Harold Gamble

Low-loss CPW lines on surface stabilized high-resistivity silicon

The authors propose a solution to the surface conduction problem in silicon monolithic microwave integrated circuits (MMICs). An LPCVD polycrystalline silicon layer is deposited over the surface of a high-resistivity silicon wafer which is then covered with a silicon dioxide layer. The polycrystalline silicon layer effectively removes, through traps, any free electrons or holes that may have been induced at the oxide-silicon interface. The CPW lines with 1.25-μm aluminum metallization on passivated HRS substrates have an attenuation loss at 30 GHz of only 1.08 dB/cm.

Design and Measurement of Reconfigurable Millimeter Wave Reflectarray Cells With Nematic Liquid Crystal

Numerical simulations are used to study the electromagnetic scattering from phase agile microstrip reflectarray cells which exploit the voltage controlled dielectric anisotropy property of nematic state liquid crystals (LCs). In the computer model two arrays of equal size elements constructed on a 15 mum thick tuneable LC layer were designed to operate at center frequencies of 102 GHz and 130 GHz. Micromachining processes based on the metallization of quartz/silicon wafers and an industry compatible LCD packaging technique were employed to fabricate the grounded periodic structures. The loss and the phase of the reflected signals were measured using a quasi-optical test bench with the reflectarray inserted at the beam waist of the imaged Gaussian beam, thus eliminating some of the major problems associated with traditional free-space characterization at these frequencies. By applying a low frequency AC bias voltage of 10 V, a 165deg phase shift with a loss 4.5-6.4 dB at 102 GHz and 130deg phase shift with a loss variation between 4.3-7 dB at 130 GHz was obtained. The experimental results are shown to be in close agreement with the computer model.

Liquid Crystal Tunable mm Wave Frequency Selective Surface

A frequency selective surface (FSS) which exploits the dielectric anisotropy of liquid crystals to generate an electronically tunable bandpass filter response at D Band (110-170 GHz) is presented. The device consists of two printed arrays of slot elements which are separated by a 130-mum thick layer of liquid crystals. A 3% shift in the filter passband occurs when the substrate permittivity is increased by applying a control signal of 10 V. Measured results show that the insertion loss increases from -3.7 dB to -10.4 dB at resonance (134 GHz), thus demonstrating the potential to create a FSS which can be switched between a transmitting and a reflecting structure.

Characterization of masking materials for deep glass micromachining

In this paper the characterization of different masking materials for the fabrication of flow channels or thin diaphragms in aluminosilicate glass substrates (Corning 1737) is presented. Materials such as photoresist, polysilicon and gold were investigated with concentrated hydrofluoric acid, HF 48% used as an isotropic etchant. The use of single material masks restricts the useable etch depth to less than 250 µm. Surface and material imperfections result in weaknesses in the masking layer and subsequent penetration by the etchant. An etch depth of greater than 300 µ mw as achieved using a combination of thick SU-8 photoresist and polished polycrystalline silicon as the masking material. The two materials act as double protection to the glass substrate and the etch depth obtained is approximately three to six times larger than those published for standard photoresist or SU-8 etch mask.

94 GHz Dual-Reflector Antenna With Reflectarray Subreflector

The design, construction and measured performance is described of an offset parabolic reflector antenna which employs a reflectarray subreflector to tilt the focused beam from the boresight direction at 94 GHz. An analysis technique based on the method of moments (MoM) is used to design the dual-reflector antenna. Numerical simulations were employed to demonstrate that the high gain pattern of the antenna can be tilted to a predetermined angle by introducing a progressive phase shift across the aperture of the reflectarray. Experimental validation of the approach was made by constructing a 28 times 28 element patch reflectarray which was designed to deflect the beam 5deg from the boresight direction in the azimuth plane. The array was printed on a 115 mum thick metal backed quartz wafer and the radiation patterns of the dual reflector antenna were measured from 92.6-95.5 GHz. The experimental results are used to validate the analysis technique by comparing the radiation patterns and the reduction in the peak gain due to beam deflection from the boresight direction. Moreover the results demonstrate that this design concept can be developed further to create an electronically scanned dual reflector antenna by using a tunable reflectarray subreflector.

