Publications

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A series of Ti-rich Ni-Ti-Pt ternary alloys with 13 to 18 at. pct Pt were processed by vacuum arc melting and characterized for their transformation behavior to identify shape memory alloys (SMA) that undergo transformation between 448 K and 498 K (175 °C and 225 °C) and achieve recoverable strain exceeding 2 pct. From this broader set of compositions, three alloys containing 15.5 to 16.5 at. pct Pt exhibited transformation temperatures in the vicinity of 473 K (200 °C), thus were targeted for more detailed characterization. Preliminary microstructural evaluation of these three compositions revealed a martensitic microstructure with small amounts of Ti2(Ni,Pt) particles. Room temperature mechanical testing gave a response characteristic of martensitic de-twinning followed by a typical work-hardening behavior to failure. Elevated mechanical testing, performed while the materials were in the austenitic state, revealed yield stresses of approximately 500 MPa and 3.5 pct elongation to failure. Thermal strain recovery characteristics were more carefully investigated with unbiased incremental strain-temperature tests across the 1 to 5 pct strain range, as well as cyclic strain-temperature tests at 3 pct strain. The unbiased shape recovery results indicated a complicated strain recovery path, dependent on prestrain level, but overall acceptable SMA behavior within the targeted temperature and recoverable strain range.

The stress impact of the CMOS and III-V heterogeneous integration environment on device electrical performance is being characterized. Measurements from a partial heterogeneous integration fabrication run will be presented to provide insight into how the backside source vias, alternatively referred to as through-silicon-carbide vias (TSCVs), used within the heterogeneous integration environment impacts GaN HEMT device-level DC performance.

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Concentrating solar energy and transforming it into electricity is clean, economical and renewable. One design of solar power plants consists of an array of heliostats which redirects sunlight to a fixed receiver tower and the generated heat is converted into electricity. Currently, the angles of elevation of heliostats are controlled by motors and drives that are costly and require diverting power that can otherwise be used for producing electricity. We consider replacing the motor and drive system of the heliostat with a photosensitive polymer design that can tilt the mirror using the ability of the polymer to deform when subjected to light. The light causes the underlying molecular structure to change and subsequently, the polymer deforms. The deformation of the polymer is quantified in terms of photostrictive constitutive relations. A mathematical model is derived governing the behaviour of the angle of elevation as the photostrain varies. Photostrain depends on the composition of the polymer, intensity and temperature of light and angle of light polarization. Preliminary findings show a photomechanical rod structural design can provide 60° elevation for temperatures of about 40°C. A photomechanical beam structural design can generate more tilt at lower temperatures. The mathematical analysis illustrates that photostrains on the order of 1% to 10% are desired for both rod and beam designs to produce sufficient tilt under most heliostat field conditions. © 2014 SPIE.

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We have developed a complete process module for fabricating front end of line (FEOL) through silicon vias (TSVs). In this paper we describe the integration, which relies on using thermally deposited silicon as a sacrificial material to fill the TSV during FEOL processing, followed by its removal and replacement with tungsten after FEOL processing is complete. The uniqueness of this approach follows mainly from forming the TSVs early in the FEOL while still ultimately using metal as the via fill material. TSVs formed early in the FEOL can be formed at comparatively small diameter, high aspect ratio, and high spatial density. We have demonstrated FEOL-integrated TSVs that are 2 μm in diameter, over 45 μm deep, and on 20 μm pitch for a possible interconnect density of 250,000/cm2. Moreover, thermal oxidation of silicon can be used to form the dielectric isolation. Thermal oxidation is conformal and robust in the as-formed state. Finally, TSVs formed in the FEOL alleviate device design constraints common to vias-last integration. © 2009 IEEE.

Contrary to popular opinion, fully resolved speckles may not be the best option for interferometric applications where it is often advantageous to have unresolved speckles with up to hundreds of speckles in a single camera pixel. This paper seeks to elucidate the effect of unresolved speckles on electronic speckle pattern interferometry (ESPI) and laser Doppler velocimetry (LDV). Related techniques such as temporal speckle pattern interferometry (TSPI) and ultrasonic imaging can also benefit from the ideas presented in this paper. Speckle statistics will be briefly outlined as background to the main topic of optimizing speckle fields for use in interferometry. The complementary speckle-size analysis for LDV is compared to previous published results on ESPI.

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The widefield laser Doppler velocimeter is a new measurement technique that significantly expands the functionality of a traditional scanning system. This new technique allows full-field velocity measurements without scanning, a drawback of traditional measurement techniques. This is particularly important for tests in which the sample is destroyed or the motion of the sample is non-repetitive. The goal of creating ''velocity movies'' was accomplished during the research, and this report describes the current functionality and operation of the system. The mathematical underpinnings and system setup are thoroughly described. Two prototype experiments are then presented to show the practical use of the current system. Details of the corresponding hardware used to collect the data and the associated software to analyze the data are presented.