SnO2-based gas sensors have been widely synthesized and used for the detection of various hazardous gases. However, the use of doped SnO2 in sensing applications has recently attracted increased interest due to the formation of a synergistic effect between the dopant and the host. Moreover, in the case of a surface acoustic wave (SAW) sensor, the piezoelectric material used in the fabrication of the sensor plays a crucial role in defining the response of the SAW sensor. As a ferroelectric material, barium strontium titanate (Ba0.6Sr0.4TiO3) has recently been studied due to its intriguing dielectric and electromechanical properties. Its high acoustic velocity and coupling coefficient make it a promising candidate for the development of acoustic devices; however, its use as a piezoelectric material in SAW sensors is still in its infancy. In this paper, we present the design, fabrication and validation of an indium doped SnO2-based SAW gas sensor on Ba0.6Sr0.4TiO3 thin film for room temperature (RT) applications. Pulsed laser deposition was used to deposit thin films of Ba0.6Sr0.4TiO3 and indium-doped SnO2. Different characterization techniques were employed to analyze the morphology and crystallization of the films. The performance of the fabricated sensor was validated by exposing it to different concentrations of ethanol and then analyzing the recorded frequency shift. The sensor exhibited fast response (39 s) and recovery (50 s) times with a sensitivity of 9.9 MHz/Δ. Moreover, the sensor had good linear response and reproducibility. The fabricated indium-doped SnO2-based SAW gas sensor could be suitable for practical room temperature applications.

Metallic transition-metal dichalcogenides are emerging as promising electrode materials for applications such as 2D electronic devices owing to their good electrical conductivity. In this study, a high-performance humidity sensor based on NbTe2 electrode material and an indium-doped SnO2 thin film sensing layer was fabricated using a pulsed laser deposition system. The morphology, structural, elemental compositions, and electrical properties of the as-deposited samples were characterized. Additionally, the humidity sensing response of the fabricated sensor with In-doped SnO2 (8:92 wt%) sensing film was evaluated in a wide range of relative humidity at room temperature. The results demonstrated that the humidity sensor based on In-doped SnO2 exhibited a high sensitivity of 103.1 Ω/%RH, fast response and recovery times, a low hysteresis value, good linearity, and repeatability. In addition, the sensor had good long-term stability, with a variation in impedance of less than 3%. The results indicated that the humidity sensor could be suitable for practical humidity sensing applications.

A modified varactor device using Barium Strontium Titanate (Ba0.6Sr0.4TiO3) thin films for low loss millimeter wave frequency applications is demonstrated in this paper. MIM (Metal Insulator Metal) varactor devices with splits in the signal line presented in this work has >7:1 tunability for 35-50 GHz frequency range. The overall capacitance of the device changes from 0.19 pF to 0.025 pF with 0V-10V DC bias voltage applied. The device has very low insertion loss of 0.9 dB with 10 V DC bias voltage applied at 50 GHz.

This study proposed a novel sprout-shaped defected ground structure (DGS) and provided a feasible method for DGS devices to achieve tunability using a phase change material. The proposed structure has a 1.45 mm by 1.6 mm DGS size and has 13.5 dB rejection at 4 GHz for a single unit. The rejection can be enhanced to 50.2 dB by cascading two units. The fabricated device exhibits a maximum tunable range from 4.1 GHz to 6 GHz and verifies the potential of 58% tunability.

This paper explores the potential of phase change materials (PCM) for dynamically tuning the frequency response of a dumbbell u-slot defected ground structure (DGS)-based band stop filter. The DGSs are designed using co-planar waveguide (CPW) line structure on top of a barium strontium titanate (Ba0.6Sr0.4TiO3) (BST) thin film. BST film is used as the high-dielectric material for the planar DGS. Lower insertion loss of less than −2 dB below the lower cutoff frequency, and enhanced band-rejection with notch depth of −39.64 dB at 27.75 GHz is achieved by cascading two-unit cells, compared to −12.26 dB rejection with a single-unit cell using BST thin film only. Further tunability is achieved by using a germanium telluride (GeTe) PCM layer. The electrical properties of PCM can be reversibly altered by transitioning between amorphous and crystalline phases. We demonstrate that incorporating a PCM layer into a DGS device allows for significant tuning of the resonance frequency: a shift in resonance frequency from 30.75 GHz to 33 GHz with a frequency shift of 2.25 GHz is achieved, i.e., 7.32% tuning is shown with a single DGS cell. Furthermore, by cascading two DGS cells with PCM, an even wider tuning range is achievable: a shift in resonance frequency from 27 GHz to 30.25 GHz with a frequency shift of 3.25 GHz is achieved, i.e., 12.04% tuning is shown by cascading two DGS cells. The results are validated through simulations and measurements, showcasing excellent agreement.

