Silicon Microtechnology Research Articles

Tensile strain in Ge membranes induced by SiGe nanostressors

The monolithic integration of photonic functionality into silicon microtechnology is widely advanced. Yet, there is no final solution for the realization of a light source compatible with the prevailing complementary metal-oxide-semiconductor technology. A lot of research effort focuses on germanium (Ge) on silicon (Si) heterostructures and tensile strain application to Ge is accepted as one feasible route to make Ge an efficient light emitter. Prior work has documented the special suitability of Ge membranes to reach the high tensile strain. We present a top-down approach for the creation of SiGe stressors on Ge micro-bridges and compare the obtained strain to the case of an attached bulk-like Ge layer. We could show that the Ge influenced by a SiGe stressor is under tensile strain; absolute strain values are of the order of 0.7% for both micro-bridge and bulk. The relative strain induced by the nanostructures in the micro-bridge is 1.3% due to the high sharing of elastic energy between nanostructures and bridges.

Grain Boundary Engineering to Improve Ionic Conduction in Thin Films for Micro-SOFCs

New emerging disciplines are specifically devoted to study trivial and non-trivial effects resulting from working in the nanoscale, however, the implementation of these nanostructures in real devices is still a major challenge. Thin film deposition and silicon microtechnology is probably the most promising and straightforward combination for the reliable integration of nanomaterials in real devices. In particular, the implementation of pure ionic and mixed ionic/electronic conductors (MIECs) in thin film form allows the miniaturization of multiple solid state devices such as solid oxide fuel cells (SOFCs). In this work, we will present the implementation of novel nanoionics concepts in micro-SOFCs by using micro and nanofabrication technologies. We will put special attention on the contribution of grain boundaries to the mass transport properties in interface-dominated materials such as thin films. Grain boundary engineering will be presented as a powerful tool for reducing the resistance associated to electrolytes and even control the intrinsic transport nature and performance of MIEC materials.

Grain Boundary Engineering to Improve Ionic Conduction in Thin Films for Micro-SOFCs

New emerging disciplines are specifically devoted to study trivial and non-trivial effects resulting from working in the nanoscale, however, the implementation of these nanostructures in real devices is still a major challenge. Thin film deposition and silicon microtechnology is probably the most promising and straightforward combination for the reliable integration of nanomaterials in real devices. In particular, the implementation of pure ionic and mixed ionic/electronic conductors (MIECs) in thin film form allows the miniaturization of multiple solid state devices. A simple combination of three oxides properly integrated in silicon enables anode/electrolyte/cathode structures for the fabrication of solid oxide fuel cells (SOFCs). These micro-SOFCs represent a new family of micro-power generators that will drive a revolution in portable power generation [1]. In this lecture, we will talk about the implementation of novel nanoionics concepts in micro-SOFCs by using micro and nanofabrication technologies. We will put special attention on the contribution of grain boundaries to the mass transport properties in interface-dominated materials such as thin films. Grain boundary engineering will be presented as a powerful tool for reducing the resistance associated to electrolytes [2] and even control the intrinsic transport nature and performance of MIEC materials [3].

Improved Thermal Behavior of Multiple Linked Arrays of Silicon Nanowires Integrated into Planar Thermoelectric Microgenerators

Low-dimensional structures have been shown to be promising candidates for enhancing the thermoelectric properties of semiconductors, paving the way for integration of thermoelectric generators into silicon microtechnology. With this aim, dense arrays of well-oriented and size-controlled silicon nanowires (Si NWs) obtained by the chemical vapor deposition (CVD)-vapor–liquid–solid (VLS) mechanism have been implemented into microfabricated structures to develop planar unileg thermoelectric microgenerators (μTEGs). Different low-thermal-mass suspended structures have been designed and microfabricated on silicon-on-insulator (SOI) substrates to operate as microthermoelements using p-type Si NW arrays as the thermoelectric material. To obtain nanowire arrays with effective lengths larger than normally attained by the VLS technique, structures composed of multiple ordered arrays consecutively bridged by transversal microspacers have been fabricated. The successive linkage of multiple Si NW arrays enabled the development of larger temperature differences while preserving good electrical contact. This gives rise to small internal thermoelement resistances, enhancing the performance of the devices as energy harvesters.

