Bottom-gate Top-contact Configuration Research Articles

High-performance organic field effect transistor of liquid crystalline organic semiconductor using silver electrodes with bottom-gate top-contact configuration

We have investigated organic field effect transistors (OFETs) fabricated with liquid crystalline organic semiconductor, 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-10), and silver (Ag) source-drain electrodes. Ph-BTBT-10 OFETs using Ag source-drain electrodes in bottom-gate top-contact configuration exhibit high mobility of 8.2 cm2 Vs−1, which is similar to those of gold (Au) electrodes. Contact resistance of Ph-BTBT-10 OFETs using Ag electrodes achieved 0.49 kΩcm by transfer length method, which is lower than those of Au electrodes, 2.7 kΩcm. Ph-BTBT-10 OFET using Ag source-drain electrodes in bottom-gate top-contact configuration is a promising candidate for high-performance and low-cost OFETs.

Characteristics assessment of TFT through 2D simulation under different material and structural configurations

This paper presents a performance analysis of indium-gallium-zinc-oxide (IGZO)- and pentacene-based top-gate-top-contact (TGTC) and bottom-gate-top-contact (BGTC) thin film transistors (TFTs). Extensive simulation has been performed to assess the performances in terms of threshold voltage, subthreshold slope, on-off current ratio, mobility, and figure of merit (FoM). Results indicate a trade-off between mobility and current ratio with respect to the permittivity of the dielectric layer, where tantalum oxide (Ta2O[Formula: see text] provides the optimum result in terms of FoM. The mobility of IGZO is significantly higher for both structures, whereas the current ratio for IGZO is higher than pentacene in the BGTC configuration. Comparing the structural configurations, Ta2O5-IGZO-based BGTC achieves [Formula: see text] and [Formula: see text] better mobility and current ratio, respectively, over TGTC structures. The threshold voltage of IGZO-based TFT is observed to increase with the permittivity of the dielectric in TGTC configuration but decrease in BGTC configuration. Meanwhile, the increase in oxide and active layer thicknesses causes a decrease in the threshold voltage. Moreover, both mobility and current ratio improve with a decrease in oxide or active layer thickness. Maximum mobility of 32.30[Formula: see text]cm2/Vs and a maximum current ratio of 7.54E+08 are achieved for Ta2O5-IGZO-based BGTC TFT with 10[Formula: see text][Formula: see text]m channel thickness and 5[Formula: see text][Formula: see text]m oxide thickness.

Submicron Channel Length High-Performance Metal Oxide Thin-Film Transistors

In this work, we present a new fabrication methodology to enable high-performance thin-film transistor (TFT) with submicron channel length. The method can exceed the resolution limit of a conventional photolithography compatible with large-area substrates such as a glass or a plastic. The lift-off and back-channel etching techniques were employed to delineate the channel in the bottom-gate top-contact configuration. The Al-doped InZnSnO TFTs with 0.8 μm channel length were successfully fabricated. Field-effect mobility of over 50 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Vs, subthreshold swing of 90 mV/dec, on/off current ratio of > 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> , and turn-on voltage of -0.24 V were obtained. Considering the compatibility with the current manufacturing process and facility, we expect that the method can be incorporated in an easy and cost-effective way into the TFT array for high-performance large-area electronics.

Asymmetrical [1]Benzothieno[3,2-b][1]benzothiophene (BTBT) derivatives for organic thin-film and single-crystal transistors

[1]benzothieno[3,2-b][1]benzothiophene (BTBT) derivatives are very famous organic semiconductors, however, researches on vacuum stability reveal that the BTBT core is unstable in vacuum, which was not conducive to systematically study the relationship between molecular structure and OFET performance. Two asymmetrical novel molecules based on BTBT adopting a new synthetic route were synthesized, namely TBTBT1 and TBTBT2, together with their optical, electrochemical and thermal characterizations were reported in this paper. The asymmetrical molecules were integrated as active layers on thin-film and single-crystal transistors with bottom-gate top-contact configuration, displaying p-type performance. Single crystal devices of TBTBT1 and TBTBT2 exhibit maximum mobility of 0.24 cm2V−1s−1 and 0.33 cm2V−1s−1, respectively. Moreover, both TBTBT1 and TBTBT2 single crystals demonstrated higher vacuum stability than BTBT, which provides opportunity for the easy fabrication of thin-film and single-crystal OFETs. Besides, the stable core molecules would enable further study of substituents effects to the packing motifs and OFET performance, which helps to understand the structure-property relationships to their undeveloped derivatives.

Importance of active layer positioning on gate electrode in organic thin-film transistors

ABSTRACTWe describe the importance of active layer positioning for a gate electrode in organic thin-film transistors (TFTs). For this study, we utilizea numerical simulation based on 2-D Atlas, which is a two-dimensional technology computer aided design (so called 2D TCAD) software tool created by Silvaco. Variation in the electrical characteristics of pentacene TFTs is systematically explored by changing the mismatch length (LM) between the active layer and gate electrode in the bottom-gate top-contact configuration. It is found that as the LM increases, the electrical performance of pentacene TFTs is exponentially degraded in terms of drain current on/off characteristics. In particular, we explain this phenomenon by examining variations in charge distribution and gate electric field in the TFT channel region byincreasing the LM.

