Monolithically integrated 780-nm-band high-power and 650-nm-bandlaser diodes with real refractive index guided self-aligned structure

780-nm-band high-power and 650-nm-band laser diodes (LDs) with real refractive index guided self-aligned (RISA) structures are monolithically integrated for the first time. High-power and fundamental transverse mode operation at an output power of 100-mW continuous wave (CW) up to 80°C is attained for the 780-nm-band LD. For the 650-nm-band LD, high temperature and fundamental transverse mode operation at an output power of 10-mW CW up to 80°C is obtained     

An active integrated retrodirective transponder for remoteinformation retrieval-on-demand

A retrodirective transponder based on a novel compact phase-conjugating mixer with conversion gain has been developed. The active circuit uses one port for both incoming and outgoing signals, enabling a reduction of circuit size, and the balanced structure provides suppression of undesired signals. By using a modulated local oscillator, the circuit can modulate the received signal in order to retransmit local information to the remote site. A microstrip antenna is integrated with the phase conjugator and the whole system was fabricated on a single substrate, enabling a one-card system. A four-element prototype array with 0.5λ₀ array spacing demonstrated excellent measured retrodirectivity. Additionally, a simplified binary-phase-shift-keying signal transmitted by the array is recovered successfully at the source location, demonstrating great potential for remote tagging and wireless sensor applications     

A multigigabit DRAM technology with 6F2 open-bitlinecell, distributed overdriven sensing, and stacked-flash fuse

A multigigabit DRAM technology was developed that features a low-noise 6F² open-bitline cell with fully utilized edge arrays, distributed overdriven sensing for operation below 1 V, and a highly reliable post-packaging repair scheme using a stacked-flash fuse. This technology, which can be used to fabricate a 0,13-μm 180-mm² 1-Gb DRAM assembled in a 400-mil package, was verified using a 57.6-mm², 200-MHz array-cycle, 256-Mb test chip with 0.109-μm² cells     

Temperature compensated sapphire-rutile microwave whisperinggallery mode resonator

A 2 μm-thick film of rutile (TiO₂) was deposited on a sapphire disk using a sol-gel method to realise a temperature compensated microwave resonator operating in whispering gallery mode configuration. The resonator, though not yet completely optimised, shows turnover temperatures ranging from 40 to 60 K depending on the mode azimutal number. For the WGH_7,0,0 mode at 9.4 GHz, the Q-factor is of the order of 1.5×10⁶ at 46 K. The technique appears easy to implement and can be used for the design of a high-frequency stability microwave source     

Exploiting the on-chip inductance in high-speed clock distributionnetworks

On-chip inductance effects can be used to improve the performance of high-speed integrated circuits. Specifically, inductance improves the signal slew rate (the rise time), virtually eliminates short-circuit power consumption and reduces the area of the active devices and repeaters inserted to optimize the performance of long interconnects. These positive effects suggest the development of design strategies that benefit from on-chip inductance. An example of a clock distribution network is presented to illustrate the process in which inductance can be used to improve the performance of high-speed integrated circuits     

Methodology for studying the impact of intrinsic stress on thereliability of the electroless Ni UBM structure

A methodology for evaluating the reliability and the impact of intrinsic stresses on the electroless Ni under bump metallurgy (UBM) structure is presented. The first part of this work will address the testing methodology, which uses a pressure sensing device to determine the intrinsic stress in Ni due to the plating process. An optical method is used to capture deformation in the sensing device due to the Ni plating process. A finite element model is then used to calculate the intrinsic stress in the Ni film using the deformation output from the optical measurements. The second part of this work will address a predictive model used to determine the reliability of applying intrinsic stress values to a low cost electroless Ni UBM structure during the bump formation and solder reflow process. The combined work of the testing and predictive methodology provides a more effective and accurate method of predicting the Ni UBM reliability     

