Silicon Nanowire Field Effect Transistor Sensors with Minimal Sensor-to-Sensor Variations and Enhanced Sensing Characteristics

Abstract

Silicon nanowire field effect transistor (FET) sensors have demonstrated their ability for rapid and label-free detection of proteins, nucleotide sequences, and viruses at ultralow concentrations with the potential to be a transformative diagnostic technology. Their nanoscale size gives them their ultralow detection ability but also makes their fabrication challenging with large sensor-to-sensor variations, thus limiting their commercial applications. In this work, a combined approach of nanofabrication, device simulation, materials, and electrical characterization is applied toward identifying and improving fabrication steps that induce sensor-to-sensor variations. An enhanced complementary metal-oxide-semiconductor-compatible process for fabricating silicon nanowire FET sensors on 8 in. silicon-on-insulator wafers is demonstrated. The fabricated nanowire (30 nm width) FETs with solution gates have a Nernst limit subthreshold swing (SS) of 60 ± 1 mV/decade with ∼1.7% variations, whereas literature values for SS are ≥80 mV/decade with larger (>10 times) variations. Also, their threshold voltage variations are significantly (∼3 times) reduced, compared to literature values. Furthermore, these improved FETs have significantly reduced drain current hysteresis (∼0.6 mV) and enhanced on-current to off-current ratios (∼10). These improvements resulted in nanowire FET sensors with the lowest (∼3%) reported sensor-to-sensor variations, compared to literature studies. Also, these improved nanowire sensors have the highest reported sensitivity and enhanced signal-to-noise ratio with the lowest reported defect density of 2.1 × 10 eV cm, in comparison to literature data. In summary, this work brings the nanowire sensor technology a step closer to commercial products for early diagnosis and monitoring of diseases.

The influence of geometry and other fundamental challenges for bio-sensing with field effect transistors

“…As represented in Fig. 5c, d, the analytes captured beyond the Debye length do not influence the Gao et al (2012); Hahm and Lieber 2004;Li et al (2004); Lin et al (2009); Zheng et al (2010) NW arrays 1E−13 to 1E−16 50 to 3600 Lu et al (2014); Zhang et al (2015) Planar FETs 1E−4 to 1E−7 300 to 54,000 1E−5 to 1E−7 300 to 1200 Braeken et al (2008); Freeman et al (2007); Sakata et al (2005); Shin et al 2004); Uno et al (2007); Xu et al (2016); Zafar et al (2018); Zayats et al (2006) Fig . 3 a-d Schematics of the iso-concentration diffusion lines (in blue) in close proximity and further from the sensor surface on planar, silicon nanowire, nanowires array, and high aspect ratio Fin FET, respectively.…”

“…However, all these devices will continue to face the fundamental challenges of analyte mass transport, charge screening of free ions, and non-specific binding issues. While the ability to work with all these materials improves, the silicon technology offers a great control in the mass fabrication possibilities (Rani et al 2018) (Zafar et al 2018). The combination of different approaches shown in this review may, in the near future, provide valid solutions for the clinical demand of a fast, sensitive, selective, and cost-effective biosensor able to detect multiple biomarkers.…”

High-Speed and Direction-Controlled Formation of Silicon Nanowire Arrays Assisted by Electric Field

“…Low-dimensional silicon (Si) nanostructures displayed remarkable electronic, mechanical, and optoelectronic properties that could act as building elements of functional devices and applications [1][2][3], such as field-effect transistors, biosensors, and photovoltaic cells [4][5][6][7][8][9]. To form the regular arrays of Si nanostructures, metalassisted chemical etching has been considered the prevailing strategy that even enabled to form Si nanowire (SiNW) arrays on planar substrates [10,11], powders [12,13], and pyramidal structures [14].…”

Conductometric Sensing with Individual InAs Nanowires

“…The large surface-to-volume ratio is considered as one of the key advantages for the increased sensor response of nanowire-based devices [18,19,20,21]. Different NW materials [20,22,23,24], sensed molecules [21,25,26,27], device architectures [28,29,30], and signal transduction methods [31] are currently being studied. The realization of all-electrical devices using semiconducting nanowires as the sensing element is particularly attractive because it enables ready signal transduction and integration into miniaturized systems [15].…”

“…The interaction between the NW surface and the adsorbed molecules causes a local modification of the energy band structure in the semiconductor, which affects the electrical transport properties [18]. Nanowires made of different semiconducting materials have been exploited in field effect transistors for sensing applications [20,29,32,33,34], providing useful insights into the understanding of the specific physical mechanisms related to the ability of nanowire devices in detecting different types of analytes.…”