@article{nath_fathelbab_lam_ghosh_aygun_gard_maria_kingon_steer_2006, title={Discrete Barium Strontium Titanate (BST) thin-film interdigital varactors on alumina: Design, fabrication, characterization, and applications}, ISBN={["978-0-7803-9541-1"]}, ISSN={["2576-7216"]}, DOI={10.1109/mwsym.2006.249652}, abstractNote={Discrete barium strontium titanate (BST) thin-film capacitors in industry standard 0603 footprint are introduced and characterized. BST capacitors have a voltage-dependent permittivity, enabling BST thin-film capacitors to be used as tuning elements in frequency agile devices. The capacitance changed by 1.5:1 at 35 V (116 kV/cm) bias. The temperature dependence of the capacitance was measured to be less than plusmn 20 % from -100 degC to +100 degC. A 2nd-order tunable combline bandpass filter on FR4 substrate has been implemented using the discrete BST varactors. The filter showed a center frequency tuning of 22% from 2.14 GHz to 2.61 GHz upon application of 130 V (433 kV/cm) bias. The zero-bias insertion loss was 4.9 dB which decreased to 2.9 dB at the high bias state. The return loss was better than 11 dB over the tuning range. Nonlinear characterization of the filter using two-tone test and a digitally-modulated CDMA 2000 signal showed an IP3 of +32 dBm and an ACPR of better than -50 dBc up to 26 dBm of input power, respectively}, journal={2006 IEEE MTT-S INTERNATIONAL MICROWAVE SYMPOSIUM DIGEST, VOLS 1-5}, author={Nath, Jayesh and Fathelbab, Wael M. and Lam, Peter G. and Ghosh, Dipankar and Aygun, Seymen and Gard, Kevin G. and Maria, J. -P. and Kingon, Angus I. and Steer, Michael B.}, year={2006}, pages={552–555} }
 @article{victor_nath_ghosh_boyette_maria_steer_kingon_stauf_2006, title={Noise characteristics of an oscillator with a barium strontium titanate (BST) varactor}, volume={153}, ISSN={["1350-2417"]}, DOI={10.1049/ip-map:20050068}, abstractNote={The phase noise of an oscillator with a thin-film barium strontium titanate (BST) capacitive tuning element, or varactor, is characterised and benchmarked against the same oscillator with a silicon semiconductor junction varactor. Phase noise tracks closely with varactor Q within a specific voltage range as expected. Compared to the semiconductor varactor-based oscillator, the BST-based oscillator demonstrates reduced phase noise degradation near zero volts, but greater phase noise degradation when operated near breakdown.}, number={1}, journal={IEE PROCEEDINGS-MICROWAVES ANTENNAS AND PROPAGATION}, author={Victor, A and Nath, J and Ghosh, D and Boyette, B and Maria, JP and Steer, MB and Kingon, AI and Stauf, GT}, year={2006}, month={Feb}, pages={96–102} }
 @article{ghosh_laughlin_nath_kingon_steer_maria_2006, title={Tunable high-quality-factor interdigitated (Ba, Sr)TiO3 capacitors fabricated on low-cost substrates with copper metallization}, volume={496}, ISSN={["0040-6090"]}, DOI={10.1016/j.tsf.2005.09.025}, abstractNote={Interdigitated capacitors containing the field-tunable ferroelectric Ba0.75Sr0.25TiO3, polycrystalline alumina substrates, and copper metallization have been fabricated. Dielectric layers were prepared by magnetron sputtering, while the Cu metallization was evaporated. The dielectric tunability of the Ba0.75Sr0.25TiO3 was 40% at an applied electric field of 12 V/μm. This corresponds to a 3-μm electrode gap width and a 35 V dc bias. Low-frequency (1 MHz) loss tangent measurements indicate a dielectric Q (quality factor) of ∼100 while microwave measurements reveal a zero bias device Q of ∼30 at 26 GHz. These values are comparable or superior to numerous reports of barium strontium titanate interdigitated capacitors prepared using single crystalline substrates and noble metallization. As such, this technology is significantly less expensive and more amenable to large-volume manufacturing.}, number={2}, journal={THIN SOLID FILMS}, author={Ghosh, D and Laughlin, B and Nath, J and Kingon, AI and Steer, MB and Maria, JP}, year={2006}, month={Feb}, pages={669–673} }
