A comparative analysis of thin-film transistors using aligned and random-network carbon nanotubes

The purpose of this project is to investigate the characterization of carbon nanotube (CNT) thin-film transistors based on two solution-based fabrication methods: dielectrophoretic deposition of aligned CNTs and self-assembly of random-network CNTs. The electrical characteristics of aligned and random-network CNT transistors are studied comparatively. In particular, the selection effect of metallic and semiconducting CNTs in the dielectrophoresis process is evaluated experimentally by comparing the output characteristics of the two transistors. Our results demonstrate that the self-assembly method produces a stronger field effect with a much higher on/off ratio (I _on /I _off ). This phenomenon provides evidence that the metallic CNTs are more responsive to dielectrophoretic forces than their semiconducting counterparts under common deposition conditions. In addition, the nanotube–nanotube cross-junctions in random-network CNT films create additional energy barriers and result in a reduced electric current. Thus, additional consideration must be applied when using different fabrication methods in building CNT-based electronic devices.     

Laser printing and characterization of semiconducting polymers for organic electronics

Hybrid organic/inorganic thin-film transistors (TFTs) with bottom-contact configuration were fabricated using the Laser Induced Forward Transfer (LIFT) process. The semiconducting polymer P3HT was laser printed from a donor to a receiver substrate in order to form the active layer of the TFTs. With a single laser pulse, P3HT pixels were successfully printed. The printed material was analyzed morphologically by means of Optical Microscopy and its thickness was measured by profilometry. In addition, structural characterization of P3HT thin films before and after laser printing took place by using UV-Visible absorption spectroscopy and X-Ray Diffraction. It was found that the crystallinity of the investigated films is improved upon annealing. An organic thin-film transistor (OTFT) with laser printed P3HT pixel as a channel layer was then fabricated. The OTFTs indicated a field-effect mobility up to 2.23?10^?4 cm²/Vs and an on/off ratio on the order of 10–100.     

氧化锌锡薄膜晶体管的研究

在ITO玻璃基底上用射频磁控溅射技术生长氧化锌锡(ZnSnO)沟道有源层、用PECVD生长SiO₂薄膜作为薄膜晶体管的栅绝缘层研制了薄膜晶体管(TFT), 器件的场效应迁移率最高达到μ_n=9.1 cm²/(V ·s),阈值电压-2 V,电流开关比为10⁴. 关键词： 氧化锌锡 薄膜晶体管 场效应迁移率     

Room-temperature fabrication of ultra-thin ZrOx dielectric for high-performance InTiZnO thin-film transistors

In this letter, indium–titanium–zinc–oxide thin-film transistors with zirconium oxide (ZrO_x) gate dielectric were fabricated at room temperature. In the devices, an ultra-thin ZrO_x layer was formed as the gate dielectric by sol–gel process followed by ultraviolet (UV) irradiation. The devices can be operated under a voltage of 4 V. Enhancement mode operations with a high field-effect mobility of 48.9 cm²/V s, a threshold voltage of 1.4 V, a subthreshold swing of 0.2 V/decade, and an on/off current ratio of 10⁶ were realized. Our results demonstrate that UV-irradiated ZrO_x dielectric is a promising gate dielectric candidate for high-performance oxide devices.     

Surface-modified lead–zirconium-titanate system for solution-processed ferroelectric-gate thin-film transistors

We propose the use of a La₂O₃ (LO) film as the capping layer for improvement of a semiconductor/insulator interface in a solution-processed indium–tin–oxide (ITO) ferroelectric-gate thin-film transistor (FGT) device. It is demonstrated that the LO layer acts as a good barrier film not only for preventing the interdiffusion between the ITO semiconductor and lead–zirconium-titanate (PZT) insulator layers, but also for stabilizing the PZT surface structure. The fabricated FGT device exhibited high I _on/I _off, large M _w, high μ _FE and improved retention time of about 10⁹, 3.5 V, 7.94 cm²?V^?1?s^?1 and 1 day, respectively, which are comparable to or better than those obtained with FGTs fabricated by means of conventional vacuum processes. We also point out that the key origin of the interface improvement is likely due to the incorporation of La into the PZT system, forming a La surface-modified PZT system which is more stable than the pure PZT in terms of Pb volatility and formation of oxygen vacancies.     

