W. De Ceuninck

A comparison between state-of-the-art ‘gilch’ and ‘sulphinyl’ synthesised MDMO-PPV/PCBM bulk hetero-junction solar cells

Abstract To obtain photovoltaic devices based on electron donating conjugated polymers with a higher efficiency, a major breakthrough was realised by mixing the polymers with a suitable electron acceptor, thereby enhancing the rate for photo-induced charge generation by several orders. State-of-the-art organic bulk hetero-junction photovoltaic cells are based on an interpenetrating donor–acceptor network in the bulk to form efficient nanostructured p–n junctions in the organic materials. Devices made with ‘Gilch’ poly(2-methoxy-5-(3′,7′-dimethyl-octyloxy))- p -phenylene vinylene, (MDMO-PPV), as an electron donor and (6,6)-phenyl-C 61 -butyric-acid (PCBM) (a soluble C60 derivative) as an electron acceptor yielded the highest efficiency until now in this class of devices. A power conversion efficiency of approximately η e ≥2.5% (electrical power out/incident light power) under AM 1.5 illumination was reported. The ‘gilch’ route is a direct synthetic route. The ‘sulphinyl’ route is a promising, indirect precursor-route towards MDMO-PPV. Due to the non-symmetric monomer, so-called ‘head-to-head’ and ‘tail-to-tail’ additions are excluded to a higher level in comparison to the ‘gilch’ route. This difference between both materials makes them interesting candidates to compare them in the state-of-the-art photovoltaic devices. Preliminary results indicate that the ‘sulphinyl’ MDMO-PPV/PCBM bulk hetero-junction solar cells attain a power conversion efficiency of nearly η e =3% (electrical power out/incident light power), have a higher fill factor, incident photon per converted electron value (IPCE) and short circuit current. It is indicated that the observed solar cell characteristics are related to the defect level of the conjugated polymer used.

The stability of Pt heater and temperature sensing elements for silicon integrated tin oxide gas sensors

Abstract Good performance of alarm systems and environmental as well as industrial control methods requires an optimal operation of the gas sensors involved. An essential point related to this challenge is an accurate control of the sensor working temperature. Therefore, the stability of the Ti/Pt heater element used in tin oxide thin film gas sensors has been investigated. It turns out that the heater element is influenced by diffusion and oxidation processes taking place during thermal treatment. This is illustrated by RBS, AES and XPS measurements. The modifications in chemical composition are also found to influence the electrical characteristics R 0 and TCR of the heater.

A Comprehensive Model for Hot Carrier Degradation in LDMOS Transistors

This paper presents a comprehensive yet physical model for hot carrier degradation in LDMOS transistors. The only model input parameters are the gate and drain voltage Vds and Vgs , the internal device temperature and the device width W. The model allows calculating AC degradation performance out of the DC hot carrier data. A physical explanation of the observed effects is provided, and important differences between LDMOS and standard CMOS are highlighted

Heat-transfer-based detection of L-nicotine, histamine, and serotonin using molecularly imprinted polymers as biomimetic receptors

AbstractIn this work, we will present a novel approach for the detection of small molecules with molecularly imprinted polymer (MIP)-type receptors. This heat-transfer method (HTM) is based on the change in heat-transfer resistance imposed upon binding of target molecules to the MIP nanocavities. Simultaneously with that technique, the impedance is measured to validate the results. For proof-of-principle purposes, aluminum electrodes are functionalized with MIP particles, and l-nicotine measurements are performed in phosphate-buffered saline solutions. To determine if this could be extended to other templates, histamine and serotonin samples in buffer solutions are also studied. The developed sensor platform is proven to be specific for a variety of target molecules, which is in agreement with impedance spectroscopy reference tests. In addition, detection limits in the nanomolar range could be achieved, which is well within the physiologically relevant concentration regime. These limits are comparable to impedance spectroscopy, which is considered one of the state-of-the-art techniques for the analysis of small molecules with MIPs. As a first demonstration of the applicability in biological samples, measurements are performed on saliva samples spiked with l-nicotine. In summary, the combination of MIPs with HTM as a novel readout technique enables fast and low-cost measurements in buffer solutions with the possibility of extending to biological samples. FigureHeat-transfer based detection with molecularly imprinted polymers

A new degradation model and lifetime extrapolation technique for lightly doped drain nMOSFETs under hot-carrier degradation

Abstract The hot-carrier degradation of lightly doped drain nMOSFETs is studied in detail. The degradation proceeds in a two-stage mechanism, involving first a series resistance increase and saturation, followed by a carrier mobility reduction. The degradation behaviour of a characteristic MOSFET parameter is modelled over the complete degradation range, from 0.02 up to more than 10%. Furthermore, the introduction of a simultaneous non-linear least-square fit of the degradation curves has been successful for predicting the complete degradation behaviour at normal operating conditions.

