41 research outputs found

    Investigation of large-signal performance on BST thin film varactors for microwave device applications

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    The development of future wireless communication and information systems is driven towards small-scaled and lighter-weight systems with the capability of being more adaptable and reconfigurable. The emergence of ferroelectric materials such as barium strontium titanate (BST) which has high dielectric tunability and low microwave loss at room temperature has sparked research interest in the last 20 years due to the developments in device electronics and material technology. One of the major areas where BST can play a significant role is in the RF and microwave systems. BST thin film in paraelectric phase exhibits a nonlinear characteristic when an electric field is applied and the physical tuning of its dielectric permittivity is fundamental in realising an electronically tunable microwave component known as a variable capacitor or varactor. The aim of this PhD research is to investigate the large-signal performance of BST thin film varactors fabricated on sapphire substrates for microwave device applications. Sapphire exhibits excellent microwave properties with very low loss at microwave frequencies, presents close lattice match to BST thin film and has a relatively low cost. A novel method for the theoretical analysis of the third-order intermodulation distortion (IM 3 ) in BST thin film interdigital capacitors (IDCs) was established. BST thin films were initially grown directly on r-plane sapphire substrates, which have the potential to be integrated with existing semiconductor technologies through silicon-on-sapphire (SoS) process. Two circuit topologies - the “dual” and “series dual” BST varactor circuits - were proposed for linearity improvement and their theoretical models, along with simulated and measured results, were presented. Low IM 3 was demonstrated and experimentally verified. By proper selective biasing, very low nulls were observed in both dual and series dual BST varactor circuit topologies. This indicated minimum distortion. An investigation of the power handling capability of BST thin film varactors fabricated on c-plane sapphire substrate was established. The research objective was to analyse the effects of varying the geometry of the BST IDC on the shape of the nonlinear C-V curves. Depending on the geometry selections, the C-V curves will become narrower or broader. The optimised narrow, broad and intermediate curves were demonstrated and their 1 dB compression points were extracted. The relationships between their tunabilities and 1 dB compression points were subsequently shown by simulations and measurements

    10 GHz Low Loss Liquid Metal SIW Phase Shifter for Phased Array Antenna

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    This paper presents a proof of concept demonstrator for a pair of novel phase shifters based on substrate integrated waveguide (SIW) technology. Gallium-based liquid metal (LM) is used to reconfigure each phase shifter. The paper presents LM phase shifters that, for the first time, have a phase shifting range of 360⁰. The phase shifters have a small electrical size, and they are intended for use within phased array antenna applications. The paper also presents a design procedure for the phase shifters. The procedure has been used to design two phase shifters operating at 10 GHz. The design process can be readily scaled for operation at other frequencies. The proposed phase shifters are reciprocal and bidirectional and they have very low insertion loss. A series of reconfigurable LM vias are used to achieve the phase shift. Each of LM via is activated once a drill hole is filled with LM and it is deactivated once LM is removed. Using this method; it is possible to achieve a phase shift step ranging from 1° to 100° using a single LM via. Moreover, the overall phase shift can be extended to 360° by employing several LM vias in series inside the SIW. The proposed phase shifters have an insertion loss lower than 3 dB and provide a total phase shifting range of approximately 360° in eight steps of approximately 45° each. This enables the proposed two phase shifters to have an extraordinary Figure of Merit (FoM) of 131.3 ⁰/dB and 122.4 ⁰/dB

    Studies on microwave antennas : passive intermodulation distortion in antenna structures and design of microstrip antenna elements

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    Passive intermodulation (PIM) measurements of antennas and the design of dual-polarised microstrip antenna elements are investigated in this thesis. The emphasis is on the development of a passive intermodulation source localisation method and on the studies of the PIM source behaviour under various impedance loading conditions. Passive intermodulation distortion can be harmful in wireless communication systems where the difference between the transmitted and the received power is large such as in GSM base stations. One of the most critical components is the antenna. As the antennas become more complex, the risk of getting excessive PIM distortion increases. Therefore, the antenna designer needs to have knowledge about the PIM phenomenon and proper tools to investigate various antenna structure configurations. The concept of PIM near-field measurement is introduced and the implementation of the equipment for the GSM 900 frequency band is presented. The performance of the scanner is analysed and demonstrated with measurements. The scanner is capable of locating PIM sources in antennas and other open structures down to −110 dBm when the transmitted power is 43 dBm. The limiting factors of the scanner sensitivity are considered and several sensitivity measurements are performed. An analysis of the impedance loading effects on PIM measurements is carried out. The conducted measurements support the theory that the loading impedance effects can be several decibels, when the source or load return loss is less than 20 dB, which is the case with many filters and antennas used in base stations. Dual-polarised antenna elements are needed in various array antenna applications. Two compact antenna element designs with moderate bandwidth and dual polarisation are introduced in the 12 GHz frequency band. The elements use a dual-resonant structure in order to achieve an impedance bandwidth of 16 % (Lretn > 10 dB). The arrangement of the antenna feeds results in an isolation of 35 dB between the ports.reviewe

