Thermal conductivity of ultrathin nano-crystalline diamond films determined by Raman thermography assisted by silicon nanowires

Abstract

The thermal transport in polycrystalline diamond films near its nucleation region is still not well understood. Here, a steady-state technique to determine the thermal transport within the nano-crystalline diamond present at their nucleation site has been demonstrated. Taking advantage of silicon nanowires as surface temperature nano-sensors, and using Raman Thermography, the in-plane and cross-plane components of the thermal conductivity of ultra-thin diamond layers and their thermal barrier to the Si substrate were determined. Both components of the thermal conductivity of the nano-crystalline diamond were found to be well below the values of polycrystalline bulk diamond, with a cross-plane thermal conductivity larger than the in-plane thermal conductivity. Also a depth dependence of the lateral thermal conductivity through the diamond layer was determined. The results impact the design and integration of diamond for thermal management of AlGaN/GaN high power transistors and also show the usefulness of the nanowires as accurate nano-thermometers.

Temperature-Dependent Thermal Resistance of GaN-on-Diamond HEMT Wafers

“…Due to the columnar growth and coalescence of CVD polycrystalline diamond, strong gradients in the thermal conductivity are present from the nucleation surface towards the growth direction within the diamond [18]. One benefit of the transient thermoreflectance is that it probes the effective dia of the diamond as grown on GaN, which represents the spatially weighted average over the 100 m diamond thickness in the growth direction.…”

Thermal characterization of polycrystalline diamond thin film heat spreaders grown on GaN HEMTs

“…The power density was set at a typical value of 5 W/mm, dissipated in a 0.5 lm-long, 100 nm-thick volume at the drain edge of the gate foot where most Joule heating occurs. 50 Given that the cross-plane thermal conductivity is always higher than the in-plane thermal conductivity for this columnar PCD, 51 the experimental value can thus be used to determine an upper limit of the expected thermal benefit of PCD. By adding a PCD heat spreader on top of the device sourcedrain opening, Fig.…”

Impact of diamond seeding on the microstructural properties and thermal stability of GaN-on-diamond wafers for high-power electronic devices

“…This makes the GaN/diamond interface the critical region to be optimized in order to maximize the performance of devices. In recent years significant improvements in the thermal transport properties of the GaN/diamond interface have been achieved; for example the optimization of the GaN/diamond interfacial dielectric layer and the improved thermal properties of diamond near its nucleation site at the GaN/diamond interface [9][10][11]. As a consequence of these advances in understanding, it is now considered possible to achieve the best device characteristics by further optimizing the thermal transport at and/or near the GaN/diamond interface.…”