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Suppression of Acoustic Resonances in All-Oxide Varactors

Walk, Dominik and Kienemund, Daniel and Agrawal, Prannoy and Salg, Patrick and Zeinar, Lukas and Komissinskiy, Philipp and Alff, Lambert and Jakoby, Rolf and Maune, Holger (2020):
Suppression of Acoustic Resonances in All-Oxide Varactors.
pp. 139-142, IEEE, IEEE/MTT-S International Microwave Symposium (IMS 2020), virtual Conference, 04.-06.08., e-ISSN 2576-7216, ISBN 978-1-7281-6816-6,
DOI: 10.1109/IMS30576.2020.9224035,
[Conference or Workshop Item]

Abstract

Barium strontium titanate (BST) thin-film varactors promise very good performance in RF frontends in terms of low loss and high tunability. However, their application is commonly limited to lower GHz frequencies. For higher frequencies, acoustic resonances drastically reduce the device quality in metal-insulator-metal (MIM) structures under bias voltage. In this work, this limitation is overcome by replacing the metal electrodes with conducting oxides that structurally match to BST and, therefore, avoid acoustic impedance mismatch. A detailed analytic model is derived, incorporating electric and acoustic behavior. Four samples with an oxide bottom electrode and varying BST thickness are characterized and fitted by the derived model with very high accuracy. Each shows a significantly reduced degradation due to acoustic loss. A model-wise comparison of stacks with metal and oxide electrodes demonstrates the strong benefit of all-oxide varactors, the possibility of complete suppression of acoustic resonances.

Item Type: Conference or Workshop Item
Erschienen: 2020
Creators: Walk, Dominik and Kienemund, Daniel and Agrawal, Prannoy and Salg, Patrick and Zeinar, Lukas and Komissinskiy, Philipp and Alff, Lambert and Jakoby, Rolf and Maune, Holger
Title: Suppression of Acoustic Resonances in All-Oxide Varactors
Language: English
Abstract:

Barium strontium titanate (BST) thin-film varactors promise very good performance in RF frontends in terms of low loss and high tunability. However, their application is commonly limited to lower GHz frequencies. For higher frequencies, acoustic resonances drastically reduce the device quality in metal-insulator-metal (MIM) structures under bias voltage. In this work, this limitation is overcome by replacing the metal electrodes with conducting oxides that structurally match to BST and, therefore, avoid acoustic impedance mismatch. A detailed analytic model is derived, incorporating electric and acoustic behavior. Four samples with an oxide bottom electrode and varying BST thickness are characterized and fitted by the derived model with very high accuracy. Each shows a significantly reduced degradation due to acoustic loss. A model-wise comparison of stacks with metal and oxide electrodes demonstrates the strong benefit of all-oxide varactors, the possibility of complete suppression of acoustic resonances.

Publisher: IEEE
ISBN: 978-1-7281-6816-6
Uncontrolled Keywords: acoustic resonance, BST, ferroelectric, modeling, suppression, thin-film varactors
Divisions: 11 Department of Materials and Earth Sciences
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences > Material Science > Advanced Thin Film Technology
18 Department of Electrical Engineering and Information Technology
18 Department of Electrical Engineering and Information Technology > Institute for Microwave Engineering and Photonics > Photonics and Optical Communications
18 Department of Electrical Engineering and Information Technology > Institute for Microwave Engineering and Photonics
Event Title: IEEE/MTT-S International Microwave Symposium (IMS 2020)
Event Location: virtual Conference
Event Dates: 04.-06.08.
Date Deposited: 20 Nov 2020 09:04
DOI: 10.1109/IMS30576.2020.9224035
Projects: This work was funded by the Deutsche Forschungsgemeinschaft (DFG) within Nos. KO 4093/1-1 and JA 921/31-1, as well as the Federal Ministry of Education and Research (BMBF) VIP+ Project No. 03VP0l150.
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