    Phased Array Antenna System Enabled by Liquid Metal Phase Shifters

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    Investigation into nonlinearity of frequency agile antennas

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    A series of investigations were undertaken to assess the tuning range, gain and linearity of frequency reconfigurable varactor loaded patch antennas with design frequencies ranging from 1.4 – 1.8GHz. These parameters were assessed using simulation and measurements, including two-tone testing of the fabricated antennas in an anechoic chamber. To understand the effects of the antenna’s design on tunability, gain and linearity, six separate investigations were undertaken. These were (i) effects of design frequency and antenna substrate properties (ii) location of varactors on the antenna (iii) number of varactors loading antenna (iv) use of abrupt and hyperabrupt varactor (v) use of common cathode configurations (vi) use of common cathode configuration with parasitic patches with U-slots cut outs. It was found that the greater the area reduction in a patch, compared to a patch with no varactor, the greater tunability achieved. The reduction of a patch size from varactor loading decreases the gain of the antenna. Increasing the number of varactors on the patch improves linearity and tunability. Using a common cathode configuration of varactors on the radiating edge of an antenna maintains tunability while improving the linearity. These findings led to a novel type of antenna that uses the common cathode configuration of varactors with parasitic patches with U-slot cut outs to maintain gain across the frequency band whilst maintaining linearity and tunability

    Nonlinear characterisation of reconfigurable antennas

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    The lack of references on nonlinearity issue faced in reconfigurable antennas has motivated the work described in this thesis. The nonlinear behaviour is caused by active switches introduced on the radiating structure of the reconfigurable antennas. Depending on the type of active switches deployed on the antenna, the nonlinearity could be severe, which could have serious implications for antenna operation. Thus, the issue of nonlinearity in reconfigurable antennas should not be ignored and nonlinearity measurements should be performed to ensure the nonlinear performance is within an acceptable level. A set of nonlinearity measurements has been identified and performed on the proposed reconfigurable PIFAs. Prototypes are presented with PIN diode and E-PHEMT switches. For the purpose of comparison, measurements were also made with the active switch replaced with a copper bridge for linear interconnection. The nonlinearity performance can be evaluated from the measurement values of third-order intermodulation distortion (IMD3) products, ratio of IMD3 products to carrier, IMD3 products asymmetry, third-order input intercept point (IIP3) and 1-dB gain compression point (P1_1−_-d_dB_B). The measurements are performed when the antenna is transmitting signals. All measurements are performed on the state-of-the-art, 4-port ZVA67 Rohde & Schwarz VNA. Based on the nonlinearity measurements, it can be concluded that the presence of active switches has compromised the nonlinearity of the reconfigurable antennas. This is evident from the appearance of strong IMD3 products at the frequency of interest. In addition, the power-series-based approximation of 10 dB difference between the measured P1_1−_-d_dB_B and IIP3 is shown to be reasonable. Moreover, this work has demonstrated that the ratio of the IMD3 products to carrier does not vary significantly with radiation angles

