Bioinspired High Tolerant Vein–Membrane Al2O3 Coating

The vein–membrane structure inspired by insect wings is applied to the artificial structural design of materials, with the aim of enhancing the intrinsic low strain tolerance and bonding strength of Al₂O₃ coating. Al₂O₃ platelets with high aspect ratio are used as veins, forming a bioinspired vein–membrane structure along with the Al₂O₃ membrane. Further, Al₂O₃ platelets take “root” in the substrate, forming a bioinspired root–soil interlocking structure. The greatest highlight of this coating is that it can restrict the cracks to the submicron area enclosed by the vein. The multi-bioinspired structure enabled the Al₂O₃ coating to sustain strains as high as 8%, which is 2 orders of magnitude higher than the reported failure strain of Al₂O₃ film. The bonding strength is also increased by at least five times. The vein–membrane structure opens a novel technological space for the artificial structural design of materials.     

Investigation of silicon-based light emitting diode sub-mounts: Enhanced performance and potential for improved reliability

Aluminum nitride (AlN) and aluminum oxide (Al₂O₃) ceramic light emitting diode (LED) sub-mounts are the most widely used package substrate for recently-developed high-brightness (HB) LED package applications because they exhibit superior thermal conductivity compared to conventional printed circuit board (PCB) package substrates. Nonetheless, the Al₂O₃ ceramic sub-mount exhibits thermal conductivity in an unacceptable range, and manufacturing the AlN ceramic sub-mount is problematic due to high material cost and difficult processing. Wafer-level packaging (WLP) technology has shown noticeable improvements in manufacturing and silicon exhibits outstanding thermal conductivity. Thus silicon might become an alternative package substrate for HB LEDs. This research studied the feasibility of replacing conventional ceramic sub-mounts with WLP LED sub-mounts. The performance features of thermal dissipation, insulation, and high temperature reliability of LED sub-mounts with variable SiO₂ thickness were analyzed and compared to the results obtained from conventional Al₂O₃ and AlN ceramic sub-mounts. Experimental results show that silicon LED sub-mounts lead to better thermal dissipation performance than do Al₂O₃ ceramic sub-mounts, and the results also reveal acceptable insulation performance and high temperature reliability for silicon sub-mounts.     

Blue–Green Emission in Terbium‐Doped Alumina (Tb:Al2O3) Transparent Ceramics

Alumina (Al₂O₃) is one of the most versatile ceramics, utilized in an amazing range of structural and optical applications. In fact, chromium‐doped single crystal Al₂O₃ was the basis for the first laser. Today, most photoluminescent (PL) materials rely on rare earth (RE) rather than transition‐metal dopants because RE doping produces greater efficiencies and lower lasing thresholds. RE‐doped alumina could provide an extremely versatile PL ceramic, opening the door for a host of new applications and devices. However, producing a transparent RE:Al₂O₃ suitable for PL applications is a major challenge due to the very low equilibrium solubility of RE (～10^?3%) in Al₂O₃ in addition to alumina's optical anisotropy. A method is presented here to successfully incorporate Tb³⁺ ions up to a concentration of 0.5 at% into a dense alumina matrix, achieving a transparent light‐emitting ceramic. Sub‐micrometer alumina and nanometric RE oxide powders are simultaneously densified and reacted using current‐activated, pressure‐assisted densification (CAPAD), often called spark plasma sintering (SPS). These doped ceramics have a high transmission (～75% at 800 nm) and display PL peaks centered at 485 nm and 543 nm, characteristic of Tb³⁺ emission. Additionally, the luminescent lifetimes are long and compare favorably with lifetimes of other laser ceramics. The high transparencies and PL properties of these ceramics have exciting prospects for high energy laser technology.     

基于板上封装技术的大功率LED热分析

根据大功率LED板上封装(COB)技术的结构特点,提出三种COB方法.第一种方法是把芯片直接键合在铝制散热器k(COB-III型),另外两种方法是分别把芯片键合在铝基板上和铝基板的印刷线路板上(COB-II和COB-I型),并对三种COB的热特性进行有限元模拟、实验测量和对照分析.结果表明:在环境温度为30℃时,采用第...     

