James Becker

A planar probe double ladder waveguide power divider

The successful demonstration of a 1:4 power divider using microstrip probes and a WR-430 rectangular waveguide is presented. The 15-dB return loss bandwidth of the nonoptimized structure is demonstrated to be 22% and its 0.5-dB insertion loss bandwidth 26%. While realized through conventional machining, such a structure is assembled in a fashion consistent with proven millimeter and submillimeter-wave micromachining techniques. Thus, the structure presents a potential power dividing and power combining architecture, which through micromachining, may be used for applications well above 100GHz.

Thin film growth of semiconducting Mg2Si by codeposition

Ultrahigh vacuum evaporation of magnesium onto a hot silicon substrate (⩾200 °C), with the intention of forming a Mg2Si thin film by reaction, does not result in any accumulation of magnesium or its silicide. On the other hand, codeposition of magnesium with silicon at 200 °C, using a magnesium-rich flux ratio, gives a stoichiometric Mg2Si film which can be grown several hundreds of nm thick. The number of magnesium atoms which condense is equal to twice the number of silicon atoms which were deposited; all the silicon condenses while the excess magnesium in the flux desorbs. The Mg2Si layers thus obtained are polycrystalline with a (111) texture. From the surface roughness analysis, a self-affine growth mode with a roughness exponent equal to 1 is deduced.

Fully micromachined finite-ground coplanar line-to-waveguide transitions for W-band applications

A fully micromachined finite-ground coplanar (FGC) line-to-waveguide transition for W-band applications has been designed, fabricated, and tested. The transition utilizes a printed E-plane probe, inserted into the broad sidewall of a micromachined waveguide. This type of transition plays an important role in many applications where coupling between the popular FGC line and a waveguide is required. Excellent performance across the entire W-band of such a transition is presented in this paper. The investigated waveguide, micromachined in silicon using the deep reactive ion etching technique, demonstrates its potential as an alternative to costly conventional waveguides at high frequencies. A similar transition with a micromachined waveguide formed via bulk micromachining using a wet etchant is also demonstrated. The free-standing probe utilized in this second transition proves the potential of such transitions to be applicable well into the submillimeter and terahertz range.

Growth mechanism and optical properties of semiconducting Mg 2 Si thin films

Abstract Reactive deposition of magnesium onto a hot silicon substrate (200–500°C) does not result in any accumulation of magnesium or its silicide — the condensation coefficient of magnesium being zero. On the other hand, co deposition of magnesium with silicon at 200°C, using a magnesium-rich flux ratio, gives a stoichiometric Mg 2 Si film. The number of magnesium atoms which condense is equal to twice the number of silicon atoms which were deposited. The Mg 2 Si layers are polycrystalline with a (111) texture. These stoichiometric silicide films still show a tendency to sublimate; whereas capping with an oxide results in extensive intermixing during annealing. The Mg 2 Si films thus obtained exhibit optical transparency at sufficiently long wavelength, and an absorption edge. Extraction of the absorption coefficient from the data, and analysis of its energy dependence suggest an indirect bandgap of ∼0.74 eV, plus direct transitions at ∼0.83 and ∼0.99 eV.

A finite ground coplanar line-to-silicon micromachined waveguide transition

Circuits operating in the terahertz frequency range have traditionally been developed using hollow metal waveguides, which, due to the small wavelength at these operating frequencies, must be correspondingly small in cross section. As a result of the high cost of conventional precision machining of such small waveguides, alternate fabrication methods continue to be explored. Silicon micromachining has been suggested as a potential means to produce waveguides in a more cost-effective manner for operation at these frequencies. This paper presents a transition structure that couples the popular finite ground coplanar transmission line to a W-band silicon micromachined waveguide, forming a fully micromachined module. The waveguide is formed via bulk micromachining using a wet etchant, resulting in a diamond cross section. The consequences of utilizing a diamond waveguide in place of the more common rectangular waveguide are considered and potential means of developing rectangular-walled waveguides in silicon are noted. A Ka-band microwave model of a similar transition to a conventional rectangular waveguide is also demonstrated.

A Planar Compatible Traveling-Wave Waveguide-Based Power Divider/Combiner

The operation of a planar compatible traveling-wave power divider and combiner structure is presented. Design guidelines of the scalable structure are presented as are simulated and measured results of two- and four-way devices at -band frequencies. A transmission line model of the divider/combiner is presented to provide additional insight into its operation. The measured 15-dB return-loss bandwidth of the structure is on the order of 20% with a power combining efficiency as high as 90% around the design frequency. The measured structure exhibited a 15-dB return-loss bandwidth of 15% with a power combining efficiency of approximately 80%.

Reflection high-energy electron diffraction patterns of carbide-contaminated silicon surfaces

Carbon contamination of silicon surfaces is a longstanding concern for growers of thin films who utilize silicon wafer substrates. This contamination often takes the form of epitaxial β‐SiC particles which grow after the decomposition of adsorbed carbon‐bearing molecules, and the subsequent reaction of the freed carbon with the silicon substrate. Positive identification of such SiC contamination is possible via reflection high‐energy electron diffraction (RHEED). To provide a complete demonstration and analysis of the relevant RHEED patterns, we prepared within a ‘‘silicon molecular beam epitaxy’’ system carbide‐contaminated silicon surfaces using procedures intended to foster such contamination. With conventional RHEED instrumentation, we obtained transmission electron diffraction patterns which resulted from the passage of the RHEED electron beam laterally through the SiC particles. Comparison with theoretically predicted patterns positively identifies the β‐SiC phase and shows that the particles are ep...

ReSi2 thin‐film infrared detectors

Two types of thin‐film infrared‐sensing devices have been investigated using the narrow band‐gap semiconductor, rhenium disilicide (Eg∼0.1 eV). These are the ReSi2/n‐Si heterojunction internal photoemission (HIP) detector and the ReSi2 thin‐film photoconductor. The HIP device was found to be rectifying and to obey a Fowler‐type law with a long‐wavelength cutoff of ∼2.1 μm (0.59 eV) at room temperature. In hopes of approaching the fundamental limit for a ReSi2‐based photonic detector, ∼12 μm (0.1 eV), the ReSi2 photoconductor was explored. Indeed, the spectral response (measured at 10 K) of the ohmic photoconductor was found to extend to 6 μm (the present limit of our measurement equipment), with no indication of a detection cutoff.

Silicon micromachined interconnects for on-wafer packaging of MEMS devices

A silicon micromachined on-wafer packaging scheme for RF MEMS switches is proposed that has excellent performance at K-band. The designed RF transition has an insertion loss of 0.1 dB and a return loss of 32 dB at 20 GHz along with a 55% bandwidth of operation. A novel fabrication technique previously presented is utilized for patterning the RF interconnects inside micromachined silicon cavities. The fabrication process is designed so as to be completely compatible with the MEMS switch process, hence allowing the parallel fabrication of all the components on one wafer. The on-wafer packages require no external wiring to achieve signal propagation and thus have potential for lower loss and better performance at higher frequencies.

Multilevel finite ground coplanar line transitions for high-density packaging using silicon micromachining

A 3D photolithographic technique is exploited to produce finite ground coplanar (FGC) transmission lines that transition into and out of silicon micromachined cavities. Each transition was found to introduce an average loss of less than 0.08 dB across the 2-40 GHz range for a cavity depth of 110 /spl mu/m. The demonstration of this technology is a significant step toward fully realizing the circuit packaging capabilities of micromachined silicon and offers the possibility of novel, broadband vertical transitions.