Ronald Coutu
Marquette University, Electrical and Computer Engineering, Faculty Member
- Phase Change Materials, Pulsed Laser Deposition, III-V Semiconductors, Crystallization, Phase Change Materials (PCM), MEMS design: Sensors and Actuators, and 3 moreRF Microwave switches, + Mechatronics and Embedded System Applications + R&D on Microtechnology (Micromechanics, Microfluidics/Microactuators, Sensors and MEMS in Medical & Aerospace Applications), and Sensors and Sensingedit
Photovoltaic research and technology have grown exponentially in recent years due to the continuing and increasing global demand for energy. However, to be economical for global production and utilization, the efficiency of solar cells... more
Photovoltaic research and technology have grown exponentially in recent years due to the continuing and increasing global demand for energy. However, to be economical for global production and utilization, the efficiency of solar cells must increase without escalating manufacturing costs. Because of the abundance of silicon and vast knowledge obtained from silicon study, exhaustive exploitation of silicon-based solar cell design is vital to meet both criteria. Positive thermal control and improved photon recycling are two methods to increase solar cell efficiency. A recently developed hybrid multi-junction silicon (HMJ-Si) solar cell architecture was designed to positively manage these two factors, as well as the common resulting photonic interference pattern generated from the electrical contact gratings. Because of the integrated air gap between two stacked silicon substrates, this sandwiched-cavity imparted a 1.70C differential temperature. The top and bottom substrates were electrically connected in parallel via a copper o-ring with a thickness of 385μm which was the optimal, calculated air gap distance for photon propagation wavelengths of 800nm-1100nm. The HMJ-Si solar cell was tested using a solar simulator with an air mass 1.5 full spectrum sunlight output and a class II pyranometer with a spectral response of 310nm-2800nm. The HMJ-Si solar cell demonstrated photovoltaic efficiency of 8-10%.
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Electroactive polymer (EAP) has recently been receiving significant attention as smart materials for actuators and sensors for novel micro fabricated devices. Polymer film devices have demonstrated use as pressure sensors and shown... more
Electroactive polymer (EAP) has recently been receiving significant attention as smart materials for actuators and sensors for novel micro fabricated devices. Polymer film devices have demonstrated use as pressure sensors and shown potential for harvesting energy from the natural environment. Fabrication of sensing devices using copolymer films has been accomplished using standard lithography process. Materials such as P(VDF-TrFE) (polyvinyledenedifluoride-tetrafluoroethylene) copolymer films (1 m thick or less) were evaluated and presented a large relative permittivity and greater piezoelectric-phase without stretching. Mechanical analysis of experimental structures was also provided and led to key design rules for key post-processing steps to control the performance of the devices. Further investigations will be used to identify suitable micro-electro-mechanical systems (MEMs) structures.
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In this paper, we report on the electrical properties of the phase change (PC) material, Germanium Telluride (GeTe), and discuss the fabrication and testing of GeTe resistors. Vertical and horizontal GeTe resistors are fabricated and... more
In this paper, we report on the electrical properties of the phase change (PC) material, Germanium Telluride (GeTe), and discuss the fabrication and testing of GeTe resistors. Vertical and horizontal GeTe resistors are fabricated and tested through resistance measurements before and after substrate heating and joule heating performed by voltage pulsing. Resistance changes of six orders of magnitude and four orders of magnitude are demonstrated by substrate heating and voltage pulsing, respectively. The horizontal resistor designs are shown to be impractical for low voltage applications due to the their large inter-electrode distances. Various sizes of GeTe resistors ranging from 15×15×0.4 μm3 to 3×3×0.09 μm3 are tested and a relationship is demonstrated between GeTe resistor length and the threshold voltage pulse required for phase change.
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This paper presents a comparison between microcontact pairs of Au-Au, Au-Ru and Au-RuO2. The contact pairs were made with an evaporated Au lower planar contact and sputtered Au, Ru or RuO2 upper hemispherical contact. The RuO2 was... more
This paper presents a comparison between microcontact pairs of Au-Au, Au-Ru and Au-RuO2. The contact pairs were made with an evaporated Au lower planar contact and sputtered Au, Ru or RuO2 upper hemispherical contact. The RuO2 was reactively sputtered in both a 10% and 25% O2:Ar environment. The evolution of the contact area was observed by actuating the micro-contact to 1, 10(exp 2), 10(exp 3), 5 x 10(exp 3), 10(exp 4), 5 x 10(exp 4), 10(exp 5), 5 x 10(exp 5), 10(exp 6), 5 x 10(exp 6) and 10(exp 7) cycles. The micro-contacts were actuated using an external, calibrated point load. To examine the micro-contact performance, the contact resistance and force required to close the contact were monitored simultaneously throughout testing. At the above stated end point, the microcontact was folded back to evaluate the wear of the upper hemispherical and planar lower contact. The contacts were also examined with an scanning electron microscope to investigate the contact surfaces. This paper will present the contact evolution between contact pairs of Au-Au, Au-Ru and Au-RuO2 microcontacts between 1 and 10(exp 7) cycles. It was found that the contact resistance for the Au/Ru was 1.7 Omega, Au/RuO2 10% was 1.36 Omega, Au/RuO2 25% was 0.036 Omega.