 @inproceedings{victor_nath_ghosh_aygun_nagy_maria_kingon_steer_2006, title={Voltage controlled GaN on Si HFET power oscillator using thin?film ferroelectric varactor tuning}, DOI={10.1109/eumc.2006.281206}, abstractNote={A 1.6 GHz power oscillator with a GaN-on-Si heterostructure field effect transistor (HFET) is reported. The voltage-controlled oscillator used a thin-film barium strontium titanate (BST) interdigital varactor as the tuning element. The surface-mount varactor was fabricated using sputtered BST film and copper metallization on alumina. An output power of 1.6 W (32 dBm) is obtained with a DC conversion efficiency of 25.5%. Flat tuning sensitivity of 500 kHz/V, 49 MHz linear frequency tuning, and power flatness of better than 0.5 dB are obtained with 0-100 V tuning voltage. The maximum oscillator phase noise is -81.4 dBc/Hz at 100 kHz offset}, booktitle={Proceedings of the 36th European Microwave Conference, (EuMW2006), Manchester, UK}, publisher={London: Horizon House}, author={Victor, A. and Nath, J. and Ghosh, D. and Aygun, S. and Nagy, W. and Maria, J.-P. and Kingon, A. I. and Steer, M. B.}, year={2006}, pages={87–90} }
 @article{nath_ghosh_fathelbab_maria_kingon_franzon_steer_2005, title={A tunable combline bandpass filter using Barium Strontium Titanate interdigital varactors on an alumina substrate}, ISBN={["0-7803-8845-3"]}, ISSN={["2576-7216"]}, DOI={10.1109/mwsym.2005.1516670}, abstractNote={Barium strontium titanate (BST) has a field-dependent permittivity that enables it to be used as a dielectric in a voltage-tunable capacitor or varactor. A tunable combline bandpass filter was designed and characterized using BST varactors fabricated on a polycrystalline alumina substrate with copper metallization and is 14 mm /spl times/ 14 mm in size. The center frequency of the filter varies from 1.6 to 2.0 GHz with the application of 200 V tuning voltage. A 25% tuning range was achieved using tuning field strength of 300 kV/cm. The zero bias insertion loss was 6.6 dB and this decreased to 4.3 dB at the high bias state. The return loss was better than 10 dB.}, journal={2005 IEEE MTT-S INTERNATIONAL MICROWAVE SYMPOSIUM, VOLS 1-4}, publisher={Piscataway, NJ: IEEE}, author={Nath, J and Ghosh, D and Fathelbab, W and Maria, JP and Kingon, AI and Franzon, PD and Steer, MB}, year={2005}, pages={595–598} }
 @article{nath_ghosh_maria_kingon_fathelbab_franzon_steer_2005, title={An electronically tunable microstrip bandpass filter using thin-film barium-strontium-titanate (BST) varactors}, volume={53}, ISSN={["1557-9670"]}, DOI={10.1109/TMTT.2005.854196}, abstractNote={A tunable third-order combline bandpass filter using thin-film barium-strontium-titanate varactors and fabricated on a sapphire substrate is reported. Application of 0-200-V bias varied the center frequency of the filter from 2.44 to 2.88 GHz (16% tuning) while achieving a 1-dB bandwidth of 400 MHz. The insertion loss varied from 5.1 dB at zero bias to 3.3 dB at full bias, while the return loss exceeded 13 dB over the range. The third-order intercept of the filter was found to be 41 dBm.}, number={9}, journal={IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES}, author={Nath, J and Ghosh, D and Maria, JP and Kingon, AI and Fathelbab, W and Franzon, PD and Steer, MB}, year={2005}, month={Sep}, pages={2707–2712} }
