Experimental-Numerical Comparison for a High-Density Data Center: Hot Spot Heat Fluxes in Excess of 500 W/ft $^{2}$

This paper uses previously published experimental data to present a comparison between test results and numerical simulations. The example considered is a large 7400 ft$^{2}$ data canter that houses over 130 heat-producing racks (1.2 MW) and 12 air conditioning units. Localized hot spot heat fluxes were measured to be as high as 512 W/ft$^{2}$ (5.5 kW/m$^{2}$ ) for a 400 ft$^{2}$ (37 m$^{2}$ ) region. A numerical model based on Computational Fluid Dynamics (CFD) was constructed using inputs from the measurements. The rack inlet air temperature was considered to be the basis for experimental versus numerical comparison. The overall mean rack inlet temperature predicted numerically at a height of 1.75 m is within 4 $^{circ}$ C of the test data with a rack-by-rack standard deviation of 3.3 $^{circ}$C.      

A 25-MHz Self-Referenced Solid-State Frequency Source Suitable for XO-Replacement

Recent trends in the development of integrated silicon frequency sources are discussed. Within that context, a 25-MHz self-referenced solid-state frequency source is presented and demonstrated where measured performance makes it suitable for replacement of crystal oscillators (XOs) in data interface applications. The frequency source is referenced to a frequency-trimmed and temperature-compensated 800-MHz free-running $LC$ oscillator (LCO) that is implemented in a standard logic CMOS process and with no specialized analog process options. Mechanisms giving rise to frequency drift in integrated LCOs are discussed and supported by analytical expressions. Design objectives and a compensation technique are presented where several implementation challenges are uncovered. Fabricated in a 0.25-$mu$m 1P5M CMOS process, and with no external components, the prototype frequency source dissipates 59.4 mW while maintaining ${pm} 152$ ppm frequency inaccuracy over process, ${pm} 10hbox{%}$ variation in the power supply voltage, and from ${-}$ 10 $^{circ}$ C to 80 $^{circ}$ C. Variation against other environmental factors is also presented. Nominal period jitter and power-on start-up latency are 2.75 ps$_{rm rms}$ and 268 $mu$s, respectively. These performance metrics are compared with an XO at the same frequency.      

Interfacial Reaction Between Molten Sn-Bi Based Solders and Electroless Ni-P Coatings for Liquid Solder Interconnects

This paper reports on the interfacial reactions and lifetime of electroless Ni-P coatings in contact with molten Sn-Bi based solders. A layer of approximately 4 $mu{hbox{m}}$ thick electroless Ni-P in contact with the molten Sn-58Bi solder began to fail at 48 h at temperatures between 200 $^{circ}{hbox{C}}$ and 240 $^{circ}{hbox{C}}$ . Elemental additions to modify the solder, included 1–2wt.% of Al, Cr, Si, Zn, Ag, Au, Ru, Ti, Pt, Nb, and Cu. Of these, only Cu modified the interfacial intermetallic compound growth from ${hbox{Ni}}_{3}{hbox{Sn}}_{4}$ to $({hbox{Cu,Ni}})_{6}{hbox{Sn}}_{5}$ , resulting in significantly decreased consumption rates of the Ni-P substrate in contact with the molten solder and increasing the lifetime of the Ni-P layer to between 430 and 716 h. Micro cracks were observed in all but the thinnest Ni-P layers, allowing the solder to penetrate.      

High Temperature Characteristics of Coplanar Waveguide on R-Plane Sapphire and Alumina

This paper presents the characteristics of coplanar waveguide transmission lines on R-plane sapphire and alumina over the temperature range of 25 $^{circ}$ C–400 $^{circ}$ C and the frequency range of 45 MHz–50 GHz. A thru-reflect-line calibration technique and open circuited terminated stubs are used to extract the attenuation and effective permittivity. It is shown that the effective permittivity of the transmission lines and, therefore, the relative dielectric constant of the two substrates increase linearly with temperature. The attenuation of the coplanar waveguide varies linearly with temperature through 200 $^{circ}$C, and increases at a greater rate above 200 $^{circ}$ C.      

Comparative Study of High-Power Continuous-Wave Laser Performance of Yb-Doped Vanadate Crystals

A comprehensive experimental investigation has been conducted into the high-power continuous-wave (CW) laser performance of isostructural Yb-doped vanadates, including three ordered crystals of Yb:YVO $_{4}$, Yb:GdVO $_{4}$, and Yb:LuVO $_{4}$, and two mixed ones with compositional disorder: Yb$_{0.007}$ :Y$_{0.407}$ Gd$_{0.586}$ VO$_{4}$ and Yb$_{0.015}$ :Lu$_{0.52}$ Gd$_{0.465}$ VO$_{4}$ . The CW laser operation of the different vanadates is compared under nearly identical experimental conditions by using a high-power diode laser as the pump source. In addition to the output characteristics of the individual vanadate lasers, the polarization properties and optical bistability exhibited in the laser oscillation are also discussed. The spectroscopic properties closely related to the laser performance are compared and summarized for these Yb-doped vanadates.      

