High Thermal Conductivity Transfer-Printed Polycrystalline Diamond Membranes for Device- and Chip-Level Thermal Management

The thermal conductivity of polycrystalline diamond (PCD) thin films can vary by more than an order of magnitude due to differences in the microstructure. PCD films often undergo columnar growth where the grain size increases with the film thickness. Therefore, phonon-grain boundary scattering significantly impacts the thermal conductivity and interfacial thermal transport. In this work, to utilize PCD membranes (PCDm) as transfer-printed heat spreaders for high-power electronic devices and chiplets, a fabrication process was developed where the defective and low thermal conductivity nucleation region of the PCD film is removed to form a high-thermal-conductivity membrane. The temperature-dependent anisotropic thermal conductivity of a ∼2.4 μm-thick PCDm (with the nucleation region removed) and the thermal boundary conductance (TBC) across the PCDm/Si interface were characterized via time-domain thermoreflectance (TDTR). The measured out-of-plane (κ_out = 304 ± 82 W m⁻¹ K⁻¹) and in-plane thermal conductivities (κ_in = 136 ± 31 W m⁻¹ K⁻¹) of the nucleation region-free membrane are significantly higher than those (κ_out = 187 ± 41 and κ_in = 103 ± 17 W m⁻¹ K⁻¹) for an as-grown ∼3.3 μm-thick PCDm that includes the nucleation region. The measured interfacial TBC at the PCDm/Si interface was determined to be 5.8 MW m^-2 K⁻¹, which is lower than typical values for PCD films directly grown on Si. Thermal modeling of a single-finger GaN high electron mobility transistor (HEMT) shows that a top-side integrated PCDm reduces the channel peak temperature by ∼10%. Simulation results suggest that the high-thermal-conductivity PCDm can serve as effective means for the cooling of high-power electronic devices and 3D-integrated circuits if the TBC is improved via optimization of the transfer-printing process.