New Probe and Microscopy Technique Illuminates Defects in Materials
Using new focus ion beam probe techniques in combination with electron microscopy techniques previously developed in their lab, Penn State researchers have developed original methods for finding and analyzing material defects in capacitors and multilayer actuators that are ubiquitous in most electronic devices on the market.
A team from the Center for Dielectric Studies that included Clive Randall, Elizabeth Dickey, Gai-Ying Yang, and Paul Moses developed the technique in conjunction with Kemet Corporation, a major producer of capacitors, located in Greenville SC.
Gai-Ying Yang examines samples using transmission electron microscopy in Penn State's Materials Characterization Laboratory.
"This is a collaborative endeavor between Kemet, which has vast experience in producing commercial multilayer ceramic capacitors (billions a year), and Penn State, with our long-established history of research in capacitor materials and with the analytical tools necessary to understand the physical origins of material degradation," says Dr. Dickey.
The ability to characterize and predict failure in capacitor materials has increasing importance as the size of capacitors shrink and the dielectric layers are reduced to submicron thickness. Within the next ten years, according to Dickey, multilayer capacitors based on barium titanate will have layers with thicknesses on the order of 0.2 micrometers, with each capacitor containing hundreds of layers.
"With this method, the manufacturer can know which samples and which processes are likely to result in failure to the capacitor," says Dr. Yang. "I can see, for instance, that where there should be metal, there may be oxide instead, which is not good. Some parts of the manufacturing process may be producing good materials and other parts not."
Using a Voltage Contrast SEM at very low voltage, the researchers can see a region that is locally imperfect and measure the amount of electrical leakage, a clue to the potential for failure of the capacitor. Then, in a new technique developed within the last month by their group, they use a focused ion beam (FIB) microprobe with a diameter as small as .1 micron to do electrical measurements and characterize the defect.
Using the FIB, samples are extracted from the weak points of capacitors for more detailed electrical and structural analysis. A statistical approach is applied and modeled to better understand the onset of total leakage of a device from its microscopic origins. This link between structure property relations and statistical analysis will help any company involved in multilayer actuators, capacitors, and fuel cells to refine their manufacturing processes and improve their products, according to Dr. Randall.
In regular conference calls with Kemet scientists, the Penn State researchers share the results of their analysis. "Using our experience and our analytical tools and techniques that is very useful for our industrial partners," Yang says.
Kemet Corp. is one of 24 industry and governmental partners in the Center for Dielectric Studies. The National Science Foundation, which is a CDS member, provided the funding to purchase the FIB through the NSF Major Research Instrumentation Program. The FIB is a new addition to Penn State's world-class characterization facility, the Materials Characterization Lab, a part of the Materials Research Institute.
To view bright field TEM images download For writer MRI.ppt
The Center for Dielectric Studies in Penn State's Materials Research Institute is the nation's longest running federally sponsored joint university/industry collaboration. Visit them on the web at: www.mri.psu.edu/centers/cds/ .
By Walt Mills, wem12@psu.edu, 814-865-0285
