Dans cette thèse, trois approches différentes ont été étudiées pour des dispositifs photoniques accordables basés sur la technologie MEMS. Premièrement, la structure à double barrière optique a été étudiée numériquement et expérimentalement, sous forme de commutateur thermo-optique, polariseur commutable et de jonctions tunnel optiques intégrées en tant que système WDM reconfigurable. Le dispositif est fabriqué sur substrat silicium SOI utilisant le procédé de gravure profonde. Les dispositifs optiques tunnel sont contrôlés électro-thermiquement, le temps de commutation mesuré correspondant est de plusieurs microsecondes. Deuxièmement, des structures de propagation de lumière lente à base de méta matériaux constitués de cellules unitaires sous forme d’anneaux fendus couplés, sont numériquement analysés. Les résultats des simulations montrent que la conception de SRRs (Split Ring Resonator) couplés améliore l'accordabilité de la permittivité et de la perméabilité effectives de 70 et 200 fois, respectivement. On peut trouver des applications potentielles dans le stockage de données, des circuits photoniques, les communications optiques et les biocapteurs. Enfin, un méta matériau accordable magnétique est démontré en utilisant la technologie MEMS. Il démontre une approche unique pour contrôler les propriétés optiques des méta matériaux par l'évolution des dimensions géométriques et les formes des cellules unitaires / In this PhD project, three different approaches have been studied for tunable photonic devices based on MEMS technology. First, the optical double barrier structure has been numerically studied and experimentally demonstrated as the thermo-optical switch, switchable polarizer and optical tunneling junctions integrated as reconfigurable WDM system. Second, the slow light structure using metamaterial with coupled split ring unit cells is numerically analyzed. Finally, a tunable magnetic metamaterial is demonstrated using MEMS technology. The first major work is to use the optical tunneling effects to design MEMS based photonic devices. Three different tunable photonic devices has been demonstrated using thermo-optical tuning. a thermo-optic switch is realized using MEMS technology. The device is fabricated on silicon-on-isolator wafer using deep etching process. The transmission of the optical switch is controlled by the optical length of the central rib which is thermally controlled by the external pumping current. In experiment, it measures a switching speed of 1 us and an extinction ratio of 30 dB. A switchable polarizer is demonstrated using the double optical barrier structure which transmit the light with one polarization state and filter out the others. In experiment it measures a PER of lager than 23 dB when the pumping current is above 60mA. The switching time is shorter than 125 us which is limited by the polarization analyzer used in the experiment. A MEMS reconfigurable add-drop multiplexer is realized by applied the optical tunneling structure to the ribbed waveguide. The tunable add-drop multiplexer is based on Y-shape optical double barriers tunneling junction which are realized by MEMS technology

Tese de mestrado integrado. Engenharia Electrotécnica e de Computadores (Major Telecomunicações). Faculdade de Engenharia. Universidade do Porto. 2010

Reconfigurable impedance matching networks are an integral part of multiband radio-frequency (RF) transceivers. They are used to compensate for the input/output impedance variations between the different blocks caused by switching the frequency band of operation or by adjusting the output power level. Various tuning techniques have been developed to construct tunable impedance matching networks employing solid-state p-i-n diodes and varactors. At millimeter-wave frequencies, the increased loss due to the low quality factor of the solid-state devices becomes an important issue. Another drawback of the solid-state tuning elements is the increased nonlinearity and noise at higher RF power levels. The objective of the research described in this thesis is to investigate the feasibility of using RF microelectromechanical systems (RF-MEMS) technology to develop reconfigurable impedance matching networks. Different types of tunable impedance matching networks with improved impedance tuning range, power handling capability, and lower insertion loss have been developed. Another objective is to investigate the realization of a fully integrated one-chip solution by integrating MEMS devices in standard processes used for RF integrated circuits (RFICs). A new CMOS-MEMS post-processing technique has been developed that allows the integration of tunable RF MEMS devices with vertical actuation within a CMOS chip. Various types of CMOS-MEMS components used as tuning elements in reconfigurable RF transceivers have been developed. These include tunable parallel-plate capacitors that outperform the available CMOS solid-state varactors in terms of quality factor and linearity. A tunable microwave band-pass filter has been demonstrated by employing the proposed RF MEMS tunable capacitors. For the first time, CMOS-MEMS capacitive type switches for microwave and millimeter-wave applications have been developed using TSMC 0.35-µm CMOS process employing the proposed CMOS-MEMS integration technique. The switch demonstrates an excellent RF performance from 10-20 GHz. Novel MEMS-based reconfigurable impedance matching networks integrated in standard CMOS technologies are also presented. An 8-bit reconfigurable impedance matching network based on the distributed MEMS transmission line (DMTL) concept operating at 13-24 GHz is presented. The network is implemented using standard 0.35-µm CMOS technology and employs a novel suspended slow-wave structure on a silicon substrate. To our knowledge, this is the first implementation of a DMTL tunable MEMS impedance matching network using a standard CMOS technology. A reconfigurable amplifier chip for WLAN applications operating at 5.2 GHz is also designed and implemented. The amplifier achieves maximum power gain under variable load and source impedance conditions by using the integrated RF-MEMS impedance matching networks. This is the first single-chip implementation of a reconfigurable amplifier using high-Q MEMS impedance matching networks. The monolithic CMOS implementation of the proposed RF MEMS impedance matching networks enables the development of future low-cost single-chip RF multiband transceivers with improved performance and functionality.

