Practical Applications of Tunnel Field Effect Transistors

Traditional metal-oxide-semiconductor field effect transistor scaling has advanced successfully over 50 years providing significant increases in transistor count per chip and operating frequency, thus enabled the built of ever more performant and complex systems. Approaching to atomic scales, the energy efficiency of the transistors is severely compromised due to short channel effects and the explosion in the leakage current. Although the introduction of new materials and structures postpone the confrontation with theoretical limitations, 2D scaling strategy is fast approaching its limits. Thus alternative strategies have to be engineered for future growth of chip functionalities. Accepting the nanometer-limitation and with exchange of nanometer scale priority for femtojoule priority, energy efficiency has become the new yardstick. One approach being intensively investigated is to build transistors with steep switching characteristics offering high on/off current ratios. The principle of thermionic emission limits the subthreshold swing of MOSFETs to 60mV/dec at room temperature and consequently their energy efficiency. In this regard, new frontiers are opened by using new device physics (band to band tunneling, impact ionization, ferroelectric materials etc.) to minimize the energy per operation. In this work, tunneling field effect transistors which which work based on band-to-band tunneling process are evaluated focusing on their benefits in terms of energy/power saving for logic operations. Thanks to their superior subthreshold swing compared to CMOS, TFETs can offer higher performance for the same leakage level or better energy efficiency for the same performance at low operating voltages. Key device characteristics of TFETs are benchmarked and their reflection on the circuit performance are discussed based on simulations of primitive building blocks. Temperature sensitivity of TFETs that is investigated experimentally shows that TFETs are suitable for temperature sensitive applications, since they show less variation compared to thermionic emission based FETs under wide temperature ranges. Lastly, innovative ways of exploiting TFETs for capacitorless DRAMs and optical sensing are presented.