Integration of microelectronic chips in microfluidic systems on printed circuit board

A new scheme for the integration of small semiconductor transducer chips with microfluidic structures on printed circuit board (PCB) is presented. The proposed approach is based on a packaging technique that yields a large and flat area with small and shallow (∼44 µm deep) openings over the chips. The photocurable encapsulant material used, based on a diacrylate bisphenol A polymer, enables irreversible bonding of polydimethylsiloxane microfluidic structures at moderate temperatures (80 °C). This integration scheme enables the insertion of transducer chips in microfluidic systems with a lower added volume than previous schemes. Leakage tests have shown that the bonded structures withstand more than 360 kPa of pressure. A prototype microfluidic system with two detection chips, including one inter-digitated electrode (IDE) chip for conductivity and one ion selective field effect transistor (ISFET) chip for pH, has been implemented and characterized. Good electrical insulation of the chip contacts and silicon edge surfaces from the solution in the microchannels has been achieved. This integration procedure opens the door to the low-cost fabrication of complex analytical microsystems that combine the extraordinary potential of both the microfluidics and silicon microtechnology fields.

High efficiency nano-focusing kinoform optics for synchrotron radiation

Modern synchrotron sources have provided for decades intense beams of photons over a large energy spectrum. The availability of improved optics and detectors has opened up new opportunities for the study of matter at the micrometre and nanometre scale in many disciplines. Whilst exploitation of micro-focused beams occurs almost daily in many beamlines, the production of beams of 100 nm is achieved on few instruments which use specialised optics. Refractive lenses, zone plates, curved mirrors, multilayers, and multilayer Laue lenses, can all focus x-rays to less than 50 nm under strict beam stability conditions. Focusing the synchrotron radiation to beam sizes smaller than 10 nm is considered the ultimate goal for the current decade. Silicon micro-technology has so far provided some of the most advanced x-ray refractive lenses; we report on design and characterisation of a novel silicon kinoform lens that is capable of delivering nano-beams with high efficiency.

A planar refractive x-ray lens made of nanocrystalline diamond

Diamond has unique properties which make it the ideal material for use in synchrotron instrumentation. X-ray optics made of diamond are almost transparent, they possess strength, and are subject to very low thermal expansion; therefore they will be able to withstand the powerful beams generated by fourth-generation light sources without compromising brilliance. For this reason, several groups are attempting fabrication of refractive lenses and zone plates made of diamond. Lithography and, in general, microfabrication technology, are the ultimate tools for the innovation of synchrotron focusing optics. We propose to combine modern silicon microtechnology with advanced deposition methods to fabricate nanocrystalline-diamond lenses for third- and fourth-generation synchrotron sources. The fabrication method is described here and microfocusing synchrotron tests are illustrated.

Intracellular Polysilicon Barcodes for Cell Tracking

During the past decade, diverse types of barcode have been designed in order to track living cells in vivo or in vitro, but none of them offer the possibility to follow an individual cell up to ten or more days. Using silicon microtechnologies a barcode sufficiently small to be introduced into a cell, yet visible and readily identifiable under an optical microscope, is designed. Cultured human macrophages are able to engulf the barcodes due to their phagocytic ability and their viability is not affected. The utility of the barcodes for cell tracking is demonstrated by following individual cells for up to ten days in culture and recording their locomotion. Interestingly, silicon microtechnology allows the mass production of reproducible codes at low cost with small features (bits) in the micrometer range that are additionally biocompatible.

Silicon cylinder spiral coil for nuclear magnetic resonance spectroscopy of nanoliter samples

AbstractThis contribution presents a new high sensitivity microdetector designed for high resolution proton NMR at 750 MHz (17.6 T) of sample volumes ranging from 5 to 40 nl. The desired volume of fluid is placed in a sealed 330/200 μm outer/inner diameter glass capillary and is then situated in the center of the detection coil. The high quality factor detection coils are fabricated using silicon microtechnology. The materials from which the device is constructed are specially shaped to improve the homogeneity of the static magnetic field within the sample. Adverse effects of the finite, nonspherical sample geometry on the spectral resolution are mitigated by employing sample rotation up to 2.5 kHz at the magic angle. The new detector exhibits linewidths of smaller than 3.0 Hz (0.004 ppm) and a signal‐to‐noise ratio in the spectral domain of higher than 4,000 per μmol of water. Results with respect to sensitivity, spectral resolution, and total sample volume are given and put into context with already published microprobes. © 2009 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 35B: 11–22, 2009

Integration of a carbon nanotube based electrode in silicon microtechnology to fabricateelectrochemical transducers

An original approach was developed and validated for the fabrication of a carbon nanotube(CNT) electrode synthesized directly onto a carbon buffer thin film deposited on a highlydoped monocrystalline silicon surface. The buffer layer of amorphous carbon thin film wasdeposited by physical vapour deposition on the silicon substrate before CNTsynthesis. For this purpose, nickel was deposited on the carbon buffer layer byan electrochemical procedure and used as a catalyst for the CNT growth. TheCNT synthesis was achieved by plasma enhanced chemical vapour deposition(PECVD) in an electron cyclotron resonance (ECR) plasma chamber using aC2H2/NH3 gas mixture. In order to evaluate the electrochemical behaviour of the CNT-basedelectrode, the carbon layer and the silicon/carbon interface were studied. The resultingbuffer layer enhanced the electronic transport from the doped silicon to the CNTs. Theelectrode surface was studied by XPS and characterized by both SEM and TEM. Theelectrochemical response exhibited by the resulting electrodes modified with CNTs was alsoexamined by cyclic voltammetry. The whole process was found to be compatible withsilicon microtechnology and could be envisaged for the direct integration of microsensors onsilicon chips.

