[Show abstract][Hide abstract] ABSTRACT: A feasibility and performance study of electrically reconfigurable nanowire transistors with selectable pFET and nFET operations is presented. The challenges toward circuit implementation are evaluated based on transient simulations of logic circuits. A novel physical structure capable of computing a NAND as well as NOR function is introduced. The new approach provides a flexible platform to develop and test fine-grain reconfigurable circuits and systems.
IEEE Electron Device Letters 01/2014; 35(1):141-143. · 2.79 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Silicon nanowires offer unique properties like inherent small diameters, quasi 1-dimensional current transport and the flexibility to combine materials that cannot be combined in bulk or thin film structures. Based on these properties electron devices, sensors as well as solar cells and lithium batteries can be envisioned that significantly outperform their thin film or bulk counterparts. The expectation, that the ultimate MIS device will be based on silicon nanowires gives this technology the potential for a seamless integration into integrated electronic systems. This paper gives an overview of important device applications of silicon nanowires. Starting with nanowire fabrication, the different device concepts and their important features will be introduced.
physica status solidi (RRL) - Rapid Research Letters 10/2013; 7(10):793-799. · 2.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present novel multifunctional nano-circuits built from nanowire transistors that uniquely feature equal electron and hole conduction. Thereby, the mandatory requirement to yield energy efficient circuits with a single type of transistor is shown for the first time. Contrary to any transistor reported up to date, regardless of the technology and semiconductor materials employed, the dually active silicon nanowire channels shown here exhibit an ideal symmetry of current-voltage device characteristics for electron (n-type) and hole (p-type) conduction as evaluated in terms of comparable currents, turn-on threshold voltages and switching slopes. The key enabler to symmetry is the selective tunability of the tunneling transmission of charge carriers as rendered by the combination of the nanometer-scale dimensions of the junctions and the application of radially compressive strain. To proof the advantage of this concept we integrated dually active transistors into cascadable and multi-functional one-dimensional circuit strings. The nano-circuits confirm energy efficient switching and can further be electrically configured to provide four different types of operation modes compared to a single one when employing conventional electronics with the same amount of transistors.
[Show abstract][Hide abstract] ABSTRACT: Over the past years, high-k dielectrics have been incorporated into modern semiconductor devices. One example is ZrO2, which has been introduced in memory applications. This paper elucidates some difficulties with pure ZrO2 like unintended crystallization during the growth of the dielectric and the evolution of the monoclinic phase, which reduces the k-value. The admixture of Sr is shown as a solution to circumvent those issues. A detailed structural analysis for a varying stoichiometry ranging from pure ZrO2 to the perovskite SrZrO3 is given. The detected crystal structures are correlated to our observations of the dielectric properties obtained by an electrical characterization. (C) 2013 AIP Publishing LLC.
Journal of Applied Physics 01/2013; 113(22). · 2.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present a multi channel Schottky-barrier (SB) field effect transistor (FET) based platform for chemical sensor applications and investigate its sensitivity on channel length. Designed transistors consist of parallel assembled bottom up grown silicon nanowires with a mean diameter of 20 nm. Focusing on investigations of devices with different channel lengths, we demonstrate that different optimum sensing regimes exist and they are determined by the device geometry. These target at different realizations and operation schemes. The sensitivities of the SB-FETs in linear and subthreshold regime are extracted from analysis of the pH response of silicon nanowire sensor devices.
[Show abstract][Hide abstract] ABSTRACT: Metal-Insulator-Metal capacitors, with ZrO2/Al2O3/ZrO2 (ZAZ)-nanolaminate thin-films as a dielectric layer, exhibit reduced leakage currents compared to corresponding capacitors based on pure ZrO2 while maintaining a sufficiently high dielectric constant for the DRAM application. This work is a comparative study demonstrating how the incorporation of a small amount of Al is responsible for the suppression of crystallization during deposition. Extensive electrical characterization leads to the identification of a defect band which conductive atomic force microscopy shows to be formed along crystallite grain boundaries, extending through the entire ZrO2-film. The incorporation of a sub-layer of Al2O3 prevents these grain boundaries resulting in an effective reduction of leakage currents, despite the film being in the nanocrystalline phase, necessary for it to exhibit the required high dielectric constant. A transport model based on phonon assisted trap to trap tunneling is proposed. (C) 2013 AIP Publishing LLC.
Journal of Applied Physics 01/2013; 113(19). · 2.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present novel Schottky barrier field effect transistors consisting of a parallel array of bottom-up grown silicon nanowires that are able to deliver high current outputs. Axial silicidation of the nanowires is used to create defined Schottky junctions leading to on/off current ratios of up to 10(6). The device concept leverages the unique transport properties of nanoscale junctions to boost device performance for macroscopic applications. Using parallel arrays, on-currents of over 500 mu A at a source-drain voltage of 0.5 V can be achieved. The transconductance is thus increased significantly while maintaining the transfer characteristics of single nanowire devices. By incorporating several hundred nanowires into the parallel array, the yield of functioning transistors is dramatically increased and deviceto-device variability is reduced compared to single devices. This new nanowirebased platform provides sufficient current output to be employed as a transducer for biosensors or a driving stage for organic light-emitting diodes (LEDs), while the bottom-up nature of the fabrication procedure means it can provide building blocks for novel printable electronic devices.
