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The epitaxial, single phase (100) Ba_0.5Sr_0.5TiO₃ (BST) films with thin interfacial layer of BST (x=0.4) were deposited on LAO (100) substrates using Pulse Laser Deposition (PLD). These films were characterized in terms of their phase formation and structural growth characteristics using X-ray diffraction and Atomic Force Microscopy respectively. The dielectric properties are strongly affected by the substrate type, post deposition annealing time, and temperature. In order to verify all these properties, thin interfacial-buffer layers of BST (10, 20, 50 nm) were introduced to relieve the stress induced between the film and the substrate. The variations of dielectric constant and ferroelectric properties of as deposited films are discussed in detail. The high tunability, low dielectric loss and low leakage current of these films make them attractive candidates for fabricating tunable dielectric devices. The observed dielectric properties of the BST-films are attributed to homo-epitaxial interfacial layer, which is responsible for the increase in the dielectric constant and tunability.

In this paper, a brief review on reversible dielectric nonlinearity (RDN) was presented and the mechanism of tunability for ferroelectric ceramics was discussed in several different scale levels, such as atomic level (intrinsic nonlinearity described by ferroelectric thermodynamic theory), nano-meter scale (polar nano-region response), submicron scale (ferroelectric domain and domain wall motion), micron scale (polycrystalline structure of ceramics and surface layer) and macroscopic scale (field induced phase transition). It suggests that RDN is a multi-scale phenomenon and is temperature and frequency-sensitive. The halving field E₀ in Roberts' Equation may be a good attempt for the quantitating of RDN. The stability of RDN in paraelectric phase is also mentioned.

Microfabrication of tunable negative refraction materials used in many experimental studies currently relies on the change of the component or the geometrical structure. We theoretically demonstrate magnetically controlled negative permeability in the composite composed of magnetic nanowires (N_i). A magnetic-field-dependent permeability was clearly observed by changing the applied magnetic field, which directly proves the tunable feature of the composite with a small external magnetic field. The simulation results suggest that magnetic nanowires composite can be an alternative route to realizing tunable negative refraction.

In order to investigate the effect of argon introduction on the structural and physical properties of Ba_0.6Sr_0.4TiO₃ (BST) films, epitaxial BST films have been grown by pulsed laser deposition (PLD) on (001) oriented Nb-SrTiO₃ (STON) substrates in the ambient gas of pure oxygen and the mixture of argon and oxygen, respectively. The atomic force microscopy (AFM) reveals that the sample deposited in the mixture of argon and oxygen has a bigger grain size than that deposited in pure oxygen. The dielectric properties of two BST films have been investigated using the Pt/BST/STON parallel plate capacitors. The tunability and the figure of merit (FOM) of the BST film deposited in the mixture gas are about 41% and 7.07 at a DC bias voltage of 8 V at room temperature, which are better than 32% and 4.51, for BST film deposited in pure oxygen. On account of the introduction of argon, the leakage current density of the BST film deposited in the mixture gas has fallen by almost five times, and the leakage current mechanism is both in accordance with ohmic conductive mechanism.

A novel scheme for tunable optofluidic optical coupler is proposed by combining directional coupling waveguide structures with microfluidic channel. The normalized optical power at two output ports can be dynamically manipulated by controlling the refractive index of liquid mixture in microfluidic channel. Its optical performance is numerically investigated by employing the beam propagation method (BPM). The simulated results show that the dynamic range of over 45 dB, and optical loss of below 0.06 dB can be easily achieved, and furthermore the dependence of polarization states and operation wavelength in the range from 1500 nm to 1600 nm are very low in our designed device. In addition, the tunable optofluidic coupler has advantages including simple structure and large fabrication tolerance. Accordingly, our proposed device offers a new approach for manipulating optical power output, which has wide potential application in optofluidic systems.

In this paper, a new quadrature oscillator employing two dual output second-generation current conveyors (DO-CCIIs), two resistors and two grounded capacitors is proposed. The proposed quadrature oscillator has only resistors but no capacitors connected in series to $X$ terminals of the DO-CCIIs; thus, it can be operated at high frequencies. It can be tuned electronically by replacing dual output second-generation current controlled current conveyors instead of DO-CCIIs and removing both resistors. It can provide two output currents in opposite sign. Nevertheless, its resonance frequency can be simultaneously controlled by two resistors. Also, a dual output differential voltage current conveyor (DO-DVCC) based quadrature oscillator which employs a canonical number of only grounded passive components is proposed. A number of simulation results based on SPICE program and an experimental test result are included to exhibit performance, workability and effectiveness of the proposed quadrature oscillators.

In this paper, a novel complementary metal-oxide semiconductor (CMOS) transistors based first-order voltage-mode all-pass filter is proposed. The filter circuit employs six metal-oxide semiconductor (MOS) transistors and minimal number of passive components, i.e., a resistor and a capacitor. The core of the proposed filter is a CMOS inverting amplifier with unity gain. The proposed circuit exhibits some attractive features such as compact design, high input impedance and ability to provide non-inverting and inverting all-pass responses simultaneously. Additionally, it does not require any kind of passive element matching constraints. Furthermore, by replacing the passive resistor with an active negative channel metal-oxide semiconductor (NMOS) transistor, the proposed filter is enriched with the much-desired feature of tunability. The theoretical behavior is tested and demonstrated by carrying SPICE simulations using TSMC 0.18$\mu$m level-7 CMOS process parameters.

