Mechatronic systems designed to comply to new EU directives are studied through interconnections by electronic or photonic probes, SEM, TEM, SE or 3D Tomography. Leaded and lead free modules assembled by standard interconnection technologies are studied for robustness relative to thermal accelerated life tests. Results obtained from JEOL 6060LV SEM and Optical Microscopy show that although slow growth rate of inter-metallics (IMC) is consistent with expected reliability, they are responsible for propagation of cracks especially in the presence of gold on PCB side. Innovative Low Temperature Joining (LTJ) technology applied to nano or micro silver pastes which should reduce IMC effects are tested on mechatronic systems. Results obtained from SEM, TEM and 3D Tomography will be shown as well as non destructive Spectroscopic Ellipsometry studies of samples. Pressureless LTJ technology is unsuitable for robust interconnection.

The introduction of high-speed services for fiber-optic access subscribers has led to a huge growth in data traffic. The rapid diversification of services means that next generation networks must be built quickly, economically and reliably.

A high temperature laser allows us to eliminate the thermo-electric cooler conventionally needed in a transmitter module, which results in reductions in cost, power consumption and size. Moreover, a high-power laser provides a wide tolerance when coupling optical fibers. In addition, a high-power pump laser is needed to realize a wide-band and high-power erbium-doped fiber amplifier. This makes high-performance laser chips one of the keys to achieving highly reliable and cost-effective systems.

In terms of laser reliability, we must clarify the degradation mechanism and postpone or suppress degradation if we are to achieve a reliable high-performance laser. We have analyzed degraded lasers using the optical beam induced current (OBIC) technique. When there are nonradiative recombination centers in the degraded region, the OBIC intensity decreases with increases in recombination density. This technique has the advantages of being non-destructive and highly sensitive. In addition, it provides high space resolution in degradation analyses.

The OBIC is measured through the window of a transistor outline (TO) can before and after aging. Then, by using the same LDs we can detect an OBIC change for several aging times. We can both detect the degraded region and layer, and estimate the degree of laser degradation by employing the relative OBIC intensity prior to aging. This OBIC technique is useful for analyzing the degree of laser degradation.

Moreover, the incident wavelength can be changed by changing the optical source in the OBIC measurement setup, which in turn changes the absorption layer and the penetration distance. Some degraded laser layers are reveled by using these several wavelengths absorbed in different layers. In addition, degradation in the waveguide interior is detected by using an incident wavelength with long penetration. Thus, by monitoring the OBIC intensity at several wavelengths as well as before and after aging, we are able to discuss sudden and wear-out laser failures. In our presentation, we will introduce examples using the OBIC technique that contributed to the improvement of laser reliability.

To pursue further performance improvement of semiconductor devices, threedimensional (3D) chip integration with TSV would be one of the key technologies in the next decade. Inter Chip Fill (ICF) is a resin to fill gaps between chips, and it would be an important component for highly reliable and durable 3D integrated devices. High performance 3D devices require fine pitch interconnections with small bumps for high pin count with high bandwidth. Smaller bumps lead to narrow gap design between stacked chips inevitably, and the narrow gap is expected to reduce heat resistance and thermo-mechanical stress. However it makes resin filling and flux cleaning processes harder. A preapplied ICF process is one of the potential methods to fill the narrow gaps with a resin. The material is halfcured resin applied on a wafer by spin-coating or film-lamination before chip integration. Flux cleaning process can be eliminated by adding fluxing function in the resin components. Major concerns of multiple chip 3D stacking process are repeated high temperature cycles of metal-joining, and long process time as a result. We are proposing “Stack Joining process” that enables 3D multi chip joining at one time instead of sequential chip by chip joining. In this process, multiple chips are aligned and temporarily stacked sequentially using adhesivity which the ICF has between Tg and initiation temperature of polymerization, and finally all metal bumps of stacked chips are melted and joined altogether. This process can substantially reduces repeated high temperature cycles and process time. As a result this technique could mitigate degradation of device materials.

We successfully stacked chips by using the pre-applied ICF which was designed for advanced 3D chip stack having full area array and narrow gap (less than 10um) connections. In this paper, we explain the Stack Joining process flow and conditions. We also discuss the cause of mechanical stress within the stacked chip and required material features of the pre-applied ICF and device structure to reduce the stress.

We have investigated the effect of post-growth rapid thermal annealing (RTA) at different temperature on two InAs/GaAs bilayer quantum dots samples with different spacer thicknesses (7.5nm and 8.5nm). It is found that when RTA temperature gradually increases, there is usual blue shift of ground state emission peak wavelength for the sample having thinner spacer but for the other sample the emission peak sustains at same peak wavelength position upto a higher annealing temperature. The dots inside the sample with less spacer thickness dissolute much earlier (beyond 700°C annealing temperature) in comparison to the other sample. The structural and optical characterization has been done by cross sectional transmission electron microscope (XTEM) and low temperature photoluminescence (PL) experiments respectively.

