Isolated Island Structure Research Articles

Effects of electrodeposited Co–W and Co–Fe–W diffusion barrier layers on the evolution of Sn/Cu interface

In 3D IC, a high-efficiency diffusion barrier layer is urgently required for Sn/Cu micro-bumps, to inhibit the formation of Cu–Sn intermetallic compounds (IMCs). In this work, the barrier performance of electrodeposited Ni, Co–9W, Co–20W, Co–20Fe–10W and Co–36Fe–17W were studied. After aging at 150 °C for 672 h, the thicknesses of the IMCs formed between Sn and these barriers were determined. Among the five barriers studied, Co–36Fe–17W exhibited the best barrier effect, with a thickness of 0.61 μm. At the Sn/Co–W interface, CoSn3 IMC and Co–W–Sn were formed, while at the Sn/Co–Fe–W interface, CoSn3 IMC, FeSn2 IMC, and Co–Fe–W–Sn were observed. The layered CoSn3 IMC gradually evolved into an isolated island structure as the Fe and W concentration rose at the Sn/Co–Fe–W samples. The growth of CoSn3 in the Sn/Co–W and Sn/Co–Fe–W samples involved a competition between diffusion control and interfacial reaction control. The presence of W atoms effectively inhibited Co diffusion, while the FeSn2 IMC layer acted as a barrier, suppressing the nucleation of CoSn3. The synergistic effect of these factors contributed to the excellent barrier properties of the Co–Fe–W layer. This research establishes a scientific basis for selecting barriers that exhibit superiority in advanced packaging.

Effect of Gd addition on the structural and magnetic properties of L1-FePt alloy thin films

The impact of Gd addition on the structural and magnetic properties of L10-FePt alloy thin films, which were sputter-deposited on MgO(001) substrates at 800°C, was investigated. A rapid deterioration of L10 chemical ordering along with a strong amorphization effect is observed with addition of Gd. At more than 20 at. % Gd, additional crystalline phases occur. Due to the diminishing L10 chemical order, the perpendicular magnetic anisotropy (PMA) gets strongly reduced from about 3 down to 1 MJ/m3 with addition of 14 at. % Gd. For higher Gd concentrations, the easy axis of magnetization turns fully in-plane due to dominating magnetic shape anisotropy. Furthermore, the saturation magnetization gets reduced with Gd addition due to the antiferromagnetic coupling between the Fe and Gd magnetic moments. Also, the Curie temperature can be lowered. Interestingly, with addition of Gd, a change in film morphology takes place, changing from an isolated island structure to a more continuous film morphology, which is of particular interest for samples with low Gd concentration as these films exhibit still strong PMA but rather low coercive fields.

Thermal treatment for enhancing performance of NiO/Ag/NiO transparent conducting electrode fabricated via magnetron radio-frequency sputtering

A NiO/Ag/NiO (NAN) transparent conducting electrode (TCE) is fabricated using a low-cost magnetron-sputtering system. The effects of various thicknesses of the Ag intermediate layer and different annealing temperatures on the optical and electrical properties of the prepared TCEs are investigated comprehensively. A NAN TCE with a thin (8 nm) Ag layer demonstrates a slightly lower average transmittance than that with a 10 nm Ag layer because the thinner Ag layer appears as an isolated island structure, resulting in higher optical absorption. As the Ag thickness increases to 10 nm, the isolated islands become connected to each other and form a continuous thin film. As the Ag thickness increases, the carrier concentration and mobility increase and the formation of a continuous dense film, which decrease the resistivity and sheet resistance of the NAN TCE. The NAN TCE with a 14-nm intermediate Ag layer exhibits a sheet resistance of 3.67 Ω/sq, which is much lower than that (34 Ω/sq) of a single ITO electrode. The NAN TCE with a 10-nm Ag exhibits the highest figure-of-merit (FOM) than others. The annealing significantly increases the FOM from 2.5 × 10–4 to 1.2 × 10–2 Ω−1, respectively, for the as-deposited NAN TCE with a 10-nm Ag layer and the NAN TCE annealed at 400 °C. However, the performance of NAN TCE degrades at higher annealing temperature (500 °C).

