At IEEE's International Electron Devices Meeting 2015 (IEDM) in Washington DC (Dec. 7-9), the Belgium-based research center imec presented three novel aluminum gallium nitride (AlGaN)/ gallium nitride (GaN) stacks featuring optimized low dispersion buffer designs. Moreover, imec optimized the epitaxial p-GaN growth process on 200 mm Silicon wafers, achieving e-mode devices featuring beyond state-of-the-art high threshold voltage and high drive current.

To achieve a good, current-collapse-free device operation in AlGaN/GaN-on-Silicon (Si) devices, dispersion must be kept to a minimum. Trapped charges in the buffer between the GaN-based channel and the silicon substrate are known to be a critical factor in causing dispersion. Imec compared the impact of different types of buffers on dispersion and optimized three types: a classic step-graded buffer, a buffer with low-temperature AlN interlayers, and a super lattice buffer. These three types of buffers were optimized for low dispersion, leakage and breakdown voltage over a wide temperature range and bias conditions.

The researchers also optimized the epitaxial p-GaN growth process demonstrating improved electrical performance of p-GaN HEMTs, achieving a beyond state-of-the-art combination of high threshold voltage, low on-resistance and high drive current (V_t >2 V, R_ON = 7 Ω.mm and I_d >0.4 A/mm at 10 V). The P-GaN HEMT results outperformed their MISHEMT counterparts.

Imec’s offering includes a complete 200 mm CMOS-compatible 200 V GaN process line that features excellent specs on e-mode devices. Its program allows partners early access to next-generation devices and power electronics processes, equipment and technologies, and speed up innovation at shared costs. Current R&D focuses on improving the performance and reliability of e-mode devices, while in parallel pushing the boundaries of the technology through innovation in substrate technology, higher levels of integration and exploration of novel device architectures.

www.imec.be