Distributed Bragg Reflectors (DBRs) remain critical to the fabrication of various nitride based optoelectronic devices. In particular, DBRs are often employed for cavity formation in Resonant Cavity Light Emitting Diodes (RCLEDs) to enhance and obtain a more directional emission and also in Vertical Cavity Surface Emitting Lasers (VCSELs). As a result, epitaxially grown reflectors are attractive for direct integration in the device, reduced processing requirements, and the formation of narrow cavities. In the III-Nitride material system, Aluminum Nitride (AlN) and Gallium Nitride (GaN) offer a large contrast in refractive index and are therefore well suited for fabricating DBRs with high reflectivity and wide bandwidths using relatively few periods. However, material cracking arising from to the 2.4% lattice mismatch and difference in thermal expansion coefficient decreases reflectivity and is detrimental to the efficiency of subsequent device fabrication. Several techniques, such as superlattice insertion layers or the growth of AlxIn1-xN layers, have been employed to reduce strain and cracking in such structures. In this work, results of the use of indium as a surfactant in the Metal Organic Vapor Phase Epitaxy (MOVPE) of AlN/GaN DBRs will be discussed. Specifically, this study targets AlN/GaN DBRs with peak reflectivity at ranging from 465 nm to 540 nm. Indium has been used as a surfactant during growth by introducing trimethylindium into the system. It has been shown that crack formation is dependent on the flow of the indium precursor despite minimal indium incorporation into the lattice. Image processing techniques were used to quantify the crack length per square millimeter and it was observed that indium has a significant effect on the crack formation and can be used to reduce the total crack length in these structures by a factor of two.

InP-based HBTs for ultrahigh speed optical communications systems operation at over 40 GHz require a long-term stability under high current injection conditions, such as current densities of 2 or 5 mA/μm2. We achieved high reliability by suppressing surface recombination and emitter-metal-related crystalline degradation.

Changes in the electric properties of devices due to temperature and bias stress were evaluated. The reduction in DC current gain due to surface recombination had the activation energy of 1.7 eV without current density dependence, and the lifetime of HBTs for this degradation mode is predicted to be over 1×108 hours at 125°C. The emitter metal diffusion and disruption of uniformity of the atomic composition were observed by transmission electron microscopy and energy dispersive X-ray spectroscopy in HBTs with the conventional Ti/Pt/Au emitter, whereas suppression of those degradations was observed in HBTs with refractory metal of Mo and W. The emitter resistance was estimated to evaluate the contact layer degradation. The critical time was one order larger for HBTs with refractory metal than for HBTs with conventional metal. The activation energies for resistance increases were 2.0 and 1.65 eV for the current density of 2 and 5 mA/μm2, respectively, for all types of emitter electrodes.

The effectiveness of the refractory metal electrode for improving device reliability was confirmed, especially in high-current-density operation, which is essential for applying InP HBTs in high-speed ICs.

We investigated the degradation mechanism of GaN LEDs due to the application of a high d.c. stressing current. To identify the underlying process for device failure we examined the effects of the InGaN quantum well growth parameters on the hot-electron hardness of the devices. Systematic characterizations on the degradations in the microstructural, thermoreflectance, and low frequency noise properties of the devices were performed.

The gate oxides of Si based MOSFET devices are subjected to a high field in order to induce defects in the oxide bulk and at the Si/SiO2 interface. The defects are characterized by a series of gate to source capacitance and conductance measurements. Shifts in the flat band voltage and the threshold voltage are observed and are related to the position of charged defects. The difference of the equivalent charge between the two types of defects is also determined. Conductance measurements are performed to determine the difference of interface states concentration as a function of the high field exposure time.

The formation and evolution of hydrogen- and vacancy-related donor and acceptor states were studied in helium-implanted and subsequently hydrogen plasma-treated n-type Float-Zone (FZ) silicon wafers by means of two-point-probe Spreading Resistance (SR) measurements. He+-implantation was executed at 3.75 MeV and 11 MeV at fluences of 1×1014 cm−2. Post-implantation 13.56-MHz RF-plasma hydrogenations were carried out at 150 W either for 15 min or 1 hour, applying substrate temperatures between 350 °C and 500 °C. Enhanced donor concentrations as well as acceptor-like states were observed in the subsurface layers of the treated FZ Si samples after 15-min post-implantation H-plasma exposures. Under appropriate process conditions, the latter ones compensated for the n-type doping, so that even buried p-type layers were created. The experimental results indicated that oxygen played a central role in the formation of the acceptor-like states.

