A poly-Si thin film transistor fabricated by new excimer laser recrystallization employing floating active structure

We fabricated a high-performance polycrystalline silicon (poly-Si) thin film transistor (TFT) by new excimer laser annealing (ELA) method employing floating active structure. The new simple ELA method produces large lateral grains exceeding 4 μm. A novel poly-Si TFT that exhibits very high mobility (μ_FE=331 cm²/V s) and low leakage current has been successfully fabricated by single laser irradiation on selectively floating a-Si layer. Uniform lateral grains have been obtained with wide ELA process window.     

Technology demonstration of a novel poly-Si nanowire thin film transistor

A simple process flow method for the fabrication of poly-Si nanowire thin film transistors(NW-TFTs) without advanced lithographic tools is introduced in this paper.The cross section of the nanowire channel was manipulated to have a parallelogram shape by combining a two-step etching process and a spacer formation technique.The electrical and temperature characteristics of the developed NW-TFTs are measured in detail and compared with those of conventional planar TFTs(used as a control).The as-demonstrated NW-TFT exhibits a small subthreshold swing(191 mV/dec),a high ON/OFF ratio(8.5 × 10~7),alow threshold voltage(1.12 V),a decreased OFF-state current,and a low drain-induced-barrier lowering value(70.11 mV/V).The effective trap densities both at the interface and grain boundaries are also significantly reduced in the NW-TFT.The results show that all improvements of the NW-TFT originate from the enhanced gate controllability of the multi-gate over the channel.     

Pulsed laser crystallization of hydrogen-free a-Si thin films for high-mobility poly-Si TFT fabrication

The possibility to fabricate high-mobility polysilicon TFTs by nanosecond pulsed laser crystallization of unhydrogenated amorphous Si thin films has been investigated. Two types of lasers have been used: a large area ( 1 cm²) single ArF excimer laser pulse and a small diameter ( 100 m) frequency-doubled Nd:YAG laser beam, working in the scanning regime. Processed films have been characterized in detail by different optical and microscopic techniques. Device performances indicate that the best results are achieved with the excimer laser leading to high mobility values (up to 140 cm²/Vs) which are much larger than in polysilicon TFTs fabricated onto the same quartz substrates by low-temperature thermal (630° C) crystallization of amorphous Si films (_fe55 cm²/Vs).     

Impedance spectra of thin permalloy films with a nanoisland structure

The behavior of the impedance spectra of island permalloy films prepared through vacuum evaporation onto optically polished glass-ceramic substrates has been investigated in the frequency range from 0.0001 to 100 MHz. A resistor-capacitor model of the films has been developed and the model parameters, for which there is a good agreement with experimental data on the frequency dependences of the real and imaginary components of the impedance, have been determined. The specific features in the behavior of the electrical and physical characteristics with variations in the thickness of the sample and the gap between the measuring electrodes have been investigated. It has been found that the relative permittivity of the films under investigation reaches values ɛ ∼ 10⁷–10⁸. The structural relaxation times have been calculated.     

The influence of a poly-Si intermediate layer on the crystallization behaviour of Ni-Ti SMA magnetron sputtered thin films