The transport properties of W-doped thermochromic V1-xWxO2 (x=0 and 0.0074) thin films prepared by pulsed laser deposition were studied to understand the effect of doping on the electrical properties of these films. Temperature dependent magneto-transport measurements (Hall effect) in magnetic fields up to 9 Tesla were performed on thin film vanadium dioxide (VO2) across the Mott metal-insulator transition (MIT). The Hall carrier density increases by 4 orders of magnitude at MIT. The Hall mobility varies little across the MIT and remains low at ~ 0.05 cm2 /V sec. The majority carriers are electrons. Magneto-resistance is small and positive. Comparison of the three Hall parameters including carrier concentration, conductivity and mobility between various doping levels on both metallic and insulating state are reported and a model has been proposed. A correlation between carrier concentration and conductivity of VO2 films is observed but doesn’t exist between carrier concentration and mobility.

Development of high permittivity dielectrics is critical for the electrical field management in devices made with ultra-wide bandgap (UWBG) semiconductors such as <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\beta$</tex> -Ga <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> . High permittivity dielectrics are typically deposited at high temperatures and their integration with low temperature atomic-layer deposition (ALD) processed dielectrics offers a significant challenge. In this article, we studied the quality of high permittivity dielectric <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{Ba}_{\mathrm{x}}\text{Sr}_{1-\mathrm{x}}\text{TiO}_{3}$</tex> deposited using pulsed laser deposition (PLD) on ALD-grown SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> and investigated the electronic properties of this dielectric stack formed on (010) <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\beta$</tex> -Ga <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn-doped substrates. We varied the PLD deposition parameters (such as temperature and target composition) and identified conditions that can withstand an effective breakdown electric field ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$E_{eff, BD}$</tex> ; calculated in reference to SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> ) of > 30 MV/cm within the dielectric stack while maintaining low leakage ≤ 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−8</sup> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$E_{eff} &lt; 5.8-7.6\ \text{MV}/\text{cm}$</tex> . Interface defect characterization in the devices exhibited a high defect density at the SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> / <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\beta$</tex> -Ga <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> interface.

Journal Article In Operando Transmission Electron Microscopy Studies on Diffusion-Induced Phenomena at Dielectric-Electrode Interfaces in Ge2Te3-Based Memristor Devices Get access Krishnamurthy Mahalingam, Krishnamurthy Mahalingam Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB, OHUnited States Corresponding author: krishnamurthy.mahalingam.ctr@afrl.af.mil Search for other works by this author on: Oxford Academic Google Scholar Austin Shallcross, Austin Shallcross Department of Electrical and Computer Engineering, University of Dayton, Dayton, OH, United States Search for other works by this author on: Oxford Academic Google Scholar Cynthia T Bowers, Cynthia T Bowers Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB, OHUnited States Search for other works by this author on: Oxford Academic Google Scholar Derek Winner, Derek Winner Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB, OHUnited States Search for other works by this author on: Oxford Academic Google Scholar Albert Hilton, Albert Hilton Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB, OHUnited States Search for other works by this author on: Oxford Academic Google Scholar Sabyasachi Ganguli, Sabyasachi Ganguli Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB, OHUnited States Search for other works by this author on: Oxford Academic Google Scholar Eunsung Shin, Eunsung Shin Department of Electrical and Computer Engineering, University of Dayton, Dayton, OH, United States Search for other works by this author on: Oxford Academic Google Scholar Guru Subramanyam Guru Subramanyam Department of Electrical and Computer Engineering, University of Dayton, Dayton, OH, United States Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 29, Issue Supplement_1, 1 August 2023, Pages 1611–1612, https://doi.org/10.1093/micmic/ozad067.827 Published: 22 July 2023

