Tunable complex oxide thin films have generated a lot of interest in recent years due to their potential to become a core technology in the new generation of multiple communications devices. These films are grown via different deposition methods and frequently postprocessed in order to enhance their dielectric properties. This paper discusses an alternative postprocessing technique where complex oxide thin films grown by radio frequency (RF) magnetron sputtering have been treated with an external microwave field instead of a conventional furnace. The treated films and untreated reference film were characterized for their microstructure and dielectric properties. The obtained results indicate a significant reduction in dielectric losses and leakage current in the microwave processed films as opposed to the untreated reference. The results are discussed together with potential additional benefits of the proposed approach.

Design, fabrication and characterization of an active single-negative metamaterial device in the terahertz (THz) spectrum is presented. The device is constructed by vertical split-ring unit cells which incorporate a Ba0.6Sr0.4TiO3 (BST) thin film whose dielectric constant can be altered by applying DC bias to change the capacitance of the split-ring resonators. A numerical model of the device that predicts a resonant frequency as a function of BST dielectric constant is presented. The resonant frequency shift due to the applied DC bias is experimentally verified and correlated with the model. The resonant frequency shift occurs as a direct result of the bias controlled index of refraction change in BST which significantly enhances the device response speed and durability compared with previously demonstrated micro-electro-mechanical systems based tunable metamaterial devices. In addition, this device can be used to characterize dielectric properties of the tunable oxide thin films in low THz spectrum (such as tunability) for many applications.

: We have developed novel metamaterial devices and metastructures with new electronic and optoelectronic (OE) properties and used them to design and fabricate devices, such as slow-light, low-loss waveguides, terahertz modulators, and wideband radio frequency (RF) antennas with new functionalities. These devices will provide basic building blocks for future chip-scale semiconductor-integrated OE circuits and provide new capabilities over a wide range of frequencies from microwaves, terahertz, and into the infrared in Command, Control, Communications, Computers, Intelligence, Surveillance and Reconnaissance systems. We focused on 3 different types of metamaterial devices as basic building blocks. These are low-loss, slow-light, hollow-core metastructure waveguides for chip-scale-integrated OE/RF photonic circuit; metamaterial devices for terahertz communication/sensing/imaging; and tunable RF metamaterials. Some of our major accomplishments in this area of study include developing and demonstrating the world s first silicon-based slow-light metastructure hollow-core waveguide, developing and demonstrating new tunable terahertz metamaterial devices, and designing and fabricating terahertz metastructure hollow-core waveguide. The DSI project has resulted in 14 publications, 1 US patent, 1 invention disclosure, and 1 press release.

SrTiO3 (STO) thin films were grown simultaneously via the metal organic chemical vapor deposition (MOCVD) technique on two different substrates: platinized sapphire and platinized TiO2/SiO2/Si. The thin films were analyzed for stoichiometry, crystallinity, surface roughness, and average grain size. Dielectric properties of the thin films such as dielectric constant, loss, and leakage current characteristics were measured and compared. We demonstrate that the MOCVD technique is an appropriate method for fabrication of STO thin films with excellent structural, microstructural, dielectric, and insulation properties. Comparative analysis of the films yielded an unexpected result that the thin film with a higher mismatch in thermal expansion coefficient between the substrate (Si) and the deposited STO film yielded a higher dielectric constant with respect to that of STO/sapphire. The dielectric loss for both films were similar (tan δ = 0.005 at 100 kHz), however, the leakage current for the film with a higher dielectric constant was three orders of magnitude higher. An explanation of these results is presented and discussed.

: Barium Strontium Titanate (BST) is a complex oxide material with ferroic properties which has been considered for applications ranging from non-volatile memory to microwave tunable devices. When grown in bulk films BST forms a continuum of domains. It is theorized however, that when the material can be grown on the order of a single domain, its properties will drastically change. To exploit the ferroic properties of BST we developed a device fabrication method utilizing self-aligned etching to create metal-insulator-metal (MIM) varactors. As part of this method we employed reactive ion etching (RIE) to remove BST and create cylindrical island stacks consisting of platinum top electrodes, atop a layer of BST, atop a platinum bottom electrode film, all on top of a sapphire substrate. Here we report and compare the results of a study on using RIE to remove BST using combinations of three gas, argon (Ar), carbon tetrafluoride (CF4), and sulfur hexafluroride (SF6).

