P. Eliáš

Conformal AZ5214-E resist deposition on patterned (1?0?0) InP substrates

A draping technique was studied to deposit thin, visco-elastic AZ5214-E resist layers from a water surface over planar and patterned substrates. A visco-elastic AZ5214-E layer forms on the water surface when a drop of AZ5214-E makes contact with it. The drop spreads out within a fraction of a second because of a large positive difference in surface tension between water and AZ5214-E. The spreading mechanism lies in the ability of PGMEA (AZ5214-E liquid constituent) to form hydrogen bonds with water. We brought AZ5214-E drops to make contact with water at 20 ± 0.1 °C via adhesive forces to form AZ5214-E layers on the water surface of (1) circular and (2) square shapes. In case (1), the layers, formed from drops of V = 3 µl, had thickness t ≈ c ⋅ 4V/πΦ−2 for Φ c ⋅ 4V/πΦ−2 for larger Φ. In case (2), the layers had t ≈ a + bV for V between 7 and 12 µl on square-shaped water surfaces of constant area A = 34.5 mm × 34.5 mm. All layers exhibited microscopic waviness with an average thickness uniformity u ~ 91%, and submicron waviness with a root-mean-square roughness σ ~ 12 nm and a lateral correlation length ξ ~ 32 µm. AZ5214-E sheets coated conformally high mesa objects with sharp convex and concave edges: 61 µm high ridges confined to ~35°-inclined facets and 9 µm high ridges confined to negatively sloped facets. The draping technique can be used to deposit conformal AZ5214-E layers over non-planar substrates for non-planar device processing.

Approaching the pT range with a 2DEG InGaAs/InP Hall sensor at 77 K

Abstract The noise of two-dimensional electron gas InGaAs/InP Hall sensors of various dimensions was studied. In the first part of the work we show that for large-scale sensors (>0.2 mm linear dimension) at 77 K and at 1 kHz, a sensitivity better then 1 nT can be achieved. The second part of present work deals with the noise measurements of 2 and 10 μm sensors dependent on bias current, frequency, applied magnetic field and temperature. It was found that the low-frequency noise of the 10 μm sensor rapidly increased for applied magnetic field, but the noise of the 2 μm sensor is a complicated function of temperature and magnetic field: for low temperatures and fields 1–3 T is the low-frequency noise of the sensor suppressed.

OMCVD growth of InP and InGaAs on InP non-planar substrates patterned with {110} quasi facets

Non-planar low-pressure organometallic chemical vapour deposition (LP OMCVD) of InP and InGaAs was performedon patterned(1 0 0) semi-insulating InP substrates. The patterns were 15- mm-high long mesa ridges bounded by (1 1 0) and ð1 % Þ quasi facets and(1 0 0) top surfaces. Growth rates andsurface morphologies on the facets were studied using scanning electron microscopy (SEM), atomic force microscopy (AFM) and optical microscopy. Both InP andInGaAs nucleatedsufficiently on the facets. While InP layers were smooth, InGaAs nucleatedthrough facetted trapezoidal islands. The mechanism of facetting is qualitatively discussed. The InGaAs facetting as well as accompanying roughness were partly suppressedat lower growth temperatures. r 2001 Elsevier Science B.V. All rights reserved.

Crystallographic dependence of OMVPE InGaAs/InP lateral growth on patterned (100) InP substrates prepared by wet etching

Abstract InP layers and InP/InGaAs structures were grown at 600°C using OMVPE on non-planar wet-etch InP substrates with patterns aligned at various angles Θ within [010] and [01-1] as well as [001] and [0-11]. The patterns were 15-μm-high ordinary mesa-shaped ridges with the sidewall facet angle α dependent on the alignment angle Θ. Within 0.5°

SWITCHING MAGNETIZATION MAGNETIC FORCE MICROSCOPY --- AN ALTERNATIVE TO CONVENTIONAL LIFT-MODE MFM

Switching Magnetization Magnetic Force Microscopy — An Alternative to Conventional Lift-Mode MFM In the paper we present an overview of the latest progress in the conventional lift-mode magnetic force microscopy (MFM) technique, achieved by advanced MFM tips and by lowering the lift height. Although smaller lift height offers improved spatial resolution, we show that lowered tip-sample distance mixes magnetic, atomic and electric forces. We describe an alternative to the lift-mode procedure - Switching Magnetization Magnetic Force Microscopy [SM-MFM], which is based on two-pass scanning in tapping mode AFM with reversed tip magnetization between the scans. We propose design and calculate the magnetic properties of such SM-MFM tips. For best performance the tips must exhibit low magnetic moment, low switching field, and single-domain state at remanence. The switching field of such tips is calculated for Permalloy hexagons.