    Autonomous smart antenna systems for future mobile devices

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    Along with the current trend of wireless technology innovation, wideband, compact size, low-profile, lightweight and multiple functional antenna and array designs are becoming more attractive in many applications. Conventional wireless systems utilise omni-directional or sectored antenna systems. The disadvantage of such antenna systems is that the electromagnetic energy, required by a particular user located in a certain direction, is radiated unnecessarily in every direction within the entire cell, hence causing interference to other users in the system. In order to limit this source of interference and direct the energy to the desired user, smart antenna systems have been investigated and developed. This thesis presents the design, simulation, fabrication and full implementation of a novel smart antenna system for future mobile applications. The design and characterisation of a novel antenna structure and four-element liner array geometry for smart antenna systems are proposed in the first stage of this study. Firstly, a miniaturised microstrip-fed planar monopole antenna with Archimedean spiral slots to cover WiFi/Bluetooth and LTE mobile applications has been demonstrated. The fundamental structure of the proposed antenna element is a circular patch, which operates in high frequency range, for the purpose of miniaturising the circuit dimension. In order to achieve a multi-band performance, Archimedean spiral slots, acting as resonance paths, have been etched on the circular patch antenna. Different shapes of Archimedean spiral slots have been investigated and compared. The miniaturised and optimised antenna achieves a bandwidth of 2.2GHz to 2.9GHz covering WiFi/Bluetooth (2.45GHz) and LTE (2.6GHz) mobile standards. Then a four-element linear antenna array geometry utilising the planar monopole elements with Archimedean spiral slots has been described. All the relevant parameters have been studied and evaluated. Different phase shifts are excited for the array elements, and the main beam scanning range has been simulated and analysed. The second stage of the study presents several feeding network structures, which control the amplitude and phase excitations of the smart antenna elements. Research begins with the basic Wilkinson power divider configuration. Then this thesis presents a compact feeding network for circular antenna array, reconfigurable feeding networks for tuning the operating frequency and polarisations, a feeding network on high resistivity silicon (HRS), and an ultrawide-band (UWB) feeding network covering from 0.5GHz to 10GHz. The UWB feeding network is used to establish the smart antenna array system. Different topologies of phase shifters are discussed in the third stage, including ferrite phase shifters and planar phase shifters using switched delay line and loaded transmission line technologies. Diodes, FETs, MMIC and MEMS are integrated into different configurations. Based on the comparison, a low loss and high accurate Hittite MMIC analogue phase shifter has been selected and fully evaluated for this implementation. For the purpose of impedance matching and field matching, compact and ultra wideband CPW-to-Microstrip transitions are utilised between the phase shifters, feeding network and antenna elements. Finally, the fully integrated smart antenna array achieves a 10dB reflection coefficient from 2.25GHz to 2.8GHz, which covers WiFi/Bluetooth (2.45GHz) and LTE (2.6GHz) mobile applications. By appropriately controlling the voltage on the phase shifters, the main beam of the antenna array is steered ±50° and ±52°, for 2.45GHz and 2.6GHz, respectively. Furthermore, the smart antenna array demonstrates a gain of 8.5dBi with 40° 3dB bandwidth in broadside direction, and has more than 10dB side lobe level suppression across the scan. The final stage of the study investigates hardware and software automatic control systems for the smart antenna array. Two microcontrollers PIC18F4550 and LPC1768 are utilised to build the control PCBs. Using the graphical user interfaces provided in this thesis, it is able to configure the beam steering of the smart antenna array, which allows the user to analyse and optimise the signal strength of the received WiFi signals around the mobile device. The design strategies proposed in this thesis contribute to the realisation of adaptable and autonomous smart phone systems

    Phased Array Antenna System Enabled by Liquid Metal Phase Shifters

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    This paper introduces a proof of concept design for the first phased array antenna design enabled by liquid metal (LM) technology. The proposed LM phased array antenna system is based on substrate integrated waveguides (SIW) to excite an 1×4 printed dipole antenna array. To effectively control the phase distribution on SIW power dividers, the liquid metals performed as a shorting pin along the body of the SIW are implemented. The proposed LM integrated SIW structure enables a large-phase tuning ratio of 360°. This new LM based phase shifters perform stable, low loss and wideband performance for the phased antenna array. In addition, a reconfigurability of the phase controls on the proposed phased antenna array can be realized when the LMs are filled in and out on the designated vias on the SIWs. To validate the proposed antenna array, simulation and measurement are carried out in this work. A prototype of the proposed LM phased array antenna operates at 10 GHz is measured, which confirms the array can have a 12% impedance bandwidth and the maximum gain of 8.3dBi with the scanning range of ±38° along the end-fire direction. This proposed technology is reliable and cost-effective for wideband phased array application