The red deer antler: Bioinspired design of an Al[sbnd]Si composite with a fenestrated network-particle structure

Conventional AlSi materials always have a coarse and discontinuous Si structure, which limits their application as thermal management materials. Fortunately, nature has evolved efficient strategies to form complex microstructures that exhibit excellent wear resistance and thermal properties; one such example is found in the red deer antler. Here, inspired by the antler structure, AlSi composites with a novel fenestrated network-particle structure (FN) and with a common isolated island structure (II) are designed and prepared. Subsequently, the dynamic formation of FN is tracked and studied using computational fluid dynamics (CFD) simulation. To investigate the reinforcement mechanisms of FN, the wear resistances and thermal properties of FN and II are compared and analyzed. Simulation and experimental results show that the reconstruction of a semi-continuous structure promotes the formation of a striated structure, whereas flowing Si particles provide some sites for the formation of the fenestrated structure. The dynamic formation of FN is strongly influenced by the convection–diffusion process and the flow path. Moreover, this biomimetic FN structure exhibits better wear resistance and thermal properties than II, owing to its strong structural support and high expansion resistance. This work is expected to provide new perspectives on the microstructural design of thermal management materials with good wear resistance.

Study on the interfacial bonding mechanism of Al/Mg gradient material

Ti/Al/Mg impedance-graded material sheet is an alternative to the homogeneous single-layer sheets, which has been presented to improve shielding performance through the high efficient absorption and dissipation of fragment kinetic energy. Nevertheless, one limitation of the Ti/Al/Mg gradient material is associated with the weak Al/Mg interface. The purpose of this study is to investigation the interfacial bonding mechanism of Al/Mg gradient material interface. Microstructure characteristics at the Al/Mg interface have been investigated. It shows that an isolated island structure preferentially generates at the crystal defect as a consequence of interdiffusion, which is composed of Al3Mg2 and Al12Mg17. Then such intermetallic compounds (IMCs) grow to continuous layers with distinct convex. Finally, the interface is fully transformed into flat. A theoretical analysis and calculation have been carried out to explain the thermodynamically feasibility of IMCs. The evolution mechanism of voids at the interface is also discussed. Fractographic analysis performed on selected specimens shows typical brittle cleavage fracture characteristics, and detailed analyses reveal that the fracture failure is associated with brittle IMCs.

Comparison of microstructures and magnetic properties in FePt alloy films deposited by direct current magnetron sputtering and high power impulse magnetron sputtering

Single-layered FePt films of 30 nm thickness with random orientation are produced by direct current magnetron sputtering (DCMS) deposited directly onto Corning 1737 glass substrates and then post-annealed at 700 °C for 30 min. In films produced by high power impulse magnetron sputtering (HiPIMS) however, a strong (001) texture of L10 FePt film with isolated island structure is achieved and presents high perpendicular magnetic anisotropy after post-annealing under the same conditions. This is due to the compressive stress in as-deposited FePt films being enhanced greatly by HiPIMS. The films achieved by HiPIMS possess perpendicular coercivity, saturation magnetization and perpendicular squareness of 14.2 kOe, 620 emu/cm3 and 0.98, respectively, which reveal HiPIMS as a good technique to produce single-layered FePt films with high perpendicular magnetic properties.

