Research On Preheating Of Y And Mn Alternately Doped BST Films

Owing to good ferroelectric and dielectric properties, BST film has become a research hotspot. Its’ good properties offers great chance to be applied in varies microwave tunable devices such as shifters, DRAM et al. But application in these devices require two contions: high tunability and low dielectric loss. However pure BST can not meet two needs at the same time. To overcome these drawbacks, our research team has done many researches such as improving the preparation method, using different kind of doping, so far, it achieved many progress. And our team found that adding a preheating process in sol-gel method would effectively improve the properties of BST. So based on our previous research, Y/Mn alternately doped BST, denoted as Y/Mn-BST has been prepared using sol-gel method, also the phase structure and dielectric properties has been analysised using XRD, SEM and C-V test results. The research results are as follows:1. Proper preheating process could siginificantly improve the dielectric properties of BST films, not only remains high tunability, but also effectively decrease the dielectric loss. Preheated under 600℃, the crystallization of Y/Mn-BST strengthened with the increasing of Mn doping concentration. As to the dielectric loss, with the increasing of Mn doping concentration, it decreased first from 2.03% to 1.98% and then increased to 2.44%.And when Mn concentration is 2mol%, the Y/Mn-BST shows best tunable properties with a tunability of 52.10%. While preheated under 650℃, the 3mol%Mn/1mol%Y shows best crystallization with largest grain size. And with the increasing of Mn doping concentration, the dielectric loss decreased first and then increased. And 2mol%Mn/1mol%Y shows a great tunability of 61.6%.2. Preheated under 550℃, Y/Mn-BST films achieved better dielectric properties with lower loss and high tunability. The 2mol%Mn/1mol%Y, 3mol%Mn/1mol%Y, 5mol%Mn/1mol%Y shows a minimum dielectric loss at 0.79%, 0.97%, 0.92% respectively. Properties of these level could satisfy the application needs well.3. A new kind of preheating method called “graded preheating” has been brought out based on the previous preheating research. It means using a different temparature for each layer of Y/Mn-BST. The first layer is preheated under 550℃, the next layer’s preheating temperature increased by 20℃, so the last layer would be preheated under 650℃. Using the new preheating process, dielectric roperties of Y/Mn-BST has beem siginificantly improved which can be illustrated by the SEM results, films under graded preheating process shows more average grain size and less pinholes. As to the dielectric properties, 2mol%Mn/1mol%Y film displays a maxmum, minimum dielectric loss and tunability of 1.4%, 0.49% and 50.2%, when Mn doping concentration increased to 3mol%, max loss and min loss is still very low at 1.3% and 0.404%. With Mn doping concentration increased further, dielectric loss increased a little, but still remains a lower level. All results above showed the “graded preheating” is a suerior preheating method. Also films using “graded preheating” process showed better frequency stability than films under traditional preheating method. For instance, max capacitance and min capacitance of 6%Mn/1%Y film at 1MHz is 106 pF and 52.6pF,while at 100 kHz, is 110 pF and 54.5pF, datas are very close.