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Thin films of Yttrium Iron Garnet (YIG) are grown by radio frequency magnetron non reactive sputtering system on quartz and Gadolinium Gallium Garnet (GGG) for optical applications or alumina substrates for microwave applications. A post deposition annealing is needed to obtain the crystallization of YIG films and the magnetic properties which are correlated with the magneto-optical properties. Their crystallographic, morphologic and magnetic properties are explored. The variation of Faraday rotation is studied versus the wavelength. For both optical substrates, quartz and GGG, results are comparable with the literature for bulk material. A microwave isolator was realized with YIG thin film on alumina substrate in a coplanar configuration. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Ferrites have magnetic properties suitable for electronic applications, especially in the microwave range (circulators and isolators). Hexagonal ferrite, such as barium ferrite (BaFe12O19 or BaM), are of great interest for microwave device applications because of their large resistivity and high permeability at high frequencies. BaM films, 1–10 μm thick, were deposited under optimized conditions by RF magnetron sputtering on alumina and silicon substrates. After deposition, films were amorphous and needed a post-deposition annealing at 800 °C to crystallize and to present magnetic properties. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results showed that BaM films deposited on alumina and silicon substrates presented a good crystallization, a smooth surface and no cracks. Ba, Fe and O depth profiles obtained by secondary ion mass spectroscopy (SIMS) showed that the films have a good in-depth uniformity. The film residual stress was evaluated using curvature measurements. Whatever the substrate type, the films are in compression after deposition. Upon annealing and crystallization, a tensile stress adds up in relation with crystalline arrangements. Finally, regarding the magnetic properties measured using a vibrating sample magnetometer (VSM), the optimized saturation magnetization of such films reached 500 mT and the coercive force 325 kA/m. These values are close to that of the bulk BaM.

International audience; We present a thermo-resistance based micro-calorimeter using a glass/platinum/PDMS prototyping technology which is more flexible than the existing silicon based technology for lab on a chip device integration. Resistance monitoring and fluid injection techniques are optimized in order to reduce thermal noises and improve the detection sensibility. We used neutralization acid-base reaction to evaluate the device capability in determination of both reagent concentration and reaction enthalpy. We also performed a glucose/glucose oxy-dase enzymatic reaction to illustrate the advantage of using PDMS device for the studies of aerobic reaction.

Investigations of the thermal drifts of the resistivity and gauge factors of polysilicon are needed to extend its use as a transducing material for high temperature piezoresistive microsensor applications. Longitudinal gauge factors of LPCVD B-doped and rapid thermal-annealed polysilicon films, patterned onto oxidized silicon using a clamped beam technique, have been measured in the 20–200 °C temperature range as a function of the doping concentration between 8 × 10 18 and 10 20 cm −3 . The gauge factors have been simulated as a function of the B-concentration and the temperature, starting from experimental data for the polysilicon resistivity and literature data for the hole resistivity and the piezoresistive effect in monocrystalline silicon. Only a model involving a significant piezoresistive effect at grain boundaries can adequately fit the temperature dependent gauge factors of polysilicon.

Silicon on insulator (SOI) pressure sensors show potential applications in high temperature environment. However, as a result of thermal mismatch, large stresses usually exist in the composite SiO 2 /Si membranes which would provide an otherwise promising substrate for such sensors. These stresses can significantly influence the long term reliability of such membranes. In this work a high spatial resolution (10 μm 2 ) Raman spectroscopy method has been used to measure the localized stresses over an oxidized membrane, thus yielding stress maps. The method is based on the frequency shift of the Raman line at 520 cm −1 . Shift between 0.05 and 1 cm −1 are observed. A three-dimensional commercially available finite element modeling (FEM) software (ANSYS) has been used to modelize the thermal stress distribution over the complete micromachined bilayer membrane. Its validity has been checked out through optical profilometer deflection measurements. The experimental Raman shifts were compared with those calculated using stresses from FEM and a biaxial stress hypothesis. Finally, the sensitivity of Raman stress mapping method for high temperature SOI pressure sensors is discussed.

