– A new type of NO2 gas sensor has been made using the Floating Gate Field Effect Transistor (FG-FET) sensor system. 200 nm ZnO films were deposited on Si/Ti/Pt electrodes, which are mounted on FG-FET chips. SEM and EDX characterization methods were employed to study the surface of these films. The change in the work function of the film due to their interaction with NO2 has been measured at various temperatures and relative humidities. The sensor exhibits high sensitivity and selectivity to 1-20 ppm NO2 at a temperature range between room temperature and 165°C. With t50~10 s, the response time is quite fast. Index Term-Gas Sensor, Floating Gate Field Effect Transistor (FG-FET), Zinc Oxide, Nitrogen Dioxide.

Different substrate cleaning procedures were used before fabrication of pin diodes by silicon molecular beam epitaxy (MBE). We investigated the quality of these diodes in order to demonstrate the superior quality of in situ low energy plasma cleaning in ultra-high vacuum (UHV). The plasma-cleaned substrates can be transported through air and processed in another MBE chamber without any additional cleaning steps. Moreover, the deposited layers are stable to high-temperature treatment (900°C) without any degradation effects in device quality.

Ultra thin titanium films in the range of a few nanometers have been deposited on monocrystalline lithiumtantalate (LiTaO3) followed by deposition of 400nm pure aluminum (Al). Texture measurements by means of electron backscatter diffraction show that the thickness of the intermediate titanium (Ti) layer significantly influences texture and grain structure of the overlying Al film. Increasing the thickness of the Ti layer from 0nm to 20nm leads to a change of aluminums texture from unoriented polycrystalline over highly oriented in single direction to highly oriented in twin structure.

Avalanche photodiodes are widely used in a variety of applications. However, they need a high supply voltage. We propose to use the Impact Ionization MOSFET (IMOS) as an optical detector because it could substitute the high drain voltage by an internal amplification mechanism. Therefore, a much lower supply voltage would be needed. We fabricated devices as the first proof of principle and showed that the proposed concept works. We identified the most important problem of the actual devices and will do further research in order to improve the performance and reach towards the performance of avalanche photodiodes.

To explore mechanical stress durability of thin aluminum–scandium (AlSc) films, 0.86GHz nano resonators with AlSc electrodes have been manufactured. Four different samples have been prepared altering the Sc content in the alloy between 0.0% and 2.5%. A final lift-off step accomplished manufacture procedure of the devices. The resonators have been operated with heavy load to determine power durability. The resonators with AlSc electrodes show increased power durability compared to conventional Al metallized devices. Texture and grain structure of all films have been investigated by means of electron backscatter diffraction (EBSD) and atomic force microscopy (AFM). Material fatigue of electrodes has been visualized by scanning electron microscopy (SEM). The refined grain structure of these alloys can explain the enhanced mechanical stress durability of AlSc electrodes.

The impedance spectra of tellurium films with interdigital platinum electrodes were investigated in air at temperatures between 10 and 50 degrees C. Cole-Cole analysis made it possible to assess time constants, resistance, and capacitance of the film at characteristic frequencies and the dependence of these parameters on aging and temperature.Aging under normal conditions over 12 months led to a relative increase of only similar to 5% in film impedance at the characteristic frequency. However, aging noticeably influences the electrical resistance of the film at high (>500 kHz) frequencies, and capacitance diminished after 12 months by more than 50% throughout the spectrum.Scanning electron microscopy confirmed that the effect of aging is due to structural changes in the film. Temperature does not influence the capacitance of the film but uncommonly influences its resistance, which reaches a maximum at around 20 degrees C. This is ascribed to desorption of oxygen previously adsorbed from the environment. (C) 2008 Elsevier B.V. All rights reserved.

For the first time we present high temperature electrical characteristics of the vertical Impact Ionization MOSFET. The design of this device suppresses efficiently leakage currents at high temperatures and therefore guarantees MOSFET functionality up to several hundred degC. At 250degC a very good IonToff ratio of 10 5 as well as leakage currents in the nA range are demonstrated. This makes this device suitable for high temperature applications like automotive.