Temperature-Insensitive Dual-Comb Filter Based on Multimode Interference Ti : LiNbO $_{3}$ Waveguide

A temperature-insensitive dual-comb filter has been demonstrated for the first time by multimode interference based on a Ti : LiNbO$_{3}$ channel waveguide. The phase difference between comb filters was about 180 $^{circ}$. We only observed less than ${pm}$0.125-nm variation of the center wavelength of the filter during temperature change from 20 $^{circ}$C to 50 $^{circ}$C. The measured extinction ratio and channel spacing of the comb filter were about ${-}$25 dB and 3.2 THz, respectively.      

Flexible Organic Light-Emitting Diodes Using a Metal Peel-Off Method

Organic light-emitting diodes were fabricated on a glass–MgO$_{x}$–Ag layered substrate and separated between Ag and MgO$_{x}$ interface, showing the bending properties. Adhesive force decreased from 18 to 1.4 gf/cm after insertion of the MgO$_{x}$ layer between the Ag and glass. The Ag–O component in Ag $3d_{5/2}$ spectra and O–Ag (ionic bond) component in O $1s$ spectra increased as the MgO$_{x}$ layer was thickened. This supports that Ag oxidized to AgO$_{x}$ while the thickness of MgO$_{x}$ increased, resulting in a reduction of the adhesive forces of Ag layer. Therefore, it is concluded that a metal at the interface with a metal oxide is easily oxidized, reducing the adhesive forces and enabling the peel-off process.      

Continuous-Wave Electrically Pumped 1.55-$mu$m Edge-Emitting Platelet Ridge Laser Diodes on Silicon

We report the successful integration on silicon of small footprint, low-threshold electrically pumped edge-emitting lasers by a new approach incorporating microcleaving technology to produce 6-$mu$ m-thick platelet lasers with cleaved facets, microscale pick. and place assembly to position them on the substrate, and diaphragm pressure solder bonding to attach/connect them permanently in place. InP-based ridge-waveguide platelet lasers integrated on silicon lase at 1550-nm continuous-wave to 55 $^{circ}$C (pulsed to 80 $^{circ}$C) with output powers as high as 26.8 mW, external differential quantum efficiencies as high as 81%, and threshold currents as low as 18 mA.      

Zn$_{1 - x}$Mg$_{x}$ O Homojunction-Based Ultraviolet Photodetector

Zn$_{1 - {x}}$ Mg$_{x}$ O p-n photodiodes were fabricated on (0001) sapphire substrates using a pulsed laser deposition technique with different Mg contents. Ti–Au and Ni–Au metals deposited using vacuum evaporation were used as n-type and p-type contacts, respectively. The X-ray diffraction analysis showed the Zn$_{1 - {x}}$Mg$_{x}$O double layers have a single phase hexagonal wurtzite structure. The optical bandgap of Zn$_{1 - {x}}$Mg$_{x}$O films has been tuned from 3.27 to 4.26 eV by increasing the Mg content ${x} =0.0$ to ${x}=0.34$. Correspondingly, the cutoff wavelength of the resultant detectors varies from 380 to 284 nm. Zn$_{1 - {x}}$Mg$_{x}$O p-n photodiodes with different Mg contents exhibit very good performance, with a very low dark current (${≪}$ 20 pA) at the bias voltage of 10 V. The ultraviolet to visible rejection ratio is more than three orders of magnitude.      

Frequencies and Wavelengths From a New Far-Infrared Lasing Gas: $^{13}$ CHD$_{2}$ OH

The first laser action produced by the partially deuterated isotopic form of methanol, $^{13}$ CHD$_{2}$ OH, has been observed. With this laser medium, eight far-infrared laser emissions were discovered having wavelengths ranging from 33.8 to 80.9 $mu$m. A three-laser heterodyne system was used to measure the frequencies for these newly discovered laser lines and are reported with fractional uncertainties of ${pm}3 times 10^{-7}$. The offset frequency of the CO$_{2}$ pump laser was measured with respect to its center frequency for each $^{13}$CHD$_{2}$OH laser emission.      