Flexible and semi-transparent perovskite solar cells

Organic-inorganic hybrid perovskite solar cells have experienced a skyrocketing photoelectric conversion efficiency (PCE) increase in recent years, and become the “rock star” in the field of solar cells. After only 4 years, the certificated PCE of these materials based solid state solar cells have reach the maximum 22.1%, which is comparable to the highest PCE of the commercial silicon-based solar cells and higher than those of the organic solar cells and the dye-sensitized solar cells. Besides the promising efficiency, these materials surpass its competitors with the adaptability to solution- process at low-temperature and in air, and better flexibility, which can lead to lower large-scale production cost and more application potential for wearable electronics. The outstanding device performance of the hybrid perovskite solar cells have attracted intensive research interest, and besides increasing the PCE, lots of efforts have been focused on functional diversification for this solar cells. Compare to the commercial solar cells based on rigid silicon, organic- inorganic hybrid perovskite materials exhibit better flexibility which is beneficial for applications in flexible electronic devices, and due to the mild preparation conditions and the solution processablity, it is easy to prepare a variety of nanostructures. Those advantages have expanded the application scope of the hybrid perovskite materials, especially for fabricating flexible and semi-transparent solar cells which have potential use in building integrated photovoltaic such as solar cell windows and solar cell curtains. Here in this review, we focus on the recent progress of the flexible and semi-transparent solar cells based on organic-inorganic hybrid perovskite materials. In the part of the flexible hybrid perovskite solar cells, two mainstream device structures, namely planar and fiber-shaped devices, are discussed and the device structure and materials selection are analyzed in detail. As for the planar flexible perovskite solar cells, the choosing of the low-temperature processable function materials for the solar cells seems to be one of key factors due to the fact that most flexible planar substrates are vulnerable to the high-temperature treatments. As for the fiber-shaped perovskite solar cells, the choosing of the proper transparent conductive electrode materials is crucial which should have a good balance between the transparency and conductivity, and due to the difficulty of forming high-quality perovskite function layer on the curved surface of a certain wire, the prepare methods have to be upgraded too. In the part of the semi-transparent hybrid perovskite solar cells, two main strategies (reducing film thickness and forming isolated island structure) are discussed and a lot of reported preparation methods are analyzed in detail. As for the former strategy of reducing film thickness, the advantages are the comparatively higher PCE, easier manufacture and better controllability and the disadvantage is the unfavorable brownish color. As for the latter strategy of forming isolated island structure, the advantage is the better full-spectrum transmission and the disadvantages are comparatively more complicated manufacture and worse controllability. The whole paper has presented the development of the flexible and semi-transparent perovskite solar cells so far and gave detailed discussions for the reported works. Based on these analyzations, the organic-inorganic hybrid perovskites will find their special and unique position in the field of flexible and semi-transparent solar cells and may aggressively push the field forward.

Erratum: Frequency selective surface with switchable polarization

ABSTRACTThis article presents a novel frequency selective surface (FSS) with switchable polarization, which is realized using the improved cross slots with embedded strips and isolated island structure. The transmission characteristics of FSS unit cell for both horizontal polarization and vertical polarization are simulated with CST. And a FSS made of an array of 20 X 20 cells is implemented on the substrate Rogers RO4003. The experiment results show that the proposed FSS can obtain polarization switching through short and open circuits for X‐band application. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:515–518, 2014; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.28123. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1729, 2014

Frequency selective surface with switchable polarization

ABSTRACTThis article presents a novel frequency selective surface (FSS) with switchable polarization, which is realized using the improved cross slots with embedded strips and isolated island structure. The transmission characteristics of FSS unit cell for both horizontal polarization and vertical polarization are simulated with CST. And a FSS made of an array of 20 × 20 cells is implemented on the substrate Rogers RO4003. The experiment results show that the proposed FSS can obtain polarization switching through short and open circuits for X‐band application. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:515–518, 2014

Single-pulse drilling study on Au, Al and Ti alloy by using a picosecond laser

Picosecond laser single pulse ablation of Au, Al and Ti alloy (Ti6Al4V) was experimentally investigated with a laser pulse width of 10 ps at a wavelength of 1064 nm for potential industrial micromachining applications. The diameters, depths and morphologies of the drilled craters were studied. Two novel phenomena were found: as hole diameters decreased with fluence, a change of slope of the trend line indicated a change in ablation mechanism for Al and Ti alloy, metallic materials with short electron-phonon coupling times (<10 ps), while Au showed no such transition: an isolated island structure was also observed on Au due to significant melt expulsion. A one-dimensional two-temperature model has been used to discriminate different ablation phenomena. It is shown that metallic materials with different electron–phonon coupling constant have different ablation characteristics in the ps regime. This study could be very helpful for metallic material micromachining with high repetition rate ps lasers pulses which indicates that high throughput may be achieved as well as good machining quality.