A combination of ArF-Excimer laser assisted techniques has been used for depositing and modifying ultra thin amorphous Si/Ge bi-layer structures. The first step consisted in producing, at low substrate temperatures, thin bi-layer coatings through Laser induced Chemical Vapour Deposition (LCVD) in both, large areas as well as in small regions of Si(100) wafers. In the second step, these bi-layer structures have been modified through Pulsed Laser Induced Epitaxy (PLIE) for obtaining heteroepitaxial SiGe alloys with a thin buried Ge rich layer, while keeping a shallow upper Si rich surface with good crystalline quality. Threshold for epitaxial alloy formation has been determined by Raman spectroscopy and estimated to be above 200mJ/cm2. Optical profilometry has been used for evaluating the thickness of the structures and the lateral dimensions of patterned features. SEM, TOF-SIMS and XPS have been used to corroborate the results. For testing IC compatibility, some samples have been overgrown with epitaxial Si and etched through conventional IC processing techniques, revealing that the laser processed layers are suitable to be used as sacrificial layers for producing Micro-Electro-Mechanical Systems (MEMSs) or Silicon-on-Nothing (SON) devices.

For conventional MOSFETs band-to-band tunnelling has to be avoided because it causes unintentional leakage currents. On the other hand the Tunnel FET, which basically consists of a gated pin-diode, takes advantage of tunnelling. The influence of technological parameters on device performance as well as scaling rules will be discussed. Finally it will be shown that band gap engineering with SiGe and the incorporation of high-k dielectrics strongly improve current slope and maximum ON current. A future device performance comparable or even better than the conventional MOSFET is predicted.

A new hydrogen sensor based on a heterogeneous polymer-platinum layer is presented. The sensor is based on the well-known floating gate field effect transistor (FG-FET [1]), which is shown in fig. 1. This type of sensor is capable of detecting various gas species [1,2,3] by measuring the work function change of a well chosen sensitive layer on which the target gas molecules are adsorbed. In the past platinum [1] or palladium [4] films as well as some heterogeneous metal oxide - platinum layers [5] have been used as sensitive materials for hydrogen detection. The main insufficiency of all these sensors is the low upper detection limit of about 2 % of hydrogen and the instabilities of the baseline in combination with its analogous detection behavior. To overcome these deficits we developed a new heterogeneous polymer - platinum system acting as sensitive layer. Using this new combination of materials, the FG-FET response to different concentrations is proportional only below a certain limit. Above this limit, the signal immediately steps to a maximum value. As this switching point is tunable, a new operation mode was developed, allowing precise hydrogen concentration measurements up to concentrations of at least 4 %.

Probing over active area (POAA) is gaining more influence in modern semiconductor production. Because of the existing bonding technology aluminum is still used as last metal layer. Whereas it is assumed that the problems during probing are mainly caused by the native aluminum oxide on the pad surface we will show, that other contaminations must be considered as well, especially fluorine. A possible cleaning step to improve the probing performance will be shown and discussed.

A new type of hydrogen sensor based on a floating gate field effect transistor (FG-FET) with a n-octadecyltrichlorsilane (ODTS) modified platinum layer of 20 nm in thickness as a gas sensitive layer is presented. The modifications stabilize the sensor signal even at temperatures up to 125degC. The surface of polycrystalline platinum is well known to act as sensitive layer for hydrogen detection in a FG -FET at room temperature. In the presence of hydrogen containing air the work function of a platinum surface is reduced up to 0.5 eV by the adsorption of atomic hydrogen. Unfortunately at temperatures above 60degC a high coverage of atomic oxygen occurs at the platinum surface. This raises the work function again, immediately after the hydrogen exposure so that the hydrogen concentration is no longer exactly detectable. With the deposition of a thin layer of ODTS, we were able to modify the platinum surface preventing it from being covered by oxygen during hydrogen exposure. A detailed model of the reactions at the platinum surface, which leads to the shift in work function, is given. Changes of the reaction paths by the modification are explained.

Effect of O-2, N-2 and H2O to electrical behavior of tellurium-based films as well as cross-sensitivity to NO2 gas has been studied at temperatures between 20 and 70 degrees C.The increase of oxygen partial pressure in N-2 + O-2 carrier gas results in a nearly linear decreasing of the film resistance. The complete impulsive substitution of nitrogen by oxygen decreases the resistance of the film with similar to 6% in 1.5 h, which is far below the much faster response of 50% with 1.5 ppm NO2.The effect of humidity is more perceptible. At room temperature the resistance of the films increases with 15% at 58% RH, but humidity has negligible effect at temperatures higher than 50 degrees C. At an appropriate temperature, humidity does not interfere with NO2.Our results suggest that effect of water vapour is due to simple physical adsorption, whereas effect of oxygen and nitrogen is the consequence of "week" chemisorption of these molecules on the film surface. The NO, sensing mechanism involves "strong" chemisorption due to interaction between odd electrons of nitrogen dioxide molecules and lone-pair electrons of tellurium-based chalcogenides. (c) 2006 Elsevier B.V. All rights reserved.

