Measurement of stresses in Cu and Si around through-silicon via by synchrotron X-ray microdiffraction for 3-dimensional integrated circuits

Through-silicon via (TSV) has been used for 3-dimentional integrated circuits. Mechanical stresses in Cu and Si around the TSV were measured using synchrotron X-ray microdiffraction. The hydrostatic stress in Cu TSV went from high tensile of 234 MPa in the as-fabricated state, to ?196 MPa (compressive) during thermal annealing (in situ measurement), to 167 MPa in the post-annealed state. Due to this stress, the keep-away distance in Si was determined to be about 17 μm. Our results suggest that Cu stress may lead to reliability as well as integration issues, while Si stress may lead to device performance concerns.     

Integrated circuit design for physical unclonable function using differential amplifiers

A physical unclonable function (PUF) based on process variations on silicon wafers is a very promising technology which finds various applications in identification and authentication, but only a few integrated circuits have been reported so far. As those circuits are vulnerable to power supply noises, switching noises and environmental variations, they lead to a reliability issue such as time-varying or metastable responses. To resolve this issue, this letter proposes a new integrated circuit design for PUFs using differential amplifiers. The feasibility of the proposed circuit has been theoretically analyzed and validated through HSPICE simulations for the previous and proposed circuits.     

Molecular Dynamics Simulation of MBE Growth of CdTe/ZnTe/Si

We simulate in three dimensions molecular beam epitaxial (MBE) growth of CdTe/ZnTe/Si using classical molecular dynamics. Atomic interactions are simulated with Stillinger–Weber potentials, whose parameters are obtained by fitting to experimental data or density function theory-calculated distortion energies of the component crystals. The effects of substrate temperature and atomic species flux ratios on epilayer morphology are investigated. The agreement between simulations and experiments suggests that this model has reasonable ability to predict the microstructures of CdTe/ZnTe/Si grown by MBE.     

Four-point probe characterization of 4H silicon carbide

We report on four-point probe measurements on SiC wafers as such measurements give erratic data. Current-voltage measurements on n-type SiC wafers doped to 3 × 10¹⁸ cm⁻³ are non-linear and single probe I-V measurements are symmetrical for positive and negative voltages. For comparison, similar measurements of p-type Si doped to 5 × 10¹⁴ cm⁻³ gave linear I-V, well-defined sheet resistance and the single probe I-V curves were asymmetrical indicating typical Schottky diode behavior. We believe that the reason for the non-linearity in four-point probe measurements on SiC is the high contact resistance. Calculations predict the contact resistance of SiC to be approximately 10¹² Ω which is of the order of the input resistance of the voltmeter in our four-point probe measurements. There was almost no change in two-probe I-V curves when the spacing between the probes was changed from 1 mm to 2 cm, further supporting the idea that the I-V characteristics are dominated by the contact resistance.     

Laser direct imaging of transparent indium tin oxide electrodes using high speed stitching techniques

To accomplish an electrode patterning in large area, we present a high speed stitching technique used in an ultraviolet laser processing system and investigate the interaction between laser beams and indium tin oxide (ITO) thin films deposited on glass substrates. After optimizing the process parameters of the laser direct imaging (LDI) for the large-area electrode patterning, the ablated lines looked like regularly fish-scale marks of about a 40 μm diameter and a 120 nm depth around the processing path. The parameters includes the laser power of 1W, the scanning speed of galvanometers of 800 mm/s, and the laser pulse repetition frequency of 50 kHz. Moreover, the resistance value of the ablated ITO thin film is larger than 200MΩ that is electrically insulated from the other regions of electrode structure. LDI technology with UV laser beam has great potential applications in patterning on wafer or sapphire substrates and patterning a conductive layer deposited on the touch panels for semiconductor and optoelectric industries, respectively.     

On the affordances of the MaxEP principle

Optimality principles have long been popular in the natural sciences and enjoyed much successes in various applications. However these principles seem to be disparate, each applied in limited contexts and there are far too many of them causing some consternation among scientists and philosophers of science regarding the ad-hoc nature of the optimality arguments. In this paper, we discuss the Maximum entropy production (MaxEP) as a plausible over-arching principle to understand stable configurations in fluid mechanics and related problems. The MaxEP being based upon sound physical arguments and in the immutable laws of thermodynamics along with the fact that it has been successfully co-opted across disciplines makes it worthy of attention. We discuss various physical and metaphysical aspects of this principle and use it to analyze some model problems regarding patterns in particle sedimentation such as sedimentation of a particle in Newtonian and non-Newtonian fluids and stable deformation of a falling droplet.     

