<p>Couplers are one of the most frequently used passive devices in microwave circuitry. The main function of a coupler is to divide (or combine) a radio frequency signal into (from) two separate signals by a specific ratio and phase difference. With the need for smaller electronic devices, a reduction in the area of a distributed coupler would prove to be valuable. The purpose of this research is to develop, simulate, fabricate and test high aspect ratio microstructure couplers that are smaller in area than existing distributed couplers, and have comparable or better performance. One method used to reduce the area of a distributed coupler is to replace single or multiple transmission lines with lumped element equivalent circuits. One category of lumped elements that has not been extensively implemented is high aspect ratio lumped elements. High aspect ratio lumped elements fabricated with deep X-ray lithography are able to take advantage of using the vertical dimension, and reduce their planar area. In this thesis high aspect ratio lumped elements are used in the design of 3-dB microstructure couplers that show significant area reduction compared to equivalent distributed couplers.</p> <p>The designs of the microstructure couplers were based on the lumped element equivalent circuits of a 3-dB branch-line and a 3-dB rat-race distributed coupler. Simulations were performed to determine the lumped element values that would provide the largest 3-dB bandwidth while still maintaining close to ideal coupling and through values, return loss bandwidth, isolation bandwidth, and phase. These lumped element values were then implemented in the microstructure coupler designs as high aspect ratio microstructure lumped elements. 3-D electromagnetic simulations were performed which verified that the structures behaved electrically as couplers. The microstructure couplers were designed to be 220 &#x00B5;m tall nickel structures with capacitance gap widths of 6 µm.</p> <p>Fabrication of the microstructure couplers using deep X-ray lithography was performed by the microfabrication group at IMT/KIT in Karlsruhe, Germany. Before testing, detailed visual inspection and the etching of the structures was performed at the Canadian Light Source.</p> <p>A total of five microstructure couplers were tested. Four of the tested couplers were based on the 3-dB branch-line coupler, and the fifth coupler was based on the 3-dB rat-race coupler. The microstructure branch-line design that had the best overall results was fabricated on quartz glass substrate and had an operation frequency of 5.3 GHz. The 3-dB bandwidth of the coupler was measured to be better than 75.5% and extrapolated to be 95.0%. At the centre frequency the through and coupled values were -4.32 dB and -4.44 dB. The phase difference between the couplers output ports was designed to be 90.0° and was measured to be 95.8°. The ±5° phase bandwidth was measured to be 12.7% and the isolation bandwidth was 28.8%. The measured results from the other couplers were comparable to simulation results.</p> <p>The main advantage of the microstructure coupler designs over existing distributed couplers is that the microstructure couplers show a significant area reduction. The branch-line microstructure designs were at least 85% smaller in area than their distributed equivalent on quartz glass. The rat-race microstructure design showed an area reduction of 90% when compared to its distributed equivalent on quartz glass.</p>

