Millimeter Wave Substrate Integrated Waveguide Antennas: Design and Fabrication Analysis

The paper presents a new concept in antenna design, whereby a photo-imageable thick-film process is used to integrate a waveguide antenna within a multilayer structure. This has yielded a very compact, high performance antenna working at high millimeter-wave (mm-wave) frequencies, with a high degree of repeatability and reliability in antenna construction. Theoretical and experimental results for 70 GHz mm-wave integrated antennas, fabricated using the new technique are presented. The antennas were formed from miniature slotted waveguide arrays using up to 18 layers of photo-imageable material. To enhance the electrical performance a novel folded waveguide array was also investigated. The fabrication process is analysed in detail and the critical issues involved in the fabrication cycle are discussed. The losses in the substrate integrated waveguide have been calculated. The performance of the new integrated antenna is compared to conventional metallic, air-filled waveguide antennas, and also to conventional microstrip antenna arrays operating at the same frequencies

Thick-Film and LTCC Passive Components for High-Temperature Electronics

At this very moment an increasing interest in the field of high-temperature electronics is observed. This is a result of development in the area of wide-band semiconductors’ engineering but this also generates needs for passives with appropriate characteristics. This paper presents fabrication as well as electrical and stability properties of passive components (resistors, capacitors, inductors) made in thick-film or Low-Temperature Co-fired Ceramics (LTCC) technologies fulfilling demands of high-temperature electronics. Passives with standard dimensions usually are prepared by screen-printing whereas combination of standard screen-printing with photolithography or laser shaping are recommenced for fabrication of micropassives. Attainment of proper characteristics versus temperature as well as satisfactory long-term high-temperature stability of micropassives is more difficult than for structures with typical dimensions for thick-film and LTCC technologies because of increase of interfacial processes’ importance. However it is shown that proper selection of thick-film inks together with proper deposition method permit to prepare thick-film micropassives (microresistors, air-cored microinductors and interdigital microcapacitors) suitable for the temperature range between 150°C and 400°C

A Two-Stage Process for Laser Prototyping of Microwave Circuits in LTCC Technology

An improved technique for laser prototyping of microwave circuits in low-temperature cofired ceramic (LTCC) technology is presented. This builds on the method of laser machining of conductor layers in unfired LTCC tapes. The proposed process presents the hybrid approach of circuit fabrication by employing both unfired and post fired laser machining of LTCC substrate, hence giving more flexibility of realizing multilayer components. This allows the low-tolerance microwave structures like couplers and filters to be fabricated on the outer layers because shrinkage uncertainty is no longer a problem. Track widths and gaps of 30 μm are demonstrated with an edge definition of ±2 μm. A stripline coupler and a four-layer spiral inductor is successfully fabricated using this technique to demonstrate the process. The improved process can produce high-precision microwave and millimeter-wave components on the outer layers and provides rapid system-in-package prototyping for research and development

Modern Microelectronic Technologies in Fabrication of RFID Tags

This paper presents fabrication of RFID tags, especially antennas for HF band (13.56 MHz), on cheap flexible substrates. The physicochemical, geometrical, DC and AC electrical properties as well as long-term stability (under thermal, moisture-thermal and mechanical exposures) have been characterized for several low-temperature polymer thick-film conductive films made on various paper or foil substrates. Resistance measurement during curing has been used for investigation of polymerization velocity, which is very important for increase of process capacity

Design rules to optimize the layout of multilayer circuit packages at 100GHz

New data are presented on the effects of coupling between conductors in a highly integrated, multilayer circuit working at high millimeter wave frequencies. Design rules have been developed to summarize the results and provide guidance to the circuit designer on the minimum spacing between conductors in a multilayer package.</p

Low cost fabrication processing for microwave and millimetre-wave passive components

Microwave and millimetre-wave technology has enabled many commercial applications to play a key role in the development of wireless communication. When dissipative attenuation is a critical factor, metal-pipe waveguides are essential in the development of microwave and millimetre-wave systems. However, their cost and weight may represent a limitation for their application. In the first part of this work two 3D printing technologies and electroless plating were employed to fabricate metal pipe rectangular waveguides in X and W-band. The performance for the fabricated waveguides was comparable to the one of commercially available equivalents, showing good impedance matching and low attenuation losses. Using these technologies, a high-performance inductive iris filter in W-band and a dielectric flap phase shifter in X-band were fabricated. Eventually the design and fabrication of a phased antenna array is reported. For microwave and millimetre-wave applications, system-on-substrate technology can be considered a very valuable alternative, where bulky coax and waveguide interconnects are replaced by low-loss transmission lines embedded into a multilayer substrate, which can include a wide range of components and subsystems. In the second part of this work the integration of RF MEMS with LTCC fabrication process is investigated. Three approaches to the manufacture of suspended structures were considered, based on laser micromachining, laser bending of aluminium foil and hybrid thick/thin film technology. Although the fabrication process posed many challenges, resulting in very poor yield, two of the solution investigated showed potential for the fabrication of low-cost RF MEMS fully integrated in LTCC technology. With the experience gained with laser machining, the rapid prototyping of high aspect ratio beams for silicon MEMS was also investigated. In the third part of this work, a statistical study based on the Taguchi design of experiment and analysis of variance was undertaken. The results show a performance comparable with standard cleanroom processing, but at a fraction of the processing costs and greater design flexibility, due to the lack of need for masks.Open Acces

