Vladimir Vasilyev

Gold-Plated Micromachined Millimeter-Wave Resonators Based on Rectangular Coaxial Transmission Lines

Resonators based on microfabricated rectangular coaxial (recta-coax) transmission lines are presented. The resonators were fabricated using a multilayered nickel electroplating process that enables the fabrication of three-dimensional structures. As a method to improve performance, gold was plated on the resonators using an electroless process. A model for predicting the effect of the plating on a resonator quality (Q) factor is presented and verified by measurements. Measured resonators show that the plating can increase the Q factor of nickel resonators by over 50% at frequencies above 44 GHz. Utilizing gold plating, 50-Omega resonators are demonstrated at 44 and 60 GHz with unloaded Q factors of 213.1 and 242.3, respectively

Highly conductive homoepitaxial Si-doped Ga2O3 films on (010) β-Ga2O3 by pulsed laser deposition

Si-doped Ga2O3 thin films were fabricated by pulsed laser deposition on semi-insulating (010) β-Ga2O3 and (0001) Al2O3 substrates. Films deposited on β-Ga2O3 showed single crystal, homoepitaxial growth as determined by high resolution transmission electron microscopy and x-ray diffraction. Corresponding films deposited on Al2O3 were mostly single phase, polycrystalline β-Ga2O3 with a preferred (20 1 ¯ ) orientation. An average conductivity of 732 S cm−1 with a mobility of 26.5 cm2 V−1 s−1 and a carrier concentration of 1.74 × 1020 cm−3 was achieved for films deposited at 550 °C on β-Ga2O3 substrates as determined by Hall-Effect measurements. Two orders of magnitude improvement in conductivity were measured using native substrates versus Al2O3. A high activation efficiency was obtained in the as-deposited condition. The high carrier concentration Ga2O3 thin films achieved by pulsed laser deposition enable application as a low resistance ohmic contact layer in β-Ga2O3 devices.

Three dimensional micromachining for millimeter-wave circuits

Recent advances in three dimensional metal micromachining processes provide new opportunities for millimeter-wave circuit fabrication. Using these processes, enclosed transmission lines can operate to frequencies over 200 GHz, have very low crosstalk, and be routed arbitrarily. These processes also allow the integration of resonators with quality factors in excess of 500 allowing low loss filters to be fabricated at the same time as the transmission lines. Finally, the precision of the processes allows the design and realization of passive components such as cross-overs and couplers. The further development of these processes will enable highly integrated millimeter-wave systems.

Black Aluminum: a novel anti-reflective absorbing coating

Black absorbing and antireflective coatings have many optical sensing applications. A process to deposit Black Aluminum, a novel anti-reflective coating has been discovered. Black Aluminum films with controlled thickness were deposited on silicon and their reflection spectra were investigated. In addition, to test the effectiveness of this new material at the device level, pyroelectric devices were fabricated with Black Aluminum acting as the absorbing layer. Significant enhancement in the pyroelectric response is reported for devices coated with Black Aluminum as compared to devices without the Black Aluminum absorbing layer.

Characterization of Eu- and Y-polytantalate Films Deposited by RF Diode Sputtering

Using radio frequency (RF) diode sputtering of sintered stoichiometric (Eu,Y) 2 O 3 :7Ta 2 O5 ceramic targets, thin films (0.2–0.6 m) of Eu- and Y-polytantalates, and their solid solution Eu x Y 1-x Ta7O19 were deposited on fused silica, Si (100) and sapphire (001) substrates under various sputtering conditions. As-grown films were amorphous, and were crystallized by post-annealing in oxygen at 900 to 1000 °C. The influences of deposition gases (Ar and O 2 -partial pressure) substrate material, deposition time, substrate temperature, and post-annealing time and temperature on the structural, morphological and photo-luminescence (PL) properties of Eu 3+ -ions in the films have been studied and compared to properties of sintered (Eu,Y)Ta 7 O 19 ceramic and EuTa 7 O 19 single crystals.

Si content variation and influence of deposition atmosphere in homoepitaxial Si-doped β-Ga2O3 films by pulsed laser deposition