Development of high permittivity dielectrics is critical for the electrical field management in devices made with ultra-wide bandgap (UWBG) semiconductors such as $\beta$-Ga2O3. High permittivity dielectrics are typically deposited at high temperatures and their integration with low temperature atomic-layer deposition (ALD) processed dielectrics offers a significant challenge. In this article, we studied the quality of high permittivity dielectric $\text{Ba}_{\mathrm{x}}\text{Sr}_{1-\mathrm{x}}\text{TiO}_{3}$ deposited using pulsed laser deposition (PLD) on ALD-grown SiO2 and investigated the electronic properties of this dielectric stack formed on (010) $\beta$-Ga2O3 Sn-doped substrates. We varied the PLD deposition parameters (such as temperature and target composition) and identified conditions that can withstand an effective breakdown electric field ($E_{eff, BD}$; calculated in reference to SiO2) of > 30 MV/cm within the dielectric stack while maintaining low leakage ≤ 10−8 A/cm2 at $E_{eff} < 5.8-7.6\ \text{MV}/\text{cm}$. Interface defect characterization in the devices exhibited a high defect density at the SiO2/ $\beta$-Ga2O3 interface.

Development of high permittivity dielectrics is critical for the electrical field management in devices made with ultra-wide bandgap (UWBG) semiconductors such as $\beta$ -Ga 2 O 3 . High permittivity dielectrics are typically deposited at high temperatures and their integration with low temperature atomic-layer deposition (ALD) processed dielectrics offers a significant challenge. In this article, we studied the quality of high permittivity dielectric $\text{Ba}_{\mathrm{x}}\text{Sr}_{1-\mathrm{x}}\text{TiO}_{3}$ deposited using pulsed laser deposition (PLD) on ALD-grown SiO 2 and investigated the electronic properties of this dielectric stack formed on (010) $\beta$ -Ga 2 O 3 Sn-doped substrates. We varied the PLD deposition parameters (such as temperature and target composition) and identified conditions that can withstand an effective breakdown electric field ( $E_{eff, BD}$ ; calculated in reference to SiO 2 ) of > 30 MV/cm within the dielectric stack while maintaining low leakage ≤ 10 −8 A/cm 2 at $E_{eff} < 5.8-7.6\ \text{MV}/\text{cm}$ . Interface defect characterization in the devices exhibited a high defect density at the SiO 2 / $\beta$ -Ga 2 O 3 interface.

V_1− x W_ x O_2 is known to be a reliable thermochromic material for multiple practical applications due to its insulator to metal transition temperature controlled by W dopping. In this paper, we present electrical and optical properties of V_1− x W_ x O_2 thin films synthesized by PLD technique. In this respect, the electrical resistance, the refractive index ( n ), and extinction coefficient ( k ) as a function of temperature from 25 to 80 °C and wavelength ranging from 500 to 3000 nm were obtained using conventional 4-probe resistance and ellipsometry methods. The direct and indirect bandgap values at different doping levels and temperatures have been calculated using n and k versus energy data and compared with thermally activated bandgap from electrical resistance. A decrease in direct and indirect bandgaps with temperature and wavelength was observed with doping and temperature. Comparison between thermal and optical bandgap demonstrates that activated thermal bandgap is only comparable with the lowest optical indirect bandgap. Graphical abstract

This study analyzes the effects of adding a SmScO3 (SSO) buffer layer to the sapphire substrate for barium strontium titanate (BST) thin film varactors. The varactors are fabricated on SSO buffered sapphire substrates at two different electrode and BST thicknesses. The devices are tested from 0 to 40 GHz, applying a DC bias. capacitance vs voltage, and Q vs voltage were obtained from the swept frequency scattering parameters. The study also demonstrates an overall higher tuning ratio and competitive Q for the SSO buffered devices.

V1−xWxO2 is known to be a reliable thermochromic material for multiple practical applications due to its insulator to metal transition temperature controlled by W dopping. In this paper, we present electrical and optical properties of V1−xWxO2 thin films synthesized by PLD technique. In this respect, the electrical resistance, the refractive index (n), and extinction coefficient (k) as a function of temperature from 25 to 80 °C and wavelength ranging from 500 to 3000 nm were obtained using conventional 4-probe resistance and ellipsometry methods. The direct and indirect bandgap values at different doping levels and temperatures have been calculated using n and k versus energy data and compared with thermally activated bandgap from electrical resistance. A decrease in direct and indirect bandgaps with temperature and wavelength was observed with doping and temperature. Comparison between thermal and optical bandgap demonstrates that activated thermal bandgap is only comparable with the lowest optical indirect bandgap.

