A reconfigurable reflectarray which exploits the dielectric anisotropy of liquid crystals (LC) has been designed to operate in the frequency range from 96 to 104 GHz. The unit cells are composed of three unequal length parallel dipoles placed above an LC substrate. The reflectarray has been designed using an accurate model which includes the effects of anisotropy and inhomogeneity. An effective permittivity that accounts for the 'real effects' of the LC has also been used to simplify the analysis and design of the unit cells. The geometrical parameters of the cells have been adjusted to simultaneously improve the bandwidth, maximize the tunable phase-range and reduce the sensitivity to the angle of incidence. The performance of the LC based unit cells has been experimentally evaluated by measuring the reflection amplitude and phase of a reflectarray consisting of 52 x 54 identical cells. The good agreement between measurements and simulations validates the analysis and design techniques and demonstrates the capabilities of the proposed reflectarray to provide beam scanning in F band.

Germanium is one of the most promising materials for high performance infra-red photovoltaic devices. High quality single-crystal germanium on insulator structures can be produced by a Rapid Melt Growth process. Experiments show that thin-film germanium deposited by physical vapor deposition provides better quality in comparison with chemical vapor deposition. The longitudinal optical Ge-Ge peak in Raman spectrum is shifted from the expected 300.2 cm-1 position due to tensile stress resulting from the thermal expansion differences of the materials. The importance of silicon in the rapid melt process is confirmed by the fact that germanium films on sapphire substrates yielded polycrystalline structure. Films produced at high temperature (980 oC) show full width at half maximum values of 3.3 cm-1 indicating good crystalline quality, comparable to bulk germanium (3.2 cm-1). Thus demonstrating the potential to produce low cost high quality germanium films.

This paper describes a serpentine flexure spring design and fabrication process development for radio frequency microelectromechanical (RF MEMS) capacitive switches with coplanar waveguide (CPW) lines. Sputtered tungsten is employed as the CPW line conductor instead of Au, a non-Si compatible material. The bridge membrane is fabricated from Al. The materials and fabrication process can be integrated with CMOS and SOI technology to reduce cost. Results show the MEMS switch has excellent performance with insertion loss 0.3dB, return loss -27dB at 30GHz and high isolation -30dB at 40GHz. The process developed promises to simplify the design and fabrication of RF MEMS on silicon.

Novel diode test structures have been manufactured to characterize long-range dopant diffusion in tungsten silicide layers. A tungsten silicide to p-type silicon contact has been characterized as a Schottky barrier rectifying contact with a silicide work function of 4.8 eV. Long-range diffusion of boron for an anneal at 900degC for 30 min has been shown to alter this contact to become ohmic. Long-range diffusion of phosphorus with a similar anneal alters the contact to become a bipolar n-p diode. Bipolar diode action is demonstrated experimentally for anneal schedules of 30 min at 900deg C, indicating long-range diffusion of phosphorus ( ~ 38 mum). SIMS analysis shows dopant redistribution is adversely affected by segregation to the silicide/oxide interface. The concept of conduit diffusion has been demonstrated experimentally for application in advanced bipolar transistor technology.

Silicon on insulator (SOI) substrates offer a promising platform for monolithic high energy physics detectors with integrated read-out electronics and pixel diodes. This paper describes the fabrication and characterisation of specially-configured SOI substrates using improved bonded wafer ion split and grind/polish technologies. The crucial interface between the high resistivity handle silicon and the Sol buried oxide has been characterised using both pixel diodes and circular geometry MOS transistors. Pixel diode breakdown voltages were typically greater than 100 V and average leakage current densities at 70 V were only 55 nA/cm(2). MOS transistors subjected to 24 GeV proton irradiation showed an increased Sol buried oxide trapped charge of only 3.45 x 10(11) cm(-2) for a dose of 2.7 Mrad. (C) 2008 Elsevier Ltd. All rights reserved.

