The purpose of this paper is to provide an overview of the innovative design and manufacturing strategies that have led to the creation of a new class of freestanding Frequency Selective Surface (FSS) with unrivalled electromagnetic, thermal and structural performances. These structures, when deployed as free space electromagnetic filters, provide passive remote sensing instruments with multispectral capability by separating the scene radiation into separate frequency channels. Ultra-low loss spatial beam splitting enables high sensitivity receivers to detect weak molecular emissions at mm to sub-mm wavelengths, independent of the polarisation and angular direction of the propagating waves. This new generation of FSS is shown to satisfy the technically challenging performance and functionality that is required for next generation Earth observation radiometers. Moreover, building on this work we present a new concept for creating electronically tunable quasi optical switches based on a reconfigurable FSS structure that is suitable for deployment in future radiometer calibration arrangements.

This paper presents recent developments in Liquid Crystal-based reflectarray antennas for mm-wave applications, future perspectives for this technology and its particular use in SATCOM applications.

This paper describes the design of a frequency selective surface (FSS) which provides transmission of 228 - 230 GHz radiation and rejection from 164 - 191.3 GHz with insertion losses under 0.25 dB for TE wave polarization at 45° incidence. This state-of-the art filter topology consists of two air spaced freestanding perforated screens, comprising unit cell elements of resonant slots folded for the purpose of miniaturisation to enhance angular stability. The reported geometry enhances the angular stability (45° ± 10°) of the FSS beyond what is possible with canonical linear slots and satisfies the stringent electromagnetic performance requirements for signal demultiplexing in the quasi-optical feed train of the Microwave Sounder (MWS) instrument.

An electronically tunable reflection polarizer which exploits the dielectric anisotropy of nematic liquid crystals (LC) has been designed, fabricated and measured in a frequency band centered at 130 GHz. The phase agile polarizing mirror converts an incident slant 45° signal upon reflection to right hand circular (RHCP), orthogonal linear (-45 °) or left hand circular (LHCP) polarization depending on the value of the voltage biasing the LC mixture. In the experimental set-up this is achieved by applying a low frequency bias voltage of 0 V, 40 V and 89 V respectively, across the cavity containing the LC material.

Fermi-level pinning of aluminium on n-type germanium (n-Ge) was reduced by insertion of a thin interfacial dielectric by atomic layer deposition. The barrier height for aluminium contacts on n-Ge was reduced from 0.7 eV to a value of 0.28 eV for a thin Al2O3 interfacial layer (similar to 2.8 nm). For diodes with an Al2O3 interfacial layer, the contact resistance started to increase for layer thicknesses above 2.8 nm. For diodes with a HfO2 interfacial layer, the barrier height was also reduced but the contact resistance increased dramatically for layer thicknesses above 1.5 nm. (C) 2014 AIP Publishing LLC.

Nematic liquid crystals (LC) offer the capability to electronically reconfigure their dielectric permittivity tensor by applying a low AC voltage. This feature can find pertinent applications in submm-wave antenna technology in developing reconfigurable devices. In this contribution we review recent developments for the dielectric characterization of nematic liquid crystal samples at mm wavelengths and describe their applications in reconfigurable reflectarray antenna and tunable linear to circular polarization reflectors. The paper describes the theoretical aspects which underpin the technology that is employed for the realization, packaging and testing.

This paper investigates the characteristics of silicon piezoresistors with various dopin g concentrations and Length/Width dimensions at micro level. The silicon piezoresistors have been produced by conventional fabrication methods. The measurements are conducted on silicon test chips where p-type resistors are fabricated on n type (100) silicon substrates along the <110> direction. A fou r point bending setup has been designed and fabricated for characterizing the piezoresistor sets. The f our point bending setup is used to apply uniform uniaxi al stress along the <110> direction. This experimental result demonstrates a good linear relationship between resistance change and stress applied. The effect of doping concentration on temperature sensitivity is also investigated.

