(Invited) Innovative Sharp Switching Devices

Abstract

Two families of sharp-switching SOI devices are discussed: tunneling field-effect transistors (TFETs) and band-modulation feedback transistors. The TFET is a reverse-biased PIN gated diode, where the gate voltage controls the electric field in the interband P +/N + tunneling junction. Although the TFET current can in principle be switched faster than the subthreshold current of a MOSFET, experimental results have been disappointing to date. Several technological solutions for improving the I ON current and subthreshold swing are reviewed. An innovative solution is to integrate a TFET with a bipolar transistor in a single device (BET-FET), where the bipolar current gain serves to amplify the tunneling current. A different approach is to use band modulation and feedback. The Z2-FET has a TFET-like PIN configuration but is operated in forward bias. In the off-state, the diode current is blocked by electrostatic gate-controlled barriers. When the gate bias reaches a turn-on value, the device switches abruptly (< 1 mV/decade) to a high I ON. We discuss the physical mechanism and unchallenged performance of the Z2-FET, and propose several CMOS-compatible applications, such as 1T-DRAM and SRAM, chemical sensors, logic and protection circuits.