High Temperature LTCC based SiC Double-sided Cooling Power Electronic Module

This objective of this dissertation research is to investigate a module packaging technology for high temperature double-sided cooling power electronic module application. A high-temperature wire-bondless low-temperature co-fired ceramic (LTCC) based double-sided cooling power electronic module was designed, simulated and fabricated. In this module, the conventional copper base plate is removed to reduce the thermal resistance between the device junctions to the heat sink and to improve the reliability of the module by eliminating the large area solder joint between the power substrate and the copper base plate. A low-temperature co-fired ceramic (LTCC) substrate with cavities and vias is used as the dielectric material between the top and bottom substrates and it also serves as the die frame. A nano silver attach material is used to enable the high-temperature operation. Thermal and thermo-mechanical simulations were performed to evaluate the advantages of the LTCC double-sided power module structure and compared to other reported module structures and its wire-bonded counterpart. The junction-to-case thermal resistance for the power module without a copper base plate is 0.029oC/W, which is smaller than that of the power module with a copper base plate. Thermo-mechanical simulation reveals that double-sided cooling power modules generate higher thermal stresses when compared to that of the single-sided cooling power modules which indicates the trade-off between the junction temperature and the thermo-mechanical stress. Electrical and thermal characterizations were performed to test the functionality of the fabricated module using a 1200V rated voltage blocking capability. The forward and reverse characteristics of the SiC power MOSFET and SiC diode module were tested to 200°C and they demonstrated the functionality of the power module. The junction-to-ambient thermal resistance of the proposed module is shown to reduce by 11% compared to the wire-bonded equivalent which shows an improvement of the thermal performance of the double-sided cooling structure. Finally, the reliability of the several power substrates was evaluated based on the thermal stress and fatigue life simulation of the bonding layer to determine the mechanical weakest spots of the power module. Thermal cycling experiments were also conducted to validate the simulation results

Multilayer microwave structures using thick-film technology.

Multilayer techniques, in conjunction with thick-film technology have been applied to the design and fabrication of several multilayer microwave structures to achieve the low cost and high performance goals set by modern microwave circuits and systems. To provide accurate material parameters for the design of multilayer thick-film components, a novel slit cavity resonator method has been developed that enables the relative permittivity and loss tangent of dielectric samples to be measured easily, and with high accuracy. A particular feature of this method is that it can be used to measure thick-film samples that are normally only available in relatively thin layers in a two-layer format. Rigorous electromagnetic analysis on a slit cavity has been performed that accounts for the effect of the fringing fields and the radiation from the slits. The method has been verified through measurement on several thick-film materials over X-band. Both the analytical methods and the fabrication techniques for multilayer microwave microstrip structures are presented. Several multilayer thick-film microstrip line test structures have been designed and characterised, and these provide a basic database for the design of multilayer microstrip components. A new design procedure for the multilayer end-coupled filter has been developed that enables the designer to arrive at the physical dimensions of the multilayer structure based on the filter specification. This design technique is effective as it combines the accuracy of electromagnetic (EM) analysis and the efficiency of circuit simulation. The multilayer gap, which is the most critical element of multilayer end-coupled filters, has been characterised using EM analysis and the data is incorporated into a circuit simulator. Measured and simulated results are presented that verify the new design technique. A 40% bandwidth has been achieved experimentally, which shows a very significant improvement over conventional single layer structures, where the bandwidth achievable is normally less than 5%. Novel, octave band DC blocks have been designed, fabricated and tested using a new multilayer format. The tight coupling required between the coupled lines in this component was realized by overlapping these lines in a multilayer structure. Very good agreement was obtained between measured and simulated data. The multilayer approach was also applied to the design of coupled line bandpass filters where a measured 80% bandwidth was achieved. For the first time, the properties of multilayer coupled lines using a range of different thick-film dielectrics are examined using their coupled-mode parameters. Design curves for multilayer coupled lines are obtained, that provide important information on the design of multilayer directional couplers. A practical design strategy for multilayer directional couplers is developed, which overcomes the problem of excessive computation that is normally associated with the electromagnetic optimization of multilayer circuit designs. The methodology has been verified through the design and measurement of wide bandwidth 2dB and 3dB directional couplers that were fabricated using multilayer, thick-film technology. New techniques for the design and fabrication of multilayer microwave thick-film components have thus been established, both theoretically and through practical circuit fabrication and measurement