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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 900[degrees]C 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 900[degrees]C, indicating long-range diffusion of phosphorus (~38/[micro]m). 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. Index Terms--Diffusion processes, diodes, doping, tungsten compounds.

The traditional use of Scotch tape for exfoliating layers of two-dimensional (2D) transition metal dichalcogenides (TMDs) has been compared with a gel-assisted mechanical exfoliation technique, using MoS2 as a representative TMD. The gel-assisted exfoliation process, which makes use of both Scotch tape and a gel film, is superior to the use of Scotch tape alone, as it gives a higher probability of obtaining larger surface area few-layer flakes. A quantitative analysis has been made between the samples prepared by the two techniques. The total density of flakes transferred onto a sample by Scotch tape alone was much higher than when using the gel film. However, most of the transferred flakes were several microns in thickness with lateral dimensions <10 µm. Therefore, the higher percentage of few-layer flakes with large lateral dimensions (> 20 µm) transferred using gel film is very advantageous. Since samples prepared using gel film have fewer flakes, the contacting of potential thin flakes on the sample can be done conveniently. Also, unlike Scotch tape, the gel film does not leave adhesive residue on the substrate. Optical microscopy, contrast difference measurements and Raman spectroscopy were used for identification of the few-layer MoS2 flakes. [ABSTRACT FROM AUTHOR]

This paper reports the design, manufacture, and characterization of a new frequency selective surface (FSS) structure which meets the demanding requirements for transmission of 50.2–57.7 GHz radiation simultaneously for TE and TM polarizations at 45° incidence, and reflection of signals in four discrete higher frequency bands centered at 89, 165.5, 183.3, and 229 GHz. The FSS is required for a quasi-optical network, which was developed during the preparatory breadboarding of the microwave sounder instrument. The 100 mm diameter ultrawideband FSS must exhibit ≤0.25 dB loss for all signals in the above bands, and has to satisfy the requirements of the space environment. The FSS is formed by a periodic metal film array sandwiched between two 0.83 mm thick, optically flat, fused quartz substrates. It has 19 000 unit cells composed of two compact resonant slot elements, a meandering elliptical annulus and a folded dipole. Spectral transmission and reflection measurements in the 50–230 GHz frequency range yielded results that are in excellent agreement with numerical predictions. [ABSTRACT FROM PUBLISHER]

The design, fabrication, and measured results are presented for a reconfigurable reflectarray antenna based on liquid crystals (LCs) which operates above 100 GHz. The antenna has been designed to provide beam scanning capabilities over a wide angular range, a large bandwidth, and reduced side-lobe level (SLL). Measured radiation patterns are in good agreement with simulations, and show that the antenna generates an electronically steerable beam in one plane over an angular range of 55° in the frequency band from 96 to 104 GHz. The SLL is lower than -\mathbf13\;\mathbfdB for all the scan angles and -\mathbf18\;\mathbfdB is obtained over 16% of the scan range. The measured performance is significantly better than previously published results for this class of electronically tunable antenna, and moreover, verifies the accuracy of the proposed procedure for LC modeling and antenna design. [ABSTRACT FROM PUBLISHER]

The buried oxide (BOX) layer in silicon on insulator (SOI) was replaced by a compound buried layer (CBL) containing layers of SiO2 , polycrystalline silicon (polysilicon), and SiO2 . The undoped polysilicon in the CBL acted as a dielectric with a higher thermal conductivity than SiO2 . CBL provides a reduced thermal resistance with the same equivalent oxide thickness as a standard SiO2 buried layer. Thermal resistance was further reduced by lateral heat flow through the polysilicon. Reduction in thermal resistance by up to 68% was observed, dependent on polysilicon thickness. CBL SOI substrates were designed and manufactured to achieve a 40% reduction in thermal resistance compared with an 1.0- \mum~SiO2 BOX. Power bipolar transistors with an active silicon layer thickness of 13.5 \mum manufactured on CBL SOI substrates showed a 5%–17% reduction in thermal resistance compared with the standard SOI. This reduction was dependent on transistor layout geometry. Between 65% and 90% of the heat flow from these power transistors is laterally through the thick active silicon layer. Analysis confirmed that CBL SOI provided a 40% reduction in the vertical path thermal resistance. Devices employing thinner active silicon layers will achieve the greater benefit from reduction in vertical path thermal resistance offered by CBL SOI. [ABSTRACT FROM AUTHOR]

Two models that can predict the voltage-dependent scattering from liquid crystal (LC)-based reflectarray cells are presented. The validity of both numerical techniques is demonstrated using measured results in the frequency range 94–110 GHz. The most rigorous approach models, for each voltage, the inhomogeneous and anisotropic permittivity of the LC as a stratified media in the direction of the biasing field. This accounts for the different tilt angles of the LC molecules inside the cell calculated from the solution of the elastic problem. The other model is based on an effective homogeneous permittivity tensor that corresponds to the average tilt angle along the longitudinal direction for each biasing voltage. In this model, convergence problems associated with the longitudinal inhomogeneity are avoided, and the computation efficiency is improved. Both models provide a correspondence between the reflection coefficient (losses and phase-shift) of the LC-based reflectarray cell and the value of biasing voltage, which can be used to design beam scanning reflectarrays. The accuracy and the efficiency of both models are also analyzed and discussed. [ABSTRACT FROM PUBLISHER]

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\,\times\,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. [ABSTRACT FROM AUTHOR]

Novel diode test structures have been manufactured to characterize long-range dopant diffusion in tungsten suicide layers. A tungsten silicide to p-type silicon contact has been characterized as a Schottky barrier rectifying contact with a suicide work function of 4.8 eV. Long-range diffusion of boron for an anneal at 900 °C for 30 mm 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 mm at 900 °C, indicating long-range diffusion of phosphorus (~38 nm). 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. [ABSTRACT FROM AUTHOR]