The cleaning of silicon (Si) surfaces is a very important issue for the fabrication of novel semiconductor devices on the nanoscale. Established methods for the removal of organic impurities and the native or chemical oxide are often combined with high temperature desorption steps. However, devices with small feature sizes will be unfunctional if, for example, out-diffusion of dopants is not prevented. In this paper we present two possible processes for low-temperature cleaning: an atomic hydrogen source, based on dissociative adsorption of hydrogen at a heated tantalum (Ta) surface and a hydrogen DC plasma source as a part of an UHV cluster tool. The influence of atomic hydrogen on carbon and oxide removal is surveyed and the existing model for native oxide etching with an argon/hydrogen DC plasma is adapted.

Effect of O2, N2 and H20 to electrical behaviour of tellurium-based films has been studied at temperatures between 20 degC and 70 degC. The increase of oxygen partial pressure in N O2+ O2 carrier gas results in a nearly linear decreasing of the film resistance. The complete impulsive substitution of nitrogen by oxygen decreases the resistance of the film with ~6 % in 1.5 hours. The effect of humidity is more perceptible. At room temperature the resistance of the films increase with 15 % at 58%RH, but humidity has a negligible effect at temperatures higher than 50degC. The results suggest that effect of water vapour is due to simple physical adsorption, whereas effect of oxygen and nitrogen is the consequence of "week" chemisorption of these molecules on the film surface

For safety reasons, while handling fuel cells, hydrogen concentrations of 0.1 -3% and above need to be detected. Low power hydrogen sensors, based on a Field Effect Transistor (FET), have been in use for about 25 years. In the past platinum and palladium were often used as gas sensitive layers. Unfortunately in the required concentration range, the Pt based sensors have a poor selectivity at room temperature and were not stable at operating temperatures above 60degC. To solve this problem Pt with a porous tin oxide (SnO2) top layer is used as a chemically sensitive electrode in a Floating Gate Field Effect Transistor (FG -FET). The results show that the SnO2 film on Pt stabilizes the sensor signal response between room temperature and 135degC. Also the sensor response time with t50 < 10s is quite fast and the cross sensitivity to other gases compared to pure Pt is reduced.

This paper presents experimental results of a novel vertical impact ionisation MOSFET (I-MOS). The device consists of a vertical gated triangular barrier diode (TBD), also know as planar doped barrier MOSFET (PDBFET). At low drain-source voltages the behaves like a conventional MOSFET. Drain-source voltages of more than 1.5 V activate gate controlled impact ionization in the sub-50 nm n-channel device, resulting in a subthreshold swing of 20 mV/decade at room temperature. The device shows an excellent ION/IOFF ratio of 2.5 times 108 in this mode

Experimental results of p-channel silicon vertical tunnel field-effect transistors down to sub-50 nm channel length are shown. As predicted by two-dimensional simulations, we show that the device on-current is nearly independent of channel length scaling. As the drain current is determined by electrons tunneling from the valence band to the conduction band, we show that mobility does not play any role in determining the device characteristics. Low temperature measurements reveal weak positive temperature coefficient in the transfer characteristics due to the dependence of bandgap on temperature. However, as expected for the silicon devices, low on-current is observed. Thus, we propose a lateral tunnel FET on SiGe-on-insulator with high on-currents and symmetric performance in n-channel as well as p-channel operating modes.

High-k gate dielectric La2O3 thin films have been deposited on Si(100) substrates by molecular beam epitaxy (MBE). Al/La2O3/Si metal-oxide–semiconductor capacitor structures were fabricated and measured. A leakage current of 3×10−9A/cm2 and dielectric constant between 20 and 25 has been measured for samples having an equivalent oxide thickness (EOT) 2.2nm. The estimated interface state density Dit is around 1×1011eV−1cm−2. EOT and flat-band voltage were calculated using the NCSU CVC program. The chemical composition of the La2O3 films was measured using X-ray photoelectron spectrometry and Rutherford backscattering. Current density vs. voltage curves show that the La2O3 films have a leakage current several orders of magnitude lower than SiO2 at the same EOT. Thin La2O3 layers survive anneals of up to 900°C for 30s with no degradation in electrical properties.

Sensing characteristics of tellurium-based thin films for NO2 monitoring was studied systematically. The influence of contact materials, thermal treatment, temperature and thickness of the samples on the electrical conductivity and sensitivity to NO2 with respect to scanning electron microscopy analyses is given. The possibility is shown to optimize the properties of the films for the development of a simple and stable NO2 sensor device with rapid response/recovery time and low operating temperature. The sensing mechanism is discussed for the direct interaction of gaseous species with lone-pair electrons of chalcogen atoms.