    Strontium titanate based films for tunable device applications

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    Doutoramento em CiĂȘncia e Engenharia de MateriaisO SrTiO3 (ST) cristaliza com a estrutura da perovesquite e apresenta propriedades de um paraelĂ©ctrico quĂąntico; isto Ă©, exibe um aumento continuo da permitividade dielĂ©ctrica com o decrĂ©scimo da temperatura atĂ© 4K, seguido de um patamar de valor constante atĂ© cerca de 0K. A presença de imperfeiçÔes na rede, tais como defeitos pontuais, impurezas e tensĂ”es podem modificar apreciavelmente as propriedades do ST puro e mesmo induzir ferroelectricidade. Neste trabalho foi conduzido um estudo sistemĂĄtico da estrutura, microestrutura e comportamento dielĂ©ctrico de filmes finos nĂŁo dopados e dopados de ST policristalino preparados por sol gel e depositados sobre diferentes substratos. As propriedades dielĂ©ctricas foram estudadas numa gama alargada de temperatura e frequĂȘncia do campo elĂ©ctrico. A caracterização dielĂ©ctrica dos filmes foi efectuada em função da temperatura e frequĂȘncia desde o regime das frequĂȘncias rĂĄdio (rf), terahertz (THz-TDS) e infra vermelho (IR). As caracterĂ­sticas cristalogrĂĄficas e microestuturais dos filmes de ST foram analisadas por difracção de raios X (DRX), espectroscopia de Raman, microscopia electrĂłnica de varrimento (SEM) e de transmissĂŁo (TEM), espectroscopia de Rutherford Backscattering (RBS). Foi feito um estudo detalhado da dinĂąmica de rede destes materiais. É mostrado neste trabalho que filmes finos de ST nĂŁo dopados e crescidos em diferentes substratos (Al2O3/Pt, Si/SiO2/TiO2/Pt, (LaAlO3)0.3- (Sr2AlTaO6)0.7/Pt, SrTiO3/Pt and MgO/Pt) apresentam diferentes caracterĂ­sticas estruturais e propriedades elĂ©ctricas, directamente dependentes das tensĂ”es criadas nos filmes. Nos grĂŁos dos filmes de ST depositados sobre substratos de MgO/Pt devido Ă s elevadas tensĂ”es compressivas originadas pelo substrato observam-se deslocaçÔes do tipo “slip band dislocations”, Enquanto que o modo TO1 de filmes de ST depositados sobre Al2O3 se comporta de maneira muito semelhante aos cristais de ST na gama de temperatura entre 300K e 150K, o modo TO1 dos filmes de ST depositados sobre substratos de MgO apresenta-se endurecido, o que se pode explicar pela influĂȘncia das tensĂ”es geradas nos filmes pelo substrato. Filmes de ST com as tensĂ”es compressivas mais elevadas, depositados sobre substratos de MgO/Pt exibem os valores mais elevados da parte real da permitividade dielĂ©ctrica (Δâ€Č), a maior resposta histerĂ©tica da polarização em função do campo elĂ©ctrico aplicado e os maiores valores da sintonabilidade dielĂ©ctrica (nr), em oposição aos filmes de ST, depositados sobre substratos de Al2O3/Pt com as tensĂ”es tractoras mais elevadas. Neste trabalho Ă© tambĂ©m salientada a importĂąncia dos aspectos tecnolĂłgicos da preparação por sol gel, na qualidade dos filmes finos de ST, que se reflecte nos valores elevados de Δâ€Č and nr, que sĂŁo obtidos por pela introdução de camadas intermĂ©dias tampĂŁo (buffer layers) e pelo aumento da temperatura de queima de 750o C para 900o C. Com base em previsĂ”es teĂłricas, de que o deslocamento de iĂ”es de pequenas dimensĂ”es (“off centre”) como o Mg, nos locais dos iĂ”es Sr da rede induzem uma anomalia na resposta dielĂ©ctrica do ST, foi estudada a incorporação de Mg na rede dos filmes de ST. Foi observado que o limite de solubilidade sĂłlida de Mg na rede de ST Ă© dependente do local da rede no qual ocorre a incorporação do dopante e da temperatura do tratamento tĂ©rmico. Aumentando a temperatura do tratamento tĂ©rmico decresce a solubilidade do magnĂ©sio nos filmes de Sr1-xMgxTiO3 de x > 0.30 a 750o C para x < 0.15 a 900o C. De acordo com este estudo, o Mg nĂŁo induz um estado ferroelĂ©ctrico nem um comportamento do tipo relaxor em filmes finos de titanato de estrĂŽncio preparados por sol gel, quer quando a substituição ocorre nos locais A ou B da rede do ST. A estrutura, dinĂąmica de rede e propriedades dielĂ©ctricas de filmes finos de ST dopados com Bi sĂŁo tambĂ©m apresentados neste trabalho e discutidos pela primeira vez. Nos filmes de Sr1-1.5xBixTiO3 o modo TO1 torna-se mais duro e independente da temperatura e uma relaxação a baixas frequĂȘncias aparece com o aumento do conteĂșdo de Bi. A posição do mĂĄximo de Δâ€Č dos filmes estudados desloca-se para temperaturas mais altas com o aumento da concentração de Bi e com o aumento da frequĂȘncia. A presença de “clusters” de dimensĂ”es nanomĂ©tricas e dos iĂ”es de Bi em posição “off centre” causa uma relaxação dielĂ©ctrica complexa. A relaxação dielĂ©ctrica induzida segue, a lei de Arrhenius para as amostras com baixo teor de Bi (x < 0.04), e a relação de Vogel-Fulcher para as amostras com as concentraçÔes de dopante mais elevadas (0.04 ≀ x ≀ 0.167). A dispersĂŁo da frequĂȘncia de Δâ€Č em filmes finos de Sr1-1.5xBixTiO3 com pequenos teores de Bi Ă© ligeiramente suprimida, quando em comparação