Device characteristics of perylene-based transistors and inverters prepared with hydroxyl-free polymer-modified gate dielectrics and thermal post-treatment

Organic field-effect transistors (OFETs) and complementary inverters were produced on the basis of n-type N,N′-dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C8) using the neutral cluster beam deposition (NCBD) method. Significant improvements in surface morphology and crystallinity were observed after the surface modification of SiO₂ gate dielectric layers with hydroxyl-free polymer insulators such as polymethylmethacrylate (PMMA) and cyclic olefin copolymer (COC), and thermal post-treatment. Electric characteristics and operational stability of PTCDI-C8-based OFETs were also clearly enhanced after the surface modification, and in particular, the thermally post-treated OFETs with COC-modified SiO₂ gate dielectrics exhibited a high room-temperature mobility of 0.68 cm²/V s. Two structural types (generic vs. encapsulated) of inverters in top-contact configuration were fabricated by integration of the p-type pentacene and n-type PTCDI-C8 OFETs using COC-modified SiO₂ gate dielectrics. Due to the increased electron mobilities and good coupling between p- and n-type OFETs, hysteresis-free, fast-switching inverters were realized with high gains of ∼20 in the first and third quadrants of voltage transfer characteristics under ambient conditions. The device characteristics of the encapsulated inverters monitored as a function of the time were well maintained with slight degradation.     

Fabrication and characterization of pentacene-based transistors with a room-temperature mobility of 1.25 cm/Vs

Pentacene-based transistors produced by a novel neutral cluster beam deposition method were characterized, and the effects of the surface pretreatments were examined. Atomic force microscopy and X-ray diffraction showed that the cluster beams were quite efficient in growing high-quality, crystalline thin films on SiO₂ substrates at room-temperature without any thermal post-treatment, and that an amphiphilic surfactant, octadecyltrichlorosilane (OTS), enhances the packing density and crystallinity significantly. The observed field-effect mobilities (μ_eff) were among the best reported thus far: 0.47 and 1.25 cm²/Vs for the OTS-untreated and -pretreated devices, respectively. The device performance was found to be consistent with the estimated trap density and activation energy, which were derived from the transport characteristics for the temperature dependence of μ_eff in the range of 10−300 K.     

红绿掺杂有机电致发光器件发光性能的研究

制备了结构为ITO/MoO₃(x nm)/NPB(40nm)/CBP:14%GIr1(12.5nm)/CBP:6%R-4b(5nm)/C BP:14% GIr1(12.5nm)/BCP(10nm)/Alq₃( 40nm)/LiF(1nm)/Al(100nm)的红绿磷光器件,G Ir1和R-4B分别为新型绿色和 红色磷光染料,采用绿-红-绿掺杂顺序,结合BCP对空穴的有效限制作用,研究了不同MoO ₃厚度器件的发光 机理。结果表明,在MoO₃为40nm时,器件发光性能较好,在电压 为5V、亮度为100cd·m－2时,得到最大的 电流效率为16.91cd·A－1。为提高器件光效,增加TCTA电子 阻挡层,获得了最高电流效率20.01cd·A－1。原因主要是, TCTA的HOMO能级介于NPB和CBP之间,促进空穴注入;TCTA较高的三线态能量对发光层激子的 限制。     

ZnO Thin Film, Device, and Circuit Fabrication using Low-Temperature PECVD Processes

We report undoped ZnO films deposited at low temperature (200°C) using plasma-enhanced chemical vapor deposition (PECVD). ZnO thin-film transistors (TFTs) fabricated using ZnO and Al₂O₃ deposited in situ by PECVD with moderate gate leakage show a field-effect mobility of 10 cm²/V s, threshold voltage of 7.5 V, subthreshold slope <1 V/dec, and current on/off ratios >10⁴. Inverter circuits fabricated using these ZnO TFTs show peak gain magnitude (dV _out/dV _in) ~5. These devices appear to be strongly limited by interface states and reducing the gate leakage results in TFTs with lower mobility. For example, ZnO TFTs fabricated with low-leakage Al₂O₃ have mobility near 0.05 cm²/V s, and five-stage ring-oscillator integrated circuits fabricated using these TFTs have a 1.2 kHz oscillation frequency at 60 V, likely limited by interface states.     

Superior suppression of gate current leakage in Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Si<Subscript>3</Subscript>N<Subscript>4</Subscript> bilayer-based AlGaN/GaN insulated gate heterostructure field-effect transistors

AlGaN/GaN-based metal-insulator-semiconductor heterostructure field-effect transistors (MIS-HFETs) with Al₂O₃/Si₃N₄ bilayer as insulator have been investigated in detail, and compared with the conventional HFET and Si₃N₄-based MIS-HFET devices. Al₂O₃/Si₃N₄ bilayer-based MIS-HFETs exhibited much lower gate current leakage than conventional HFET and Si₃N₄-based MIS devices under reverse gate bias, and leakage as low as 1×10⁻¹¹ A/mm at −15 V has been achieved in Al₂O₃/Si₃N₄-based MIS devices. By using ultrathin Al₂O₃/Si₃N₄ bilayer, very high maximum transconductance of more than 180 mS/mm with ultra-low gate leakage has been obtained in the MIS-HFET device with gate length of 1.5 μm, a reduction less than 5% in maximum transconductance compared with the conventional HFET device. This value was much smaller than the more than 30% reduction in the Si₃N₄-based MIS device, due to the employment of ultra-thin bilayer with large dielectric constant and the large conduction band offset between Al₂O₃ and nitrides. This work demonstrates that Al₂O₃/Si₃N₄ bilayer insulator is a superior candidate for nitrides-based MIS-HFET devices.