Total Stack Thickness Research Articles

Robot-assisted non-destructive testing of automotive resistance spot welds

A commercially available matrix phased array (MPA) ultrasonic imaging system was successfully integrated into a robot-assisted automated non-destructive testing (NDT) method for resistance spot weld applications. The NDT system utilizes a dual-time gate feature, where optimized time gate positions and widths were determined for near-normal incidence inspections of spot welds in thin materials. The effects of probe contact pressure and ultrasonic beam incident angle were also studied using the robot arm. Based on the current robot-assisted automated NDT results, an optimized contact pressure of 0.5 lb, and an incidence angle of ± 0.5o relative to the normal direction were determined. Under these optimum probe contact conditions, it was found that a measurement uncertainty of less than 5% can be achieved when the gate position is set to be between one-half and two-third positions of the total part thickness, along with a gate width equals to one-third of the total stack thickness.

Comparative Study of Printed Multilayer OLED Fabrication through Slot Die Coating, Gravure and Inkjet Printing, and Their Combination

In this study, multilayer organic light-emitting diodes (OLEDs) consisting of three solution-processed layers are fabricated using slot die coating, gravure printing, and inkjet printing, techniques that are commonly used in the industry. Different technique combinations are investigated to successively deposit a hole injection layer (poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)), a cross-linkable hole transport layer (N,N′-bis(4-(6-((3-ethyloxetan-3-yl)methoxy)-hexyloxy)phenyl)-N,N′-bis(4-methoxyphenyl)biphenyl-4,4′-diamin (QUPD)), and a green emissive layer (TSG-M) on top of each other. In order to compare the application techniques, the ink formulations have to be adapted to the respective process requirements. First, the influence of the application technique on the layer homogeneity of the different materials is investigated. Large area thickness measurements of the layers based on imaging color reflectometry (ICR) are used to compare the application techniques regarding the layer homogeneity and reproducible film thickness. The total stack thickness of all solution-processed layers of 32 OLEDs could be reproduced homogeneously in a process window of 30 nm for the technique combination of slot die coating and inkjet printing. The best efficiency of 13.3 cd A−1 is reached for a process combination of slot die coating and gravure printing. In order to enable a statistically significant evaluation, in total, 96 OLEDs were analyzed and the corresponding 288 layers were measured successively to determine the influence of layer homogeneity on device performance.

Multilayer coatings for Bloch surface wave optical biosensors

Sensors using surface plasmon resonance (SPR) are established as the method of choice in label-free optical biosensing. Their sensitivity for small refractive index changes at the surface originates from the enhanced evanescent field at the surface of a thin metal layer. However, the small number of well-suited metals (Ag, Au) with fixed optical constants limits a further refinement of the SPR performance in terms of dispersion and resonance width. An alternative can be found in Bloch Surface Waves (BSW) sustained at specially designed dielectric multilayer stacks with low absorption losses. Due to the low losses an enormous narrowing of the resonance is obtained, promising the reduction of the detection limit for such a label-free sensor. In order to deposit these multilayers on plastic sensor chips, plasma ion assisted vacuum evaporation (PIAD) was applied as deposition method. SiO2, TiO2, and Ta2O5 single layer properties were balanced in terms of absorption losses, stability in aqueous environment and film stress. Dielectric multilayer stacks could be designed in a way, that resonance performance is optimal and the total stack thickness as low as possible. Optimized Bloch stacks were successfully coated on a large number of polymer chips. The application could be demonstrated by the detection of cancer biomarkers using an analytical instrument that was developed with the BSW chips as core element.

Al2O3/TiO2 multilayer thin films grown by plasma enhanced atomic layer deposition for organic light-emitting diode passivation

Aluminum oxide (Al2O3) and titanium dioxide (TiO2) films deposited on flexible polyethersulfone substrates by plasma-enhanced atomic layer deposition have been investigated for transparent barrier applications. The effects of the induced plasma power on the passivation properties were investigated as function of film thickness and substrate temperature. The optimum plasma power and substrate temperature were investigated through measurements of the refractive index and packing density of the Al2O3 and TiO2 films. In this research, three different barrier structures were investigated for the purpose of improving water vapor barrier characteristics. A low water vapor transmission rate of approximately 5×10−3g/m2·day or below was achieved with two pairs of Al2O3/TiO2 stacks with a total stack thickness of 40nm deposited at 80°C. The passivation performance of the multilayer film was investigated using an organic light-emitting diode. The coated device lifetime was 267h, which was 41 times longer than that of an uncoated sample.

Characterisation of force–displacement curve in self-pierce riveting

A systematic study of the force–displacement curve of the self-piercing riveting (SPR) process and associated sample characterisation have been carried out in this work. Carbon steel sheet with three different thicknesses and steel rivets with three different hardness levels have been used to examine their impact on the force–displacement characteristic curve. The force–displacement curve is segmented into four different stages, which give the signature of the quality of the joint depending on different process variables. This study shows that the force–displacement curve can be used to monitor the quality of the joint within the same process parameters (rivet length and hardness, total stack thickness and die geometry).

