Thick capacitive meshes on polyimide substrates 358k Arne Lüker, Oren Sternberg, Herbert Hein, Joachim Schulz and Karl-Dieter Möller; Infrared Physics & Technology 45 (2004) 153–157

Abstract: Thick capacitive meshes of nickel on substrates of thickness 25 µm have been produced by electroplating into a photoresist mould. The Micro-Stripes program by Flomerics has been used for the interpretation of the experimentally measured far infrared spectrum. The measured reflection resonance mode and the transmission wave guide mode agree well with the analytical predictions.

Abstract: Future phased array transmit/receive (T/R) modules require wide bandwidth, low loss switches to replace the circulator at the power amplifier (PA) output. Circulators have inherent drawbacks including high cost, inability to integrate and physical size. Currently protection of the low noise amplifier (LNA) is required because of poor isolation. Consequently a cost, size and weight reduction as well as increased performance are expected when using a T/R switch. Currently no wide bandwidth switches with high power handling capability are available. Field Effect Transistor (FET) implementations lack either power or bandwidth and sacrifice insertion loss. MicroElectroMechanical (MEM) RF switch technology has been demonstrated to exhibit very low insertion loss with multi-octave performance at microwave frequencies however, silicon or GaAs MEMS switches lack high power handling capabilities. As a consequence of the physical properties of diamond, thermal conductivity and hardness, Diamond MEMS offer the potential of outstanding performance. The high Youngs Modulus (stiffness) enables high switching speeds. It has the highest thermal conductivity among solids allowing efficient power dissipation lending itself to the potential integration for high power systems on chip. The University of Ulm is recognized as a center of excellence for Diamond synthesis and device fabrication. Switches are identified in the TDM research theme as a selected topic of high interest to the DTC.

Abstract: Tunable capacitors with a Cu/Pb_xSr_1-xTiO₃/Cu parallel-plate structure have been fabricated using a layer transfer method. The use of a Cu bottom electrode results in a giant electrode Q-factor x capacitor area product of Q_elecA=3.79x10⁵ µm² at 1 GHz. The dielectric constant at room temperature is 420 and the tunability amounts to 73% near a breakdown voltage of 35 V. The major advantages of the layer transfer method include low electrode losses, the freedom to select an auxiliary substrate and seed layer for ferroelectric film growth irrespective of their high-frequency properties, and the possibility to utilize a large variety of device substrates as they no longer act as template for film growth

Abstract: Free standing metal screens have long been used as band pass filters in the infrared (IR) wavelength region. One adjusts the screens’ periodicity constant, its opening-to-periodicity aspect ratio and its thickness to achieve desired infrared transmission properties. Here we concentrate on thick screens in the near IR wavelength region (1–2 lm). In addition to experiments and simulations we have considered the role of screen imperfection on its transmission characteristics. Uneven surfaces, inclined and sometimes rough walls of the screen and waveguide channels may be the result of thick-film lithography which is used in the process for screen manufacturing. Understanding these effects is crucial to applications of these filters in the entire IR region.

Abstract: Diamond cantilever actuators show high resonance frequencies but need also high actuation forces, pointing towards piezoelectric actuation by a PZT/diamond unimorph. In this study lead zirconate titanate (Pb(Zr,Ti)O₃, PZT) layers have been deposited onto nanocrystalline diamond films by sol–gel deposition, to realize high-speed MEMS actuators. The fabrication technology is based on self-aligned patterning and on optical lithography. A mechanical resonance frequency of 3.9 MHz has been obtained for 30 µm cantilever length dominated by the nanodiamond Young's modulus of approximately 1000 GPa.

Abstract: In pursuit of thin film ferroelectric materials for frequency agile applications that are both easily adapted to large area deposition and also high performance, an investigation has been carried out into sol-gel deposition of 3% Mn doped
Pb0.4Sr0.6TiO3. Large area capability has been demonstrated by growth of films with good crystallinity and grain structure on 4 in. Si wafers. Metal-insulator-metal capacitors have also been fabricated and development of an improved de-embedding technique that takes parasitic impedances fully into account has enabled accurate extraction of the high frequency dielectric properties of the PbxSr1-xTiO3 films. Practically useful values of ε~1000, tanδ~0.03, and tunability 50% have been obtained in the low gigahertz range
1–5 GHz. Peaks in the dielectric loss due to acoustic resonance have been modeled and tentatively identified as due to an electrostrictive effect with an electromechanical coupling coefficient of 0.04 at an electric field of 240 kV/cm which is potentially useful for tunable thin film bulk acoustic wave devices.

Abstract: Sol–gel derived Pb₄₀Sr₆₀TiO₃ (PST) thin film has been investigated as a diffusion barrier for integrating in PbZr₃₀Ti₇₀O₃ (PZT) device structures on Si substrates. PST film was deposited on SiO₂/Si substrate and annealed at a relatively low temperature range of 550–600 °C producing a crack-free, smooth and textured surface. Following deposition on PST/SiO2/Si template PZT thin film was crystallised exhibiting random grain orientations and an insertion of the bottom Pt/Ti electrode forming PZT/Pt/Ti/PST/SiO₂/Si stacks promoted the preferred PZT (111) perovskite phase. PZT (111) peak intensity gradually decreased along with slight increase of the PZT (110) peak with increasing annealing temperature of the buffer PST film. The dielectric and ferroelectric properties of the PZT with barrier PST deposited at 550 °C were assessed. The dielectric constant and loss factor were estimated as 390 and 0.034 at 100 kHz respectively and the remnant polarisation was 28 µC/cm² at 19 V. The performance of the PZT/PST device structures was compared to similar PZT transducer stacks having widely used barrier TiO₂ layer.

Abstract: Auger spectroscopy was used to study the compositional change in the interfacial region between ferroelectric thin films, namely lead strontium titanate (PST) and lead zirconate titanate (PZT), and commercially available Si substrates with a 200 nm thick thermal oxide layer. Both PST and PZT thin films were prepared via a sol–gel spin coating method. The thin films from both materials were annealed under the same conditions (temperature and time). It was found that strontium stops the lead diffusion into SiO₂ by forming SrSiO₃/Sr₂SiO₄ and SrO, maintaining a well defined SiO₂ region, while PbSiO₃ is formed in the PZT/SiO₂ system. These results are important for a general understanding of interdiffusions in material interfaces in particular for the realization of future high-dielectric-constant (high-k) oxide layers and for the next generation of advanced electronic devices.

      

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