Monthly Archives: August 2014

12.5 A/350 V AlGaN/GaN-on-Si MOS-HEMT with low specific on-resistance and minimal threshold hysteresis

An AlGaN/GaN metal-oxide semiconductor (MOS) high-electron mobility transistor (HEMT) on silicon substrate was obtained with 8 nm Al2O3 gate dielectric films grown using atomic layer deposition. The MOS-HEMT shows a low specific on-resistance of 0.57 Ω·mm2, a large maximum saturate drain current of 12.5 A and a minimal threshold hysteresis of 0.05 V. Low specific on-resistance, large maximum saturate drain current and minimal threshold hysteresis show that the fabricated MOS-HEMT is very suitable for power switching applications.

New building blocks for [small pi]-conjugated polymer semiconductors for organic thin film transistors and photovoltaics

J. Mater. Chem. C, 2014, Accepted ManuscriptDOI: 10.1039/C4TC01201A, Feature ArticleYinghui He, Wei Hong, Yuning LiRapidly growing research interests in the field of printed electronics, especially polymer-based organic thin film transistors (OTFTs) and organic photovoltaics (OPVs), stem from the dramatically improved performance of these devices,...The content of this RSS Feed (c) The Royal Society of Chemistry

Effects of hydrogen plasma treatment on the electrical behavior of solution-processed ZnO transistors

The effects of hydrogen plasma treatment on the active layer of top-contact zinc oxide thin film transistors are reported. The transfer characteristics of the reference devices exhibited large hysteresis effects and an increasing positive threshold voltage (VTH) shift on repeated measurements. In contrast, following the plasma processing, the corresponding characteristics of the transistors exhibited negligible hysteresis and a very small VTH shift; the devices also possessed higher field effect carrier mobility values. These results were attributed to the presence of functional groups in the vicinity of the semiconductor/gate insulator interface, which prevents the formation of an effective channel.

On the structural-optical properties of Al-containing amorphous Si thin films and the metal-induced crystallization phenomenon

Amorphous (a-)Si-based materials always attracted attention of the scientific community, especially after their use in commercial devices like solar cells and thin film transistors in the 1980s. In addition to their technological importance, the study of a-Si-based materials also present some interesting theoretical-practical challenges. Their crystallization as induced by metal species is one example, which is expected to influence the development of electronic-photovoltaic devices. In fact, the amorphous-to-crystalline transformation of the a-SiAl system has been successfully applied to produce solar cells suggesting that further improvements can be achieved. Stimulated by these facts, this work presents a comprehensive study of the a-SiAl system. The samples, with Al contents in the ∼0−15 at. % range, were made in the form of thin films and were characterized by different spectroscopic techniques. The experimental results indicated that: (a) increasing amounts of Al changed both the atomic structure and the optical properties of the samples; (b) thermal annealing induced the crystallization of the samples at temperatures that depend on the Al concentration; and (c) the crystallization process was also influenced by the annealing duration and the structural disorder of the samples. All of these aspects were addressed in view of the existing models of the a-Si crystallization, which were also discussed to some extent. Finally, the ensemble of experimental results suggest an alternative method to produce cost-effective crystalline Si films with tunable structural-optical properties.

Achieving above 30% external quantum efficiency for inverted phosphorescence organic light-emitting diodes based on ultrathin emitting layer

Publication date: October 2014 Source:Organic Electronics, Volume 15, Issue 10 Author(s): Jun Liu , Xindong Shi , Xinkai Wu , Jing Wang , Zhiyuan Min , Yang Wang , Meijun Yang , Chin H. Chen , Gufeng He High efficiency inverted phosphorescence organic light-emitting diodes (PhOLEDs) based on ultrathin undoped and doped emitting layer (EML) have been developed. Compared to conventional device, the inverted PhOLED with 0.5nm undoped EML exhibits significantly larger external quantum efficiency (EQE), due to effective energy transfer from the excited host to the emitter. According to the atomic force microscopy image of EML, the 0.5nm emitter sandwiched by two hosts can be considered as the emitter doped in two hosts. The inverted device with intentionally doped ultrathin EML (1.5nm) exhibits the maximum EQE of 31.1%, which is attributed to optimized charge balance and preferred horizontal orientation of emitter. However, such inverted device has large efficiency roll-off at high brightness because of triplet–triplet annihilation process within the ultrathin EML. This can be improved by broadening the doped EML. The inverted device with 10.5nm doped EML has about EQE of 20 % at 10,000cd/m2. It is expected that our inverted PhOLED will promote development of high efficiency active-matrix organic light-emitting diodes based on the n-type Indium Gallium Zinc Oxide thin film transistor. Graphical abstract Highlights

On the mode of operation in electrolyte-gated thin film transistors based on different substituted polythiophenes

