Hydrothermal BaxSr1-xTiO3 Powders for Multilayer Capacitors
Prof. Elliott SlamovichMatt Slone
Project Objectives
• Hydrothermal production of BaxSr1-xTiO3 powders
• Tape cast powders to form thin films
• Fabricate MLCCs from films
• Test dielectric properties of films and capacitors
Review
• Capacitors
• BaxSr1-xTiO3 ceramics
• Tape casting
Capacitors• A capacitor is a device used to store potential energy in an
electric field
• Typical capacitors consist of two conducting plates separated by a dielectric material
• Energy is stored as a result of the shifting of ions in the dielectric acting to oppose an applied electric field.
Diagram: Callister, Materials Science and Engineering An Introduction, 5th ed. 2000.
Multilayered Ceramic Capacitors
• In parallel-plate capacitors C = oA / d• For greatest capacitance, increase area and
decrease thickness• Capacitor size can be conserved by stacking many
very thin capacitors
BaTiO3 / SrTiO3 Ceramics
• Both have perovskite crystal structure, allowing the formation of a solid solution
• Have very high dielectric constants at their Curie Temperatures
• The curie temperature of the BaxSr1-xTiO3 can be controlled by the Ba / Sr ratio in the solid solution
• Tc of BaTiO3 is 120oC, Tc of SrTiO3 is –50oC
Tape Casting• Process to form thin, uniform sheets of ceramic material
• Ceramic powder mixed into an slurry containing solvent, binder, and dispersant.
• Slurry is cast into a soft, flexible green tape
• Solvent evaporation, binder burnout, and sintering are performed to obtain solid ceramic material
Diagram: Mistler; Twiname, Tape Casting Theory and Practice, 2000.
Powder Production
• BaxSr1-xTiO3 powders produced using a hydrothermal process
• Reactions performed with solution properties: – The ratio (Ba + Sr) / Ti = 2 – (Ba +Sr) concentration of 0.8M– NaOH concentration of 1M
• Typical yield of about 30g of powder from 500ml of solution
Powder XRD
Slip Composition
Component BaxSr1-xTiO3 powder
Hypermer KD-1
Methyl Ethyl Ketone
Ethanol
Acryloid B-72
Butyl Benzyl Phthalate
Wt %
60.70 0.61 13.40 13.40 8.09 3.79
Function Ceramic Dispersant Solvent Solvent Binder Plasticizer
Tape Casting
• Each of the final four powders was tape cast with a doctor blade height of 300 m
• Green tape thickness ranged from 110 m to 135 m
• Thickness varied up to 25 m for a given tape
Laminating
• Tapes were cut using a circular die 25 mm in diameter
• Circles were stacked to a thickness of about 1.5 mm
• Stacks were pressed in the die at a pressure of 18 MPa and a temperature of 230oF
Binder Burnout and Sintering
• Binder burnout attempted on laminates at 420oC for 2 hours with a ramp of 15oC / hr
• Each of the samples cracked during the process
Successes
• Hydrothermal process adapted to suit production needs
• Slip composition for the tape casting of hydrothermally produced BaxSr1-xTiO3 was developed
• Tape casting and laminating procedure was determined
Further Studies
• Refine binder burnout procedure
• Examine sintering of laminates
• Examine dielectric properties of laminates
Acknowledgements
• Prof. Elliott Slamovich
• Jacob Jones
• Huiwen Xu
• Dave Roberts