This paper suggests a new operational transconductance amplifier (OTA) based electronically tunable transimpedance-mode first-order universal filter (FOUF). The suggested FOUF produces all-pass (AP), high-pass (HP) and low-pass (LP) filter responses simultaneously. It employs three OTAs, two grounded resistors and only one grounded capacitor. Owing to use of grounded passive elements, the suggested FOUF is suitable for integrated circuit implementation. It operates at low power supply voltages. Additionally, the resonance frequency of the suggested AP filter can be adjusted in a wide frequency range. However, the suggested FOUF consists of only one matching condition. Moreover, a sinusoidal quadrature oscillator (QO) application that is derived from the suggested FOUF topology is given. The suggested FOUF and its QO application are simulated by using 0.18-$\mu$m TSMC technology parameters in the SPICE program to validate the presented theory. Finally, an experimental test is performed to demonstrate workability of the suggested AP filter.

Active tuning of elastic wave band gaps received significant attention in the recent past. To this end, soft dielectric elastomers (DEs) have indicated great promise owing to their capability to undergo large reversible deformations and deformation-dependent constitutive properties. In this paper, we investigate the longitudinal wave band gaps an infinite periodic soft functionally graded dielectric elastomer subjected to electro-mechanical biasing fields. Material properties of the functionally graded DE are described by the power law. The nonlinear hyperelastic compressible neo–Hookean model is employed for characterizing the constitutive behavior of the soft functionally graded dielectric elastomer. The finite element method with Bloch–Floquet theory is employed for finding the band-structure of the infinitely periodic soft functionally graded DE structure. A parametric study brings out the effect of biasing fields and power law exponent on the band gap characteristics. The biasing mechanical prestress, the electric displacement field show significant influence on position and the width of band gaps. The inferences reported here can find their potential use in the design of soft DE wave devices with tunable band structures.

We have systematically studied the dielectric properties of epitaxial barium strontium titanate, Ba_1-xSr_xTiO₃(x = 0.0, 0.1, 0.2, …, 1.0), films on MgO substrates grown by pulsed laser deposition. The dielectric properties of Ba_1-xSr_xTiO₃ films at a frequency of 1 MHz and room temperature are a strong function of Ba/Sr ratio. The degree of electric field dependent dielectric constant is more pronounced with decrease of x values. The largest dielectric tunability and the figure of merit (or tunability/loss) are obtained at x = 0.3 and at x = 0.4, respectively.

Ba(Sn_0.02Ti_0.98)O₃ thin films (BTS) were prepared by sol-gel route and deposited by spin-coating on commercial Pt/Ti/SiO₂/Si substrates. By modifying the annealing conditions from 750°C for 1 h to 950°C for 15 min, the grain size increased from 60 nm to 110 nm due to the increased driving force. The dielectric permittivity ε′ and tunability n_r are correlated with the grain size: these parameters increase with the grain size. At room temperature for the BST film annealed at 950°C, a record value of 76% of tunability is obtained at 10 kHz. This very high value of tunability makes BaSnTiO₃ a very good candidate for tunable devices.

Contrast with conventional dielectric tunable materials such as barium strontium titanate (BST), here, we report one new dielectric tunable behavior for Sr_1-xPr_xTiO₃ system at low temperature. Giant dielectric tunability is confirmed in this system. More importantly, the efficient dielectric tunability can be realized just using small bias field. In addition, critical threshold electric field is also confirmed. This phenomenon may be related with the competition interaction of polar state with quantum fluctuations.

Ba(Sn_0.02Ti_0.98)O₃ thin films (BTS) were prepared by sol–gel route and deposited by spin-coating on commercial Pt/Ti/SiO₂/Si substrates. By modifying the annealing conditions from 750°C at 1 h to 950°C at 15 min, the relative tunability n_r at 100°C in the paraelectric state increased from 45 to 70% while the DC dielectric permittivity ε′(0) increased as well. The evolutions of ε′(E) and n_r(E) are explained from Devonshire thermodynamic formalism. The very high value of tunability of 70% is explained by the grain size increase of our BTS thin films and the decrease of the dead layer effect when the annealing conditions are optimized.

Misfit strain, lattice parameter, polarization, permittivity, and tunability of Ba${}_{0.6}$Sr${}_{0.4}$TiO₃ thin films onto Ba${}_x$Sr_1−xTiO₃-buffered stainless steel (SS) substrates are computed via a modified phenomenological model. When the Ba/Sr ratio of Ba${}_x$Sr_1−xTiO₃ buffer layer grows, the permittivity and tunability first increase and then decrease with the maximum at $x$ = 0.75. The highest tunability of such films prepared by the sol-gel technique can reach 32.5% at the electric field of 320 kV/cm when $x$ = 0.8. The strains are qualitatively analyzed through combining XRD, Raman, and theoretical calculation. The computed data are generally supported by experimental lattice parameters, permittivities, and tunabilities, which show that polycrystalline BST thin films with smaller compressive strain obtain higher dielectric response, and that inserting buffer layer could regulate the strains and dielectric properties of BST thin films.

