The thesis presents a Sierpinski Carpet fractal antenna array designed at 24 GHz for automotive radar applications. Miniaturized, high performance and low cost antennas are required for this application. To meet these specifications a fractal array has been designed for the first time on Low Temperature Co-fired Ceramic (LTCC) based substrate. LTCC provides a suitable platform for the development of these antennas due to its properties of vertical stack up and embedded passives. The complete antenna concept involves integration of this fractal antenna array with a Fresnel lens antenna providing a total gain of 15dB which is appropriate for medium range radar applications. The thesis also presents a comparison between the designed fractal antenna and a conventional patch antenna outlining the advantages of fractal antenna over the later one. The fractal antenna has a bandwidth of 1.8 GHz which is 7.5% of the centre frequency (24GHz) as compared to 1.9% of the conventional patch antenna. Furthermore the fractal design exhibits a size reduction of 53% as compared to the patch antenna. In the end a sensitivity analysis is carried out for the fractal antenna design depicting the robustness of the proposed design against the typical LTCC fabrication tolerances.

This thesis proposes a novel dual passband filter architecture and develops a design flow and synthesis method for this architecture. The technical contents include the fundamental passband filter design and the further methods for generating the higher second passband and the multiple transmission zeros. This thesis organizes a design flow based on analytical formulation for the proposed dual passband filter architecture. One can follow this design flow to substitute the filter specifications into the formulation and then can obtain the necessary element values for the filter architecture that match the specified specifications. The dual passband filter architecture is finally implemented on LTCC substrate for WLAN (IEEE 802.11 a/b/g) applications with verification of S parameters using EM-simulation and actual measurement.

The incorporation of active piezoelectric elements and fluidic components into micro-electromechanical systems (MEMS) is of great interest for the development of sensors, actuators, and integrated systems used in microfluidics. Low temperature cofired ceramics (LTCC), widely used as electronic packaging materials, offer the possibility of manufacturing highly integrated microfluidic systems with complex 3-D features and various co-firable functional materials in a multilayer module. It would be desirable to integrate high performance lead zirconate titanate (PZT) based ceramics into LTCC-based MEMS using modern thick film and 3-D packaging technologies. The challenges for fabricating functional LTCC/PZT devices are: 1) formulating piezoelectric compositions which have similar sintering conditions to LTCC materials; 2) reducing elemental inter-diffusion between the LTCC package and PZT materials in co-firing process; and 3) developing active piezoelectric layers with desirable electric properties. The goal of present work was to develop low temperature fired PZT-based materials and compatible processing methods which enable integration of piezoelectric elements with LTCC materials and production of high performance integrated multilayer devices for microfluidics. First, the low temperature sintering behavior of piezoelectric ceramics in the solid solution of Pb(Zr0.53,Ti0.47)O3-Sr(K0.25, Nb0.75)O3 (PZT-SKN) with sintering aids has been investigated. 1 wt% LiBiO2 + 1 wt% CuO fluxed PZT-SKN ceramics sintered at 900oC for 1 h exhibited desirable piezoelectric and dielectric properties with a reduction of sintering temperature by 350oC. Next, the fluxed PZT-SKN tapes were successfully laminated and co-fired with LTCC materials to build the hybrid multilayer structures. HL2000/PZT-SKN multilayer ceramics co-fired at 900oC for 0.5 h exhibited the optimal properties with high field d33 piezoelectric coefficient of 356 pm/V. A potential application of the developed LTCC/PZT-SKN multilayer ceramics as a microbalance was demonstrated. The final research focus was the fabrication of an HL2000/PZT-SKN multilayer piezoelectric micropump and the characterization of pumping performance. The measured maximum flow rate and backpressure were 450 μl/min and 1.4 kPa respectively. Use of different microchannel geometries has been studied to improve the pumping performance. It is believed that the high performance multilayer piezoelectric devices implemented in this work will enable the development of highly integrated LTCC-based microfluidic systems for many future applications.

