An Electronically Tuned Bandstop Filter Using BST Varactors

Abstract

This paper presents an investigation of a tunable bandstop filter using Barium-Strontium-Titanate (BST) varactors. 3-pole bandstop filter with varactors is fabricated onMgO substrate. It is measured at the center frequency from 8.77 to 9.26 GHz and its maximum rejection is more than 26 dB at the stop band while the insertion loss at the pass band is less than 2 dB.

High tunable Ba<SUB align="right">0.5Sr<SUB align="right">0.5TiO<SUB align="right">3 thin film deposited on silicon substrate with MgO buffer layer

“…Ba x Sr 1-x TiO 3 (BST) has been widely studied as the dielectric material for frequency agile devices, due to its highly non-linear dependence of the dielectric permittivity on the electric field around room temperature (Chun et al, 2008;Nath et al, 2005;Auciello et al, 2004). For application in frequency agile devices, it is desirable to have as high tunability and as low a dielectric loss as possible.…”

“…The crystal parameter of MgO is a = b = c = 0.421 nm, which is close to that of BST (about 0.39 nm). The single crystal MgO has been used as a microwave substrate (Chun et al, 2008). However, the high cost of MgO crystal restrains the popularity of massive production (Yoon et al, 2006).…”

Tunable band-stop filter based on single RF MEMS capacitive shunt switch with meander arm inductance

“…However, SAW filters are limited in frequency (<3 GHz). A survey of the recent literature reveals that apart from the traditional active [2] and distributed RC passive [3] notch filters, novel tunable band-stop filter topologies using photonic [4] or electromagnetic band gap (EBG) structures [5], quarter wavelength open stubs, radial stubs or slotted ground structures [6][7][8], complementary split ring resonators (CSRR) utilising metamaterials [9], lumped LC circuits [10,11], multilayer ferromagnetic resonance [12] and bulk acoustic wave (BAW) resonators [13] are chosen as alternatives to address similar problems. In general, all of the above approaches are quite complex systems, requiring large silicon areas (>6 mm in length) and exhibiting moderate performances.…”

“…Ferroelectric materials (such as BST, PZT or PST) have recently been used as varactors in tunable microwave circuits [6,11]. However, they are not usually integrated with the filter fabrication process and the insertion losses are relatively high.…”

Textured BST Thin Film on Silicon Substrate: Preparation and Its Applications for High Frequency Tunable Devices

“…The crystal parameter of MgO is a = b = c = 0.42 nm, which is close to that of BST (about 0.39 nm). The single crystal MgO has been used as a microwave substrate [14]. However, the high cost of MgO crystal restrains the popularity of massive production [15].…”