Indium oxide, tin oxide and indium tin oxide nanostructure growth by vapor deposition

Indium oxide, tin oxide and indium tin oxide nanowires have been grown by vapor deposition on Si and quartz substrates. Under the growth conditions used, pure SiO_x nanowires, a mixture of SiO_x and indium oxide, tin oxide or indium tin oxide nanostructures, or pure indium oxide, tin oxide or indium tin oxide nanostructures could be obtained at different substrate temperatures. The growth mechanism of the obtained nanostructures at different substrate temperatures is discussed. Optical and electrical properties of the deposited pure indium oxide, tin oxide or indium tin oxide nanostructures have been measured, and low sheet resistances on quartz substrates have been obtained for indium oxide and indium tin oxide nanostructures.     

高迁移率非晶铟镓锌氧化物薄膜晶体管的制备与特性研究

由于铟镓锌氧化物(IGZO) 薄膜具有高迁移率和高透过率的特点, 它作为有源层被广泛的应用于薄膜晶体管(TFT). 本文利用磁控溅射方法制备了TFT的有源层IGZO和源漏电极, 用简单低成本的掩膜法控制沟道的尺寸, 制备了具有高迁移率、底栅结构的n型非晶铟镓锌氧化物薄膜晶体管 (IGZO-TFT). 利用X 射线衍射仪(XRD) 和紫外可见光分光光度计分别测试了IGZO薄膜的衍射图谱和透过率图谱, 研究了IGZO薄膜的结构和光学特性. 通过测试IGZO-TFT的输出特性和转移特性曲线, 讨论了IGZO有源层厚度对IGZO-TFT特性的影响. 制备的IGZO-TFT器件的场效应迁移率高达15.6 cm²·V^-1·s^-1, 开关比高于10⁷. 关键词： 非晶铟镓锌氧化物 薄膜晶体管 有源层     

Enhancement of long-term stability of pentacene thin-film transistors encapsulated with transparent SnO2

The long-term stability of pentacene thin-film transistors (TFTs) encapsulated with a transparent SnO₂ thin-film prepared by ion beam-assisted deposition (IBAD) was investigated. After encapsulation process, our organic thin-film transistors (OTFTs) showed somewhat degraded field-effect mobility of 0.5 cm²/(V s) that was initially 0.62 cm²/(V s), when a buffer layer of thermally evaporated 100 nm SnO₂ film had been deposited prior to IBAD process. However, the mobility was surprisingly sustained up to 1 month and then gradually degraded down to 0.35 cm²/(V s) which was still three times higher than that of the OTFT without any encapsulation layer after 100 days in air ambient. The encapsulated OTFTs also exhibited superior on/off current ratio of over 10⁵ to that of the unprotected devices (∼10⁴) which was reduced from ∼10⁶ before aging. Therefore, the enhanced long-term stability of our encapsulated OTFTs should be attributed to well protection of permeation of H₂O and O₂ into the devices by the IBAD SnO₂ thin-film which could be used as an effective inorganic gas barrier for transparent organic electronic devices.     

Fabrication of a solution-processed thin-film transistor using zinc oxide nanoparticles and zinc acetate

We have fabricated a solution-processed ZnO thin-film transistor without vacuum deposition. ZnO nanoparticles were prepared by the polyol method from zinc acetate, polyvinyl pyrrolidone, and diethyleneglycol. The solution-processable semiconductor ink was prepared by dispersing the synthesized ZnO in a solvent. Inverted stagger type thin-film transistors were fabricated by spin casting the ZnO ink on the heavily doped Si wafer with 200 nm thick SiO₂, followed by evaporation of Cr/Au source and drain electrodes. After the drying and heat treatment at 600 C, a relatively dense ZnO film was obtained. The film characteristics were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). In order to obtain the electrical properties of the solution-derived transistor, the on–off ratio, threshold voltage, and mobility were measured.     

