Kelvin probe microscopy for reliability investigation of RF-MEMS capacitive switches

In this work, we investigate the charging and reliability of interlayer dielectric materials that are used in the fabrication process of advanced RF-MEMS switches. In particular, the charge stored on the surface of a dielectric and the dynamic of this charge at nanometric scale are studied. More attention is given to the decay of the deposited charge by a variety of means: (1) surface conduction, (2) surface charge spreading due to self repulsion and (3) charge injection in the bulk of dielectric material. Kelvin force microscopy (KFM) measurements were performed for various injection time and bias voltage. These results suggest a dynamic charge and allow to predict the amount of charge injected into the dielectric.     

Kelvin probe force microscopy of hole leakage from the active region of a working injection-type semiconductor laser diode

A method that enables direct observation and quantitative characterization of carrier leakage from the active region of working semiconductor light-emitting diodes and lasers is developed on the basis of Kelvinprobe microscopy. The method is used to reveal, on the surface of the mirror surfaces of high-power InGaAs/AlGaAs/GaAs laser diodes, minority holes arriving from the active region and spreading to the surface regions over the n-type emitter and n-type substrate. It is shown that holes can move through surface channels formed by regions of surface band bending to distances of tens of micrometers from the place where they originally appear at the surface. It is demonstrated that, as the injection current increases, the amount of leakage gradually grows and stabilizes after the onset of lasing.     

Work function difference of naphthyl end-capped oligothiophene in different crystal alignments studied by Kelvin probe force microscopy

The performance of organic semiconductor devices is strongly affected by the interface energetics at the junctions between the constituent materials. A large group of organic semiconductors consists of rodlike small molecules that crystallize upon deposition with a molecular orientation dependent on the specifics of the molecule–molecule and molecule–substrate interactions. By means of Kelvin probe force microscopy (KPFM), this work studies naphthyl end-capped oligothiophene, 5,50-bis(naphth-2-yl)-2,20-bithiophene (NaT2), deposited on samples of pristine ${\text{SiO}}_2$ and samples of graphene-covered ${\text{SiO}}_2$. The crystal molecular orientation of NaT2 is dependent on the substrate on which it is deposited. On ${\text{SiO}}_2$, the NaT2 molecules are predominately upright standing, forming crystallites with distinct terrace heights of $2.0\pm 0.1\text{nm}$. Measurements indicate formation of an initial wetting layer in the NaT2-${\text{SiO}}_2$ system for the upright standing molecules. When deposited on graphene, the molecules additionally form fibrous structures with heights of $10-115\text{nm}$ consisting of molecules lying down (face-on orientation). Using KPFM, a difference in the local contact potential difference (CPD) of upright standing NaT2 and face-on oriented structures on graphene is measured to be $-0.16\pm 0.04\text{V}$, indicating a work function difference between the two system configurations, which is confirmed through Density Functional Theory calculations.     

Moisture absorption and diffusion characterisation of packaging materials––advanced treatment

Unlike thermo-mechanical properties, moisture properties of packaging materials are rarely reported, even though moisture has been known to be at least as damaging as temperature to plastic packaging. This is in part due to the lack of characterisation knowledge for such properties.This paper tries to address this issue through a comprehensive presentation of the characterisation techniques for moisture sorption and diffusion properties. Special focuses are given to advanced treatments on unique characteristics of polymeric packaging materials. The effect of aspect ratio of the test specimen on characterisation accuracy has been analysed and correction factor has been formulated. Two techniques for characterising anisotropic diffusivity are presented and illustrated with actual experimental data on organic laminates. The techniques and challenges of characterising moisture diffusivity at high temperature are presented. A new insight into the causes and physics of non-Fickian adsorption in polymeric packaging materials is presented along with a technique to alleviate the associated characterisation challenge.     

Atomic force microscopy with carbon nanotube probe resolves the subunit organization of protein complexes

Among many scanning probe microscopies, atomic force microscopy (AFM) is a useful technique to analyse the structure of biological materials because of its applicability to non-conductors in physiological conditions with high resolution. However, the resolution has been limited to an inherent property of the technique; tip effect associated with a large radius of the scanning probe. To overcome this problem, we developed a carbon nanotube probe by attaching a carbon nanotube to a conventional scanning probe under a well-controlled process. Because of the constant and small radius of the tip (2.5-10 nm) and the high aspect ratio (1:100) of the carbon nanotube, the lateral resolution has been much improved judging from the apparent widths of DNA and nucleosomes. The carbon nanotube probes also possessed a higher durability than the conventional probes. We further evaluated the quality of carbon nanotube probes by three parameters to find out the best condition for AFM imaging: the angle to the tip axis; the length; and the tight fixation to the conventional tip. These carbon nanotube probes, with high vertical resolution, enabled us to clearly visualize the subunit organization of multi-subunit proteins and to propose structural models for proliferating cell nuclear antigen and replication factor C. This success in the application of carbon nanotube probes provides the current AFM technology with an additional power for the analyses of the detailed structure of biological materials and the relationship between the structure and function of proteins.     

