IMEC demonstrated the potential of FinFETs by realizing the world’s first operational RF circuits and operational amplifiers using FinFETs with 45nm physical gate length and a metal-gate high-k gate stack. For applications at relatively low frequencies (below 5GHz) that demand a high-gain, FinFET technology offers better circuit performance than planar bulk CMOS. The speed of FinFETs still has to be improved for applications at higher frequencies.

The intrinsic gain of 45nm bulk devices drops to values that make it very difficult to realize high-gain operational amplifiers. By contrast, FinFETs have higher intrinsic amplification thanks to a better control of the short-channel effects. With the current status of the FinFET technology however, the maximum cut-off frequency of FinFETs is only 100GHz, almost 3 times lower than with planar bulk CMOS. This is due to the series resistance of the fins and the lower mobility at the sidewalls of the fins. As a consequence, FinFETs show good performance characteristics for circuits up to 5GHz, and even higher performance than planar transistors for lower frequencies.

To demonstrate the potential of 45nm FinFETs, IMEC researchers have realized the world’s first functional analog and RF circuits using FinFETs with a metal-gate high-k gate stack and transistors with a physical gate length down to 45 nm. A two-stage opamp with 50 dB gain and a 28 GHz tunable oscillator were designed, processed and successfully tested.

Future work will focus on increasing the speed of the FinFETs, by increasing mobility, decreasing the relatively large series resistances and/or decreasing extrinsic capacitors between gate and drain. A bulk FinFET option is explored in research. 

“Scaling beyond 45nm demands significant changes in process modules such as gate materials and/or device structures,” said Luc Van den hove, Vice President Silicon Process and Device Technology at IMEC. “An early assessment of the potential of the different options for their analog/RF performance is needed to maintain a competitive position. Therefore, this research forms an important aspect within our sub-45nm CMOS research.” www.imec.be