Flower-like patterns are numerically investigated when the schematic Rb four-level relevant transition is reduced to the lower two Zeeman sub-levels via the adiabatic elimination of the upper states. These flower-like patterns are the signature of small aspect ratio while typical patterns like squares are displayed in the opposite limit. Depending on the relative weights of diffraction effects and nonlinearities, they display, or not, self-similar shapes in the near and the far field.

The structural, electrical, and piezoresistive properties of in situ boron‐doped thin silicon layers deposited by plasma‐enhanced chemical‐vapor deposition at 320 °C on oxidized silicon substrates and subjected to a rapid thermal anneal (1100 °C for 20 s) have been investigated. Macroscopic electrical parameters derived from resistivity and Hall‐effect measurements were compared to microscopic characteristics deduced from optical data to explain the low‐temperature coefficients of resistance measured on this polycrystalline material. Finally, the piezoresistivity gauge factors of these heavily doped layers are discussed in view of their internal stress state and of other structural characteristics.

This work focuses on the properties of 10–15 μm thick barium M-type hexaferrite (BaFe 12 O 19 or BaM) films deposited by non-reactive RF magnetron sputtering on alumina substrates. High deposition rates were achieved through deposition at room temperature and operation at an RF power of 100 W. By varying sputtering gas pressure, the dc magnetic properties were correlated with structural, morphological and compositional properties obtained by X-ray diffraction (XRD), atomic force microscopy (AFM) and Rutherford backscattering spectrometry (RBS), respectively. A deposition pressure of P =3 Pa enables one to reach the best compromise between high deposition rate (0.75 μm/h) and adequate crystallographic, stoichiometric and magnetostatic properties. Finally the gyromagnetic properties at high frequency were assessed through the characterization of coplanar isolator up to 60 GHz. As such, hexaferrite films prepared using this technique may offer opportunities for the next generation of self-biased planar microwave devices.

The attractive properties of coplanar waveguides with or without ferrite thin films are presented in this article.The microwave characteristics are measured from 1 to 55 GHz. Also, analytical calculations and simulations are performed. The influence of ferrite thin film with remanent magnetization in-plane or out-of-plane is studied. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 2007–2010, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25393

International audience; The preparation of Yttrium Iron Garnet films (YIG) presenting controlled magnetic properties is of great interest for miniaturization of RF passive components. The present work deals with the integration of YIG ferrite sputtered films for coplanar circulators. These components must work at frequencies above 10GHz, and they must be compatible with mass-production and low-cost process. The YIG films (of thickness 15 μm) are deposited on an alumina substrate by RF magnetron sputtering. Their structural mechanical and magnetic properties in the millimetre wave range are optimised to enable the film's integration. A circulator is fabricated using such prepared film, and its properties in the microwave range are characterised using a network analyzer and a probing system.

International audience; The development of telecommunications networks requires low-cost microwave and millimeter waves integrated devices. Among the microwave devices based on the non-reciprocity of ferrites, circulators are the most important. A typical use of circulators is in communication equipment (mobile phone and low power radar detection). Their operation allows to combine emission and detection using the same antenna. This work concerns the characterization of barium hexaferrite sputtered films and the device integration for the development of an integrated circulator working at a frequency of 40 GHz.