Material property, compatibility, and reliability issues in diamond-enhanced, GaAs-based plastic packages

The mechanical performance and reliability of various Al₂O₃ ceramics were evaluated with intended applications as insulator frames for radio frequency/microwave power packages. Considering variations in base-flange material properties (CuW, CuMoCu), base-flange thickness (0.040 in., 0.020 in.), assembly process material (AgCu, Cu) assembly process temperature (860°C, 1080°C), and Al₂O₃ insulator material (96%, 99%, 20% ZrO₂/Al₂O₃, ZTA), finite element analysis (FEA) spatially resolved the fabrication-induced stresses during the assembly of CuW/Al₂O₃ and CuMoCu/Al₂O₃ structures and showed the critical regions to be the frame corners at the metal base-flange/Al₂O₃ interface. Bend strengths (four-point) and Weibull distributions were determined for each Al₂O₃ material and coupled with the FEA-predicted stresses for the various package configurations and assembly processes, the failure probabilities (P_f ) for the various CuW/Al₂O₃ and CuMoCu/Al₂O₃ structures were calculated. The CuMoCu-based structures exhibited the greatest warp deformation (concave upward, +), and highest stress and failure probability for all Al₂O₃ insulator varieties. The CuW-based structures exhibited an order-of-magnitude lower warp deformation (concave downward, −), an order-of-magnitude lower stress in the Al₂O₃, and in excess of seven orders-of-magnitude lower failure probability than CuMoCu-based structures, for all Al₂O₃ insulator varieties. Confirmational experiments were conducted using AgCu and direct-bond copper (DBC) assembly processes for selected varieties of CuW/Al₂O₃ and CuMoCu/Al₂O₃ structures. Al₂O₃ failure sites were identified using radiographic, ultrasonic and optical techniques and were in good agreement with model predictions of suspect structures and failure location. The strength and reliability data were considered in conjunction with relative cost for the Al₂O₃ ceramics to select an optimum frame insulator for the application.     

Highly Conductive Porous Graphene/Ceramic Composites for Heat Transfer and Thermal Energy Storage

A novel architecture of 3D graphene growth on porous Al₂O₃ ceramics is proposed for thermal management using ambient pressure chemical vapor deposition. The formation mechanism of graphene is attributed to the carbothermic reduction occurring at the Al₂O₃ surface to initialize the nucleation and growth of graphene. The graphene films are coated on insulating anodic aluminum oxide (AAO) templates and porous Al₂O₃ ceramic substrates. The graphene coated AAO possesses one‐dimensional isolated graphene tubes, which can act as the media for directional thermal transport. The graphene/Al₂O₃ composite (G‐Al₂O₃) contains an interconnected macroporous graphene framework with an extremely low sheet electrical resistance down to 0.11 Ω sq^?1 and thermal conductivity with 8.28 W m^?1 K^?1. The G‐Al₂O₃ provides enormous conductive pathways for electronic and heat transfer, suitable for application as heat sinks. Such a porous composite is also attractive as a highly thermally conductive reservoir to hold phase change materials (stearic acid) for thermal energy storage. This work displays the great potential of CVD direct growth of graphene on dielectric porous substrates for thermal conduction and electronic applications.     

Low-power organic field-effect transistors and complementary inverter based on low-temperature processed Al2O3 dielectric

Organic-based complementary inverter could be a key component in future flexible and portable electronic products, which require low-power operation, high operating stability and flexible compatibility at the same time. A simple method for making excellent Al₂O₃ gate dielectric is developed toward the target, and it is a low-cost solution process with a low annealing temperature compatible with plastic substrates. Utilizing the Al₂O₃ dielectric, both p-type and n-type low-voltage organic field-effect transistors (OFETs) are realized. The device operating voltage is down to ±3 V, and the On/Off ratio is up to 10⁶. The hole and electron field-effect mobilities are 2.7 cm²/V and 0.2 cm²/V, respectively, and the subthreshold swing is as small as about 110 mV/decade. The high quality of the Al₂O₃ dielectric results in high operating stability of the devices. The p-type and n-type OFETs are integrated to achieve a low-power complementary inverter with a large gain, which can be successfully fabricated on a flexible substrate.     