Shape memory alloy Ni-Ti thin films as sputtered are amorphous if the substrate is not intentionally heated during deposition. Therefore, these films have to be heat treated to induce crystallization in order to exhibit the shape-memory effect. Several films have been prepared by dc magnetron sputtering and then studied concerning the influence of the type of substrate (single-crystal Si, polycrystalline Si) on the crystallization kinetics and the final structure. The structural development of the films during crystallization (at a constant temperature of 430 °C) has been studied by X-ray diffraction in grazing incidence geometry off-plane (GIXD) at a synchrotron-radiation beamline. These experiments allow us to establish a correlation between the deposition conditions and the kinetics of crystallization. For films deposited at an electrode distance of 70 mm on a Si(100) substrate, a longer crystallization time is needed compared with films obtained at 40 mm, for otherwise fixed deposition parameters. The analysis of the nucleation kinetics by using the Johnson–Mehl–Avrami equation leads to exponents between 2.6 and 3. The presence of an intermediate layer of poly-Si drastically enhances the crystallization process. Additionally, ex situ annealing of identical samples at 500 °C during 1 h and complementary characterization of the structure and morphology of the films by cross-sectional transmission electron microscopy and selected-area electron diffraction were performed. The temperature dependence of the electrical resistivity was measured, identifying the phase transformation temperature ranges. An increase of the overall resistivity with the precipitation of Ni₄Ti₃ has been detected. Results obtained by X-ray reflectometry and GIXD suggest that during crystallization excess nickel is driven into an amorphous region ahead of the crystal/amorphous interface, thus leading to a higher concentration of Ni at the surface and further precipitation of Ni₄Ti₃. PACS 81.15.Cd; 61.10.Nz; 68.55.Jk     

A low on-resistance buried current path SOI p-channel LDMOS compatible with n-channel LDMOS

A novel low specific on-resistance(R on,sp) silicon-on-insulator(SOI) p-channel lateral double-diffused metal-oxide semiconductor(pLDMOS) compatible with high voltage(HV) n-channel LDMOS(nLDMOS) is proposed.The pLDMOS is built in the N-type SOI layer with a buried P-type layer acting as a current conduction path in the on-state(BP SOI pLDMOS).Its superior compatibility with the HV nLDMOS and low voltage(LV) complementary metal-oxide semiconductor(CMOS) circuitry which are formed on the N-SOI layer can be obtained.In the off-state the P-buried layer built in the NSOI layer causes multiple depletion and electric field reshaping,leading to an enhanced(reduced) surface field(RESURF) effect.The proposed BP SOI pLDMOS achieves not only an improved breakdown voltage(BV) but also a significantly reduced Ron,sp.The BV of the BP SOI pLDMOS increases to 319 V from 215 V of the conventional SOI pLDMOS at the same half cell pitch of 25 μm,and R on,sp decreases from 157 mΩ·cm2 to 55 mΩ·cm2.Compared with the PW SOI pLDMOS,the BP SOI pLDMOS also reduces the R on,sp by 34% with almost the same BV.     

Magnetoresistance in thin wires with granular structure

We report on studies of magnetotransport properties and structure at 5–300 K temperature region in glass-coated microwires prepared from immiscible (Co₁₀Cu₉₀ and Co₂₉Ni₂₅Mn₁Cu₄₅) elements. The crystalline structure consists of nanocrystals of Co (Ni) and Cu with average grain size below 30 nm. Considerable magnetoresistance (MR) (up to about 18%) is found in Co₁₀Cu₉₀ microwires depending on fabrication parameters. Magnetic field dependence of MR of Co₁₀Cu₉₀ microwires is completely un-hysteretic showing monotonic decay with magnetic field. On the other hand, MR (up to about 4%) is also found in as-prepared and annealed Co₂₉Ni₂₅Mn₁Cu₄₅ microwires. Annealing of Co₂₉Ni₂₅Mn₁Cu₄₅ microwires (973 K) results in increasing of the coercivity (H_c) from 65 up to 750 Oe. Annealed Co₂₉Ni₂₅Mn₁Cu₄₅ sample exhibits considerable hysteresis on magnetic field dependence of MR. Neutron and X-ray diffraction allows to attribute changes in magnetic properties and MR after annealing of Co₂₉Ni₂₅Mn₁Cu₄₅ microwires to the decomposition of the metastable phase.     