Reconfigurable impedance matching networks are an integral part of multiband radio-frequency (RF) transceivers. They are used to compensate for the input/output impedance variations between the different blocks caused by switching the frequency band of operation or by adjusting the output power level. Various tuning techniques have been developed to construct tunable impedance matching networks employing solid-state p-i-n diodes and varactors. At millimeter-wave frequencies, the increased loss due to the low quality factor of the solid-state devices becomes an important issue. Another drawback of the solid-state tuning elements is the increased nonlinearity and noise at higher RF power levels. The objective of the research described in this thesis is to investigate the feasibility of using RF microelectromechanical systems (RF-MEMS) technology to develop reconfigurable impedance matching networks. Different types of tunable impedance matching networks with improved impedance tuning range, power handling capability, and lower insertion loss have been developed. Another objective is to investigate the realization of a fully integrated one-chip solution by integrating MEMS devices in standard processes used for RF integrated circuits (RFICs). A new CMOS-MEMS post-processing technique has been developed that allows the integration of tunable RF MEMS devices with vertical actuation within a CMOS chip. Various types of CMOS-MEMS components used as tuning elements in reconfigurable RF transceivers have been developed. These include tunable parallel-plate capacitors that outperform the available CMOS solid-state varactors in terms of quality factor and linearity. A tunable microwave band-pass filter has been demonstrated by employing the proposed RF MEMS tunable capacitors. For the first time, CMOS-MEMS capacitive type switches for microwave and millimeter-wave applications have been developed using TSMC 0.35-µm CMOS process employing the proposed CMOS-MEMS integration technique. The switch demonstrates an excellent RF performance from 10-20 GHz. Novel MEMS-based reconfigurable impedance matching networks integrated in standard CMOS technologies are also presented. An 8-bit reconfigurable impedance matching network based on the distributed MEMS transmission line (DMTL) concept operating at 13-24 GHz is presented. The network is implemented using standard 0.35-µm CMOS technology and employs a novel suspended slow-wave structure on a silicon substrate. To our knowledge, this is the first implementation of a DMTL tunable MEMS impedance matching network using a standard CMOS technology. A reconfigurable amplifier chip for WLAN applications operating at 5.2 GHz is also designed and implemented. The amplifier achieves maximum power gain under variable load and source impedance conditions by using the integrated RF-MEMS impedance matching networks. This is the first single-chip implementation of a reconfigurable amplifier using high-Q MEMS impedance matching networks. The monolithic CMOS implementation of the proposed RF MEMS impedance matching networks enables the development of future low-cost single-chip RF multiband transceivers with improved performance and functionality.

No description available.

