Electrical and optical properties of deep-red top-surface-emittinglasers

By studying thermal behavior of all-MBE surface-emitting lasers, barrier heights and optimum cavity design parameters are obtained. The barrier heights for holes between hetero-interfaces of Al_0.3Ga_0.7As-Al_0.65Ga_0.35As and AlAs-Al_0.65Ga_0.35As (Δx=-0.35) are measured to be 77 meV at zero bias for the deep-red top-surface-emitting laser. The barrier height decreases linearly with forward bias voltage, explaining the nonlinearity in current-voltage characteristics of the top-surface-emitting laser. The contribution of electrons to electrical resistance is estimated to be negligibly small compared to that of holes for the structure consisting of Δ_x =0.35. Minimum threshold current and maximum differential quantum efficiency observed around 200 K indicate slight mismatch between gain maximum and Fabry-Perot resonance for the deep-red top-surface-emitting laser     

Chemiluminescent and Antioxidant Micelles as Theranostic Agents for Hydrogen Peroxide Associated‐Inflammatory Diseases

Hydrogen peroxide (H₂O₂) is one of essential oxygen metabolites in living organisms, but is generated in large amounts during inflammatory responses. Therefore, H₂O₂ has great potential as diagnostic and therapeutic markers of several inflammatory and life‐threatening diseases. Here, chemiluminescent and antioxidant micelles are reported as novel theranostic agents for H₂O₂‐associated inflammatory diseases. The chemiluminescent micelles composed of amphiphilic block copolymer Pluronic F‐127, hydroxybenzyl alcohol‐incorporated copolyoxalate (HPOX) and fluorescent dyes perform peroxalate chemiluminescence reactions to detect H₂O₂ as low as 100 nM and image H₂O₂ generated in inflamed mouse ankles. The micelles encapsulating HPOX reduce the generation of reactive oxygen species in lipopolysaccharide (LPS)‐activated macrophages by scavenging overproduced H₂O₂ and releasing antioxidant hydroxybenzyl alcohol (HBA). They also exert inhibitory effects on H₂O₂‐induced apoptosis. HPOX‐based chemiluminescent and antioxidant micelles have great potential as a theranostic agent for H₂O₂‐associated inflammatory diseases.     

Chip warpage model for reliability prediction of delamination failures

A new experimental method to predict reliability for ACA type packages under temperature cycling is developed and proposed. The method introduces a new damage parameter that can be easily measured by experiment. It is proved that the linear elastic parameter, dw/dT which represents the rate of change of chip warpage with respect to temperature, efficiently reflects the common failure mechanism of ACA type packages, the interfacial delamination between the chip and the adhesive. It is demonstrated, both experimentally and numerically, that the size of delamination affects the warpage behavior of the chip. The dw/dT of the chip is monitored in real time using laser interferometers under thermal fatigue cycles up to 3000. The gradual decrease in warpage due to progressive increase in delamination is clearly emerged. As a result, a reliability curve that can predict the size of delamination and remained life is obtained. The new long-term reliability prediction method developed in this study can be applied to various advanced packages, e.g. underfilled flip–chip or TSV stacked chip packages, that embrace interfacial delamination as primary failure mode.     

Characteristics of solderable electrically conductive adhesives (ECAs) for electronic packaging

This study investigated the effect of the viscosity of the ECAs using a low-melting-point alloy (LMPA) filler on its bonding characteristics. The curing behaviors of the ECAs were determined using Differential Scanning Calorimetry (DSC), and ECA temperature-dependant viscosity characteristics were observed using a torsional parallel rheometer. The wetting test was conducted to investigate the reduction capability of ECAs and the flow-coalescence-wetting behavior of the LMPAs in ECAs. Electrical and mechanical properties were determined and compared to those with commercial ECAs and eutectic tin/lead (Sn/Pb) solder. In the metallurgically interconnected Quad Flat Package (QFP) joint, a typical scallop-type Cu–Sn intermetallic compound (IMC) layer formed at the upper SnBi/Cu interface after curing process. On the other hand, a (Cu, Ni)₆Sn₅ IMC layer formed on the SnBi/ENIG interface. In addition, the fracture surface exhibited by cleavage fracture mode and the fracture was propagated along the Cu–Sn IMC/SnBi interface. The extremely low-level viscosity of ECAs had a significant influence on the flow-coalescence-wetting behavior of the LMPAs in ECAs and also on the interconnection properties. Stable interconnected assemblies showed good electrical and mechanical properties.     

CdSe-sensitized inorganic–organic heterojunction solar cells: The effect of molecular dipole interface modification and surface passivation

CdSe-sensitized heterojunction solar cells composed of mesoscopic TiO₂/CdSe/P3HT (poly-3-hexylthiophene) were constructed, and the negative molecular dipole of 4-methoxybenzenethiol (MBT) and the ZnS passivation layer were used as interface modifiers to improve device performance. Through the interface modification between TiO₂/CdSe and P3HT using MBT and by ZnS surface passivation, the power conversion efficiency of the modified solar cell was greatly enhanced from 1.02% to 1.62% under 1 sun illumination.     

