Post Fabrication Research Articles

Performance and stability of “partly covered” photoelectrochromic devices for energy saving and power production

This work comprises an experimental study on various factors affecting the stability of “partly covered” photoelectrochromic (PEC) devices. The fabricated devices were stored in the dark at open circuit conditions and at regular time intervals, transmittance spectra for coloration and bleaching were taken and I–V measurements were conducted. This methodology revealed that the PEC devices, after passing a transitional period of about 10days post fabrication, seem to stabilize or to decay at a lower rate.The annealing temperature of the anode and the composition of the electrolyte affect drastically the operation and stability of the devices. By annealing the anode at 350°C for 40min and using a commercial electrolyte, developed for high performance dye sensitized solar cells, stable devices were fabricated (nearly 10months of shelf life), but with reduced reversibility.In order to improve the reversibility two different strategies were tried. The first one was the electrochemical treatment of the anode, before incorporation into the device, and the other was to alter the composition of the electrolyte. Reversible devices with shelf life exceeding 5months were fabricated using an anode annealed at 100°C and an electrolyte consisting of 0.5M LiI/0.005M I2/0.5M 4-TBP/ACN. Electrolytes specifically designed for PEC devices need to be developed for optimum operation.

Influence of Annealing Condition on TSV Pumping and Microstructure Evolution

Stacking of ICs using three-dimensional (3D) integration technology helps in significantly reducing wiring lengths, interconnection latency, and power dissipation while enhancing performance. Through silicon vias (TSVs) are regarded as a key enabling technology for 3D IC integration which assists in the realization of highly miniaturized and complex next-generation systems. Due to the thermal expansion (CTE) mismatch between copper and silicon, the copper in silicon vias tends to pump up as a result of thermal-mechanical stress during the post fabrication processes and/or during the lifetime of chip usage. One way to minimize or get rid of copper pumping is through heat treatment, for instance annealing or aging. The TSV wafers could be annealed right after copper plating process, or after chemical mechanical polish (CMP) process, or both. The residual stress might be thoroughly released by repeating annealing and CMP processes several times, however, the cost for fabricating the TSVs is increasing drastically, which is mainly attributed to the use of expensive CMP. To lower down the cost and minimize the CMP steps is one of the concerns from industry. In this paper, we report the thermal mechanical assessment of Cu pumping treated at different annealing conditions. moreover, the impact of different integration approaches on the TSV pumping behavior is also investigated. The finite element analysis method, ANSYS, is used to model and simulate the copper pumping at different temperatures, as shown in Fig.1. The pumping is measured by optical profiler, BRUKER ContourGT-X3, as shown in Fig.2. It has been found out that the copper grain size increases with annealing temperature, which is potentially contributed to larger protrusion. The preliminary results show that the annealing after copper plating process affects the microstructure evolution and pumping of TSVs. Figure 1

Preparation of a porous conductive scaffold from aniline pentamer-modified polyurethane/PCL blend for cardiac tissue engineering.

A novel biodegradable electroactive polyurethane containing aniline pentamer (AP) was blended with polycaprolactone (PCL). The prepared blend (PB) and PCL were further fabricated in to scaffolds using a mixture of poly(ethylene glycol) and salt particles in a double porogen particulate leaching and compression molding methodology. Scaffolds held open and interconnected pores having pore size ranging from several μm to 150 µm. PB scaffolds had compression modulus and strength of 4.1 and 1.3 MPa, respectively. The conductivity of the scaffold was measured as 10(-5) ± 0.09 S .cm(-1) and preserved for at least 100 h post fabrication. Scaffolds supported neonatal cardiomyocytes adhesion and growth with PB showing more extensive effect on the expression of the cardiac genes involved in muscle contraction and relaxation (troponin-T) and cytoskeleton alignment (actinin-4). Our results highlight the potential of incorporation of AP as an electroactive moiety for induction of cardiomyocyte proliferation and repair of damaged heart tissue.