Effects of artificial micro- and nano-structured surfaces on cell behaviour

Substrate topography, independently of substrate chemistry, has been reported to have significant effects on cell behaviour. Based on the use of fabrication techniques developed by the silicon microtechnology industry, numerous studies can now be found in the literature analyzing cell behaviour as to various micro- and nano-features such as lines, wells, holes and more. Most of these works have been found to relate the micro- and nano-sized topographical features with cell orientation, migration, morphology and proliferation. In recent papers, even the influence of substrate nanotopography on cell gene expression and differentiation has been pointed out. However, despite the large number of papers published on this topic, significant general trends in cell behaviour are difficult to establish due to differences in cell type, substrate material, feature aspect-ratio, feature geometry and parameters measured. This paper intends to compile and review the relevant existing information on the behaviour of cells on micro- and nano-structured artificial substrates and analyze possible general behavioural trends.

A silicon microfluidic chip integrating an ordered micropillar array separation column and a nano-electrospray emitter for LC/MS analysis of peptides

This article presents the development and performance of new silicon microfluidic devices, called E-spray chips, integrating both a reversed-phase separation column and a nano-electrospray emitter. The microchips are made according to standard silicon microtechnology procedures including photolithography, deep reactive ion etching and molecular bonding. The separation column is a perfectly ordered 2-dimensional array of squared micropillars, directly etched in the silicon substrate, and the electrospray emitter is a planar nib-like nanotip. Two chemical procedures for the separation column reversed-phase coating were tested: (i) a liquid phase “chip by chip” process with a C18-alkylated silane and (ii) a vapour phase collective process with a C10-perfluorated silane. Analyses of standard tryptic digests of cytochrome c in hydrodynamic pumping mode have demonstrated good quality spray and effective separation performance of these microdevices with a higher retention capacity for C10-perfluorated coating. These new microchips, which can be produced on a very large scale by a mass production process, from microfabrication to chemical treatment, appear to be very promising analytical tools for proteomics research.

A silicon beam-based microcantilever nanoelectrosprayer

Silicon microtechnology is used to fabricate microcantilever based nanoelectrospray emitter chips. The chips are composed of beam-based microcantilevers which form a microfluidic capillary slot terminating in a tip having micrometric dimensions. An original combined microfluidic and micromechanical analysis takes into account microfluidic capillary forces encountered at microsystems dimensions; we propose that such forces can be positively harnessed to effectively reduce tip dimensions to a sub-micron scale. An optimised fabrication process is presented based on silicon-on-insulator technology. The emitter chips were characterised using electrospray ionisation mass spectrometry; we were able to detect the protein lysozyme at a concentration as low as 100 fmol μL −1 (100 nM) and additionally generate peptide mass fingerprints from enzymatic proteolysis of the protein myoglobin. Together these data clearly indicate the usefulness of such electrospray ionisation emitter chips in biomolecular work in general and potentially in the field of proteomics.

Porous silicon-based optical biochips

In this paper, we present our work on an optical biosensor for the detection of the interaction between a DNA single strand and its complementary oligonucleotide, based on the porous silicon (PSi) microtechnology. The crucial point in this sensing device is how to make a stable and repeatable link between the DNA probe and the PSi surface. We have experimentally compared some functionalization processes which modify the PSi surface in order to covalently fix the DNA probe on it: a pure chemical passivation procedure, a photochemical functionalization process, and a chemical modification during the electrochemical etching of the PSi. We have quantitatively measured the efficiency of the chemical bond between the DNA and the porous silicon surface using Fourier transform infrared spectroscopy (FT-IR) and light induced photoluminescence emission. From the results and for its intrinsic simplicity, photochemical passivation seems to be the most promising method. The interaction between a label-free 50 µM DNA probe with complementary and non-complementary oligonucleotides sequences has been also successfully monitored by means of optical reflectivity measurements.

Electronic detection of DNA by its intrinsic molecular charge.