 @article{ghosh_laughlin_nath_kingon_steer_maria_2005, title={High Q (Ba, Sr) TiO3 interdigitated capacitors fabricated on low cost polycrystalline alumina substrates with copper metallization}, volume={26}, DOI={10.1002/9780470291252.ch13}, abstractNote={Barium Strontium Titanate (BST) ferroelectric thin films are attractive for radio frequency and microwave applications. However, for many non-military uses, the high cost of conventionally processed devices is a limitingfactor. This high cost stems from the use of single-crystalline sapphire, MgO, or LaAlO 3 substrates and Pt or Au metallization commonly used. Here we present a device process and materials complement offering a low cost alternative. Planar interdigitated capacitors Ba 0 . 7 5 Sr 0 . 2 5 TiO 3 (BST) thin films with chromium/copper top electrodes were fabricated on polycrystalline alumina substrates using a single step photolithographic technique and lift-off. RF magnetron sputtering was used for fabrication of BST thin films while Cu thin films were thermally evaporated The dielectric tunability of the Ba 0 . 7 5 Sr 0 . 2 5 TiO 3 IDCs was 40 % for an applied electric field of 120 kV/cm, which corresponds to 3 μm electrode gap spacing and a 35 volt dc bias. Low frequency (1MHz) loss measurements reveal a dielectric Q ∼ 100 while a device Q of ∼ 30 is obtained at 26 GHz. The reduction of Q between 0.1 and 26 GHz can be attributed to the metallization. Leakage current measurements of the BST planar varactors show current densities of 1.0 x 10 - 6 A / cm 2 for an electric field of 100 kV/cm. These dielectric characteristics (tunability and Q value) are comparable to numerous reports of IDCs with BST films prepared on expensive single crystalline substrates using noble metallization. As such, this technology is significantly less expensive, and amenable to large volume manufacturing.}, number={5}, journal={Ceramic Engineering and Science Proceedings}, author={Ghosh, D. and Laughlin, B. J. and Nath, J. and Kingon, A. I. and Steer, M. B. and Maria, J. P.}, year={2005}, pages={125–132} }
 @article{victor_nath_ghosh_boyette_maria_steer_kingon_stauf_2004, title={A voltage controlled oscillator using Barium strontium titanate (BST) thin film varactor}, ISBN={["0-7803-8451-2"]}, DOI={10.1109/rawcon.2004.1389079}, abstractNote={Barium strontium titanate (BST) has a field-dependent permittivity and can be used as a dielectric in voltage tunable capacitors or varactors. These BST-based varactors are passive devices and have significantly different properties compared to semiconductor varactors. A voltage tunable oscillator using a BST thin film varactor was designed and characterized. The frequency of oscillation varied from 34.8 MHz to 44.5 MHz (28% tuning) upon application of 7 V tuning voltage. The VCO gain was 1.38 MHz/V and the 2nd harmonic was over 23 dB below the fundamental throughout the tuning range.}, journal={RAWCON: 2004 IEEE RADIO AND WIRELESS CONFERENCE, PROCEEDINGS}, author={Victor, A and Nath, J and Ghosh, D and Boyette, B and Maria, JP and Steer, MB and Kingon, AI and Stauf, GT}, year={2004}, pages={91–94} }
 @inproceedings{nath_ghosh_maria_steer_kingon_stauf_2004, title={Microwave properties of BST thin film interdigital capacitors on low cost alumina substrates}, ISBN={1580539920}, booktitle={Proceedings of the 34th European Microwave Conference (EuMc), Amsterdam}, publisher={London: Horizon House}, author={Nath, J. and Ghosh, D. and Maria, J.-P. and Steer, M. B. and Kingon, A. I. and Stauf, G. T.}, year={2004}, pages={1497–1500} }