Thin-film electroluminescent devices excited by a linearly rising voltage

The average and instantaneous luminances of a thin-film electroluminescent device (TFELD) are determined as functions of the voltage rise time by solving kinetic equations for the concentration of excited emission centers in the electroluminescent layer of the device. It is shown theoretically and experimentally that the dependences of the average and peak luminances, the external and internal quantum yield, the energy yield, and the luminous efficacy as functions of the voltage rise time all have a maximum, and the position of that maximum depends on the frequency of the driving voltage. The calculated and experimental dependences make it possible to determine the main parameters of the electroluminescence process: the collisional excitation cross section for the emission centers, the concentration of emission centers, and the transition probability of the emission centers to an excited state, as well as the radiative and nonradiative recombination probabilities of these and other centers. Zh. Tekh. Fiz. 69, 58–63 (February 1999)     

Effect of driving voltage pulse shape on the luminance of thin-film electroluminescent devices

The dependence of the average luminance on the parameters of the metal-insulator-semiconductor-insulator-metal structures in thin-film electroluminescent devices (TFELDs) and on the excitation conditions is found by solving kinetic equations for the variation in the concentration of excited emission centers in the phosphor layer of TFELDs for different driving voltage pulse shapes (triangular, trapezoidal, sinusoidal, and rectangular with an exponential leading edge). It is shown that for equal amplitudes and pulse repetition rates of a sign-changing symmetric voltage, the average luminance and luminous efficacy of TFELDs increase as the rate of rise of the voltage is increased for different driving voltage pulse shapes in the following sequence: triangular, sinusoidal, trapezoidal, rectangular. The calculations are confirmed by experiment. Zh. Tekh. Fiz. 69, 64–69 (February 1999)     

低声阻抗复合压电陶瓷的研究及应用

本文研究了我们所配制夹心结构复合压电材料低声阻抗的特性。实验表明，夹心复合压电陶瓷材料的声阻抗，与所用陶瓷材料的种类，气孔率，孔径，样品厚度以及工艺制备过程有关。实验证明，研制特定阻抗的材料是可行的，最后，用研制的新材料成功地应用于混凝土、Ｃ／Ｃ复合材料等非金属材料的超声检测中。     

Isophorone derivative as red dopant for organic electroluminescent devices

The donor–acceptor functionalized molecule, bis(4-(2-(3,3-dicyanomethylene-5,5-dimethyl-1-cyclohexylidene)vinyl)phenyl)(1-naphthyl)amine (DPN-4CN), with symmetrical structure, was investigated for its application in optoelectronic devices. Red organic light-emitting diodes (OLEDs) were fabricated by doping DPN-4CN in tris(8-hydroxyquinolino) aluminum (Alq₃) as red emitters, with a structure of ITO/NPB/Alq₃:DPN-4CN/BCP/Alq₃/LiF/Al. The device with a doping concentration of 2.5 wt% showed pure red emission with λ_max at 654 nm and CIE coordinates of (0.62, 0.36), a high brightness of 5080 cd m⁻² at a driving voltage of 12 V, a current efficiency of 2.14 cd A⁻¹ and an external quantum efficiency of 1.07% at a current density of 20 mA cm⁻². The current efficiencies and CIE coordinates of the device were almost constant over a current density from 1 to 200 mA cm⁻².     

Different Er centres in Si and their use for electroluminescent devices

At low temperatures, Er in Si produces a big variety of spectra in the 1.5 μm region which can be identified by high-resolution spectroscopy as being due to either interstitial Er or different complexes of Er with oxygen, intrinsic defects and other light impurities. Although the luminescence yield can be improved by codoping with light elements (C, N, O, F, etc.) all of these centres show strong thermal quenching of the luminescence above 150–200 K. There is, however, one type of rather broad spectrum in heavily Er- and O- doped Si, which is seen up to temperatures of 400 K and above. This spectrum can be excited in Si by hot electrons generated in a reverse biased diode. The same spectrum appears also in other Si related materials like porous Si and in silica with the same temperature dependence. In these materials, excitation spectroscopy is possible and it shows also close agreement of the excitation spectra. From these findings we infer that Er is incorporated in another surrounding and we propose Si–Er–O nano-precipitates since the spectra of other candidates, like Er₂O₃, are clearly different. We review recent work on the excitation and quenching mechanisms and we discuss consequences for technology.     

