Improvement In Field-effect Mobility Research Articles

Improvement in carrier mobility through band-gap engineering in atomic-layer-deposited In-Ga-Zn-O stacks

This paper reports the performance improvement of heterojunction channel field-effect transistor using an atomic-layer-deposited InGaZnO (IGZO) channel on basis of a band alignment. The heterojunction stack consisted of a 5 nm-thick In0.61Ga0.16Zn0.23O confinement layer (CL) and a 2 nm-thick In0.52Ga0.32Zn0.15O barrier layer (BL). Band-gap engineering through cation composition and thickness modulation of each layers allowed free electron diffusion from the In0.52Ga0.32Zn0.15O BL to the In0.61Ga0.16Zn0.23O CL and carriers confinement in CL, leading to the improvement in field-effect mobility. The control transistor with 5 nm-thick IGZO CL layer had a mobility of 33.4 cm2/Vs, whereas the heterojunction transistor with 2 nm-thick IGZO BL exhibited a higher mobility of 50.7 cm2/Vs as well as low gate swing of 89 mV/decade as a result of carrier transporting boosting. Moreover, the corresponding heterojunction channel transistors exhibited better gate bias stability due to the mitigation of gap states creation and passivating behavior by introducing the 2 nm-thick IGZO BL.

Improvement of Field-effect Mobility in Top-gate Organic Field-effect Transistors Using Solution-processed Molybdenum Trioxide Hole Injection Layers

Improvement of Field-effect Mobility in Top-gate Organic Field-effect Transistors Using Solution-processed Molybdenum Trioxide Hole Injection Layers

Effect of pre-aggregation in solution state on the performance of organic field-effect transistors with indacenodithiophene-co-benzothiadiazole

We study the effect of solvent and pre-aggregated solution formed in a binary solvent system to achieve high performance organic field-effect transistors (OFETs) with indacenodithiophene-co-benzothiadiazole (IDT-BT) polymer. To quantify the degree of pre-aggregation, we selected a binary solvent system consisting of a mixture of good (chloronaphthanlene (CN), bp = 259 °C) and bad (2-methoxyl ethanol (2-ME), bp = 124 °C) solvents with various mixing ratios from 0 to 30 v% with the help of a Hansen solubility parameters program. The formation of pre-aggregated IDT-BT polymer was identified in an 8:2 CN:2-ME solvent ratio via a red-shift in a UV–vis absorption spectrum. The off-center spin coated IDT-BT OFETs from 8:2 ratio (CN:2-ME) solution exhibited more than double the improvement in field effect mobility (μFET = 1.38 ± 0.19 cm2/Vs) due to efficient charge injection through the smooth semiconducting film surface fabricated by the off-center spin-coating process from the polymer pre-aggregate in the binary solvent system with an appropriate mixing ratio.

Role of SiOxNy surface passivation layer on stability improvement and kink effect reduction of ELA poly silicon thin film transistors

The role of SiOxNy thin layer growth on excimer laser annealed (ELA) polysilicon, by N2O plasma treatment, on the stability improvement under prolonged operation and bias stress of TFT was investigated. After NH3 plasma treatment, field effect mobility in p-channel TFT devices increased from 50 to 76cm2V−1s−1, ON/OFF current ratio improved to 4.6×107, threshold voltage shrank from −9.8V to −7.7V and kink effect in the ID-VD characteristics was diminished. Using NH3 plasma treatment combined with SiOxNy layer indicated a lesser effectiveness in decreasing interface states, but better in reducing of the influence of mobile charges on TFT performance, than the previous approaches. An improvement in field effect mobility of 60.5cm2V−1s−1, excellent stability under bias stress of ±1MV·cm−1 for 2h with ΔVth~0.1V were achieved. We found that under NH3 plasma treatment combined with SiNxOy thin layer; the effect of hot carrier injection were reduced significantly due to creating the SiN, and SiO bonding at the interface of gate insulator and active layer. This result indicated that thin film transistor using NH3 plasma treatment with SiOxNy passivated layer promises to improve TFT performances with high field effect mobility, high ON/OFF current ratio, low leakage current and excellent stability.

