The evaluation of the world’s first MOSFETs with epitaxially-grown rare-earth high-k gate dielectrics is the main issue of this work. Electrical device characterization has been performed on MOSFETs with high-k gate oxides as well as their reference counterparts with silicon dioxide gate dielectric. In addition, by means of technology simulation with TSUPREM4, models of these devices are established. Current-voltage characteristics and parameter extraction on the simulated structures is conducted with the device simulator MEDICI. Measured and simulated device characteristics are presented and the impact of interface state and fixed charge densities is discussed. Device parameters of high-k devices fabricated with standard poly-silicon gate and replacement metal gate process are compared.

The first-principles calculation of pristine, B-, Al-, Ga-, Sb-, and Bi-doped blue phosphorene (BlueP) with adsorbed SO2, NO, and NO2 gas molecules including the transport and optical properties is reported. The electronic structures of pristine and doped BlueP are investigated, and the modifications in electronic band structures and density (DOS) of states are studied. The most considerable adsorption energies of BlueP after being exposed to paramagnetic gas molecules NO and NO2 show excellent sensitivity to the considered gas molecules, which is confirmed by the current-voltage characteristics. The pristine and doped BlueP can be encouraging alternatives for new-generation optical gas sensors due to notable alterations in the pristine and doped BlueP optical spectra.

Recently, unique novel characteristics of ambipolar transistors have been explored in various forms on both device and cell level. Most of these so called reconfigurable or polarity controllable devices are based on silicon nanowires, carbon nanotubes or similar gate-all-around topologies, thus requiring sophisticated or even non-standard manufacturing processes. Such complex processes limit the capability to build large circuits, due to associated maturity issues and cost.Here, we preview the DeFET technology, featuring our ambipolar, electrostatically-doped planar device based on an FDSOI CMOS-compatible manufacturing process. After a short introduction to the device itself, we present characteristics of full-swing DeFET XOR gate. For the XOR gate, we show a reduction from 12 transistors in classical CMOS to 8 transistors in DeFET technology.

Ambipolar transistors have emerged recently and are presented on device and cell level. The ability to conduct both electrons and holes is often provided by the use of silicon nanowires, carbon nanotubes or similar gate-all-around topologies. Large scale integration of these devices is difficult due to the complex manufacturing process. In this paper we present an ambipolar "Dehancement Mode Field Effect Transistor (DeFET)" which is an electrostatically doped planar device. After introducing the device itself, we show its performance by analyzing it in the TCAD simulation of a digital inverter configuration. We present characteristics of our full output swing CMOS-style inverter and compare it to an inverter which consists of MOSFETs from a similar 180nm SOI technology. The bias for the electrostatic doping of the DeFETs is provided by the cell supply voltages, therefore no additional voltage has to be provided to reconfigure our ambipolar DeFET as n-type or p-type with performance similar to 180nm SOI MOSFETs.

We report on a method to mass-fabricate graphene-based ultra-sensitive gas sensors on oxidized silicon wafers without the need to transfer graphene layers. By means of catalytic chemical vapor deposition (CCVD) several hundred nanocrystalline graphene field-effect transistors (ncGFETs), which are very sensitive to various toxic gases, have been fabricated directly on a single wafer and are subsequently characterized. This approach allows low-cost integration of graphene-devices for gas sensing applications in a silicon CMOS environment.