Effect of morphological and physicochemical properties of dielectric-organic semiconductor interfaces on photoresponse of organic phototransistors

We investigate the effect of the interfacial properties between a polymer dielectric and an organic semiconductor (OS) layers on the photoresponse properties of an organic phototransistor (OPT). Three different polymer materials having different interfacial properties, poly(methyl methacrylate), amorphous fluoropolymer CYTOP, and poly(4-vinylphenol), were used as gate insulators for the OPTs in a bottom-gate top-contact configuration. For the trapping and detrapping processes of minority carriers, the physicochemical nature and the density of functional group of the dielectric material were found to more dominantly govern the photoresponsive properties of the OPT than the morphological effect. Our molecular level description provides a useful guideline to select a proper dielectric material, being used as a gate insulator, for optical applications of the OPTs such as optical memory devices and optical sensors.

Numerical simulation study of organic nonvolatile memory with polysilicon floating gate

A polysilicon-based organic nonvolatile floating-gate memory device with a bottom-gate top-contact configuration is investigated, in which polysilicon is sandwiched between oxide layers as a floating gate. Simulations for the electrical characteristics of the polysilicon floating gate-based memory device are performed. The shifted transfer characteristics and corresponding charge trapping mechanisms during programing and erasing (P/E) operations at various P/E voltages are discussed. The simulated results show that present memory exhibits a large memory window of 57.5 V, and a high read current on/off ratio of ≈ 103. Compared with the reported experimental results, these simulated results indicate that the polysilicon floating gate based memory device demonstrates remarkable memory effects, which shows great promise in device designing and practical application.

Electrical Instability in Pentacene Transistors with Mylar and PMMA/Mylar Gate Dielectrics Transferred by Lamination Process

This study deals with electrical instability under bias stress in pentacene-based transistors with gate dielectrics deposited by a lamination process. Mylar film is laminated onto a polyethylene terephthalate (PET) substrate, on which aluminum (Al) gate is deposited, followed by evaporation of organic semiconductor and gold (Au) source/drain contacts in bottom gate top contact configuration (Device 1). In order to compare the influence of the semiconductor/dielectric interface, a second organic transistor (Device 2) which is different from the Device 1 by the deposition of an intermediate layer of polymethyl methacrylate (PMMA) onto the laminated Mylar dielectric and before evaporating pentacene layer is fabricated. The critical device parameters such as threshold voltage (VT), subthreshold slope (S), mobility (μ), onset voltage (Von) and Ion/Ioff ratio have been studied. The results showed that the recorded hysteresis depend on the pentacene morphology. Moreover, after bias stress application, the electrical parameters are highly modified for both devices according to the regimes in which the transistors are operating. In ON state regime, Device 1 showed a pronounced threshold voltage shift associated to charge trapping, while keeping the μ, Ioff current and S minimally affected. Regardless of whether Device 2 exhibited better electrical performances and stability in ON state, we observed a bias stress-induced increase of depletion current and subthreshold slope in subthreshold region, a sign of defect creation. Both devices showed onset voltage shift in opposite direction.

Comparative study of source–drain contact metals for amorphous InGaZnO thin‐film transistors

AbstractIn this work, we compared the thin‐film transistor (TFT) characteristics of amorphous InGaZnO TFTs with six different source–drain (S/D) metals (MoCr, TiW, Ni, Mo, Al, and Ti/Au) fabricated in bottom‐gate bottom‐contact (BGBC) and bottom‐gate top‐contact (BGTC) configurations. In the BGTC configuration, nearly every metal can be injected nicely into the a‐IGZO leading to nice TFT characteristics; however, in the BGBC configuration, only Ti/Au is injected nicely and shows comparable TFT characteristics. We attribute this to the metal‐containing deposits in the channel and the contact oxidation during a‐IGZO layer sputtering in the presence of S/D metal. In bias‐stress stability, TFTs with Ti/Au S/D metal showed good results in both configurations; however, in the BGTC configuration, not all the TFTs showed as good bias results as Ti/Au S/D metal TFTs. We attribute this to backchannel interface change, which happened because of the metal‐containing deposits at the backchannel during the final the SiO2 passivation.

Thin film transistors fabricated by evaporating pentacene under electric field

Organizing the pentacene molecules with respect to the substrate is an essential prerequisite for achieving high field effect mobility in organic thin film transistors. Here, we report electrical characteristics of bottom gate, top contact Sin++/SiO2/pentacene/gold thin film transistors using electric field assisted thermal evaporation of pentacene. We find that the field assisted devices exhibit a five-fold enhancement in the field effect mobility, along with improvement in the saturation current as compared with a standard device. Simulation of electric field distribution in the substrate-electrode arrangement due to the application of external voltage during pentacene deposition shows an existence of a non-uniform electric field in the bottom gate top contact configuration and hence another configuration that avoids metal before pentacene deposition is proposed. The observed improvement in the transistor characteristics of field assisted device is explained by ab-initio calculation of anisotropy in the polarizability of isolated pentacene molecule, followed by an estimate of molecules that would align due to the field. Furthermore, the preferential molecular alignment in field deposited pentacene films is confirmed using X-ray diffraction and atomic force microscopy.