Printed nanocomposite heat sinks for high-power, flexible electronics

Date of Award

2021

Degree Name

Ph.D. in Chemical and Materials Engineering

Department

Department of Chemical and Materials Engineering

Advisor/Chair

Christopher Muratore

Abstract

The planar and rigid nature of silicon-based electronics limit their reliability and integration into the next generation of electronics, like the Internet of Things (IoT) and wearable sensors. Unconventional electronics integrated with soft materials typically exhibit thermally limited performance due to low interfacial conductance and poor substrate thermal conductivity. To combat these issues, graphite nanoplatelets (GNPs) were used to increase the thermal conductivity of a flexible polydimethylsiloxane (PDMS) substrate by creating a percolating network of high thermal conductivity filler, increasing the substrate conductivity from 0.2 W-m-1K-1 to upwards of 1.8 W-m-1K-1, more than 9 times enhancement. This substrate material retained other useful properties including rheological behavior necessary for additive manufacturing, high temperature stability (upwards of 300C), flexibility (4 MPa compression modulus) and strong adhesion to device materials. This work is the first to demonstrate the direct transfer of the thinned AlGaN/GaN high electron mobility transistors (HEMTs) to the flexible polymeric nanocomposite substrate without an adhesive layer. The devices transferred to the PDMS composite substrates exhibited significantly lower self-heating temperatures experimentally (e.g., delta T = 24C at 30 mW) than those on PDMS when operated at comparable powers (15-50 mW), validating computational model results. These lower operating temperatures directly facilitate the operation of the devices at higher saturation currents and powers. The higher thermal conductivity of the PDMS composite substrate promotes heat conduction away from the device channel and effectively behaves as a flexible heat sink, which contributing to the high operating powers of 6 W-mm-1, especially compared to conventional flexible electronic substrates with low thermal conductivities (i.e. PDMS with no fillers). Additionally, the reduction of device temperatures at target operating powers result in longer anticipated device lifetimes and improved reliability. As evidence of the robust nature of this substrate-device pair, the transferred flexible devices remained adhered to the substrate and retained their performance with no observed reduction in saturation current even after subjection to 100 cyclic bending cycles to a bend radius of 33 mm and 15 mm. Further device performance improvements were demonstrated computationally via the optimization of the heat sink substrate's material properties and architecture, using COMSOL Multiphysics software. This work highlights the need for thermal management in flexible electronics for high-power operation and provides a solution to address the thermal limitations.

Keywords

Materials Science, Engineering, flexible electronics, additive manufacturing, composites, graphite nanoplatelets, PDMS, HEMT, GaN, thermal management

Rights Statement

Copyright © 2021, author.

Link to Full Text

Share

COinS