The advent of ferroelectric thin films with strong piezoelectric response has enabled the development of new nano- and micro-electromechanical systems (NEMS/MEMS) capable of large displacements at low voltage levels, aiming to be compatible with complementary metal oxide semiconductor industry. Key to all of these applications is the ability to process ferroelectric materials with maximized electromechanical coupling and to integrate them into the devices. With the continuous drive towards miniaturization of devices for piezoelectric and electronic applications, processing of ultrathin ferroelectric films with maintained large electromechanical coupling is essential to the development of high performance NEMS and MEMS. The piezoelectric response of ferroelectric thin films is profoundly affected by the texture and microstructural characteristics of the material and is severely reduced at sub-micron thickness ranges. For the first time, reproducible synthesis of dense, highly textured and phase-pure PZT thin films was achieved via chemical solution deposition. The consistent processing of ferroelectric thin films resulted in the elimination of the coupling effects of crystallographic anisotropy, porosity and in general microstructural characteristics on the functional properties of the films. This enabled effective study of the key parameters influencing the electromechanical response of the ferroelectric thin films, such as crystallite size (thickness dependence), chemical heterogeneities and substrate clamping. Reproducible synthesis of highly (100)-textured PZT ultrathin films enabled the study of the size effects on the dielectric and piezoelectric response of these films in the thicknesses ranging from 20 up to 260nm. Dielectric and piezoelectric responses of the films monotonically decreased in thinner films. For PZT films at MPB, a critical thickness, ~50nm was observed below which the extrinsic contributions to the dielectric responses of the films are heavily suppressed. After the study and acknowledgment of the severe reduction of the piezoelectric response in ferroelectric ultrathin film, several factors affecting piezoelectric response of ferroelectric films were studied in order to maximize the response especially at low film thickness ranges: chemical homogeneity, residual stresses and substrate clamping as well as using alternative material systems; relaxor ferroelectrics. In particular, a major part of the piezoelectric (and dielectric) response of the PZT has extrinsic sources such as domain or phase boundary motion and vibrations. Special attention was paid throughout this investigation into understanding extrinsic origins in PZT thin films and different approaches was utilized to further activate and enhance their contributions. Focusing on the chemical homogeneity of the ferroelectric films, Different routes were used to process ultrathin films (<200nm) with maintained functional properties. Superior piezoelectric properties - 40% higher piezoelectric response than in conventionally processed films - were achieved in highly (100)-oriented PZT superlattice-like films with controlled compositional gradient centered around MPB composition on Si substrates. Superlattice (SL) or heterolayered ferroelectric thin films consist of alternate layers of ferroelectric materials, or phases, with a compositional gradient normal to the substrate. The dynamic motion of “artificially created” phase boundaries between layer to layer tetragonal and rhombohedral phases participated in the extrinsic contributions to the films’ dielectric and piezoelectric response. This approach led to processing of 200 nm SL films with d33,f values as high as some of the best previously reported data for 1 to 2 µm-thick PZT films. Furthermore, comprehensive processing optimization was carried out on relaxor-ferroelectric PMN-PT thin films. Dense, highly (100)-textured PMN-PT films were synthesized exhibiting the highest d33,f coefficients reported so far in the literature (210pm/V) for corresponding thickness ranges. Control of the microstructural characteristics - texture and density – throughout the whole film thickness was necessary to obtain films with maximized functional properties. To study the effect of substrate clamping on the piezoelectric performance of the films, the Si substrate in PZT and PMN-PT films were back-side etched via dry etching in an inductively coupled plasma reactor. This approach is similar the final state of the films for MEMS applications, where the Si substrate is mostly removed in order to have a free-standing or semi-free standing ferroelectric membrane or cantilever. A giant enhancement in the piezoelectric d33,f coefficient of the substrate-released samples was observed with respect to the films on the virgin substrate. The response increased by at least one order of magnitude from ~75-200 pm/V (for different PZT film thicknesses ranging from 300nm to 1 µm) to ~1500 to 4500 pm/V at reduced Si thickness. Experimental observations in macroscopic dielectric and piezoelectric characterization and microscopic piezo-response force microscopy of the samples indicate larger extrinsic contributions, -possibly with domain dynamic source- to the functional responses of the films in back-side etched samples. A fundamental change in the pattern of the electromechanical activity of the grains between the released and clamped films was observed in the band-excitation piezo-force microscopy investigations; A breakdown of the clustered pattern in the electromechanical activity of the grains in the PZT film. This giant enhancement promises a new pathway for greatly improved electromechanical properties which has a huge potential to enable high performance future device applications.

