Beta-phase gallium oxide and diamond fused through hydrophilic direct bonding

Beta-phase gallium oxide (β-Ga₂ O₃) is a new ultrawide bandgap semiconductor that has the potential to usher in the next generation of high-power electronics. Still, when it comes to high-voltage operations of the electric grid and electric vehicles, thermal management remains a challenge.

One possible solution is to integrate β-Ga₂O₃ with a heat spreader made from diamonds, which has extraordinarily high thermal conductivity. But material defects from various integration applications have hindered progress because of the highly mismatched crystal lattices of the two materials.

In a new approach, Matsumae et al. adapted hydrophilic direct-bonding that enabled atomic bonding of the two materials at relatively low temperature.

As part of preparations for direct bonding, the researchers cleaned the diamond substrates with a standard piranha solution, resulting in the β-Ga₂O₃and diamond surfaces adhering to each other via van der Waals forces (the weakly attractive interactions between neutral atoms) and hydrogen bonds.

β-Ga2O3 thin films were directly bonded onto diamond substrates by annealing at 250 degrees Celsius. Warping occurred only at the outermost edges, while the chemical bond formation increased interfacial strength without defects in the bonded regions.

“It is remarkable that the direct bonding occurred through typical surface cleaning steps and low temperature annealing under atmospheric air conditions,” author Takashi Matsutake said. “Thus, we believe that the proposed bonding method is feasible using simple laboratory-scale equipment and has the potential to be used in large scale manufacturing.”

The researchers plan to next evaluate the electrical properties at the β-Ga₂O₃-diamond interface and to find ways to minimize the lattice distortion at the outermost surface regions, including optimizing prebonding treatment and bonding temperature.

Source: “Low-temperature direct bonding of β-Ga₂O₃ and diamond substrates under atmospheric conditions,” by Takashi Matsumae, Yuichi Kurashima, Hitoshi Umezawa, Koji Tanaka, Toshimitsu Ito, Hideyuki Watanabe, and Hideki Takagi, Applied Physics Letters (2020). The article can be accessed at https://doi.org/10.1063/5.0002068 .