Temperature dependence inflection point in Ultra-Thin Si directly on Insulator (SDOI) MOSFETs: An influence to key performance metrics

An inflection point on the behaviour of MOSFET over wide range of temperatures (T) influences performance of both analog and digital circuits. This work is an investigation to find the point of inflection at which the temperature coefficient is zero of Ultra-Thin Si directly on Insulator (UT-SDOI) single gate (SG), double gate (DG), and gate stack double gate (GS-DG), n-MOSFET over wide range of temperatures (100–400K) through 2-D device simulation. The interface trapped charges which are common during the pre and post fabrication process are also considered in the simulation. The impact of T on various performance metrics like on current (Ion), off current (Ioff), on–off current ratio (Ion/Ioff), subthreshold slope (SS), Q-factor, intrinsic gate delay (τ), energy delay product (E⋅τ), transconductance (gm), output conductance (gd), intrinsic gain (AV), cut off frequency (fT) and sweet spot have been analyzed extensively to benchmark the device behaviour. The impact of temperature compensation point (TCP) over various performances for three typical devices is compared. This validates an opportunity for nanoscale MOSFETs in designing the circuits used for various applications.

Self-Aligned Bottom-Gate InGaZnO Thin-Film Transistor with Source and Drain Regions Formed by Selective Deposition of Fluorinated SiNx Passivation

Since the report of an amorphous InGaZnO thin-film transistor (IGZO TFT)[1], many researches have been focused on achieving high performance and high stable oxide TFTs for next generation display. Bottom-gate type with a SiOx etch-stopper have been widely employed for IGZO TFTs. However, one of serious drawbacks of this structure is a large parasitic capacitance of gate-to- drain (CGD) and source (CGS) due to overlap between gate and source/drain (S/D) electrodes. It is known that large parasitic capacitance reduces operation speed of the TFT circuits and induces signal delay of the TFT backplane. Moreover, large CGDof select TFTs in organic light emitting diode (OLED) display strongly influences uniformity of the luminescence of the pixels because the CGD is the main cause of kickback/feedthrough voltage which influences an operation voltage of driving TFTs. Self-aligned (SA) structure is an essential for reducing parasitic capacitance in the TFTs. There are several reports of IGZO homojunction with highly conductive IGZO for source/drain regions which were formed by selective exposure of Ar, H2, or He plasma or ion implantation. [2-4] On the other hand, the IGZO homojunction was demonstrated by hydrogen diffusion from hydrogenated SiNx (SiNx:H) deposited on top of the IGZO.[5] In this paper, we developed the IGZO homojunction with thermally stable S/D regions that was formed by a direct deposition of fluorinated SiNx (SiNx:F) on top of the IGZO. By combining the back-side exposure (BSE) technique and IGZO homojunction formed by the direct deposition of SiNx:F, the SA IGZO TFT are demonstrated.Figure 1(a) and 1(b) show cross sectional views of the SA IGZO TFT with SiOx and SiN:F passivation, respectively. First, Cr gate electrode was formed on a glass substrate. Next, a 150-nm thick SiOx for gate insulator, a 45-nm-thick IGZO for active channel, and a 100-nm-thick SiOx for etch stopper (ES) were deposited. Then, ES layer was aligned by the BSE technique used gate electrode as a mask, and was etched by a dry etching with CF4/O2 plasma. After patterning of the IGZO channel as an active channel, fluorinated SiNx (SiN:F) for passivation was deposited by an inductively-coupled plasma chemical vapour deposition using SiF4+N2 gas mixture as shown in FIg. 1(b). Note that hydrogen-free gas chemistry was used for the SiNx:F deposition. An IGZO TFT with SiOx passivation (deposited by conventional plasma-CVD using SiH4/N2O/N2 gases) was also fabricated for comparison as shown in Fig. 1(a). S/D electrodes were formed by ITO via contact holes. It is noted that there is no overlap region between gate and S/D electrodes. The TFT properties were measured after post fabrication annealing at 300 ºC in N2 for 1h.Figure 1(c) and 1(d) show transfer characteristics of the IGZO TFTs with SiOx and SiNx:F passivation, respectively. On current of the IGZO TFT with SiOx passivation was suppressed due to series resistance of the S/D region. This result indicates that ES dry etching with CF4/O2 plasma did not contribute to form highly conductive S/D region. In contrast, the TFT with SiNx:F passivation exhibited good electrical properties with the field effect mobility of ~10 cm2/Vs. The bottom-gate SA IGZO TFT with homojunction can be achieved by a direct deposition of SiNx:F on the S/D regions.Authors would like to thank Tokyo Electron Co., Ltd. for their supports and useful discussion regarding the SiNx:F films. This work is supported in part by JSPS KAKENHI Grant No. 23560408. [Ref]1) Nomura et al., Nature 432, 488 (2004)2) J.-S. Park et al., Appl. Phys. Lett. 90, 262106 (2007)3) H. Jeong et al., Appl. Phys. Lett. 104, 022115 (2014)4) R. Chen et al., IEEE Elec. Dev. Lett., 33, 1150 (2012)5) A. Sato et al, Appl. Phys. Lett. 94, 133502 (2009)