<p>Couplers are one of the most frequently used passive devices in microwave circuitry. The main function of a coupler is to divide (or combine) a radio frequency signal into (from) two separate signals by a specific ratio and phase difference. With the need for smaller electronic devices, a reduction in the area of a distributed coupler would prove to be valuable. The purpose of this research is to develop, simulate, fabricate and test high aspect ratio microstructure couplers that are smaller in area than existing distributed couplers, and have comparable or better performance. One method used to reduce the area of a distributed coupler is to replace single or multiple transmission lines with lumped element equivalent circuits. One category of lumped elements that has not been extensively implemented is high aspect ratio lumped elements. High aspect ratio lumped elements fabricated with deep X-ray lithography are able to take advantage of using the vertical dimension, and reduce their planar area. In this thesis high aspect ratio lumped elements are used in the design of 3-dB microstructure couplers that show significant area reduction compared to equivalent distributed couplers.</p> <p>The designs of the microstructure couplers were based on the lumped element equivalent circuits of a 3-dB branch-line and a 3-dB rat-race distributed coupler. Simulations were performed to determine the lumped element values that would provide the largest 3-dB bandwidth while still maintaining close to ideal coupling and through values, return loss bandwidth, isolation bandwidth, and phase. These lumped element values were then implemented in the microstructure coupler designs as high aspect ratio microstructure lumped elements. 3-D electromagnetic simulations were performed which verified that the structures behaved electrically as couplers. The microstructure couplers were designed to be 220 &#x00B5;m tall nickel structures with capacitance gap widths of 6 µm.</p> <p>Fabrication of the microstructure couplers using deep X-ray lithography was performed by the microfabrication group at IMT/KIT in Karlsruhe, Germany. Before testing, detailed visual inspection and the etching of the structures was performed at the Canadian Light Source.</p> <p>A total of five microstructure couplers were tested. Four of the tested couplers were based on the 3-dB branch-line coupler, and the fifth coupler was based on the 3-dB rat-race coupler. The microstructure branch-line design that had the best overall results was fabricated on quartz glass substrate and had an operation frequency of 5.3 GHz. The 3-dB bandwidth of the coupler was measured to be better than 75.5% and extrapolated to be 95.0%. At the centre frequency the through and coupled values were -4.32 dB and -4.44 dB. The phase difference between the couplers output ports was designed to be 90.0° and was measured to be 95.8°. The ±5° phase bandwidth was measured to be 12.7% and the isolation bandwidth was 28.8%. The measured results from the other couplers were comparable to simulation results.</p> <p>The main advantage of the microstructure coupler designs over existing distributed couplers is that the microstructure couplers show a significant area reduction. The branch-line microstructure designs were at least 85% smaller in area than their distributed equivalent on quartz glass. The rat-race microstructure design showed an area reduction of 90% when compared to its distributed equivalent on quartz glass.</p>

Modern communication systems require high performance radio frequency (RF) and microwave circuits and devices. This is becoming increasingly challenging to realize in the content of cost/size constraints. Integrated circuits (ICs) satisfy the cost/size requirement, but performance is often sacri¯ced. For instance, high quality factor (Q factor) passive components are difficult to achieve in standard silicon-based IC processes.<p>In recent years, microelectromechanical systems (MEMS) devices have been receiving increasing attention as a possible replacement for various on-chip passive elements, offering potential improvement in performance while maintaining high levels of integration. Variable capacitors (varactor) are common elements used in various applications. One of the MEMS variable capacitors that has been recently developed is built using deep X-ray lithography (as part of the LIGA process). This type of capacitor exhibits high quality factor at microwave frequencies.<p>The complementary metal oxide semiconductor (CMOS) technology dominates the silicon IC process. CMOS becomes increasingly popular for RF applications due to its advantages in level of integration, cost and power consumption. This research demonstrates a CMOS voltage-controlled oscillator (VCO) design which is used to investigate methods, advantages and problems in integrating LIGA-MEMS devices to CMOS RF circuits, and to evaluate the performance of the LIGA-MEMS variable capacitor in comparison with the conventional on-chip CMOS varactor. The VCO was designed and fabricated using TSMC 0.18 micron CMOS technology. The core of the VCO, including transistors, resistors, and on-chip inductors was designed to connect to either an on-chip CMOS varactor or an off-chip LIGA-MEMS capacitor to oscillate between 2.6 GHz and 2.7 GHz. Oscillator phase noise analysis is used to compare the performance between the two capacitors. The fabricated VCO occupied an area of 1 mm^2.<p>This initial attempt at VCO fabrication did not produce a functional VCO, so the performance of the capacitors with the fabricated VCO could not be tested. However, the simulation results show that with this LIGA-MEMS capacitor, a 6.4 dB of phase noise improvement at 300 kHz offset from the carrier is possible in a CMOS-based VCO design.

