Promising Gate Dielectric Material Research Articles

High-Performance, Transparent Solution-Processed Organic Field-Effect Transistor with Low-k Elastomeric Gate Dielectric and Liquid Crystalline Semiconductor: Promises and Challenges

The highly flexible and stretchable polymer elastomer having a low dielectric constant (k ∼ 2.6), called poly(dimethylsiloxane) (PDMS), is a promising gate dielectric material for solution-processed organic field-effect transistors (OFETs). A detailed understanding of PDMS-based OFETs is required to extend its application to flexible electronic devices. The present work discusses about the promises and challenges of PDMS-based solution-processed OFETs using a liquid crystal (LC), 2-decyl-7-phenyl-benzothienobenzothiophene (Ph-BTBT-10), as a semiconducting channel material. The liquid crystal-OFET (LC-OFET) exhibits high electrical performance such as a high hole mobility of ∼22 cm2 V–1 s–1, a low threshold voltage (<1 V), and a high current on/off ratio of 105. The OFETs also show high optical transparency (>90%). The electrical performance of LC-OFETs is observed to have a significant correlation with the annealing temperature of the Ph-BTBT-10 layer and is also influenced by different operating conditions such as air, nitrogen, and vacuum. The OFETs demonstrate anomalous bias stress behavior and hysteresis, which are also addressed.

Low-k polymer gate dielectric selection for organic thin-film transistors (OTFTs) using material selection methodologies

Performance parameters of an organic thin-film transistor (OTFT) and their relation to the material parameters of the gate dielectric are analyzed. Based on the analysis, the surface energy, dielectric constant, glass-transition temperature, and breakdown field are identified as key parameters. Various multicriteria decision-making approaches, viz. multiobjective optimization using simple ratio analysis (MOOSRA), technique for order preference by similarity to ideal solution (TOPSIS) and Vlsekriterijumska Optimizacija I KOmpromisno Resenje (VIKOR), are used to solve the material selection problem. Various low-k polymers are analyzed, and it is observed that CYTOP is a promising gate dielectric material for OTFTs, with good agreement between the MOOSRA, VIKOR, and TOPSIS regarding this choice.

Control of Concentration of Nonhydrogen-Bonded Hydroxyl Groups in Polymer Dielectrics for Organic Field-Effect Transistors with Operational Stability.

Poly(4-vinylphenol) (PVP) is a promising gate dielectric material for organic field-effect transistors (OFETs) and circuits fabricated on plastic substrates. Thermal cross-linking of PVP with a cross-linker, such as poly(melamine- co-formaldehyde) methylated(PMF), at a high temperature (above 170 °C) is widely considered an effective method to remove residual hydroxyl groups that induce polarization effects in the dielectric bulk. However, the threshold voltage shift in transfer characteristics is still observed for an OFET with a PVP-PMF dielectric when it is operated at a slow gate voltage sweep rate. The present study examines the cause of the undesired hysteresis phenomenon and suggests a route to enable a reliable operation. We systematically investigate the effect of the PVP-PMF weight ratio and their annealing temperature on the transfer characteristics of OFETs. We discover that the size of the hysteresis is closely related to the concentration of nonhydrogen-bonded hydroxyl groups in the dielectric bulk and this is controlled by the weight ratio. At a ratio of 0.5:1, a complete elimination of hysteresis was observed irrespective of the annealing temperature. We finally demonstrate a highly reliable operation of small-molecule-based OFETs fabricated on a plastic substrate at a low temperature.

Effect of Ti Content on Physical Properties and Electrical Characteristics of High-k Yb2TiO5 Gate Dielectrics for InZnSnO Thin-Film Transistors

In this study, we investigated the impact of Ti content on structural properties and electrical characteristics of high-k Yb2TiO5 gate dielectrics for amorphous indium–zinc–tin-oxide (a-InZnSnO) thin-film transistor (TFT) devices. The Yb2TiO5 thin films with different Ti plasma conditions were integrated in metal-insulator-metal structures to check the electrical capabilities. The Yb2TiO5 a-InZnSnO TFT device fabricated at the 120 W condition exhibited excellent electrical characteristics in terms of a small threshold voltage (VTH) of 0.14 V, a low subthreshold swing of 202 mV/decade, a large field-effect mobility of 29.8 cm2/V-s, and a high Ion/Ioff current ratio of 2.7×108. In addition, the VTH stability of Yb2TiO5 a-InZnSnO TFT device was studied under both positive bias stress and negative bias stress conditions. The Yb2TiO5 thin film is a promising gate dielectric material for the fabrication of a-InZnSnO TFTs.

Sol‐gel derived TiNb2O7 dielectric thin films for transparent electronic applications

AbstractTo reduce power consumption of transparent oxide‐semiconductor thin film transistors, a gate dielectric material with high dielectric constant and low leakage current density is favorable. According to previous study, the bulk TiNb2O7 with outstanding dielectric properties may have an interest in its thin‐film form. The optical, chemical states and surface morphology of sol‐gel derived TiNb2O7 (TNO) thin films are investigated the effect of postannealing temperature lower than 500°C, which is crucial to the glass transition temperature. All films possess a transmittance near 80% in the visible region. The existence of non‐lattice oxygen in the TNO film is proposed. The peak area ratio of non‐lattice oxygen plays an important role in the control of leakage current density of MIM capacitors. Also, the capacitance density and dissipation factor were affected by the indium tin oxide (ITO) sheet resistance at high frequencies. The sample after postannealing at 300°C and electrode‐annealing at 150°C possesses a high dielectric constant (&gt;30 at 1 MHz) and a low leakage current density (&lt;1 × 10−6 A/cm2 at 1 V), which makes it a very promising gate dielectric material for transparent oxide‐semiconductor thin film transistors.

