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Very good crystallinity and highly c-axis-oriented aluminum nitride (AlN) thin films are sputtered on titanium (Ti) to fabricate thin piezoelectric cantilevers. Raman spectroscopy measurements and X-ray diffraction (XRD) indicate the high quality of these AlN films. A fabrication process, fully CMOS compatible, is developed to realize slender piezoelectric microcantilevers. Actuation enhancement for the AlN piezoelectric cantilevers is achieved by coating the slender beams with a thin PECVD silicon nitride (SiN) layer. Very good linearity and high displacement, up to 19.5 nm for 200 μm long cantilevers and 4.25 nm for 100 μm long cantilevers for 1 V actuation at quasi-static mode, are obtained with a 500 nm SiN top layer. These displacement values are three times larger than our previously reported values for cantilevers without SiN layer coating. This makes these cantilevers, without the need of employing nonstandard metals such as platinum (Pt), very promising for micro/nanoactuators.

The collapse of photoresist patterns in high aspect ratio patterning is a defect that may reduce the production yield drastically. Recently, a novel method to reduce the pattern collapse was successfully applied: the rinse of the photoresist patterns with a cationic surfactant solution. In a previous study it was shown that one chosen surfactant adsorbs on both untreated photoresist surfaces and photoresist films that had undergone the whole photolithographic process. For this surfactant best pattern collapse reduction coincides with the formation of surfactant aggregates on the photoresist surface and with a maximum receding contact angle on processed photoresist. The present study investigates the influence of the hydrocarbon chain length of the surfactant on the pattern collapse reduction. The adsorption of surfactants of various chain length on unexposed and exposed photoresist was observed using null-ellipsometry and zeta potential measurements. Increasing the surfactant chain length shifts the adsorption domains to lower concentrations. It leads to an increased adsorbed amount and maximum contact angle as well as to a better pattern collapse reduction.

The wetting behavior of a liquid polymer on top of a supported glassy polymer film is investigated with real (optical microscopy, phase measuring interference microscopy, and scanning force microsc...

In thin film geometry, the interplay between dewetting and phase separation or microphase separation controls the morphology of the polymeric structures resulting on a solid support. For the model system of polystyrene, polyparamethylstyrene and the diblock copolymer of the two homopolymers, the regime of ultrathin films is addressed experimentally. Evolving structures are probed with real and reciprocal space analysis techniques such as the optical microscopy, phase measuring interference microscopy, scanning force microscopy, neutron or x-ray reflectivity and grazing incidence small angle neutron or x-ray scattering approaches. The effective interface potential of the solid support is tuned by means of a change of the silicon substrate coating. Coating layers of silicon oxide, polyamide and polyimide are under investigation. A power law behaviour describing the most prominent in-plane length as a function of the initially prepared film thickness is observed. All reported structures have been prepared on large scale surfaces, such as typical Si wafers with 100 mm diameter.

We present first-principles calculations of ballistic spin injection in Fe/GaAs and Fe/ZnSe junctions with orientation (001), (111), and (110). We find that the symmetry mismatch of the Fe minority-spin states with the semiconductor conduction states can lead to extremely high spin polarization of the current through the (001) interface for hot and thermal injection processes. Such a symmetry mismatch does not exist for the (111) and (110) interfaces, where smaller spin injection efficiencies are found. The presence of interface states is found to lower the current spin polarization, both with and without a Schottky barrier. Finally, a higher bias can also affect the spin injection efficiency.

The enhanced thermal stability of thin polymer bilayer films against dewetting is investigated. Stabilization results from the addition of a random functional copolymer. The model system consists of a silicon substrate covered with a bilayer of amorphous polyamide (PA), followed by a fully deuterated polystyrene (PSd). While the PA sublayer is stable against dewetting, the addition of a PSd homopolymer film allows dewetting to occur during annealing. By blending the PSd top layer with a fully protonated copolymer poly(styrene-co-maleic anhydride) (SMA2), containing 2% maleic anhydride groups in the chain, its dewetting process is retarded. This increase in stability is investigated as a function of copolymer and annealing time. Scanning force microscopy (SFM) is applied to determine the surface root-mean-square roughness and to check the stabilization effect. Information about the density profile is aquired from specular neutron reflectivity measurements. In addition, grazing incidence small angle neutron...

The technique of scanning small-angle X-ray scattering with a microsized beam (SM-SAXS) has been used to study crack propagation in poly(methyl methacrylate) (PMMA). Two pieces of PMMA are welded t...

The stability of thin diblock copolymer films with respect to the annealing above the microphase separation temperature is investigated on long time scales and at different film thicknesses. Poly(styrene-block-p-methylstyrene) diblock copolymer films on top of silicon substrates are examined with scanning force microscopy and off-specular X-ray scattering. At film thickness below the lamellar spacing of the bulk material a dewetting is observed. The kinetics of the film destabilization are explainable within a spinodal dewetting model. The observed dewetting structures belong to a wet dewetting. In the case of film thicknesses which enable the buildup of a few lamellae no sign of instability was detected.