Effect of solder creep on the reliability of large area die attachment

High temperature solders have been widely used for power device die attachment. One typical solder is Pb92.5In5Ag2.5, which is a ternary eutectic alloy with a eutectic temperature of 310°C. Such a Pb-based solder has a low Young's modulus, a low yield strength, and a high strain prior to failure. So it can be used to attach large size silicon die to mismatched substrates. In this paper, stresses and strains have been studied on a large size power MOSFET attachment using the Pb92.5In5Ag2.5 solders. A commercial finite element analysis software is employed as the simulation tool. Three types of substrates, pure copper, copper–tungsten composite, and pure molybdenum are used in the study, where molybdenum has the closest coefficient of thermal expansion to silicon. In addition to the plastic deformation simulation of the solder, a creep model of the solder was incorporated due to the low melting temperature of the solder alloy. Firstly, stresses and strains are calculated during the cooling cycle after attachment. It is found that the creep strain is the dominant plastic strain at low cooling rate (10°C/min). Also, the maximum Von Mises stress in the Si chip is decreased from 174 to 62.7 MPa after adding creep strain. As expected, the maximum creep strain happens to the die-to-copper substrate attach. Simulation on temperature cycling is done from −55°C to +150°C. The peak Von Mises stress occurs at the low temperature extreme and holds steadily during the soaking period, indicating insignificant contribution from creep. The Von Mises stress at the high temperature extreme is much lower and decreases with holding time. Significant plastic deformation of the solder layer is observed in cooling cycles. For silicon to copper substrate attach, its plastic deformation increases with each cycle. For all three substrates used, considerable solder creep is observed at heating cycles. The creep strain is much larger than the rate-independent plastic strain in the solder alloy for all three types of substrates. It is concluded that solder creep is the dominant factor affecting long term reliability of power semiconductor die attachment.     

MBE-grown ZnSSe thin films on ITO substrates for liquid-crystal light valve applications

The MBE growth of ZnSSe alloy thin films on ITO substrates using ZnS and Se sources was studied and various structural and opto-electronic properties of the as-grown thin films were characterised. The XRD rocking curves resulting from these films indicate that the as-grown polycrystalline ZnSSe thin films have a preferred orientation along (1 1 1) direction. The evaluated crystal sizes as deduced from the FWHM of the XRD layer peaks were found to show a strong growth temperature dependence with the optimised temperature at about 290°C. TEM measurements done on these thin films also indicate a similar growth temperature dependence. The TEM cross-sectional micrograph of the sample grown at the optimised temperature shows a well-defined columnar structure whose nucleation seems to be highly correlated with the ITO grains. UV responsivity as high as 0.01 A/W and more than three orders of magnitude in rejection power for wavelengths longer than 450 nm have been achieved. It was also found that the sample grown at the optimised temperature has the lowest resistivity of 4.3×10¹¹ Ω cm, which provides a good match with that of a liquid-crystal layer. These results indicate that MBE-grown ZnSSe thin film is a promising candidate as the photoconductive material of liquid-crystal light valves for UV imaging applications.     

Growth-temperature-dependent optical and acetone detection properties of ZnO thin films

Zinc oxide (ZnO) thin films were prepared onto glass substrates at moderately low growth temperature by two-stage spray pyrolysis technique. The effects of growth temperature on structural, optical and acetone detection properties were investigated with X-ray diffractometry, a UV-visible spectrophotometer, photoluminescence (PL) spectroscopy and a homemade gas sensor testing unit, respectively. All the films are polycrystalline with a hexagonal wurtzite phase and exhibit a preferential orientation along [002] direction. The film crystallinity is gradually enhanced with an increase in growth temperature. The optical measurements show that all the films are physically highly transparent with a transmittance greater than 82% in the visible range. The band gap of the film is observed to exhibit a slight red shift with an increasing growth temperature. The PL studies on the films show UV/violet PL band at ～ 395 nm. Among all the films investigated, the film deposited at 250 ℃ demonstrates a maximum sensitivity of 13% towards 20 ppm of acetone vapors at 300 ℃ operating temperature.     

PSOBLAP: Particle Swarm Optimization-Based Bandwidth and Link Availability Prediction Algorithm for Multipath Routing in Mobile Ad Hoc Networks

Wireless Personal Communications - In mobile ad hoc network (MANET), optimal path identification is the main problem for implementing the Multipath routing technique. MANET desires an efficient...