Microstructure and electric property of MgO/Fe/MgO tri-layer films forming a nano-granular system

For tunneling magnetoresistance (TMR) devices using ferromagnetic nano particle films, the size, dispersion and number of nano particles are important factors. Relating to this, single layered Fe films (thickness: t = 0.5 – 10.0 nm) sandwiched between two MgO (2 nm thick) layers were fabricated by molecular beam epitaxy. By depositing at T s = RT (room temperature), the Fe layer had an isolated island structure for less than 1 nm thick. Correspondingly, the negative magnetoresistance effect was observed, which is characteristic of TMR. By increasing T s, the resistivity and the magnetoresistance (MR) ratio was increased. In this study, it was found that the optimal parameters for the growth of nano particle MgO/Fe/MgO based films are t = 0.5 – 1.0 nm and T s = RT − 120 °C.

Particulate structure of FePt thin films enhanced by Au and Ag alloying

The additions of Au and Ag to FePt thin film change the film structure from an interconnected network to a completely isolated island structure. In particular, the Ag addition led to an isolated particulate structure smaller than 100nm, which increased the coercivity from 5.4to20.5kOe. Energy filtered elemental mapping did not show evidence for the precipitation or segregation of Au and Ag.

Formation of thin calcium carbonate films with aragonite and vaterite forms coexisting with polyacrylic acids and chitosan membranes.

CaCO3 crystallization on a chitosan membrane was studied using diffusion of (NH4)2CO3 vapors into a CaCl2 solution containing differing added amounts of two polyacrylic acids (PAAs) with molecular weights of ca. 2.0 x 10(3) and ca. 4.5 x 10(4). The coexistence of PAA and the chitosan membranes produced thin CaCO3 island crystals, which developed into a continuous CaCO3 film on the membranes. Continuous CaCO3 films consisting of only aragonite formed on the chitosan membranes at the optimum amount of PAA. When the amount of PAA is not optimum, the polymorph of CaCO3 switches from aragonite to vaterite, and the morphology has a tendency to become an isolated island structure. The formation of the aragonite and vaterite island crystals and the appearance of a range of added PAA suitable for their formation are explained by the action of two parallel phenomena: (a) the high concentration of Ca2+ ions in the chitosan membrane vicinity is achieved by the interaction between the -COO- groups of PAA adsorbed by the -NH3+ groups of the chitosan membrane through an electrostatic force and free Ca2+ ions in the CaCl2 solution, which produces the high supersaturation with CaCO3 in the membrane vicinity during CO2 diffusion; (b) PAA, remaining as mobile carboxylic anions in the CaCO3 solution, inhibits the growth of the CaCO3 island crystals by its adsorption. The CaCO3 supersaturation in the membrane vicinity is controlled by regulating the balance of these phenomena, which leads to the formation of the desired CaCO3 polymorph.

Agglomeration of Copper Thin Film in Cu/Ta/Si Structure

Copper agglomeration in Cu(100nm)/Ta(50urn)/Si structure deposited by ion beam deposition was examined. Copper thin films were annealed at 650°C for 1 to 60 min in hydrogen atmosphere. The surface morphology, crystalline microstructure and electrical resistivity were investigated by field-emission scanning electron microscopy, X-ray diffraction and Van der Pauw method, respectively. Experimental results revealed that nucleation and growth of voids ocurred in the copper film annealed for 5 min. Further annealing made the film a connected island structure and then isolated island structure.