Optimisation of a thick-film 10–400 N force sensor

The ring-on-ring bending principle allows the fabrication of simple, low-cost thick-film piezoresistive sensors for compressive forces in the 10–400 N range. However, some imperfections are encountered in its basic embodiment, such as relatively high force-signal hysteresis and nonrepeatability (up to ca. 5%). These shortcomings were studied in this work, and major improvements have been achieved. Hysteresis was found to be mainly due to friction at the outer support ring, and was considerably reduced by inserting a compliant silicone glue ring. The same glue ring was used to permanently bond the sensor to a rigid base, thereby giving well-defined and constant boundary conditions and also considerably improving the repeatability of the sensitivity. Overall, hysteresis and repeatability error were reduced down to a level of ca. 1%.     

Part average analysis – A tool for reducing failure rates in automotive electronics

As the complexity of technical systems increases, it is a matter of course that the quality requirements made on the assemblies, modules and components which are used increase as well. The Part Average Analysis (PAA) reveals a software-based methodical approach which can be used to improve the reliability and availability of technical functions in an efficient manner. The PAA is used to observe anomalies in functions or parameters to measure during the production process, reliably indicating a concealed defect. Components with a high risk of failure are rejected and are not installed in the vehicle (prevention). In this paper, the method will be presented, the mathematical model explained and experiences with automotive suppliers will be reported.     

AFM的DNA样品制备技术研究

AFM应用中最为关键的一步无疑是样品的制备。本文介绍DNA样品制备的几种主要方法,通过实验发展了两种适合对DNA及其碎片进行长度测量和做统计分析的制样方法,它们分别采用APS-云母和纯云母为衬底。这两种方法不仅丰富了DNA样品制备方法,对推广AFM在生物研究中的应用也具有重要意义。     

Influence of interfaces on electrical characteristics formation in monocrystalline silicon–noncrystalline ultrathin oxide – polycrystalline silicon structures

In this article, the electrically active centres (EAC) in a noncrystalline ultrathin oxide layer and at its interfaces with a monocrystalline silicon substrate and a polycrystalline silicon gate were investigated. These centres are (1) the fixed oxide charge centres in the ultrathin oxide layer and (2) the traps at its interfaces and in the polysilicon gate layer. In order to study these centres and to estimate their space and energy distributions, the modified C–V technique was applied. Among the results obtained, the significant role of the outer interface (polysilicon–ultrathin oxide) in the formation of electrical characterisitics and its sensitivity to the technological operations which possibly has an effect on the degree of its hydrogenation ought to be emphasised.     

A probe for the measurement of electrical unbalance of networks anddevices

A probe has been developed to measure residual electrical unbalance of nominally balanced networks and devices. In the form described, it makes convenient the use of single-ended 50 Ω instruments to measure electrical unbalance of wire pair networks and two-terminal devices. For electromagnetic compatibility (EMC) planning purposes, a knowledge of the electrical unbalance at signal interfaces in wire pair networks generally allows quantitative prediction of the conversion of wanted differential mode signals into unwanted radiated disturbances which can interfere with reception of radiocommunication services. The probe was first described to the CISPR in 1988. Since then, several other groups have also found it useful for measuring the electrical unbalance of telecommunication networks and devices. It has also been used to measure the differential mode signals and common mode disturbances at signal interfaces on balanced data signaling networks     

An Extension of MISEP for Post–Nonlinear–Linear Mixture Separation

Mutual information separation (MISEP) is a versatile independent component analysis (ICA) algorithm that can be used to handle linear and nonlinear mixtures. By incorporating the a priori information of mixtures, an extended MISEP method is proposed in this brief to recover the source signals from the post–nonlinear–linear (PNL-L) mixtures. One group of multilayer perceptrons and two linear networks are used as the unmixing system, and another group of multilayer perceptrons is used as the auxiliary network. The learning algorithm of the system parameters is obtained by maximizing the output entropy with the gradient ascent method. Experimental results demonstrate that the proposed method is effective and efficient for PNL-L mixture separation.      

Flicker noise spectroscopy – a new method of studying non-stationary effects in electrical conductivity of oxides

This work shows the possibilities of the application of a new phenomenological approach known as flicker noise spectroscopy (FNS) in studying the non-equilibrium effects in d.c. and a.c. electrical conductivities of oxides (local phase transitions under the influence of high electric fields and local heating effects, generation of space charges, memory effects, pre-breakdown instabilities, influence of environment, etc.).The FNS method is very informative in describing dynamic effects, which assist the electrical current flow through thin (20–60 nm) oxide films formed at the Si surface by its electrochemical oxidation. Polarity of the voltage applied to the structure and polarization history (whether the voltage increases or decreases) essentially influence the electrical noise, first of all, a degree of dynamic memory in a sequence of individual bursts contribute to the noise signal.     

