Cortisol is a hormone released in response to stress and is a major glucocorticoid produced by adrenal glands. Here, we report a wearable sensory electronic chip using label-free detection, based on a platinum/graphene aptamer extended gate field effect transistor (EG-FET) for the recognition of cortisol in biological buffers within the Debye screening length. The device shows promising experimental features for real-time monitoring of the circadian rhythm of cortisol in human sweat. We report a hysteresis-free EG-FET with a voltage sensitivity of the order of 14 mV/decade and current sensitivity up to 80% over the four decades of cortisol concentration. The detection limit is 0.2 nM over a wide range, between 1 nM and 10 µM, of cortisol concentrations in physiological fluid, with negligible drift over time and high selectivity. The dynamic range fully covers those in human sweat. We propose a comprehensive analysis and a unified, predictive analytical mapping of current sensitivity in all regimes of operation.

We report the fabrication process and performance characterization of a fully integrated ferroelectric gate stack in a WSe2/SnSe2 Tunnel FETs (TFETs). The energy behavior of the gate stack during charging and discharging, together with the energy loss of a switching cycle and gate energy efficiency factor are experimentally extracted over a broad range of temperatures, from cryogenic temperature (77 K) up to 100 °C. The obtained results confirm that the linear polarizability is maintained over all the investigated range of temperature, being inversely proportional to the temperature T of the ferroelectric stack. We show that a lower-hysteresis behavior is a sine-qua-non condition for an improved energy efficiency, suggesting the high interest in a true NC operation regime. A pulsed measurement technique shows the possibility to achieve a hysteresis-free negative capacitance (NC) effect on ferroelectric 2D/2D TFETs. This enables sub-15 mV dec−1 point subthreshold slope, 20 mV dec−1 average swing over two decades of current, ION of the order of 100 nA µm−2 and ION/IOFF > 104 at Vd = 1 V. Moreover, an average swing smaller than 10 mV dec−1 over 1.5 decades of current is also obtained in a NC TFET with a hysteresis of 1 V. An analog current efficiency factor, up to 50 and 100 V−1, is achieved in hysteresis-free NC-TFETs. The reported results highlight that operating a ferroelectric gate stack steep slope switch in the NC may allow combined switching energy efficiency and low energy loss, in the hysteresis-free regime.

Tungsten disulfide is an emerging 2D material with unique electrical and optical properties. Although chemical vapor deposition and mechanical exfoliation lead to large‐area layers, sonication solvent‐based exfoliation is a convenient method to realize mono‐ and few‐layer flakes. Herein, a mixture of dimethyl‐sulfoxide (DMSO) and water as a safe, facile, and user‐friendly exfoliation solvent for the synthesis of large‐scale WS2 sheets is investigated. While water molecules weaken the Van der Waals force between the stacked layers, DMSO molecules facilitate the exfoliation process. To improve exfoliation and achieve large‐area sheets, plasma pretreatment is exploited on bulk WS2 prior to the exfoliation process. For this purpose, O2 and H2 gases are used to carry out the plasma pretreatment. The oxygen plasma treatment is shown to be an effective strategy, leading to large‐area features. Moreover, inert gases as He and Ar are used to obtain small sheets. Transmission electron microscopy, atomic force microscopy, Raman spectroscopy, and dynamic light scattering analyses are used to understand the mechanism of exfoliation and study the effects of various parameters as water temperature, plasma power, and duration.

HfO2-based ferroelectrics are considered a promising class of materials for logic and memory applications due to their CMOS compatibility and ferroelectric figures of merit. A steep-slope field-effect-transistor (FET) switch is a device for logic applications in which a ferroelectric gate stack exploits a stabilized negative capacitance regime capable to differentially amplify the surface potential in a metal–oxide–semiconductor FET structure, resulting in the improvement of the subthreshold swing and overdrive. In a number of relevant studies of negative capacitance, intrinsic (thermodynamic) switching is assumed, since alternative switching scenarios predict undesirable hysteretic responses in logic devices. However, there is little support from the experimental data showing that the polarization reversal in HfO2-based ferroelectrics is really driven by the intrinsic switching mechanism. In this work, polarization hysteresis loops are measured over wide temperature ranges on polycrystalline Si-doped HfO2 (Si:HfO2) capacitors. The analysis herein, which is based on the classic Landau–Ginzburg–Devonshire theory, yields the temperature-dependent dielectric susceptibility values, which fit the Curie–Weiss law. The extrapolated Curie temperature value is in line with the data obtained for other HfO2-based ferroelectrics using different techniques. The work also illustrates a method to evaluate the ferroelectric equivalent negative capacitance value and range of voltages, aiming at study and optimization of a stabilized negative capacitance FET. This study indicates that the intrinsic switching provides an adequate description of the polarization hysteresis in Si:HfO2 films. This confirms the usability of hafnia-based ferroelectrics for negative capacitance logic devices, and the important role that the intrinsic mechanism plays in the dielectric response of these materials.

No abstract