Authentication labels based on guided-mode resonant filters

A guided-mode resonance (GMR) filter with wide angular tolerances is experimentally demonstrated as an authentication label illuminated with unpolarized white light. The proposed filter, based on a free-standing silicon nitride membrane suspended on a silicon substrate, is fabricated by using anisotropic wet etching to remove the substrate beneath the silicon nitride layer. Both grating and waveguide structures without a lower cladding layer, i.e., a substrate, are fabricated simultaneously on a silicon nitride membrane. Since the silicon nitride is transparent within the spectra of visible and infrared light, such suspended-membrane-type GMR filters are well suited for applications within the visible spectrum. Moreover, the high refractive index of silicon nitride allows the proposed filters to have strongly modulated gratings and an immunity to high angular deviation. The measured reflection resonance has an angular tolerance up to +/-5 degrees under normal incidence for the wavelength of 629.5 nm.     

光栅光阀器件的结构改进与制作工艺研究

根据光栅光阀的工作原理,在结构上对传统的光栅光阀器件进行了改进,分析了改进后光栅光阀器件的光学特性、结构特性,以及制作工艺流程.改进后的光栅光阀结构中硅基底上设有二氧化硅隔离层,隔离层上沉积无定形硅作为牺牲层,可动梁的材料是氮化硅,固定梁为蒸镀的金属铝层.通过离子刻蚀的方法刻蚀图形,用化学腐蚀方法掏空牺牲层得到所需桥梁状结构.研究表明改进后的器件黑区范围小,驱动电压较低,光学效率较高,具有潜在的应用前景.     

光栅光阀器件的结构改进与制作工艺研究

根据光栅光阀的工作原理,在结构上对传统的光栅光阀器件进行了改进,分析了改进后光栅光阀器件的光学特性、结构特性,以及制作工艺流程.改进后的光栅光阀结构中硅基底上设有二氧化硅隔离层,隔离层上沉积无定形硅作为牺牲层,可动梁的材料是氮化硅,固定梁为蒸镀的金属铝层.通过离子刻蚀的方法刻蚀图形,用化学腐蚀方法掏空牺牲层得到所需桥梁状结构.研究表明改进后的器件黑区范围小,驱动电压较低,光学效率较高,具有潜在的应用前景.     

Dual material insulator SOI-LDMOSFET: A novel device for self-heating effect improvement

The silicon-on-insulator (SOI) power devices show good electrical performance but they suffer from inherent self-heating effect (SHE), which limits their operation at high current levels. The SHE effect is because of low thermal conductivity of the buried oxide layer. In this paper we propose a novel silicon on insulator lateral double diffused MOSFET (SOI-LDMOSFET) where the buried insulator layer under the active region consists of two materials in order to decrease the SHE. The proposed structure is called dual material buried insulator SOI-LDMOSFET (DM-SOI). Using two-dimensional and two-carrier device simulation, we demonstrate that the heat dissipation and the SHE can be improved in a conventional SOI-LDMOSFET by replacement of the buried oxide with dual material buried insulator (silicon nitride and silicon oxide) beneath the active region. The heat generated in the active silicon layer can be flowed through the buried silicon nitride layer to the silicon substrate easily due to high thermal conductivity of silicon nitride. Furthermore, the channel temperature is reduced, negative drain current slope is mitigated and electron and hole mobility is increased during high-temperature operation. The simulated results show that silicon nitride is a suitable alternative to silicon dioxide as a buried insulator in SOI structures, and has better performance in high temperature.     