A pure dielectric metamaterial absorber with broadband and thin thickness based on a cross-hole array structure

A pure dielectric metamaterial absorber with broadband and thin thickness is proposed, whose structure is designed as a periodic cross-hole array. The pure dielectric metamaterial absorber with high permittivity is prepared by ceramic reinforced polymer composites. Compared with those with low permittivity, the absorber with high permittivity is more sensitive to structural parameters, which means that it is easier to optimize the equivalent electromagnetic parameters and achieve wide impedance matching by altering the size or shape of the unit cell. The optimized metamaterial absorber exhibits reflection loss below -10 dB in 7.93 GHz-35.76 GHz with a thickness of 3.5 mm, which shows favorable absorption properties under the oblique incidence of TE polarization (±45°). Whether it is a measured or simulated value, the strongest absorbing peak reaches below -45 dB, which exceeds that of most metamaterial absorbers. The distributions of power loss density and electric and magnetic fields are investigated to study the origin of their strong absorbing properties. Multiple resonance mechanisms are proposed to explain the phenomenon, including polarization relaxation of the dielectric and edge effects of the cross-hole array. This work overcomes the shortcomings of the narrow absorbing bandwidth of dielectrics. It demonstrates that the pure dielectric metamaterial absorber with high permittivity has great potential in the field of microwave absorption.     

Properties of disordered Mo3Ge thin films with A15 structure

Heavy ion irradiation of A15 Mo₃Ge with the low transition temperature T_c = 1.45 K raises T_c to ? 6 K. For the first time in A15 compounds a T_c degradation (≈ 3 K) after having passed through a maximum is observed until near 3.5 K the saturation value is reached. The effects on T_c are interpreted by variations of the deduced (H'_c2, ?) density of states at the Fermi level. This picture consistently explains the T_c degradation of the high-T_c A15 compounds.     

周期调制结构平面薄膜电爆炸实验研究

在金属层表面引入微结构以实现对Z箍缩等离子体形成和发展过程中不稳定性的调控具有重要研究价值.在“强光一号”装置上(峰值电流~1.4 MA,上升时间~100 ns),开展了针对具有一维周期性凹槽调制结构的金属薄膜的电爆炸实验研究.实验负载采用外推型平面结构,基底为30μm厚铝膜,刻蚀周期为2 mm,刻蚀深度约为10μm.通过激光阴影成像、激光干涉成像和可见光自辐射成像等系统进行联合诊断.实验结果表明刻蚀结构对等离子体发展过程的不稳定性特征产生了明显调制作用,原本征波长也受到抑制,微结构周期对不稳定结构波长产生趋同效应;未刻蚀一侧边界层同样受刻蚀层结构的影响,在不稳定结构上表现出相似形貌,且内外侧不稳定性特征的耦合关联性增强;刻蚀凹槽处在爆炸过程中膨胀更为迅速,形成的表面等离子体结构与初始结构反相;在刻蚀结构的几何突变处会形成细长的等离子体喷流,在二分之一刻蚀波长处出现波谱特征峰.理论分析表明电流密度调制造成电热不稳定性分布改变是调控作用产生的重要原因.     

A plasma frequency modulation model for constructing structure material with arbitrary cross-section thin metallic wires

Considering the fact that just the electrons confined in the region of the skin depth will actually affect the plasma frequency due to the skin effect, a model for constructing epsilon-near-zero (ENZ) metamaterials through the arranged thin metallic wires with arbitrary cross-section is developed, utilizing the perimeter approximation. With our model, plasma frequency can be freely modulated just by the variance of the metallic wire perimeter, irrespective of the cross-section shape of wires. The finite element method (FEM) and S-parameters retrieval method were employed to numerically simulate the plasma frequencies, which have verified the validity of the theoretical model.     

A hybrid photodiode with planar heterojunction structure consisting of ZnO nanoparticles and CuPc thin film

A photodiode with planar heterojunction was fabricated using copper (II) phthalocyanine (CuPc) organic semiconductor and zinc oxide (ZnO) inorganic nanoparticles (NPs, ～5 nm). The current–voltage (I–V) characteristics of ITO/ZnO NPs/CuPc/Ag device in dark and under illumination with a solar simulator were investigated in detail. The measurement results showed that the device exhibited good rectifying behavior in dark and under illumination. A rectification ratio (RR) of 15.44 at 1.95 V was achieved for the device under 100 mW/cm² illumination power. Also, the RR of the device as a function of light intensity was observed. The photoresponsive mechanism of the photodiode was illuminated in term of its energy band diagram.     