Low temperature co-fired ceramic (LTCC) electronic packaging materials are applied for their electrical and mechanical properties, high reliability, chemical stability and ease of fabrication. Three dimensional features can also be prepared allowing integration of microfluidic channels and cavities inside LTCC modules. Mechanical, optical, electrical, microfluidic functions have been realized in single LTCC modules. For these reasons LTCC is attractive for biomedical microfluidics and Lab-on-a-Chip systems. However, commercial LTCC systems, optimized for microelectrics applications, have unknown cytocompatibility, and are not compatible with common surface functionalization chemistries. The first goal of this work is to develop biocompatible LTCC materials for biomedical applications. In the current work, two different biocompatible LTCC substrate materials are conceived, formulated and evaluated. Both materials are based from well-known and widely utilized biocompatible materials. The biocompatibilities of the developed LTCC materials for in-vitro applications are studied by cytotoxicity assays, including culturing endothelial cells (EC) both in LTCC leachate and directly on the LTCC substrates. The results demonstrate the developed LTCC materials are biocompatible for in-vitro biological applications involving EC. The second goal of this work is to develop functional capabilities in LTCC microfluidic systems suitable for in-vitro and biomedical applications. One proposed application is the evaluation of oxygen tension and oxidative stress in perfusion cell culture and bioreactors. A Clark-type oxygen sensor is successfully integrated with LTCC technique in this work. In the current work, a solid state proton conductive electrolyte is used to integrate an oxygen sensor into the LTCC. The measurement of oxygen concentration in Clark-type oxygen sensor is based on the electrochemical reaction between working electrode and counter electrode. Cyclic voltammetry and chronoamperometry are measured to determine the electrochemical properties of oxygen reduction in the LTCC based oxygen sensor. The reduction current showed a linear relationship with oxygen concentration. In addition, LTCC sensor exhibits rapid response and sensitivity in the physiological range 1─9 mg/L. The fabricated devices have the capabilities to regulate oxygen supply and determination of local dissolved oxygen concentration in the proposed applications including perfusion cell culture and biological assays.

Energy distribution in a conventional magnetic component is generally not at a designer's disposal. In a conventional toroidal inductor, the energy density is inversely proportional to the square of the radius. Thus, a designer would be unable to prescribe uniform field distribution to fully utilize the inductor volume for storing magnetic energy. To address this problem a new inductor design, called a "constant-flux" inductor, is introduced in this thesis. This new inductor has the core and windings configured to distribute the magnetic flux and energy relatively uniformly throughout the core volume to achieve power density higher than that of a conventional toroidal inductor. The core of this new inductor design is made of concentric cells of magnetic material, and the windings are wound in the gaps between the cells. This structure is designed to avoid crowding of the flux, thus ensuring lower core energy losses. In addition, the windings are patterned for shorter length and larger area of cross-section to facilitate lower winding energy losses. Based on this approach, a set of new, constant flux inductor/transformer designs has been developed. This design set is based on specific input parameters are presented in this thesis. These parameters include the required inductance, peak and rms current, frequency of operation, permissible dc resistance, material properties of the core such as relative permeability, maximum permissible magnetic flux density for the allowed core loss, and Steinmetz parameters to compute the core loss. For each constant flux inductor/transformer design, the winding loss and core loss of the magnetic components are computed. In addition, the quality factor is used as the deciding criterion for selection of an optimized inductor/transformer design. The first design presented in this thesis shows that for the same maximum magnetic field intensity, height, total stored energy, and material, the footprint area of the new five-cell constant-flux inductor is 1.65 times less than that of an equivalent conventional toroidal inductor. The winding loss for the new inductor is at least 10% smaller, and core loss is at least 1% smaller than that in conventional inductors. For higher energy densities and taller inductors, an optimal field ratio of the dimensions of each cell (α = Rimin/Rimax) and a larger number of cells is desired. However, there is a practical difficulty in realizing this structure with a larger number of cells and higher field ratio α. To address this problem, an inductor design is presented that has a footprint area of a three-cell constant-flux inductor (α = 0.6) that is 1.48 times smaller in comparison to an equivalent conventional toroidal inductor. For the same maximum magnetic flux density, height, material, and winding loss, the energy stored in this new three-cell constant-flux inductor (α = 0.6) is four times larger than that of an equivalent conventional toroidal inductor. Finally, new designs for application-specific toroidal inductors are presented in this thesis. First, a constant-flux inductor is designed for high-current, high-power applications. An equivalent constant-flux inductor to a commercially available inductor (E70340-010) was designed. The height of this equivalent inductor is 20% less than the commercial product with the same inductance and dc resistance. Second, a constant-flux inductor design of inductance 1.2 µH was fabricated using Micrometal-8 for the core and flat wire of 0.97 mm x 0.25 mm for the conductor. The core material of this inductor has relative permeability < 28 and maximum allowed flux density of 3600 Gauss. The dc resistance of this new, constant flux inductor was measured to be 14.4 mΩ. / Master of Science