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Internet of Things, Big data, connected technologies, and advanced materials are spearheading the growth of an increasingly competitive wind power sector. Wind power market has seen “tremendous growth” in recent years, and will reach even... more
Internet of Things, Big data, connected technologies, and advanced materials are spearheading the growth of an increasingly competitive wind power sector. Wind power market has seen “tremendous growth” in recent years, and will reach even greater heights as IoT technology advances. The primary hot researches in this field focus on wind farm producibility, safety and reliability, and financial risk management. Therefore, essential questions in a topical farm are as follows: How long wind turbines can work efficiently? When is the best time for maintenance? Which measures can be used for essential monitoring of the system? How reliable are the selected measurements to guarantee the safety and predictability of the wind farm? To address the above concerns and design a reliable framework for health monitoring of wind turbines, critical components in wind turbines such as gearboxes, blade, power converter, and others parts are investigated using a recommended IoT platform. The priory goal is to develop IoT system to monitor wind turbine using available measurements through IoT's sensors. Then, potential faults are identified by a diagnosis unit using data mining approaches.
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In microelectromechanical systems (MEMS) ohmic contact switches, reliability is of great concern where billions of cycle operation is a requirement. Microcontact surface tribology plays the critical role in determining their reliability... more
In microelectromechanical systems (MEMS) ohmic contact switches, reliability is of great concern where billions of cycle operation is a requirement. Microcontact surface tribology plays the critical role in determining their reliability and performance. In this work, a novel, simple, quick and efficient test fixture has been designed and assembled to study the contact resistance, contact force, adhesion force, and contamination associated with the microcontact. In support of developing the test fixture, we evaluated the performance limitations of each components (i.e. piezoelectric actuators, force sensors, nanomax stage) independently. Force versus position, force versus voltage, and position versus voltage data have been collected for each test fixture components under direct current (DC) condition. A customized stage fixture has been 3D printed for holding the microcontact support structure. We use Thorlab’s state-of-the-art nanomax stage to provide nanometric positioning and precise alignment between the microcontact area and the force sensor on three orthogonal axes. We fabricate a novel contact support structure to test the feasibility of our test fixture and collect force and resistance data simultaneously at the rate of $\sim$5 KHz using LabView. Data obtained from the test fixture will provide significant information to design a robust and reliable MEMS switch for future DC and RF applications.
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Transitional metal oxides have generated considerable interest in electronics and other engineering applications over the last few decades. These materials show several orders of magnitude metal-insulator transition (MIT) when triggered... more
Transitional metal oxides have generated considerable interest in electronics and other engineering applications over the last few decades. These materials show several orders of magnitude metal-insulator transition (MIT) when triggered by an external stimuli. In this paper, an MIT (Vanadium Dioxide (VO2)) -based bimorph cantilever shows promising performance due to its large volumetric work density, ultrafast response, and reliability. This this work, we propose and simulate a cantilever actuated via VO2 for a micro-contact switch. Our results show VO2 based actuators show promising performance in terms of deflection, resonance frequency, and lifetime.
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Metamaterials in the terahertz range or higher typically have gaps that are far from an ideal parallel plate due to microfabrication limitations on feature size. This work examines the exact solution to the square parallel plate capacitor... more
Metamaterials in the terahertz range or higher typically have gaps that are far from an ideal parallel plate due to microfabrication limitations on feature size. This work examines the exact solution to the square parallel plate capacitor and finds a valid approximation for capacitance in non-ideal geometries, when the gap size is comparable or larger than the dimensions of the plates.
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The effects of bending a 2-dimensional planar array of rectangular split-ring resonators (SRRs) is observed by mounting the array to varying diameter HDPE cylinders. By studying the transmission of pulsed THz light through the... more
The effects of bending a 2-dimensional planar array of rectangular split-ring resonators (SRRs) is observed by mounting the array to varying diameter HDPE cylinders. By studying the transmission of pulsed THz light through the SRR-cylinder system, it shown that the resonant frequency and response of the arrays are tunable as a function of the radius of curvature.
