Highly efficient magnetically tunable high frequency spur-line notch filter

https://doi.org/10.1016/j.cap.2020.03.015Get rights and content

Highlights

  • A novel two step approach for the fabrication of cobalt ferrite nanorods (CFO NRs) without using any template.

  • Demonstration of spur-line based magnetically tunable bandstop filter in the flip-chip configuration using CFO NRs.

  • A great tuning (~8.7%) is achieved in the presence of low bias magnetic field.

Abstract

We report a cobalt ferrite nanorods (CFO NRs) based magnetically tunable spur-line notch filter where vertically aligned CFO NRs has been grown on silver nanoparticles coated silicon substrate. The CFO NRs are coupled with high frequency spur-line bandstop filter in flip-chip configuration and the device showed excellent tunable microwave properties in the presence of a low bias magnetic field. The center frequency of the tunable filter is ~16.4 GHz which is shifted to ~14.9 GHz with ~8.7% tunability by applying bias magnetic field ~320 Oe. The magnetic field tuning of the center frequency is explained on the basis of the change in permeability value of the CFO NRs with bias magnetic field as the NRs are used in the partially magnetized state. For validation, permeability value is also calculated by using numerical equations. The experimental reflection of the device has been supported with a simulation using CST microwave studio software.

Graphical abstract

FIG. (a) Schematic of the spur-line bandstop filter design with CFO NRs in the flip-chip geometry (b) Measured transmission characteristics of spur-line bandstop filter and (c) Shift in the center frequency with bias magnetic field.

Image 1
  1. Download : Download high-res image (187KB)
  2. Download : Download full-size image

Introduction

There has been a lot of interest in developing tunable microwave filters (bandpass and bandstop) for advance communication and satellite technology to detect the RF-microwave frequencies and also their use to reduce the problem of undesirable frequencies present in the signal. For the future development, the demand of magnetic materials based filters is continuing growing because of their unique and interesting tunable characteristics based nanoscale microwave devices [1,2]. Magnetic ferrites can be a most promising signal processing materials for microwave device applications due to their low loss, moderate to high saturation magnetization, tunable anisotropy field and high permeability with high selectivity at higher frequencies [[3], [4], [5]]. The nonreciprocity nature of ferrites also makes it vital for many devices like isolators [6], phase shifters [7] and circulators [8] in the radar and communication technology at higher frequencies (1–50 GHz). Another important feature of these devices is the tuning of the center frequency in the presence of bias magnetic field. Efforts have been made for magnetic thin film based tunable microwave filters [9] but few reports are published on nanostructure based microwave filters [10,11]. Ferromagnetic resonance (FMR) based tunable microwave devices have been reported in last many years which shows the very nice tuning of central frequency [12], but these devices require high magnetic field for tuning because of its operation in the saturated state where the value of the permeability (μr) is ~1. Ferrites used in the partially magnetized state can overcome this problem where the value of the permeability (μr) varies from 0 to 1, and the device can show a prominent tuning in the presence of low bias magnetic field.

Among the ferrites, cobalt ferrite (CoFe2O4) offers the advantage over other materials due to their high stability and higher Curie temperature [13,14]. Cobalt ferrite structure grows in an inverse spinel, or partially inverse spinel form depends upon the synthesis methods and growth conditions. The general form is represented as AB2O4 (A = Fe, Bdouble bondCo, Fe) where A and B represent the tetrahedral and octahedral sites, in which Co exist at the tetrahedral site, and Fe exists at both octahedral and tetrahedral sites with equal distribution in the inverse spinel state.

Recently, few reports have been published on the synthesis of cobalt ferrite nanorods/nanowires structures [15,16] in which AAO (anodic aluminum oxide) is used as a template but to the best of our knowledge, there is no study on the growth of directly aligned CFO nanorods on the substrate without using any template. These CFO nanorods can be a potential candidate for tunable microwave filters application in the partially magnetized state.

In this report, we have synthesized dense arrays of single phase vertically aligned cobalt ferrite nanorods (CFO NRs) on Ag nanoparticles coated silicon substrate through electrodeposition method without using any template and fabricated magnetically tunable microwave filter by coupling the CFO NRs with L-shaped spur-line notch filter. This coupled device shows the tunability of ~8.7% in the unsaturated state of ferrite material in the presence of a low bias magnetic field.

