μFE Values Research Articles

High performance electric-double-layer amorphous IGZO thin-film transistors gated with hydrated bovine serum albumin protein

Device performance of amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs) has been improved greatly by using bovine serum albumin (BSA) as the top gate dielectric. BSA is a natural protein with acidic and basic amino acid residues, which is easily hydrated in air ambient. A typical a-IGZO TFT with hydrated BSA as the top gate dielectric exhibits a field-effect mobility (μFE) value of 113.5cm2V−1s−1 in saturation regime and a threshold voltage (VTH) value of 0.25V in air ambient. The excellent device performance can be well explained by the formation of electric double layers (EDLs) near the interfaces of a-IGZO/hydrated BSA and hydrated BSA/gate electrode. The reliability issue of a-IGZO TFTs gated with hydrated BSA has been also investigated by using the life time test without encapsulation. The VTH value increases and μFE,sat value reduces slightly for the a-IGZO TFT and remain stabilized over 60days.

Facile Route to the Controlled Synthesis of Tetragonal and Orthorhombic SnO2 Films by Mist Chemical Vapor Deposition.

Two types of tin dioxide (SnO2) films were grown by mist chemical vapor deposition (Mist-CVD), and their electrical properties were studied. A tetragonal phase is obtained when methanol is used as the solvent, while an orthorhombic structure is formed with acetone. The two phases of SnO2 exhibit different electrical properties. Tetragonal SnO2 behaves as a semiconductor, and thin-film transistors (TFTs) incorporating this material as the active layer exhibit n-type characteristics with typical field-effect mobility (μ(FE)) values of approximately 3-4 cm(2)/(V s). On the other hand, orthorhombic SnO2 is found to behave as a metal-like transparent conductive oxide. Density functional theory calculations reveal that orthorhombic SnO2 is more stable under oxygen-rich conditions, which correlates well with the experimentally observed solvent effects. The present study paves the way for the controlled synthesis of functional materials by atmospheric pressure growth techniques.

High mobility 4H-SiC (0001) transistors using alkali and alkaline earth interface layers

Alkali (Rb and Cs) and alkaline earth (Ca, Sr, and Ba) elements have been investigated as interface passivation materials for metal-oxide-semiconductor field-effect transistors (MOSFETs) on 4H-SiC (0001). While the alkali elements Rb and Cs result in field-effect mobility (μFE) values > 25 cm2/V·s, the alkaline earth elements Sr and Ba resulted in higher μFE values of 40 and 85 cm2/V·s, respectively. The Ba-modified MOSFETs show a slight decrease in mobility with heating to 150 °C, as expected when mobility is not interface-trap-limited, but phonon-scattering-limited. With a Ba interface layer, the interface state density 0.25 eV below the conduction band is ∼3 × 1011 cm−2 eV−1, lower than that obtained with nitric oxide passivation. Devices show stable threshold voltage under 2 MV/cm gate bias stress at 175 °C, indicating no mobile ions. Secondary-ion mass spectrometry shows that the Sr and Ba stay predominantly at the interface after oxidation anneals.

Materials and interfaces issues in pentacene/PTCDI-C8 ambipolar organic field-effect transistors with solution-based gelatin dielectric

Gelatin is a natural protein, which works well as the gate dielectric for pentacene/N,N-dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C8) ambipolar organic field-effect transistors (OFETs) in air ambient and in vacuum. An aqueous solution process was used to form the gelatin gate dielectric film on poly(ethylene terephthalate) (PET) by spin-coating and subsequent casting. Pentacene morphology and interface roughness are two major factors affecting the electron and hole field-effect mobility (μFE) values of pentacene/PTCDI-C8 ambipolar OFETs in vacuum and in air ambient. In contrast, water absorption in gelatin has higher contribution to the electron and hole μFE values in air ambient. The ambipolar performance of pentacene/PTCDI-C8 ambipolar OFETs depends on their layer sequence. For example, when PTCDI-C8 is deposited onto pentacene, i.e. in the structure of PTCDI-C8/pentacene, unbalanced ambipolar characteristics appear. In contrast, better ambipolar performance occurs in the structure of pentacene/PTCDI-C8. The optimum ambipolar characteristics with electron μFE of 0.85cm2V−1s−1 and hole μFE of 0.95cm2V−1s−1 occurs at the condition of pentacene (40nm)/PTCDI-C8 (40nm). Surprisingly, water absorption plays a crucial role in ambipolar performance. The device performance changes tremendously in pentacene/PTCDI-C8 ambipolar OFETs due to the removal of water out of gelatin in vacuum. The optimum ambipolar characteristics with electron μFE of 0.008cm2V−1s−1 and hole μFE of 0.007cm2V−1s−1 occurs at the condition of pentacene (65nm)/PTCDI-C8 (40nm). The roles of layer sequence, relative layer thickness, and water absorption are proposed to explain the ambipolar performance.