磁绝缘线振荡器的起振电压与注入电压关系的分析

粒子模拟和实验研究发现磁绝缘线振荡器(MILO)的起振电压会随注入工作电压的增大而增大, 通过进一步的分析与研究, 找到了引起该现象的根本原因, 即随着注入工作电压的增大, 工作电压上升前沿的斜率必然增大, 上升前沿斜率的增大必然引起起振电压的增大, 当斜率无限大时, MILO的起振电压等于工作电压. 因此, 工作电压上升前沿斜率的变化是引起MILO器件起振点变化的根本原因; 当注入电压上升沿的斜率固定不变时, 同一MILO器件的起振点不变, 即对应的起振电压值不变; 当注入电压上升沿的斜率增大时, 同一MILO器件的起振点对应的起振电压值随之增大. 对MILO器件的自磁绝缘临界电流公式进行了部分修正. 关键词： 磁绝缘线振荡器 工作电压 起振电压 工作曲线     

Surface preparation and characterization of indium tin oxide substrates for organic electroluminescent devices

Received: 10 March 1998 / Accepted: 21 September 1998 / Published online: 24 February 1999     

Comments on the nature of ballistic transport in small semiconductor devices at low applied voltage

A simple one-dimensional scattering model is proposed to calculate the apparent low field conductivity for small semiconductor devices in the near ballistic regime. Size dependence of the conductivity and voltage vs distance profiles in the sample are investigated.     

Synthesis and characterization of composites for microwave devices

The present study described the synthesis and assessment of different properties of ferrite-polymer composites. These composites were fabricated by the appropriate mixture of ferrite nanoparticles and polypyrrole. A versatile chemical technique known as co-precipitation was applied in the preparation of ferrite materials. The in-situ polymerization scheme was chosen to synthesize the polymeric polypyrrole base. A series of samples with zero to hundred percent ferrite contents were prepared. These include pure ferrite sample, pure polypyrrole sample, FP-1(25% ferrite, 100% polypyrrole), FP-2 (50% ferrite, 100% polypyrrole), FP-3 (75% ferrite, 100% polypyrrole) and FP-4 (100% ferrite, 100% polypyrrole). These samples were analyzed to evaluate the surface morphology, structural properties as well as magnetic properties. The shape of hysteresis loop showed the ferromagnetic nature of the synthesized composites. On the basis of the results of current study, the samples with 25% and 50% ferrite ratio may be suitable for the hyperthermia.     

新颖材料器件为全息显示带来的新机遇

三维显示是人类获取身临其境视觉信息的有效途径,其中全息技术能够提供人眼所需的全部深度信息,被认为是理想的三维显示方式.然而受目前显示器件的限制,如可刷新调制器件的时间-空间(时空)带宽积受限、海量数据云处理速率限制、图像质量不高的问题等,全息显示技术的发展进入了瓶颈期.为了提高显示质量、扩大时空带宽积、提升系统性能,需要发展崭新的全息显示器件,从根本上解决目前遇到的问题.超颖材料、超构表面以及二维材料等诸多新颖材料的涌现为全息显示带来新的机遇.超颖材料(表面)通过特殊设计,利用远小于波长的超构单元实现对波前各向同性或各向异性的振幅与相位的特异调控,进而将全息信息映射到超颖材料(表面)全息显示器件上,通过调控光波实现各种显示.发展可刷新的超构(表面、二维)材料并应用于动态全息显示中是未来的重要方向.虽然现有的新颖器件还面临着各种问题,但它们可为全息显示的发展提供潜在的可行性和新的视角与发展动力.     

High performance InAlN/GaN high electron mobility transistors for low voltage applications

A high performance InAlN/GaN high electron mobility transistor(HEMT) at low voltage operation(6–10 V drain voltage) has been fabricated. An 8 nm InAlN barrier layer is adopted to generate large 2 DEG density thus to reduce sheet resistance. Highly scaled lateral dimension(1.2 μm source–drain spacing) is to reduce access resistance. Both low sheet resistance of the InAlN/GaN structure and scaled lateral dimension contribute to an high extrinsic transconductance of 550 mS/mm and a large drain current of 2.3 A/mm with low on-resistance(Ron) of 0.9 ?·mm. Small signal measurement shows an f_T/f_(max) of 131 GHz/196 GHz. Large signal measurement shows that the InAlN/GaN HEMT can yield 64.7% –52.7%(V_(ds)= 6–10 V) power added efficiency(PAE) associated with 1.6–2.4 W/mm output power density at 8 GHz. These results demonstrate that GaN-based HEMTs not only have advantages in the existing high voltage power and high frequency rf field, but also are attractive for low voltage mobile compatible rf applications.     