Enhanced light trapping for the silver nanoparticles embedded in the silica layer atop the silicon substrate

The optical properties of the structures with silver nanoparticles embedded in the silica layer atop the silicon substrate are simulated by the finite-difference time-domain method. The effects of nanoparticle size, period, silica layer thickness, and the angle of incidence of the illuminated light on optical transmissions are studied. It is found that there is the red-shift for the maximum of the total light transmitting into the silicon substrate as the silica layer thickness increases. The electric field intensity distributions and the average power densities for the structure with largest optical transmission is studied, and the strong electric field intensities are found in the silica regions surrounding to the silver nanoparticles, which can help the light energy going into the silicon substrate. By controlling the structure parameters, the optical transmissions of the structures with the silica layer can have higher optical transmissions than the cases without the silica layer. The silica layer plays the role as the graded refractive index layer between the air and the silicon substrate, and the light power from the incident wave can transmit into the silicon substrate with less optical reflections for choosing a suitable silica layer thickness. A guideline to design the structures with high optical transmissions for the solar spectra is given. This study cannot only be useful for the solar cells applications, but also other antireflection applications.     

基于一种易于制作的混合型表面等离激元波导结构的超紧凑截线滤波器

提出并分析了一种结构紧凑的截线型滤波器。该滤波器建立在一种硅基混合型表面等离激元波导结构上。与通常的混合等离激元结构相比,该波导结构在制作时只需对顶部的一层硅材料进行刻蚀,不需在光刻步骤进行对准和套刻,工艺简单易行。该截线滤波器由一截突柱波导与直波导耦合组成,并采用三维时域有限差分方法对其频谱响应进行模拟计算。计算结果表明该滤波器与现有文献中的二维金属-绝缘体-金属波导截线滤波器具有类似的频谱特性。另外,还进一步分析了截线部分及波导自身尺寸对器件输出频谱的影响。     

Fabrication of freestanding nanoscale gratings on silicon-on-insulator wafer

We report a bottom-up process for the fabrication of freestanding nanoscale gratings on silicon-on-insulator (SOI) wafer. Freestanding membrane devices suffer deflection due to the residual stress of the buried oxide layer of SOI wafer. The deflection will affect the device shape and result in the fracture problem for devices fabricated on thin silicon membrane. The bottom-up process is developed to overcome the fabrication issue for thin silicon membrane gratings. The silicon handle layer is removed through back wafer etching of silicon, where the buried oxide layer acts as an etch stop layer. The grating structures are then defined on thin silicon device layer by electron beam lithography and generated by fast atom beam etching. The grating structures are finally released in vapor HF to form the freestanding nanoscale gratings. The freestanding linear/circular gratings, 1,500-nm period grating with the grating width of 200- and 850-nm period grating with the grating width of 100 nm, are successfully achieved on 260-nm silicon device layer.     

Formation of oriented rodlike nickel silicide precipitates during magnetron deposition of carbon and nickel on silicon

Formation of rodlike structures elongated in the 〈100〉 and 〈010〉 directions of silicon crystal was observed during magnetron codeposition of carbon and nickel on (100) silicon substrate with a natural oxide layer. Rodlike structures did not form during deposition in similar conditions on (111) silicon substrate. It has been revealed that the rodlike structures represent epitaxial nickel silicide precipitates. The results of experimental study of the composition, structure, and shape of forming silicide clusters as a function of the silicon substrate orientation and the codeposited layer thickness are presented.     

Electrophysical properties of dielectric films in MDM-structures

Using the methods of reactive cathode sputtering in a low-voltage, penning-discharge installation, dielectric films from silica, silicon nitride, aluminum nitride, etc. are obtained. Parameters of the films in MDM structures, their optical properties and porosity are investigated as a function of the deposition rate, substrate temperature and reaction gas pressure. It is found out that the films from silicon nitride exhibit the highest dielectric strength and those from silicon dioxide show the least dielectric loss.     

Electroluminescence of Si-SiO2 structures subjected to sequential ion implantation with silicon and carbon

The electroluminescence of Si-SiO₂ structures subjected to sequential implantation with 130-and 60-keV silicon ions and 60-keV carbon ions into a silicon dioxide layer is investigated. It is found that implantation of the structures with silicon and carbon ions is responsible for the electroluminescence bands with maxima at energies of approximately 2.7 and 4.3 eV. It is assumed that these bands are associated with the formation of silylene centers. Postimplantation annealing leads to a decrease in the intensity of the observed electroluminescence bands and gives rise to a shoulder in the short-wavelength wing of the band with a maximum at 2.7 eV.     