Comparison of effect of 5 MeV proton and Co-60 gamma irradiation on silicon NPN rf power transistors and N–channel depletion MOSFETs

NPN transistors and N-channel depletion metal oxide semiconductor field effect transistors (MOSFETs) were irradiated with 5?MeV protons and ⁶⁰Co gamma radiation in the dose ranging from 1?Mrad(Si) to 100?Mrad(Si). The different electrical characteristics of the NPN transistor such as Gummel characteristics, excess base current (ΔI_B), dc current gain (h_FE), transconductance (g_m), displacement damage factor (K) and output characteristics were studied as a function of total dose. The different electrical characteristics of N-channel MOSFETs such as threshold voltage (V_th), density of interface trapped charges (ΔN_it), density of oxide trapped charges (ΔN_ot), transconductance (g_m), mobility (µ) and drain saturation current (I_DSat) were studied systematically before and after irradiation in the same dose ranges. A considerable increase in the base current (I_B) and decrease in the h_FE, g_m and collector saturation current (I_CSat) were observed after irradiation in the case of the NPN transistor. In the N-channel MOSFETs, the ΔN_it and ΔN_ot were found to increase and V_th, g_m, µ and I_DSat were found to decrease with increase in the radiation dose. The 5?MeV proton irradiation results of both the NPN transistor and N-channel MOSFETs were compared with ⁶⁰Co gamma-irradiated devices in the same dose ranges. It was observed that the degradation in 5?MeV proton-irradiated devices is more when compared with the ⁶⁰Co gamma-irradiated devices at higher total doses.     

Influence of high energy electron irradiation on the characteristics of polysilicon thin film transistors

The influence of high energy electron (23 MeV) irradiation on the electrical characteristics of p-channel polysilicon thin film transistors (PSTFTs) was studied. The channel 220 nm thick LPCVD (low pressure chemical vapor deposition) deposited polysilicon layer was phosphorus doped by ion implantation. A 45 nm thick, thermally grown, SiO2 layer served as gate dielectric. A self-alignment technology for boron doping of the source and drain regions was used. 200 nm thick polysilicon film was deposited as a gate electrode. The obtained p-channel PSTFTs were irradiated with different high energy electron doses. Leakage currents through the gate oxide and transfer characteristics of the transistors were measured. A software model describing the field enhancement and the non-uniform current distribution at textured polysilicon/oxide interface was developed. In order to assess the irradiation-stimulated changes of gate oxide parameters the gate oxide tunneling conduction and transistor characteristics were studied. At MeV dose of 6×10¹³ el/cm², a negligible degradation of the transistor properties was found. A significant deterioration of the electrical properties of PSTFTs at MeV irradiation dose of 3×10¹⁴ el/cm² was observed.     

A hydrogen peroxide electrochemical sensor based on Ag nanoparticles grown on ITO substrate

In this article, the Ag nanoparticles were synthesized on indium tin oxide conducting glass (ITO) substrate using the electrochemical deposition method. The morphology analysis of the deposits using scanning electron microscope (SEM) reveals that the sizes and densities of the Ag nanoparticles were tuned by varying the time of electrodeposition. The structure of the deposits was characterized by X-ray diffraction (XRD). The prepared Ag nanoparticles electrode was then applied to detect hydrogen peroxide (H₂O₂) in 0.01 M pH 7.0 phosphate buffer medium. The present electrochemical sensing platform exhibited good electrocatalytic activity towards the reduction of H₂O₂. The detection sensitivity of the sensor was 0.237 mA mM⁻¹. This method is very simple, inexpensive, and undemanding, thus it should be extensively applied in many fields for the detection of H₂O₂.     

Properties of C60 thin film transistor based on polystyrene

This paper reports that the n-type organic thin-film transistors have been fabricated by using C60 as the active layer and polystyrene as the dielectric.The properties of insulator and the growth characteristic of C60 film were carefully investigated.By choosing different source/drain electrodes,a device with good performance can be obtained.The highest electron field effect mobility about 1.15 cm 2 /(V·s) could reach when Barium was introduced as electrodes.Moreover,the C60 transistor shows a negligible 'hysteresis effect' contributed to the hydroxyl-free of insulator.The result suggests that polymer dielectrics are promising in applications among n-type organic transistors.     