It has been shown that CVD iron from a FC(CO)5 precursor deposits selectively on dielectric surfaces over tungsten surfaces. No similar selective CVD mechanism for titanium and aluminium to SiO2 surfaces was observed. It was established that the selectivity between the tungsten surface and the SiO2 surface could be enhanced through the oxidation of the tungsten surface. Depositions carried out on oxidised tungsten (WOX) and SiO2 substrates showed that iron layers up to 0.5 gm thick with a resistivity of 18 mu Omega cm can be deposited with excellent selectivity. The selective mechanism is attributed to the electrochemical properties of the tungsten or WOX layer, which prevents the reduction of the iron precursor. Selectivity loss was attributed to defects or impurities adsorbed to the tungsten surface. (c) 2007 Elsevier B.V. All rights reserved.

The preferential deposition of CVD iron on silicon dioxide (SiO2) surfaces over tungsten (W) surfaces has been demonstrated. Depositions carried out on patterned W/SiO2 substrates have shown that layers up to a thickness of 180nm with a resistivity value of 19μΩcm can be successfully deposited, exhibiting 100% selectivity; i.e. 180nm of iron was deposited on the oxide surface whilst no deposition occurs on the tungsten surface. For longer deposition times, some iron nucleation was observed on the tungsten surface. It was found that the thickness of the deposited iron layer was inversely proportional to the exposed silicon dioxide surface area.

Cobalt layers are deposited in the presence of magnetic field by chemical vapor deposition (CVD). Magnetic properties of layers fabricated with and without the presence of a magnetic field are studied and compared.

Tetrahedral amorphous carbon (ta-C) and nitrogenated tetrahedral amorphous carbon films (ta-CNx), deposited by double bend off plane Filtered Vacuum Cathodic Arc were annealed up to 1000 °C in flowing argon for 2 min. Modifications on the chemical bonding structure of the rapidly annealed films, as a function of temperature, were investigated by NEXAFS, X-ray photoelectron and Raman spectroscopies. The interpretation of these spectra is discussed. The results demonstrate that the structure of undoped ta-C films prepared at floating potential with an arc current of 80 A remains stable up to 900 °C, whereas that of ta-CNx containing 12 at.% nitrogen is stable up to 700 °C. At higher temperatures, all the spectra indicated the predominant formation of graphitic carbon. Through NEXAFS studies, we clearly observed three π* resonance peaks at the "'N K edge structure. The origin of these three peaks is not well established in the literature. However our temperature-dependant study ascertained that the first peak originates from CN bonds and the third peak originates from the incorporation of nitrogen into the graphite like domains.

This paper presents the results obtained on cobalt layers after rapid thermal annealing in N2 ambient at temperatures between 525 and 800°C. The cobalt layers were deposited by chemical vapor deposition from Co(CO)3NO on to oxidized-Si substrates at 450°C. As the anneal temperature increases from 525to800°C the percentage layer resistivity decrease goes from 35% to 55%. The lowest resistivity achieved was ∼11μΩcm for 300-nm-thick layers and ∼14μΩcm for 180-nm layer annealed in the range of 650–800°C. XRD analysis shows that a mixture of fcc and hcp cobalt grains is present in the as-deposited material. As the annealing temperature increases the fcc Co peaks increase due to crystallization of the material. This was confirmed by surface and microstructure analysis using SEM and AFM. The grain size had significantly increased to 200–300nm ranges for both 180- and 300-nm layers. From the hysteresis loops it was found that the coercivity values are significantly reduced to 25Oe from 350 and 140Oe due to high-temperature annealing to give soft magnetic property.

