Carbon Nanotube Radio-Frequency Transistors on Polycrystalline Diamond Substrates

Carbon nanotube (CNT) field-effect transistors (FETs), considered as a promising building block for radio-frequency/terahertz electronics, can be further enhanced in performance through adopting a substrate with high thermal conductivity, low parasitic effect, and acceptable cost. In this work, we develop a technology to fabricate aligned CNT array-based FETs on a polycrystalline diamond (PD) substrate to achieve excellent heat dissipation and low substrate loss for RF applications. Specifically, a spin-on glass (SOG) layer is deposited on the PD substrate to significantly reduce the surface roughness, which is favorable for the formation of high-quality channel, contact, and gate stack in FETs. The fabricated CNT RF FETs on the SOG-treated PD substrate present cut-off frequencies (ft/fmax) of 191/211 GHz, a 35% improvement compared to those on pristine PD, while basically maintaining its excellent thermal conduction.