Measurement of In-Plane Thermal Conductivity Using Suspended SiNx Islands

Abstract

In order to measure in-plane thermal conductivity, electrical resistivity, and Seebeck Coefficient of Phononic Crystals (PnCs) a micro device is designed and fabricated to host different nano-scale samples. The device is comprised of two SiNx suspended membranes with patterned by Pt on top and covered by AlN. The Pt deposited on these two membranes or islands are dual-purpose temperature sensors and heaters. One side of a sample can be attached to each of the two islands. In this way 1-D heat flow can be established in the material to be tested. Covering the islands with AlN enhances the uniformity of temperature on each sensor. Moreover, AlN is an excellent electrical insulator, and it protects the platinum sensors from different sources of doping such as gallium ions used for patterning, depositing, mounting, or demounting different samples on the islands. This ensures the thermo-electric properties of the sensors on the platform do not change after each measurement. Using this design, it is demonstrated that one platform can be used for measurement of a silicon slab and then a separate measurement of a 1-D PnC fabricated from the same sample. The 1-D PnC had a Si-W structure that was fabricated using a Focused Ion Beam (FIB) and a Gas Injection System (GIS) capable of depositing W.

Thermal conductivity and nanocrystalline structure of platinum deposited by focused ion beam

“…The thermal conductivity of a sample is determined using a 1D technique wherein the sample is placed between a hot and a cold island [15,21,22]. The authors' rendition of this technique allows measurement of different micro/nano structures on a single platform, which minimizes systematic errors.…”

“…The platform used for characterization is the same platform previously used by the authors to characterize two silicon films (500 and 260 nm thick) and a silicon nitride thin film. This platform has also been used in other work by the authors to measure the thermal resistance of a 1D Phononic Crystal [21].…”

“…A carbon nanofiber with diameter of 80 nm and length of 12.5 μm (see figure 5) is transferred with a mico-manipulator and affixed by FIB deposited Pt. Details for the processing of the nanofiber used can be found elsewhere [38,39], and transferring and affixing of nanofibers is a common process for thermal characterization [15,17,18,[20][21][22].…”

“…Numerous studies using this technique of 'micro-welding' show the growing importance of this application [16][17][18][19][20]. Although researchers have studied the thermal conductivity of nano/micro structures affixed to measurement devices by FIB deposited platinum [21,22], the thermal conductivity of these FIB deposited platinum films is still uncharacterized. A direct measurement of the thermal conductivity for FIB deposited platinum has the potential to remove or reduce erroneous effects in many measurements involving this material for the purpose of micro-welding [15,17,21].…”