Fabrication And Electrical Properties Of Electrostatic Silicon-based MEMS Capacitors

As a new type of modern micro energy storage device in recent time,MEMS capacitors with their characteristics of size miniaturization,high integration and low price,are excepted to combine with silicon integration technology to be a good application prospect in the microelectronic energy storage device industry.Among them,electrostatic MEMS capacitors have been expected a promising application prospects due to their superiorities of all solid state for combining with silicon technology,thus,achieving mass integrated production of energy storage devices.Despite their ascendancy,the energy density of electrostatic MEMS capacitors has yet far from satisfactory.In order to better the low energy density of electrostatic MEMS capacitors and the high cost of MEMS thin film deposition processes such as chemical vapor deposition and pulsed laser deposition,in this paper,aiming at increasing the specific surface area of the capacitor electrode and the dielectric constant of the dielectric layer film respectively,two kinds of electrostatic silicon-based MEMS capacitors are proposed.One is prepared by simple anodization on a three-dimensional grooved silicon substrate to form metal-medium-metal?MIM?structure electrostatic capacitor,the other is conducted by sol-gel method for forming Na_0.5Bi_0.5Cu₃Ti₄O₁₂?NBCTO?film with high dielectric constant to fabricate metal-medium-silicon?MIS?structure electrostatic capacitor.?1?Spatial groove arrays on silicon substrates are etched by combining photolithography with wet etching to improve their specific surface area.The effect of mask size,KOH concentration,isopropanol?IPA?and other factors on morphology of three-dimensional groove are mainly investigated.It is concluded that the best etching depth and three-dimensional groove morphology is obtained when the groove spacing of mask plate is 75?m,water bath temperature for etching is 65?,and mixed etching solution is 5 mol/L KOH and1 mol/L IPA.The normalized estimation of the three-dimensional array groove increases the specific surface area of the silicon substrate by about 70.3%.?2?TiO₂ film prepared by simple constant anodization at room temperature to construct a MIM structured electrostatic capacitor is presented.During this process,the influence of different voltage of anodization on capacitance characteristics of MIM capacitors is investigated.It is found that the electrostatic capacitor formed with anodizing voltage of 20 V had a good capacitance characteristics.For this capacitor,it has a biggest energy density of 4.2 J/cm³,a better capacitance density of 7.91fF/?m²,and an outstanding leakage current density of 5.93 nA/cm² at 2 V.In addition,by testing and analyzing the CVS reliability of the capacitor,it is found that the capacitor has a good capacitance reliability,and only 0.02 fF/um² was changed when the 3 V voltage was implemented for 10000 s.?3?A MIS electrostatic capacitor composed of NBCTO thin films with high dielectric constant is prepared on silicon substrate by sol-gel method.The effect of sintering temperature of 650??750?and 850?on the C-V and I-V characteristics of MIS electrostatic capacitors is discussed.The experiment shows that NBCTO electrostatic film sintered at 750?has the best capacitance performance.It has a biggest energy density of 6.53 J/cm3 at 25 V,and a biggest capacitance density of 907 nF/cm²,and a good leakage current density of 5.16?A at 1 V.Furthermore,this electrostatic capacitor also exhibits a good capacitance characteristics in dielectric layer charging analysis.