Chemical Vapour Deposition (CVD) of cobalt was deposited from a liquid source precursor of cobalt tricarbonyl nitrosyl (Co(CO) 3 NO) on to oxidised < 100 > silicon wafers. The cobalt layers were deposited at 450∘C at 1.5 torr chamber pressure of hydrogen for 15 min processing time with various precursor flow rates. X-ray diffraction studies of the cobalt films reveal both hcp and fcc peaks. The vibrating sample magnetometer (VSM) yields coercivity (Hc) 167 Oe and 364 Oe for 46 nm and 30 nm thickness layers respectively at room temperature and squareness (S) M r / M s (remanence/saturation of magnetisation) value of ∼ 1. The study of magnetic properties of the cobalt suggests that magnetisation is dependent on grain size and therefore thickness. The grain size was observed by atomic force microscopy (AFM). Magnetic images were observed by magnetic force microscopy (MFM) and analyzed in terms of domain structure. The surface domain structure was recorded with the tip lift height 100 nm so that the magnetic interactions arising produced the topography effect. Where there is repulsive interaction the intensity is recorded as a bright region and where the interaction is attractive the intensity is recorded as a dark region.

SOI substrates incorporating a thermal via (TV) in the buried oxide layer (BOX) were successfully produced. Various via refill were attempted and all were found to bond successfully. Inspection of the bond interface showed no micro void formation due to the thermal via. Raman analysis verified that the introduction of a buried TV structure did not cause stress in the adjacent SOI. Electrical measurements confirmed the breakdown voltage of the TV structure was similar to that of the blanket depositions and the integrity of the layers were not adversely affected by the fabrication process.

The design and simulation of a novel silicon Schottky diode for nonlinear transmission line (NLTL) applications is discussed in this paper. The Schottky diode was fabricated on a novel silicon-on-silicide-on-insulator (SSOI) substrate for minimized series resistance. Ion implantation technology was used as a low-cost alternative to molecular beam epitaxy to approximate the delta (/spl delta/) dopi...

Epitaxial CoSi2 layers were successfully produced on (1 0 0) silicon substrates by rapid thermal annealing of cobalt layer deposited by CVD. The epitaxial layer had a resistivity of 66 muOmega cm for a similar to100 nm layer. The relatively high resistivity is attributed to discontinuities and contamination in the layer. Cobalt silicide formation was found to be dependent on the deposition temperature of the CVD process and the thickness of the cobalt layer. The deposition of a PVD Ti/TiN capping layer was found to allow silicide formation at lower temperatures as the titanium reduces the interface oxide. (C) 2004 Elsevier B.V. All rights reserved.

Silicon–germanium alloy layers will be employed in the source–drain engineering of future MOS transistors. The use of this technology offers advantages in reducing series resistance and decreasing junction depth resulting in reduction in punch-through and SCE problems. The contact resistance of metal or metal silicides to the raised source–drain material is a serious issue at sub-micron dimensions and must be minimised. In this work, tungsten silicide produced by chemical vapour deposition has been investigated as a contact metallization scheme to both boron and phosphorus doped polycrystalline Si1−xGex, with 0 ≤ x ≤ 0.3. Cross bridge Kelvin resistor (CKBR) structures were fabricated incorporating CVD WSi2 and polycrystalline SiGe. Tungsten silicide contacts to control polysilicon CKBR structures have been shown to be of high quality with specific contact resistance ρc values 3 × 10−7ohmcm2 and 6 × 10−7ohmcm2 obtained to boron and phosphorus implanted samples respectively. The SiGe CKBR structures show that the inclusion of Ge yields a reduction in ρc for both dopant types. The boron doped SiGe exhibits a reduction in ρc from 3 × 10−7 to 5 × 10−8ohmcm2 as Ge fraction is increased from 0 to 0.3. The reduction in ρc has been shown to be due to (i) the lowering of the tungsten silicide Schottky barrier height to p-type SiGe resulting from the energy band gap reduction, and (ii) increased activation of the implanted boron with increased Ge fraction. The phosphorus implanted samples show less sensitivity of ρc to Ge fraction with a lowest value in this work of 3 × 10−7ohmcm2 for a Ge fraction of 0.3. The reduction in specific contact resistance to the phosphorus implanted samples has been shown to be due to increased dopant activation alone.

