Self-aligning planarization and passivation for integration applications in III-V semiconductor devices

This work reports an easy planarization and passivation approach for the integration of III-V semiconductor devices. Vertically etched III-V semiconductor devices typically require sidewall passivation to suppress leakage currents and planarization of the passivation material for metal interconnection and device integration. It is, however, challenging to planarize all devices at once. This technique offers wafer-scale passivation and planarization that is automatically leveled to the device top in the 1-3-/spl mu/m vicinity surrounding each device. In this method, a dielectric hard mask is used to define the device area. An undercut structure is intentionally created below the hard mask, which is retained during the subsequent polymer spinning and anisotropic polymer etch back. The spin-on polymer that fills in the undercut seals the sidewalls for all the devices across the wafer. After the polymer etch back, the dielectric mask is removed leaving the polymer surrounding each device level with its device top to atomic scale flatness. This integration method is robust and is insensitive to spin-on polymer thickness, polymer etch nonuniformity, and device height difference. It prevents the polymer under the hard mask from etch-induced damage and creates a polymer-free device surface for metallization upon removal of the dielectric mask. We applied this integration technique in fabricating an InP-based photonic switch that consists of a mesa photodiode and a quantum-well waveguide modulator using benzocyclobutene (BCB) polymer. We demonstrated functional integrated photonic switches with high process yield of >90%, high breakdown voltage of >25 V, and low ohmic contact resistance of /spl sim/10 /spl Omega/. To the best of our knowledge, such an integration of a surface-normal photodiode and a lumped electroabsorption modulator with the use of BCB is the first to be implemented on a single substrate.     

Multiobjective evolutionary clustering of Web user sessions: a case study in Web page recommendation

In this study, we experiment with several multiobjective evolutionary algorithms to determine a suitable approach for clustering Web user sessions, which consist of sequences of Web pages visited by the users. Our experimental results show that the multiobjective evolutionary algorithm-based approaches are successful for sequence clustering. We look at a commonly used cluster validity index to verify our findings. The results for this index indicate that the clustering solutions are of high quality. As a case study, the obtained clusters are then used in a Web recommender system for representing usage patterns. As a result of the experiments, we see that these approaches can successfully be applied for generating clustering solutions that lead to a high recommendation accuracy in the recommender model we used in this paper.     

Perinatal Obesity Induces Hepatic Growth Restriction with Increased DNA Damage Response,Senescence, and Dysregulated Igf-1-Akt-Foxo1 Signaling in Male Offspring of Obese Mice

Maternal obesity predisposes for hepato-metabolic disorders early in life. However, the underlying mechanisms causing early onset dysfunction of the liver and metabolism remain elusive. Since obesity is associated with subacute chronic inflammation and accelerated aging, we test the hypothesis whether maternal obesity induces aging processes in the developing liver and determines thereby hepatic growth. To this end, maternal obesity was induced with high-fat diet (HFD) in C57BL/6N mice and male offspring were studied at the end of the lactation [postnatal day 21 (P21)]. Maternal obesity induced an obese body composition with metabolic inflammation and a marked hepatic growth restriction in the male offspring at P21. Proteomic and molecular analyses revealed three interrelated mechanisms that might account for the impaired hepatic growth pattern, indicating prematurely induced aging processes: (1) Increased DNA damage response (γH2AX), (2) significant upregulation of hepatocellular senescence markers (Cdnk1a, Cdkn2a); and (3) inhibition of hepatic insulin/insulin-like growth factor (IGF)-1-AKT-p38-FoxO1 signaling with an insufficient proliferative growth response. In conclusion, our murine data demonstrate that perinatal obesity induces an obese body composition in male offspring with hepatic growth restriction through a possible premature hepatic aging that is indicated by a pathologic sequence of inflammation, DNA damage, senescence, and signs of a possibly insufficient regenerative capacity.     