A 300 nW, 15 ppm/$^{circ}$C, 20 ppm/V CMOS Voltage Reference Circuit Consisting of Subthreshold MOSFETs

A low-power CMOS voltage reference was developed using a 0.35 $mu$m standard CMOS process technology. The device consists of MOSFET circuits operated in the subthreshold region and uses no resistors. It generates two voltages having opposite temperature coefficients and adds them to produce an output voltage with a near-zero temperature coefficient. The resulting voltage is equal to the extrapolated threshold voltage of a MOSFET at absolute zero temperature, which was about 745$~$mV for the MOSFETs we used. The temperature coefficient of the voltage was 7 ppm/ $^{circ}$C at best and 15 ppm/$^{circ}$C on average, in a range from ${-}$ 20 to 80$^{circ}$ C. The line sensitivity was 20 ppm/V in a supply voltage range of 1.4–3 V, and the power supply rejection ratio (PSRR) was ${-}$45 dB at 100 Hz. The power dissipation was 0.3 $mu$W at 80$^{circ}$C. The chip area was 0.05 mm$^2$ . Our device would be suitable for use in subthreshold-operated, power-aware LSIs.      

Operation of a 25-Gb/s Direct Modulation Ridge Waveguide MQW-DFB Laser up to 85 $^{circ}$ C

We demonstrated a 25-Gb/s direct modulation up to 85 $^{circ}$C with a 1.3- $mu$m InGaAlAs ridge-waveguide multiple-quantum-well distributed-feedback laser. The dependence of the relaxation oscillation frequency on current was 3.3 GHz/mA$^{1 / 2}$, and this is the highest value ever reported for 200-$mu$m-long lasers in the 1.3-$mu$m wavelength region. The $alpha$ parameter was around 2.7 at 25 $^{circ}$C, and an error-free operation after a 10-km single-mode fiber transmission was obtained up to 85 $^{circ}$C.      

Conductively Cooled 637-nm InGaP Broad-Area Lasers and Laser Bars With Conversion Efficiencies Up to 37% and a Small Vertical Far Field of 30$^{circ}$

Highly efficient operation of 637-nm broad-area (BA) laser diodes and laser bars with a small vertical far field of 30$^{circ}$ (full-width at half-maximum) is reported. The laser structure consists of an InGaP quantum well embedded in AlGaInP waveguide layers and n-AlInP and p-AlGaAs cladding layers. Single BA emitters with a stripe width of 30 $mu$m emitted a maximum continuous-wave (CW) power of 540 mW at 15 $^{circ}$ C. Six-millimeter-wide laser bars with 12 30- $mu$m-wide emitters (filling factor of 6%) reached CW power levels of 5.4 W at 15 $^{circ}$C. The maximum conversion efficiency of single lasers and laser bars at 15 $^{circ}$ C was 37% and 31%, respectively.      

Fiber Inline Core–Cladding-Mode Mach–Zehnder Interferometer Fabricated by Two-Point CO$_{2}$ Laser Irradiations

We report a fiber inline Mach–Zehnder-type core–cladding-mode interferometer fabricated by two-point CO$_{2}$ laser irradiations on a single-mode fiber. The laser irradiations caused efficient light coupling from the core mode to the lower order cladding modes and vise versa. High-quality interference spectra with a fringe visibility of about 20 dB were observed for four different interferometer lengths (5, 10, 20, and 40 mm). The temperature sensitivity of the device with a length of 5 mm was measured to be 0.0817 nm/$^{circ}$C. The sensitivity for refractive index measurement of the device was comparable with a long-period fiber grating of LP$_{04}$ cladding mode.      

The Measurement of Ion Diffusion in Epoxy Molding Compounds by Dynamic Secondary Ion Mass Spectroscopy

The primary focus of this research was the measurement of ion diffusion in a common epoxy molding compound used to encapsulate microelectronic devices. Ion diffusion measurements were made by exposing the encapsulant materials to aqueous solutions of 2M sodium chloride, and making measurements by Dynamic Secondary Ion Mass Spectrometry. The diffusion dependency of temperature exposure of the encapsulants to aqueous salt solutions at 75 $^{circ}$C, 85 $^{circ}$C, 100 $^{circ}$C, 125 $^{circ}$C, 150 $^{circ}$C and 175 $^{circ}$C and post-mold curing for 2, 4, 6, and 8 h at 175 $^{circ}$C was evaluated. The ion diffusion was found to depend on the glass transition temperature of the encapsulant. The rate of ion diffusion above the glass transition temperature of the encapsulant was faster than predicted by an Arrhenius plot of the diffusion coefficient as a function of temperature below the glass transition temperature. Post-mold curing of the encapsulant decreased the diffusion of chloride ions in the encapsulant. Ion diffusion was shown to be slower than moisture diffusion in the encapsulant by approximately nine orders of magnitude.      