There are a significant number of microwave applications, where improvement of such qualities as manufacturing costs, size, weight, power consumption, etc. have attracted much research interest. In order to meet these requirements, new technologies can be actively involved in fabrication of microwave components with improved characteristics. One such fabrication technology is called LIGA (a German acronym with an English translation of lithography, electroforming, and moulding) that allows fabrication of high aspect ratio (tall) structures, and only recently is receiving growing attention in microwave component fabrication.<p> The characteristics of high aspect ratio microstrip and coplanar waveguide (CPW) transmission lines are investigated in this thesis. Very low impedance high aspect ratio CPW transmission lines can be realized. A high aspect ratio microstrip folded half wavelength open loop resonator is introduced. Effective configurations for external and bypass gap coupling with open loop resonators are given. Filters with transmission zeros in the stopband, consisting of high aspect ratio single mode open loop resonators are presented to demonstrate the advantages of high aspect ratio structures in realizing lower external quality factors or tight coupling. The transmission zeros are created by novel coupling routings. Some of the filters are fabricated and the filter responses are measured to validate high aspect ratio coupling structures. High aspect ratio diplexers with increased channel isolation are also designed by appropriately combining filters with transmission zeros.<p> A wideband bandpass filter design method, based on the electromagnetic bandgap (EBG) concept is introduced in this thesis. The wideband filters are miniaturized as a result of using the EBG concept in design. An EBG based wideband filter consisting of unit cells that are realized by using high aspect ratio CPW stepped impedance resonators is also presented. The main advantage of this approach is that the high aspect ratio CPW structures make short unit cells practically realizable, resulting in compact filter structure.

Modern communication systems require high performance radio frequency (RF) and microwave circuits and devices. This is becoming increasingly challenging to realize in the content of cost/size constraints. Integrated circuits (ICs) satisfy the cost/size requirement, but performance is often sacri¯ced. For instance, high quality factor (Q factor) passive components are difficult to achieve in standard silicon-based IC processes.<p>In recent years, microelectromechanical systems (MEMS) devices have been receiving increasing attention as a possible replacement for various on-chip passive elements, offering potential improvement in performance while maintaining high levels of integration. Variable capacitors (varactor) are common elements used in various applications. One of the MEMS variable capacitors that has been recently developed is built using deep X-ray lithography (as part of the LIGA process). This type of capacitor exhibits high quality factor at microwave frequencies.<p>The complementary metal oxide semiconductor (CMOS) technology dominates the silicon IC process. CMOS becomes increasingly popular for RF applications due to its advantages in level of integration, cost and power consumption. This research demonstrates a CMOS voltage-controlled oscillator (VCO) design which is used to investigate methods, advantages and problems in integrating LIGA-MEMS devices to CMOS RF circuits, and to evaluate the performance of the LIGA-MEMS variable capacitor in comparison with the conventional on-chip CMOS varactor. The VCO was designed and fabricated using TSMC 0.18 micron CMOS technology. The core of the VCO, including transistors, resistors, and on-chip inductors was designed to connect to either an on-chip CMOS varactor or an off-chip LIGA-MEMS capacitor to oscillate between 2.6 GHz and 2.7 GHz. Oscillator phase noise analysis is used to compare the performance between the two capacitors. The fabricated VCO occupied an area of 1 mm^2.<p>This initial attempt at VCO fabrication did not produce a functional VCO, so the performance of the capacitors with the fabricated VCO could not be tested. However, the simulation results show that with this LIGA-MEMS capacitor, a 6.4 dB of phase noise improvement at 300 kHz offset from the carrier is possible in a CMOS-based VCO design.

There are a significant number of microwave applications, where improvement of such qualities as manufacturing costs, size, weight, power consumption, etc. have attracted much research interest. In order to meet these requirements, new technologies can be actively involved in fabrication of microwave components with improved characteristics. One such fabrication technology is called LIGA (a German acronym with an English translation of lithography, electroforming, and moulding) that allows fabrication of high aspect ratio (tall) structures, and only recently is receiving growing attention in microwave component fabrication.<p> The characteristics of high aspect ratio microstrip and coplanar waveguide (CPW) transmission lines are investigated in this thesis. Very low impedance high aspect ratio CPW transmission lines can be realized. A high aspect ratio microstrip folded half wavelength open loop resonator is introduced. Effective configurations for external and bypass gap coupling with open loop resonators are given. Filters with transmission zeros in the stopband, consisting of high aspect ratio single mode open loop resonators are presented to demonstrate the advantages of high aspect ratio structures in realizing lower external quality factors or tight coupling. The transmission zeros are created by novel coupling routings. Some of the filters are fabricated and the filter responses are measured to validate high aspect ratio coupling structures. High aspect ratio diplexers with increased channel isolation are also designed by appropriately combining filters with transmission zeros.<p> A wideband bandpass filter design method, based on the electromagnetic bandgap (EBG) concept is introduced in this thesis. The wideband filters are miniaturized as a result of using the EBG concept in design. An EBG based wideband filter consisting of unit cells that are realized by using high aspect ratio CPW stepped impedance resonators is also presented. The main advantage of this approach is that the high aspect ratio CPW structures make short unit cells practically realizable, resulting in compact filter structure.

