Search

The integration of AlGaN/GaN thin film transistors onto diamond substrates enables the efficient dissipation of device heat, thus providing a boost in performance and reliability of current high-frequency GaN power amplifiers. In this paper, we show 3 GHz load-pull measurements of GaN transistors on silicon (Si) and single crystalline diamond (SCD) as fabricated by our recently presented direct low-temperature bond process. After the transfer onto SCD, the efficiency and output power are increased by 15%, which is explained by a calculated temperature difference of ∼100 K. In addition, the temperature between individual gate fingers is reduced such that the output power density (Pout) is independent of the amount of fingers. A drawback of our GaN epilayer is identified in the huge thermal resistance of the buffer layer so that the heat spreading performance of our technology is significantly impaired. Nevertheless, we demonstrate a large GaN-on-diamond output power of 14.4 W at a Pout of 8.0 W/mm. [ABSTRACT FROM AUTHOR]

Direct low-temperature bond technologies for III-nitride thin film devices are of great interest to both improve device performance and enable on-wafer integration with other semiconductor technologies. However, thin films released from their growth substrate are rather rough and difficult to prepare for direct bonding. Here, we present a bond technique, which transforms a thin AlN surface layer into a 30 nm solid aluminum hydroxide bond layer. This chemical process is based on the dissolution of AlN and recrystallization of aluminum hydroxides within several nanometers of interfacial water, thereby restructuring and adapting the interfaces to form a homogeneous bond contact without any interfacial voids. AlGaN/GaN microwave transistors bonded on diamond demonstrate an excellent electrical, thermal, and mechanical performance of this bond technology for high-frequency devices as well as many other III-nitride applications. [ABSTRACT FROM AUTHOR]

Mechanical and electrical properties of Al2O3 films are compared for plasma-assisted atomic layer deposition (ALD) and thermal ALD on two substrates, GaAs and Si, of different thermal expansion coefficient. Films with stable chemical structure and mechanical residual stress could be produced by both techniques without inducing any damage to sensitive multiquantum-well structures. However, the as-deposited residual stress in the plasma ALD Al2O3 films is lower and decreases, while that in the thermal ALD films increases with the deposition temperature. Moreover, the stress hysteresis observed upon thermal cycles is much lower for the plasma ALD films compared to that for the thermal ALD films. The biaxial elastic modulus (BEM or stiffness parameter) increases with the deposition temperature for both ALD films, being higher for the plasma ALD than that for the thermal ALD at a given temperature. The higher BEM is reflected in better electrical properties of the films. Thus, the leakage current of metal-oxide-semiconductor capacitors with the plasma ALD-Al2O3 film is three orders of magnitude lower and the breakdown voltage 20% higher than that of the capacitors with the thermal ALD film. [ABSTRACT FROM AUTHOR]