Research Interests: Engineering, Physics, Materials Science, Optics, Computer Engineering, and 15 moreMagnetic Materials, Metamaterials, Optoelectronics, Curvature, Bending, Metamaterial, Resonator, Cylinder, Substrates, ARRAYS, Electrical and Computer Engineering, Resonant Frequency, Terahertz radiation, Radius of Curvature, and Planar
While recent years have seen great advances in the generation, detection, and application of terahertz frequency radiation, this region of the electromagnetic spectrum still suffers from a lack of efficient and effective frequency... more
While recent years have seen great advances in the generation, detection, and application of terahertz frequency radiation, this region of the electromagnetic spectrum still suffers from a lack of efficient and effective frequency specific optical components. While such terahertz devices do exist, they are often limited by the materials they are based on and a lack of frequency selectivity and tunability. Metamaterial devices can provide frequency resonant behavior in the form of transmissive and reflective filters. Such a frequency selective surface can also be made tunable via the use of a flexible substrate. In this talk, we will highlight work involving the design, fabrication, and characterization of terahertz metamaterial devices based on flexible substrates. Finite element method simulations have been utilized to design a split-ring resonator (SRR) structure on a flexible SU8 polymer substrate with a targeted 250 GHz resonant response. Multiple configurations of SRR arrays have been fabricated on free standing SU8 substrates. These devices have subsequently been characterized using terahertz time-domain spectroscopy and imaging systems. The metamaterial devices have shown selective transmission and reflection over a narrow range of frequencies near the targeted resonance at 250 GHz. Details of both the design, fabrication, and characterization will be discussed.
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The demonstrated benefits provided by Atomic Layer Deposition (ALD) in producing films of exceptional uniformity, and conformality, has set the stage for its use in large area, and batch processing applications. Two key elements which... more
The demonstrated benefits provided by Atomic Layer Deposition (ALD) in producing films of exceptional uniformity, and conformality, has set the stage for its use in large area, and batch processing applications. Two key elements which drive the adoption of ALD for these applications are the ability to scale the film processes from small to large size substrates, and for the effective throughput to be increased in a manner consistent with volume production needs. In this paper we discuss the results of scaling processes from small format substrates to large format substrates, along with a presentation of the parameters which influence throughput. Additionally we describe the basic underpinnings of batch and roll-to-roll ALD systems, and the design factors which must be considered when used in a high volume setting.
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Germanium telluride (GeTe) is a chalcogenide phase change material which is nonvolatile and changes its phase from amorphous state to a highly conductive crystalline state at approximately 180–230°C temperature, dropping the material’s... more
Germanium telluride (GeTe) is a chalcogenide phase change material which is nonvolatile and changes its phase from amorphous state to a highly conductive crystalline state at approximately 180–230°C temperature, dropping the material’s resistivity by six orders of magnitude. These temperature-induced states lead to different physical and chemical properties, making it a suitable candidate for optical storage, reconfigurable circuit, high-speed switching, terahertz (THz), and satellite applications. Besides, GeTe-based devices offer complementary metal oxide-semiconductor (CMOS) compatibility and simplified, low-cost fabrication processes. In this chapter, three applications of GeTe will be discussed. They are as follows: (1) how GeTe can be utilized as DC and RF switching material with their high OFF/ON resistivity ratio, (2) how GeTe can contribute to current THz technology as split-ring resonators and modulators, and (3) effect of threshold voltage on GeTe for reconfigurable circu...
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Germanium telluride (GeTe) is a chalcogenide phase change material which is nonvolatile and changes its phase from amorphous state to a highly conductive crystalline state at approximately 180–230°C temperature, dropping the material’s... more
Germanium telluride (GeTe) is a chalcogenide phase change material which is nonvolatile and changes its phase from amorphous state to a highly conductive crystalline state at approximately 180–230°C temperature, dropping the material’s resistivity by six orders of magnitude. These temperature-induced states lead to different physical and chemical properties, making it a suitable candidate for optical storage, reconfigurable circuit, high-speed switching, terahertz (THz), and satellite applications. Besides, GeTe-based devices offer complementary metal oxide-semiconductor (CMOS) compatibility and simplified, low-cost fabrication processes. In this chapter, three applications of GeTe will be discussed. They are as follows: (1) how GeTe can be utilized as DC and RF switching material with their high OFF/ON resistivity ratio, (2) how GeTe can contribute to current THz technology as split-ring resonators and modulators, and (3) effect of threshold voltage on GeTe for reconfigurable circu...