There are a significant number of microwave applications, including active antenna arrays, wireless communication systems, navigational applications, etc., where improvement of such qualities as manufacturing costs, size, weight, power consumption, etc. is still on the agenda of todays RF design. In order to meet these requirements, new technologies must be actively involved in fabrication of RF components with improved characteristics. One of such fabrication technologies is called LIGA, used before primarily in fluidics, photonics, bioengineering, and micromechanics, and only recently receiving growing attention in RF component fabrication. One of the RF components suffering limitations in performance due to limitations in fabrication capabilities is the compact single metal layer (SML) coupled-line 3-dB coupler, also called hybrid, required in some applications thanks to its ability to divide power equally and electrically isolate the output from the input. In todays practical edge-coupled SML coupler designs, the level of coupling is limited by the capabilities of the photolithographic process to print the coupled lines close enough for tight coupling and it is usually no tighter that 8 dB. A promising way to overcome this limitation is increasing the area of metallic interface of the coupled lines, thus increasing the mutual capacitance of the lines, and inherently the coupling between them. This should be preferably done with keeping the coupler compact with respect to the footprint area, which is attained by making taller conductors, i.e. employing the third dimension. In contrast with previously used RF component fabrication processes, LIGA is the technology that allows the designer to explore the third dimension and build tall conductors while being also able to use small features. When the two-dimensional edge-coupled SML couplers are extended into the three-dimensional structures, they rather become the side-coupled SML couplers. Tall-conductor coupled lines have been characterized in this work to reveal their dependence on their geometry and a 3-dB SML coupler with tall conductors has been developed and fabricated using LIGA at the Institute for Microstructure Technology (IMT), Karlsruhe, Germany. The simulation and measurement results demonstrate the potentially superior performance of LIGA couplers, and the promising capabilities of LIGA for fabrication of RF microstructures.

There are a significant number of microwave applications, including active antenna arrays, wireless communication systems, navigational applications, etc., where improvement of such qualities as manufacturing costs, size, weight, power consumption, etc. is still on the agenda of todays RF design. In order to meet these requirements, new technologies must be actively involved in fabrication of RF components with improved characteristics. One of such fabrication technologies is called LIGA, used before primarily in fluidics, photonics, bioengineering, and micromechanics, and only recently receiving growing attention in RF component fabrication. One of the RF components suffering limitations in performance due to limitations in fabrication capabilities is the compact single metal layer (SML) coupled-line 3-dB coupler, also called hybrid, required in some applications thanks to its ability to divide power equally and electrically isolate the output from the input. In todays practical edge-coupled SML coupler designs, the level of coupling is limited by the capabilities of the photolithographic process to print the coupled lines close enough for tight coupling and it is usually no tighter that 8 dB. A promising way to overcome this limitation is increasing the area of metallic interface of the coupled lines, thus increasing the mutual capacitance of the lines, and inherently the coupling between them. This should be preferably done with keeping the coupler compact with respect to the footprint area, which is attained by making taller conductors, i.e. employing the third dimension. In contrast with previously used RF component fabrication processes, LIGA is the technology that allows the designer to explore the third dimension and build tall conductors while being also able to use small features. When the two-dimensional edge-coupled SML couplers are extended into the three-dimensional structures, they rather become the side-coupled SML couplers. Tall-conductor coupled lines have been characterized in this work to reveal their dependence on their geometry and a 3-dB SML coupler with tall conductors has been developed and fabricated using LIGA at the Institute for Microstructure Technology (IMT), Karlsruhe, Germany. The simulation and measurement results demonstrate the potentially superior performance of LIGA couplers, and the promising capabilities of LIGA for fabrication of RF microstructures.

Graduation date: 1993

Not available / text