Polarization Properties of Photoluminescence of Anisotropic Polymer Films Containing Aligned Au Nanorods and Semiconductor Nanoparticles of Various Shape

Semiconductors - Anisotropic polymer films containing aligned Au nanorods and semiconductor nanoparticles of various shape were fabricated. The photoluminescence of semiconductor nanoparticles in...     

RF-MEMS load sensors with enhanced Q-factor and sensitivity in a suspended architecture

In this paper, we present and demonstrate RF-MEMS load sensors designed and fabricated in a suspended architecture that increases their quality-factor (Q-factor), accompanied with an increased resonance frequency shift under load. The suspended architecture is obtained by removing silicon under the sensor. We compare two sensors that consist of 195 μm × 195 μm resonators, where all of the resonator features are of equal dimensions, but one’s substrate is partially removed (suspended architecture) and the other’s is not (planar architecture). The single suspended device has a resonance of 15.18 GHz with 102.06 Q-factor whereas the single planar device has the resonance at 15.01 GHz and an associated Q-factor of 93.81. For the single planar device, we measured a resonance frequency shift of 430 MHz with 3920 N of applied load, while we achieved a 780 MHz frequency shift in the single suspended device. In the planar triplet configuration (with three devices placed side by side on the same chip, with the two outmost ones serving as the receiver and the transmitter), we observed a 220 MHz frequency shift with 3920 N of applied load while we obtained a 340 MHz frequency shift in the suspended triplet device with 3920 N load applied. Thus, the single planar device exhibited a sensitivity level of 0.1097 MHz/N while the single suspended device led to an improved sensitivity of 0.1990 MHz/N. Similarly, with the planar triplet device having a sensitivity of 0.0561 MHz/N, the suspended triplet device yielded an enhanced sensitivity of 0.0867 MHz/N.     

A Monolithic Phased Array Using 3-bit Distributed RF MEMS Phase Shifters

This paper presents a novel electronically scanning phased-array antenna with 128 switches monolithically implemented using RF microelectromechanical systems (MEMS) technology. The structure, which is designed at 15 GHz, consists of four linearly placed microstrip patch antennas, 3-bit distributed RF MEMS low-loss phase shifters, and a corporate feed network. MEMS switches and high-Q metal-air-metal capacitors are employed as loading elements in the phase shifter. The system is fabricated monolithically using an in-house surface micromachining process on a glass substrate and occupies an area of 6 cm times 5 cm. The measurement results show that the phase shifter can provide nearly 20deg/50deg/95deg phase shifts and their combinations at the expense of 1.5-dB average insertion loss at 15 GHz for eight combinations. It is also shown by measurements that the main beam can be steered to required directions by suitable settings of the RF MEMS phase shifters.     

Efficiency calculation of feed structures and optimum number of antenna elements in a subarray for highest G/T

For an antenna array, different feed structure topologies may yield the same radiation characteristics. However, different topologies may result in different efficiency and noise performance. In this paper, parallel arm antenna arrays are analyzed for efficiency and noise temperature using the noise equivalent line length method (NELL) with the number of antenna elements in a subarray as a parameter. It is shown that efficiency of an antenna array feed structure as well as its noise temperature can be calculated using the NELL method. The comparison of the two parameters, efficiency and noise temperature, yield the optimum number of antenna elements in a subarray of a parallel arm antenna array for the highest G/T ratio.     

Creating and Validating Embedded Assertion Statecharts

Integrating formal assertions into the modeling, implementation, and testing of statechart-based designs can enhance a rapid system prototyping system's robustness by providing runtime monitoring and recovery from assertion failures. An iterative process for developing and verifying statechart prototype models augmented with statechart assertions using the StateRover tool lets system designers write formal specifications using statechart assertions. It also enables them to use JUnit-based simulation to validate statechart assertions and to test statechart prototype models augmented with statechart assertions. A case study using a safety-critical computer assisted resuscitation algorithm software prototype for a casualty intravenous fluid infusion pump illustrates the process.