SEM and AFM characterisation of high-mesa patterned InP substrates prepared by wet etching

Abstract The aim of this study has been to optimise a reliable technological process that would be capable of producing quality mesa etches (40 μm high) into (100) SI InP substrates yielding well-defined smooth (211) faceted walls and (100) bottom etched planes. Such well-defined patterned substrates can serve for non-planar overgrowth experiments with the aim to create 2DEGs at tilted heterostructures and finally to design and manufacture novel magnetic-field sensors. Using xHCl:1H3PO4 solutions well-defined smooth (211)A surfaces were produced for 0.5

Dirichlet sets, Erdős-Kunen-Mauldin theorem, and analytic subgroups of the reals

We prove strengthenings of two well-known theorems related to the Lebesgue measure and additive structure of the real line. The first one is a theorem of Erdős, Kunen, and Mauldin stating that for every perfect set there exists a perfect set of measure zero such that their algebraic sum is the whole real line. The other is Laczkovichs theorem saying that every proper analytic subgroup of the real line is included in an F σ set of measure zero. Using the strengthened theorems we generalize the fact that permitted sets for families of trigonometric thin sets are perfectly meager.

Conformal, planarizing and bridging AZ5214-E layers deposited by a 'draping' technique on non-planar III?V substrates

A draping technique was tested for the deposition of positive-tone AZ5214-E photo-resist layers on non-planar (1 0 0)-oriented III–V substrates, which had a variety of three-dimensional (3D) topographies micromachined in them that consisted, e.g., of mesa ridges confined to side facets with variable tilt, inverted pyramidal holes and stubs confined to perpendicular side facets. All objects were sharp-edged. In each draping experiment, an AZ5214-E sheet was (1) formed floating on the water surface, (2) lowered onto a non-planar substrate and (3) draped over it during drying to form either self-sustained, or conformal, or planarizing layers over the non-planar substrates. The draping process is based on the depression of the glass transition temperature Tg of AZ5214-E material induced by penetrant water molecules that interact with AZ5214-E. During the process, the molecules are initially trapped under an AZ5214-E sheet and then transported out through the sheet via permeation. The water–AZ5214-E interaction modifies the stiffness κ of the sheet. The magnitude of the effect depends on temperature T and on partial water vapour pressure difference p(T, P, κ): the net effect is that Tg = f(C(T, P), p(T, P, κ)) is lowered as the concentration C of water increases with T and p, where P is the permeability of the sheet. The interaction depressed the Tg of the sheets as low as or lower than 53 °C for 6 µm thick sheets. At room temperature T Tg, the sheet becomes rubbery and mouldable by adhesion and capillary forces. As a result, it can either contour or planarize the topography depending on its geometry and thickness of the sheet.

Covering for category and trigonometric thin sets

In this work we consider several combinatorial principles satisfied for cardinals smaller than cov(M), the covering number of the ideal of first category sets on real line. Using these principles we prove that there exist N 0 -sets (similarly N-sets, A-sets) which cannot be covered by fewer than cov(M) pD-sets (A-sets, N-sets, respectively). This improves the results of our previous paper (1997).

Characterisation of InGaAs/InP microscopic Hall probe arrays with a 2DEG active layer

Abstract Highly-sensitive cryogenic microscopic Hall probe arrays based on an epitaxial InGaAs/InP heterostructure with a two-dimensional electron gas (2DEG) were prepared and characterised in high magnetic fields at 0.3 K. A model of the heterostructure including a self-consistent description of coupled Poisson and Schrodinger equations was solved to optimise its design. Test arrays exhibit a constant 2DEG concentration at 4.2–100 K, which gives a temperature coefficient lower than 100 ppm °C −1 . The magnetic sensitivity is ≥1250 VA −1 T −1 . Quantum oscillations in the 2DEG structure in high magnetic fields at temperatures below 4.2 K can be suppressed by increasing bias current supplied to the arrays respecting their dimensions. Noise characteristics at 300 K are also presented.