The paper aims at understanding the tunneling process in epitaxial magnetic tunnel junctions. Firstly, we stress the importance of the complex band structure of the insulator for the tunneling of the metal electrons. For large insulator thicknesses the tunneling current is carried by very few states, i.e., those states in the gap of the semiconductor having the smallest imaginary component of the k-vector. In the case of GaAs, ZnSe and MgO these are Δ1-states at the Γ -point. Secondly, we discuss the role of resonant interface states for tunneling. Based on simple model calculations and ab initio results we demonstrate that for symmetrical barriers the minority conductance can be dominated in an intermediate thickness range by few ‘hot spots’ in the surface Brillouin zone, arising from resonant interface states. In these hot spots full transmission can still be obtained, when all other states are already strongly attenuated, so that the usual exponential decay can be considerably delayed.

This article concerns the adsorption of the diblock polyampholyte poly(methacrylic acid)-block-poly((dimethylamino)ethyl metharylate) (PMAA-b-PDMAEMA) from aqueous solution on silicon substrates. The investigated polyampholyte is characterized by a small molecular weight around 15,000 g/mol and a big positively charged PDMAEMA block. The adsorbed amount determined by ellipsometry was strongly influenced by the pH of the adsorption solution. Using dynamic light scattering polyampholytic structures with diameters around 50 nm were found in aqueous solution. The hydrodynamic diameter was hardly affected by changing the pH of the polymer solution. Analogous regular structures were also found by scanning force microscopy (SFM) and grazing incidence, small angle X-ray scattering (GISAXS) at the silicon surface after the adsorption process. While SFM provides a topographical image of a small part of the adsorbed polyampholytic layer, GISAXS was used to get a statistical description of the lateral surface structures. The adsorbed structures were highly regular and their sizes were nearly pH independent over a large pH region. Only directly at the isoelectric point of the polyampholyte larger adsorbed structures were observed. Compared with earlier investigated PMAA-b-PDMAEMA systems we are now able to prepare highly regular polyampholytic structures at silicon surfaces. There are two kinds of interactions for the adsorbed micelles. First, the charged block of the chains is directly attracted to the substrate via electrostatic interactions, while the uncharged part of the chains is only hydrophobically attracted via the hydrophobic core of the adsorbed micelle.

The surface topography and the chemical morphology of poly(styrene-block-paramethylstyrene) diblock copolymers confined within isolated drops are investigated. The drop geometry imposes a two-dimensional spatial restriction. With scanning force microscopy, the film thickness dependence of the mean drop distance as the basic topographical feature is determined. In addition to large drops, a second smaller droplet structure is observed among the drops. The comparison of grazing incidence small-angle scattering using X-rays and neutrons shows that inside the drops the diblock copolymer orients into perpendicular lamellae with respect to the substrate surface. Compared to the bulk, the lamellar spacing is stretched parallel to the substrate.

We calculate the current spin polarization and the interface resistance of Fe/GaAs and Fe/ZnSe (001) spin injection junctions from first principles, including also the possibility of a Schottky barrier. From our results of interface resistance we estimate the barrier thickness needed for efficient spin injection if the process is nonballistic.

We studied the retardation of the dewetting process due to the addition of a functional copolymer in a polymer bilayer film. The model system consists of fully deuterated polystyrene (PS-d) on top of an amorphous polyamide (PA) sublayer on silicon substrates. Bilayer films were prepared with different content (0, 5, 10 and 30 vol. %) of a statistical copolymer (protonated styrene maleic anhydride acid (SMA2) containing 2% MA groups along the chain) being capable of forming hydrogen bonds with PA. The as-prepared as well as the annealed samples were investigated by neutron-reflectivity (NR) experiments, scanning force microscopy and optical microscopy. A significant retardation of dewetting is observed with the addition of SMA2. From model fits of NR curves the scattering length density profiles perpendicular to the sample surface were determined and an enrichment layer of SMA2 is detected. Retardation is explained by the intermixing of SMA2 and PS-d at the interface.

The lateral structures of dried adsorbed binary mixtures of star polymers were investigated. Blends of protonated and deuterated polybutadiene stars were prepared from cyclohexane solutions and adsorbed onto silicon substrates. The number of arms and the molecular weight of the arms was varied. With grazing incidence small angle scattering techniques (GISAS) and scanning force microscopy (SFM), different dominant in-plane length scales were determined. The morphology of these structures is dominated by blob-like structures created from single stars or agglomerates of star polymers.

