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Thermoelectric properties of bismuth-doped magnesium silicide obtained by the self-propagating high-temperature synthesis

Bucholc Bartosz, Kaszyca Kamil, Śpiewak Piotr, Mars Krzysztof, Kruszewski Mirosław J., Ciupiński Łukasz, Kowiorski Krystian, Zybała Rafał

Bulletin of the Polish Academy of Sciences. Technical Sciences

2022

Vol. 70, nr 3

art. no. e141007

Doping is one of the possible ways to significantly increase the thermoelectric properties of many different materials. It has been confirmed that by introducing bismuth atoms into Mg sites in the Mg2Si compound, it is possible to increase career concentration and intensify the effect of phonon scattering, which results in remarkable enhancement in the figure of merit (ZT) value. Magnesium silicide has gained scientists’ attention due to its nontoxicity, low density, and inexpensiveness. This paper reports on our latest attempt to employ ultrafast self-propagating high-temperature synthesis (SHS) followed by the spark plasma sintering (SPS) as a synthesis process of doped Mg2Si. Materials with varied bismuth doping were fabricated and then thoroughly analyzed with the laser flash method (LFA), X-ray diffraction (XRD), scanning electron microscopy (SEM) with an integrated energy-dispersive spectrometer (EDS). For density measurement, the Archimedes method was used. The electrical conductivity was measured using a standard four-probe method. The Seebeck coefficient was calculated from measured Seebeck voltage in the sample subjected to a temperature gradient. The structural analyses showed the Mg2Si phase as dominant and Bi2Mg3 located at grain boundaries. Bismuth doping enhanced ZT for every dopant concentration. ZT = 0.44 and ZT=0.38 were obtained for 3wt% and 2wt% at 770 K, respectively.

Technologia SLID w montażu GaN-on-Si do podłoży Cu

Kisiel Ryszard, Śpiewak Piotr, Kruszewski Mirosław J.

Przegląd Elektrotechniczny

2021

R. 97, nr 2

60--63

Analizowano proces montażu chipów GaN-on-Si do podłoży Cu w oparciu o pasty Ag. Wykorzystano dwa zjawiska: zgrzewania dyfuzyjnego do połączenia między metalizacją montażową chipu Si i pastą Ag oraz zjawisko dyfuzji w fazie ciekłej (SLID – Solid-Liquid Interdiffusion) do połączenia między podłożem Cu a warstwą pasty Ag. Stosowano jeden profil temperaturowy: suszenie 70C&10min+ SLID 250C&5min oraz dyfuzję w fazie stałej 200C&60min. Uzyskano połączenie o dobrej adhezji (powyżej 10 MPa) oraz zadowalającej rezystancji cieplnej (ok. 0,05 K/W).

The application of SLID technology for the assembly of GaN-on-Si chips on Cu substrate using Ag paste is considered. The assembly process is based on: sintering for creation interface between Au metallization on Si chips and Ag paste as well as SLID process for creation interface between Ag paste and Cu substrate with Sn metallization. One temperature profile was applied: drying (70C&10min) + SLID (250C&5 min) + sintering (200C&60 min) in air. Connection is characterized by good adhesion (above 10 MPa) and low thermal resistance (0,05 K/W).