Thousands of reports have demonstrated the exceptional performance of sensors based on carbon nanotube (CNT) transistors, with promises of transformative impact. Yet, the effect of long-term bias stress on individual CNTs, critical for most sensing applications, has remained uncertain. Here, we report bias ranges under which CNT transistors can operate continuously for months or more without degradation. Using a custom characterization system, the impacts of defect formation and charge traps on the stability of CNTbased sensors under extended bias are determined. In addition to breakdown, which is well-known, we identify three additional operational modes: full stability, slow decay, and fast decay. We identify a current drift behavior that reduces dynamic range by over four orders of magnitude but is avoidable with appropriate sensing modalities. Identification of these stable operation modes and limits for nanotube-based sensors addresses concerns surrounding their development for a myriad of sensing applications.

Two-dimensional (2D) materials offer exciting possibilities for numerous applications, including next-generation sensors and field-effect transistors (FETs). With their atomically thin form factor, it is evident that molecular activity at the interfaces of 2D materials can shape their electronic properties. Although much attention has focused on engineering the contact and dielectric interfaces in 2D material-based transistors to boost their drive current, less is understood about how to tune these interfaces to improve the long-term stability of devices. In this work, we evaluated molybdenum disulfide (MoS 2 ) transistors under continuous electrical stress for periods lasting up to several days. During stress in ambient air, we observed temporary threshold voltage shifts that increased at higher gate voltages or longer stress durations, correlating to changes in interface trap states (ΔN it ) of up to 10 12 cm −2 . By modifying the device to include either SU-8 or Al 2 O 3 as an additional dielectric capping layer on top of the MoS 2 channel, we were able to effectively reduce or even eliminate this unstable behavior. However, we found this encapsulating material must be selected carefully, as certain choices actually amplified instability or compromised device yield, as was the case for Al 2 O 3 , which reduced yield by 20% versus all other capping layers. Further refining these strategies to preserve stability in 2D devices will be crucial for their continued integration into future technologies.

Tailoring the properties of two-dimensional (2D) crystals is important for both understanding the material behavior and exploring new functionality. Here we demonstrate the alteration of MoS 2 and metal-MoS 2 interfaces using a convergent ion beam. Different beam energies, from 60 eV to 600 eV, are shown to have distinct effects on the optical and electrical properties of MoS 2. Defects and deformations created across different layers were investigated, revealing an unanticipated improvement in the Raman peak intensity of multilayer MoS 2 when exposed to a 60 eV Ar + ion beam, and attenuation of the MoS 2 Raman peaks with a 200 eV ion beam. Using cross-sectional scanning transmission electron microscopy (STEM), alteration of the crystal structure after a 600 eV ion beam bombardment was observed, including generated defects and voids in the crystal. We show that the 60 eV ion beam yields improvement in the metal-MoS 2 interface by decreasing the contact resistance from 17.5 kΩ • µm to 6 kΩ • µm at a carrier concentration of n 2D = 5.4 × 10 12 cm −2. These results advance the use of low-energy ion beams to modify 2D materials and interfaces for tuning and improving performance in applications of sensors, transistors, optoelectronics, and so forth.

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Interest in point-of-care diagnostics has led to increasing demand for the development of nanomaterial-based electronic biosensors such as biosensor field-effect transistors (BioFETs) due to their inherent simplicity, sensitivity, and scalability. The utility of BioFETs, which use electrical transduction to detect biological signals, is directly dependent upon their electrical stability in detection-relevant environments. However, BioFET device structures vary substantially, especially in electrode passivation modalities. Improper passivation of electronic components in ionic solutions can lead to excessive leakage currents and signal drift, thus presenting a hinderance to signal detectability. Here, we harness the sensitivity of nanomaterials to study the effects of various passivation strategies on the performance and stability of a biosensing platform based on aerosol-jet-printed carbon nanotube thin-film transistors. Specifically, nonpassivated devices were compared to devices passivated with photoresist (SU-8), dielectric (HfO 2 ), or photoresist + dielectric (SU-8 followed by HfO 2 ) and were evaluated primarily by initial performance metrics, large-scale device yield, and stability throughout long-duration cycling in phosphate buffered saline. We find that all three passivation conditions result in improved device performance compared to nonpassivated devices, with the photoresist + dielectric strategy providing the lowest average leakage current in solution (∼2 nA). Notably, the photoresist + dielectric strategy also results in the greatest yield of BioFET devices meeting our selected performance criteria on a wafer scale (∼90%), the highest long-term stability in solution (<0.01% change in on-current), and the best average on/off-current ratio (∼10 4 ), hysteresis (∼32 mV), and subthreshold swing (∼192 mV/decade). This passivation schema has the potential to pave the path toward a truly high-yield, stable, and robust electrical biosensing platform.