Abstract : Infrared (IR) detectors have found wide-spread use in military applications including night-vision, rifle sights, surveillance gear, and tracking and guidance systems (1). These detectors provide a means for information collection and increased situational awareness, allowing for threat identification and informed decision making. The IR sensors used in these detectors can be categorized into two classes Photon (or quantum) and Thermal depending on the physics of operation. Photon detectors operate by the creation of an electrical signal in semiconducting material produced from the electronic absorption of incoming photons, and the signal is read as a photocurrent or at a photovoltaic p-n junction. These detectors can provide high-sensitivity and fast refresh rates and are typically found in applications with high-sensitivity requirements. Unfortunately, these detectors require sub-100 K cooling to lower thermal noise for optimal performance making them both bulky and expensive (2).

In order to enhance the permittivity and tunability of the dielectric component, a thin film dielectric composite consisting of a radio frequency sputtered SrTiO3 (STO) buffer layer and metalorganic solution deposited Mg-doped BaxSr1−xTiO3 (Mg-BST) thin film overgrowth was developed using affordable industry standard processes and materials. The effect of the STO buffer layer thickness on the dielectric response of the heterostructure was investigated. Our results demonstrate that the composite film heterostructure, evaluated in the metal-insulator-metal configuration Pt/STO/Mg-BST/Pt on sapphire substrate, with the thinner (9–17 nm) STO buffer layers possessed enhanced permittivity (εr ∼ 491) with respect to the thicker 41 nm buffer layer (εr ∼ 360) and that of a control Mg-BST film without a STO buffer layer (εr ∼ 380). Additionally, the composite film with the thinner buffer layers were shown to have low losses (tan δ ∼ 0.02), low leakage characteristics (J = 7.0 × 10−9 A/cm2), high breakdown voltage (VBR > 10 V), a large grain microstructure (∼125 nm), and smooth pin-hole free surfaces. The enhanced permittivity of the composite dielectric film resulted from three major factors: (i) the template-effect of the thin STO buffer layer on the thicker Mg-BST over-layer film to achieve a large grain microstructure, (ii) the low viscosity of the metallo-organic solution deposition (MOSD) solution, which ensured heterogeneous nucleation of the Mg-BST overgrowth film on the surface of the STO buffer layer, and (iii) minimization of the low permittivity grain boundary phase (TiO2−x phase). The dielectric response of the BST can be explained using a thermodynamic model taking into account interlayer electrostatic and electromechanical interactions. Additionally, Mg doping of the BST enabled low loss and low leakage characteristics of the heterostructure. The large permittivity, low loss, low leakage characteristics, and defect free surfaces of the composite dielectric heterostructure promote tunable device miniaturization and hold the potential to enable enhanced electromagnetic coupling in ferromagnetic/high permittivity dielectric heterostructures, which in turn would facilitate the realization of integrated charge mediated voltage controlled magnetic radio frequency/microwave communication devices.

Isothermal (700 °C) ultraviolet annealing (UVA) processing of crystallized Ba0.60Sr0.40TiO3 (BST) thin films for exposure times up to 225 min films has been studied. The BST films, grown on PtSi wafers via the metalorganic solution deposition (MOSD) technique, were crystallized via conventional furnace annealing (CFA) prior to UVA treatment, and the effects of UV annealing time on the structural, dielectric, and insulation properties were evaluated. The experimental results demonstrated significantly improved structural, dielectric, and insulation properties for the UVA films. Specifically, lattice parameter contraction (toward that of bulk BST60/40) and a 20% reduction in loss were observed for the UVA treated films with respect to the CFA/control film. Leakage current characteristics were found to be the most sensitive characterization technique to access material property modification as a result of UVA exposure time. Specifically, the 225 min UVA exposure time resulted in a three-order of magnitude reduction in leakage current density compared to the CFA film, and the lowest value observed was 1.06 × 10−7 A/cm2 at E = 300 kV/cm. The useable tunability (tunability value at the maximum acceptable leakage current, 500 pA) was found to be elevated by a factor of two with respect to that of the CFA/control BST film (52.31%/UVA film vs. 18.5%/control film). It is suggested that the improved material properties are due to the mitigation of unwanted oxygen vacancies within the film after UV-annealing. A mechanistic model is presented and discussed.

