Estudo de amplificadores operacionais de transcondutância projetados com túnel-FETs e MOSFETs fabricados em estruturas de nanofios

Abstract

Tunnel Field Effect Transistors (TFET) have gained great interest by the academy in the recent years due to the possibility of achieving subthreshold slopes lower than 60 mV/dec, that is the theoretical limit of the MOSFET in room temperature. This is possible thanks to its main conduction mechanism based on band to band tunneling. This work intends to study operational transconductance amplifiers (OTA) designed with nanowire TFETs with different source materials (Si, SiGe and Ge) to verify its advantages and disadvantage in relation to nanowire silicon MOSFETs (channel length of 220 nm). Experimental measurements were used to create lookup tables that are used to model the devices through the Verilog-A language. By using the software Spectre, from Cadence, the models were initially used to perform basic analog integrated circuit simulations like current mirror, common source amplifier and differential amplifier. The effect of the gate current (IG) in two-stage amplifiers was also verified, showing that extra attention is required regarding the circuit bias, especially in the cases of Si and Ge-source TFETs. Finally, different OTAs were designed using the different technologies and compared. All the TFET OTAs presented a voltage gain superior to the MOSFET circuit, being at least 34 dB larger in all configurations considered, with the circuit projected with the Ge-source TFET presenting the largest voltage gain (105 dB). All the TFET OTAs have a power consumption at least one order of magnitude smaller (Ge-source) than the MOSFET circuit, being able to consume up to three orders less power (Si-source) in circuits with the same size and biased at the same transistor efficiency (gm/ID). However, the MOSFET circuit has a bandwidth-gain product (GBW) of at least one order of magnitude larger than the TFET OTAs. For circuits with the same power consumption and with an increase in the voltage gain of the MOSFET OTA as a project goal, the circuits with TFET with SiGe and Ge-source have a GBW (1 MHz and 2 MHz) in the same order of magnitude than the MOSFET OTA (4,7 MHz). Therefore, the TFETs studied have presented advantages in applications of low power and low frequency, in special the TFET with Ge source have presented a good compromise between gain and GBW and the Si TFET that has a voltage gain comparable to the Ge-source TFET, while consuming less power.