Integration of polycrystalline Ga2O3 on diamond for thermal management

Abstract

Gallium oxide (Ga2O3) has attracted great attention for electronic device applications due to its ultra-wide bandgap, high breakdown electric field, and large-area affordable substrates grown from the melt. However, its thermal conductivity is significantly lower than that of other wide bandgap semiconductors such as SiC, AlN, and GaN, which will impact its ability to be used in high power density applications. Thermal management in Ga2O3 electronics will be the key for device reliability, especially for high power and high frequency devices. Similar to the method of cooling GaN-based high electron mobility transistors by integrating it with high thermal conductivity diamond substrates, this work studies the possibility of heterogeneous integration of Ga2O3 with diamond for thermal management of Ga2O3 devices. In this work, Ga2O3 was deposited onto single crystal diamond substrates by atomic layer deposition (ALD) and the thermal properties of ALD-Ga2O3 thin films and Ga2O3-diamond interfaces with different interface pretreatments were measured by Time-domain Thermoreflectance (TDTR). We observed very low thermal conductivity of these Ga2O3 thin films (about 1.5 W/m-K) due to the extensive phonon grain boundary scattering resulting from the nanocrystalline nature of the Ga2O3 film. However, the measured thermal boundary conductance (TBC) of the Ga2O3diamond interfaces are about 10 times larger than that of the Van der Waals bonded Ga2O3diamond interfaces, which indicates the significant impact of interface bonding on TBC.Furthermore, the TBC of the Ga-rich and O-rich Ga2O3-diamond interfaces are about 20% smaller than that of the clean interface, indicating interface chemistry affects interfacial thermal transport. Overall, this study shows that a high TBC can be obtained from strong interfacial bonds across Ga2O3-diamond interfaces, providing a promising route to improving the heat dissipation from Ga2O3 devices with lateral architectures.

Applications and Impacts of Nanoscale Thermal Transport in Electronics Packaging

“…transmission functions from AMM, DMM, AGF, or phonon wave-packet method [71,257,[267][268][269][270][271][272][273]. Within the framework of MD methods, nonequilibrium MD (NEMD) [274][275][276] and interface conductance modal analysis [115,143,[277][278][279][280][281][282][283] are usually applied to predict h BD . The advantages of MD are that the anharmonic phonon scattering is included from the higher-order force constants of empirical interatomic potentials, and the interface structures are quite flexible, that complex interfacial details (like strong interfacial disorder and interfaces with dimensional mismatch) can be simulated.…”

“…Recently, there are several studies of considering anharmonicity in AGF [270,279], but there are still some limitations like high computational costs and inaccuracy from estimated scattering rate at interfaces. At interfaces between two crystalline materials, because of the growth limitation, the crystalline quality of one or both of the materials near the interface is usually not very good or the interfacial bonding is not very strong from different growing methods, like evaporation [262], CVD [115,280], and atomic layer deposition [281,284]. The low-quality polycrystalline or even amorphous region near the interface will have reduced thermal conductivity compared to bulk crystal and will contribute an additional thermal resistance, and that thermal resistance might impede the thermal transport from devices, especially for high frequency applications.…”

Thermal Conductivity of β-Phase Ga2O3 and (AlxGa1–x)2O3 Heteroepitaxial Thin Films

“…The film size effect on the thermal conductivity of polycrystalline Ga 2 O 3 thin films grown via open atmosphere annealing of a GaN surface has been reported; the measured thermal conductivities of films with a thickness range from 12.5 to 895 nm increased from 0.34 to 8.85 W/m·K. Polycrystalline Ga 2 O 3 thin films grown onto single crystalline diamond substrates via atomic layer deposition were shown to exhibit a very low thermal conductivity of 1.5–1.76 W/m·K for the film thickness range of 28–115 nm . This was found to be caused by the nanocrystalline nature of the films with an average grain size of 10–20 nm.…”

“…The film size effect on the thermal conductivity of polycrystalline Ga 2 O 3 thin films grown via open atmosphere annealing of a GaN surface has been reported; 34 the measured 35 This was found to be caused by the nanocrystalline nature of the films with an average grain size of 10−20 nm. It should be noted that the materials used in the aforementioned studies lack information regarding the film orientation due to the polycrystalline nature and do not meet requirements (e.g., electronic transport characteristics) for optoelectronic/electronic-grade materials.…”

Surface zeta potential and diamond growth on gallium oxide single crystal

“…It is a well known fact that higher operation temperature in high power devices can lead to significantly lower lifetimes [29,30]. One way researchers have overcome this problem is by exfoliating gallium oxide [26,27,31] or by growing gallium oxide on single crystal diamond(thermal conductivity ∼ 2000 W/mK) substrates [32]. Another approach that has been recently demonstrated is low temperature bonding of single crystal diamond on β-Ga 2 O 3 [33].…”