相变材料与超表面复合结构太赫兹移相器

利用相变材料嵌入超表面组成复合结构实现太赫兹移相器,该器件自上而下依次为二氧化钒嵌入金属层、液晶、二氧化钒嵌入金属层、二氧化硅层.通过二氧化钒的相变特性和液晶的双折率特性同时作用实现对器件相位调控.随着外加温度变化二氧化钒电导率发生改变,器件的相位随之产生移动,同样的对液晶层施加不同的电压导致液晶折射率发生变化,器件相位也会有影响.经过这两种介质共同作用,最终实现对太赫兹波相位有效调控.仿真结果验证了该相移器在频率f=0.736 THz时,太赫兹移相器的最大相移量达到355.37°,在0.731—0.752 THz(带宽为22 GHz)频率范围相移量超过350°.这种基于相变材料与超表面复合结构为灵活调控太赫兹波提供了一种新思路,将在太赫兹成像、通信等领域有着广泛的应用前景.     

Investigation of the interaction between electrical discharges and low resistivity silicon substrates

In this work the impact of single discharge pulses in air on single-crystalline, p-type silicon having a low bulk resistivity of 0.009-0.012 Ω cm is investigated. Compared to platinum specimens, the craters in silicon have lateral dimensions which are about one order of magnitude larger despite comparable values for the melting point and the melting energy. This finding is attributed to the substantially higher bulk resistivity of silicon leading a higher energy input into the substrate when spark loaded. The energy generated by joule heating is, however, distributed across a larger area due to a current spreading effect. To study the impact of different surface properties on the sparking behaviour, the crater formation on the silicon substrate is investigated applying coatings with different material properties, such as sputter-deposited aluminium layers and thermally-grown silicon dioxide. In general, the crater characteristics formed on unmodified silicon is not influenced when a thin aluminium layer of 24 nm is deposited. At higher film thickness above 170 nm, the sparking energy is almost completely absorbed in the top layer with low influence on the underlying silicon substrate. In the case of a dielectric top layer with a thickness of 155 nm, the formation of many small distinct craters is supported in contrast to a 500 nm-thick SiO₂ film layer where the generation of a single crater with a large area is energetically favoured. A surface roughness of several nm on the silicon probes has no measurable effect on crater formation when compared to an original surface characteristic with values in the sub-nm range.     

Triangular pattern formation on silicon through self-organization of GaN nanoparticles

Nanoparticles of gallium nitride, synthesized by a low-temperature reaction between triethyl gallium and ammonia, were introduced onto silicon wafers containing a thin layer of chemically prepared silicon dioxide. At room temperature, the nanoparticles form unstructured agglomerates on the surface. However, upon annealing the samples beyond the decomposition temperature of the silicon dioxide layer, the gallium nitride particles self-organize to form triangular structures. The pattern formation is attributed to the domain separation associated with the (1 × 1)-(7 × 7) surface phase transformation followed by selective incorporation of the nanoparticles.     

X-ray spectral analysis of the interface of a thin Al<Subscript>2</Subscript>O<Subscript>3</Subscript> film prepared on silicon by atomic layer deposition

The extent and phase chemical composition of the interface forming under atomic layer deposition (ALD) of a 6-nm-thick Al₂O₃ film on the surface of crystalline silicon (c-Si) has been studied by depthresolved, ultrasoft x-ray emission spectroscopy. ALD is shown to produce a layer of mixed Al₂O₃ and SiO₂ oxides about 6–8 nm thick, in which silicon dioxide is present even on the sample surface and its concentration increases as one approaches the interface with the substrate. It is assumed that such a complex structure of the layer is the result of interdiffusion of oxygen into the layer and of silicon from the substrate to the surface over grain boundaries of polycrystalline Al₂O₃, followed by silicon oxidation. Neither the formation of clusters of metallic aluminum near the boundary with c-Si nor aluminum diffusion into the substrate was revealed. It was established that ALD-deposited Al₂O₃ layers with a thickness up to 60 nm have similar structure.     

