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Low-frequency noise is a significant limitation on the performance of nanoscale electronic devices. This limitation is especially important for devices based on two-dimensional (2D) materials such as graphene and transition metal dichalcogenides (TMDs), which have atomically thin bodies and, hence, are severely affected by surface contaminants. Here, we investigate the low-frequency noise of transistors based on molybdenum disulfide (MoS2), which is a typical example of TMD. The noise measurements performed on bilayer MoS2 channel transistors show a noise peak in the gate-voltage dependence data, which has also been reported for graphene. To understand the peak, a trap decay-time based model is developed by revisiting the carrier number fluctuation model. Our analysis reveals that the peak originates from the fact that the decay time of the traps for a 2D device channel is governed by the van der Waals bonds between the 2D material and the surroundings. Our model is generic to all 2D materials and can be applied to explain the V, M and Λ shaped dependence of noise on the gate voltage in graphene transistors, as well as the noise shape dependency on the number of atomic layers of other 2D materials. Since the van der Waals bonding between the surface traps and 2D materials is weak, in accordance with the developed physical model, an annealing process is shown to significantly reduce the trap density, thereby reducing the low-frequency noise.

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Electrocardiography (ECG) is the most common and extensively used vital sign monitoring method in modern healthcare systems. Different designs of ambulatory ECG systems were developed as alternatives to the commonly used 12-lead clinical ECG systems. These designs primarily focus on portability and user convenience, while maintaining signal integrity and lowering power consumption. Here, a wireless ECG monitoring system is developed using flexible and dry capacitive electrodes for long-term monitoring of cardiovascular health. Our capacitive-coupled dry electrodes can measure ECG signals over a textile-based interface material between the skin and electrodes. The electrodes are connected to a data acquisition system that receives the raw ECG signals from the electrodes and transmits the data using Bluetooth to a computer. A software application was developed to process, store, and display the ECG signal in real time. ECG measurements were obtained over different types of textile materials and in the presence of body movements. Our experimental results show that the performance of our ECG system is comparable to other reported ECG monitoring systems. In addition, to put this research into perspective, recent ambulatory ECG monitoring systems, ECG systems-on-chip, commercial ECG monitoring systems, and different state-of-the-art ECG systems are reviewed, compared, and critically discussed.

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