Investigation of silicon grain structure and electrical characteristics of TFTs fabricated using different crystallized silicon films by atmospheric pressure micro-thermal-plasma-jet irradiation

Amorphous silicon (a-Si) films were crystallized using three grain growth modes induced by micro-thermal-plasma-jet (µ-TPJ) irradiation and applied to the channel regions of thin-film transistors (TFTs). Solid phase crystallization (SPC) formed microcrystalline grains and showed a lower crystallinity of 70%, whereas leading wave crystallization (LWC) and high-speed lateral crystallization (HSLC) formed significantly larger grains than the TFT channel region. The SPC-TFT showed a lower field-effect mobility (μFE) due to the small grain size and the existence of many grain boundaries, whereas LWC- and HSLC-TFT channels were formed by only single grains and showed a μFE higher than 300 cm2 V−1 s−1 in the n-channel. The defect density of HSLC was smaller than that of LWC; consequently, the HSLC-TFT performed better than the LWC-TFT. The maximum μFE values of n- and p-channel HSLC-TFTs were 418 and 224 cm2 V−1 s−1, respectively.

Solution-based silk fibroin dielectric in n-type C60 organic field-effect transistors: Mobility enhancement by the pentacene interlayer

A pentacene interlayer of 2 nm thick is inserted between fullerene (C60) and the solution-based silk fibroin dielectric in C60 organic field-effect transistors (OFETs). The pentacene interlayer assists to improve crystal quality of the C60 layer, leading to the increase of field-effect mobility (μFE) from 0.014 to 1 cm2 V−1 s−1 in vacuum. The μFE value of the C60 OFET is further enhanced to 10 cm2 V−1 s−1 when the OFET is exposed to air in a relative humidity of 55%. Generation of mobile and immobile charged ions in solution-based silk fibroin in air ambient is proposed.

Enhanced mobility of organic thin film transistors by water absorption of collagen hydrolysate gate dielectric

Collagen hydrolysate is a nature protein, which works well as the gate dielectric for organic thin film transistors (OTFTs). The pentacene OTFTs exhibit a field-effect mobility (μFE) value of 0.8 cm2V−1s−1 and an on/off ratio of 105 in vacuum. The drain current is greatly enhanced and the μFE value increases to ca. 15.5 cm2V−1s−1 when OTFTs are exposed to air. The enhancement of μFE is attributed to the interaction of water and OH-groups in collagen hydrolysate in air ambient.

Pentacene organic thin-film transistors with solution-based gelatin dielectric

Gelatin is a natural protein in the field of food, pharmaceutical and tissue engineering, which works very well as the gate dielectric for pentacene organic thin-film transistors (OTFTs). An aqueous solution process has been applied to form a gelatin thin film on poly(ethylene terephthalate) (PET) or glass by spin-coating and subsequent casting. The device performance of pentacene OTFTs depend on the bloom number (molecular weight) of gelatin. The pentacene OTFT with 300 bloom gelatin as the gate dielectric in air ambient exhibits the best performance with an average field-effect mobility (μFE) value of ca. 16cm2V−1s−1 in the saturation regime and a low threshold voltage of −1V. The high performance of the pentacene OTFT in air ambient is attributed to the water resided in gelatin. The crystal quality of pentacene is not the key factor for the high performance.