Double-layer fabrication scheme for large-area polymeric photonic crystal membrane on silicon surface by multibeam interference lithography

We report on the fabrication of two-dimensional polymeric photonic crystal membranes on the surface of silicon using visible-light multibeam interference lithography. The structures are created by the interference of three beams of a green laser. A polymer buffer layer doped with a Rhodamine B laser dye, interlaid between the lithography layer and the silicon substrate, suppresses the effects of strong reflection and nonradiative absorption of silicon on the interference pattern. Large-area defect-free photonic crystal membranes are experimentally realized on silicon surface.     

Simulation of surface-modified porous silicon photonic crystals for biosensing applications

In this work realistic biosensing structures based on the integration of porous silicon photonic crystals with polymer coating technology are presented. Microcavities and rugate filters are chosen as the photonic crystal configuration. The deposition of a polymer layer on the pore walls of these structures is proposed to improve the selectivity and sensitivity of the sensing function. A complete effective refractive index model including the polymer layer, the target and external effects like silicon oxidation has been developed in order to accurately simulate the structures. It is expected that the proposed structures could be used as low cost, highly integrated and highly sensitive biological sensors.     

Growth and optical properties of filamentary GaN nanocrystals grown on a hybrid SiC/Si(111) substrate by molecular beam epitaxy

The potential to grow filamentary GaN nanocrystals by molecular beam epitaxy on a silicon substrate with a nanosized buffer layer of silicon carbide has been demonstrated. Morphological and optical properties of the obtained system have been studied. It has been shown that the intensity of the photoluminescence spectrum peak of such structures is higher than that of the best filamentary GaN nanocrystals without the buffer silicon carbide layer by a factor of more than two.     

MEMS electrodynamic loudspeakers for mobile phones

This paper presents a MEMS structure of electrodynamic loudspeakers dedicated to mobile phone applications. The major goals are to obtain a high electroacoustic conversion efficiency and a high fidelity acoustic quality. The originalities lie in a rigid silicon membrane and in its suspension by a set of silicon beams. The moving coil is a planar copper microcoil electroplated on the silicon membrane whose microstructure was optimized for providing both rigidity and lightness of the mobile part.This paper presents different magnetic structures of the motor for this MEMS loudspeaker. These structures are ironless, only made out of permanent magnets which are bonded on the substrate. They are studied and optimized thanks to analytical formulations of the magnetic field created by the permanent magnets. Results are presented for a deep RIE etched 7.5 mm radius silicon membrane structured with 40 stiffening ribs and on a 30 μm thick microcoil with 35 turns.     

A CMOS-compatible silicon substrate optimization technique and its application in radio frequency crosstalk isolation

In this paper, a complementary metal-oxide semiconductor （CMOS）-compatible silicon substrate optimization technique is proposed to achieve effective isolation. The selective growth of porous silicon is used to effectively suppress the substrate crosstalk. The isolation structures are fabricated in standard CMOS process and then this post-CMOS substrate optimization technique is carried out to greatly improve the performances of crosstalk isolation. Three-dimensional electro-magnetic simulation is implemented to verify the obvious effect of our substrate optimization technique. The morphologies and growth condition of porous silicon fabricated have been investigated in detail. Furthermore, a thick selectively grown porous silicon （SGPS） trench for crosstalk isolation has been formed and about 20dB improvement in substrate isolation is achieved. These results demonstrate that our post-CMOS SGPS technique is very promising for RF IC applications.