Ultrathin nano-sized Al2O3 strips on the surface of por-Si

The objective of this paper is to obtain nano-sized Al₂O₃ strips on the surface of nanoporous silicon surface as well as fundamental investigations of structural, optical and morphological properties of the materials.While analysing the results, we were able to prove for the first time that the use of ion plasma sputtering allows one to obtain ultrathin nanostructured Al₂O₃ films as unidirectional fibres arranged by 300–500 nm away from one another on a porous silicon layer. Such mechanism of the growth of aluminium oxide strips is stipulated by the morphology of porous silicon layer obtained as a result of etching of the virgin silicon plate; that in turn determines distinctions in the morphology of ultra-thin Al₂O₃ film.The results of optical spectroscopy shows that the Al₂O₃ nano-sized strips of the heterophase structure of Al₂O₃/por-Si/Si(111) is good at transmitting electromagnetic radiation of 190–900 nm. It is shown that the intensity of photoluminescence excited by the heterophase structure Al₂O₃/por-Si/Si(111) is by 30% higher than that excited by the film of the porous layer.The analysis of dispersion of refractive index in the investigated systems showed that its values for the heterophase structure Al₂O₃/por-Si/Si(111) in the entire range of the wavelengths of the deflection is considerably higher than that those ones of Al₂O₃ grown under similar conditions using single-crystalline silicon Si(111). In the wavelengths of 250–500 nm the refractive index of the heterophase structure Al₂O₃/por-Si/Si(111) is similar to that one of por-Si used for growing of the heterophase structure.The observed maximum in the dispersion of the refractive index of Al₂O₃ nano-sized strips grown on por-Si is identical to the optical absorption edge of the aluminium oxide and is in the range of ~5.60 eV. This is consistent with the results of calculations of the optical absorption spectrum for the heterophase structure Al₂O₃/por-Si/Si(111).The nano-sized structured strips of Al₂O₃ films on the surface of the heterophase structure can serve as optical transmission channels and are quite efficiently introduced into the standard practices, which is of significant importance for micro- and optoelectronics.     

Effect of interfacial fluorination on the electrical properties of the inter-poly high-k dielectrics

In this paper, the reliabilities and insulating characteristics of the fluorinated aluminum oxide (Al₂O₃) and hafnium oxide (HfO₂) inter-poly dielectric (IPD) are studied. Interface fluorine passivation has been demonstrated in terminating dangling bonds and oxygen vacancies, reducing interfacial re-oxidation and smoothing interface roughness, and diminishing trap densities. Compared with the IPDs without fluorine incorporation, the results clearly indicate that fluorine incorporation process is effective to improve the insulating characteristics of both the Al₂O₃ and HfO₂ IPDs. Moreover, fluorine incorporation will also improve the dielectric quality of the interfacial layer. Although HfO₂ possesses higher dielectric constant to increase the gate coupling ratio, the results also demonstrate that fluorination of the Al₂O₃ dielectric is more effective to promote the IPD characteristics than fluorination of the HfO₂ dielectric. For future stack-gate flash memory application, the fluorinated Al₂O₃ IPD undoubtedly possesses higher potential to replace current ONO IPD than the fluorinated HfO₂ IPD due to superior insulating properties.     

Use of Al2O3 as inter-poly dielectric in a production proven 130 nm embedded Flash technology

We have successfully integrated 2 Mb arrays with SiO₂/Al₂O₃ stacks as inter-poly dielectric (IPD) fabricated in a proven 130 nm embedded Flash technology. Gate stack write/erase high voltages (HV) can be reduced by 3 V. Write/erase distributions show evidence of bit pinning which can be explained by barrier lowering along Al₂O₃ grain boundaries. Reliability assessment of the 2 Mb array reveals promising data retention and cycle endurance, indicating the absence of charge trapping in the high-k IPD. Despite several integration issues, these results demonstrate the high potential of Al₂O₃ IPDs in embedded Flash technologies.     

Oriented Growth of Al2O3:ZnO Nanolaminates for Use as Electron‐Selective Electrodes in Inverted Polymer Solar Cells

Atomic layer deposition is used to synthesize Al₂O₃:ZnO(1:x) nanolaminates with the number of deposition cycles, x, ranging from 5 to 30 for evaluation as optically transparent, electron‐selective electrodes in polymer‐based inverted solar cells. Al₂O₃:ZnO(1:20) nanolaminates are found to exhibit the highest values of electrical conductivity (1.2 × 10³ S cm^?1; more than six times higher than for neat ZnO films), while retaining a high optical transmittance (≥80% in the visible region) and a low work function (4.0 eV). Such attractive performance is attributed to the structure (ZnO crystal size and crystal alignment) and doping level of this intermediate Al₂O₃:ZnO film composition. Polymer‐based inverted solar cells using poly(3‐hexylthiophene) (P3HT):phenyl‐C₆₁‐butyric acid methyl ester (PCBM) mixtures in the active layer and Al₂O₃:ZnO(1:20) nanolaminates as transparent electron‐selective electrodes exhibit a power conversion efficiency of 3% under simulated AM 1.5 G, 100 mW cm^?2 illumination.     

