ELECTRICALLY TUNABLE MICROWAVE DEVICES USINGBST-LTCC THICK FILMS, ACTA UNIVERSITATIS OULUENSIS C Technica 366
|Kustantaja:||Oulun yliopisto|| |
|Oppiaine:||Tekniikka, matematiikka|| |
|Sijainti:||Print Tietotalo|| |
|Tekijät:||PALUKURU VAMSI KRISHNA|| |
The thesis describes electrically tunable microwave devices utilising low sintering temperature,screen printable Barium Strontium Titanate (BST) thick films. The work has been divided into twoparts. In the first section, the fabrication and microwave characterisation of BST material basedstructures compatible with Low Temperature Cofired Ceramic technology (BST-LTCC) arepresented. Three different fabrication techniques, namely: direct writing, screen printing and viafilling techniques, were used for the realisation of the structures. A detailed description of thesefabrication techniques is presented. The dielectric properties such as relative permittivity, staticelectric field dependent tunability and loss tangent of BST-LTCC structures at microwavefrequencies were characterised using coplanar waveguide transmission line and capacitiveelement techniques. The measured dielectric properties of BST-LTCC structures realised with thedifferent fabrication methods are presented, compared and discussed.
The second section describes tunable microwave devices based on BST-LTCC structures. Afrequency tunable folded slot antenna (FSA) with a screen printed, integrated BST varactor ispresented. The resonant frequency of the FSA was tuned by 3.2% with the application of 200 Vexternal bias voltage. The impact of the BST varactor on the total efficiency of the antenna wasstudied through comparison with a reference antenna not incorporating the BST varactor. Acompact, frequency tunable ceramic planar inverted-F antenna (PIFA) utilising an integrated BSTvaractor for mobile terminal application is presented. The antenna's resonant frequency was tunedby 3% with an application of 200 V bias voltage. Frequency tunable antennas with a completelyintegrated electrically tunable BST varactor with silver metallisation are introduced in this workfor the first time. The integration techniques which are described in this thesis have not beenpreviously reported in scientific literature. The last part of the thesis presents a microwave delayline phase shifter operating at 3 GHz based on BST-LTCC structures. The figure of merit (FOM)of the phase shifter was measured to be 14.2 °/dB at 3 GHz and and the device employs a novelstructure for its realisation that enabled the required bias voltage to be decreased, while stillmaintaining compliance with standard screen printing technology. The performance of the phaseshifter is compared and discussed with other phase shifters realised with the BST thick filmprocess.
The applications of BST-LTCC structures were demonstrated through frequency tuning ofantennas, varactors, and phase shifters. The low sintering temperature BST paste not only enablesthe use of highly conductive silver metallisation, but also makes the devices more compact andmonolithic.