Poster - Thur Eve - 68: Assessment of post-fabrication deformation in three styles of thermoplastic masks

This work assesses the post fabrication shrinkage of 3 styles of Aquaplast Slimline U-Frame thermoplastic masks: Aquaplast RT (Aqua S); Fibreplast (Aqua KS) which is similar to Aqua S, but contains Kevlar for improved rigidity and reduced shrinkage; and Aquaplast RT Variable Perf (Aqua YS) which is similar to Aqua S but excludes perforations along various bands for improved strength. Each mask was formed over the same rigid anthropomorphic head phantom. Immediately post-fabrication, each mask was remounted onto an optical bench, where sequences of profile photographs were acquired over the span of one week. Points marked near the forehead, nose, and chin were tracked to determine the deformation of the masks. Reproducibility of point position determination was within about 0.02 mm. After one week, all points translated primarily in the posterior direction due to mask shrinkage. Observed translations were largest for the Aqua S mask where points translated by 2.31±0.05mm on average. The Aqua YS mask yielded the smallest translations: 1.57±0.03mm, 1.20±0.03mm, and 1.54±0.03mm for points near the forehead, nose and chin respectively. The Aqua KS mask yielded somewhat greater translations: 1.57±0.02mm, 1.20±0.02mm and 1.54±0.02mm for the same respective points. Future work will characterize other mask models and measure the pressure exerted at select points by each mask on the phantom after shrinkage.

High resolution micro ultrasonic machining for trimming 3D microstructures

This paper reports on the evaluation of a high resolution micro ultrasonic machining (HR-µUSM) process suitable for post fabrication trimming of complex 3D microstructures made from fused silica. Unlike conventional USM, the HR-µUSM process aims for low machining rates, providing high resolution and high surface quality. The machining rate is reduced by keeping the micro-tool tip at a fixed distance from the workpiece and vibrating it at a small amplitude. The surface roughness is improved by an appropriate selection of abrasive particles. Fluidic modeling is performed to study interaction among the vibrating micro-tool tip, workpiece, and the slurry. Using 304 stainless steel (SS304) tool tips of 50 µm diameter, the machining performance of the HR-µUSM process is characterized on flat fused silica substrates. The depths and surface finish of machined features are evaluated as functions of slurry concentrations, separation between the micro-tool and workpiece, and machining time. Under the selected conditions, the HR-µUSM process achieves machining rates as low as 10 nm s−1 averaged over the first minute of machining of a flat virgin sample. This corresponds to a mass removal rate of ≈20 ng min−1. The average surface roughness, Sa, achieved is as low as 30 nm. Analytical and numerical modeling are used to explain the typical profile of the machined features as well as machining rates. The process is used to demonstrate trimming of hemispherical 3D shells made of fused silica.