Carrier concentration control by impurity dopants in epitaxial Ga2O3 thin films is progressing to deliver high mobility films for device structures. Si-doped Ga2O3 thin films were fabricated by pulsed laser deposition on (010) β-Ga2O3 substrates from Ga2O3 targets with 0.01–1 wt. % SiO2 yielding films with an electron mobility range consistent with other vapor growth techniques. Single crystal, homoepitaxial growth as determined by high resolution transmission electron microscopy and x-ray diffraction was observed, with a high Si dopant level causing film tensile strain as indicated by both techniques. The influence of oxygen on conductivity using different O2 pressures during deposition and O2/Ar mixtures with a fixed working pressure of 1.33 Pa was determined. With this optimized deposition pressure and atmosphere condition, a carrier concentration and mobility range of 3.25 × 1019 cm−3–1.75 × 1020 cm−3 and 20 cm2/V s–27 cm2/V s was achieved in films from Ga2O3-0.025 wt. % SiO2 and Ga2O3-1 wt. % SiO2 targets, respectively. A highest conductivity of 798 S cm−1 was achieved in films deposited at 550 °C–590 °C with targets of 0.05–1 wt. % SiO2. The electrically active and chemical Si content in films deposited at 550 °C was found to exceed the expected Si ablation target composition in all cases except the highest 1 wt. % SiO2 target attributed to imprecise target manufacturer compositional control at low SiO2 doping levels. Diminished electrical and structural quality films resulted from all targets at a 450 °C deposition temperature.Carrier concentration control by impurity dopants in epitaxial Ga2O3 thin films is progressing to deliver high mobility films for device structures. Si-doped Ga2O3 thin films were fabricated by pulsed laser deposition on (010) β-Ga2O3 substrates from Ga2O3 targets with 0.01–1 wt. % SiO2 yielding films with an electron mobility range consistent with other vapor growth techniques. Single crystal, homoepitaxial growth as determined by high resolution transmission electron microscopy and x-ray diffraction was observed, with a high Si dopant level causing film tensile strain as indicated by both techniques. The influence of oxygen on conductivity using different O2 pressures during deposition and O2/Ar mixtures with a fixed working pressure of 1.33 Pa was determined. With this optimized deposition pressure and atmosphere condition, a carrier concentration and mobility range of 3.25 × 1019 cm−3–1.75 × 1020 cm−3 and 20 cm2/V s–27 cm2/V s was achieved in films from Ga2O3-0.025 wt. % SiO2 and Ga2O3-1 wt. % SiO2 ta...

Pyroelectric response of spray-deposited BaTiO3 thin film

Pyroelectric photoresponse of aqueous spray deposited thin films containing BaTiO3 nano-crystals is reported. X-ray diffraction data indicate the presence of hexagonal BaTiO3 nano-crystals with ~20 nm crystalline domains in a matrix of some as yet unidentified nano-crystalline material. When the film is annealed at 600 C, the X-ray pattern changes significantly and indicates a conversion to one of the non-hexagonal phases of BaTiO3 as well as a complete change in the matrix. With suitable amplifier, the measured photoresponse was 40V/W. Ferroelectric hysteresis on a film with significant presence of hexagonal BaTiO3 shows saturated polarization which is about 5-times smaller than for the bulk tetragonal phase. A potential application is a patternable infrared detector for photonic and plasmonic devices, such as chip-scale spectral sensors.

Pyroelectric AlN Thin Films Used as a MEMS IR Sensing Material

The measurement and characterization of reactive sputtered aluminum nitride (AlN) thin films is presented and evaluated as a potential solution for high temperature sensing applications based on its pyroelectric response (PR). This paper provides the PR obtained for our sputtered thin films along with an in-depth film evaluation using X-ray Diffraction, X-ray Photon Spectroscopy, Scanning Electron Microscopy, and Fourier Transform Infrared Spectroscopy to assess the films crystalline orientation and material composition while evaluating surface coatings for maximum infrared absorption. We observed an ~5× PR increase in the polycrystalline AlN films when compared to epitaxial monocrystalline AlN films. A design of experiments was used to help identify the key parameters which play vital roles in obtaining high PR films. Lastly, several MEMS based array concepts are presented for future testing and characterization.

Surface plasmon enhanced rare earth fluorescence for increased imaging efficiency

Ions of rare earth metals are widely known for their versatile ultraviolet, visible, near infrared and middle infrared fluorescence; they can be excited by wavelengths ranging from the ultraviolet to near infrared. The preparation and optimization of infrared fluorescent ceramics will be discussed, as well as their thin film incorporation into plasmonic systems for fluorescent imaging with enhanced efficiency.

Stress Characterization in Si/SiO2 Spherical Shells Used in Micro-robotics

An in-depth parametric and stress analysis study was accomplished using CoventorWare™finite element method (FEM) modeling to evaluate 1–3 μm thick Si/SiO2 layers which are being used to create spherical shells of 1.0 mm in diameter to be used as a baseline for realizing cubic millimeter micro-robotics. FEM was performed on spherical shells to optimize both the level of curvature of the petal designs which, once released, deflect upward to create one component of the fully self assembled spherical shell. In addition, FEM modeling was used to determine petal spacing in an effort to maximize the total functional surface area of the self-assembled spheres for future circuit integration and electrostatic actuation which will enhance shell movement. As expected, the radius of curvature of the petal is primarily based on the design of the petal, material thicknesses, and residual stresses in the structural layers. Four different petal designs were analyzed, modeled and fabricated to determine which petal design would likely satisfy the self assembly requirement and desired spherical shape. To fabricate the shells, both bulk and thin-film micromachining processes were performed on the silicon-on-insulator (SOI) wafer. To release the spherical shells from the substrate, a multistage wet and dry etching process was used. Once the petals are released, the petals curl up, self-assembling into spherical shells.