Failure mechanisms observed in electromigration (EM) stressed dual damascene Cu/SiO₂ interconnects trees were studied and simulated. Failure sites with ‘melt patch’ or ‘crater’ are common for test structures in the top metal layer, though the occurrence of such failure modes probably depends on the passivation layer thickness. Interconnects that were EM stressed for a short time and then stressed with increasing current to induce Joule heating in the line had similar failure sites to lines that were stressed to failure under standard EM conditions. This shows that some failure mechanisms during EM could be assisted by Joule heating effect. / Singapore-MIT Alliance (SMA)

Experiments were performed using a microparticle image velocimetry (MPIV) for full field velocity distributions of electroosmotically driven flows in a 40 mm long microchannel with a square cross section of 200 µm ¡Ñ 200 µm. Electroosmotic flow bulk fluid velocity measurements were made in a range of streamwise electric field strengths from 5 to 25 kV/m. A series of seed particle calibration tests can be made in a 200 µm x 200 µm x 24000 µm untreated PDMS channel incorporating MPIV to determine the electrophoretic mobilities in aqueous buffer solutions of 1 TAE, 1 TBE, 10 mM NaCl, and 10 mM borate, respectively. A linear/nonlinear (due to Joule heating) flow rate increase with applied field was obtained and compared with those of previous studies. A parametric study, with extensive measurements was performed with different electric field strength and buffer solution concentration under a constant zeta potential at wall for each buffer. The characteristics of electroosmotic flow in square microchannels were thus investigated. Finally, a composite correlation of the relevant parameters was developed within accuracy for 99% of the experimental data.

Experiments were conducted on the investigation of the electroosmotic flow with five different electric field strength, four kinds of buffer solution concentration, six different pH values, and three kinds of microchannel geometry. Joule heating effects were also taken into consideration. Experiments were performed using a microparticle image velocimetry (MPIV) for full field velocity distributions and micro laser-induced fluorescent (£gLIF) for full field temperature distributions. It is found that the presence of Joule heating and flow area change could have a great impact on the microfluidic transportation, e.g. dispersion. Furthermore, data were presented and the relation between zeta potential and pH value were discussed in detail. It is found that, as pH > 7.5, all silanol sites are deprotonated.

This study proposed a Y-type mixer which was driven by electroosmotic flow (Ex = 5 - 25 kV/m) with 7 different mixing angles (30¢X, 60¢X, 90¢X, 120¢X, -120¢X, -90¢X, -60¢X) to enhance mixing efficiency . The mixing performance of the device was demonstrated by using micro laser-induced fluorescence (£gLIF) technology to quantify the concentration distribution in the microchannel. Also, micro particle image velocimetry (£gPIV) was used for velocity measurements and analysis. It was found that the negative mixing angle could induce larger dead zone area than the positive one. The joule heating effect was found when electric field strength was larger than 15 kV/m. The combined dead zone and joule heating effect could enhance the mixing performance slightly. Although it has only a marginal effect on the mixing length for the positive mixing angles. Negative mixing angles allow a reduction of mixer size, which means a more efficient use of material and space. Finally, the best mixing angle was found to be -60¢X.

Emissivity is an important parameter in calculating radiative cooling of a surface. In experiments at the NASA Ames hypervelocity ballistic range, one of the main errors indicated in temperature measurements is the uncertainty of emissivity for the materials under investigation. This thesis offers a method for measuring emissivity of materials at elevated temperatures at the University of Kentucky. A test specimen which consists of different sample materials under investigation and a blackbody cavity was heated in a furnace to an isothermal condition at known temperature. The emitted thermal radiation was measured and the comparison of sample and blackbody radiation yielded the desired emissivity. In addition to the furnace measurements, separate experiments were conducted in ambient air to determine how much irradiation is reflected back to the samples from the radiation shield used in the furnace to block undesired ambient radiation. Here, the sample heating was accomplished by applying a direct current across the samples. ANSYS simulations were performed to assist the design and analysis. Experiments were conducted in ambient air and a vacuum environment to verify these simulations.

No description available.

No description available.