Characteristics of large‐scale nanohole arrays for thin‐silicon photovoltaics

Nanostructured crystalline silicon is promising for thin‐silicon photovoltaic devices because of reduced material usage and wafer quality constraint. This paper presents the optical and photovoltaic characteristics of silicon nanohole (SiNH) arrays fabricated using polystyrene nanosphere lithography and reactive‐ion etching (RIE) techniques for large‐area processes. A post‐RIE damage removal etching is subsequently introduced to mitigate the surface recombination issues and also suppress the surface reflection due to modifications in the nanohole sidewall profile, resulting in a 19% increase in the power conversion efficiency. We show that the damage removal etching treatment can effectively recover the carrier lifetime and dark current–voltage characteristics of SiNH solar cells to resemble the planar counterpart without RIE damages. Furthermore, the reflectance spectra exhibit broadband and omnidirectional anti‐reflective properties, where an AM1.5 G spectrum‐weighted reflectance achieves 4.7% for SiNH arrays. Finally, a three‐dimensional optical modeling has also been established to investigate the dimension and wafer thickness dependence of light absorption. We conclude that the SiNH arrays reveal great potential for efficient light harvesting in thin‐silicon photovoltaics with a 95% material reduction compared to a typical cell thickness of 200 µm. Copyright © 2012 John Wiley & Sons, Ltd.     

Electrochemical synthesis of a double‐layer film of ZnO nanosheets/nanoparticles and its application for dye‐sensitized solar cells

A double‐layer film, consisting of an upper layer of ZnO nanosheets and a lower layer of ZnO nanoparticles (designated as ZnONS/NP), was synthesized for the photoanode of a dye‐sensitized solar cell (DSSC) by a one‐step potentiostatic electrodeposition on a conducting fluorine‐doped tin oxide substrate at 70 °C in a solution containing zinc nitrate and sodium acetate, followed by the pyrolysis of the film at 300 °C. The growth mechanism of the double‐layer nanostructure was studied by monitoring the morphological changes at various periods of electrodeposition. The effects of the concentration of acetate anion on the morphology of the double‐layer structure were also studied. The double‐layer film of ZnONS/NP showed a better self‐established light scattering property, compared with that of a thin film of ZnO nanoparticles, prepared without acetate anion. The concentration of an acetate anion in the electrolyte for the electrodeposition of the double‐layer film, the electrodeposition period, and the period for dye adsorption were optimized for obtaining the best performance for a DSSC with a photoanode consisting of the double layer. A metal‐free dye, coded as D149, was used in this research. A conversion efficiency of 4.65% was achieved for a DSSC (0.2376 cm²) with the photoanode, consisting of the double‐layer film, under 100 mW/cm² illumination in the wavelength range of 400–800 nm. X‐ray diffraction patterns, thermo gravimetric curves, elemental analysis, scanning electron microscopic images, transmission electron microscopic image, transmission spectra, and electrochemical impedance spectra were used to explain observations. Copyright © 2012 John Wiley & Sons, Ltd.     

Three‐Dimensional Block Copolymer Nanostructures by the Solvent‐Annealing‐Induced Wetting in Anodic Aluminum Oxide Templates

Block copolymers have been extensively studied over the last few decades because they can self‐assemble into well‐ordered nanoscale structures. The morphologies of block copolymers in confined geometries, however, are still not fully understood. In this work, the fabrication and morphologies of three‐dimensional polystyrene‐block‐polydimethylsiloxane (PS‐b‐PDMS) nanostructures confined in the nanopores of anodic aluminum oxide (AAO) templates are studied. It is discovered that the block copolymers can wet the nanopores using a novel solvent‐annealing‐induced nanowetting in templates (SAINT) method. The unique advantage of this method is that the problem of thermal degradation can be avoided. In addition, the morphologies of PS‐b‐PDMS nanostructures can be controlled by changing the wetting conditions. Different solvents are used as the annealing solvent, including toluene, hexane, and a co‐solvent of toluene and hexane. When the block copolymer wets the nanopores in toluene vapors, a perpendicular morphology is observed. When the block copolymer wets the nanopores in co‐solvent vapors (toluene/hexane = 3:2), unusual circular and helical morphologies are obtained. These three‐dimensional nanostructures can serve as naontemplates for refilling with other functional materials, such as Au, Ag, ZnO, and TiO₂.