| In recent years,with the rapid development of information technology and Internet technology,the high-performance and miniaturization of electronic components,module components and systems have been vigorously promoted,and switching power supplies as an indispensable component of power supply systems have also been developed.With the miniaturization and high performance of switching power supplies,the Electromagnetic Interference generated at high frequencies is becoming more and more serious,and thus the filtering performance of EMI(Electromagnetic Interference)filters is put forward higher.High-frequency and high-Q NiCoZn ferrites can be used as a key material in EMI filters,but high sintering temperature limits its combination with the current mainstream LTCC(Low Temperature Co-fired Ceramic)passive integration technology.Nevertheless it is a common method of soft magnetic ferrites to reduce the sintering temperature of ferrites by doping low melting point oxide,glass and ceramic.In this paper,the sintering properties,phase,microstructure,magnetic properties and dielectric properties of NiCoZn(NCZF)ferrite,NCZF ferrite doped with ZnOB2O3-SiO2(ZBS)glass and NCZF ferrite doped with Bi4Ti3O12(BIT)ceramic at different sintering temperatures were investigated experimentally,and the effects of the above ferrites with excellent performance on the filtering performance of EMI switching power supplies were verified.The study for NCZF ferrite found that when the NCZF ferrite is sintered at 800℃,the relevant main phase has been formed;when the sintering temperature is low,the NCZF ferrite has an excellent quality factor Q.The study for ZBS/NCZF composites found that the composites were successfully sintered at 1100℃ and the appropriate amount of doping ZBS glass can reduce the sintering temperature of NCZF ferrite;When the frequency is in the range of 1MHz to 5.8MHz,the smallest magnetic loss and the highest quality factor can be get at x=8wt%in all samples;and the ε’ is substantially stable at the frequency from 65MHz to 400MHz,reaching the maximum value of 23 at x=8wt%in all samples.The study for BIT/NCZF composites found that the BIT ceramics have been formed after calcination at 770℃.When the sintering temperature exceeds 900℃,the appropriate amount of BIT can promote the growth of NCZF ferrite grains;And the sample has a good Q value at x=6w t%in the range from 1MHz to 56MHz.And in the frequency range from 3.5MHz to 288MHz,the sample with the doping amount of x=6wt%has a tanσ<0.002 and a low dielectric loss.Through the influence of ferrites with excellent performance on the filtering performance of EMI switching power supply filter,it is found that:The filters made by the NCZF,ZBS/NCZF(8wt%ZBS doped)and BIT/NCZF(6wt%BIT doped)materials have a common mode noise rejection of 20dB at 1.5MHz,a differential mode noise suppression of 25dB at 1.5MHz and excellent noise suppression performance in the bandwidth of about 38MHz;The filter made by NCZF ferrite sintering at 1100℃has a excellent common mode noise suppression capability when the frequency is above 7 MHz and has a excellent differential mode noise suppression capability when the frequency is below 10 MHz.The filter made by NCZF ferrite doped with BIT ceramic sintering at 900℃ has a good differential mode noise suppression capability in the frequency range from 10 MHz to 15MHz;when the frequency exceeds 20MHz and the three types of ferrite are used as the differential mode inductor,the suppression effect on the differential mode noise is equivalent.Therefore,NCZF ferrite doped with BIT ceramic has a good application prospect in combination with LTCC integration technology to develop high-performance EMI filter. |
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