Fabrication And Microwave Properties Of M Type Barium Ferrites Thick/Thin Films

The rapid development of electrical imformation and communication technologies requires that the development of devices move toward more muti-function, miniaturization, leading to higher requirements in the election, fabriction and design of electrical materials. M-type barium ferrite is widely applied in microwave/ millimeter wave devices due to it has excellent chemical stability, big coercivity, high saturate magnetization and high cut-off frequency, together with high remannence, large magnetocrystalline anisotropy and low microwave loss.In this dessertation, research on low temperature co-fired of BaM as well as the fabrication and its improvements of BaM films were carried out. Firstly, the low temperature sintered BaM were fabricated with BCB additive by Solid Phase method, so that the BaM green tape which made by Tape Casting can be used in LTCC technology. It is found that the sintered temperature of BaM can be lowered to 900°C with 3wt% BCB, and it had maximal density, permeability and specific saturation magnetization. BaM can not be used in high frequency devices due to large magnetic anisotropy. Hence, CoTi ions were used to dope the Fe ion, which lead to an increase in permeability of Ba(CoTi)xFe12-xO19 ranging from 3 when x=0 to 17.5 when x=2, and magnetic anisotropy were decreased because of the Fe ions in 2b site were substituted by CoTi ions. It is also found that there are a change in lattice(a, c) and cell volume due to the difference of radius between Fe and CoTi, resulting in a distortion in single grain. Then Ba M thick film with the magnetization is 4008 Gs, remanence is 3201 Oe, squareness ratio is 80%, and FMR is 1828 Oe wse fabricated by Tape Casting. It is found that the thick films have low the crystallographic alignment degree by XRD, which lead to a high microwave loss.In order to get high oriented and low microwave loss BaM films, MOD method was used to deposit BaM film. After optmizing the ratio of EDTA and ions, the spin speed, the sintered temperature and the ammosphere, an excellent thin film was obtained with average values of 8.92 ± 1.94 nm and 6.95 ± 1.5 nm for rms and average roughness, respectively. The single grain grew in terrace, and the terrace steps in this example all measure 2.28 nm. The magnetization is 4204 Gs, remanence ratio is 96%, and anisotropy field is 16.5kOe for the thin film. The linewidth changes with frequency, creating a “W” shaped response, all the linewidths are smaller than 180 Oe, it has a smallest value of 118Oe@50 GHz and a largest value of 173Oe@60 GHz.In addition, in order to increase the working frequency of microwave/millimeter wave devices and it only needs a low external bias magnetic field; the BaM should have a larger anisotropy field. Hence, the effect of non-magnetic ion Al on the magnetic and microwave propertie of BaM was studied. It is found that hexagonal grains disapperence and more and more abnoumal grains appere when Fe ions were substituted by Al ions, and the total magnetic moment decease and super-change of Fe3+-O-Fe3+ became weaken, which lead to a decrease in saturation magnetization and Curie temperature. However, all of the samples still have high squreness ration ranging from 0.84 to 0.94. The change of HA with Al doped content is apparant, when x=0, the minimun is 16.1kOe@63K,and maximun is 16.9kOe @298K; when x=2, the minimun is 23.8kOe @61K,and maximun is 27.5kOe @298K. The AH increases linearly with increasing doped content at room temperature.Finally, due to the single phase material cannot show excellent magnetic and eletric properties simultaneous, the research on magnetoelectric properties and magnetoelectric coupling effect of magnetoelectric compostite thin films of SBT/BaM were carried out. It is found that SBT and BaM can coexist without any intermixing, the saturation magnetization is 3918 Gs, squreness ratio is 93%, and FMR is 140 Oe. Effective relative permittivity is 175, and the tunability of permittivity at 30 kV is 25%, and leakage current is only 1 mA/cm2 when applied electric field is 20 V. And this heterostructures thin film exhibits high magnetoelectic effect and constant is1.8 Oe*cm / kV.