Effect of gate insulating layer on organic static induction transistor characteristics

Organic static induction transistors, which have relatively short vertical channels, are attractive devices for their low operating voltage and high operating speed. However, a gate voltage larger than the Schottky barrier potential usually leads to a large gate leakage current and thus poor device performance. To limit the gate leakage current, we considered adding insulating layers around the gate electrode. The oxidization of aluminum during a physical vapor deposition process was used to form insulating layers around the gate electrode. The results demonstrate that by appending gate insulating layers, gate leakage currents can be effectively reduced and device characteristics, especially the on/off ratio, can be improved.     

Fabrication and characterization of polyterpenol as an insulating layer and incorporated organic field effect transistor

A non-synthetic polymer material, polyterpenol, was fabricated using a dry polymerization process namely RF plasma polymerization from an environmentally friendly monomer and its surface, optical and electrical properties investigated. Polyterpenol films were found to be transparent over the visible wavelength range, with a smooth surface with an average roughness of less than 0.4 nm and hardness of 0.4 GPa. The dielectric constant of 3.4 for polyterpenol was higher than that of the conventional polymer materials used in the organic electronic devices. The non-synthetic polymer material was then implemented as a surface modification of the gate insulator in field effect transistor (OFET) and the properties of the device were examined. In comparison to the similar device without the polymer insulating layer, the polyterpenol based OFET device showed significant improvements. The addition of the polyterpenol interlayer in the OFET shifted the threshold voltage significantly; + 20 V to −3 V. The presence of trapped charge was not observed in the polyterpenol interlayer. This assisted in the improvement of effective mobility from 0.012 to 0.021 cm²/Vs. The switching property of the polyterpenol based OFET was also improved; 10⁷ compared to 10⁴. The results showed that the non-synthetic polyterpenol polymer film is a promising candidate of insulators in electronic devices.     

ITO作为源漏电极的有机场效应晶体管

报道了一种OFET,它采用ITO作为源漏电极,聚酰亚胺为绝缘层,CuPc为半导体层.实验结果表明,该器件具有明显的场效应性质,性能较好,载流子迁移率和开关比分别达2.3×10-3 cm2/V.s、800,表明ITO是一种合适的、有前途的p型OFET源漏极材料.为此,本文对由电极材料和半导体材料间形成的接触电阻对OFET性能影响进行了分析.     

Glucose-responsive hydrogel electrode for biocompatible glucose transistor

Abstract

In this paper, we propose a highly sensitive and biocompatible glucose sensor using a semiconductor-based field effect transistor (FET) with a functionalized hydrogel. The principle of the FET device contributes to the easy detection of ionic charges with high sensitivity, and the hydrogel coated on the electrode enables the specific detection of glucose with biocompatibility. The copolymerized hydrogel on the Au gate electrode of the FET device is optimized by controlling the mixture ratio of biocompatible 2-hydroxyethylmethacrylate (HEMA) as the main monomer and vinylphenylboronic acid (VPBA) as a glucose-responsive monomer. The gate surface potential of the hydrogel FETs shifts in the negative direction with increasing glucose concentration from 10 μM to 40 mM, which results from the increase in the negative charges on the basis of the diol-binding of PBA derivatives with glucose molecules in the hydrogel. Moreover, the hydrogel coated on the gate suppresses the signal noise caused by the nonspecific adsorption of proteins such as albumin. The hydrogel FET can serve as a highly sensitive and biocompatible glucose sensor in in vivo or ex vivo applications such as eye contact lenses and sheets adhering to the skin.     

Carrier injection and transport in organic field-effect transistor investigated by impedance spectroscopy

In this research, impedance spectroscopy (IS) has been applied on top-contact pentacene organic field-effect transistors (OFETs) for characterization of the contact resistance and carrier transport properties. The various relaxation processes were analyzed based on the Maxwell–Wagner model, assuming pentacene as a dielectric material. The mobilities obtained from the IS analysis correspond well with that obtained from the current–voltage (I–V) analysis. This alternative method by IS provides an additional advantage of isolating the effect of carrier concentration when evaluating the mobility of OFETs.     

Thermionic emission model for contact resistance in organic field-effect transistor

Injection mechanism of top-contact pentacene field-effect transistor (OFET) was investigated in respect to the internal field. The contact resistance was evaluated by the transmission line method for various applied external voltages as well as various pentacene film thicknesses. The behaviour of contact resistance was described in terms of the thermionic emission model (Schottky injection) and internal electric field generated by excess charges accumulated on pentacene–gate insulator interface. It was shown that pentacene film thickness changes the internal electric field affecting the carrier injection barrier. It was concluded that the space-charge field effect made a significant contribution for smaller pentacene film thicknesses and therefore in accordance to the thermionic model was able to decrease contact resistance representing the potential drop.     

场效应管在逆变弧焊电源中的应用

论述了功率场效应管（ＶＶＭＯＳ）在逆变焊机中的应用，结果表明，将场效应管作为功率开关器件，可使逆变弧焊电源具有整机效率高，动态响应好、控制精良等特点。     

Analysis of threshold voltage shift of pentacene field effect transistor with ferroelectric gate insulator as a Maxwell-Wagner effect

The current-voltage (I-V) characteristics of pentacene filed effect transistor (FET) with ferroelectric gate insulator (P(VDF-TeFE)) is investigated to analyze the threshold voltage shift in terms of Maxwell-Wagner (MW) effect. The spontaneous polarization generated in ferroelectric gate insulator modulates the amount of accumulated charges which is injected from the source electrode, and causes threshold voltage shift. Two peaks observed in the I-V characteristics were analyzed based on a MW effect element. Results reveal that the movement of accumulated charges at the pentacene/P(VDF-TeFE) interface along the electric field in the FET, and the ferroelectric polarization of P(VDF-TeFE) are main origins of the peaks.     

