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Buried tantalate-niobate microwave varactors
KTH, School of Information and Communication Technology (ICT), Material Physics.
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.ORCID iD: 0000-0001-8774-9302
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
2007 (English)In: 2006 15TH IEEE INTERNATIONAL SYMPOSIUM ON APPLICATIONS OF FERROELECTRICS, 2007, 347-350 p.Conference paper, Published paper (Refereed)
Abstract [en]

We present characteristics of microwave variable capacitors (varactors) buried in 2.5 mu m thick AgTa0.5Nb0.5O3 (ATN) film pulsed laser deposited on sapphire single crystal. 2 gm gap interdigital capacitors (IDC) were fabricated by photolithographic, dry etching and lift-off processes. For comparison, similar IDCs were also defined on top of ATN film. Capacitance and loss tangent have been determined using a modified de-embedding technique in the microwave range 25 MHz - 40 GHz. Buried structures show higher values of capacitance and tunability, keeping the same level of losses compared to standard topped devices and resulting in an increased K-factor = tunability/tan delta. Experimental results are explained within equivalent circuit model. Besides the increased performance, the new design avoids the need of a successive planarization step, which could be required in an integration process.

Place, publisher, year, edition, pages
2007. 347-350 p.
Series
IEEE International Symposium on Applications of Ferroelectrics, ISSN 1099-4734
Keyword [en]
Silver-tantalate-niobate, voltage tunability, buried interdigital capacitors
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-6580DOI: 10.1109/ISAF.2006.4387902ISI: 000262360900084ISBN: 978-1-4244-1331-7 (print)OAI: oai:DiVA.org:kth-6580DiVA: diva2:11330
Conference
15th IEEE International Symposium on Applications of Ferroelectrics Sunset Beach, NC, JUL 30-AUG 03, 2006
Note
QC 20100906Available from: 2006-12-12 Created: 2006-12-12 Last updated: 2011-04-04Bibliographically approved
In thesis
1. Processing and On-Wafer Test of Ferroelectric Film Microwave Varactors
Open this publication in new window or tab >>Processing and On-Wafer Test of Ferroelectric Film Microwave Varactors
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Microwave materials have been widely used in a variety of applications ranging from communication devices to military satellite services, and the study of materials properties at microwave frequencies and the development of functional microwave materials have always been among the most active areas in solid-state physics, materials science, electrical and electronic engineering. In recent years, the increasing requirements for the development of high speed, high frequency circuits and systems require complete understanding of the properties of materials function at microwave frequencies. Ferroelectric materials usually have high dielectric constant, and their dielectric properties are temperature and electric field dependent. The change in permittivity as a function of electric field is the key to a wide range of applications. Ferroelectric materials can be used to fabricate capacitors for electronic industry because of their high dielectric constant, and this is important in the trend toward miniaturization and high functionality of electronic products. The simple tunable passive component based on ferroelectric films is a varactor which can be made as a planar structure and used for electrically tunable microwave integrated circuits. It is an important task to sinter highly tunable and low loss ferroelectrics, fabricate and test the properties of microwave ferroelectric components.

This thesis shows experimental results on growth, crystalline and microwave properties of Na0.5K0.5NbO3 (NKN), AgTa0.5Nb0.5O3 (ATN), Ba0.5Sr0.5TiO3 (BST) as well as AgTaO3 (ATO), and AgNbO3 (ANO) thin films. The films were grown by Pulsed Laser Deposition (PLD) and rf-magnetron sputtering techniques from stoichiometric high density ceramic NKN, ATN, ATO, ANO and BST targets onto LaAlO3 (LAO), Al2O3 (r-cut sapphire), Nd:YAlO3 single crystals and amorphous glass substrates. Advanced X-ray diffraction examinations showed NKN, ATN, BST films on LAO substrates grow epitaxially, whereas films on r-cut sapphire were found to be preferentially (00l) oriented.

Coplanar waveguide 2 µm finger gap interdigital capacitor (CPWIDC) structures were fabricated by photolithography process and metal lift-off technique. On-wafer tests up to 40 GHz were performed to characterize microwave properties of the ferromagnetic film CPWIDC devices. The measurement setup is composed of network analyzer, probe station, and microwave G-S-G probes. External electric field was applied to planar capacitors to measure tunability. Original de-embedding technique has been developed to calculate capacitance, loss tan δ, and tunability of varactors from the measured S-parameters.

NKN film interdigital capacitors on Nd:YAlO3 showed superior performance compared to ATN in the microwave range from 1 to 40 GHz. Within this range, the voltage tunability (40V, 200 kV/cm) was about 29%, loss tangent ~ 0.13, K-factor = tunability/tan δ from 152% @ 10GHz to 46% @ 40GHz. The ATN/sapphire CPWIDCs showed the lowest dispersion ~ 4.3% in whole frequency range from 1 to 40 GHz, voltage tunability 4.7% @ 20GHz and 200 kV/cm, lowest loss tangent ~ 0.068 @ 20GHz, K-factor = tunability/tan δ ranged from 124% @ 10GHz to 35% @ 40GHz.

BST film CPWIDCs on sapphire showed frequency about 17%, the highest voltage tunability ~ 22.2%, loss tangent ~ 0.137 @ 20GHz, and K-factor = 281% @ 10GHz to 95% @ 40GHz.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. x, 74 p.
Series
Trita-ICT/MAP, 2006:3
Keyword
: ferroelectrics, sodium potassium niobates, silver tantalite niobate, barium strontium titanate, thin films, pulsed laser deposition, rf magnetron sputtering, coplanar waveguide, photolithography
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-4226 (URN)
Public defence
2006-12-15, Sal D, KTH-Forum, Isafjordsg. 39, Kista, 10:00 (English)
Opponent
Supervisors
Note
QC 20100906Available from: 2008-12-23 Created: 2008-12-23 Last updated: 2010-09-06Bibliographically approved

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Khartsev, Sergiy

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