Transparent carbon nanotube-based driving electrodes for liquid crystal dispersion display devices

We report the fabrication of transparent rigid or flexible liquid crystal dispersion displays driven by electrodes prepared from coating inert substrates with stable aqueous suspensions of single-walled carbon nanotubes (SWNTs) or multiple-walled carbon nanotubes (MWNTs). The SWNT-coated electrodes exhibit a dense nanotube network with a sheet resistivity ( 25 k) about one decade lower than that of their MWNT counterparts. The electro-optical performance of the SWNT-based devices is at least equivalent to that of an indium tin oxide-based display, whereas those driven by MWNT electrodes operate at slightly higher threshold and saturation voltages. The novel, flexible display devices can be repeatedly bent without any noticeable loss of physical characteristics. PACS 42.79.Kr; 61.46.+w; 81.07.De     

Carbon nanotube–polymer composites for photonic devices

We report the fabrication of high optical quality single wall carbon nanotube polyvinyl alcohol composites and their application in nanotube based photonic devices. These show a broad absorption of semiconductor tubes centred at 1.55 μm, the spectral range of interest for optical communications. The films are used as mode-lockers in an erbium doped fibre laser, achieving 700 fs mode-locked pulses. Raman spectroscopy shows no damage after a long time continuous laser operation.     

An extremely low offset voltage AlInAs/GaInAs heterostructure-emitter bipolar transistor

A new Al_0.48In_0.52As/ Ga_0.47In_0.53As heterostructure-emitter bipolar transistor (HEBT) with a very low offset voltage of 40 mV has been fabricated by molecular beam epitaxy. From the theoretical analysis and experimental results, it is found that a 500-Å thick emitter used in the studied device can effectively eliminate the potential spike at the N–AlInAs/n–GaInAs heterointerface. However, a degenerate current gain of about 25 is obtained, attributed to the increase of recombination current at the neutral-emitter regime. This is caused by the short hole diffusion length of GaInAs, which reduces the emitter injection efficiency. Due to the small surface recombination velocity, the emitter edge-thinning design is not essential to improve the device performance of our proposed AlInAs/GaInAs HEBT.     

ZnO/FLC nanocomposites with low driving voltage and non-volatile memory for information storage applications

Nanocomposites comprises of nano sized zinc oxide (ZnO, size ~10 nm) particles and ferroelectric liquid crystal (FLC) material have been prepared and studied. The concentration of the dopant (ZnO nanoparticles) in FLC matrix varied from 0.0 to 1 wt%. Distinct nanocomposites have been used to fabricate memory device and studied through dielectric spectroscopy, optical microscopy and electro-optical methods to explore electro-optic and memory parameters. Experimental results reveal that doping of ZnO nanoparticles in FLC leads to long lasting memory and low deriving voltage in nanocomposites. The achieved prolonged memory effect in nanocomposites may attribute to the charge transfer at the interfaces. Another reason, application of applied field may lead to ion trapping effect at ZnO surface which in turn minimize the depolarized field and enhance the memory effect in nanocomposites.     

Development of 0.5-V Josephson junction array devices for quantum voltage standards

The design, fabrication, and the characterization of a 0.5-V Josephson junction array device are presented for the quantum voltage standards in the National Institute of Metrology(NIM) of China. The device consists of four junction arrays, each of which has 1200 3-stacked Nb/Nb_xSi_(1-x)/Nb junctions and an on-chip superconducting microwave circuit which is mainly a power divider enabling each Josephson array being loaded with an equal amount of microwave power. A direct current(dc) quantum voltage of about 0.5 V with a ～1-mA current margin of the 1 st quantum voltage step is obtained.To further prove the quality of NIM device, a comparison between the NIM device with the National Institute of Standards and Technology(NIST) programmable Josephson voltage standard(PJVS) system device is conducted. The difference of the reproduced 0.5-V quantum voltage between the two devices is about 0.55 nV, which indicates good agreement between the two devices. With the homemade device, we have realized a precise and applicable 0.5-V applicable-level quantum voltage.     

Experimental observation of voltage amplification using negative capacitance for sub-60 mV/decade CMOS devices

In this study, an experimental study of negative capacitance is performed in order to overcome the physical limit of subthreshold slope (SS), SS ≥ 60 mV/decade at 300 K, which is originated from (i) using the thermionic emission process in complementary metal-oxide-semiconductor (CMOS) technology and (ii) non-scalability of the thermal voltage k_BT/q (i.e., in order to realize SS lower than 60 mV/decade at 300 K). To make the surface potential higher than the gate voltage, a step-up voltage amplifier is included in the CMOS gate stack using a ferroelectric capacitor implemented with ferroelectric material. The measured SS in long-channel CMOS transistors is 13 mV per decade at 300 K. A simple connection of the ferroelectric capacitor to a complementary metal oxide semiconductor (CMOS) gate electrode would provide a new evolutionary pathway for future CMOS scaling.