Electrochromic properties of WO3 thin film onto gold nanoparticles modified indium tin oxide electrodes

Gold nanoparticles (GNPs) thin films, electrochemically deposited from hydrogen tetrachloroaurate onto transparent indium tin oxide (ITO) thin film coated glass, have different color prepared by variation of the deposition condition. The color of GNP film can vary from pale red to blue due to different particle size and their interaction. The characteristic of GNPs modified ITO electrodes was studied by UV-vis spectroscopy, scanning electron microscope (SEM) images and cyclic voltammetry. WO₃ thin films were fabricated by sol-gel method onto the surface of GNPs modified electrode to form the WO₃/GNPs composite films. The electrochromic properties of WO₃/GNPs composite modified ITO electrode were investigated by UV-vis spectroscopy and cyclic voltammetry. It was found that the electrochromic performance of WO₃/GNPs composite films was improved in comparison with a single component system of WO₃.     

Influence of self-assembled monolayer chain length on modified gate dielectric pentacene thin-film transistors

Self-assembled monolayers are widely used to modify the gate dielectric/semiconductor interface in organic thin-film transistors. By modifying the interaction between the molecular semiconductor and the substrate, thin-film ordering and the electronic properties of the semiconducting channel can be controlled. The modified semiconductor/dielectric properties result in macroscopically observed changes in the charge-carrier mobilities, threshold voltages, subthreshold swing and transfer characteristic hysteresis. The latter two are determined by the density of charge-trapping states at the interface. Here, we investigate the influence of the thickness of the self-assembled monolayer, via the alkyl chain length in n-alkyl phosphonic acid-based monolayers on SiO₂, on the electronic properties of pentacene-based organic thin-film transistors. Rather than a monotonic increase or decrease in performance with increasing chain length, we have found that the optimum performance occurs with chains of 8–10 carbon atoms. Atomic force microscopy shows a correlation between pentacene crystalline grain size and transistor performance.     

The effects of high-energy ion irradiations on the I–V characteristics of silicon NPN transistors

The silicon NPN rf power transistors were irradiated with different linear energy transfer (LET) ions such as 50?MeV Li³⁺, 80?MeV C⁶⁺ and 150?MeV Ag¹²⁺ ions in the dose range of 1–100?Mrad. The SRIM simulation was used to understand the energy loss and range of these ions in the transistor structure. The different electrical parameters such as Gummel characteristics, excess base current (ΔI_B), DC current gain (h_FE), displacement damage factor (K) and output characteristics were systematically studied before and after irradiation. The ion irradiation results were compared with ⁶⁰Co-gamma irradiation result in the same dose range. A considerable increase in base current (I_B) and a decrease in h_FE and I_CSat were observed after irradiation. The degradation in the electrical parameters was comparably very high for Ag¹²⁺ ion-irradiated transistor when compared to other ion-irradiated transistors, whereas the degradation in the electrical parameters for Li³⁺ and C⁶⁺ ion-irradiated transistors was comparable with gamma-irradiated transistor. The isochronal annealing study was conducted on the 100?Mrad irradiated transistors up to 500°C to analyze the recovery in different electrical parameters. The h_FE and other electrical parameters of irradiated transistors were almost recovered after 500°C for 50?MeV Li³⁺, 80?MeV C⁶⁺ ion and ⁶⁰Co-gamma-irradiated transistors, whereas for 150?MeV Ag¹²⁺ ion-irradiated transistor, the recovery in electrical characteristics is not complete.     