The great potential of taking advantages of PZT in a single chip to achieve inexpensive, fully-integrated, passive telemetric transponders has been shown in this paper. The processes for the sputter deposition of Pb(Zr,Ti)O3 (PZT) thin films from two different composite targets on both Si and c-plane sapphire substrates have been demonstrated. PZT thin films have been deposited by sputter technique. PZT films were deposited onto substrates (Si [(100) Cz wafer] and c-plane sapphire (0001)//Ti//Pt) followed by sputter-deposited Pt top electrodes. X-ray diffraction results showed that both sputtered PZT films were textured along the [110] direction. The degree of preference for the [110] direction was greater on sapphire substrate where the intensity of that peak is seen to be larger compared to the intensity one Si substrate. TEM data revealed that both sputtered PZT films were polycrystalline in nature. Selected area diffraction (SAD) pattern showed that the degree of disorientation between the crystallites was smaller on sapphire substrate compared to on Si substrate, which confirmed the results from the XRD. The remnant polarization Pr on sapphire substrate was larger than on Si’s. The leakage current for the 11 % Pb target sputtered film was much less than 22 % Pb target sputtered film. The breakdown voltage on sapphire substrate was the best. However, for the 11 % Pb target sputtered film’s breakdown voltage was much higher than 22 % Pb target sputtered film.

We report on an innovative isothermal post-growth/crystallization process that utilizes ultraviolet (UV)-photon irradiation. We fabricated Ba1-xSrxTiO3 (BST) thin films using metalorganic solution deposition (MOSD) and UV-photon irradiation isothermal treatment via two protocols: in situ crystallized UV-photon irradiated films, and post-crystallization UV-photon irradiated films. Isothermal UV-photon irradiation treatment improves the structural quality of the BST films, and the irradiated films possessed lattice parameters close to the bulk values, which is evidence for a reduction in oxygen vacancies. MOSD fabricated BST films crystallized via conventionally furnace annealing and subsequently exposed to UV-photon irradiation possessed improved structural, dielectric, and electrical quality.

: Well formed films of pure LiMn2O4 were obtained by spin-coating stoichiometric amounts of manganese acetate Mn(CH3COOH)2.4H2O and lithium acetate Li(CH3COOH)2.4H2O dissolved in a mixture of acetic acid (CH3COOH) and 2-methoxyethanol (H3COCH2CH2OH) onto platinum coated silicon substrates. Several coats of solution were applied to reach the desired film thickness of approximately 200nm and then annealed at various temperatures ranging from 400 C to 800 C to crystallize the films into a spinel phase. The resulting films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and atomic force microscopy (AFM). In addition, electrochemical properties were determined by cyclic voltammograms measurements. At 700 C 800 C, the films exhibited distinctly improved crystallinity and the spinel grains adopted a polyhedral shape of submicron size with well-defined edges and faces, thus enhancing particle connectivity. The films were found to deliver capacities around 0.12 mAh/cm2 up to 25 cycles.

Pulsed laser direct deposit Ni2Si Ohmic contacts were successfully fabricated on n-SiC. The electrical, structural, compositional, and surface morphological properties were investigated as a function of heat treatments ranging from 700 °C to 950 °C. The as-deposited and 700 °C annealed samples were non-Ohmic. Annealing at 950 C° yielded excellent Ohmic behavior, an abrupt void free interface, and a smooth surface morphology. No residual carbon was present within the contact film or at the film-SiC interface and the contact showed no appreciable contact expansion as a result of the 950 °C annealing process. Results of this investigation demonstrate that 950 °C annealed pulse laser deposited Ni2Si-SiC contacts possess excellent electrical, interfacial, microstructural, and surface properties, which are required for reliable device operation.

Ba0.60Sr0.40TiO3 (BST) thin films, grown via RF-sputtering and the metalorganic solution deposition (MOSD) techniques, were post-growth annealed via conventional thermal annealing (CTA) and UV-photon irradiation annealing. With respect to the conventional thermal annealed films the UV-photon irradiation annealed films possessed improved structural properties and dielectric response. The optimization of the UV-photon irradiation annealing process parameters was achieved via a detailed set of isothermal-isotemporal annealing experiments. The optimized UV-process parameters, applied to MOSD and RF sputtered BST films revealed enhanced structural materials response, i.e., a reduction in lattice parameter with extended UV-annealing time up to 225 min. The improvements in the material properties of the UV-photon irradiation annealed BST thin films are attributed to the mitigation of film of stress, hence reduction in oxygen vacancies via the UV-photon irradiation annealing process.