Dry Etching of GaAs to Fabricate Via-Hole Grounds in Monolithic Microwave Integrated Circuits

This study investigates the dry etching of 60 mm dia, 200 mm deep holes for fabrication of through substrate via holes for grounding monolithic microwave integrated circuits (MMICs), on 3-inch dia semiinsulating GaAs wafer using RIE and ICP processes with CFC and non-CFC gas chemistry, respectively. The effect of various process parameters on GaAs etch rate and resultant etch profile was investigated. Two kinds of masks, photoresist and Ni, were used to etch GaAs and performance was compared by investigating effect on etch rate, etch depth, etch profile, and surface morphology. The etch profile, etch depth, and surface morphology of as-etched samples were characterised by scanning electron microscopy. The desired 200 mm deep strawberry profile was obtained at 40 mTorr for both RIE and ICP processes with an etch rate of ~1.3 mm/min and ~4 mm/min respectively. Ni metal mask was used for RIE process due to poor photoresist selectivity, whereas ICP process utilised photoresist as mask. The vias were then metallised by depositing a thin seed layer of Ti/Au (1000 Å) using radio frequency sputtering and Au (~5 mm) electroplated to connect the frontside pad and back side ground plane. The typical parasitic inductance offered by these via for RIE and ICP processes was ~76 pH and 83 pH respectively, which is well within the acceptable limits. The developed process was finally integrated to in-house MMIC production line.Defence Science Journal, 2009, 59(4), pp.363-370, DOI:http://dx.doi.org/10.14429/dsj.59.153

CP Phases in Correlated Production and Decay of Neutralinos in the Minimal Supersymmetric Standard Model

We investigate the associated production of neutralinos $e^+e^-\to\tilde{\chi}^0_1\tilde{\chi}^0_2$ accompanied by the neutralino leptonic decay $\tilde{\chi}^0_2\to\tilde{\chi}^0_1 \ell^+\ell^-$, taking into account initial beam polarization and production-decay spin correlations in the minimal supersymmetric standard model with general CP phases but without generational mixing in the slepton sector. The stringent constraints from the electron EDM on the CP phases are also included in the discussion. Initial beam polarizations lead to three CP--even distributions and one CP--odd distribution, which can be studied independently of the details of the neutralino decays. We find that the production cross section and the branching fractions of the leptonic neutralino decays are very sensitive to the CP phases. In addition, the production--decay spin correlations lead to several CP--even observables such as lepton invariant mass distribution, and lepton angular distribution, and one interesting T--odd (CP--odd) triple product of the initial electron momentum and two final lepton momenta, the size of which might be large enough to be measured at the high--luminosity future electron--positron collider or can play a complementary role in constraining the CP phases with the EDM constraints.Comment: Revtex, 37 pages, 12 eps figure

Evo-devo and the search for homology (“sameness”) in biological systems

Developmental biology and evolutionary studies have merged into evolutionary developmental biology ("evo-devo”). This synthesis already influenced and still continues to change the conceptual framework of structural biology. One of the cornerstones of structural biology is the concept of homology. But the search for homology ("sameness”) of biological structures depends on our favourite perspectives (axioms, paradigms). Five levels of homology ("sameness”) can be identified in the literature, although they overlap to some degree: (i) serial homology (homonomy) within modular organisms, (ii) historical homology (synapomorphy), which is taken as the only acceptable homology by many biologists, (iii) underlying homology (i.e., parallelism) in closely related taxa, (iv) deep evolutionary homology due to the "same” master genes in distantly related phyla, and (v) molecular homology exclusively at gene level. The following essay gives emphasis on the heuristic advantages of seemingly opposing perspectives in structural biology, with examples mainly from comparative plant morphology. The organization of the plant body in the majority of angiosperms led to the recognition of the classical root-shoot model. In some lineages bauplan rules were transcended during evolution and development. This resulted in morphological misfits such as the Podostemaceae, peculiar eudicots adapted to submerged river rocks. Their transformed "roots” and "shoots” fit only to a limited degree into the classical model which is based on either-or thinking. It has to be widened into a continuum model by taking over elements of fuzzy logic and fractal geometry to accommodate for lineages such as the Podostemacea