We report the selective and real-time detection of label-free DNA using an electronic readout. Microfabricated silicon field-effect sensors were used to directly monitor the increase in surface charge when DNA hybridizes on the sensor surface. The electrostatic immobilization of probe DNA on a positively charged poly-l-lysine layer allows hybridization at low ionic strength where field-effect sensing is most sensitive. Nanomolar DNA concentrations can be detected within minutes, and a single base mismatch within 12-mer oligonucleotides can be distinguished by using a differential detection technique with two sensors in parallel. The sensors were fabricated by standard silicon microtechnology and show promise for future electronic DNA arrays and rapid characterization of nucleic acid samples. This approach demonstrates the most direct and simple translation of genetic information to microelectronics.

A chip system for size separation of macromolecules and particles by hydrodynamic chromatography.

For the first time, a miniaturized hydrodynamic chromatography chip system has been developed and tested on separation of fluorescent nanospheres and macromolecules. The device can be applied to size characterization of synthetic polymers, biopolymers, and particles, as an attractive alternative to the classical separation methods such as size exclusion chromatography or field-flow fractionation. The main advantages are fast analysis, high separation efficiency, negligible solvent consumption, and easy temperature control. The prototype chip contains a rectangular flat separation channel with dimensions of 1 microm deep and 1000 microm wide, integrated with a 300-pL injector on a silicon substrate. The silicon microtechnology provides precisely defined geometry, high rigidity, and compatibility with organic solvents or high temperature. All flows are pressure driven, and a specific injection system is employed to avoid excessive sample loading times, demonstrating an alternative way of lab-on-a-chip design. Separations obtained in 3 min show the high performance of the device and are also the first demonstration of flat channel hydrodynamic chromatography in practice.

Rhenium deposition on a silicon surface at the room temperature for application in microsystems

Abstract Rhenium is a refractory metal (the melting temperature is 3190 °C) which is of a certain interest for the electronic technology. In spite of such a high melting point, the electrochemical method allows us to obtain rhenium deposits at the room temperature. Such deposits can be used in the silicon microtechnology for formation of field emitters, barrier and high-resistant layers. Despite the fact that the process of rhenium electrochemical plating on metals is well-known, optimal conditions of rhenium deposition on silicon, which is the main material in state-of-the-art microsystems, are still not clear. In this paper, we report results of rhenium plating on a silicon surface. A number of solutions, deposition conditions and surface preparation methods are described in order to obtain high quality rhenium deposits on a silicon surface.

Silicon microstructures for high-speed and high-sensitivity protein identifications

Silicon microtechnology has been used to develop a microstructure toolbox in order to enable high accuracy protein identification. During the last 2 years we developed and applied monocrystalline silicon structures and established new automated protein analysis platforms. The development of a high throughput protein platform is presented where fully automated protein identifications are performed. It includes the reduction and alkylation of the protein sample in a standard 96- or 384-well plate format prior to injection of 1 μl samples into the continuous flow based microtechnology platform. The processed sample is transferred to a microchip nanovial array target using piezoelectric microdispensing. Identification is made by MALDI-TOF MS and a database search. After the initial sample reduction and alkylation period of 50 min the platform can digest and process protein samples at a speed of 100 samples in 210 min. An optional configuration of the platform, operating the dispenser in the ‘static mode’, enables on-target enrichment of low abundant proteins and peptides e.g. from 2DE samples. This makes detection at the low attomole level possible.

Thermal modelling and characterisation of micropower chemoresistive silicon sensors

There is considerable interest in the development of low-cost, low-power resistive sensors for possible application in hand-held gas monitors. In this paper we describe the fabrication of a high-temperature, resistive sensor using silicon microtechnology which lies on a sub-micron thick membrane with an embedded platinum resistance heater. A thermal model of this micro-hotplate is constructed and compared with its observed behaviour. The microsensor can be operated at temperatures of up to 600°C and has a low d.c. power consumption per sensor of 40 mW at 300°C. As the thermal time-constant of the microsensor is only about 5 ms, its average power consumption can be reduced by a factor of at least ten through an a.c. mode of operation, thus making a single device or even an array device suitable for battery-powered instruments.

Humidity sensitive field effect transistors

A new device, named humidity sensitive field effect transistors (HUSFETs), for integrated humidity sensors has been fabricated using conventional silicon microtechnology. The insulator structure of this HUSFETs is TiO 2/Si 3N 4SiO 2 and the water molecular permeable electrode is thin porous gold. The fabricated devices showed typical enhancement mode characteristics and the threshold voltage was about 2.7 V in 60% RH. It can be seen that the threshold voltages of HUSFET decreased from 3.0 to 2.4 V and the drain current increased from 208 to 464 μA according to increasing relative humidities from 30 to 90%. The sensitivity of HUSFET is 3.2 μA/RH, when the drain and gate voltages are constant.