Ferroelectric Thin Films on Si-substrate for Tunable Microwave Applications

• The thesis presents the development of microwave tunable devices based onferroelectric thin films. The main tasks in this work are the fabrication, optimization, andintegration of ferroelectric thin film into Si-MMIC. This work has been motivated byincreased interest on advanced tunable microwave components which meet therequirements of low microwave losses, high tunability, easy to integrate to largersystems, and low cost.Dielectric permittivity, tunability, and loss tangent are the most important parameters,characterizing ferroelectrics for application in tunable microwave devices. Most of theefforts in this work have been devoted to the optimization of film fabrication processes interms of microwave loss reduction. Experimental investigations of these parameters forNa0.5K0.5NbO3 (NKN), (SrTiO3) STO, Ba0.25Sr0.75TiO3 (BSTO) and (Pb, Zr) TiO3 (PZT)films are carried out in a wide frequency, DC bias, and temperature ranges. Thesemeasurements give important information about dispersion, temperature, and dc-fielddependencies of dielectric permittivity and losses. The latter are useful for understandingthe basic physical processes in ferroelectric films and help to optimize film depositionand device fabrication processes in terms of low losses, high tunability, and temperaturestability.Coplanar-plate structure is used to integrate the ferroelectric films into the siliconcircuits. Planar varactors are fabricated by depositing tunable ferroelectric films onSi/SiO2 substrates using laser ablation, RF magnetron sputtering, and sol-gel technique,followed by metal electrode deposition. Different varactor designs based on as straightgap, interdigital gap, and circular gap have been investigated and further used in thecomponents. Experiments show the capability and potential of tunable devices based onferroelectric thin films and confirm that they are competitive with other technologies likesemiconductors at frequency above 20 GHz. It is shown that NKN films in polar phaseare also useful for tunable microwave applications demonstrating low loss and goodtunability in a frequency above 20 GHz. BSTO films, which are in paraelectric phase atroom temperature, are used to fabricate microwave varactors. These varactors are used intwo different phase shifters designs. These tunable devices show more than 60°/dB figureof merit, which is one the best value reported so far.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Elektroteknik och elektronik -- Annan elektroteknik och elektronik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Electrical Engineering, Electronic Engineering, Information Engineering -- Other Electrical Engineering, Electronic Engineering, Information Engineering (hsv//eng)

Nyckelord

Phase shifter

BaxSr1-xTiO3

Tunable microwave device

Ferroelectric Varactor

Paraelectric

Filter

Na0.5K0.5NbO3

Integrated ferroelectric device

SrTiO3

Ferroelectric

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