Packaging made primarily of aluminum nitride has been developed to enclose silicon carbide-based integrated circuits (ICs), including circuits containing SiC-based power diodes, that are capable of operation under conditions more severe than can be withstood by silicon-based integrated circuits. A major objective of this development was to enable packaged SiC electronic circuits to operate continuously at temperatures up to 500 °C. AlN-packaged SiC electronic circuits have commercial potential for incorporation into high-power electronic equipment and into sensors that must withstand high temperatures and/or high pressures in diverse applications that include exploration in outer space, well logging, and monitoring of nuclear power systems. This packaging embodies concepts drawn from flip-chip packaging of silicon-based integrated circuits. One or more SiC-based circuit chips are mounted on an aluminum nitride package substrate or sandwiched between two such substrates. Intimate electrical connections between metal conductors on the chip(s) and the metal conductors on external circuits are made by direct bonding to interconnections on the package substrate(s) and/or by use of holes through the package substrate(s). This approach eliminates the need for wire bonds, which have been the most vulnerable links in conventional electronic circuitry in hostile environments. Moreover, the elimination of wire bonds makes it possible to pack chips more densely than was previously possible.
Especially notable components of packaging of this type are the following:
- AlN substrates that have high thermal conductivity [170 W/(m×K)] and a coefficient of thermal expansion (CTE) that matches that of SiC;
- Thick gold conductor film circuit traces, the adhesion and sheet resistance of which do not change measurably at 500 ∞C over time periods as long as 1,000 hours; and
- Glass passivation/sealing layers that have a breakdown potential of 2,575 V at room temperature and, at 500 ∞C, breakdown potentials of 1,100 V for encapsulation of Au conductors and 1,585 V for encapsulation of Pt conductors.
The matching of CTEs minimizes thermal stresses. Packaging interconnections are monometallic or bimetallic and able to withstand high temperatures. These and other features are known to contribute to reliability at high temperatures and are expected to extend the high-temperature functionality of the packaged electronic devices. Further research will be necessary to characterize the long-term reliability of SiC-based circuits in AlN-based packages.
This work was done by Ender Savrun of Sienna Technologies, Inc., for Glenn Research Center. For further information, access http://www.siennatech.com.
Inquiries concerning rights for the commercial use of this invention should be addressed to NASA Glenn Research Center, Commercial Technology Office, Attn: Steve Fedor, Mail Stop 4-8, 21000 Brookpark Road, Cleveland , Ohio 44135. Refer to LEW-17478.