GaAs structures with a gate dielectric based on aluminum-oxide layers

Different types of dielectrics obtained by low-temperature electron-beam sputtering are studied; these dielectrics include Al₂O₃ layers and Al₂O₃/SiO₂/Al₂O₃ three-layer compositions. The dependence of the electrical strength of Al₂O₃ layers on their thickness is determined. It is established that formation of the three-layer dielectric Al₂O₃/SiO₂/Al₂O₃ makes it possible to increase the range of operating voltages up to 60 V for structures with a gate electrode. It is shown that it is possible to control the density of charge carriers (holes) in the two-dimensional conduction channel of GaAs structures by changing the gate voltage when the Al₂O₃/SiO₂/Al₂O₃ structure is used as a gate dielectric.     

High‐Performance Micro‐Solid Oxide Fuel Cells Fabricated on Nanoporous Anodic Aluminum Oxide Templates

Micro‐solid oxide fuel cells (μ‐SOFCs) are fabricated on nanoporous anodic aluminum oxide (AAO) templates with a cell structure composed of a 600‐nm‐thick AAO free‐standing membrane embedded on a Si substrate, sputter‐deposited Pt electrodes (cathode and anode) and an yttria‐stabilized zirconia (YSZ) electrolyte deposited by pulsed laser deposition (PLD). Initially, the open circuit voltages (OCVs) of the AAO‐supported μ‐SOFCs are in the range of 0.05 V to 0.78 V, which is much lower than the ideal value, depending on the average pore size of the AAO template and the thickness of the YSZ electrolyte. Transmission electron microscopy (TEM) analysis reveals the formation of pinholes in the electrolyte layer that originate from the porous nature of the underlying AAO membrane. In order to clog these pinholes, a 20‐nm thick Al₂O₃ layer is deposited by atomic layer deposition (ALD) on top of the 300‐nm thick YSZ layer and another 600‐nm thick YSZ layer is deposited after removing the top intermittent Al₂O₃ layer. Fuel cell devices fabricated in this way manifest OCVs of 1.02 V, and a maximum power density of 350 mW cm^?2 at 500 °C.     

原子层沉积氧化铝薄膜对多晶太阳能电池表面钝化的影响

A stack of Al2O3/SiNx dual layer was applied for the back side surface passivation of p-type multi-crystalline silicon solar cells, with laser-opened line metal contacts, forming a local aluminum back surface field （local Al-BSF） structure. A slight amount of Al2O3, wrapping around to the front side of the wafer during the thermal atomic layer deposition process, was found to have a negative influence on cell performance. The different process flow was found to lead to a different cell performance, because of the Al2O3 wrapping around the front surface. The best cell performance, with an absolute efficiency gain of about 0.6% compared with the normal full Al-BSF structure solar cell, was achieved when the Al2O3 layer was deposited after the front surface of the wafer had been covered by a SiNx layer. We discuss the possible reasons for this phenomenon, and propose three explanations as the Ag paste, being hindered from firing through the front passivation layer, degraded the SiNx passivation effect and the Al2O3 induced an inversion effect on the front surface. Characterization methods like internal quantum efficiency and contact resistance scanning were used to assist our understanding of the underlying mechanisms.     

Biosensor properties of SOI nanowire transistors with a PEALD Al<Subscript>2</Subscript>O<Subscript>3</Subscript> dielectric protective layer

The properties of protective dielectric layers of aluminum oxide Al₂O₃ applied to prefabricated silicon-nanowire transistor biochips by the plasma enhanced atomic layer deposition (PEALD) method before being housed are studied depending on the deposition and annealing modes. Coating the natural silicon oxide with a nanometer Al₂O₃ layer insignificantly decreases the femtomole sensitivity of biosensors, but provides their stability in bioliquids. In deionized water, transistors with annealed aluminum oxide are closed due to the trapping of negative charges of <(1–10) × 10¹¹ cm^?2 at surface states. The application of a positive potential to the substrate (V_sub > 25 V) makes it possible to eliminate the negative charge and to perform multiple measurements in liquid at least for half a year.     