Quantitative Measurement of the Local Surface Potential of π‐Conjugated Nanostructures: A Kelvin Probe Force Microscopy Study

We describe a systematic study on the influence of different experimental conditions on the Kelvin probe force microscopy (KPFM) quantitative determination of the local surface potential (SP) of organic semiconducting nanostructures of perylene‐bis‐dicarboximide (PDI) self‐assembled at surfaces. We focus on the effect of the amplitude, frequency, and phase of the oscillating voltage on the absolute surface potential value of a given PDI nanostructure at a surface. Moreover, we investigate the role played by the KPFM measuring mode employed and the tip–sample distance in the surface potential mapping by lift‐mode KPFM. We define the ideal general conditions to obtain a reproducible quantitative estimation of the SP and we find that by decreasing the tip–sample distance, the area of substrate contributing to the recorded SP in a given location of the surface becomes smaller. This leads to an improvement of the lateral resolution, although a more predominant effect of polarization is observed. Thus, quantitative SP measurements of these nanostructures become less reliable and the SP signal is more unstable. We have also devised a semi‐quantitative theoretical model to simulate the KPFM image by taking into account the interplay of the different work functions of tip and nanostructure as well as the nanostructure polarizability. The good agreement between the model and experimental results demonstrates that it is possible to simulate both the change in local SP at increasing tip–sample distances and the 2D potential images obtained on PDI/highly oriented pyrolytic graphite samples. These results are important as they make it possible to gain a quantitative determination of the local surface potential of π‐conjugated nanostructures; thus, they pave the way towards the optimization of the electronic properties of electroactive nanometer‐scale architectures for organic (nano)electronic applications.     

New challenges to the modelling and electrical characterisation of ohmic contacts for ULSI devices

Continuing developments in semiconductor process and materials technology have enabled significant reductions to be achieved in the contact resistance R_c of devices. This reduction is commonly assessed in terms of the specific contact resistance (SCR) parameter ρ_c (Ω cm²) of the metal–semiconductor interface. Such a reduction in SCR is essential, for as device dimensions decrease, then so also must ρ_c and the corresponding contact resistance in order not to compromise the down-scaled ULSI device performance. Thus the ability to accurately model contacts and measure ρ_c is essential to ohmic contact development. The cross kelvin resistor (CKR) test structure is commonly used to experimentally measure the Kelvin resistance of an ohmic contact and obtain the specific contact resistance ρ_c. The error correction curves generated from computer modelling of the CKR test structure are used to compensate for the semiconductor parasitic resistance, thus giving the SCR value. In this paper the increased difficulty in measuring lower ρ_c values, due to trends in technology, is discussed. The challenges presented by the presence of two interfaces in silicided contacts (metal-silicide–silicon) is also discussed. Experimental values of the SCR of an aluminium–titanium silicide interface is determined using multiple CKR test structures.     

The cylindrical antenna as a probe for studying the electrical properties of media

When a base-driven cylindrical monopole (or center-driven dipole) is immersed in an arbitrary medium, the electric and magnetic fields on its surface depend not only on its length and radius but also on the effective conductivity and permittivity of the medium. These fields can be explored and measured with small probes designed to travel along the cylindrical surface of the antenna. The interpretation of the observations depends on the availability of a general theory that correctly describes the distributions of current and charge on the conductor. The results of a new theory that is valid for electrically thin monopoles up to5lambda/8(dipoles up to5lambda/4)in length over all practical ranges of conductivity and permittivity of the ambient medium, including those characteristics of under- and overdense cold plasmas, are described together with their experimental verification.     

中国LED显示屏产业发展状况综述

综述中国LED显示屏产业发展的历程、现状和将来的发展方向。     

Preparation and characterisation of Langmuir–Blodgett films of 4‐(4‐(N‐octadecyl‐N‐methylamino) phenylazo)benzoic acid

Langmuir films of the title compound have been spread on an aqueous subphase at various values of pH at 10, 15 and 20°C. Increasing pH and increasing temperature favour stable films, but at the higher subphase pH and temperature values the pressure–area isotherms exhibit a transition to aggregated forms. Tilt angles between the alkyl chains and the normal to the subphase increase with increasing subphase pH and temperature. The area per molecule for films deposited at 15 °C decreased steadily with time at a fixed surface pressure, except at the highest pH, indicating poor stability. Langmuir–Blodgett films deposited at a surface pressure of 30 mN m⁻¹ and a subphase temperature of 15 °C were of Y‐type and showed transfer ratios above unity for the lower subphase pH values. UV/visible spectra of the LB films showed features characteristic of the formation of H aggregates for deposition at the higher subphase pH values. Over long periods of time the spectra for high pH showed evidence of increasing aggregation. Small‐angle X‐ray diffraction confirmed molecular tilts larger than those deduced in the floating monolayer. Reflection–absorption infrared spectroscopy of the LB films showed differences from the bulk also indicative of significant tilt, as did surface‐enhanced Raman spectroscopy. The LB films showed weak second‐harmonic generation from 1064 nm radiation consistent with a polar film structure parallel to the substrate. Copyright © 1999 John Wiley & Sons, Ltd.