No description available.

This dissertation focuses on the development of low-temperature co-fired ceramics (LTCC) technology for power converter magnetics integration. Because magnetic samples must be fabricated with thick conductors for power applications, the conventional LTCC process is modified by cutting trenches in the LTCC tapes where conductive paste is filled to produce thick conductors to adapt to this requirement. Characterization of the ceramic magnetic material is performed, and an empirical model based on the Steinmetz equation is developed to help in the estimation of losses at frequencies between 1 MHz to 4 MHz, operating temperature between 25 °C and 70 °C, DC pre-magnetization from 0 A/m to 1780 A/m, and AC magnetic flux densities between 5 mT to 50 mT. Temperature and DC pre-magnetization dependence on Steinmetz exponents are included in the model to describe the loss behavior. In the development of the LTCC chip inductor, various geometries are evaluated. Rectangular-shaped conductor geometry is selected due to its potential to obtain a much smaller footprint, as well as the likelihood of having lower losses than almond-shaped conductors with the same cross-sectional area, which are typically a result of screen printing. The selected geometry has varying inductance with varying current, which helps improve converter efficiency at light load. The efficiency at a light-load current of 0.5 A can be improved by 30 %. Parametric variation of inductor geometry is performed to observe its effect on inductance with DC current as well as on converter efficiency. An empirical model is developed to describe the change in inductance with DC current from 0 A to 16 A for LTCC planar inductors fabricated using low-permeability tape with conductor widths between 1 mm to 4 mm, conductor thickness 180 μm to 550 μm, and core thickness 170 μm to 520 μm. An inductor design flow diagram is formulated to help in the design of these inductors. Configuring the inductor as the substrate carrying the semiconductor and the other electronic components is a next step to freeing the surface area of the bulky component and improving the power density. A conductive shield is introduced between the circuitry and the magnetic substrate to avoid adversely affecting circuit operation by having a magnetic substrate in close proximity to the circuitry. The shield helps reduce parasitic inductances when placed in close proximity to the circuitry. A shield thickness in the range of 50 μm to 100 μm is found to be a good compromise between power loss and parasitic inductance reduction. The shield is effective when its conductivity is above 10⁷ S/m. When a shield is introduced between the inductor substrate and the circuitry, the sample exhibits a lower voltage overshoot (47 % lower) and an overall higher efficiency (7 % higher at 16 A), than an inductor without a shield. A shielded active circuitry placed on top of an inductive substrate performs similarly to a shielded active circuitry placed side-by-side with the inductor. Using a floating shield for the active circuitry yields a slightly better performance than using a grounded shield. / Ph. D.

This paper deals with production of the structures fabricated using low temperature co-fired ceramics. Focus is on the lamination of raw ceramic tapes. There are presented classical thermo-compressive methods and a new method using chemical solutions for tape bonding. Describes new lamination technology and their advantages are the absence of elevated temperatures and high pressures. This method reduces using of higher temperatures and high pressure during lamination. On the other hand, chemical process of tape bonding is not flawless. There are many problems including solvent deposition, extreme sensitivity to dust and other processing parameters. It also describes the fabrication of structures by chemical way. Specifically, analyzes the method Cold Chemical Lamination and provides examples of possible deposition solvents which are needed for etching the surface of the LTCC tape during the lamination.