Very thin piezoelectric cantilevers based on AlN layers using titanium Ti thin film electrodes are fabricated and characterized. By optimizing the Ti sputtering parameters, a very low stress (156 MPa) layers stack with high crystallinity and strong (002) orientation of the AlN films is obtained. Finally, a simple fabrication process, fully CMOS compatible, is developed to realize slender (900 nm) piezoelectric microcantilevers. A resonant frequency of 19.3 kHz is measured for 200 ?m long cantilevers. The deflection of cantilever is 6 nm/V and 189 nm/V for quasistatics and resonant frequency actuation, respectively. This makes the fabricated cantilevers attractive for high-speed MEMS actuators.

The temperature increase of bulk acoustic wave filters at high RF power levels has been investigated. Self-heating due to power dissipation in the filter leads to a nonuniform frequency shift of the insertion loss. At the right filter skirt, self-heating is amplified by the negative temperature coefficient of frequency. We demonstrate that at high RF power levels, this can cause thermal instabilities resulting in an abrupt step in the insertion loss. A novel frequency transformation is introduced to describe the nonuniform frequency shift of the insertion loss as well as the thermal instabilities. A condition for the occurrence of thermal instabilities is derived. It is argued that because of this nonuniform frequency shift at high power levels, accelerated lifetime tests can overestimate the lifetime, if the stress frequency is not compensated for self-heating. Here, the frequency transformation is used to determine the stress frequencies at high RF power levels from low-power S-parameter measurements.

In this paper, the reliability requirements, thermal behaviour and failure mechanisms of solidly mounted Bulk Acoustic Wave (BAW) filters are studied. High power RF stress measurements are presented where the evolution of the surface damage of the BAW filters as a function of stress time is analysed by optical height profiling. Two different metal stacks were used. The main failure mechanism for BAW filters during high RF power stress is proposed to be acoustomigration. By comparing the stress measurements to the requirements, excellent reliability of NXP's BAW duplexers is proven.

Thin film ferroelectric capacitors have been integrated with resistors and active functions such as ESD protection into small, miniaturized modules, which enable a board space saving of up to 80%. With the optimum materials and processes, integrated capacitors with capacitance densities of up to 100 nF/mm2 and breakdown voltages of exceeding 90 V have been achieved. The integration of these high density capacitors with extremely high breakdown voltage is a revolution in the world of passive components and has not yet been achieved in any other passive integration technology. Furthermore, thin film tunable capacitors based on barium strontium titanate with high tuning range and high quality factor at 1 GHz have been demonstrated. Finally, piezoelectric thin films for piezoelectric switches with high switching speed have been realized.

Galvanic piezoelectric RF MEMS switches are presented. The switches are completely processed and characterized mechanically and electrically. The mechanic deformation and switching times are discussed. Closing of the switch can be achieved within less than 10 ?s. Electrical measurements yield contact resistances in the order of 50 ? and isolation resistance of more than 1 G?.

Dielectric, ferroelectric and piezoelectric thin films are getting more and more attention for next generation mobile communication and medical systems. Thin film technologies based on dielectric, ferroelectric and piezoelectric thin films enable System-in-Package (SiP) devices, resulting in optimal integration of various functions in one module with respect to high performance, small size and low cost. Within Philips a passive integration platform for SiP technologies is developed, comprising key functions such as RF filters, micro-electromechanical switches, high-value capacitors as well as passive and active functions integrated in small modules. The piezoelectric thin film technologies do not only play a role for RF filters, but are also a breakthrough technology for a new class of thin film ultrasonic transducers.

We report on remote p-type doping of InAs nanowires by a p-doped InP shell grown epitaxially on the core nanowire. This approach addresses the challenge of obtaining quantitative control of doping levels in nanowires grown by the vapor-liquid-solid (VLS) mechanism. Remote doping of III-V nanowires is demonstrated here with the InAs/InP system. It is especially challenging to make p-type InAs wires because of Fermi level pinning around 0.1 eV above the conduction band. We demonstrate that shielding with a p-doped InP shell compensates for the built-in potential and donates free holes to the InAs core. Moreover, the off-current in field-effect devices can be reduced up to 6 orders of magnitude. The effect of shielding critically depends on the thickness of the InP capping layer and the dopant concentration in the shell. © 2007 American Chemical Society. U7 - Export Date: 2 August 2010 U7 - Source: Scopus

In this paper, we have grown III-V nanowires by metal organic vapor phase epitaxy (MOVPE) using the vapor-liquid-solid (VLS) growth mechanism. In addition, the author discusses the fabrication and characterization of reproducible axial InP nanowire LED devices.

Piezoelectric AlN and PbZr/sub x/Ti/sub 1-x/O/sub 3/ (PZT) layers are investigated with respect to their potential for HF micro-electronic applications. High quality AlN films with strong c-axis orientation are achieved by optimum deposition conditions and by applying nucleation layers. Electromechanical coupling factors of 0.25/spl plusmn/0.03 have been found. PZT films grown via sol-gel processing show high coupling factors k of 0.4-0.6 and are therefore attractive for wide bandwidth applications.