An algorithm to calculate activation energy spectra for structural relaxation in amorphous alloys

Abstract Some years ago Gibbs et al. developed the so-called activation energy spectrum (AES) model to describe irreversible and reversible structural relaxation in amorphous alloys. This model was applied in several studies on metallic glasses to explain the observed relaxation behaviour. However, in some cases only an approximate AES of available processes was derived. In this paper we propose two algorithms which can be used to calculate an AES. The method is applied to simulated as well as to real resistance measurements.

Increasing the mean grain size in copper films and features

A new grain-growth mode is observed in thick sputtered copper films. This new grain-growth mode, also referred to in this work as super secondary grain growth (SSGG) leads to highly concentric grain growth with grain diameters of many tens of micrometers, and drives the system toward a {100} texture. The appearance, growth dynamics, final grain size, and self-annealing time of this new grain-growth mode strongly depends on the applied bias voltage during deposition of these sputtered films, the film thickness, the post-deposition annealing temperature, and the properties of the copper diffusion barrier layers used in this work. Moreover, a clear rivalry between this new growth mode and the regularly observed secondary grain-growth mode in sputtered copper films was found. The microstructure and texture evolution in these films is explained in terms of surface/interface energy and strain-energy density minimizing driving forces, where the latter seems to be an important driving force for the observed new growth mode. By combining these sputtered copper films with electrochemically deposited (ECD) copper films of different thickness, the SSGG growth mode could also be introduced in ECD copper, but this led to a reduced final SSGG grain size for thicker ECD films. The knowledge about the thin-film level is used to also implement this new growth mode in small copper features by slightly modifying the standard deposition process. It is shown that the SSGG growth mode can be introduced in narrow structures, but optimizations are still necessary to further increase the mean grain size in features.

Modelling hot-carrier degradation of LDD NMOSFETs by using a high-resolution measurement technique

Abstract By using a new, state-of-the-art measurement technique, the hot-carrier degradation of LDD nMOSFETs is studied. This high-resolution measurement technique, allows the measurement of degradation levels as low as 0.03 %. A new model based on Goo et al. [1] has been developed and verified in the full region between 0.03 up to almost 10 % for the ageing parameter I d,lin . The introduction of a simultaneous non-linear least-square fit of the degradation curves has been successful for predicting the complete degradation behaviour at real life operating conditions.

The influence of addition elements on the early resistance changes observed during electromigration testing of Al metal lines

Abstract This paper provides a critical review on early resistance changes observed during electromigration testing of Al, AlSi and AlSiCu metal lines. At present, high resolution in situ electrical resistance measurements are widely accepted as a valuable tool for the study of electromigration. It will be shown however that the results of these measurements should be interpreted with care. It will indeed be shown that, particularly for Si and/or Cu alloyed metallizations, an early resistance change measurement (during electromigration) can contain information that has no link with the damage induced by the electromigration process. A number of disturbing factors will be identified, which are all induced by temperature driven processes. The first type of disturbance is well known: the immediate change of the measured resistance with temperature steps and fluctuations (thermometer effect). The second type of disturbance is not so widely recognised. It is induced by time dependent changes that are observed over an extended period of time, following a preceding temperature step. Two types of disturbing contributions to resistance changes of this second type are identified, which will be denoted as irreversible changes and reversible changes. The irreversible resistance changes are usually observed during the first annealing of the metal line. The reversible changes are typically detected at the start of an electromigration measurement, when the current stress is switched on. It is shown that both the reversible and irreversible changes are caused by precipitation/dissolution reactions of addition elements. It is also shown that the often observed parabolic initial resistance increase that is detected at the start of electromigration experiments should be attributed to the time dependent, reversible dissolution of the addition element(s). Comparable experiments, executed however at a much reduced current level so that no Joule heating takes place, and hence no reversible processes are initiated, show that the kinetics of the purely electron-wind induced resistance changes are completely different: instead of a parabolic initial increase, an incubation time can be observed during the first stage of the measurement.

Mobile Application for Impedance-Based Biomimetic Sensor Readout

A new method is presented for smartphone-based impedance spectroscopy, especially fine-tuned for biomimetic sensor readout. Complete user control is given by means of an app while the on-board audio hardware of the smartphone or tablet PC is used to perform impedance measurements. This considerably limits the required external hardware. Disposable test strips can be mounted for convenient readout of various sensors. The system is verified on passive components and a synthetic molecularly imprinted polymer histamine sensor. The prototype design could prove a useful step toward the development of home-diagnostics biosensing applications.