In the course of an increasing awareness for the protection of public health a higher demand for environmental gas sensors, especially for the detection of volatile organic compounds and toxic gases, has been noted. Reasonably-priced devices to cover this demand can be solid-state gas sensors that can be easily fabricated and scaled using planar processing. Furthermore, an appropriate choice of materials may enable the possibility of monolithic integration within silicon CMOS circuitry thus providing the chance of co-integrating read-out and signal processing electronics on the same chip. As a two-dimensional carbon nanomaterial graphene shows a high surface-to-volume ratio and promising electronic properties for the detection of gaseous species. Detection capabilities down to a single molecule have been demonstrated by Schedin et al. [1], using a pristine graphene flake made from mechanical cleavage of highly ordered pyrolytic graphite. In this contribution we port on a novel method for graphene-based sensor fabrication. By means of a CMOS compatible method we have fabricated hundreds of transfer-free nanocrystalline graphene field-effect transistors (ncGFETs) on silicon dioxide [2], which can be used for detection of gaseous species. Under application of a HP4156A semiconductor parameter analyzer the gaseous sensitivity of our ncGFETs is electrically characterized in terms of backgate FET input characteristics as well as in a resistive configuration. For the resistive configuration the backgate bias has been fixed near the charge neutrality point of our nanocrystalline graphene devices at VBG = 0V. All measurements were done using our self-constructed vacuum probing station that can be systematically flooded with calibrated gas mixtures. The gas concentration is then derived from the vacuum pressure using the ideal gas law. Sensitivities of our ncGFETs to different volume concentrations of various toxic gases including ammonia (NH3), nitrogen dioxide (NO2), and carbon monoxide (CO) will be presented. E.g. for devices heated to 425K a sensitivity S of roughly 80% is S = (G-G0)/G0 achieved for 4 parts-per-million-volume (ppmv) of ammonia whereat NO2 already shows a sensitivity of 100% for a concentration of 4 parts-per-trillion-volume (pptv = 10-6 ppmv). The higher sensitivity of our ncGFETs compared to other graphene devices is attributed to modifications of grain boundary potential barriers, which is the dominating mechanism in e.g. SnO2-based Taguchi-type sensors [3]. Furthermore, the influence of water vapor (H2O (g)) on our devices is discussed. Nevertheless, the cross-sensitivity of Taguchi-type sensors, like our ncGFETs, remains a problem. Speciation of gas molecules is feasible by the use of sensor arrays consisting of devices with different sensitivities and electronic characteristics towards different gas species. Therefore, in order to modify the sensitivities towards the different gas species of our ncGFETs towards the different gas species we have characterized the sensitivity and responsivity at various temperatures. Furthermore, during exposure to the different gases the analysis of the backgate ncGFET input characteristics shows shifts of the charge neutrality point, as well as changes in the hysteresis of our devices. A novel method to selectively discriminate between various gaseous species, which is based on the analysis of the hysteresis in the ncGFETs will be presented and discussed. [1]F. Schedin, A. K. Geim, S. V. Morozov, E. W. Hill, P. Blake, M. I. Katsnelson and K. S. Novoselov, Nat Mater, 6, 652 (2007). [2] D. Noll and U. Schwalke, 2017 12th Ieee International Conference on Design & Technology of Integrated Systems in Nanoscale Era (Dtis 2017) (2017). [3] R. K. Srivastava, P. Lal, R. Dwivedi and S. K. Srivastava, Sensor Actuat B-Chem, 21, 213 (1994). Figure 1