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Liquid Crystals (LCs) are widely used in display devices, electro-optic modulators, and optical switches. A field-induced electrical conductivity modulation in pure liquid crystals is very low which makes it less preferable for direct... more
Liquid Crystals (LCs) are widely used in display devices, electro-optic modulators, and optical switches. A field-induced electrical conductivity modulation in pure liquid crystals is very low which makes it less preferable for direct current (DC) and radio-frequency (RF) switching applications. According to the literature, a conductivity enhancement is possible by nanoparticle doping. Considering this aspect, we reviewed published works focused on an electric field-induced conductivity modulation in carbon nanotube-doped liquid crystal composites (LC-CNT composites). A two to four order of magnitude switching in electrical conductivity is observed by several groups. Both in-plane and out-of-plane device configurations are used. In plane configurations are preferable for micro-device fabrication. In this review article, we discussed published works reporting the elastic and molecular interaction of a carbon nanotube (CNT) with LC molecules, temperature and CNT concentration effects ...
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Research of electrostrictive polymers has generated new opportunities for harvesting energy from the surrounding environment and converting it into usable electrical energy. Electroactive polymer (EAP) research is one of the new... more
Research of electrostrictive polymers has generated new opportunities for harvesting energy from the surrounding environment and converting it into usable electrical energy. Electroactive polymer (EAP) research is one of the new opportunities for harvesting energy from the natural environment and converting it into usable electrical energy. Piezoelectric ceramic based energy harvesting devices tend to be unsuitable for low-frequency mechanical excitations such as human movement. Organic polymers are typically softer and more flexible therefore translated electrical energy output is considerably higher under the same mechanical force. In addition, cantilever geometry is one of the most used structures in piezoelectric energy harvesters, especially for mechanical energy harvesting from vibrations. In order to further lower the resonance frequency of the cantilever microstructure, a proof mass can be attached to the free end of the cantilever. Mechanical analysis of an experimental bim...
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Strain sensing at high temperatures, greater than 700°F, is often difficult. Traditional strain sensing uses the piezoresistive effect, which is temperature dependent. To reduce the temperature dependence of the strain sensor one could be... more
Strain sensing at high temperatures, greater than 700°F, is often difficult. Traditional strain sensing uses the piezoresistive effect, which is temperature dependent. To reduce the temperature dependence of the strain sensor one could be built from a robust material such as silicon carbide, SiC. Making measurements using capacitive effects eliminates the effects of temperature within the sensing element. Using the more traditional MEMS material silicon is only an option at lower temperatures. Silicon has good reliability as a mechanical structure to around 900°F, and good electrical properties to 300°F. Having good properties above 700°F, silicon carbide is a robust material that has the ability to be used in high temperature MEMS applications. Using the capacitive effect for measuring strain was the original way to perform this task until the piezoresistive effect was harnessed. MEMS based capacitive strain sensors that have been built previously are known as resonant strain sensors, or the double ended tuning fork resonator. One step further from the double ended tuning fork is a novel capacitive strain sensor device. An examination of the novel approach to measure strain is performed. Modeling and simulation is presented using L-Edit and Coventorware. This asserts the device’s characteristics and gives the novel design merit to be used as a strain sensor.
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Germanium telluride (GeTe) is a phase change material that undergoes an amorphous to crystalline transition upon heating to ~ 200oC. This transition is reversible in nature and results in ~ six orders of magnitude difference in GeTe... more
Germanium telluride (GeTe) is a phase change material that undergoes an amorphous to crystalline transition upon heating to ~ 200oC. This transition is reversible in nature and results in ~ six orders of magnitude difference in GeTe resistivity which makes it a suitable candidate for data storage and other functional devices. In this work, micro-size phase change test cells were fabricated by RF sputtering GeTe thin films onto silicon (Si) wafers and Si wafers coated with silicon dioxide (SiO2), silicon nitride (Si3N4), and alumina (Al2O3) films. Two different heating methods, conductive and electrical (i.e. Joule heating), were applied to induce the phase transition mechanism in the GeTe cells. The phase change mechanisms were investigated using spectroscopic ellipsometry, thermal, electrical and radio-frequency methods. It was observed in ellipsometry that the extinction coefficient, hence the absorption coefficients of GeTe cells increases with amorphous to crystalline phase chan...