The development of passive devices using a ferrite is a major focus of current research for electronic applications in the microwave range (circulators and isolators). Hexagonal ferrite, such as barium ferrite (BaFe12O19 or BaM), which has a large resistivity and high permeability at high frequencies are indeed of great interest for microwave device applications. In this work we developed an integrated and self-biased coplanar isolator using BaM sputtered films. BaM films, 1-36 mum thick, were deposited under optimized conditions by radio frequency magnetron sputtering on alumina substrates. The films were crystallized using a 800degC thermal annealing. Isolators were then realized using patterning of coplanar waveguides (CPW) with standard lift-off technique. The slots and the central width were 300 mum wide and gold was used for the conductor lines. We evaluated the influence of various parameters on the device performances: the magnetic film's thickness, the positioning of the magnetic film (CPW deposited onto the magnetic film or directly on the substrate), the CPW metallic thickness and the polarizing field. As standard design, the CPW were deposited on the top of the magnetic film. At the remanent magnetization (no polarizing field applied), the transmission coefficients then showed a non reciprocal effect, which reached 5.4 dB per cm of line length at 50 GHz for a 26.5 mum thick BaM film. Both the insertion losses and the non-reciprocal effect measured increased with the magnetic film thickness with a saturation effect. In the second design where the CPW is deposited directly on the substrate after a selective etching of the BaM film, we measured that the non reciprocal effect reached higher values for lower BaM thicknesses than for the first design and that the insertion losses also decreased. The interaction between the field lines created by the conductors and the magnetic film was indeed favored in the second case. Finally, we show the tunability of the isolator with the polarizing field.

We describe a simple microfluidic hot strip device for the determination of nanofluids thermal conductivity at single droplet levels. The fabricated device has been used to characterize different types of reference fluids, showing a good agreement to data obtained using large volume samples. Experiments on nanotube containing ethylene glycol solutions have shown a strong increase of the fluid thermal conductivity with the increase of the carbon nanotube concentration. We believe that this method is simple and low cost which can be extended to the measurements of other types of nanofluids.

Signal processing in communication, instrumentation and radar detection requires low cost microwave and millimeter wave devices. The integration of millimeter wave passive components like isolators and circulators is thus a major issue. In these components, the nonreciprocal nature of wave propagation in ferrites plays an essential role. Hexagonal ferrites, such as barium ferrite (BaFe12O19 or BaM), which has a large resistivity and high permeability at high frequency, are of great interest for such applications. The present work deals with the characterization of barium hexaferrite sputtered films and with the device integration for the development of coplanar isolators and circulators working at frequencies around 40 GHz.The BaM films (in the thickness range of 10μm) were deposited on alumina substrate by RF magnetron sputtering at room temperature and were then crystallized using a 800°C thermal annealing. Structural properties were evaluated by X-ray diffraction and the magnetostatic properties of the film were determined using a Vibrating Sample Magnetometer (VSM) leading to assess a range of deposition conditions appropriate for device integration.Both coplanar isolators and circulators were implemented using standard lift-off technique. Coplanar circulators were designed by analytical calculation and 3D electromagnetic simulation (HFSS) supposing a saturated material and no losses. The microwave range characterization was performed using a network analyzer and a probing system with a prior OSTL calibration. The coplanar isolators were characterized both at the remanence and under a polarizing field. At the remanence, the gyroresonance occurred at 50 GHz and the nonreciprocal effect - difference between the transmission coefficient in the forward direction and in the reverse direction - was evaluated. When applying a polarizing field, the tunability of the isolator was verified experimentally. Finally first measurements on integrated coplanar circulators are currently under progress.

In order to miniaturize and self-bias a coplanar isolator, new method is to use thin magnetic films. The results presented in this paper show that this component behaves like an isolator in the 50-GHz band. The influence of the magnetic and conductor films for increasing the isolator properties is studied. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 46: 435–437, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21009

Rapid thermal annealing (RTA) has been performed on boron-implanted LPCVD polysilicon films for doses ranging from 2.10/sup14/ cm/sup-2/ to 4.10/sup15/ cm/sup-2/. We have investigated the piezoresistance through gauge factor measurements in the scope of pressure sensor applications and the electrical properties using Hall techniques. RTA was carried out at 1100/spl deg/C for 20s, 40s and 60s respectively.