com os cerĂąmicos correspondentes, o que pode ser explicado pela influĂȘncia do substrato no caso dos filmes finos. Este estudo ilustra que a incorporação de Bi na rede de ST origina um comportamento do tipo relaxor, aumentando a tunabilidade dielĂ©ctrica. Filmes finos de Sr1-1.5xBixTiO3 com elevados factores de qualidade (> 2000 numa gama de temperatura alargada) sĂŁo candidatos apropriados para utilização em sintonizadores.SrTiO3 (ST), crystallizing in the perovskite type structure, is a quantum paraelectric, i.e., it exhibits a continuous increase of the dielectric permittivity with decreasing temperature down to 4K, followed by the levelling off of the permittivity to near 0K. The presence of lattice imperfections such as strain, point defects, grain boundaries, and impurity atoms can appreciably modify the properties of pure ST and even induce ferroelectricity. In this work, systematic research on the structure, microstructure and dielectric behaviour of polycrystalline SrTiO3 - based thin films prepared by solgel is performed. The dielectric properties are studied in a wide temperature, frequency and electric field ranges. For some films the dielectric characterisation is assessed at radio-frequency (rf), time-domain terahertz (THz-TDS), and infrared (IR) spectroscopy. The crystallographic and micro structures of the undoped and doped ST films are analysed by X-ray diffraction (XRD), Raman spectroscopy, scanning and transmission electron microscopy (SEM and TEM) and Rutherford Backscattering Spectrometry (RBS) techniques. Detailed investigations of the lattice dynamics in a wide frequency range is undertaken as well. It was observed, that undoped ST films grown on different substrates (Al2O3/Pt, Si/SiO2/TiO2/Pt, (LaAlO3)0.3-(Sr2AlTaO6)0.7/Pt, SrTiO3/Pt and MgO/Pt) have different structural and dielectric properties dependent on the strain/stress effect induced by the substrate. For the case of ST films on MgO substrates the appearance of some “slip band dislocations” within the film grains was detected due to the high compressive stresses from the substrate. Whereas TO1 mode of ST films deposited on Al2O3 behaves similarly to that of ST single crystals in the temperature range from 300K to 150K. TO1 mode of ST films deposited on MgO substrate is stiffened, what can also be explained by influence of the stresses. ST films, with the highest compressive stress, deposited on MgO/Pt substrate shows the highest value of the real part of the dielectric permittivity (Δâ€Č), the largest hysteresis loop, and the highest value of the dielectric tunability (nr) in opposition to ST films, with the highest tensile stress, deposited on Al2O3/Pt substrates. The role of the technological aspects associated with the preparation of highquality sol-gel ST films is reflected in the elevated Δâ€Č and nr of ST films, obtained by introducing buffer layers, intermediately annealed at 600o C, and by increasing films annealing temperature from 750o C to 900o C. As a consequence Δâ€Č and nr of ~700 and ~50% are attained, being among the highest values reported for ST sol gel based films. Based on the theoretical prediction, that the off-centre displacements of small Mg ions at the large Sr sites can induce dielectric anomalies in ST, the incorporation of Mg in ST films was addressed in this work. Solid solubility limit of Mg was found to depend on the lattice site of incorporation and annealing temperature. Increasing annealing temperature decreases the solubility in Sr1-xMgxTiO3 thin films from x > 0.30 for 750o C to x < 0.15 at 900o C. Moreover Mg does not induce ferroelectricity or relaxor-like behaviour in strontium titanate, either located in A- or B-site of the SrTiO3 lattice. Within this work, the structure, low temperature lattice dynamics and dielectric properties of Bi doped ST films are described and discussed for the first time. In Sr1-1.5xBixTiO3 films TO1 mode becomes harder and, concomitantly a temperature independent and low-frequency relaxation appears with increasing of Bi content. The position of the maximum of Δâ€Č of the investigated films shifts to high temperatures with increasing Bi content and frequency. The presence of nanoclusters and off-centred Bi ions causes a complex relaxation dynamics in these films. The induced dielectric relaxation follows the Arrhenius law for the samples with low Bi content (x < 0.04) and the Vogel-Fulcher law for the samples with a higher doping concentration (0.04 ≀ x ≀ 0.167). The frequency dispersion of Δâ€Č in Sr1-1.5xBixTiO3 thin films with small amount of the Bi is slightly suppressed, compared to the corresponding ceramics, what can be explained by the influence of substrate. Bi incorporation in ST lattice leads to a relaxortype dielectric response, increasing the dielectric tunability. Sr1-1.5xBixTiO3 thin films with high value of the quality factor (> 2000 in wide temperature range) are appropriate candidates for using in tunable applications