Solid state gas sensors for monitoring toxins in the environment, chemical exhaust or biological samples have received increasing attention over the recent years. A promising material for this application is graphene, having demonstrated single molecule detection capability and sensitivity towards a variety of gases [1]. In this contribution we present a transfer-free production method of nanocrystalline graphene field effect transistors (nGFETs), which can be used as very sensitive gas sensors. By means of our PMMA-enhanced in situ catalytic chemical vapor deposition (CCVD) process [2] we fabricate few-layered nGFETs. By this method, hundreds of nGFETs are simultaneously fabricated on a single 2 inch oxidized, highly p-doped silicon wafer. After fabrication the individual metal catalyst sites are used as electrical contacts to the nanocrystalline graphene that bridges the gap along the insulating silicon dioxide surface (see figure 1a & b). Hereby, post-growth graphene-transfer and etching as well as cleaning steps are obsolete. Material characterization has been done using a Horiba Labram HR800 Raman microscope with a 632nm laser, yielding spectra showing strong G (1590 cm-1) and D (1350 cm-1) signatures but only a weak 2D (2700 cm-1) signal. Hence, a near edge X-ray absorption fine structure (NEXAFS) analysis at the carbon K-edge of the CCVD graphene was done and analyzed in respect to its C-C sp2 bonding structure. For that purpose, reference spectra of graphene and graphene oxide, both supplied by Graphenea, have been recorded. The NEXAFS experiments were performed at the plane grating monochromator (PGM) [3] beamline of PTB at the BESSY II synchrotron employing radiometrically calibrated instrumentation. By means of a linear combination of reference NEXAFS spectra for graphene and graphene oxide, the composition of the CCVD grown graphene layers is derived. By electrical characterization using an HP4156A precision semiconductor parameter analyzer we investigate the intrinsic electrical properties and gas sensing capabilities of our nGFETs using our self made vacuum probing station. The intrinsic properties have been tested under a vacuum pressure of 2*10-5mbar revealing a negative shift of the charge neutrality point in the input characteristics of our nGFETs, thereby verifying atmospheric hole-doping to our as-fabricated devices. Afterwards, the nGFETs have been thermally annealed under vacuum to desorb remaining adsorbents in order to restore the intrinsic properties of the devices. Subsequently, the devices have been exposed down to a concentration of 200ppbv of ammonia. As a consequence a positive shift of the charge neutrality point is recorded, indicating an increase in electron doping. During this exposure the hysteresis effect of the nGFETs is enhanced and its origin will be discussed. We will also report on the dynamical behavior (e.g. response and recovery times) of our devices in comparison to a simple commercial MQ-5 gas sensor. [1] F. Schedin, A. K. Geim, S. V. Morozov, E. W. Hill, P. Blake, M. I. Katsnelson and K. S. Novoselov; “Detection of individual gas molecules adsorbed on graphene, Nat Mater, 6, 652 (2007). [2] D. Noll, U. Schwalke; ”PMMA-enhancement of the lateral growth of transfer-free in situ CCVD grown graphene”, in 2016 13th International Multi-Conference on Systems, Signals & Devices (SSD), p. 458 (2016). [3] F. Senf, U. Flechsig, F. Eggenstein, W. Gudat, R. Klein, H. Rabus, G. Ulm, J. Synchrotron Rad. (1998) 5, 780-782. Acknowledgement The authors would like to thank PD Dr. Emanuel Ionescu and Benjamin Juretzka from Technische Universität Darmstadt for the opportunity to record Raman spectra at the group of dispersive solids. Figure 1

For the development of next-generation gas sensors with higher sensitivity, selectivity, responsivity and cost-effectiveness, carbon-based materials are a major research topic. Graphene, as a two-dimensional nanomaterial with a high surface-to-volume ratio and outstanding electronic properties, offers a good choice as a sensing layer [1]. However, for the successful application of reasonably priced graphene-based gas sensors a high fabrication yield and long-term stability are essential key requirements. Nevertheless, only few studies on the yield and reliability of graphene-based devices do exist [2]. Transfer-free nanocrystalline graphene field-effect transistors (ncGFETs), which are sensitive towards various toxic gases, including ammonia (NH3), nitrogen dioxide (NO2) and carbon monoxide (CO) can be fabricated by the use of our CMOS-compatible in situ catalytic chemical vapor deposition (CCVD) process. By this method we have fabricated hundreds of devices on oxidized two inch silicon wafers. In this contribution we report results on process yield and reliability, obtained from backgate input characteristics of 524 devices fabricated on a single two inch wafer. Electrical characterization has been performed using a Keithley SCS 4200 semiconductor parameter analyzer. The characterized ncGFETs exhibit nominal device widths of 20 µm and lengths of 3 µm and have been parameterized at a drain-to-source bias of VDS = -300 mV. The measurements reveal that 81.68 % of the fabricated ncGFETs show typical ambipolar behavior as is known from graphene devices (fig. 1). A field-effect (FE), defined via current on/off ratio, of at least 2 is observed for all of the devices within a backgate electric field strength range of ±2.4 MV/cm. Beyond that, in these devices larger field-effects are observed with 59.81 % exceeding a field-effect of 10 to 15 (10 ≤ FE < 15), 24.3% between 15 and 20 (15 ≤ FE < 20) and 7.25% larger than 20 (FE ≥ 20) (fig. 2). Due to the differences in the strength of the field-effect, material variations of our nanocrystalline graphene are expected. Moreover, by means of a statistical evaluation of the shift of the charge neutrality point the different doping levels of our devices are investigated. Furthermore, the ncGFETs show hysteresis effects that are enhanced by exposure to atmospheric environment and other gases, but are reduced in vacuum. Using the Pulsed Time-Domain Measurement (PTDM) technique [3] the surface charge trap density, which induces the hysteresis, is determined for various cases and its influence on the electrical and sensing characteristics of our device will be discussed. In addition, results on accelerated stress tests at high electrical fields and elevated temperatures will be presented as a first attempt to investigate the degradation and reliability of ncGFETs. [1] F. Schedin, A. K. Geim, S. V. Morozov, E. W. Hill, P. Blake, M. I. Katsnelson and K. S. Novoselov, Nat Mater, 6, 652 (2007). [2] A. D. Smith, S. Wagner, S. Kataria, B. G. Malm, M. C. Lemme and M. Ostling, Ieee T Electron Dev, 64, 3919 (2017). [3] R. S. Park, M. M. Shulaker, G. Hills, L. Suriyasena Liyanage, S. Lee, A. Tang, S. Mitra and H. S. Wong, ACS Nano, 10, 4599 (2016). Figure 1