High-performance GaAs metal-oxide-semiconductor capacitor by using NbAlON as high-k gate dielectric

A GaAs metal-oxide-semiconductor (MOS) capacitor using NbAlON as a gate dielectric with different Nb contents is fabricated. Experimental results show that the k value and crystallization temperature of the AlON dielectric can be improved by Nb incorporation, together with reduction in negative oxide charges. However, the interface quality and gate leakage become poorer as the Nb content increases, as confirmed by TEM and X-ray photoelectron spectroscopy results. Therefore, through comprehensively considering the advantages and disadvantages, the sample with a Nb/(Al+Nb) atomic ratio of 62.5% exhibits the best characteristics: high k value (23.3), low interface-state density (2.7 × 1012 cm−2/eV), small hysteresis (55 mV), small frequency dispersion, and low gate leakage current (2.66 × 10−5A/cm2 at Vfb + 1 V). By comparing with reported GaAs MOS devices with different high-k gate dielectrics, it can be suggested that NbAlON is a promising gate dielectric material to achieve excellent electrical performance for GaAs MOS devices.

Investigations on high-κ dielectrics for low threshold voltage and low leakage zinc oxide thin-film transistor, using material selection methodologies

This paper presents the investigations on high-κ dielectrics for low operating voltage and low leakage zinc oxide thin film transistor (ZnO TFT) using three material selection methodologies namely Ashby, technique for order preference by similarity to ideal solution (TOPSIS) and VlseKriterijumska Optimizacija I Kompromisno Resenjein in Serbian (VIKOR). Various material properties such as dielectric constant, conduction band offset to ZnO, band-gap and temperature coefficient mismatch of high κ to ZnO are investigated to find out the most promising gate dielectric material. The analysis concludes that lanthanum oxide (La2O3) is the most promising gate dielectric material for ZnO TFT transistor. The result shows a good agreement between Ashby’s, TOPSIS and VIKOR approaches.

Observation of Substrate Silicon Incorporation into Thin Lanthanum Oxide Film during Rapid Thermal Annealing

Lanthanum oxide (La2O3) has been proposed as the promising gate dielectric material for future complementary metal-oxide-semiconductor (CMOS) technology. However, unlike the conventional homopolar materials such as silicon oxide or silicon nitride, La2O3 is more ionic and in particular at the La2O3/Si interface is less thermally stable. This work investigates the chemical and compositional variations of La2O3 thin film on the silicon substrate during rapid thermal annealing by using angle-resolved x-ray photoelectron spectroscopy (ARXPS) measurements. Results show that thermal annealing at temperatures above 500 °C would result in the incorporation of substrate Si atoms deep into the bulk of the La2O3 film and forming silicate phases both at the interface and in the bulk. These effects would result in the characteristic degradation of CMOS devices.

Improvement on Interface Quality and Reliability Properties of HfAlOx MIS Capacitor with Dual Plasma Treatment

HfO2 is considered a promising gate dielectric material for sub-45 nm CMOS technology. It has been reported that incorporate Al into HfO2 forming Hf aluminates in order to increase the crystallization temperature. However, the growth of the low-k interfacial layer at high-k/Si interface during high-k dielectric deposition would result in reliability degradation. Recently, incorporating nitrogen into HfAlOx gate dielectrics has beneficial effect on reliability performance. In addition, fluorine incorporation into high-k dielectrics also could have several improvements. In this study, dual plasma (CF4 pre-treatment and N2 post-treatment) was performed on HfAlOx MIS capacitor in order to improve interface quality and the reliability properties. According to our experimental results, dual plasma treatment could improve interface quality and enhance reliability properties of HfAlOx thin films.

Thermal Properties of Ultrathin Hafnium Oxide Gate Dielectric Films

Thin-film HfO2 is a promising gate dielectric material that will influence thermal conduction in modern transistors. This letter reports the temperature dependence of the intrinsic thermal conductivity and interface resistances of 56-200-Aring-thick HfO2 films. A picosecond pump-probe thermoreflectance technique yields room-temperature intrinsic thermal conductivity values between 0.49 and 0.95 W/(mmiddotK). The intrinsic thermal conductivity and interface resistance depend strongly on the film-thickness-dependent microstructure.

Pentacene thin-film transistors with Al2O3+x gate dielectric films deposited on indium-tin-oxide glass

We report on the fabrication of pentacene thin-film transistors (TFTs) with Al2O3+x films as the gate dielectric that has been deposited on indium-tin-oxide glass by rf magnetron sputtering at room temperature. Although the Al2O3+x was expected to show lower capacitance and breakdown field than stoichiometric Al2O3, our pentacene TFTs with optimized thin Al2O3+x gate dielectric exhibited a moderately high field mobility of 0.14 cm2/V s, an outstanding subthreshold slope of 0.88 V/dec, and an on/off ratio over 106. Our work demonstrates that RT-deposited Al2O3+x is a promising gate dielectric material for organic TFTs.