated bridges have been developed for polymer thin film transistors (TFTs). It was found that...The content of this RSS Feed (c) The Royal Society of Chemistry