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Germanium Nanowire RFETs for Boosting Performance

Fig. 1
Fig. 1: Cross section image of germanium nanowire RFET with high-k/metal gate stack in omega shape.

We have recently demonstrated experimentally the world-wide first transistor based on germanium that can be programmed between electron- (n) and hole- (p) conduction, see Fig. 1. Transistors  based on germanium can be operated at low supply voltages and reduced power consumption, due to the low band gap compared to silicon.  Additionally, the realized germanium based transistors can be reconfigured between electron and hole conduction based on the voltage applied to one of the gate electrodes. This enables to realize circuits with lower transistor count compared to state-of-the-art CMOS technologies.

Fig. 2
Fig. 2: Transfer characteristics of silicon (solid) and germanium (dotted) based RFETs as determined by simulations. Lower band-gap and effective masses of Ge deliver higher on-currents and lower operation voltages.

 

 

 

 

Recent developments aim to maintain this trend by employing materials having higher mobility than silicon in the transistor channel. The approach taken solves one of the limitations in using low-bandgap channel materials such as germanium and indium-arsenide. In conventional MOSFETs made from those materials the off state is strongly degraded by a high static current and associated power loss, also originating from their small band gaps. Distinctly, in our concept the off-currents can be drastically reduced by the blocking potential induced by the program gate.

Fig. 3
Fig. 3: Benchmarking of Si and Ge RFET Technology at the  48 nm  node.

 


We have verified by measurements and simulations, that the supply voltage can be reduced by a factor of 2 and dynamic power consumption can be ~4 times lower compared to silicon based RFETs. In addition, on currents can be boosted by up to a factor of 10 without degradation of  capacitances, see Fig. 2.  This translates into a switching delay reduction of up to a factor of 10. For different device geometries performance and power consumption metrics were extracted and benchmarked with modern conventional devices, see Fig. 3. Scaled Ge RFETs are competitive compared to other modern low standby and operating power technologies. The performance boosting at the device level combined with the circuit capabilities of RFETs hold the promise of enabling new circuit applications.

 

Contact: Dr. Walter M. Weber

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