Electromagnetic Analysis of Ring-Cavity-Assisted Amplified Spontaneous Emission in Er:SiO$_{2}$/a-Si Horizontal Slot Waveguides

In this paper, we present an electromagnetic analysis of ring-cavity-assisted amplified spontaneous emission in Er$^{3 + }$-doped SiO$_{2}$ (Er:SiO$_{2}$ ). A horizontal slot geometry, consisting of a low-index Er:SiO$_{2}$ layer embedded between high-index a-Si layers, allows for a planar ring-cavity design which maintains high optical confinement in the active Er:SiO $_{2}$ material. The simulations are performed within the auxiliary differential equation–finite-difference time-domain (ADE-FDTD) scheme which couples the quantum mechanical light emission and amplification behavior of the Er:SiO$_{2}$ with the electromagnetic device behavior. We present the enhanced spontaneous emission in waveguide-coupled ring cavities with varying coupling gaps. We provide an analysis of the relationship between cavity quality factor, coupling coefficient, and enhanced spontaneous emission.      

Effect of Thermal Aging on the Microstructure Evolution and Solder Joint Reliability in Hard Disk Drive Under Mechanical Shock

The effect of thermal aging on the microstructure evolution and solder joint reliability in hard disk drive (HDD) under mechanical shock was investigated. Significant coarsening of ${hbox {Ag}}_{3} {hbox {Sn}}$ particles was found in SnAgCu solder, and ${rm AuSn}_{4}$ intermetallic compound (IMC) changed from needle-type to layer-type during aging. For as-soldered SnAgCu solder joints after mechanical shock, the cracks were initiated in ${hbox {AuSn}}_{4}$ at the corner of the solder joints, and mainly propagated along the thin ${hbox {Ni}}_{3} {hbox {Sn}}_{4}$ IMC layer. After aging at 150 $^circ$C for 21 days, the cracks were mainly propagated along the solder, ${hbox {Ni}}_{3} {hbox {Sn}}_{4}$, Au–Sn–Ni–Cu, and Au–Cu–Sn. The significant coarsening of microstructure was found in SnPb solder joints, and only microcracks were found on the surfaces of as-soldered and aged solder joints after mechanical shock.      

Corrections to “Growth of Lanthanum Manganate Buffer Layers for Coated Conductors via a Metal–Organic Decomposition Process”

In our prior paper, we reported forming (110)-oriented LaMnO$_3$ on a biaxially textured Ni-3at%W substrate. Chemical analysis of these films subsequent to publishing the paper showed only La and O—there was no Mn present in the film. The film was actually (400)-oriented La$_2$O$_3$ with the cubic bixbyite structure. Subsequent studies also showed that MnO film is not stable on Ni and Ni–W substrate surfaces at 1100 $^{circ}$C and $hbox{P}_{{rm O}2} = 10^{-16}$ atm where bulk MnO is stable.      

Near-Stoichiometric Ti : LiNbO$_{3}$ Strip Waveguides Fabricated by Standard Ti Diffusion and Post-VTE

We report near-stoichiometric (NS) Ti : LiNbO$_{3}$ waveguides fabricated by indiffusion of 4-, 5-, 6-, 7- $mu{hbox {m}}$-wide 120-nm-thick Ti-strips at 1060 $^{circ}hbox{C}$ for 10 h into a congruent $hbox{LiNbO}_{3}$ (i.e., standard Ti diffusion procedure) and post-vapour-transport-equilibration (VTE) treatment at 1100 $^{circ}hbox{C}$ for 5 h. These waveguides are NS and single-mode at 1.5 $mu{hbox {m}}$, and have a loss of 1.0/0.8 dB/cm for the TM/TE mode. In the width/depth direction of the waveguide, the mode field follows a Gauss/Hermite–Gauss profile, and the Ti profile follows a sum of two error functions/a Gauss function. The post-VTE resulted in increase of diffusion width/depth by 2.0/1.0 $mu{hbox {m}}$. A two-dimensional refractive index profile in the guiding layer is suggested.      

Linear Cascade GaN-Based Green Light-Emitting Diodes With Invariant High-Speed/Power Performance Under High-Temperature Operation

We demonstrate the performance of linear cascade green light-emitting diode (LED) arrays suited for use in plastic optical fiber (POF) communications in automobiles or harsh environments. With this three-LED array, driven by the constant voltage bias of an in-car battery output (12 V) we obtain high-speed ($sim$100-Mb/s eye-opening), high-coupling power (0.9 mW), and a very small variation of coupled power versus temperature [$-$ 0.12%$^{circ}hbox{C}^{-1}$ at room temperature (RT)] for the whole measured temperature range (i.e., RT to 120 $^{circ}$ C). Even under high bias current (100 mA) operation, our device can sustain a clear 150-Mb/s eye-opening from RT to 120 $^{circ}$C. The static and dynamic measurement results indicate that the speed and power performance of this device are less sensitive to variations in ambient temperature than are those of the red resonant-cavity LEDs utilized for POF communication.