Amorphous silicon carbide (a-SiC) is a wide-bandgap semiconductor with high robustness and biocompatibility, making it a promising material for applications in biomedical device passivation. a-SiC thin film deposition has been a subject of research for several decades with a variety of approaches investigated to achieve optimal properties for multiple applications, with an emphasis on properties relevant to biomedical devices in the past decade. This review summarizes the results of many optimization studies, identifying strategies that have been used to achieve desirable film properties and discussing the proposed physical interpretations. In addition, divergent results from studies are contrasted, with attempts to reconcile the results, while areas of uncertainty are highlighted.

Nanoporous SnO₂ thin films were elaborated to serve as sensing electrodes for label-free DNA detection using electrochemical impedance spectroscopy (EIS). Films were deposited by an electrodeposition process (EDP). Then the non-Faradic EIS behaviour was thoroughly investigated during some different steps of functionalization up to DNA hybridization. The results have shown a systematic decrease of the impedance upon DNA hybridization. The impedance decrease is attributed to an enhanced penetration of ionic species within the film volume. Besides, the comparison of impedance variations upon DNA hybridization between the liquid and vapour phase processes for organosilane (APTES) grafting on the nanoporous SnO₂ films showed that vapour-phase method is more efficient. This is due to the fact that the vapour is more effective than the solution in penetrating the nanopores of the films. As a result, the DNA sensors built from vapour-treated silane layer exhibit a higher sensitivity than those produced from liquid-treated silane, in the range of tested target DNA concentration going to 10 nM. Finally, the impedance and fluorescence response signals strongly depend on the types of target DNA molecules, demonstrating a high selectivity of the process on nanoporous SnO₂ films.

This work reports on the label-free electrical detection of DNA molecules for the first time, using silicon carbide (SiC) as a novel material for the realization of nanowire field effect transistors (NWFETs). SiC is a promising semiconductor for this application due to its specific characteristics such as chemical inertness and biocompatibility. Non-intentionally n-doped SiC NWs are first grown using a bottom-up vapor–liquid–solid (VLS) mechanism, leading to the NWs exhibiting needle-shaped morphology, with a length of approximately 2 μ m and a diameter ranging from 25 to 60 nm. Then, the SiC NWFETs are fabricated and functionalized with DNA molecule probes via covalent coupling using an amino-terminated organosilane. The drain current versus drain voltage ( I _d – V _d ) characteristics obtained after the DNA grafting and hybridization are reported from the comparative and simultaneous measurements carried out on the SiC NWFETs, used either as sensors or references. As a representative result, the current of the sensor is lowered by 22% after probe DNA grafting and by 7% after target DNA hybridization, while the current of the reference does not vary by more than ±0.6%. The current decrease confirms the field effect induced by the negative charges of the DNA molecules. Moreover, the selectivity, reproducibility, reversibility and stability of the studied devices are emphasized by de-hybridization, non-complementary hybridization and re-hybridization experiments. This first proof of concept opens the way for future developments using SiC-NW-based sensors.

Silicon nanowire (SiNW) charge based biosensors are attractive for DNA sensing applications due to their compactness and large surface-to-volume ratio. Small feature size, low production cost, repeatability, high sensitivity and selectivity are some of the key requirements for biosensors. The most common e-beam manufacturing method employed to manufacture sub-nm SiNWs is both cost and time intensive. Therefore, we propose a highly reproducible CMOS industry grade low-cost process to fabricate SiNW based field effect transistors on 4"-wafers. The 60 nm wide SiNWs reported in this paper are fabricated using the sidewall transfer lithography process which is a self-aligned-double-patterning I-line lithography process that also facilitates encapsulation of the SiNW surface with a thin HfO2 layer on which DNA probes are grafted to finalize the biosensors. Upon DNA hybridization, SiNW devices exhibit threshold voltage shift larger than the noise introduced by the exposition to saline solutions used for the bioprocesses. More specifically, based on a statistical analysis, we demonstrate that 85% of the tested devices exhibit a positive threshold voltage shift after DNA hybridization. These promising results make way for the monolithic integration of SiNW biosensors and CMOS circuitry to realize a point of care device which can offer reliable real time electrical readout.