Combined hydrogels that switch human pluripotent stem cells from self-renewal to differentiation

The ability of materials to define the architecture and microenvironment experienced by cells provides new opportunities to direct the fate of human pluripotent stem cells (HPSCs) [Robinton DA, Daley GQ (2012) Nature 481(7381):295-305]. However, the conditions required for self-renewal vs. differentiation of HPSCs are different, and a single system that efficiently achieves both outcomes is not available [Giobbe GG, et al. (2012) Biotechnol Bioeng 109(12):3119-3132]. We have addressed this dual need by developing a hydrogel-based material that uses ionic de-cross-linking to remove a self-renewal permissive hydrogel (alginate) and switch to a differentiation-permissive microenvironment (collagen). Adjusting the timing of this switch can preferentially steer the HPSC differentiation to mimic lineage commitment during gastrulation to ectoderm (early switch) or mesoderm/endoderm (late switch). As an exemplar differentiated cell type, we showed that directing early lineage specification using this single system can promote cardiogenesis with increased gene expression in high-density cell populations. This work will facilitate regenerative medicine by allowing in situ HPSC expansion to be coupled with early lineage specification within defined tissue geometries.

Focused ion beam (FIB)-induced changes in the electrochemical behavior of boron-doped diamond (BDD) electrodes

Micro- and nanostructured electrodes play a significant role in modern electroanalytical chemistry. Here, we report on the effect of focused ion beam-induced changes in the surface layers of nanocrystalline highly boron-doped diamond (BDD). The impact of gallium ions induces an amorphization of the surface layers of the BDD lattice, and hence, changes the electron transfer behavior of redox species, which electron transfer is sensitive to surface properties. These changes in heterogeneous electron transfer behavior are investigated in dependence of FIB patterning parameters. The effects of electrochemical post-milling treatments were studied for restoring the electrochemical properties. In addition, Raman spectroscopic and electron backscatter diffraction (EBSD) measurements revealed that amorphous carbon is largely removed during the post-milling electrochemical treatment at very negative potentials. Hence, FIB-based nanostructuring of BDD-electrodes with an optimized post fabrication treatment enables the fabrication of miniaturized devices based on boron-doped diamond for a wide variety of electroanalytical applications.

Analysis of the effects of applying external fields and device dimensions alterations on GaAs/AlGaAs multiple quantum well slow light devices based on excitonic population oscillation

This paper demonstrates the effects of applying magnetic and electric fields and physical dimensions alterations on AlGaAs/GaAs multiple quantum well (QW) slow light devices. Physical parameters include quantum well sizes and number of quantum wells. To the best of our knowledge, this is the first analysis of the effects of both applying magnetic/electric fields and physical parameters alterations and the first suggestion for matching the prefabrication and post fabrication tuning of the slow light devices based on excitonic population oscillations. The aim of our theoretical analysis is controlling the optical properties such as central frequency, bandwidth, and slow down factor (SDF) in slow light devices based on excitonic population oscillation to achieve better tuning. To reach these purposes, first we investigate the quantum well size and number of quantum wells alteration effects. Next, we analyze the effects of applying magnetic and electric fields to the multiple quantum well structure, separately. Finally, physical parameters and applied external fields are changed for measuring frequency shift and SDF for coherent population oscillation slow light devices. The results show the available central frequency shifts in about 1.6 THz at best. Also the SDF value improvement is about one order of magnitude. These results will be applicable for optical nonlinearity enhancements, all-optical signal processing, optical communications, all-optical switches, optical modulators, and variable true delays.

Development and characterization of novel electrically conductive PANI–PGS composites for cardiac tissue engineering applications

Cardiovascular diseases, especially myocardial infarction, are the leading cause of morbidity and mortality in the world, also resulting in huge economic burdens on national economies. A cardiac patch strategy aims at regenerating an infarcted heart by providing healthy functional cells to the injured region via a carrier substrate, and providing mechanical support, thereby preventing deleterious ventricular remodeling. In the present work, polyaniline (PANI) was doped with camphorsulfonic acid and blended with poly(glycerol-sebacate) at ratios of 10, 20 and 30vol.% PANI content to produce electrically conductive composite cardiac patches via the solvent casting method. The composites were characterized in terms of their electrical, mechanical and physicochemical properties. The in vitro biodegradability of the composites was also evaluated. Electrical conductivity increased from 0Scm−1 for pure PGS to 0.018Scm−1 for 30vol.% PANI–PGS samples. Moreover, the conductivities were preserved for at least 100h post fabrication. Tensile tests revealed an improvement in the elastic modulus, tensile strength and elasticity with increasing PANI content. The degradation products caused a local drop in pH, which was higher in all composite samples compared with pure PGS, hinting at a buffering effect due to the presence of PANI. Finally, the cytocompatibility of the composites was confirmed when C2C12 cells attached and proliferated on samples with varying PANI content. Furthermore, leaching of acid dopants from the developed composites did not have any deleterious effect on the viability of C2C12 cells. Taken together, these results confirm the potential of PANI–PGS composites for use as substrates to modulate cellular behavior via electrical stimulation, and as biocompatible scaffolds for cardiac tissue engineering applications.

