Ali Karbasi

High P-T phase transitions and P-V-T equation of state of hafnium

We measured the volume of hafnium at several pressures up to 67 GPa and at temperatures between 300 to 780 K using a resistively heated diamond anvil cell with synchrotron x-ray diffraction at the Advanced Photon Source. The measured data allows us to determine the P-V-T equation of state of hafnium. The previously described [Xia et al., Phys. Rev. B 42, 6736–6738 (1990)] phase transition from hcp (α) to simple hexagonal (ω) phase at 38 GPa at room temperature was not observed even up to 51 GPa. The ω phase was only observed at elevated temperatures. Our measurements have also improved the experimental constraint on the high P-T phase boundary between the ω phase and high pressure bcc (β) phase of hafnium. Isothermal room temperature bulk modulus and its pressure derivative for the α-phase of hafnium were measured to be B0 = 112.9 ± 0.5 GPa and B0′ = 3.29 ± 0.05, respectively. P-V-T data for the α-phase of hafnium was used to obtain a fit to a thermodynamic P-V-T equation of state based on model by Brosh ...

Micro-Dispense Direct Printing for Thermal Management Structure Using LTCC

The microelectronic manufacturing industry has been seeking improved efficiencies and faster fabrication turn-around for decades. The demand for better thermal management has been increasing in recent years and better materials and new processing techniques have been emphasized. LTCC technology has demonstrated great potential for satisfying most performance, cost and processing requirements. A novel approach for LTCC is micro-dispense direct printing which can print a wide range of materials to include a variety of screen printable thick film conductors, thick film resistors, dielectric materials and solder. Those with experience in micro-dispensing recognize the size limitation using a dispensing approach and understand that the hope of achieving smaller line widths, smaller pad sizes, and precise placement of the material is challenging. nScrypt has demonstrated the ability to build a complete branching micro-channel structure using a micro-dispensing LTCC approach. nScrypt has also demonstrated how th...

Effect of platinum metallization in cofired platinum / alumina microsystems for implantable medical applications

Typically, hermetic feedthroughs for implantable devices, such as pacemakers, use an alumina ceramic insulator brazed to a platinum wire pin. This material combination has a long history in implantable devices and is the desired structure due to the acceptance by the FDA for implantable hermetic feedthroughs. The growing demand for increased input/output (I/O) hermetic feedthroughs for implantable neural stimulator applications can be addresses by developing a new, co-fired platinum/alumina multilayer ceramic technology in a configuration that supports 300 plus I/Os, which is not commercially available. Different densification rate of platinum and alumina is the major issue in developing a high-density feedthrough. This difference in densification rate could create delamination and crack in feedthrough structure and decrease the reliability and degree of the hermeticty of the final assembly. In this paper different metallization were evaluated to minimize this difference. Additionaly the firing atmosphere...

Materials Interaction in Cofired Platinum /Alumina High Density Feedthrough for Implantable Applications

Neurostimulator applications will require much higher I/O feedthrough density for hermetic implantable enclosures, often greater than 100 I/O. This work evaluates the development of high-density platinum via structure cofired in alumina. The platinum was observed to melt when cofired at 1550°C, almost 200°C below its melting point, independent of the particle size (nano to micron size particles) or particle morphology. An analysis of the effect of particle size (nano to micron size Pt), firing atmosphere (air, hydrogen, inert), firing temperatures, intermetallic reactions and additives to control thermal expansion and adhesion strength was performed to evaluate and minimize this exothermic reaction. The interaction of platinum and alumina has been evaluated using X-ray diffraction and SEM.