Publication date: October 2014 Source:Organic Electronics, Volume 15, Issue 10 Author(s): Henrik Toss , Clément Suspène , Benoît Piro , Abderrahim Yassar , Xavier Crispin , Loïg Kergoat , Minh-Chau Pham , Magnus Berggren Organic Thin Film Transistors (OTFT), gated through an aqueous electrolyte, have extensively been studied as sensors in various applications. These water-gated devices are known to work both as electrochemical (Organic ElectroChemical Transistor – OECT) and field-effect (Organic Field-Effect Transistor – OFET) devices. To properly model and predict the response of water-gated OTFT sensors it is important to distinguish between the mechanism, field-effect or electrochemical, by which the transistor is modulated and thus how the gate signal can be affected by the analyte. In this present study we explore three organic polymer semiconductors, poly-(3-hexyl-thiophene) (P3HT), poly-(3-carboxy-pentyl-thiphene) (P3CPT) and a co-polymer P3HT–co-poly-(3-ethoxypentanoic acid-thiophene) (monomer ratio 1:6, P3HT–COOH15) in water-gated OTFT structures. We report a set of transistor characteristics, including standard output parameters, impedance spectroscopy and current transients, to investigate the origin of the mode of operation in these water-gated OTFTs. Impedance characteristics, including both frequency and voltage dependence, were recorded for capacitor stacks corresponding to the gate/electrolyte/semiconductor/source structure. It is shown that P3HT as well as P3HT–COOH15 both can function as semiconductors in water gated OTFT devices operating in field-effect mode. P3CPT on the other hand shows typical signs of electrochemical mode of operation. The –COOH side group has been suggested as a possible anchoring site for biorecognition elements in EGOFET sensors, rendering P3HT–COOH15 a possible candidate for such applications. Graphical abstract Highlights

Polymeric Mold Soft-Patterned Metal Oxide Field-Effect Transistors: Critical Factors Determining Device Performance

J. Mater. Chem. C, 2014, Accepted ManuscriptDOI: 10.1039/C4TC01530D, CommunicationSunho Jeong, Seong Jip Kim, Aryeon Kim, Yejin Jo, Jun-Young Yoon, Sun Sook Lee, Youngmin Choi, Jong Chan Won, Sahn Nahm, Kwang-Suk Jang, Yun-Ho KimIn a recent decade, the exploit of high performance, soluble oxide semiconductors have been of paramount interest as a channel layer in device architectures of thin-film transistors. The excellent device...The content of this RSS Feed (c) The Royal Society of Chemistry

Self-Aligned Bottom-Gate In—Ga—Zn—O Thin-Film Transistor With Source/Drain Regions Formed by Direct Deposition of Fluorinated Silicon Nitride

We developed a bottom-gate and self-aligned In–Ga–Zn–O thin-film transistor (IGZO TFT) with source and drain (S/D) regions that were formed by a direct deposition of fluorinated silicon nitride (SiNx:F) on top of the IGZO film (IGZO/SiNx:F). The resistivity of IGZO/SiNx:F stack for the S/D regions of the TFT ( (rho _{mathrm {mathbf {S/D}}}) ) was highly stable after annealing, and it obtained (4.1 times 10^{mathrm {mathbf {-3}}} Omega ) cm after N2 annealing at 350 °C. As a result of thermally stable (rho _{mathrm {mathbf {S/D}}}) , the TFT properties with the IGZO/SiNx:F S/D regions improved drastically compared with those of IGZO/SiOx S/D regions. The field effect mobility of 10.6 cm (^{mathrm {mathbf {2}}}cdot ) V (^{mathrm {mathbf {-1}}}cdot ) s (^{mathrm {mathbf {-1}}}) and an ON/OFF current ratio of over (10^{mathrm {mathbf {8}}}) were obtained after 300 °C annealing. The proposed method is essential for making thermally stable S/D regions for self-aligned oxide TFTs.

Removal of Negative-Bias-Illumination-Stress Instability in Amorphous-InGaZnO Thin-Film Transistors by Top-Gate Offset Structure

A highly stable, dual-gate (DG) amorphous, indium–gallium–zinc oxide (a-IGZO) thin-film transistor (TFT) with an offset top-gate (TG) is reported. Given that both gates are opaque and electrically tied together, the TG functions as a light-shield and drain-current (I ({}_{mathrm {DS}}) ) enhancer as synchronized gate-voltage (V ({}_{mathrm {GS}}) ) sweep induces bulk-accumulation (BA) at positive voltages. It is demonstrated here that regardless of the offsets between the TG and source/drain electrode, this BA a-IGZO TFT is immune to negative bias and light-illumination stress (NBIS) when the TG covers at least 50% of the channel region. Therefore, high performance BA a-IGZO TFTs that are also immune to NBIS can be designed without introducing additional parasitic capacitance that occurs when the TG overlaps the source and/or drain electrode(s).

Implementation of Fully Self-Aligned Homojunction Double-Gate a-IGZO TFTs

A simple method of fabricating fully self-aligned double-gate (SADG) homojunction a-IGZO TFTs is proposed and experimentally demonstrated for the first time. The self-alignment between the bottom- and top-gates is realized with one backside-illuminated photolithographic step; and that between the source/drain regions and the two gates is formed by both argon plasma treatment and hydrogen doping. The resulting overlap between the gate and source/drain regions is about (0.3~mu ) m. Excellent symmetry between bidirectional transfer characteristics in the fabricated SADG TFTs is observed. Moreover, the dynamic threshold voltage operation is well demonstrated, and the driving capability, electrical stress effects under tied and separate gate biases are investigated.