Thin films of Ba0.5Sr0.5TiO3 (BST) were deposited on c-plane (0001) sapphire by rf magnetron sputtering and investigated by complementary materials analysis methods. Microwave properties of the films, including tunability and Q factor were measured from 1to20GHz by patterning interdigital capacitors (IDCs) on the film surface. The tunability is correlated with texture, strain, and grain size in the deposited films. An enhanced capacitance tunability of 56% at a bias field of 200kV∕cm and total device Q of more than 15 (up to 20GHz) were achieved following postdeposition annealing at 900°C.

Polycrystalline Ba 0.6 Sr 0.4 TiO 3 ͑BST͒ films grown on r-plane sapphire exhibit strong variation of in-plane strain over the thickness range of 25-400 nm. At a critical thickness of ϳ200 nm, the films are strain relieved; in thinner films, the strain is tensile, while compressive strain was observed in the 400 nm film. Microwave properties of the films were measured from 1 to 20 GHz by the interdigital capacitor method. A capacitance tunability of 64% was observed in the 200 nm film, while thinner films showed improved Q factor. These results demonstrate the possibility of incorporating frequency agile BST-based devices into the silicon on sapphire process.

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An application is demonstrated for the much maligned standing wave in photolithography that is responsible for the sidewall corrugations in photoresist patterns. We demonstrate the realization of a polydimethylsiloxane (PDMS) scattering mask through the casting of these sidewall corrugations and their application as the masking components in an otherwise transparent bulk of PDMS. Photoresist structures with widths in the order of 80nm are realized by the application of this mask, demonstrating excellent correlation with the lateral depths of the sidewall corrugations. The continuity of the sidewall corrugations around corners makes both straight and curved lines realizable with equal simplicity.

Abstract-This paper introduces a novel branch-line 90• hybrid coupler incorporating varactor diodes which allow tuning of the frequency response. A design covering the DCS, PCS and IMT2000 cellular frequency bands (1710-2170 MHz) is presented. Given a varactor tunability of 2.5:1, simulations suggest 20 dB return loss and 3±1 dB coupling is achievable across each transmit and receive sub-band by tuning the varactors. These results offer an improvement over a conventional singlesection branch-line hybrid centred at 1950 MHz, and some miniaturisation is also achieved due to the capacitive loading. A prototype is constructed using commercially available varactor diodes, and reasonable agreement between the measured and simulated results is achieved.