Liquid resin hybridized silica sol-gels and thiol-ene elastomers were evaluated as compatible materials to form thin film, flexible multilayered structures. Liquid resins are cast and cured in air and ambient pressure on the order of minutes. Scanning Electron Microscopy (SEM) reveals homogeneous interfaces and robust interfacial adhesion under tensile and compressive stress. Thickness of the hybrid glass and thiol-ene films range from 0.80μm to 1.5μm and 8 μm to 16 μm respectively.

Proposed mechanisms so far on defect reactions in semiconductors are reexamined. Structural instability of point defects is explained in terms of the Jahn-Teller effect. It is found that the tetrahedral coordinated bonds, which do not have inversion symmetry, are not so rigid as we consider, especially for hole localization. Second topic is the phonon-kick mechanism for defect reactions under carrier injection. In order to discuss this mechanism in detail, we recall the configuration coordinate (c-c) diagram, which is often misunderstood in the literature. The proper relation is explained among the lattice distortion, the position of the electronic level in the band gap (thermal and optical depths), the total energy the multiphonon (e and h) carrier capture processes and the following induced lattice relaxation. A numerical simulation has been performed on phonon kick mechanism. It is found that a rapid increase of the transient lattice vibration around the defect is possible and the probability critically depends on the carrier concentrations and the phonon frequency distribution.

We discuss main degradation mechanisms present in nitride based laser diodes operating in 400-440 nm spectral range. We can clearly divide the aging processes into these occurring on the exposed facets of the device and into the bulk phenomena. Surface processes are predominantly connected with photochemical reactions on the laser mirrors and manifest by the formation of the carbon deposits. The nature of these photochemical reactions resembles very closely the mechanism known as Package Induced Failure observed previously in case of 980 nm laser diodes. Degradation involving bulk like effects is much less understood. The experimental results by other group are not sufficient for proposing an unambiguous model of the physical effects involved. In particular, it consists in observation related to dopants diffusion and recombination mechanisms. Magnesium diffusion from the p-type layers into the active layer was proposed as a possible degradation path. However, our study of SIMS profiles in the device subjected to over 8 000 h of electrical stress reveals no visible modification in the Mg profile. The same holds for the hydrogen spatial distribution thus substantially limiting candidates for the diffusion processes. Nevertheless, it seems that the diffusion mechanism is involved in bulk degradation. The claim is supported by two facts: well confirmed stability of the extended defects network in nitride emitters and characteristic square-root time-dependence of the degradation rate.

Recent experiments on ultrasonic measurements of non-doped and boron-doped silicon indicate that vacancies in crystalline silicon can be detected through the elastic softening at low temperature. This is attributed to enhanced response of electronic quadrupole localized at the vacancies to the elastic strain. In the present work, the electronic quadrupole moment of the vacancy orbital in silicon and their strain susceptibility are evaluated quantitatively by using the density-functional method. We show the orbital of gap state is localized around vacancy but extended over several neighbors. The effect of applied magnetic field on the vacancy orbital and its multipole structures are also investigated. We find that the results obtained from these calculations are consistent with the ultrasonic experiments.

Lateral nMOSFETs have been fabricated on 4H-SiC utilizing deposited dielectrics and gate-last processing. A bi-layer dielectric was utilized consisting of thin nitrided SiO2 covered by 25nm of Al2O3 deposited using atomic layer deposition. Field-effect mobility and threshold voltage (VT) were found to vary with SiC nitric oxide (NO) anneal temperature. High peak mobility values of 106 cm2/V·s were obtained, with a corresponding VT of 0.8 V, using an 1175 °C 20 min NO anneal of the SiC before Al2O3 deposition. Constant voltage stressing (CVS) of the gate (3 MV/cm) for 1000s induces a VT increase of only 0.12 V for the devices stressed at RT, whereas a VT shift of 0.34 V occurs for devices stressed at 150 °C. Heating unstressed devices to 200 °C reveals a stable VT with temperature. Negative charge in the gate region allows for the attainment of positive VT, while VT stability does not suffer.

Data retention is one of the major device reliabilities of NAND Flash memory. We found that the lower Refractive Index (RI) of the Passivation Silicon Oxynitride (SiON) layer deposited by PECVD, the better data retention behavior was achieved. The hydrogen content and the stress analysis of the films are analyzed to find out which is more important in this case. Generally, when the RI of SiON decreases, both parameters also decrease, so it is impossible to find out which parameter is major factor of data retention. To analyze the effects of two parameters separately, we applied two conditions which had the same H contents but quite different stress values. The final data retention levels are same in both conditions. In addition, even if the layer has the same H content, the retention characteristic is changed by how hydrogen is bonded in the film. In conclusion, the data retention characteristic can be explained by mobile ions generated by the hydrogen weakly bonded in PECVD SiON films in our experiment.