Thin films of yttrium iron garnet (YIG) are grown by radio frequency magnetron non reactive sputtering system. Thin films are crystallised by heat-treatment to obtain magneto-optical properties. On quartz substrate, the network of cracks observed on the annealed samples can be explained by the difference between the thermal expansion coefficient of substrate and YIG. Physico-chemical analysis shown that the obtained material has a correct stoichiometry and is crystallised as FCC. The Faraday rotation of thin films is measured with a classical ellipsometric system based on transmission which allows us to obtained an accuracy of 0.01 ° . The variation of Faraday rotation is studied on the one hand versus radio frequency power applied to the cathode during the deposition and on the other hand versus the applied magnetic field. The results are compared with those obtained by vibrating sample magnetometer analysis in perpendicular configuration. A maximum Faraday rotation is observed to be 1900 ° / cm at the wavelength of 594 nm for a YIG thin film formed on quartz substrate and annealed at 740 ° C . The values of the Faraday rotation coefficients obtained in the study versus the wavelength are comparable to those of the literature for the bulk material. In order to eliminate the stress due to the heat-treatment, we made some films on single crystals of gadolinium gallium garnet (1 1 1) substrates for which thermal expansion coefficient is near than the YIG one. The material crystallises with no crackles and the Faraday effect is equivalent.

The development of integrated devices combining a ferrite is a major focus of current research. Barium hexaferrite (BaFe/sub 12/O/sub 19/ or BaM), which exhibits a high anisotropy field and high coercive force are deposited on alumina substrate using an RF sputtering system. After deposition BaM films are amorphous and a post deposition thermal annealing is needed to obtain magnetic properties. The saturation magnetization and coercive force was about 500 mT and 330 kA/m. After that, coplanar lines were made with BaM thin films on alumina substrates and with gold conductor. The transmission coefficients of a barium ferrite coplanar isolator are measured up to 55 GHz. The measurements of transmission parameters S/sub 12/ and S/sub 21/ was performed by a 65 GHz vector network analyzer and a probing system. First experimental results showed an isolation of 3.3 dB/cm at 50 GHz.

The development of devices combining a ferrite with a semiconductor chip is a major focus of current research. Barium hexaferrite (BaFe12O19 or BaM) thick films are deposited here using a RF magnetron sputtering system. Films are amorphous and non magnetic after deposition. Post-deposition thermal annealing is employed to make the films crystallize. The effects of the substrate, thermal annealing process, thickness, substrate temperature on crystallographic properties and stoichiometry are studied using a X-ray diffractometry (XRD) and Rutherford back-scattering (RBS). The in-depth homogeneity of Ba, Fe and O is evaluated by secondary ion mass spectroscopy (SIMS). The study shows a good crystallization of BaM films and there is a preferential orientation among the crystallographic planes (1 0 1), (2 0 0), (2 0 3), (1 0 2), (1 1 0) and (2 0 5) when BaM films are prepared at low RF power and when the substrate is heated. For several elaboration parameters, grains size is in the range of 25 and 40 nm and BaM films are stoichiometric with regard to the target stoichiometry.

Ferrites have magnetic properties suitable for electronic applications, especially in the microwave range (circulators and isolators). Hexagonal ferrite, such as barium ferrite (BaFe12O19 or BaM), which have a large resistivity and high permeability at high frequencies are of great interest for microwave device applications.This contribution deals with BaM films, 1 to 36 microns thick, which were deposited under optimized conditions by RF magnetron sputtering. The films were then crystallized using a 800°C thermal annealing. Isolators were then realized using patterning of coplanar wave guides with standard lift-off technique. The slots and the central width were 300 μm wide, gold was used for the conductor lines. We evaluated the influence of various parameters on the device performances: the magnetic film thickness, the positioning of the magnetic film (CPW deposited onto the magnetic film or directly on the substrate) and the CPW metallic thickness. As standard design, the CPW were deposited on the top of the magnetic film. For the first design, transmission coefficients showed a non reciprocal effect, which reaches 7 dB per cm of line length at 50 GHz for a 26.5 μm thick BaM film. Both the insertion losses and the non-reciprocal effect measured increased with the magnetic film thickness with a saturation effect. In the second design where the CPW is deposited directly on the substrate, the BaM film was selectively wet etched prior to the metal deposition everywhere except between the conductors. In that case we measured that the non reciprocal effect reached high values for lower BaM thicknesses than in comparison to design # 1 and that the insertion losses also decreased. Moreover for the design # 2, also in relation with the localization of the BaM between the conductors, the non reciprocal effect improved with increasing conductor thickness as the interaction between the field lines created by the conductors and the magnetic film is then favored.