Due to the power requirements for today's microprocessors, point of load converter packaging is becoming an important issue.   Traditional thermal management techniques involved in removing heat from a printed circuit board are being tested as today's technologies require small footprint and volume from all electrical systems.  While heat sinks are traditionally used to spread heat, ceramic substrates are gaining in popularity for their superior thermal qualities which can dissipate heat without the use of a heat sink.  3D integration techniques are needed to realize a solution that incorporates the active and components together.  The objective of this research is to explore the packaging of a high current, high power density, high frequency DC/DC converter using ceramic substrates to create a low profile converter to meet the needs of current technologies. One issue with current converters is the large volume of the passive components.  Increasing the switching frequency to the megahertz range is one way to reduce to volume of these components.  The other way is to fundamentally change the way these inductors are designed.  This work will explore the use of low temperature co-fired ceramic (LTCC) tapes in the magnetic design to allow a low profile planar inductor to be used as a substrate.  LTCC tapes have excellent properties in the 1-10 MHz range that allow for a high permeability, low loss solution.  These tapes are co-fired with a silver paste as the conductor.  This paper looks at ways to reduce dc resistance in the inductor design through packaging methods which in turn allow for higher current operation and better heavy load efficiency.  Fundamental limits for LTCC technologies are pushed past their limits during this work.  This work also explores fabrication of LTCC inductors using two theoretical ideas: vertical flux and lateral flux.  Issues are presented and methods are conceived for both types of designs.  The lateral flux inductor gives much better inductance density which results in a much thinner design. It is found that the active devices must be shielded from the magnetic substrate interference so active layer designs are discussed.  Alumina and Aluminum Nitride substrates are used to form a complete 3D integration scheme that gives excellent thermal management even in natural convection.  This work discusses the use of a stacked power technique which embeds the devices in the substrate to give double sided cooling capabilities.  This fabrication goes away from traditional photoresist and solder-masking techniques and simplifies the entire process so that it can be transferred to industry.  Time consuming sputtering and electroplating processes are removed and replaced by a direct bonded copper substrate which can have up to 8 mil thick copper layers allowing for even greater thermal capability in the substrate.  The result is small footprint and volume with a power density 3X greater than any commercial product with comparable output currents.  A two phase coupled inductor version using stacked power is also presented to achieve even higher power density. As better device technologies come to the marketplace, higher power density designs can be achieved.  This paper will introduce a 3D integration design that includes the use of Gallium Nitride devices.  Gallium Nitride is rapidly becoming the popular device for high frequency designs due to its high electron mobility properties compared to silicon.  This allows for lower switching losses and thus better thermal characteristics at high frequency.  The knowledge learned from the stacked power processes gives insight into creating a small footprint, high current ceramic substrate design.  A 3D integrated design is presented using GaN devices along with a lateral flux inductor.  Shielded and Non-Shielded power loop designs are compared to show the effect on overall converter efficiency.  Thermal designs and comparisons to PCB are made using thermal imaging.  The result is a footprint reduction of 40% from previous designs and power densities reaching close to 900W/in3. / Master of Science