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Advancements in microelectromechanical system (MEMS) technology over the last several decades has been a driving force behind miniaturizing and improving sensor designs. In this work, a specialized cantilever pressure sensor was designed,... more
Advancements in microelectromechanical system (MEMS) technology over the last several decades has been a driving force behind miniaturizing and improving sensor designs. In this work, a specialized cantilever pressure sensor was designed, modeled, and fabricated to investigate the photoacoustic (PA) response of gases to terahertz (THz) radiation under low-vacuum conditions associated with high-resolution spectroscopy. Microfabricated cantilever devices made using silicon-on-insulator (SOI) wafers were tested in a custom-built test chamber in this first ever demonstration of a cantileverbased PA chemical sensor and spectroscopy system in the THz frequency regime. The THz radiation source was amplitude modulated to excite acoustic waves in the chamber, and PA molecular spectroscopy of a gas species was performed. An optical measure‐ ment technique was used to evaluate the PA effect on the cantilever sensor; a laser beam was reflected off the cantilever tip and through an iris to a pho...
Welcome to the Special Topics Section dedicated to the 2015 Holm Conference on Electrical Contacts. This Special Section contains six high-quality papers that comprehensively describe the state of the art and potential future directions... more
Welcome to the Special Topics Section dedicated to the 2015 Holm Conference on Electrical Contacts. This Special Section contains six high-quality papers that comprehensively describe the state of the art and potential future directions for topics of great interest to our readers. The Editor-in-Chief (EIC), in consultation with the other EICs, Associate Editors (AEs), and domain experts, selects the topics for the Special Sections, and a Guest Editor or AE (GE/AE) who is a leading expert in the technical area then directs the solicitation and peer review of the papers. In cases where the GE/AE is also an author, the EIC is responsible for the peer review to avoid any real or perceived conflicts of interest. Welcome to the Special Topics Section dedicated to the 2015 Holm Conference on Electrical Contacts. This Special Section contains six high-quality papers that comprehensively describe the state of the art and potential future directions for topics of great interest to our readers...
The purpose of this chapter is to familiarize the reader with metamaterials and describe terahertz (THz) spectroscopy within metamaterials research. The introduction provides key background information on metamaterials, describes their... more
The purpose of this chapter is to familiarize the reader with metamaterials and describe terahertz (THz) spectroscopy within metamaterials research. The introduction provides key background information on metamaterials, describes their history and their unique properties. These properties include negative refraction, backwards phase propagation, and the reversed Doppler Effect. The history and theory of metamaterials are discussed, starting with Veselago’s negative index materials work and Pendry’s publications on physical realization of metamaterials. The next sections cover measurement and analyses of THz metamaterials. THz Time-domain spectroscopy (THz-TDS) will be the key measurement tool used to describe the THz metamaterial measurement process. Sample transmission data from a metamaterial THz-TDS measurement is analyzed to give a better understanding of the different frequency characteristics of metamaterials. The measurement and analysis sections are followed by a section on ...
Concrete and asphalt are the primary materials used to construct roadways for motor vehicles, paths for pedestrians and bicyclists, and runways for aircraft. Solar Roadways®, Inc. (SR) proposed a novel solar pavement technology (i.e.,... more
Concrete and asphalt are the primary materials used to construct roadways for motor vehicles, paths for pedestrians and bicyclists, and runways for aircraft. Solar Roadways®, Inc. (SR) proposed a novel solar pavement technology (i.e., solar road panels (SRP)) as an alternative material and energy source. SR performed load, traction, and impact testing to use SRPs in non-critical applications like parking lots. To use SRP in public roads, engineering tests including freeze/thaw, moisture absorption, heavy vehicle, and shear testing were accomplished on “SR3” prototypes. Testing was performed at Marquette University in the Engineering Materials and Structural Testing Laboratory and the SR Pilot Project area. Moisture absorption and freeze/thaw tests showed “SR3” resistant to extreme weather and moisture environments. Heavy vehicle testing revealed no physical damage to the “SR3” after approximately 989,457 equivalent single axle loads were continuously rolled over a prototype pavement...
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In microelectromechanical systems (MEMS) switches, the microcontact is crucial in determining reliability and performance. In the past, actual MEMS devices and atomic force microscopes (AFM)/scanning probe microscopes... more
In microelectromechanical systems (MEMS) switches, the microcontact is crucial in determining reliability and performance. In the past, actual MEMS devices and atomic force microscopes (AFM)/scanning probe microscopes (SPM)/nanoindentation-based test fixtures have been used to collect relevant microcontact data. In this work, we designed a unique microcontact support structure for improved post-mortem analysis. The effects of contact closure timing on various switching conditions (e.g., cold-switching and hot-switching) was investigated with respect to the test signal. Mechanical contact closing time was found to be approximately 1 us for the contact force ranging from 10–900 μN. On the other hand, for the 1 V and 10 mA circuit condition, electrical contact closing time was about 0.2 ms. The test fixture will be used to characterize contact resistance and force performance and reliability associated with wide range of contact materials and geometries that will facilitate reliable, r...