    Reconfigurable electronics based on metal-insulator transition:steep-slope switches and high frequency functions enabled by Vanadium Dioxide

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    The vast majority of disruptive innovations in science and technology has been originated from the discovery of a new material or the way its properties have been exploited to create novel devices and systems. New advanced nanomaterials will have a lasting impact over the next decades, providing breakthroughs in all scientific domains addressing the main challenges faced by the world today, including energy efficiency, sustainability, climate and health. The electronics industry relied over the last decades on the miniaturization process based on the scaling laws of complementary metal-oxide semiconductors (CMOS). As this process is approaching fundamental limitations, new materials or physical principles must be exploited to replace or supplement CMOS technology. The aim of the work in this thesis is to propose the abrupt metal-insulator transition in functional oxides as a physical phenomenon enabling new classes of Beyond CMOS devices. In order to provide an experimental validation of the proposed designs, vanadium dioxide (VO2) has been selected among functional oxides exhibiting a metal-insulator transition, due to the possibility to operate at room temperature and the high contrast between the electrical properties of its two structural phases. A CMOS-compatible sputtering process for uniform large scale deposition of stoichiometric polycrystalline VO2 has been optimized, enabling high yield and low variability for the devices presented in the rest of the thesis. The high quality of the film has been confirmed by several electrical and structural characterization techniques. The first class of devices based on the MIT in VO2 presented in this work is the steep-slope electronic switch. A quantitative study of the slope of the electrically induced MIT (E-MIT) in 2-terminal VO2 switches is reported, including its dependence on temperature. Moreover, the switches present excellent ON-state conduction independently of temperature, suggesting MIT VO2 switches as promising candidates for steep-slope, highly conductive, temperature stable electronic switches. A novel design for the shape of the electrodes used in VO2 switches has been proposed, targeting a reduction in the actuation voltage necessary to induce the E-MIT. The electrothermal simulations addressing this effect have been validated by measurements. The potential of the MIT in VO2 for reconfigurable electronics in the microwave frequency range has been expressed by the design, fabrication and characterization of low-loss, highly reliable, broadband VO2 radio-frequency (RF) switches, novel VO2 tunable capacitors and RF tunable filters. The newly proposed tunable capacitors overcome the frequency limitations of conventional VO2 RF switches, enabling filters working at a higher frequency range than the current state-of-the-art. An alternative actuation method for the tunable capacitors has been proposed by integrating microheaters for local heating of the VO2 region, and the design tradeoffs have been discussed by coupled electrothermal and electromagnetic simulations. The last device presented in this work operates in the terahertz (THz) range; the MIT in VO2 has been exploited to demonstrate for the first time the operation of a modulated scatterer (MST) working at THz frequencies. The proposed MST is the first THz device whose working principle is based on the actuation of a single VO2 junction, in contrast to commonly employed VO2 metasurfaces
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