Tb-doped AlBNO (AlBNO:Tb) films with various composition ratios are investigated for luminescence layers of inorganic electroluminescence(EL) devices. Luminescence layers with a wide bandgap and a low dielectric constant are required to realize high performance of EL devices. The ultraviolet-visible radiation absorption measurement and capacitance-voltage (C-V) measurement show that the AlBNO:Tb films have wider bandgap and lower dielectric constant than ZnS which is put to practical use as the host material of the luminescence layer. Photoluminescence (PL) measurement indicates that PL intensity increases with increasing B composition ratio in the range of 5 % - 10 %. Moreover, the suppression factor of the PL intensity can be understood through the annealing experiment. The PL intensity of the film with 800 °C annealing is about 10 times larger than that of the film without annealing. X-ray photoelectron spectroscopy (XPS) measurement suggests that Tb4+ ions decrease compared with Tb3+ ions after annealing treatment. O atoms in the AlBNO:Tb film are dissociated from Tb and bonded to B atoms by annealing treatment. This suggests that decrease of Tb4+ ions is related to increase of the PL intensity.

The reliability of InP/InGaAs heterojunction bipolar transistors (HBTs) with highly carbon-doped and zinc-doped InGaAs base layers grown by metal-organic vapor phase epitaxy has been investigated. The Raman spectroscopy reveals that the post-growth annealing for the carbon-doped InGaAs base improves the crystallinity to become as good as that of the zinc-doped InGaAs base. However, the photoluminescence intensity remains lower than that of the zinc-doped InGaAs even after the post-growth annealing. The current gains of the carbon- and zinc-doped base InP/InGaAs HBTs are 63 and 75, respectively, and they are affected by the base crystallinity. After the 15-min current stress test, the current gains decreased by 40 and 3% from the initial current gains for zinc- and carbon-doped base HBTs, respectively, are observed. These results indicate that the carbon-doped base HBT is much more reliable than that of zinc-doped base HBT, though it has a lower current gain.

Plasma spraying is a well-established method for depositing nanostructured ceramic coatings on structural components. Two different plasma spraying techniques - solution precursor plasma spray (SPPS) and suspension plasma spray (SPS) - have been used to produce MgO-50vol% ZrO2 composite coatings. The microstructural features of the coatings were characterized using Environmental Scanning Electron Microscopy (ESEM) and X-Ray Diffractometry (XRD). The micro hardness of the coatings was measured on cross-sectional samples. The coatings produced using the SPS process with ethanol-based suspensions at a high plasma torch power (45.5 kW) exhibited the densest microstructures with hardnesses as high as ∼1350 HV. However, the backscattered electron (BSE) ESEM characterization of these coatings revealed that the coatings obtained using the SPPS technique had superior chemical homogeneity over those obtained using the SPS technique.

We demonstrated electrical characteristics of operational amplifier (OPAMP) circuits fabricated by GaN/AlGaN/GaN HEMTs operating over 100 oC. GaN/AlGaN/GaN HEMTs, with the extremely low source resistance were fabricated by multiple ion implantation, precisely controlled ion-implanted (I/I) resistors and Schottky barrier diodes were integrated on the silicon substrate. The GaN cap layer on the AlGaN was grown to decrease the gate leakage current and current collapse for AlGaN/GaN HEMTs.

Optical and schottky diode characteristics of unintentionally doped GaN films grown by MOCVD were reported. GaN epilayers were grown with different V/III ratio by varying the source ammonia (NH3) flowrate. It exhibit changes in the density of threading dislocations (TDs) and reduced carbon and oxygen impurity incorporation. The density of dislocations determined from hot-wet chemical etching and atomic force microscopy show that on decreasing the ammonia flowrate, threading dislocations decreases. Low energy positron beam was employed to study the Ga vacancies in the epilayers. S-parameter vs. positron beam energy curves clearly shows increase in SL on increasing the V/III ratio indicating that the point defects trapping positron increases. Corroborative HRXRD, Photoluminescence and Hall measurements confirm the reduction in trapping defects and threading edge dislocations with reducing V/III molar ratio. The effects of such variation of compensating centres and radiative centres as a function of MOCVD growth conditions on optical properties and schottky device characteristics like radiative decay lifetime, barrier height and reverse leakage current respectively were discussed.