A Spatial Point Pattern Analysis to Recognize Fail Bit Patterns in Semiconductor Manufacturing

The yield management system is very important to produce high-quality semiconductor chips in the semiconductor manufacturing process. In order to improve quality of semiconductors, various tests are conducted in the post fabrication (FAB) process. During the test process, large amount of data are collected and the data includes a lot of information about defect. In general, the defect on the wafer is the main causes of yield loss. Therefore, analyzing the defect data is necessary to improve performance of yiel wafer bin map (WBM) is one of the data collected in the test process and includes defect information such as the fail bit patterns. The fail bit has characteristics of spatial point patterns. Therefore, this paper proposes the feature extraction method using the spatial point pattern analysis. Actual data obtained from the semiconductor process is used for experiments and the experimental result shows that the proposed method is more accurately recognize the fail bit patterns. Keywords—Semiconductor, wafer bin map (WBM), feature extraction, spatial point patterns, contour map.

A Robust Low Power Carbon Nanotube Sensor Interface Circuit in 180 nm CMOS Technology

The design and performance of a low-cost, energy-efficient carbon nanotube sensor interface circuit (SIC) is presented that is aimed at deployable/expendable applications with the sensor operating at ambient temperatures. The submicrometer SIC is designed and fabricated in CMOS 180-nm technology and consumes a maximum of 122 μW, including a decoder and voltage follower. The SIC achieves a measurement accuracy of 1.4% over a 2.5 kΩ to 25 MΩ dynamic range of sensor resistance. A critical issue associated with a submicrometer integrated circuit implementation is satisfactory performance of the SIC for fabrication process variations that range from the slow, to typical, to fast process corners and simultaneously meeting the requirement for the very large dynamic range for sensor resistances. A robust design considering the full range of potential process variations becomes more critical as feature size is reduced. The SIC design includes an added degree for freedom for counteracting process variations during post fabrication calibration. In addition, a new design procedure is outlined and implemented to permit an accurate and efficient first order design to ensure satisfactory performance for typical, fast, and slow model parameters. The first order design is verified by complete model simulation performance, and finally selected measured results are included for a fabricated circuit.

RF CMOS active inductor band pass filter with post fabrication calibration

This paper presents an active inductor bandpass filter (BPF) architecture with selectable 50Ω driving capability and post fabrication calibration for gain, center frequency, and quality factor. The design details, and performance assessment that facilitate selecting an offline calibration mode to measure and tune post fabrication BPF performance are discussed. A specific design example for a L1/L2 channel GPS receiver is included with a BPF that is required to pass the L2 signal centered at 1.227GHz with a gain of approximately16dB at the center frequency, have a 3dB bandwidth of 30MHz (Q=41) and rejection of the L1 signal at 1.575GHz by at least 60dB relative to the center frequency. A multistage active inductor BPF 90nm CMOS design is presented that meets these specifications with typical process parameters. It is demonstrated that the post fabrication design based on typical corner analysis can be re-tuned to the desired performance for process variations across the slow and fast corners using the offline measuring and tuning control inputs.

Bio-reconstruction of root canal using dentin post

This case report describes the successful management of complicated crown fracture of left maxillary central incisor (#21) of 23-year-old male using dentin (biological) post made from human tooth. Endodontic treatment was initiated and sectional obturation was done using ProTaper gutta-percha and AH Plus sealer. The coronal space was modified to receive a human dentin post. A two-step procedure comprising direct and indirect technique of post fabrication was done to achieve the accuracy of biological post. A maxillary cuspid from an institutional tooth bank was taken, sectioned mesiodistally using a diamond disc simulating the length and thickness of mock post. Dentin post was first verified on the plaster model and then cemented in tooth #21. Core build up was done with composite and porcelain fused to metal (PFM) crown was luted. On the follow-up visits, patient was asymptomatic and radiographic evaluation revealed normal periradicular architecture. Biological posts may be good alternatives to conventional post systems as they preserve internal dentin walls, provide excellent adhesion, and resilience similar to natural tooth structure.

