We demonstrate a large area MoS₂/graphene barristor, using a transfer-free method for producing 3–5 monolayer (ML) thick MoS₂. The gate-controlled diodes show good rectification, with an ON/OFF ratio of ∼10³. The temperature dependent back-gated study reveals Richardson's coefficient to be 80.3 ± 18.4 A/cm²/K and a mean electron effective mass of (0.66 ± 0.15)m₀. Capacitance and current based measurements show the effective barrier height to vary over a large range of 0.24–0.91 eV due to incomplete field screening through the thin MoS₂. Finally, we show that this barristor shows significant visible photoresponse, scaling with the Schottky barrier height. A response time of ∼10 s suggests that photoconductive gain is present in this device, resulting in high external quantum efficiency.

A highly sensitive Gallium Nitride (GaN) diaphragm based micro-scale pressure sensor with an AlGaN/GaN heterostructure field effect transistor (HFET) deflection transducer has been designed and fabricated for high temperature applications. The performance of the pressure sensor was studied over a pressure range of 20 kPa, which resulted in an ultra-high sensitivity of ~0.76%/kPa, with a signal-to-noise ratio as high as 16 dB, when biased optimally in the subthreshold region. A high gauge factor of 260 was determined from strain distribution in the sensor membrane obtained from finite element simulations. A repeatable sensor performance was observed over multiple pressure cycles up to a temperature of 200 °C.

We report on novel microcantilever heater sensors with separate AlGaN/GaN heterostructure based heater and sensor channels to perform advanced volatile organic compound (VOC) detection and mixture analysis. Operating without any surface functionalization or treatment, these microcantilevers utilize the strong surface polarization of AlGaN, as well as the unique heater and sensor channel geometries, to perform selective detection of analytes based on their latent heat of evaporation and molecular dipole moment over a wide concentration range with sub-ppm detection limit. The dual-channel microcantilevers have demonstrated much superior sensing behavior compared to the single-channel ones, with the capability to not only identify individual VOCs with much higher specificity, but also uniquely detect them in a generic multi-component mixture of VOCs. In addition, utilizing two different dual channel configurations and sensing modalities, we have been able to quantitatively determine individual analyte concentration in a VOC mixture. An algorithm for complete mixture analysis, with unique identification of components and accurate determination of their concentration, has been presented based on simultaneous operation of an array of these microcantilever heaters in multiple sensing modalities.

In this work, a large-area MoS ₂ /graphene barristor device, with an electrically tunable Schottky barrier height, has been studied for detection of various gaseous analytes. The Schottky barrier height could be modulated by over 0.65 eV, allowing the drain current to be tuned by many orders of magnitude. Using diluted NO ₂ and NH ₃ gases as analytes, the performance of the barristor device was compared with individual MoS ₂ and graphene based planar FETs, where the barristor device outperformed its counterparts in terms of response magnitude and limit of detection. Due to the atomically thin nature of MoS ₂ and graphene, electric field applied to one material could not be fully screened from the other one, which allowed both materials to act as a composite structure when analyte molecules interacted with the barristor device. This apparently reversed the dopant behavior of NO ₂ and NH ₃ , while increasing the device sensitivity through subthreshold operation. Both conductance and capacitance based measurements are presented to highlight the charge transfer and barrier height modulation, to support the unique sensing mechanism observed in the 2D barristor device. A lower limit of detection in low ppb is established for NO ₂ and low ppm for NH ₃ , which could be further tuned by altering gate-drain bias conditions.

Using a novel quaternary algebra, several sequential circuits are designed. The quaternary logic scheme used here is obtained by extending Boolean algebra into quaternary domain. A set of operators capable of handling both coupled-binary and ordinary inputs are used to design the sequential circuit elements such as latches, flip-flops, registers and counters. Sufficient conditions for stable operation of the sequential blocks are derived mathematically and demonstrated graphically using simulated timing diagrams.