The accurate measurement of the permittivity, loss tangent and dielectric anisotropy DC bias dependence for two different liquid crystal (LC) materials in the frequency range 140-165 GHz is described. The electrical characteristics are obtained by curve fitting computed transmission coefficients to the experimental spectral response of a new class of electronically reconfigurable frequency selective surface. The periodic structure is designed to yield bandpass filter characteristics with and without an applied bias control voltage in order to measure the tunability of the LC material which is inserted in a 705 mu m-thick cavity.

A reconfigurable reflectarray-cell has been designed to provide a large tunable phase range in the frequency band 117-130 GHz. The unit-cell comprises three parallel dipoles printed on a quartz-wafer and a tunable liquid crystal (LC) placed on a cavity between the dipoles and a ground plane. The simulation results show a tunable phase-shift in a range larger than 300 degree for a 10% bandwidth and low sensitivity to the angle of incidence.

The technology for thin Ge layer transfer by hydrogen ion-cut process is characterised in this work. Experiments were carried out to determine suitable hydrogen ion implantation doses in germanium for the low temperature ion cut process by examining the formation of blisters on implanted samples. Raman and Spreading Resistance Profiling (SRP) have been used to analyse defects in germanium caused by hydrogen implants. Bevelling has been used to facilitate probing beyond the laser penetration depth. Results of Raman mapping along the projection area reveal that after post implant annealing at 400 °C, some crystal damage remains, while at 600 °C, the crystal damage has been repaired. SRP shows that some amount of hydrogen acceptor states (~1Î1016 acceptors/cm2) remain after 600 °C. These are thought to be vacancy-related point defect clusters.

Nickel germanide Schottky contacts, formed by rapid thermal annealing of thin nickel films, have been characterized on n-type germanium wafers for a range of RTA temperatures. The highest Schottky barrier heights for electrons (= 0.6-0.7 eV) were obtained for RTA temperatures of approximately 300°C. For this RTA schedule, the corresponding barrier height for holes is close to zero, ideal for Schottky contacted p-channel germanium MOSFETs. When the RTA temperature was increased to 400oC, a dramatic reduction in electron barrier height (< 0.1 eV) was observed. This RTA schedule, therefore, appears ideal for ohmic source/drain contacts to n channel germanium MOSFETs. From sheet resistance measurements and XRD characterization, nickel germanide formation was found to occur at 300oC and above. The NiGe phase was dominant for RTA temperatures up to at least 435oC.

The rapid diffusion of phosphorus and boron in WSi2 has been characterized using a novel Schottky Barrier test structure. Diffusivity of both dopant species was about 4-5 orders of magnitude higher than that reported in polycrystalline silicon. The dopant diffusivity is strongly dependent on the silicide morphology. Diffusivity measured in low temperature pre-annealed silicide is approximately an order of magnitude higher than in silicide pre-annealed at 1050°C. The dopant diffusivity in oxide lined silicide test structures was 3-4.3x10-10 cm2 s-1 at 900°C while polycrystalline silicon lined structures exhibited a higher value at 900°C of 1.5x10-9 cm2s-1. This is attributed primarily to greater segregation of dopant to the oxide-silicon interface compared to the polysilicon-silicide interface. Boron exhibited a higher diffusivity in WSi2 with diffusivity in the range 4x10-9 cm2s-1 - 1x10-8 cm2s-1 at 900°C.

An atmospheric plasma activation system has been employed to study its application on low temperature wafer bonding. High bond strength (> 2000 mJ/m2) is achieved by oxygen plasma activation on hydrophilic Si-Si and Si-SiO2 bonding at low temperature annealing. This technique has been proved to cause physical damage to thin SiO2 layers (< 0.5 µm) creating a high density of pin holes resulting in leaky oxides. When high resistivity substrates are employed the pin holes is reduced by nearly a factor of 7. A germanium disc bonded to plasma treated thin oxide on silicon was electrically connected to the substrate. The atmospheric plasma technique is currently best suited for silicon-silicon bonding, standard SOI, MMIC and MEMS technology.