Improvement in Field-Effect Mobility of Indium Zinc Oxide Transistor by Titanium Metal Reaction Method

This paper examined the effects of postdeposition annealing on the electrical properties of titanium-capped (TC) indium–zinc oxide (IZO) films and their IZO thin-film transistors. The TC IZO transistor oxidized at the temperature of 300 °C exhibited a high field-effect mobility of 61.0 cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{2}$ </tex-math></inline-formula> /Vs, low subthreshold gate swing of 110 mV/decade, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\rm th}$ </tex-math></inline-formula> of −0.4 V, and high <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I_{{\mathrm{{\scriptscriptstyle ON}}/\mathrm{{\scriptscriptstyle OFF}}}}$ </tex-math></inline-formula> ratio of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.3 \times 10^{8}$ </tex-math></inline-formula> . In addition, the positive gate bias stress-induced stability of the TC IZO transistor was better than that of the control device without metal capping treatment. This was attributed to the scavenging effect of the loosely bonded oxygen species in the IZO semiconductor by titanium thermal oxidation.

Growth-substrate induced performance degradation in chemically synthesized monolayer MoS2 field effect transistors

We report on the electronic transport properties of single-layer thick chemical vapor deposition (CVD) grown molybdenum disulfide (MoS2) field-effect transistors (FETs) on Si/SiO2 substrates. MoS2 has been extensively investigated for the past two years as a potential semiconductor analogue to graphene. To date, MoS2 samples prepared via mechanical exfoliation have demonstrated field-effect mobility values which are significantly higher than that of CVD-grown MoS2. In this study, we will show that the intrinsic electronic performance of CVD-grown MoS2 is equal or superior to that of exfoliated material and has been possibly masked by a combination of interfacial contamination on the growth substrate and residual tensile strain resulting from the high-temperature growth process. We are able to quantify this strain in the as-grown material using pre- and post-transfer metrology and microscopy of the same crystals. Moreover, temperature-dependent electrical measurements made on as-grown and transferred MoS2 devices following an identical fabrication process demonstrate the improvement in field-effect mobility.

52.4: Distinguished Paper: Electrical Properties of Amorphous InGaZnO Thin‐Film Transistors Prepared by Magnetron Sputtering with Using Kr and Xe Instead of Ar

AbstractHeavier noble gases of Kr and Xe instead of the lighter Ar during the magnetron‐sputtering deposition of amorphous indium—gallium‐zinc oxide films are introduced in fabricating their thin‐film transistors. Higher field effect mobility can be obtained by introducing heavier noble gases, while gate bias stability shows no significant difference between gas species. Raman spectroscopic analysis suggests that the disordered structure in the film is suppressed by introducing heavier noble gases. These results suggest that the introduction of heavy noble gases can reduce damage to film by ion bombardment during the sputtering depositions, resulting in the improvement of field effect mobility.

Ultrasound-Induced Ordering in Poly(3-hexylthiophene): Role of Molecular and Process Parameters on Morphology and Charge Transport

Facile methods for controlling the microstructure of polymeric semiconductors are critical to the success of large area flexible electronics. Here we explore ultrasonic irradiation of solutions of poly(3-hexylthiophene) (P3HT) as a simple route to creating ordered molecular aggregates that result in a one to two order of magnitude improvement in field effect mobility. A detailed investigation of the ultrasound induced phenomenon, including the role of solvent, polymer regioregularity (RR) and film deposition method, is conducted. Absorption spectroscopy reveals that the development of low energy vibronic features is dependent on both the regioregularity as well as the solvent, with the latter especially influential on the intensity and shape of the band. Use of either higher regioregular polymer or ultrasonic irradiation of lower regioregular polymer solutions results in high field effect mobilities that are nearly independent of the dynamics of the film formation process. Surprisingly, no distinct correlation between thin-film morphology and macroscopic charge transport could be ascertained. The relationships between molecular and process parameters are very subtle: modulation of one effects changes in the others, which in turn impact charge transport on the macroscale. Our results provide insight into the degree of control that is required for the development of reproducible, robust materials and processes for advanced flexible electronics based on polymeric materials.

Composition influence of SiN x gate insulator fabricated by radio frequency (RF) Magnetron sputtering on characteristics of organic thin-film transistors

To investigate the effect of composition of SiN x on the properties of organic thin-film transistors (OTFTs), we fabricated bottom gate top contact OTFTs devices with different composition SiN x gate insulator. Pentacene based OTFTs with SiN x insulator, prepared using an interface modification process of UV-ozone treatment, exhibited effective mobility of 0.63 cm2/Vs and on/off current ratio of 10 5. Overall improvement in field-effect mobility, threshold voltage was observed as silicon content in SiN x increases. The results demonstrate that the viability of using SiN x for OTFTs and of UV-ozone treatment could be used to improve the properties of organic thin-film transistors. The dependence of the contact angle on the SiN x film composition is evident for the untreated samples, the contact angle increases as the silicon content in the untreated nitride film increases. In contrast, the rise in contact angle across all samples after surface treatment signifies effective surface modification to promote hydrophobicity of the nitride surface. The hydrophobic surface is needed for the organic semiconductor.