Reasonably-priced devices for the detection of toxic species in the atmosphere are critical for reasons of health. Previous research work shows the promising detection capabilities of graphene. Thus, we demonstrate the gaseous response of our nanocrystalline graphene field-effect transistors that can be fabricated hundredfold on a two inch substrate by our transfer-free in situ catalytic chemical vapor deposition process. By means of Raman spectroscopy and near edge X-ray absorption fine structure nanocrystallinity of the CCVD grown graphene films within the devices can be confirmed. Using a self-constructed vacuum probing station the sensitivity of the fabricated devices is extracted from dynamic electrical sampling measurements. With respect to ammonia it is found that the sensitivity is being higher than previously reported from other groups. Moreover, a comparable responsivity is achieved. A deeper understanding of the origin of the high sensitivity, which we attribute to the nanocrystallinity, is given by backgate input characteristics under varying ammonia concentration as well as from comparison with literature results on carbon nanotube gas sensors. Furthermore, the origin and influence of ammonia on the hysteresis of our nanocrystalline graphene field-effect transistors is discussed. (C) The Author(s) 2018. Published by ECS.

In this paper we focus on the implementation of a process flow of SB-MOSFETs into the process simulator of the Synopsys TCAD Sentaurus tool-chain. An improved structure containing topography is briefly discussed and further device simulations are applied with the latest physical models available. Key parameters are discussed and finally the results are compared with fabricated SB-MOSFETs in terms of accuracy and capability of process simulations.

In this paper we focus on the implementation of a process flow of SB-MOSFETs into the process simulator of the Synopsys TCAD Sentaurus tool-chain. The improved structure containing topography is briefly discussed and further device simulations are applied with the latest physical models available for these type of devices. Afterwards, some key parameters are discussed and finally the results are compared with fabricated SB-MOSFETs in terms of accuracy and capability of process simulations.

In this paper, we demonstrate by extending TCAD simulations based on experimental data of fabricated electrostatically doped, reconfigurable planar double-gate field-effect transistors, the improved characteristics of a triple gate device design. The technological cornerstones for this general-purpose FET comprise mid-gap Schottky S/D junctions on a silicon-on-insulator substrate. The transistor type, i.e. n-type or p-type, is interchangeable during operation by applying a control-gate voltage which significantly increases the flexibility and versatility in the design of integrated circuits.