Today, every microprocessor is powered with a Voltage Regulator (VR), which is also known as a high current Point-of-Load converter (POL). These circuits are mostly constructed using discrete components, and populated on the motherboard. With this solution, the passive components such as inductors and capacitors are bulky. They occupy a considerable footprint on the motherboard. The problem is exacerbated with the current trend of reducing the size of all forms of portable computing equipment from laptop to netbook, increasing functionalities of PDA and smart phones. In order to solve this problem, a high power density POL needs to be developed. An integration solution was recently proposed to incorporate passive components, especially magnetic components, with active components in order to realize the needed power density for the POL. Today's discrete VR only has around 100W/in3 power density. The 3D integration concept is widely used for low current integrated POL. With this solution, a very low profile planar inductor is built as a substrate for the active components of the POL. By doing so, the POL footprint can be dramatically saved, and the available space is also fully utilized. This 3D integrated POL can achieve 300-1000W/in3 power density, however, with considerably less current. This might address the needs of small hand-held equipment such as PDA and Smart phone type of applications. It does not, however, meet the needs for such applications as netbook, laptop, desk-top and server applications where tens and hundreds of amperes are needed. So, although the high density integrated POL has been demonstrated at low current level, magnetic integration is still one of the toughest barriers for integration, especially for high current POL. In order to alleviate the intense thirst from the computing and telecom industry for high power density POL, the 3D integration concept needs be extended from low current applications to high current applications. The key technology for 3D integration is the low profile planar inductor design. Before this research, there was no general methodology to analyze and design a low profile planar inductor due to its non-uniform flux distribution, which is totally different as a conventional bulky inductor. A Low Temperature Co-fired Ceramic (LTCC) inductor is one of the most promising candidates for 3D integration for high current applications. For the LTCC inductor, besides the non-uniform flux, it also has non-linear permeability, which makes this problem even more complicated. This research focuses on penetrating modeling and design barriers for planar magnetic to develop high current 3D integrated POL with a power density dramatically higher than today's industry products in the same current level. In the beginning, a general analysis method is proposed to classify different low profile inductor structures into two types according to their flux path pattern. One is a vertical flux type; another one is a lateral flux type. The vertical flux type means that the magnetic flux path plane is perpendicular with the substrate. The lateral flux type means that the magnetic flux path plane is parallel with the substrate. This analysis method allows us to compare different inductor structures in a more general way to reveal the essential difference between them. After a very thorough study, it shows that a lateral flux structure is superior to a vertical flux structure for low profile high current inductor design from an inductance density point of view, which contradicts conventional thinking. This conclusion is not only valid for the LTCC planar inductor, which has very non-linear permeability, but is also valid for the planar inductor with other core material, which has constant permeability. Next, some inductance and loss models for a planar lateral flux inductor with a non-uniform flux are also developed. With the help of these models, different LTCC lateral flux inductor structures (single-turn structure and multi-turn structures) are compared systematically. In this comparison, the inductance density, winding loss and core loss are all considered. The proposed modeling methodology is a valuable extension of previous uniform flux inductor modeling, and can be used to solve other modeling problems, such as non-uniform flux transformer modeling. After that, a design method is proposed for the LTCC lateral flux inductor with non-uniform flux distribution. In this design method, inductor volume, core thickness, winding loss, core loss are all considered, which has not been achieved in previous conventional inductor design methods. With the help of this design method, the LTCC lateral flux inductor can be optimized to achieve small volume, small loss and low profile at the same time. Several LTCC inductor substrates are also designed and fabricated for the 3D integrated POL. Comparing the vertical flux inductor substrate with the lateral flux inductor substrate, we can see a savings of 30% on the footprint, and a much simpler fabrication process. A 1.5MHz, 5V to 1.2V, 15A 3D integrated POL converter with LTCC lateral flux inductor substrate is demonstrated with 300W/in3 power density, which has a factor of 3 improvements when compared to today's industry products. Furthermore, the LTCC lateral flux coupled inductor is proposed to further increase power density of the 3D integrated POL converter. Due to the DC flux cancelling effect, the size of LTCC planar coupled inductor can be dramatically reduced to only 50% of the LTCC planar non-coupled inductor. Compared to previous vertical flux coupled inductor prototypes, a lateral flux coupled inductor prototype is demonstrated to have a 50% core thickness reduction. A 1.5MHz, 5V to 1.2V, 40A 3D integrated POL converter with LTCC lateral flux coupled inductor substrate is demonstrated with 700W/in3 power density, which has a factor of 7 improvements when compared to today's industry POL products in the same current level. In conclusion, this research not only overcame some major academia problems about analysis and design for planar magnetic components, but also made significant contributions to the industry by successfully scaling the integrated POL from today's 1W-5W case to a 40W case. This level of integration would significantly save the cost, and valuable motherboard real estate for other critical functions, which may enable the next technological innovation for the whole computing and telecom industry. / Ph. D.