New semiconducting multi-branched conjugated molecules based on π-extended triphenylene and its application to organic field-effect transistor

Triphenylene derivatives are the most well-known representatives of discotic liquid crystals forming columnar mesophases. In this work, the authors report on the design and synthesis of new semiconducting materials, based on a triphenylene core, those are solution processable. These molecules have a good solubility and are applicable to soluble processing for organic field-effect transistor (OFET). Their thermal stabilities and dynamic behaviors are suitable for OFET device fabrication. In comparison with all of previous reported triphenylenes derivatives, these molecules have lower bandgap energies. As far as we know, there are few reports on the application of π-extended triphenylene systems to OFET. The semiconducting properties of these molecules were quite promising for further designs of π-extended triphenylene derivatives.     

Transient charge accumulation in pentacene field effect transistor with silver electrode

Time-resolved microscopic optical second harmonic generation (TRM-SHG) imaging was employed to study a transient charge accumulation in top-contact pentacene field effect transistor (FET) with Ag electrodes. It was demonstrated that the SHG signal at the edge of the Ag electrode decayed but remained in a steady state depending on biasing condition. An electric field formed in pentacene layer below Ag electrode activates the SHG, indicating the insufficient accumulation of injected carriers in the FET channel. By using the TRM-SHG technique transient change of the carrier density in the OFET is obtained.     

双极型光栅晶体管的瞬态特性模型及模拟分析

提出一种应用于CMOS图像传感器的新型光电检测器件-双极型光栅晶体管，并建立了其瞬态等效电路模型，利用电路模拟软件HSPICE的多瞬态分析法对双极型光栅晶体管的光电流特性进行了仿真，分析得出这种新型器件在0.6μmCMOS工艺参数下，由于引入pn注入结加速了光电荷的读出速率，光电流随外加电压呈指数式增长，与普通光栅晶体管相比，蓝光响应特性有较大改善。     

Electrical characteristics of poly(3-hexylthiophene) organic thin film transistor with electroplated metal gate electrodes on polyimide

The electroplating of the gate electrode on a flexible polyimide (PI) substrate was successfully applied to the fabrication of inverted-staggered poly(3-hexylthiophene) (P3HT) organic thin film transistors (OTFTs). The Ni gate electrode was electroplated through patterned negative photo-resist (KMPR) masks onto Cu (seed)/Cr (adhesion) layers that had been sputter-deposited on O₂-plasma-treated PI substrates. The electrical measurements of the fabricated OTFTs with the SiO₂ gate insulator indicated non-ideal output characteristics, which are similar to the model of electrical transport by a space-charge limited current (SCLC). The use of a poly(4-vinyl phenol) (PVP) and SiO₂/PVP bilayer gate dielectric produced output characteristics that were closer to the ideal TFT behavior but led to a lower effective mobility and on/off current (I_on/I_off).     

Ultraviolet light effect on electrical properties of a flexible organic thin film transistor

We have fabricated pentacene-based transistors on a transparent and flexible substrate made of polyethylene-terephthalate. We have shown that using an optical excitation at a wavelength of 365 nm photoconductivity modifies the carrier density without changing the mobility. The performance of the flexible organic phototransistors is mostly due to high-photosensitivity in the off-state with a ratio of photocurrent to dark current of about 2 10⁴. Furthermore, the response times of the phototransistor are lower than 0.1 s. These results indicate that such transistors could be potentially used in photodetectors or amplifiers ordered by an optical gate. Moreover, we have noticed that there is no significant change in the mobility value when the transistor is bent in the direction of the current flow.     

Synthesis of Si nanowires with a thermally oxidized shell and effects of the shell on transistor characteristics

Silicon nanowires (SiNWs) with a single-crystalline Si core and a thermally oxidized shell (core-shell SiNWs) were synthesized by gold-catalyzed chemical vapor deposition followed by rapid thermal oxidation. To synthesize high-quality core-shell SiNWs, the relationship between the growth parameters and the crystallinity was studied. Furthermore, the formation process of the oxide shell was analyzed in detail by transmission electron microscopy. Using SiNWs as channels, back gate-type field effect transistors (FETs) were fabricated on p-type silicon wafers. FETs with core-shell SiNWs channels exhibited smaller hysteresis in the drain current (I_d) vs. gate voltage (V_GS) characteristics and higher on/off drain current ratio (I_ON/I_OFF) than those with bare SiNWs channels.     

Fabrication and properties of flower-shaped Pt@TiO2 core-shell nanoparticles

Flower-shaped core-shell Pt@TiO₂ nanoparticles have been synthesized successfully by a simple hydrothermal route using TiF₄ as precursor. Morphology of the product was investigated by transmission electron microscopy (TEM), selected area electron diffraction (SAED) and X-ray diffraction technique. It has been revealed that the TiO₂ shells of core-shell Pt@TiO₂ nanoparticles are constructed by multiple wedge-shaped petals of TiO₂ crystals with anatase-type crystalline phase. The SAED pattern of TiO₂ shells reflecting the formation of wedge-shaped TiO₂ petals is because of the preferential growth of (004) crystal planes surrounded by (101) facets of TiO₂ crystal planes. The high phototocatalytic performance of flower-shaped core-shell Pt@TiO₂ nanoparticles is also largely attributed to the high Schottky energical barrier within Pt-TiO₂ hetero-interface and the interaction between synchronously vibrated electrons within Pt and electrons in valence band of TiO₂ crystals.