The development of devices combining a ferrite with a semiconductor chip is a major focus of current research and could make use of vacuum deposition techniques of magnetic films. Barium hexaferrite (BaFe12O19; BaM) thick films are deposited here using an rf non-reactive sputtering system. Because the as-deposited films are amorphous and non-magnetic, two kinds of post-deposition annealing are employed, which are referred to here as classic thermal annealing (CTA) and rapid thermal annealing (RTA). The effects of annealing conditions on the properties of BaM films are studied using vibrating sample magnetometry (VSM), scanning electron microscopy (SEM) with an EDX probe and X-ray diffractometry (XRD). The first results show a good stoichiometry of the layer and a crystallization above 800 °C. The magnetic properties are closed to that of the bulk BaM. Progress is still necessary to obtain a temperature more compatible with microelectronic technologies (below 500 °C).

Built-in stresses are known to induce deflections in microstructures such as composite membranes. The thermoelastic behaviour of large square SiO 2 /Si membranes with a side length from 3 to 7.5 mm, a Si thickness in the [7.7–50] μm range and a SiO 2 thickness up to 1.5 μm, was studied by optical profilometry. A very satisfactory agreement within 10% has been found between the experimental and the simulated deflections of prestressed SiO 2 /Si membranes. However, clamping conditions have been found to play a major role in built-in stress relaxation. This tendency was confirmed by Finite Element Modelling. Oxidized (up to 1.5 μm) and bare Si membranes with thicknesses from 7.7 to 50 μm were studied under pressure in the [0–1] bar range. We observed that the membrane stiffness is affected by the oxide depending on SiO 2 /Si thickness ratio. Finally, F.E.M. results are in good agreement for various membrane geometries, and the interest of this tool for the design of packaging structures is shown.

Porous silicon (PS) is generated by electrochemical etching in hydrofluoric acid (HF). Recently porous silicon has been applied to micromachining and micro-devices as an alternate material, this material being used as a sacrificial layer. This technology competes with conventional techniques like surface and bulk micromachining regarding its speed, simplicity and reduced costs. A wide range of microstructures and free-standing structures can be fabricated with a large freedom of design in relation to the isotropic behavior of the etching. A sacrificial layer may be realized fast over varying thickness (PS formation rate 45 μm/h compared to silicon bulk micromachining rate 20 μm/h for KOH etching).This contribution is devoted to the materials aspects of patterning and processing: we will show how basic microstructures (trenches, polysilicon cantilevers, polysilicon free-standing membranes) may be fabricated using a very simple process based on a single photolithography. The important points are the choice of the mask, porous silicon properties as a function of its formation parameters and the choice of the solution removing the sacrificial layer. The morphology and porosity of the porous silicon layers are indeed mainly determined by the electrolyte composition and by the current density for a given substrate type. Optimized conditions (HF 15% and 80 mA/cm2) lead us to an appropriate porous silicon. Finally the applicability of this technology for various microsensors will be underlined.

In this work related to high temperature pressure sensors, a study was undertaken on the characterisation of β-SiC thin films through X-Ray Diffraction, AFM and stress measurements. 3C-SiC films were grown on (100) Si substrate in a vertical reactor by atmospheric-pressure chemical vapour deposition (APCVD). Silane and propane were used as precursor gas and hydrogen as carrier gas. Prior to the growth, Si surfaces were annealed at 1000°C for 5 minutes and carbonized with C3H8 at 1150°C during 10 minutes. At 1350°C, SiH4, C3H8 and H2 were introduced for the SiC deposition. The atomic ratio of Si/C in the gas phase was 0.3 and the growth rate was 3 μm/h. Only the process time was varying to obtain different SiC layer thicknesses varying from 3 to 9 μm as measured by FT-IR spectrometry. Stress measurements of thin β-SiC layers deposited on thick Si substrates were performed at room temperature using the bending plate method and the Stoney's equation. The stress for a 3 μm thick SiC layer is evaluated to be in the range of 400 MPa in tension. When increasing the SiC film thickness, this stress decreases due to the relaxation of the structure with bending. SiC/Si membranes were obtained by KOH etching and studied as a function of pressure in the [0-50 mbar] range. A residual stress in the membrane was deduced from the load-deflection measurement technique reaching 105 MPa in tension.

