LMGP - Recherche Equipe Funsurf

Review by V. Stambouli 2022

The paper "Progress in SiC nanowire field-effect-transistors for integrated circuits and sensing applications" has been published in Microelectronic Engineering
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Here you will find V. Stambouli's paper
"The advantageous physical properties of bulk Silicon Carbide (SiC) in association with the anticipated enhancement of specific physical properties in one-dimensional (1D) nanostructures have inspired a series of studies focusing on nanowire (NW) fabrication and characterization as well as various devices implementation. SiC Νanowire Field Effect Transistors (NWFETs) constitute the ideal device concept to investigate the electrical properties of SiC NWs at variable temperatures under external stimuli such as electric field (application in integrated circuits) or in the presence of mechanical strain or chemical/biological species on the NW surface (application in sensors). Initial reports on SiC NW quantum transport modeling have revealed the prospect of attaining comparable performance to Si-based NWFETs. The experimental NWFET demonstrations, however, exhibit concurrently low carriers' mobility, ION/IOFF ratio and transconductance (gm) values posing hurdles in their further development. The low performance mainly originates from the high unintentional doping and unoptimized SiO2/SiC NW interface. The lack of strict control of SiC NWs bottom-up growth process, induces a very high carriers' concentration towards the degeneration limit mainly originating form unintentional nitrogen doping. Furthermore, the low interface quality as revealed by the high density of traps and fixed charges, results in gate electric field screening and indicates the necessity for further investigation of SiO2/SiC NW interface. As a consequence of both effects, the device switching-off is not achievable even for very high gate voltages. To the time being, only back-gated NWFETs with Schottky barriers (SB) at Source / Drain (S/D) regions demonstrate a well-determined switching-off and an improved performance owing to the indirect modulation of the drain current attainable by the global gate action that tunes the SB transparency. Nevertheless, devices with ohmic S/D contacts are expected to demonstrate enhanced performance upon substantially improving the fabrication process of the bottom-up grown NWs and the gate-oxide/NW interface. This was recently confirmed for devices based on top-down formed NWs, where the initial bulk SiC material had a moderate doping level. Although ohmic contacted NWFET incorporating top-down formed NW and ohmic S/D contacts still have moderate behavior, junction gate transistors (JFET) using top-down formed SiC nanochannels and nanoribbons have already demonstrated excellent performance values of ION/IOFF > 105 and gm = 8.8 mS exhibiting moreover improved thermal stability as the channel dimensions are scaled down.
The low quality of SiC NW/SiO2 interface, the high values of SiC NW surface defects and carrier concentration result in increased electron-phonon scattering effects that also limit NWs thermal conductivity at lower values compared to bulk material indicating a direct correlation between charge and phonon transport. Nevertheless, the low material quality seems to be beneficial for sensing applications and especially piezoresistive ones. Indeed the high gauge field values of SiC NWs open the path for pressure or strain sensors development.
A first proof of concept of FET-based biosensors using SiC NWs revealed the superior chemical stability of SiC NWs over Si NWs. The high bio- and hemo-compatibility as well as chemical stability of SiC combined with SiC NWFET-based electrical detection can lead to the development of biosensors with outstanding performance.
In the current article, a critical progress report of the field is presented mainly focusing on NWFETs for integrated circuits, while recent results obtained in FET-based sensors are also reviewed. At the end of the discussion, perspectives on the trends, limitations and application potential of SiCNWFETs are provided.