Based on model and ab initio calculations we discuss the effect of resonant interface states on the conductance of epitaxial tunnel junctions. In particular we show that the ``hot spots'' found by several groups in ab initio calculations of symmetrical barriers of the ${\mathbf{k}}_{\ensuremath{\Vert}}$-resolved conductance can be explained by the formation of bonding and antibonding hybrids between the interface states on both sides of the barrier. If the resonance condition for these hybrid states is met, the electron tunnels through the barrier without attenuation. Even when both hybrid states move together and form a single resonance, strongly enhanced transmission is still observed. The effect explains why, for intermediate barrier thicknesses, the tunneling conductance can be dominated by interface states, although hot spots only occur in a tiny fraction of the surface Brillouin zone.

We present {\it ab initio} calculations of the spin-dependent electronic transport in Fe/GaAs/Fe and Fe/ZnSe/Fe (001) junctions simulating the situation of a spin-injection experiment. We follow a ballistic Landauer-B\"uttiker approach for the calculation of the spin-dependent dc conductance in the linear-responce regime, in the limit of zero temperature. We show that the bulk band structure of the leads and of the semiconductor, and even more the electronic structure of a clean and abrupt interface, are responsible for a current polarisation and a magnetoresistance ratio of almost the ideal 100%, if the transport is ballistic. In particular we study the significance of the transmission resonances caused by the presence of two interfaces., Comment: 13 pages, 9 figures

We consider the spin injection from Fe into ZnSe and GaAs in the ballistic limit. By means of the ab initio SKKR method we calculate the ground state properties of epitaxial Fe|ZnSe(001) and Fe|GaAs(001) heterostructures. Three injection processes are considered: injection of hot electrons and injection of "thermal" electrons with and without an interface barrier. The calculation of the conductance by the Landauer formula shows, that these interfaces act like a nearly ideal spin filter, with spin polarization as high as 99%. This can be traced back to the symmetry of the band structure of Fe for normal incidence., Comment: 4 pages, 3 figures

A transducer (800) is provided where a membrane (830) is formed over a front substrate (615); and a piezoelectric layer (820) is formed over the membrane (830) at an active portion (821) and peripheral portions located adjacent the active portion (821). A patterned conductive layer including first and second electrodes (840, 845) is formed over the piezoelectric layer (820). Further, a back substrate structure is provided having supports (822, 824) located at the peripheral portions adjacent the active portion (821). The height (826) of the supports (822, 824) is greater than a combined height (828) of the patterned piezoelectric layer and the patterned conductive layer. Many transducers may be connected to form an array, where a controller may be provided for controlling the array, such as steering a beam of the array, and processing signals received by the array, for presence or motion detection and/or imaging, for example.

Thin film piezoelectric devices, processed in Si‐related processes, are attractive for ultrasound transducers and piezoelectric switches. Thin film ultrasound transducer enable large bandwidth (> 100%), high frequency operation. In piezoelectric micromachined ultrasonic transducers (PMUTs) the ultrasonic waves are generated by flexural motion of the membrane, which is coupled to strain in the piezoelectric film. We have investigated the piezoelectric properties of thin films for ultrasound transducers and piezoelectric switches. Thin film piezoelectric ultrasound transducers as well as piezoelectric switches have been designed, processed and characterized. Thin film piezoelectric devices with excellent quality and reliability have been realized.

We have studied the effect of impurity doping on the optical properties of indium phosphide (InP) nanowires. Photoluminescence measurements have been performed on individual nanowires at low temperatures (5¿70 K) and at low excitation intensities (0.5¿10 W/cm2). We show that the observed redshift (200 meV) and the linewidth (70 meV) of the emission of p-type InP wires are a result of a built-in electric field in the nanowires. This bandbending is induced by Fermi-level pinning at the nanowire surface. Upon increasing the excitation intensity, the typical emission from these p-InP wires blueshifts with 70 meV/decade, due to a reduction of the bandbending induced by an increase in the carrier concentration. For intrinsic and n-type nanowires, we found several impurity-related emission lines.

The paper investigates the structure formation in thin polymer blend films. Such a control of the structure formation is of great importance in many industrial applications. In this paper we follow two different routes in order to control the surface structures. One is the creation of surface structured through a dewetting of the thin films. The dewetting is archived through a plastification of the film either annealing or by swelling in a solvent atmosphere. As a result the control of this process allows to form very small and regular structures. The second route utilizes the demixing of an strongly immiscible polymer blend during preparation and yields much less defined structures. To allow a quantitative comparison if the evolving surface structures are statistically analyzed in terms of their rms-roughness and Fourier spectrum and compared with predictions from existing growth models.