No description available.

Driven by the emerging interest in the design and realization of structures with co-existing micro- and nanoscale features, various nanofabrication approaches are being developed. We show that the selective, conformal growth of a multilayer structure is a promising route for the controlled realization of various structures with size-hierarchy, including both surface (i.e., the structures of which functionalities are characterized by the interaction between their surface, and external systems, such as self-cleaning, superhydrophic substrates with dual-scale topography), and volumetric (i.e. composite materials of which functionalities rely on the intrinsic properties of nanostructures distributed throughout their volume, such as giantmagnetoresistance sensors) structures. This is realized based on a sequential multilayer electrodeposition guided by an insulating substrate with predesigned topography, referred to as template-assisted multilayer electrodeposition process. Various multiscale, multidimensional surface and volumetric hierarchical structures are demonstrated of which size scale of the nanostructures are defined by the individual layer deposition parameters, while their position and overall geometry are defined by that of the template. These structures include (1) large area (> 1 cm^2), planar, or non-planar surfaces comprised of anisotropic, nanoscale surface relief structures of wide-ranging size scale (10 nm-1 micron); and (2) thick (10-100 micron), volumetric composite material in which individual metallic layers of micron, or submicron scale thicknesses are electrically insulated from the adjacent layers by interlamination insulating layers of similar thicknesses. The utility of the fabricated structures is evaluated in a few potential application domains, i.e., nanolithography, self-cleaning, and high frequency magnetic devices.

Thesis advisor: Willie J. Padilla / Realization of an ideal electromagnetic absorber has long been a goal of engineers and is highly desired for frequencies above the microwave regime. On the other hand, the desire to control the blackbody radiation has long been a research topic of interest for scientists--one particular theme being the construction of a selective emitter whose thermal radiation is much narrower than that of a blackbody at the same temperature. In this talk, I will present the computational and experimental work that was used to demonstrate infrared metamaterial absorbers and selective thermal emitters. Based on these work, we further demonstrate an electrically tunable infrared metamaterial absorber in the mid-infrared wavelength range. A voltage potential applied between the metallic portion of metamaterial array and the bottom ground plane layer permits adjustment of the distance between them thus altering the electromagnetic response from the array. Our device experimentally demonstrates absorption tunability of 46.2% at two operational wavelengths. Parts of this thesis are based on unpublished and published articles by me in collaboration with others. The dissertation author is the primary researcher and author in these publications. The text of chapter two, chapter five, and chapter seven is, in part, a reprint of manuscript being prepared for publication. The text of chapter three is, in part, a reprint of material as it appears in Physical review letters 104 (20), 207403. The text of chapter four is, in part, a reprint of material as it appears in Physical Review Letters 107 (4), 45901. The text of chapter six is, in part, a reprint of material as it appears in Applied Physics Letters 96, 011906 / Thesis (PhD) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

Microelectromechanical systems (MEMS) are quickly becoming ubiquitous in commercial and military applications. As the use of such devices increases their reliability becomes of great importance. Although there has been significant research in the areas of MEMS errors, there is a lack of work regarding long term reliability of packaged systems. Residual thermomechanical stresses might relax over time which affects physical distances within a package, ultimately influencing the performance of a device. One reason that there has not been sufficient work performed on the long-term effects on structures might be the lack of a tool capable of characterizing the effects. MEMS devices have been measured for shape and its changes using interferometric techniques for some time now. Commercially available systems are able to make high resolution measurements, however they might lack loading options. To study aging effects on components a test might need to run continuously for days or weeks, with systematic operations performed throughout the process. Such a procedure is conducive to an automated data acquisition system. A system has been developed at WPI using a Twyman-Green interferometer and a custom software suite. The abilities of this system are demonstrated through analysis performed on MEMS tuning fork gyroscope (TFG) sensors. Specifically, shape is recorded to investigate die bond relaxation as a function of time and thermal cycle. Also presented are measurements made using stroboscopic illumination on operating gyroscopes, in situ. The effect of temperature on the performance of the sensors is investigated using a customized precision rate table.