Study On Fabrication And Modification Of Ta₂O₅ Ceramics By Spark Plasma Sintering

With the rapid development of integrated circuits,it is urgent to find the material with high dielectric constant to replace silicon-based materials in industrial production.Ta₂O₅ has been considered as one of the alternatives to silicon-based materials because of its high dielectric constant,low leakage current density,good thermal and chemical stability and easy compatibility with the current silicon process.Therefore,the preparation of Ta₂O₅ based ceramics with high dielectric properties is vital.Spark plasma sintering（SPS）is a unique heating method in the preparation of ceramic materials,and sintered compact can be obtained at lower temperature,which is expected to obtain dense Ta₂O₅ based ceramics with high dielectric properties.First,Ta₂O₅ ceramics were prepared by spark plasma sintering（SPS）at different sintering temperature,soaking time,applied pressure and heating rate.The effect of SPS sintering process on the microstructure and dielectric properties of Ta₂O₅ ceramics was studied.Ta₂O₅ ceramics can be sintered below 1360^oC via SPS to avoid cracks due to the volume effect.The Ta₂O₅ ceramics prepared by SPS show fine and uniform grains,and the density is over 99%.Dense Ta₂O₅ ceramics with dielectric constant up to 61.08 and dielectric loss as low as 0.0024 was prepared in this study.Through the optimization of the preparation process,the optimal sintering processing parameters was obtained,i.e.,sintering temperature of 1100^oC,soaking time of 5 min,applied pressure of 50 MPa and heating rate of 50^oC/min.Second,Ta₂O₅/Ti O₂ composite ceramics were prepared on the basis of the above optimum preparation process.The effects of doped Ti O2 on the phase structure,microstructure and dielectric properties of tantalum oxide-based ceramics were studied.It is found that SPS can effectively prevent the solid state reaction between Ta₂O₅ and Ti O₂;and the addition of Ti O₂ has insubstantial effect on the microstructure of Ta₂O₅based ceramics.Ti O₂ doping barely increases the dielectric constant at room temperature,but the doping of Ti O₂could improve the temperature characteristics of dielectric constant of Ta₂O₅/Ti O₂ composite ceramics.Finally,Ta₂O₅/Ti O₂ composite ceramics（designated as PH-Ta₂O₅/Ti O₂）,prapered by pre-heating powder,were fabricated under the optimal preparation process to explore the effect of H_mon-Ti Ta₁₈O₄₇ high-temperature solid solution on the dielectric properties of tantalum oxide-based ceramics.The result shows that H_mon-Ti Ta₁₈O₄₇ can be obtained by pre-heating of（Ta2O5）（1-x）（Ti O2）x powder,and the H_mon-Ti Ta₁₈O₄₇ high temperature solid solution phase is retained in ceramics with x=0.11 and 0.15 prepared by SPS.However,the H_mon-Ti Ta₁₈O₄₇ transformed to L_ort-Ta₂O₅ in all samples after heat treatment.It is difficult to obtain the ceramics with H_mon-Ti Ta₁₈O₄₇ as the main phase structure and improved dielectric constant.Nevertheless,the temperature characteristics of PH-Ta₂O₅/Ti O₂ dielectric properties are further improved compared to Ta₂O₅/Ti O₂composite ceramics.In particular,PH-Ta2O5/Ti O2（x=0.08）ceramics exhibit excellent temperature characteristics at 1 MHz.