Anti-buckling S-shaped vertical microprobes with branch springs

We propose the S-shaped vertical probes with branch springs for the wafer-level testing of IC chips. The conventional S-shaped vertical probe requires a guide structure to prevent buckling due to the large overdrive actuation involved. However, the guide structure not only increases the cost of fabrication, but it also requires a troublesome assembly procedure. In this paper, we present the S-shaped vertical probe with branch springs on the left and right sides of the main spring to prevent buckling. This probe was designed using finite-element methods and fabricated using Ni-Co electroplating. The performances of the probe for the wafer-level testing of IC chips were measured with the probe test equipments. Compared to the identical conventional S-shaped probe, the proposed probe has the overdrive (60 μm) that is 1.2 times larger and the contact force (25 mN) that is 2.5 times larger. This new S-shaped vertical probe satisfies the design requirements for a vertical probe without the guide structure and has the potential for use as a cost-effective guide-free probe card for the wafer-level testing of IC chips.     

Security analysis of pure DDP-based cipher proper for multimedia and ubiquitous device

DDP-64, based on various controlled operations, is a 64-bit Feistel-like block cipher consisting of 10 rounds with a 128-bit key. It was designed to attempt to have a high security level and a high speed performance in hardware on ubiquitous computing systems and multimedia. In this paper, however, we show that DDP-64 doesn’t have a high security level, more precisely, we show that it is vulnerable to related-key differential attack. This attack, which is much faster than the key exhaustive search, requires about 2⁵⁴ data and 2⁵⁴ time complexities. This work is the first known cryptanalytic result on DDP-64 so far.     

Understanding Boosted Selective CO2-to-CO Photoreduction with Pure Water Vapor over Hierarchical Biomass-Derived Carbon Matrix

Solar-driven CO₂ reduction reaction (CO₂RR) with water into carbon-neutral fuels is of great significance but remains challenging due to thermodynamic stability and kinetic inertness of CO₂. Biomass-derived nitrogen-doped carbon (N-C_b) have been considered as promising earth-abundant photocatalysts for CO₂RR, although their activities are not ideal and the reaction mechanism is still unclear. Herein, an efficient catalyst is developed for CO₂-to-CO conversion realized on diverse N-C_b materials with hierarchical pore structures. It is demonstrated that the CO₂-to-CO conversion preferentially takes place on positively charged carbon atoms next to pyridinic-N using two representatives treated pollens with the largest difference in pyridinic-N density and N content as model photocatalysts. Systematic experimental results indicate that surface local electric field originating from charge separation can be boosted by hierarchical pore structures, doped N, as well as pyridinic-N. Mechanistic studies reveal that positively charged carbon atoms next to pyridinic-N serve as active sites for CO₂RR, reduce the energy barrier on the formation of CO*, and facilitate the CO₂RR performance. All these benefits cooperatively contribute to treated chrysanthemum pollen catalyst exhibiting excellent CO formation rate of 203.2 µmol h⁻¹ g⁻¹ with 97.2% selectivity in pure water vapor. These results provide a new perspective into CO₂RR on N-C_b, which shall guide the design of nature-based photocatalysts for high-performance solar-fuel generation.     

Unveiled Ferroelectricity in Well-Known Non-Ferroelectric Materials and Their Semiconductor Applications

Ferroelectric materials are considered ideal for emerging memory devices owing to their characteristic remanent polarization, which can be switched by applying a sufficient electric field. However, even several decades after the initial conceptualization of ferroelectric memory, its applications are limited to a niche market. The slow advancement of ferroelectric memories can be attributed to several extant issues, such as the absence of ferroelectric materials with complementary metal–oxide–semiconductor (CMOS) compatibility and scalability. Since the 2010s, ferroelectric memories have attracted increasing interest because of newly discovered ferroelectricity in well-established CMOS-compatible materials, which are previously known to be non-ferroelectric, such as fluorite-structured (Hf,Zr)O₂ and wurtzite-structured (Al,Sc)N. With advancing material fabrication technologies, for example, accurate chemical doping and atomic-level thickness control, a metastable polar phase, and switchable polarization with a reasonable electric field can be induced in (Hf,Zr)O₂ and (Al,Sc)N. Nonetheless, various issues still exist that urgently require solutions to facilitate the use of the ferroelectric (Hf,Zr)O₂ and (Al,Sc)N in emerging memory devices. Thus, ferroelectric (Hf,Zr)O₂ and (Al,Sc)N are comprehensively reviewed herein, including their fundamental science and practical applications.     

Mobile Robot Navigation Using Wireless Sensor Networks Without Localization Procedure

In this paper, algorithms for navigating a mobile robot through wireless sensor networks are presented. The mobile robot can navigate without the need for a map, compass, or GPS module while interacting with neighboring sensor nodes. Two navigation algorithms are proposed in this paper: the first uses the distance between the mobile robot and each sensor node and the second uses the metric calculated from one-hop neighbors’ hop-counts. Periodically measuring the distance or metric, the mobile robot can move toward a point where these values become smaller and finally come to reach the destination. These algorithms do not attempt to localize the mobile robot for navigation, therefore our approach permits cost-effective robot navigation while overcoming the limitations of traditional navigation algorithms. Through a number of experiments and simulations, the performance of the two proposed algorithms is evaluated.