An atmospheric plasma activation system has been employed to study its application on low temperature wafer bonding. Oxygen activation on PECVD oxide for bonding of temperature sensitive materials shows no pin hole when activating oxide with thickness more than 0.25 microns. Activation on thermal oxide by helium plasma also shows a pin hole free oxide. Bond strength approximately 1000 mJ/m2 is achieved after 250 degree celcius post-bond anneal which is about twice the bond strength of non-activated samples. Multiple UV components from the helium plasma were detected by spectograph. These UV spectra might have contributed to the bond strength enhancement in Si-SiO2 bonding.

Germanium (Ge) has been bonded to fine grain alumina (Al2O3) by means of a polished polycrystalline silicon interface layer. After room temperature bonding and subsequent bond strength annealing at 150 oC for 24 hrs, the germanium layer was ground and polished to 100µm. Low temperature Tungsten (W) gate circular geometry devices, W/L = 9, fabricated on this layer exhibited effective mobility values of 150 cm2/Vs. This is much lower than results obtained on equivalent devices on bulk Ge. Improvement in the germanium polish process resulted in transistors with an effective mobility of 415 cm2/Vs, comparable to that of the bulk Ge devices. Low temperature measurement, down to temperatures of 173 K, showed an improvement in device performance resulting in both an increase in effective mobility to 591 cm2/Vs and a decrease in sub threshold slope from 180 mV/dec to 60 mV/dec indicating a reduction in leakage current.

Hydrogen implantation of germanium is a promising technique for layer transfer. However, both the implantation process, and subsequent heat treatment can create defects in the transferred layer, which detrimentally effect the performance of devices fabricated on these transferred layers. In this study, implanted Germanium wafers were given various anneals and analysed optically and by spreading resistance, to gain insight on the nature of such defects. GeOI layers were produced by thermal splitting of implanted germanium wafers bonded to sapphire handle substrates.

Novel test diode structures have been manufactured to characterise dopant diffusion in tungsten silicide layers. Bipolar diode action is demonstrated experimentally for anneal schedules of 30 minutes at 900degC, indicating long- range diffusion of phosphorus (~ 38 mum). The work function of the silicide was found to be 4.8 eV. SIMS analysis shows dopant redistribution is effected by the segregation to the silicide/oxide interface. The concept of conduit diffusion has been demonstrated experimentally for application in advanced bipolar transistor technology.

Monolithic active pixel detectors in SOI (Silicon On Insulator) technology are novel sensors of ionizing radiation, which exploit SOI substrates for the integration of readout electronics and a pixel detector. Some important parameters of the devices are breakdown voltage and leakage current. The paper addresses recent developments in the field of the technology of the SOI detectors, which lead to improvement of reliability and current-voltage characteristics of the sensors.

Silicon-on-insulator (SOI) substrates incorporating tungsten silicide ground planes (GPs) have been shown to offer the lowest reported crosstalk figure of merit for application in mixed signal integrated circuits. The inclusion of the silicide layer in the structure may lead to stress or defects in the overlying SOI layers and resultant degradation of device performance. It is therefore essential to establish the quality of the silicon on the GPSOI substrate. MOS capacitor structures have been employed in this paper to characterize these GPSOI substrates for the first time. High quality MOS capacitor characteristics have been achieved with minority carrier lifetime of similar to 0.8 ms. These results show that the substrate is suitable for device manufacture with no degradation in the silicon due to stress or metallic contamination resulting from the inclusion of the underlying silicide layer.

Advanced integrated circuits may employ SOI substrates and incorporate both analogue and digital systems on a single chip. These system-on-chip integrated circuits are susceptible to cross talk noise generated by the digital components. This paper addresses the issue and describes an SOI substrate produced by wafer bonding which incorporates a tungsten silicide ground plane layer. This ground plane layer suppresses the cross talk yielding a20 dB improvement in performance compared with alternative techniques. Double gate MOS capacitor structures have been manufactured on these GPSOI substrates and the overlying silicon layer has been shown to be of high quality, unaffected by the underlying silicide. The buried insulator layer incorporates undoped polysilicon which has been shown to act as a dielectric layer.