Ferrite Magnetic Thin Film And Its Application In On-Chip Inductors

For the needs of high frequency,miniaturization,high integration,and high reliability of electronic equipment,ferrite thin film inductors have superior application value and development potential.Based on the demand for soft ferrite thin film inductors in So C,this dissertation carried out two parts of research,preparation of high-performance ferrite thin films and the fabrication of thin-film inductors by semiconductor technology,and conducted in-depth study of the competitive relationship between magnetization and resistance,and relationship between magnetization mechanism and magnetic domain structure,has solved the key issues of anisotropy regulation,low-temperature crystallization of ferrite thin films,and compatibility with semiconductor processes.Among them,the research work of high-performance ferrite thin films is based on two deposition techniques:magnetron sputtering and spin spray deposition.Firstly,based on magnetron sputtering,the main composition of the sputtering target,the sintering time of the sputtering target,and the magnetic field induction of magnetron sputtering were studied.The results show that:?1?Increasing the content of Cu O in the target,the magnetocrystalline anisotropy of NiZn ferrite will continue to decrease.Taking into account the sintering densification and ion distribution,when the Cu O content is 4.0 mol%,higher M_s can be obtained.The increase in grain size caused by the fluxing effect of Cu O in NiZn ferrite will also make a great contribution to the improvement of magnetic permeability.?2?Through Lorentz electron microscope characterization and magnetic spectrum dispersion fitting,as sintering time of the target increases,domain wall motion mechanism gradually became the main magnetization contribution.When the operating temperature was increased from 22°C to 100°C,the ratio of the two magnetization mechanisms contributed by domain wall motion and spin rotation first increases and then remains unchanged.For the sample with an average grain size of 10.8?m,the change in anisotropy has a greater impact on the domain wall motion mechanism at 80°C.?3?When a parallel induced magnetic field is applied during the sputter deposition of ferrite thin film,iron cations tend to occupy the octahedral position,resulting in a decrease in the lattice constant,an increase in?400?preferred orientation,and an increase in saturation magnetization and magnetic permeability.By calculating the cation distribution and the effective magnetocrystalline anisotropy constant,the random anisotropy theory is used to explain the increase in<K>and the decrease in coercivity.With the magnetic field-induced anisotropy,the ferromagnetic exchange length gradually decreases,realizing an increase in anisotropy while reducing coercivity in NiZn ferrite.Then,based on the spin-spray deposition,four parts of research work including the composition,oxidant concentration,substrate type,and magnetic field induction were carried out.NiZn ferrite thin film was successfully prepared at about 120°C with low-temperature crystallization,which solved the compatibility of soft magnetic thin film and semiconductor process.The results show that:?1?When the iron content increases,the micromorphology and magnetic properties of NiZn ferrite change significantly.The?222?preferred orientation in the spin-sprayed NiZn ferrite thin film is because the growth mechanism of the thin film mainly comes from the close packing of B-site iron and oxygen ions on the?222?crystal plane,and the uniform triangular grain morphology has also confirmed The existence of?222?preferred orientation.The first-order reversal curve measurement shows that the grain size distribution becomes wider in the presence of?222?preferred orientation.In the process of increasing iron content,the main magnetization mechanism changes from spin rotation to domain wall motion,which improves magnetic permeability.?2?Increasing the oxidant Na NO₂concentration,the average grain size and saturation magnetization of the thin film gradually increase;when the oxidant concentration is too high,the?222?preferred orientation growth of the thin film is destroyed,and the grains appear agglomeration and uneven growth.At the same time,the triangular flake-like grains are transformed into spherical grains.The increase of the average grain size makes the magnetization mechanism of the thin film dominated by domain wall motion.?3?The excessively high thermal conductivity of the substrate will cause the crystallization reaction of ferrite no longer be restricted to the substrate surface,and the chemical reaction will occur in the liquid with high temperature,resulting in a higher deposition rate and larger grain size,but the saturation magnetization and permeability appear to decrease.?4?Increasing the in-plane parallel induced magnetic field,the?222?preferred orientation of NiZn ferrite gradually weakened.On the surface morphology,with the disappearance of the?222?preferred orientation,the grains of the sample gradually changed from triangular flake-like grains to uniform spherical grains.The decrease of the average grain size and the decrease of the density result in the simultaneous decrease of the coercivity and saturation magnetization of the thin film.The magnetic field-induced in-plane anisotropy conflicts with the?222?preferred orientation growth of the thin film itself,which reduces the permeability of the spin-sprayed NiZn ferrite thin film.Finally,using the design of the toroidal solenoid thin film inductor,the COMSOL simulation of the thin film inductor was carried out,and the production and testing of the thin film inductor were completed.The results show that:?1?when the magnetic thin film is introduced,the more the number of turns,the greater the increase in the inductance value of the magnetic thin film.The quality factor exhibits the opposite law of the air-core coil in the low-frequency band.The more the number of turns,the quality factor The higher the operating frequency,the more the number of turns,the lower the quality factor;the increase in the width of the magnetic thin film can increase the total magnetic flux of the magnetic thin film and increase the inductance value of the inductor.At the same time,the quality factor of the inductor also increases with the increase in width of magnetic thin film.However,as the width of the magnetic thin film increases,the parasitic loss gradually increases,and the improvement of the quality factor becomes lower with the increase in thickness;the increase in the thickness of the magnetic thin film can increase the inductance and quality factor of the inductor.?2?Use a probe station to measure the on-chip thin-film inductors.After integrating a 1?m ferrite magnetic thin film,the inductance L and quality factor Q are respectively increased from 5.88 n H and 1.18 for air-core inductors to 7.21 n H at 100 MHz.And 1.7,the increase was 22.6%and 44%respectively.