THz Frequency Selective Surface Filters for Earth Observation Remote Sensing Instruments

The purpose of this paper is to review recent developments in the design and fabrication of Frequency Selective Surfaces (FSS) which operate above 300 GHz. These structures act as free space electromagnetic filters and as such provide passive remote sensing instruments with multispectral capability by separating the scene radiation into separate frequency channels. Significant advances in computational electromagnetics, precision micromachining technology and metrology have been employed to create state of the art FSS which enable high sensitivity receivers to detect weak molecular emissions at THz wavelengths. This new class of quasi-optical filter exhibits an insertion loss <;0.3 dB at 700 GHz and can be designed to operate independently of the polarization of the incident signals at oblique incidence. The paper concludes with a brief overview of two major technical advances which will greatly extend the potential applications of THz FSS.

Spatial demultiplexing in the submillimeter wave band using multilayer free-standing frequency selective surfaces

In this paper, we show that a multilayer freestanding slot array can be designed to give an insertion loss which is significantly lower than the value obtainable from a conventional dielectric backed printed frequency selective surface (FSS). This increase in filter efficiency is highlighted by comparing the performance of two structures designed to provide frequency selective beamsplitting in the quasioptical feed train of a submillimeter wave space borne radiometer. A two layer substrateless FSS providing more than 20 dB of isolation between the bands 316.5-325.5 GHz and 349.5-358.5 GHz, gives an insertion loss of 0.6 dB when the filter is orientated at 45/spl deg/ incidence in the TM plane, whereas the loss exhibited by a conventional printed FSS is in excess of 2 dB. A similar frequency response can be obtained in the TE plane, but here a triple screen structure is required and the conductor loss is shown to be comparable to the absorption loss of a dielectric backed FSS. Experimental devices have been fabricated using a precision micromachining technique. Transmission measurements performed in the range 250-360 GHz are in good agreement with the simulated spectral performance of the individual periodic screens and the two multilayer freestanding FSS structures.

Surface electromigration in copper interconnects

Abstract RF-magnetron sputter deposited copper films have been characterised in terms of microstructure, stress and resistivity. The electromigration behaviour of this copper has been compared to that of sputtered aluminium. Atomic Force Microscopy has been used to study the void sites. The morphology of the damaged regions, together with the microstructural information, has been used to gain an insight into the mechanism by which electromigration voiding proceeds. The observed void sites in copper are entirely different from those in aluminium; hence a different failure mechanism must be responsible. The voiding process for copper can be explained by a grain-boundary grooving model, and it was observed that surface impurities controlled the damage mechanism and the resulting void morphology.

Ultralow silicon substrate noise crosstalk using metal Faraday cages in an SOI technology

Ultralow substrate crosstalk is demonstrated using a novel metal Faraday cage isolation scheme in silicon-on-insulator technology. Over ten times reduction in crosstalk is demonstrated up to 10 GHz, compared to previously reported substrate crosstalk suppression technologies.

Substrate crosstalk suppression capability of silicon-on-insulator substrates with buried ground planes (GPSOI)

Experimental s/sub 21/ transmission crosstalk studies have been conducted on silicon-on-insulator substrates with buried ground planes (GPSOIs) where a 2 /spl Omega/ per square metal-silicide buried ground plane existed between a 15 /spl Omega/-cm p-type silicon substrate and a 1 /spl mu/m thick buried CVD oxide layer. Locally grounded transmission test structures fabricated on GPSOI were found to exhibit 20 dB increased crosstalk suppression compared to published data for high resistivity (200 /spl Omega/-cm) SOI substrates incorporating capacitive guard rings over a frequency range from 500 MHz to 50 GHz. This represents an order of magnitude improvement in crosstalk power suppression capability compared to existing state-of-the-art suppression techniques in silicon substrates.