Enhanced optical absorption in nanopatterned silicon thin films with a nano-cone-hole structure for photovoltaic applications

In this paper, the optical properties of the silicon nano-cone-hole (NCH) structure array are studied. The ultimate efficiency of the optimized NCH array is enhanced by 23.11% compared to an optimized nanohole array of the same thickness. The absorptance enhancement of the NCH arrays is attributed to its lowered reflectance, more supported resonant modes, and enhanced mode interaction. The angular dependence of ultimate efficiency is also investigated.     

Transformation of a Gaussian pulse upon reflection from a resonant thin film structure

Peculiarities of Gaussian pulse reflection from a thin film with a resonance frequency dependence of the permittivity on a substrate with material parameters not depending on frequency are studied. Results of numerical analysis of equations determining the light field distribution in the reflected pulse are presented. The effect of the angle of incidence, carrier frequency, and duration of the incident pulse on the shift and transformation of the reflected pulse envelope is considered.     

A white-lighting LED system with a highly efficient thin luminous film

In this work, a highly effective white light-emitting diode (LED) system is realized by a combination of an LED and a photonic crystal (PC-) structured luminous film. The emission intensity of the PC-structured luminous film emission is enhanced by a factor of ca. 10.6 compared with that of the planar film. The light from the system can give rise to an intense white emission with CIE coordinates (0.33, 0.38). The total emission intensity is over twice greater than that of the usual LED system. Additionally, the emission of the PC-structured films can be switched flexibly. The strategy proposes an efficient and facile method for high excitation and extraction of the luminous film, and it shows great potential for a bright white lighting with excellent colour matching.     

A thin radar-infrared stealth-compatible structure:Design,fabrication,and characterization

A thin radar-infrared stealth-compatible structure with reflectivity below -10 dB in the whole radar X wave band and infrared emissivity less than 0.3 in the infrared region of 8μm-14 μm is reported. The designed stealth-compatible structure consists of metallic frequency selective surface （MFSS）, resistive frequency selective surface （RFSS）, and metal backing from the top down, and it is only 2. l-mm thick. The MFSS is made up of some divided low infrared emissivity metal copper films, and the RFSS consists of a capacitive array of square resistive patches. They are placed close together, working as an admittance sheet because of a mutual influence between them, and the equivalent admittance sheet greatly reduces the thickness of the whole structure. The proposed stealth-compatible structure is verified both by simulations and by experimental results. These results indicate that our proposed stealth-compatible structure has potential applications in stealth fields.     

N/P沟道MOSFET1/f噪声的统一模型

对n／p两种沟道类型、不同沟道尺寸MOSFET的1／f噪声特性进行了实验和理论研究.实验结 果表明，虽然nMOSFET的1／f噪声幅值比pMOSFET大一个数量级，但是其噪声幅值均表现出和 有效栅压的平方成反比、和漏压的平方成正比、和沟道面积成反比的规律.基于该实验结果 ，认为MOSFET的1/f噪声产生机理为位于半导体_氧化物界面附近几个纳米范围内的氧化层陷 阱通过俘获和发射过程与沟道交换载流子，在引起载流子数涨落的同时也通过库仑散射导致 沟道载流子迁移率的涨落.在这两种涨落机理的基础上，引入了氧化层陷阱的分布特征及其 与沟道交换载流子的隧穿和热激活两种方式，建立了MOSFET l／f噪声的统一模型.实验结果 和本文模型符合良好. 关键词： 1/f噪声 MOSFET 氧化层陷阱 涨落