Nano Research 01/2013; 6(6):381-388. · 7.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An investigation of the electrical properties of the interface between nano-crystalline, pyrolytic carbon, and silicon is presented. We have deposited conductive carbon films on silicon substrates by the pyrolysis of ethene and structured them into Schottky diodes in order to evaluate the electrical properties of the interface. The results show that the Schottky barrier to n-doped silicon is 0.46 eV, whereas for p-doped silicon, it is 0.66 eV. The carbon to n-type silicon barrier height is comparable to the values for metal silicide contacts in commercial devices. The results imply that no interfacial layer is formed and show the absence of Fermi-level pinning.
Journal of Applied Physics 06/2012; 111(12). · 2.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Surface functionalization of NiSi2-Si-NiSi2 nanowire heterostructures, acting as Schottky-junction field effect transistors (SB-FETs) represent a promising route for biosensor applications. Axially Ni- silicidized silicon nanowires exhibit a very sharp metal-semiconductor interface, thus forming a well defined and reproducible Schottky barrier. These barriers determine the current through the wire and can be changed by small molecules chemiadsorbed on the nanowire surface. We report that surface modifications can alter the polarity of the devices. This severe influence on the charge transport implies ultrahigh sensitivity for nanowire SB-FETs.
Proceedings of IMCS 2012 – The 14th International Meeting on Chemical Sensors, Nuremburg; 05/2012
[Show abstract][Hide abstract] ABSTRACT: Over the past 30 years electronic applications have been dominated by complementary metal oxide semiconductor (CMOS) devices. These combine p- and n-type field effect transistors (FETs) to reduce static power consumption. However, CMOS transistors are limited to static electrical functions, i.e., electrical characteristics that cannot be changed. Here we present the concept and a demonstrator of a universal transistor that can be reversely configured as p-FET or n-FET simply by the application of an electric signal. This concept is enabled by employing an axial nanowire heterostructure (metal/intrinsic-silicon/metal) with independent gating of the Schottky junctions. In contrast to conventional FETs, charge carrier polarity and concentration are determined by selective and sensitive control of charge carrier injections at each Schottky junction, explicitly avoiding the use of dopants as shown by measurements and calculations. Besides the additional functionality, the fabricated nanoscale devices exhibit enhanced electrical characteristics, e.g., record on/off ratio of up to 1 × 10(9) for Schottky transistors. This novel nanotransistor technology makes way for a simple and compact hardware platform that can be flexibly reconfigured during operation to perform different logic computations yielding unprecedented circuit design flexibility.
[Show abstract][Hide abstract] ABSTRACT: This work elucidates the role of the Schottky junction in the electronic transport of nanometer-scale transistors. In the example of Schottky barrier silicon nanowire field effect transistors, an electrical scanning probe technique is applied to examine the charge transport effects of a nanometer-scale local top gate during operation. The results prove experimentally that Schottky barriers control the charge carrier transport in these devices. In addition, a proof of concept for a reprogrammable nonvolatile memory device based on band bending at the Schottky barriers will be shown.
[Show abstract][Hide abstract] ABSTRACT: CaTiO3 layers with varying thicknesses in metal-insulator-metal capacitor stacks were deposited at 550 °C using radio-frequency magnetron sputtering. The combination of electrical and transmission electron microscopy measurements allows a correlation of k-value and leakage current to the degree of crystallinity. Experiments show that higher crystallinity and, therefore, higher k-values lead to increasing leakage currents and change of conduction mechanisms. However, leakage currents are significantly reduced when crystallites are embedded in an amorphous matrix. Selective growth of these crystallites is owed to cube-on-cube nucleation of CaTiO3 on 011 Pt.
[Show abstract][Hide abstract] ABSTRACT: We present a theoretical framework for the calculation of charge transport through nanowire-based Schottky-barrier field-effect transistors that is conceptually simple but still captures the relevant physical mechanisms of the transport process. Our approach combines two approaches on different length scales: (1) the finite element method is used to model realistic device geometries and to calculate the electrostatic potential across the Schottky barrier by solving the Poisson equation, and (2) the Landauer-Büttiker approach combined with the method of non-equilibrium Green's functions is employed to calculate the charge transport through the device. Our model correctly reproduces typical I-V characteristics of field-effect transistors, and the dependence of the saturated drain current on the gate field and the device geometry are in good agreement with experiments. Our approach is suitable for one-dimensional Schottky-barrier field-effect transistors of arbitrary device geometry and it is intended to be a simulation platform for the development of nanowire-based sensors.
[Show abstract][Hide abstract] ABSTRACT: In this paper we present the investigation of high-k dielectrics in a metal–insulator–metal structure. We show the physical and electrical properties of ZrO2 and SrxZr(1−x)Oy grown through sputter deposition. Uncontrolled crystallization of ZrO2 during the growth into a mixture of different phases was observed. As a consequence, the k-value was suppressed. Stabilization of the amorphous phase of the as grown films could be achieved by the admixture of SrO. This enabled controlled crystallization into a single phase after performing post-deposition annealing. The k-value of the annealed SrxZr(1−x)Oy was determined to be 33.
[Show abstract][Hide abstract] ABSTRACT: Silicon nanowires are currently being considered as possible candidates for Beyond-CMOS electronic applications. One attractive nanowire transistor concept is the Schottky junction FET where the source and drain regions are metallic. The most appropriate device geometry to couple the gate potential to the junctions is an axial metal / semiconductor / metal nanowire heterostructure. Here, NiSi2 / Si / NiSi2 nanowire heterostructures are fabricated and used as the core of our transistors. Characteristic advantages of these structures are the abrupt and homogeneous Schottky interfaces formed. In contrast to most Schottky FETs the clear definition of the junction area, as given by the nanowire cross-section has the prospect of reducing device to device variability.