Memristor devices fabricated using the chalcogenide Ge 2 Te 3 phase change thin films in a metal-insulator-metal structure are characterized using thermal and electrical stimuli in this study. Once the thermal and electrical stimuli are applied, cross-sectional transmission electron microscopy (TEM) and X-ray energy-dispersive spectroscopy (XEDS) analyses are performed to determine structural and compositional changes in the devices. Electrical measurements on these devices showed a need for increasing compliance current between cycles to initiate switching from low resistance state (LRS) to high resistance state (HRS). The measured resistance in HRS also exhibited a steady decrease with increase in the compliance current. High resolution TEM studies on devices in HRS showed the presence of residual crystalline phase at the top-electrode/dielectric interface, which may explain the observed dependence on compliance current. XEDS study revealed diffusion related processes at dielectric-electrode interface characterized, by the separation of Ge 2 Te 3 into Ge- and Te- enriched interfacial layers. This was also accompanied by spikes in O level at these regions. Furthermore, in-situ heating experiments on as-grown thin films revealed a deleterious effect of Ti adhesive layer, wherein the in-diffusion of Ti leads to further degradation of the dielectric layer. This experimental physics-based study shows that the large HRS/LRS ratio below the current compliance limit of 1 mA and the ability to control the HRS and LRS by varying the compliance current are attractive for memristor and neuromorphic computing applications.

V 1− x W x O 2 is known to be a reliable thermochromic material for multiple practical applications due to its insulator to metal transition temperature controlled by W dopping. In this paper, we present electrical and optical properties of V 1− x W x O 2 thin films synthesized by PLD technique. In this respect, the electrical resistance, the refractive index ( n ), and extinction coefficient ( k ) as a function of temperature from 25 to 80 °C and wavelength ranging from 500 to 3000 nm were obtained using conventional 4-probe resistance and ellipsometry methods. The direct and indirect bandgap values at different doping levels and temperatures have been calculated using n and k versus energy data and compared with thermally activated bandgap from electrical resistance. A decrease in direct and indirect bandgaps with temperature and wavelength was observed with doping and temperature. Comparison between thermal and optical bandgap demonstrates that activated thermal bandgap is only comparable with the lowest optical indirect bandgap. Graphical abstract

High-quality, phase-change vanadium dioxide (VO2), and tungsten (W)-doped VO2 thin films were synthesized using a pulsed laser deposition system and comprehensively studied using structural, electrical, microwave, and optical measurements. The nanostructures and compositions were characterized using X-ray diffraction, Rutherford backscattering, scanning electron microscopy, X-ray photoelectron spectroscopy, and high-angle annular dark-field images recorded in a scanning transmittance electron microscope. The electrical resistivity ratio was in the order of 104 and the microwave transmission ratio was greater than 25 dB between the insulating and metallic states. Additionally, the measured complex refractive indices obtained from ellipsometry were comparable to the values reported in the literature. Moreover, the films preheated to 50°C exhibited switching times in the order of milliseconds between the insulating and metallic states.

In this paper, a tunable spiral inductor integrated with vanadium dioxide (VO2) thin film on coplanar waveguide (CPW) transmission line is proposed. The tunable inductance is achieved by using the reversible, thermally controlled VO(2)thin film. VO(2)is one of metal to insulator phase transition (MIT) materials, which can be a potential solution for reconfigurable RF/microwave wireless communication systems. The VO(2)based tunable inductors were fabricated on the sapphire substrate. A model is used to study the fingerprints of MIT and verify the nature of transition in the film. The scattering parameter measurements are taken in the frequency range from 10 MHz to 8 GHz with 801 points. The equivalent circuits have been used to characterize the behavior of tunable inductors and extract the equivalent component values, which show excellent matching to the measured S parameters. The measured results have shown an inductance tunability of 35.24% (3.856 nH-2.498 nH) at 4 GHz.