Semiconductor nanowires surrounded by cylindrical Al2O3 shells

The GaN, GaP, InP, Si₃N₄, SiO₂/Si, SiC, and ZnO semiconductor nanowires were synthesized by a variety of growth methods, and they were wrapped cylindrically with amorphous aluminum oxide (Al₂O₃) shells. The Al₂O₃ was deposited on these seven different semiconductor nanowires by atomic layer deposition (ALD) at a substrate temperature of 200°C using trimethylaluminum (TMA) and distilled water (H₂O). Transmission electron microscopy (TEM) images taken for the nanowires revealed that Al₂O₃ cylindrical shells surround uniformly all these semiconductor nanowires. Our TEM study illustrates that the ALD of Al₂O₃ has an excellent capability to coat any semiconductor nanowires conformally; its coating capability is independent of the chemical component, lattice structure, and growth direction of the nanowires. This study suggests that the ALD of Al₂O₃ on nanowires is one of the promising methods to prepare cylindrical dielectric shells in coaxially gated, nanowire field-effect transistors (FETs).     

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.     

Rear‐Passivated Ultrathin Cu(In,Ga)Se2 Films by Al2O3 Nanostructures Using Glancing Angle Deposition Toward Photovoltaic Devices with Enhanced Efficiency

In this work, for the first time, the addition of aluminum oxide nanostructures (Al₂O₃ NSs) grown by glancing angle deposition (GLAD) is investigated on an ultrathin Cu(In,Ga)Se₂ device (400 nm) fabricated using a sequential process, i.e., post‐selenization of the metallic precursor layer. The most striking observation to emerge from this study is the alleviation of phase separation after adding the Al₂O₃ NSs with improved Se diffusion into the non‐uniformed metallic precursor due to the surface roughness resulting from the Al₂O₃ NSs. In addition, the raised Na concentration at the rear surface can be attributed to the increased diffusion of Na ion facilitated by Al₂O₃ NSs. The coverage and thickness of the Al₂O₃ NSs significantly affects the cell performance because of an increase in shunt resistance associated with the formation of Na₂Se_X and phase separation. The passivation effect attributed to the Al₂O₃ NSs is well studied using the bias‐EQE measurement and J–V characteristics under dark and illuminated conditions. With the optimization of the Al₂O₃ NSs, the remarkable enhancement in the cell performance occurs, exhibiting a power conversion efficiency increase from 2.83% to 5.33%, demonstrating a promising method for improving ultrathin Cu(In,Ga)Se₂ devices, and providing significant opportunities for further applications.     

Memory Effect of Metal-Insulator-Silicon Capacitor with HfO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Multilayer and Hafnium Nitride Gate

Metal-insulator-silicon capacitors have been fabricated using novel insulators of SiO₂/HfO₂-Al₂O₃-HfO₂ (HAH)/Al₂O₃ and metallic HfN gate, exhibiting a program-erasable characteristic. The memory capacitor presents a large memory window of 2.4 V under +12 V program/–14 V erase for 10 ms, no erase saturation, and sufficient electron- and hole-trapping efficiencies such as an electron density of ∼7 × 10¹² cm^–2 under 13 V program for 0.5 ms and a hole density of ∼4 × 10¹² cm^–2 under –12 V erase for 0.5 ms. The observed properties are attributed to the introduction of high permittivity atomic-layer-deposited HAH/Al₂O₃ as well as high work function HfN gate. The related mechanism is addressed accordingly.     

Low temperature aluminum oxide deposition using trimethylaluminum

Aluminum oxide films (amorphous and γ-Al₂O₃) have been deposited by the oxidation of trimethy1aluminum. Process parameters have been evaluated and optimized to obtain reasonable growth rates and film properties for deposition temperatures between 300 and 400° C. Values of the dielectric constant (7.5 – 7.8), the dielectric strength (7.5 – 7.9 × 10⁶ V/cm), the index of refraction (1.54 – 1.67), and the resistivity (> 10 ohm-cm) compare favorably with Al₂O₃, films grown with other processes at higher deposition temperatures. Film analysis by secondary ion mass spectrometry identified a distribution of carbon and sodium impurities.