Infrared (IR) imaging is a key technology in a variety of military and civilian applications, especially for night vision and remote sensing. Compared with cryogenically cooled IR sensors, uncooled infrared imaging devices have the advantages of being low cost, light weight, and superior reliability. The electro-thermal analysis of a microbolometer pixel is critical to determine both device performance and reliability. To date, most microbolometer analysis research has focused on performance optimization and computation of thermal conductance directly from the geometry. However, modeling of the thermal distribution across the microbolometer pixel is critical for the comprehensive analysis of system performance and reliability. Therefore, this thesis investigates the electro-thermo-mechanical characteristics of a microbolometer pixel considering the effects of joule heating and incoming IR energy. The contributions of the present research include the electro-thermal models for microbolometer and methods of validating thermal distribution using experimental results. The electro-thermal models explain the effect of microbolometer material properties and geometry on device performance and reliability. The research also contributes methods of estimating the thermal conductivity of microbolometer, which take into account different heat transfer mechanisms, including radiation and convection. Previous approaches for estimating the thermal conductance of uncooled microbolometer consider heat conduction via legs from the geometry of the pixel structure and material properties [2]. This approach assumes linear temperature distribution in the pixel legs structure. It also leaves out the various electro-thermal effects existing for multilayer structures. In the present research, a different approach is used to develop the thermal conductance of microbolometer pixel structure. The temperature distribution in the pixel is computed from an electro-thermal model. Then, the average temperature in the pixel microplate and the total heat energy generated by joule heating is utilized to compute the thermal conductance of the structure. The thesis discusses electro-thermal and thermo-mechanical modeling, simulation and testing of Polysilicon Multi-User MEMS Process (PolyMUMPs®) test devices as the groundwork for the investigation of microbolometer performance and reliability in space applications. An electro-thermal analytical and numerical model was developed to predict the temperature distribution across the microbolometer pixel by solving the second order differential heat equation. To provide a qualitative insight of the effect of different parameters in the thermal distribution, including material properties and device geometry, first an explicit formulation for the solution of the electro-thermal coupling is obtained using the analytical method. In addition, the electro-thermal model, which accounts for the effect of IR energy and radiation heat transfer, spreading resistance and transient conditions, was studied using numerical methods. In addition, an analytical model has been developed to compute the IR absorption coefficient of a Thin Single Stage (TSS) microbolometer pixel. The simulation result of this model was used to compute absorbed IR energy for the numerical model. Subsequently, the temperature distribution calculated from the analytical model is used to obtain the deflections that the structure undergoes, which will be fundamental for the reliability analysis of the device. Finite element analysis (FEA) has been simulated for the selected device using commercial software, ANSYS® multiphysics. Finite element simulation shows that the electro-thermal models predict the temperature distribution across a microbolometer pixel at steady-state conditions within 2.3% difference from the analytical model. The analytical and numerical models are also simulated and results for a temperature distribution within 1.6% difference. In addition, to validate the analytical and numerical electro-thermal and thermo-mechanical models, a PolyMUMPs® test device has been used. The test results showed a close agreement with the FEM simulation deflection of the test device.

This research presents a detection scheme for analyzing the temperature distribution produced by the Joule heating effect nearby the channel wall in a microfluidic chip utilizing a temperature-dependent fluorescence dye. An advanced optical microscope system¡Xtotal internal reflection fluorescence microscope (TIRFM) is used for measuring the temperature distribution on the inner channel wall at the point of electroosmotic flow in an electrokinetically driven microfluidic chip. In order to meet the short working distance of the objective-type TIRFM, microscope cover glass are used to fabricate the microfluidic chips. The short fluorescence excitation depth from a TIRFM makes the intensity information obtained is not sensitive to the channel depth variation which ususally biases the measured results while using conventional epi-fluorescence microscope (Epi-FM). Therefore, a TIRFM can precisely describe the temperature profile of the distance within hundreds of nanometer of the channel wall where consists of the Stern layer and the diffusion layer for an electrokinetic microfluidic system. In order to investigate the temperature distribution produced by the Joule heating effect for electrokinetically driven microchips, this study not only measures the temperature on the microchannel wall by the proposed TIRFM but also measures the temperature inside the microchannel by an Epi-FM. In addition, this research presents a method to reduce the Joule heating effect and enhance the separation efficiency of DNA biosamples in a chip-based capillary electrophoresis (CE) system utilizing pulse DC electric fields. Since the average power consumption is reduced by the pulse electric fields, the Joule heating effect can be significantly reduced. Results indicate the proposed TIRFM method provides higher measurement sensitivity over the Epi-FM method. Significant temperature difference along the channel depth measured by TIRFM and Epi-FM is experimentally observed. In addition, the measured wall temperature distributions can be the boundary conditions for numerical investigation into the Joule heating effect. The proposed method gives a precise temperature profile of microfluidic channels and shows the substantial impact on developing a simulation model for precisely predicting the Joule heating effect in microfluidic chips. Moreover, in the research of reducing the Joule heating effect and enhancing the separation efficiency in a chip-based CE system utilizing pulse electric fields, the experimental and numerical investigations commence by separating a mixed sample comprising two fluoresceins with virtually identical physical properties. The separation level is approximately 2.1 times higher than that achieved using a conventional DC electric field. The performance of the proposed method is further evaluated by separating a DNA sample of Hae III digested £XX¡V174 ladder. Results indicate the separation level of the two neighboring peaks of 5a (271 bp) and 5b (281 bp) in the DNA ladder is as high as 120% which is difficult to be achieved using a conventional CE scheme. The improved separation performance is attributed to a lower Joule heating effect as a result of a lower average power input and the opportunity for heat dissipation during the zero-voltage stage of the pulse cycle. Overall, the results demonstrate a simple and low-cost technique for achieving a high separation performance in CE microchips.