The physical influence of temperature down to the cryogenic regime is analyzed in a comprehensive study and the comparison of IV and III-V Schottky barrier (SB) double-gate MOSFETs. The exploration is done using the Synopsys TCAD Sentaurus device simulator and first benchmarked with experimental data. The important device physics of both SB-MOSFETs and conventional MOSFETs are reviewed. The impact of temperature on device performance down to the liquid-nitrogen regime is then explored. We find reduced drive currents in SB-MOSFETs fabricated on small effective mass materials and that SB lowering can significantly improve SB-MOSFETs, especially at low temperatures.

In this paper we present a simulation framework to account for the Schottky barrier lowering models in SBMOSFETs within the Synopsys TCAD Sentaurus tool-chain. The improved Schottky barrier lowering model for field emission is considered. A strategy to extract the different current components and thus accurately predict the onand off-current regions are adressed. Detailed investigations of these components are presented along with an improved Schottky barrier lowering model for field emission. Finally, a comparison for the transfer characteristics is shown for simulation and experimental data.

In this paper we present a simulation framework to account for the Schottky barrier lowering models in SB-MOSFETs within the Synopsys TCAD Sentaurus tool-chain. The improved Schottky barrier lowering model for field emission is considered. A strategy to extract the different current components and thus predict accurately the on- and off-current regions are adressed.

In this paper, we illustrate by simulation and extend our previous work by demonstration of fabricated devices of electrostatically doped, reconfigurable planar field-effect-transistors with dual work function metal gates. The technological cornerstones for this dual-gated general purpose FET contain Schottky S/D junctions on a silicon-on-insulator substrate. The transistor type, i.e. n-type or p-type FET, is electrically selectable in operation by applying a control-gate voltage which significantly increases the versatility and flexibility in the design of digital integrated circuits.

In this paper, we demonstrate by simulation the feasibility of electrostatically doped and therefore reconfigurable planar field-effect-transistor structure which is based on our already fabricated and published Si-nanowire devices. The technological cornerstones for this dual-gated general purpose FET contain Schottky S/D junctions on a silicon-on-insulator substrate. The transistor type, i.e. n-type or p-type FET, is electrically selectable on the fly by applying an appropriate control-gate voltage which significantly increases the versatility and flexibility in the design of digital integrated circuits.

The success of integrated silicon technology is based on the down-scaling of minimum feature sizes of silicon field-effect devices (MOSFETs) in a complementary circuit configuration (CMOS) according to Moore's Law. Reducing the feature size provides more components per chip and higher speed. However, this continuous miniaturization of MOSFETs will come to an end as CMOS scaling will soon approach atomic dimensions. To take computation beyond Moore's Law requires breaking at least with two major paradigms: (1) High computing performance is directly related to high switching speeds of the single device and (2), the separation of memory and computing. In this work we report on a novel adaptive nanowire field-effect transistor (a-NWFET) architecture which provides a release from paradigms (1) as well as (2). The fabricated a-NWFETs are originally ambipolar nanowire devices, using midgap Schottkybarrier contacts as source and drain (S/D) electrodes. The final unipolar a-NWFET device type (i.e. NMOS or PMOS) can be created by applying an electric bias at the back-gate. The ability to select the transistor type by the application of an electrical signal to the back-gate adds to the versatility of the device concept, where the two complementary device types are interchangeable on the fly. A simple and versatile device structure for logic and intrinsic memory applications with the potential to realize novel reconfigurable logic architectures and hardware-based neural networks will be presented.

In this paper, we present experimental results and simulation data of an electrostatically doped and therefore voltage-programmable, planar, CMOS-compatible field-effect transistor (FET) structure. This planar device is based on our previously published Si-nanowire (SiNW) technology. Schottky barrier source/drain (S/D) contacts and a silicon-on-insulator (SOI) technology platform are the key features of this dual-gated but single channel universal FET. The combination of two electrically independent gates, one back-gate for S/D Schottky barrier modulation as well as channel formation to establish Schottky barrier FET (SBFET) operation and one front-gate forming a junctionless FET (JLFET) for actual current control, significantly increases the temperature robustness of the device.