Rapid thermal annealing (RTA) has been performed on boron-implanted LPCVD polysilicon films for doses ranging from 2 × 1014 to 4 × 1015 cm−2. We have investigated the piezoresistance through gauge-factor measurements in the scope of pressure-sensor applications and the electrical properties using Hall techniques. RTA has been carried out at 1100 °C for 20, 40 and 60 s, respectively. Gauge factors and electrical parameters deduced from Hall-effect measurements (resistivity, mobility, carrier density) are reported. We observe a reduction of the resistivity for longer RTA treatments, which is due to an enhancement of the mobility. Moreover, the carrier concentration does not depend on the heat-treatment duration. The gauge factor does not show a very strong dependence on the annealing duration but rather on the implantation dose. Finally, thermal budgets with shorter duration (1100 °C, 5 s) or lower temperature (1050 °C, 20 s) do not lead to uniform boron concentration throughout the film thickness.

Composite SiO2/Si membranes are used in various type of sensors among them, resonant and pressure sensors. However due to a large thermal mismatch, residual induced stresses may affect the devices long term reliability especially for thin membranes (˜5 μm). In this study, we have characterized test structures consisting of SiO2/Si membranes with respective thickness ratio between 2 and 10. Micro-Raman Spectroscopy, well known to be an accurate, non destructive method to determine residual stresses in microelectronic devices, has shown to be a powerful testing technique to measure local stresses on micromachined structures such as membranes, with a high spatial (10 μm2 ) and stress resolution (8 MPa). At room temperature, Raman line (520 cm−1) shifts between 0.05 and 1 cm−1 are observed. Highest frequency shifts of 1cm−1 corresponds to a 230 MPa biaxial stress. Finite Element analysis (ANSYS) was used to model the thermal stress distribution over the micromachined bilayer membrane, yielding a satisfactorily agreement with the experimental results over a large membrane area. The Finite Element analysis was correlated with optical profilometer deflection measurements. Membrane deflections up to 48 μm (more than 10 times the membrane thickness) have been measured. Furthermore, Micro-Raman Spectroscopy results up to 300°C are shown and related to temperature dependent deflection measurements.

Rapid thermal processing is evaluated as a low cost and flexible single wafer technology to develop SOI pressure sensors, allowing the fabrication of polycrystalline piezoresistors on thermally grown silicon dioxide with a turnaround time of a few minutes. The growth kinetics and the microstructure of polysilicon films obtained by rapid thermal chemical vapour deposition using an argon-silane gas mixture are investigated as a function of the process pressure and temperature. Polysilicon films deposited at 5 mbar and at temperatures lower than 750 °C exhibit high compressive stresses and grain sizes of about 30 nm due to a high level of oxygen contamination. At 1 mbar the lower oxygen contamination enables to deposit well crystallized films, with residual tensile stresses comparable to those of classical low pressure chemical vapour deposition polysilicon and with grain sizes reaching 55 nm. Longitudinal gauge factors of boron-implanted piezoresistors patterned on polysilicon films deposited at 5 mbar and 720 °C show a maximum of 20–22 in the 2×10 19 -4×10 19 cm −3 doping range. Longitudinal gauge factors of 25–32 are measured for piezoresistors made from boron-diffused polysilicon deposited at 5 mbar and 850 °C, thus illustrating the flexible capabilities of rapid thermal processing for the silicon microsystem technology.

