Wolfgang H. Krautschneider

Stabilization of higher-κ tetragonal HfO2 by SiO2 admixture enabling thermally stable metal-insulator-metal capacitors

The authors report the relationship between HfO2 crystalline phase and the resulting electrical properties. Crystallization of amorphous HfO2 into the monoclinic phase led to a significant increase in leakage current and formation of local defects. Admixture of 10% SiO2 avoided formation of these defects by stabilization of the tetragonal phase, and concurrently increased the permittivity to 35. This understanding enabled fabrication of crystalline HfO2 based metal-insulator-metal capacitors able to withstand a thermal budget of 1000°C while optimizing capacitance equivalent thickness (<1.3nm) at low leakage [J(1V)<10−7A∕cm2].

Hole trap related hysteresis in pentacene field-effect transistors

We have investigated hysteresis in pentacene-based field-effect transistors with SiO2 as gate dielectric. A clear hysteresis behavior in transfer and output characteristics is reported. Measurements show that the observed hysteresis is due to hole trapping in the pentacene film. Long time constants of the trapping/detrapping mechanism are demonstrated through transient measurements. An initialization routine to be performed prior to measurements is proposed to enable reproducible and reliable measurements on pentacene transistors.

Spin-cast composite gate insulation for low driving voltages and memory effect in organic field-effect transistors

The authors report on a solution-processed composite film based on poly(vinylidene fluoride/trifluoroethylene) copolymer and barium titanate (BT) nanopowder, to be used as ferroelectric high-κ gate insulation in organic field-effect transistors (OFETs). Flexible films of up to 50vol% BT powder content are produced by preparing homogeneous dispersion of the powder in the polymer solutions. The films exhibited high specific volume resistivities combined with dielectric constants of up to 51.5 at 1kHz. Low-voltage OFETs with ferroelectric hysteresis and good memory retention properties were demonstrated by using the composite films.

Impact of soft and hard breakdown on analog and digital circuits

The influence of gate oxide breakdown of one MOS transistor on the functionality of simple analog and digital circuits is studied. The main changes in the transistor behavior such as the additional gate current as well as transconductance and threshold voltage degradation are pointed out and their respective impact on circuit characteristics is analyzed. With this approach, it is possible to identify critical transistors during the design stage and implement appropriate countermeasures. Depending on the application, some circuits may be functional even after breakdown of one of their transistors.

Charge-based capacitance measurements (CBCM) on MOS devices

A new simple method of measuring capacitance-voltage characteristics of MOS devices is presented. Proceeding from the charge-based capacitance measurement technique suggested recently, a compact test structure with high resolution has been developed, which only requires measurement of do quantities. The method was tested on a 0.6-/spl mu/m CMOS process with small and large area capacitors and compared to well-known high-frequency capacitance-voltage results. Beside using a reference structure, a second means of extracting parasitic effects is demonstrated for small structures. The test structure allows measurements in a wide frequency range with high accuracy and low noise contribution at small capacitance levels.

Wavelength-selective organic field-effect phototransistors based on dye-doped poly-3-hexylthiophene

The authors present a strategy to manufacture wavelength-selective field-effect phototransistors by employing dye-doped poly-3-hexylthiophene (P3HT) as a semiconducting layer. The dye doping of the semiconductor P3HT was achieved by blending organic molecules—coumarin 6, oxazine 1, and nile red—into the conjugated organic polymer. Illuminating these transistors with monochromatic light in the range of 400–700nm resulted in varying conductivities for certain wavelengths in dependence on the particular dye. This effect is attributed to the photogeneration of excitons on the dye molecules, which are subsequently transferred to the conjugated polymer.The authors present a strategy to manufacture wavelength-selective field-effect phototransistors by employing dye-doped poly-3-hexylthiophene (P3HT) as a semiconducting layer. The dye doping of the semiconductor P3HT was achieved by blending organic molecules—coumarin 6, oxazine 1, and nile red—into the conjugated organic polymer. Illuminating these transistors with monochromatic light in the range of 400–700nm resulted in varying conductivities for certain wavelengths in dependence on the particular dye. This effect is attributed to the photogeneration of excitons on the dye molecules, which are subsequently transferred to the conjugated polymer.

Model for the voltage and temperature dependence of the soft breakdown current in ultrathin gate oxides

The voltage and temperature dependence of the soft breakdown conduction mechanism in metal-oxide-semiconductor capacitors and transistors with ultrathin dielectric layers is investigated. A physical derivation of the quantum point contact model and its parameters is presented, which incorporates the smearing of the Fermi function at the electrodes as well as the effect of thermal vibrations of the constriction’s bottleneck. The model also takes into account the boundary conditions at the two ends of the breakdown path by considering the semiconductor band bending occurring in the nondamaged surrounding device area. Good agreement between model and experimental curves is found. Because of its analytical nature, the proposed model can be implemented in circuit simulators.

Memristive operation mode of floating gate transistors: A two-terminal MemFlash-cell

A memristive operation mode of a single floating gate transistor is presented. The device resistance varied accordingly to the charge flow through the device. Hysteretic current-voltages including a resistance storage capability were observed. These experimental findings are theoretically supported by a capacitive based model. The presented two-terminal MemFlash-cell can be considered as a potential substitute for any memristive device (especially for reconfigurable logic, cross-bar arrays, and neuromorphic circuits) and is basically compatible with current Si-fabrication technology. The obvious trade-off between a memristive device based on a state-of-the-art silicon process technology and power consumption concerns will be discussed.

Synthesis of an organic conductive porous material using starch aerogels as template for chronic invasive electrodes

We report the development of an organic conducting mesoporous material, as coat for invasive electrodes, by a novel methodology based on the use of starch aerogel as template. The poly(3,4-ethylenedioxythiophene) (PEDOT) aerogel was synthesized by polymerization of 3,4-ethylenedioxythiophene within a saturated starch aerogel with iron (III) p-toluenesulfonate (oxidizing agent) and subsequent removal of the polysaccharide template, followed by supercritical CO2 drying. The chemical structure and oxidation state of the resulting material were studied by Raman spectroscopy. The morphology and surface properties of the obtained nanoporous material were investigated by scanning electron microscopy (SEM), micro computed tomography (μCT) and nitrogen adsorption-desorption techniques. The composition and thermal behaviour were evaluated by energy dispersive spectroscopy (EDS) and thermogravimetric analysis (TGA) respectively. A preliminary biocompatibility test verified the non-cytotoxic effects of the PEDOT aerogel. The large surface area and wide pore size distribution of the PEDOT conductive aerogel, along with its electrical properties, enable it to be used as extracellular matrix scaffold for biomedical applications.

Modeling random telegraph signals in the gate current of metal–oxide–semiconductor field effect transistors after oxide breakdown

Measurements of random telegraph signals (RTS) in the gate current of n-channel metal–oxide–semiconductor field effect transistors (MOSFETs) after oxide breakdown are presented. Two types of behavior of the time constants and the relative amplitudes of the signals as a function of gate voltage are observed. A theory relating time constants and relative amplitudes of the fluctuations to the energetic and geometric trap location in the oxide is developed. This theory is also applicable to the commonly observed RTS in the drain current of undamaged MOSFETs.