Multi-functional Si- and Ge-based transistors enabling adaptive analog and digital circuits

Abstract

Reconfigurable field-effect transistors (RFETs), as emerging nanoelectronic devices, offer an interesting approach to counteract scaling-related limitations by increasing the functionality of the individual transistor unit, thereby achieving advantages in terms of resource- and energy efficiency. In light of the persistent and ever-increasing demand for enhanced performance and reduced power consumption in data-driven computation and processing, the development of alternative device concepts is imperative. These concepts, such as reconfigurable transistors, are essential for overcoming the limitations of conventional devices, thus facilitating application-specific, energy- and resource-efficient implementations. In this regard, the implementation of Germanium (Ge) provides distinct benefits, especially due to its lower effective masses and the associated barrier, which enhance on-state currents while allowing lower threshold voltages and, consequently, supply voltages that promote energy efficiency. Accordingly, a Ge-based RFET with symmetric n- and p-type operation, featuring both high on-state and sufficiently low off-state currents, is implemented. The obtained device platform, therefore, by passes the challenges of contact and valence-band pinning in Al-Ge junctions, as well as oxide formation, by completely encapsulating the Ge layer with the implemented Al-Si-Ge heterojunction and gate oxide stack, enabling reproducible and stable electrical behavior. Following the idea of functional diversification, thereby enabling resource- and area efficiency integration, as well as obtaining functionality which is conventionally unattainable or hard to achieve, the potential of the proposed Ge-based RFET towards additional operation modes in terms of negative differential resistance (NDR) as well as negative differential transconductance (NDT) is examined. The results show remarkable metrics that enhance state-of-the-art NDR- and NDT-based devices, while enabling cointegration within conventional complementary metal-oxide-semiconductor (CMOS) platforms.The potential of RFET-based analog circuits is highlighted by investigations into fundamental circuits that are made adaptive by the multi-gate architecture and by gating induced control of the underlying RFET. These RFET-based analog circuits consequently support the adaptation of circuit properties, such as amplification, to application-specific requirements, enabling the compensation of inequalities induced by fabrication-related device-to-device variability and the switching of functionality. Moreover, by leveraging the NDT effect, multi-value logic (MVL) circuits can be implemented, as demonstrated by a possible ternary inverter circuit, highlighting the potential of the Ge-based RFET forco-integration with conventional CMOS technology while enabling enriched functionality.In this regard, the proposed functionally diversified Ge-based RFET exhibits promising properties for implementing energy-efficient, application-tailored building blocks in analog and digital (MVL) circuits.