Modelling of contact effects in microcrystalline silicon thin-film transistors

Hydrogenated microcrystalline silicon has recently emerged as a promising material system for large-area electronic applications such as thin-film transistors and solar cells. In this paper, thin-film transistors based on microcrystalline silicon were realized with charge carrier mobilities exceeding 40 cm²/Vs. The electrical characteristics of the microcrystalline silicon thin-film transistors are limited by the influence of contact effects. The influence of the contact effects on the charge carrier mobility was investigated for transistors with different dimensions of the drain and source contacts. The experimental results were compared to an electrical model which describes the influence of the drain and source contact dimension on the transistor parameters. Furthermore, the Transmission Line Method was applied to investigate the contact effects of the thin-film transistors with different drain and source contact dimensions. Finally, optimized device geometries like the channel length of the transistor and dimension of the drain and source contacts were derived for the microcrystalline transistors based on the electrical model.     

Improving the color purity and efficiency of blue organic light-emitting diodes (BOLED) by adding hole-blocking layer

This work demonstrates the fabrication of a bright blue organic light-emitting diode (BOLED) with good color purity using 4,4′-bis(2,2-diphenylvinyl)-1,1′-biphenyl (DPVBi) and bathocuproine (BCP) as the emitting layer (EML) and the hole-blocking layer (HBL), respectively. Devices were prepared by vacuum deposition on indium tin oxide (ITO)-glass substrates. The thickness of DPVBi used in the OLED has an important effect on color and efficiency. The blue luminescence is maximal at 7670 cd/m² when 13 V is applied and the BCP thickness is 2 nm. The CIE coordinate at a luminance of 7670 cd/m² is (0.165, 0.173). Furthermore, the current efficiency is maximum at 4.25 cd/A when 9 V is applied.     

Highly uniform electrochromic tungsten oxide thin films deposited by e-beam evaporation for energy saving systems

In the last few decades, there has been a surge of interest in using tungsten oxide thin films as an active layer of electrochromic device. These devices have several practical applications such as smart window of buildings and automobile glazing for energy saving. The main objective of this work was to construct highly homogeneous and uniform e-beam evaporated amorphous WO_3-x based films into electrochromic devices, which were fully characterized for switching speed, coloration efficiencies and cycling voltammetry responses. Fabricated devices contain indium doped transparent oxide coated glass as the transparent conductive electrode, ～200?nm thickness of WO_3-x as the cathodically coloring material and a lithium perchlorate based conducting gel electrolyte. X-ray diffraction patterns indicate that all as-deposited films are amorphous. Experimental results showed that both solid and liquid electrolyte electrochromic devices are initially very transparent that exhibit perfect optical modulation and coloration efficiency (up to 68.7?cm²/C and 52.6?cm²/C at 630?nm, respectively) due to easier intercalation of the Li⁺ within their structure. One of the more significant findings to emerge from this study is that e-beam coated electrochromic devices based on tungsten oxide thin films showed superior performance among to other coating methods. Therefore, excellent reversibility of color change behavior is attractive for pertinent use in electrochromic energy storage devices.     

大面积金纳米线光栅的制备

利用激光干涉光刻和金纳米颗粒胶体溶液制备了宽度在100 nm以下且总面积达到平方厘米量级的金纳米线光栅结构.制备过程中,首先在表面镀有厚度约为200 nm的铟锡氧化物薄膜的面积为1 cm×1 cm的玻璃基片表面旋涂光刻胶,然后利用紫外激光干涉光刻制备光刻胶纳米光栅结构.有效控制干涉光刻过程中的曝光量、显影时间,获得小占空比的光刻胶光栅.再以光刻胶纳米光栅作为模板,旋涂金纳米颗粒胶体溶液.充分利用金纳米颗粒胶体溶液在光刻胶表面浸润性差的特点,限制旋涂后留存在光刻胶光栅槽中金纳米颗粒的数量,从而达到限制金纳米线宽度的目的.最后在250℃将样品进行退火处理5 min.获得了周期为400 nm且占空比小于1:4的金纳米线光栅结构,其有效面积为1 cm².以波导共振模式与粒子等离子共振模式间耦合作用为特征的光谱学响应特性验证了波导耦合金属光子晶体的成功制备,为小传感体积新型生物传感器的开发提供了性能良好的金属光子晶体芯片.