Heavily boron-doped (4×1019 < [B] >1021 cm-3) polycrystalline silicon thin films on oxidized silicon cantilevers were studied by FTIR spectroscopy. The experimental reflectance spectra (400–7000 cm-l) were compared to those expected for a poly-Si/SiO2/c-Si/SiO2 multilayer where the doped layer is described by a simple Drude model. The resulting free carrier concentration and conductivity were checked against electrical measurements.The optical response of the polycrystalline layer in the medium infrared range (400–3000 cmn−1) was shown to be affected by a static uniaxial stress applied along the film plane by a four point bending mechanical device. The resulting microscopic piezoresistivity longitudinal gauge factors in the 15 - 25 range are in close agreement with those deduced from conventional electrical piezoresistivity measurements on sub-millimeter size patterns. The effective range of applicability of this contactless method and the potential application of such layers to temperature-independent miniature pressure sensors are discussed

An investigation into the structural, electrical and piezoresistive properties of SOI (silicon-on-insulator) type structures is reported. The aim of our work is to evaluate how deposition and annealing conditions may change these properties. Various characterization experiments have been undertaken in order to investigate LPCVD and PECVD thin films. A theoretical model for the piezoresistivity is developed that requires experimentally determined parameters (active dopant concentration, grain size, texture, resistivity, barrier height). Moreover, the hypothesis of constant strain or stress has been considered for the spatial average. The measured gauge factors, in the range 25–45 for LPCVD films and 20–30 for PECVD films, fall in the tight interval defined by the theoretical estimates.

The electrical and piezoresistive properties of in-situ doped PECVD silicon films deposited on oxided silicon wafers have been investigated. One series of films was deposited in the so-called microcrystalline state at 450°C. The other set of samples was deposited in the amorphous state at 320°C and subjected to rapid thermal annealing. Structural properties (grain size, texture, residual stress) were evaluated experimentally through TEM and grazing angle X ray diffraction and related to the measured gauge factor. A maximum longitudinal gauge factor of 28 is measured in the case of advantageously textured microcrystalline material, the magnitude of the gauge factor decreasing sharply for randomly oriented material. For the amorphous deposited and subsequently annealed material, the longitudinal gauge factor is in the range 22–27 depending on dopant concentration. These experimental features are compared to the results of a theoretical approach of piezoresistance in polysilicon. We derive various expressions of the gauge factor according to the assumptions of either constant stress or constant strain within the aggregate. In the case of untextured films, analytical Voigt-Reuss-Hill averages for the elements of piezoresistive and elastoresistive tensors lead to greatly simplified expressions. Theoretical estimates are shown to be in reasonable agreement with the experimental measurements. This confirms the great potential of PECVD microcrystalline and polycrystalline silicon for strain gauges.

We investigate the electrical properties of polycrystalline silicon thin films implanted with arsenic or boron ions. Two types of post-implantation annealing have been performed on the samples: a conventional thermal annealing (CTA) and a rapid thermal annealing (RTA). We find that RTA improves the electrical properties. Measurements of gauge factors have been carried out on both films. We conclude that RTA can be applied successfully in thin film silicon integrated sensor technology.

The development of devices that combine a magnetic material with a semiconductor chip is a major focus of current research. Barium hexaferrite (BaFe12O19 or BaM) thick films are deposited here using a rf sputtering system. The films are amorphous and nonmagnetic after deposition. Postdeposition thermal annealings are employed to obtain magnetic properties. The effects of the substrate, thermal annealing and thickness of BaM on the magnetic properties are studied using a vibrating sample magnetometer. The initial results show good magnetic properties for the two subtrates studied and after thermal annealing above 800 °C. The magnetic properties of the thick films are close to the bulk (BaM) ones.

The development of integrated devices combining a ferrite is a major focus of current research. Barium hexaferrite (BaFe12O19 or BaM) thick films are deposited here using a RF sputtering system. Films are amorphous and non magnetic after the deposition. Post-deposition thermal annealings are employed to ensure magnetic properties. Coplanar lines were made with BaM thick films on alumina substrates and with gold conductor. First experimental results showed an isolation of 3.3 dB/cm at 50 GHz.