Ba(Mg${}_{1∕3}$Nb${}_{2∕3})$O₃ (BMN) doped and undoped Ba${}_{0.45}$Sr${}_{0.55}$TiO₃ (BST) thin films were deposited via radio frequency magnetron sputtering on Pt/TiO₂/SiO₂/Al₂O₃ substrates. The surface morphology and chemical state analyses of the films have shown that the BMN doped BST film has a smoother surface with reduced oxygen vacancy, resulting in an improved insulating properties of the BST film. Dielectric tunability, loss, and leakage current (LC) of the undoped and BMN doped BST thin films were studied. The BMN dopant has remarkably reduced the dielectric loss ($\sim$38%) with no significant effect on the tunability of the BST film, leading to an increase in figure of merit (FOM). This is attributed to the opposing behavior of large Mg${}^{2+}$ whose detrimental effect on tunability is partially compensated by small Nb${}^{5+}$ as the two substitute Ti${}^{4+}$ in the BST. The coupling between ${\text{Mg}}_{\mathrm{\text{Ti}}}^{″}$ and V${}_{\mathrm{\text{O}}}^{••}$ charged defects suppresses the dielectric loss in the film by cutting electrons from hopping between Ti ions. The LC of the films was investigated in the temperature range of 300–450K. A reduced LC measured for the BMN doped BST film was correlated to the formation of defect dipoles from ${\text{Mg}}_{\mathrm{\text{Ti}}}^{″}$, V${}_{\mathrm{\text{O}}}^{••}$ and Nb${}_{\mathrm{\text{Ti}}}^{•}$ charged defects. The carrier transport properties of the films were analyzed in light of Schottky thermionic emission (SE) and Poole–Frenkel (PF) emission mechanisms. The result indicated that while the carrier transport mechanism in the undoped film is interface limited (SE), the conduction in the BMN doped film was dominated by bulk processes (PF). The change of the conduction mechanism from SE to PF as a result of BMN doping is attributed to the presence of uncoupled Nb${}_{\mathrm{\text{Ti}}}^{•}$ sitting as a positive trap center at the shallow donor level of the BST.

The influence of temperature on the dielectric properties of sol-gel routed spin-coated molybdenum trioxide (MoO${}_3)$ thin film has been investigated. Prepared films were annealed at temperatures 250${}^{\circ }$C, 350${}^{\circ }$C and 400${}^{\circ }$C. The phase transformation from amorphous to $\alpha$-orthorhombic phase with preferential orientation (0 2 2) has been found by XRD for the film annealed above 250${}^{\circ }$C. The vibration modes of $\alpha$-orthorhombic MoO₃ have been examined by Raman spectrum. The predominant Raman’s band of $\alpha$-orthorhombic MoO₃ thin film has been found at the frequency range 1000–600cm${}^{-1}$. Using the UV–Vis spectrum, the band gap of the film is found to be 3.3–3.8eV. The surface morphology of the MoO₃ films has been examined by scanning electron microscope. The AC conductivity measurement of the MoO₃ film has been carried out in the frequency range 10–10⁶ Hz. The frequency dependence of the impedance has been plotted in the complex plane. The variation of the capacitance and dielectric constant of MoO₃ film with respect to temperature and frequency has been analyzed. Tunability of capacitance and figure of merit of the film are also determined.

In this paper, a tunableMicroElectro Mechanical Systems Nuclear Magnetic Resonance (MEMS NMR) receiver front-end, which consists of three main parts, is presented. In the first part, a proper microcoil for detecting ${}^{1}H$ and ${}^{19}F$ with complete specifications regarding the sample is optimized to get the better Signal to Noise Ratio (SNR) and quality factor (Q). In the second part, the passive network is discussed and the amounts of the desired capacitor and the desired tunability range are calculated and based on the calculations and the fabrication process, a new MEMS tunable capacitor is presented. Due to the large capacitance value of the required capacitor, the proposed capacitor has a fixed part with a capacitance value of 28pf and a variable part with a tunability range of 193% (2.25pf–6.6pf) with 1.5 A applied to a thermal actuator. A buckling effect due to the weight of the fingers of the capacitor and thermal stress after the release is analyzed and a fabrication process based on the routine processes is proposed. In the third part, a low noise amplifier (LNA) is presented for the proposed receiver with a gain of 47.6dB at the bandwidth of 384 MHz and noise figure of 0.5$nv∕\sqrt{\mathrm{\text{Hz}}}$.

In this work, modeling and investigation of surface microcoils and also the capacitor are conducted using finite element simulation in COMSOL Multiphysics and post-processing. The method for obtaining signal sensitivity and SNR of the microcoils are based on the MR signal generation by employing the principle of reciprocity.