Bochum, Universiẗat, Diss., 2001.

Wafer probing is a testing process to inspect semiconductor wafers before packaging for defects by checking the electrical conductivity via physical contact between the wafers and the probe card. During the contact process, the shape of the probe needle and the mounting configuration onto the probe card have large influences on the stresses and contact force that the probe needles experience. In this paper, static performance of a vertical-type probe needle integrated with floating mount technology is analyzed with a nonlinear finite element analysis. The comparison between fixed mount and floating mount technologies is a part of the analyses. The geometry of a vertical probe needle is optimized to minimize the stress that occurs during the overdrive process, while maintaining adequate force for proper contact with the wafer. Effects of major overall dimensions of probe needle on the maximum stress and contact force is analyzed first, and then curvature of the probe needle body is optimized by employing a constrained minimization function, fmincon, in MATLAB. The maximum stress in the vertical probe pin at 125 ??m overdrive is effectively reduced from 1339 MPa to 972 MPa by applying floating mount technology over the fixed mount, and further reduced to 666 MPa by applying the optimization scheme. The final optimized design induced the contact force of 5.217 gf, which is in the range of the required contact force of 5 to 8 gf. Fatigue life increased from 19,219 cycles to 108,129 by applying floating mount over fixed mount, and further increased to 830,596 for the optimized design.

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In this thesis, a chirp-controlled pump-probe system has been developed to investigate the role of chirp in mode-locking mechanism. By modulating pump power and focusing condition, power, chirp, and wavelength dependent transient reflectivity ( £GR /R), pulse duration, and amplitude ratio in pump-probe measurement for the multiply-strained-quantum-well saturable Bragg reflector (SSBR) are presented. According this study, one can find a more efficient and stable mode-locking mechanism through proper chirp arrangement inside cavity. Compared to the case of transform-limited pump condition, shorter fast-carrier-lifetime and smaller amplitude ratio of slow and fast relaxation contribution are observed in negative chirp excitation condition. Meanwhile, we can see that there is a shorter fast-carrier-lifetime and a smaller amplitude ratio in case of excitation pulse with -25000 ( fs^2 ) chirp or increasing fluence ¡]2 £gm/cm^2->12 £gm/cm^2 ¡^. The results show that the pulse compression strength is stronger in -25000 ( fs^2 ) chirp and full with the tendency demonstrated by pulse shaping factor. All of these experimental results show that -25000 ( fs^2 ) chirp is the best chirped control condition to make mode-locking more efficient and stable. In addition, with the increasing fluence ¡]2 ->12 £gm/cm^2 ¡^, three times of saturable fluence, a more stable and efficient mode-locking condition is expectable.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references (leaves 92-95). Available also in a digital version from Dissertation Abstracts.

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This dissertation introduces scanning probe microscopy (SPM) and describes the construction and design of a home built low temperature magnetic force microscope (MFM). Then the magnetic coatings on atomic force microscope cantilevers with a focused ion beam (FIB) will be explained. This technique allows the convenient deposition of complex or expensive materials such as CoCrPt. With the MFM tip coated by FIB, the ferromagnetic domain structure of a La[subscript 0.67]Ca[subscript 0.33]MnO₃ film is studied as a function of an in-plane magnetic field below room temperature. Next I will discuss the use of chemically-synthesized FePt nanocrystals as a good candidate for high density storage media. This nanocrystal film showed sintering problems during the annealing process, which is essential to make FePt a hard ferromagnet. A silica overcoating method was used to prevent nanocrystal sintering, which allowed the MFM study of films made from these nanocrystals. I will also discuss resistance measurements of the FePt nanocrystals.

Nanowires are sensitive to external influences such as surface charges or external electric fields. An Atomic Force Microsope (AFM) is modified to perform back gating and tip gating measurements in order to understand the interaction between an external field, and surface charge and nanowire conductance. A 2D finite element method (FEM) model is developed to simulate the measured conductance. The model shows that surface states play a critical role in determining nanowire conductance. A 3D FEM model is developed to examine the influence of the AFM tip on the lateral resolution of the AFM tip in the electrostatic measurement. The radius of the AFM tip determines the lateral resolution of the tip. However, carrier concentration in the nanowire establishes a lower limit on the lateral resolution, for small tip radii. These results enable one to optimize Scanning Probe Microscopy experiments as well as inform sample preparation for nanowire characterization.