Very low subthreshold swing normally-off diamond FET and its logic inverters

A normally-off field effect transistor with 15 nm LaB6 gate material directly deposited on hydrogen-terminated diamond surface has been fabricated and characterized. The reason for the normally-off operation could be attributed to the low work function of LaB6 layer, which can deplete holes in the channel. Due to the formation of C–B bond of interface and the thin thickness of LaB6, the subthreshold swing is as low as 70.6 mV/dec and interface state density is as low as 2 × 1011 cm−2eV−1. The maximum drain current density (IDSmax), extrinsic transconductance (Gm), threshold voltage (VTH), and on/off ratio for the device with 8-μm gate length are −60 mA/mm, 5 mS/mm, −1.1 V, and 109, respectively. The low-field mobility (μ0) without vertical-field degradation is 187 cm2/V s. The trapped charge density and fixed charge density are 8.75 × 1011 and 1.26 × 1012 cm−2, respectively. The LaB6/H-diamond logic inverters coupling with different load resistors show distinct inversion characteristics with a peak gain of 4.7 V/V.