Section snippets

Experimental methods

In electrodeposition process, three electrode assembly was used where, Ag NPs coated Si substrate work as a working electrode, platinum sheet as counter electrode and the Ag/AgCl (saturated KCl) has been taken as a reference electrode. The sulphate precursors of cobalt (0.02 M) and iron (0.04 M) with boric acid (adjust the pH value of solution) were used as a liquid electrolyte, and the schematic set-up of the deposition process of CFO NRs is shown in Fig. 1. The sulphates of cobalt (0.02 M)

Characterization techniques

The surface morphology study of the sample has been carried out by the field emission scanning electron microscope (FESEM- FEI Quanta 200F SEM). The phase identification and structural analysis of electrodeposited CFO NRs were carried out by the X-ray diffraction (XRD) technique with Philips diffractometer by using the Cu-Kα radiation (λ = 1.54 Å). Raman spectroscopy set-up of RainishawInvia was also used for the phase confirmation of the CFO material where Argon ion laser (λ = 768 nm) was used

Results and discussion

Initially, Ag film was found discontinuous in nature however, after the annealing at 200 °C, morphology of thin film changed and growth of Ag nanoparticles take place. Fig. 2(a) shows FESEM micrographs of annealed (200 °C) Ag nanoparticles, deposited on Si substrates and average particle size was found to be ~80 nm. After the electrodeposition, the CFO NRs grown on Ag nanoparticles coated Si substrate, where Ag NPs used as a seed layer and the well-aligned dense assembly of CFO NRs is shown in

Conclusions

To conclude, we have successfully grown aligned cobalt ferrite nanorods on Ag nanoparticles coated silicon substrate and demonstrated an easy way of the fabrication of magnetically tunable filter where these CFO NRs are coupled with the L-shaped spur-line bandstop filter in the flip-chip configuration. This tunable filter showed the tuning of ~8.7% for applied field 320 Oe. This tuning in the center frequency is explicated with the change in permeability value of the material in the presence

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The use of several facilities at Nano research facilities (funded by the Ministry of Electronics and Information technology) and at Centre for Applied Research in Electronics, IIT Delhifor this work are gratefully acknowledged. One of us (DS) is thankful to science & engineering research board (SERB) for the award of national postdoc fellowship (NPDF, File Number: PDF/2018/003091).

References (21)

  • Y. Xu et al.

    Ordered CoFe2O4 nanowire arrays with preferred crystal orientation and magnetic anisotropy Electro

    Acta

    (2009)
  • P. Chandramohan et al.

    Cation distribution and particle size effect on Raman spectrum of CoFe2O4

    J. Solid State Chem.

    (2011)
  • K. Bi et al.

    Magnetically tunable wideband microwave filter using ferrite-based metamaterials

    Appl. Phys. Lett.

    (2015)
  • K. Bi et al.

    Magnetically tunable microwave bandpass filter structure composed of ferrite rods and metallic slits Appl

    Phys. Lett.

    (2015)
  • Li Yin et al.

    Electric-field tunable perpendicular magnetic anisotropy in tetragonal Fe4N/BiFeO3 heterostructures Appl

    Phys. Lett.

    (2017)
  • I.C. Nlebedim et al.

    Systematic study of electronic and magnetic properties for Cu12–xTMxSb4S13 (TM = Mn, Fe, Co, Ni, and Zn) tetrahedrite

    J. Appl. Phys.

    (2014)
  • R. Sai et al.

    Oriented nanometric aggregates of partially inverted zinc ferrite: one-step processing and tunable high-frequency magnetic properties

    J. Appl. Phys. B

    (2015)
  • V.V. Kerckhoven et al.

    Substrate integrated waveguide isolator based on ferromagnetic nanowires in porous alumina template

    Appl. Phys. Lett.

    (2014)
  • G.J. Deng et al.

    A novel high power X-band ferrite phase shifter

    Rev. Sci. Instrum.

    (2017)
  • B. Peng et al.

    Self-biased microstrip junction circulator based on barium ferrite thin films for monolithic microwave integrated circuits

    IEEE Trans. Magn.

    (2011)
There are more references available in the full text version of this article.

Cited by (0)

View full text