  Hot-spots are considered among the unavoidable consequences of the high
integration density of 3D-ICs. Eliminating hot spots requires employing
efficient cooling techniques. Using embedded channels, liquid cooling systems
can be designed to deliver the right amount of coolant to each spot of the
chip. In this study, numerical analysis is used to investigate the cooling of a
20 W hot spot using embedded channels employing three coolants: water, Freon
(R22), and liquid nitrogen (LN). The investigation of thermal management and
stress show that, although LN provides the lowest operating temperature (164
K), it causes the highest stress (355 MPa) at 100 mm/s inlet velocity. The
study also shows that, coolant delivery using parallel channels results in a
wide variation of local temperatures and stress. This stress variation may form
high-stress spots, which may cause circuit failure, performance degradation, or
yield reduction. Therefore, cooling systems and chip fabrication should be
designed to ensure the elimination of high-stress hot spots.