High performance Zn–Sn–O thin film transistors with Cu source/drain electrode

AbstractZn–Sn–O (ZTO) thin film transistors (TFTs) were fabricated with a Cu source/drain electrode. Although a reasonably high mobility (μFE) of 13.2 cm2/Vs was obtained for the ZTO TFTs, the subthreshold gate swing (SS) and threshold voltage (Vth) of 1.1 V/decade and 9.1 V, respectively, were inferior. However, ZTO TFTs with Ta film inserted as a diffusion barrier, exhibited improved SS and Vth values of 0.48 V/decade and 3.0 V, respectively as well as a high μFE value of 18.7 cm2/Vs. The improvement in the Ta‐inserted device was attributed to the suppression of Cu lateral diffusion into the ZTO channel region. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Mobility enhancement by using silk fibroin in F16CuPc organic thin film transistors

High performance n-type F16CuPc organic thin-film transistors (OTFTs) were fabricated on polyethylene terephthalate (PET) using silk fibroin as the gate dielectric. The average field-effect mobility (μFE) value in the saturation regime is 0.39cm2V−1s−1 approximately one order of magnitude higher than the reported values in the literature. A typical F16CuPc OTFT exhibits an on/off current ratio of 9.3×102, a low threshold voltage of 0.65V, and a subthreshold swing value of 730mV/decade. The enhancement of μFE results from very good crystal quality of F16CuPc on silk fibroin, supported by grazing incidence X-ray diffraction (GIXD) data.

Investigation on the relationship between channel resistance and subgap density of states of amorphous InGaZnO thin film transistors

The demand for amorphous InGaZnO (a-IGZO) thin film transistors (TFTs) has increased due to their transparent properties. In this paper, we report on the relationship between the subgap density of states (DOS), field-effect mobility (μFE), and unit channel length resistance (rch) on the electrical properties of a-IGZO TFTs. The three tested structures had the same channel width/length and gate insulator thickness with different gate insulator materials, SiNX, SiOX, and SiOX/SiNX. Compared to TFTs with low subgap DOS levels, TFTs with high subgap DOS levels have low μFE values due to the relatively large rch values.

Investigation on the Doping Dependence of Solution-Processed Zinc Tin Oxide Thin Film and Thin-Film Transistors

The effect of the tin (Sn) concentration in zinc tin oxide (ZTO) films fabricated using a spin-coating process and its effect on ZTO channel thin film transistors (TFTs) with various Sn concentrations were examined. Spin-coated ZTO films with various Sn concentrations were nanocrystalline and had high transmittance (>85%) in the visible region. As the Sn concentration increased, the carrier concentration and resistivity of the nanocrystalline ZTO (nc-ZTO) films ranged from 9.6 × 1014 cm−3 to 2.2 × 1016 cm−3 and from 1.5 × 103 Ω-cm to 1.6 × 102 Ω-cm, respectively. The nc-ZTO channel TFTs that were deposited as a function of Sn and Zn concentrations exhibited a subthreshold gate voltage swing (S) of 1.1–1.2 V decade−1, an on/off ratio of 105–106, a threshold voltage (Vth) of -0.8–1.7 V, and a μFE value of 2.4–2.6 cm2 V−1 s−1. The threshold voltage shift toward the negative gate bias as the Sn concentration in the nc-ZTO TFTs increased indicates the existence of sufficient charge carriers needed to form conductive channels.

Impact of high-k TiOx dielectric on device performance of indium-gallium-zinc oxide transistors

We investigated the effect of the high-k TiOx (k∼40) gate dielectric on the mobility (μFE) of indium-gallium-zinc oxide (IGZO) transistors. As the thickness of the TiOx layer at the interface of the IGZO channel and SiNx gate dielectric layer increased from 2 to 8 nm, the μFE value was monotonously reduced from 9.9 to 1.8 cm2/V s. The degradation of the mobility was attributed to the Coulomb scattering mechanism rather than the phonon scattering mechanism of the high-k TiOx layer based on the behavior of the temperature-dependent mobilities for all of the IGZO transistors.

Magnetic properties of amorphous B-rich R-Fe-B alloys

The magnetic properties of amorphous and crystallized B-rich R-Fe-B alloys with R=Y, Pr, Nd, and Gd have been studied from 4.2 to 300 K using ac susceptibility and SQUID magnetometry. The amorphous samples with R=Y, Pr, and Nd show spin-glass-type transitions with ordering temperatures at about 150, 200, and 250 K, respectively. The magnetization of the samples is found to decrease from light to heavy rare earths to yttrium corresponding to μFe values from 1.35 to 0.74 μB. The magnetic properties can be explained by a noncollinear arrangement of the rare-earth and Fe magnetic moments. Crystallized samples consist of multiple phases with R1.1Fe4B4 as the majority phase; for the 12% Nd sample Fe2B is believed to be one of the minority phases while for 13% Nd the minority phase is R2Fe14B.