Thesis Title : "Design and Development of Hybrid Capillary-Wicking and Micro-Delivery Architectures for Cooling in Advanced Packaging"

Name of the Student : Mr. Nishant Kumar Sharma
Degree Registered   : Ph.D. (Engineering) 
Advisor             : Prof. Prosenjit Sen, CeNSE
Date                 : 23rd July 2026 (Thursday) 4:00PM

Venue               : CeNSE Seminar Hall
Abstract:

The continued increase in power density and integration complexity of modern electronic systems,
 such as AI accelerators, high-performance processors, and heterogeneous chiplet-based systems, 
has made high-heat-flux thermal management a critical bottleneck in advanced packaging. 
Although logic circuits typically dissipate spatially averaged heat fluxes on the order of 10-100 W cm⁻², 
while operating below approximately 100-80 °C, localized near-junction hotspots can exceed 1 kW cm⁻². 
Such highly non-uniform thermal loads generate severe temperature gradients, thermo-mechanical stresses, 
interfacial deformation, and accelerated material degradation, ultimately compromising device reliability. 
Thus, emphasizing the need for cooling technologies capable of removing intense, localized heat fluxes at 
small temperature differences. Conventional heat spreaders, vapor chambers, and cold plates primarily reject 
heat at the package boundary and are therefore limited by intervening thermal resistances and restricted 
access to buried hotspots. This thesis develops a multiscale thermal-management framework that integrates 
passive capillary liquid transport, phase-change heat removal, closed-loop cooling, and vertical thermal 
routing for advanced electronic packages.

The first part of the work investigates hierarchical nano-textured superhydrophilic wicks to improve the 
surface wettability for liquid transport. Their liquid-transport behavior is examined through capillary rise, 
wire-level hemiwicking, junction-mediated liquid accumulation, pore initiation, meniscus evolution, and pore filling. 
Geometrical, energetic, and transport frameworks are developed to understand the hemi-wicking and pore-wicking dynamics. 
The results demonstrate that wick performance is governed by a coupled balance among capillary pressure, liquid-storage 
capacity, wire-junction connectivity, and pore accessibility.

The thermal performance of these nano-textured surfaces is subsequently characterized under capillary-fed operation. 
Distinct regimes of sub-saturated evaporation, onset of nucleate boiling, stable liquid-film boiling, meniscus recession, 
and capillary dryout are identified. Comparisons between mesh geometries and layer numbers reveal that local evaporation 
efficiency and maximum sustainable heat flux are controlled by different structural features. Multilayer configurations 
further enhance performance through parallel liquid pathways, interlayer channels, additional liquid-vapor interfaces, 
and improved rewetting. The capillary evaporators are further evaluated in open- and closed-loop configurations for direct-on-chip cooling.

To address hotspots that cannot be contacted directly, high-density interconnect structures are developed as 
vertical thermal conduits for routing heat from buried device regions to an accessible surface where a 
capillary-fed evaporator can be integrated. These interconnects were further explored for high-density, 
low-pitch direct metal-to-metal bonding for heterogeneous integration of chiplets, both for low-thermal-budget
and thermally sensitive substrates. In addition, a shape-memory-alloy-actuated peristaltic micropump is developed 
as an enabling component for controlled fluid delivery and active augmentation of closed-loop operation. 
A thermally decoupled mechanical isolation interface is introduced to transmit actuation while limiting 
parasitic heat leakage from the actuator to the fluidic conduit.

Together, this work establishes an advanced packaging-oriented thermal framework that combines passive 
capillary replenishment, thin-film evaporation, capillary-fed boiling, closed-loop operation, and vertical 
heat routing. The developed concepts provide design principles for compact cooling architectures in heterogeneous electronic packages.