A comparative study of plasma-enhanced chemical vapor gate dielectrics for solution-processed polymer thin-film transistor circuit integration

This paper considers plasma-enhanced chemical vapor deposited (PECVD) silicon nitride (SiNx) and silicon oxide (SiOx) as gate dielectrics for organic thin-film transistors (OTFTs), with solution-processed poly[5,5′-bis(3-dodecyl-2-thienyl)-2,2′-bithiophene] (PQT-12) as the active semiconductor layer. We examine transistors with SiNx films of varying composition deposited at 300 °C as well as 150 °C for plastic compatibility. The transistors show over 100% (two times) improvement in field-effect mobility as the silicon content in SiNx increases, with mobility (μFE) up to 0.14 cm2/V s and on/off current ratio (ION/IOFF) of 108. With PECVD SiOx gate dielectric, preliminary devices exhibit a μFE of 0.4 cm2/V s and ION/IOFF of 108. PQT-12 OTFTs with PECVD SiNx and SiOx gate dielectrics on flexible plastic substrates are also presented. These results demonstrate the viability of using PECVD SiNx and SiOx as gate dielectrics for OTFT circuit integration, where the low temperature and large area deposition capabilities of PECVD films are highly amenable to integration of OTFT circuits targeted for flexible and lightweight applications.

Thin-Film Morphology Control in Naphthalene-Diimide-Based Semiconductors: High Mobility n-Type Semiconductor for Organic Thin-Film Transistors

In organic thin film transistors (OTFT), the morphology and microstructure of an organic thin film has a strong impact on the charge carrier mobility and device characteristics. To have well-defined and predictable thin film morphology, it is necessary to adapt the basic structure of semiconducting molecules in a way that results in an optimum crystalline packing motif. Here we introduce a new molecular design feature for organic semiconductors that provides the optimized crystalline packing and thin film morphology that is essential for efficient charge-carrier transport. Thus, cyclohexyl end groups in naphthalene diimide assist in directing intermolecular stacking leading to a dramatic improvement in field effect mobility. Accordingly, OTFT devices prepared with vapor deposited N,N′-bis(cyclohexyl) naphthalene-1,4,5,8-bis(dicarboximide) (1) regularly exhibit field effect mobility near 6 cm2/(V s), which is one of the highest carrier mobilities reported for either n- or p-type organic semiconducting thin...

SiC MOSFET Channel Mobility Dependence on Substrate Doping and Temperature Considering High Density of Interface Traps

In prior work we have proposed a mobility model for describing the mobility degradation observed in SiC MOSFET devices, suitable for being implemented into a commercial simulator, including Coulomb scattering effects at interface traps. In this paper, the effect of temperature and doping on the channel mobility has been modelled. The computation results suggest that the Coulomb scattering at charged interface traps is the dominant degradation mechanism. Simulations also show that a temperature increase implies an improvement in field-effect mobility since the inversion channel concentration increases and the trapped charge is reduced due to bandgap narrowing. In contrast, increasing the substrate impurity concentration further degrades the fieldeffect mobility since the inversion charge concentration decreases for a given gate bias. We have good agreement between the computational results and experimental mobility measurements.

Flexible Organic Field-Effect Transistors Based on the Composites with the Same Thiophene Backbone by Wet Process

Organic field-effect transistors (OFETs) based on a composite with the same thiophene backbone were fabricated by spin coating using an annealing solution of poly(3-hexylthiophene) (PAT6) and α, ω-dihexylsexithiophene (DH-6T). The morphology of grains on the non-octadecyltrichlorosilane (OTS) treated and OTS treated gate insulators is granular and tube-like, respectively. The different morphologies of the OFETs with non-OTS treated and OTS-treated gate insulators result in the improvement of field-effect mobility. In the case of poly(ethylene naphthalate) substrate, an OFET with an 89 wt% DH-6T composite corresponding to two molecules of DH-6T per hexylthiophene repeating unit had a carrier mobility of 0.019 cm 2 /Vs.