Interfacial thermal conductance of transfer-printed metal films.

Deterministic assembly of microdevices by transfer-printing is an advanced manufacturing technology that enables the heterogeneous integration of disparate materials on largearea substrates. [ 1–5 ] All active electronic devices generate heat as a byproduct of their operation and thermal management of transfer-printed assemblies must be a consideration whenever the heat fl ux is large. While the thermal conductivities of most materials used in microelectronics are well known, the thermal conductance of interfaces formed by transfer-printing is unknown. We report studies of the thermal conductance of interfaces formed by transfer-printing of Au and Au(Pd) alloy thin fi lms, 100 μ m × 100 μ m in area and 100 nm thick, on amorphous SiO2 , hydrogen-terminated Si(001), and singlecrystal Al2O3 substrates. We fi nd that the thermal conductance Gt of transfer-printed interfaces spans a relatively small range, 10 < Gt < 40 MWm−2K−1 despite signifi cant differences in the thermal conductivity of the substrates and interfaces roughness. These values of Gt are smaller than the conductance of interfaces formed by physical vapor deposition but orders of magnitude larger than the conductance of pressed contacts between macroscopic polished surfaces. The relatively small thermal resistance of transfer-printed interfaces will not create a signifi cant thermal management problem in most applications of transfer-printing but will be a concern in high-power technologies that involve extremely large heat fl uxes, > 10 kW cm − 2 . The thermal conductance G of interfaces formed by physical vapor deposition of metal fi lms on dielectric substrates has been studied extensively. G is the transport coeffi cient that relates the heat fl ux J Q to the temperature drop Δ T at an interface, JQ = G T . The observed values span a large range, from a low conductance of G ≈ 10 MWm−2K−1 for Bi deposited on hydrogen-terminated diamond [ 6 ] to a high conductance [ 7 ] of G ≈ 700 MWm−2K−1 for epitaxial TiN/MgO. Often,