Microfabricated Solid State Thin Film Lithium Batteries

ABSTRACTThis work presents recent advances in the development and the integration of a solid state thin film battery, to work as a high voltage energy source for RF-MEMS powering. Micro-electro-mechanical systems require similarly miniaturized power sources. Up to day, microbatteries are realized with mechanical masks, this method doesn't allow dimensions below several decades of mm2 of active area, and besides the whole process flow is done under controlled atmosphere so as to ensure materials chemical stability (mainly lithiated materials). Within this context, Microelectronics micro-fabrication procedures (photolithography, Reactive Ion Etching…) are used to reach both miniaturisation (100×100 μm2 targeted unit cell active area) and microelectronic IC technological compatibility. The whole process is realized in clean room environment. The thin film battery is composed of three active layers. First the positive electrode layer of crystalline vanadium pentoxide c-V2O5, the next level presents then the solid state electrolyte, a glassy ionic conducting material commonly known as “LiPON”. Finally, a negative electrode top level is realized by the evaporation of metallic lithium. The total stack thickness is of about 10 μm. A final wafer level packaging step is then realized to avoid reactivity with air and moisture. Specific attention will be put on the microfabrication processes developed for the positive electrode and the electrolyte (etching chemistry, resist stripping…). Several electrochemical characterizations (spectroscopic electrochemical impedance, charge-discharge cycling) were performed before and after micro-fabrication process steps so as to evaluate any possible effect on the electrochemical behaviour of the different studied layers.

Process characterization for tapered contact etch

We report the characterization of contact etch processes which give variable sidewall taper angles. Patterning at 248 nm gave contact holes at ∼0.19 μm diameter in photoresist over organic bottom anti reflection coating (BARC). The contact stack and test structures (BARC/oxide/SiN, 5–10 kA total stack thickness) were etched in a medium-density TEL dipole ring magnetron (DRM) system. Bottom hole diameters ranging from 0.17 down to 0.10 μm could be obtained by varying the oxide etch process, which included C4F8 or C5F8, O2, and Ar. A moderate etch selectivity of ∼8:1 (oxide: SiN etch rate ratio) was determined for the main taper process. Etched patterned wafers were characterized using top-down critical dimension scanning electron microscopy (CD-SEM), cross-section SEM, and transmission electron microscopy. Ex situ surface analysis of etched blanket wafers using x-ray photoelectron spectroscopy showed only small dependence of the surface fluorocarbon film thickness and composition on taper etch process cond...

Crystalline quality and interface sharpness of ZnSe/ZnS xSe 1- x superlattices on GaAs: analysis by Raman spectroscopy and X-ray diffractometry

ZnSe/ZnS x Se 1- x strained layer superlattices were grown by atmospheric-pressure metalorganic vapour phase epitaxy (MOVPE) on GaAs substrates. As group VI precursors for ZnS x Se 1- x the combination of diethyl-selenium (DESe) with either diethyl-sulphur (DES) or with H 2S was applied, while we used diethyl-zinc (DEZn) for group II. We investigated the influence of sulphur stabilization during growth interruptions. For the analysis of the structural superlattice properties a combination of Raman spectroscopy and X-ray diffractometry was employed. DES-grown structures with 120 periods, grown at 480°C, show a very good lateral homogeneity of the composition, a high crystal quality and very regular periodicity, which leads in the DCXD profiles to narrow satellite peaks and even pendellösung fringes from the total stack thickness, while in the Raman spectrum the regular modulated structure results in narrow folded acoustical phonon peaks. These results demonstrate the capability of MOVPE to grow high quality ZnSe/ZnS x Se 1- x superlattices.

A high-quality stacked thermal/LPCVD gate oxide technology for ULSI

By stacking thermal and high-quality LPCVD (low-pressure chemical vapor deposition) SiO/sub 2/ films, gate oxides with very low defect densities are demonstrated. Whereas previous reports suggested that a thick layer of LPCVD oxide can improve the stacked gate oxide defect density, it is demonstrated that even 25 AA of LPCVD oxide is sufficient to dramatically reduce the defect density compared to thermal oxide films. The projected scaling limit for this technology is estimated to be as low as 70 AA for the total stack thickness. An optimized thermal/LPCVD oxide technology is very promising as the gate dielectric for sub-half-micrometer CMOS technology.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Evidence for collective exchange modes in Co/Pd multilayers observed by Brillouin light scattering (abstract)

Recently, exchange-dominated collective spin-wave excitations have been predicted for multilayered structures consisting of alternating magnetic and nonmagnetic layers.1 These types of collective excitations exist for nonzero propagation wave vectors if the magnetic layers are exchange coupled across the spacer layers.1 The modes are the collective counterpart to the optic dipolar-exchange mode observed in magnetic double layers by Vohl, Barnás and Grünberg.2 For a multilayer with N periods of bilayer thickness Λ there exist N modes which, in the absence of exchange coupling, form the well-known band of dipolar collective spin-wave excitations. The modes are dominantly surface-mode-like at the upper band edge and mostly bulk-mode-like at the lower band edge. With the onset of exchange coupling the stack bulk modes are shifted to higher frequencies and become exchange-mode-like in character. In the full exchange coupling limit these modes become the so-called standing spin waves of the total multilayer stack, and their frequencies depend on the stack thickness NΛ. The stack surface mode in this limit becomes the surface Damon–Eshbach mode of a single film of thickness NΛ. Brillouin light-scattering experiments have been performed on magnetron-sputtered Co/Pd multilayers.3,4 The number of atomic layers (AL) is the same in each Co and Pd layer. The number of periods was chosen to be N=8 and 30, with Λ varying between 4 and 140 Å. In the case of N=30 a strong increase of spin-wave frequencies for all but the stack surface mode is observed for d&amp;lt;8 AL. Decreasing d0 increases the interlayer exchange coupling and the band of collective bulklike modes increases in frequency to become a band of exchange-dominated modes. Depending on the strength of the coupling (i.e., spacer layer thickness), this band can have frequencies higher than that of the stack surface mode. From the crossing regime the maximum exchange coupling length is estimated to be 10 Å. For samples with N=8, collective exchange modes were not observed. Model calculations show that for N=8 the expected frequency increase near the onset of interlayer exchange coupling is much steeper than in the N=30 case, which might prohibit their experimental observation. Also, the cross section is reduced by a factor of 4 due to the smaller total stack thickness.