Infrared (IR) imaging is a key technology in a variety of military and civilian applications, especially for night vision and remote sensing. Compared with cryogenically cooled IR sensors, uncooled infrared imaging devices have the advantages of being low cost, light weight, and superior reliability. The electro-thermal analysis of a microbolometer pixel is critical to determine both device performance and reliability. To date, most microbolometer analysis research has focused on performance optimization and computation of thermal conductance directly from the geometry. However, modeling of the thermal distribution across the microbolometer pixel is critical for the comprehensive analysis of system performance and reliability. Therefore, this thesis investigates the electro-thermo-mechanical characteristics of a microbolometer pixel considering the effects of joule heating and incoming IR energy. The contributions of the present research include the electro-thermal models for microbolometer and methods of validating thermal distribution using experimental results. The electro-thermal models explain the effect of microbolometer material properties and geometry on device performance and reliability. The research also contributes methods of estimating the thermal conductivity of microbolometer, which take into account different heat transfer mechanisms, including radiation and convection. Previous approaches for estimating the thermal conductance of uncooled microbolometer consider heat conduction via legs from the geometry of the pixel structure and material properties [2]. This approach assumes linear temperature distribution in the pixel legs structure. It also leaves out the various electro-thermal effects existing for multilayer structures. In the present research, a different approach is used to develop the thermal conductance of microbolometer pixel structure. The temperature distribution in the pixel is computed from an electro-thermal model. Then, the average temperature in the pixel microplate and the total heat energy generated by joule heating is utilized to compute the thermal conductance of the structure. The thesis discusses electro-thermal and thermo-mechanical modeling, simulation and testing of Polysilicon Multi-User MEMS Process (PolyMUMPs®) test devices as the groundwork for the investigation of microbolometer performance and reliability in space applications. An electro-thermal analytical and numerical model was developed to predict the temperature distribution across the microbolometer pixel by solving the second order differential heat equation. To provide a qualitative insight of the effect of different parameters in the thermal distribution, including material properties and device geometry, first an explicit formulation for the solution of the electro-thermal coupling is obtained using the analytical method. In addition, the electro-thermal model, which accounts for the effect of IR energy and radiation heat transfer, spreading resistance and transient conditions, was studied using numerical methods. In addition, an analytical model has been developed to compute the IR absorption coefficient of a Thin Single Stage (TSS) microbolometer pixel. The simulation result of this model was used to compute absorbed IR energy for the numerical model. Subsequently, the temperature distribution calculated from the analytical model is used to obtain the deflections that the structure undergoes, which will be fundamental for the reliability analysis of the device. Finite element analysis (FEA) has been simulated for the selected device using commercial software, ANSYS® multiphysics. Finite element simulation shows that the electro-thermal models predict the temperature distribution across a microbolometer pixel at steady-state conditions within 2.3% difference from the analytical model. The analytical and numerical models are also simulated and results for a temperature distribution within 1.6% difference. In addition, to validate the analytical and numerical electro-thermal and thermo-mechanical models, a PolyMUMPs® test device has been used. The test results showed a close agreement with the FEM simulation deflection of the test device.