Clinical and Technical Considerations of Luting Agents for Fixed Prosthodontics

Clinical and Technical Considerations of Luting Agents for Fixed Prosthodontics

Stability of contamination-free gold and silver nanoparticles produced by nanosecond laser ablation of solid targets in water

Preparation of noble metal nanoparticle (NPs) colloids using pulsed laser ablation in water has an inherent advantage compared to the different chemical methods used, especially when biological applications of the colloids are considered. The fabrication method is simple and the NPs prepared in this way are contamination free.The method of laser ablation of a solid target in water is applied in the present work in order to obtain gold and silver NP colloids. The experiment was preformed by using the fundamental wavelength (1064nm) of a Nd:YAG laser system. The target immersed in double distilled water was irradiated for 20min by laser pulses with duration of 15ns and repetition rate of 10Hz. The sedimentation and aggregation of NPs in the colloids, stored at constant temperature, as a function of the time after preparation were investigated. The analyses are based on optical transmission spectroscopy in UV and vis regions. The change of the plasmon resonance wavelength as a function of time was studied. Zeta potential measurement was also utilized to measure the charge of the NPs in the colloids. The size distribution of the NPs and its change in time was determined by transmission electron microscopy (TEM). On the basis of the results obtained, the optimal conditions of post fabrication manipulation with gold and silver colloids are defined in view of producing stable NPs with a narrow size distribution.

Patterning the Cathode Catalyst Layer - Membrane Interface of a PEMFC for Elevated Power Density

Nafion patterned by electron beam lithography coupled with dry etching was tested for electrochemical performance in a proton exchange membrane fuel cell. Bare (neither patterned nor etched) and blanket etched Nafion membranes were also tested for comparison. Membrane electrode assemblies (MEA) were formed by sputtering Pt onto both sides of a membrane using a shadow mask to selectively expose 1 cm2 of geometric area. The blanket etched membrane produced the best performance with a power density of ~170 mW/cm2. The maximum power density for the patterned MEA was smaller compared to the bare and blanket etched Nafion membranes. Furthermore, the etched MEA initially displayed low open circuit potential. Its diminished performance was attributed to contamination artifacts from the fabrication process. A post fabrication hydrogen peroxide wash prior to MEA assembly led to a higher open circuit potential and improved performance.

Bendable Heat Pipes Using Sintered Metal Felt Wicks

This work describes the effect bending within the adiabatic section has on the performance of heat pipes. The heat pipes described herein are bendable post fabrication and are distinct from heat pipes fabricated in bent configurations and from flexible heat pipes. The effect of bending on performance and performance limits was both calculated and measured. The heat pipes used for testing were the copper-water variety. The wick was made from sintered copper felt and provided the bendability feature of these heat pipes. The concept of copper equivalence to reduce performance measurements data was used via benchmark test data against solid copper pipes.

Annealing Effects on Electrical and Optical Properties of N-ZnO/P-Si Heterojunction Diodes

The effects of post fabrication annealing on the electrical characteristics of n-ZnO/p-Si heterostructure are studied. The nanorods of ZnO are grown by aqueous chemical growth (ACG) technique on p-Si substrate and ohmic contacts of Al/Pt and Al are made on ZnO and Si. The devices are annealed at 400 and 600 °C in air, oxygen and nitrogen ambient. The characteristics are studied by photoluminescence (PL), current–voltage (I-V) and capacitance - voltage (C-V) measurements. PL spectra indicated higher ultraviolet (UV) to visible emission ratio with a strong peak of near band edge emission (NBE) centered from 375-380 nm and very weak broad deep-level emissions (DLE) centered from 510-580 nm. All diodes show typical non linear rectifying behavior as characterized by I-V measurements. The results indicated that annealing in air and oxygen resulted in better electrical characteristics with a decrease in the reverse current.