Tungsten and tungsten nitride layers have been deposited by plasma-enhanced chemical vapor deposition (PECVD). Tungsten layers deposited at low deposition temperatures T∼150 °C using this method showed good uniformity over dielectric and silicon substrate areas. As the deposition temperature decreased, the silicon consumed during the deposition reaction decreased, at T∼150 °C no silicon consumption was measurable. PECVD tungsten nitride layers were deposited directly on oxidized silicon substrates with no requirement for a nucleation layer. As the NH3 flow rate was increased, whilst maintaining all other parameters constant, deposited layers were found to change from metal tungsten to tungsten-rich amorphous layer to W2N. The resistivity of the layers was found to be high compared to published literature for higher-temperature deposited layers. The high resistivity is attributed to the incorporation of fluorine into the layer at low deposition temperatures. A deposition process was established for smooth amorphous tungsten-rich W x N layers at 150 °C.

This paper reports the fabrication of SSOI (Silicon on Silicide On Insulator) substrates with active silicon regions only 0.5μm thick, incorporating LPCVD low resistivity tungsten silicide (WSi x ) as the buried layer. The substrates were produced using ion splitting and two stages of wafer bonding. Scanning acoustic microscope imaging confirmed that the bond interfaces are essentially void-free. These SSOI wafers are designed to be employed as substrates for mm-wave reflect-array diodes, and the required selective etch technology is described together with details of a suitable device.

Silicon rich WSix was deposited by CVD onto 100mm diameter 〈100〉 silicon substrates. It is reported that the anneal temperature and anneal time determines the properties of the final WSi2 layer. A comparison is presented between rapid thermal annealing (RTA) and furnace annealing, with regard to resistivity, stress and microstructure. Reflectance measurements were also carried out on the annealed samples. It was found that furnace annealed layers were less stressed than the RTA layers. It is proposed that this is due to less silicon incorporation into the final WSi2 layer during furnace annealing. The RT annealed substrates, consistently exhibited a lower resistivity over the furnace annealed substrates. It is proposed that this was due to the enhanced grain growth experienced by the RTA substrates. The post anneal microstructure was determined using AFM. The reflectance of the layers yielded by both types of anneal was measured. The RTA layers proved to be consistently poorer than furnace annealed layers, due to the surface roughness caused by the enhanced grain growth.

The deposition of tungsten by silane reduction of WF 6 was investigated to determine the effect of the deposition chemistry on the layer properties. The influence of the deposition chemistry on the titanium adhesion layer was also investigated. To perform a direct comparison of the effect of the deposition parameters on the layer properties layers of equal thickness were deposited. In order to do this the deposition rates first had to be established experimentally. When the SiH 4 WF 6 ratio was maintained constant at 1 and the deposition temperature increased the resistivity of the layers decreases, and the roughness increased significantly. When the temperature was maintained constant at 450 °C and the SiH 4 WF 6 ratio was varied, it was found that the resistivity remained constant until the tungsten transformed to beta phase tungsten. At this transformation point the stress of the deposited layer and the roughness were seen to decrease significantly. It was found when the correct chemistry was applied at deposition temperatures up to 400 °C the initial reaction between the WF 6 and the Ti could be eliminated or reduced.

The standard method of depositing tungsten is by LPCVD using SiH4-H-2-WF6 chemistry at temperatures of >300 degrees C. This work has studied the use of PECVD with H-2-WF6 for tungsten deposition. It was found that at deposition temperatures below 200 degrees C, the layers are polycrystalline beta phase tungsten, resistivity 50 mu Omega cm. Annealing at 900 degrees C decreases the resistivity to 10 mu Omega cm. The tungsten layers deposited at 200 degrees C and above are of the alpha phase and exhibit an as deposited resistivity of 15 mu Omega cm for 150nm layers. For the layers deposited on titanium at T>300 degrees C the initial deposition is dominated by the reduction of WF6 by the titanium until a self limiting thickness is produced. This results in titanium fluoride species being incorporated at the titanium-tungsten interface.