Ylva Bäcklund

Fabrication of 45/spl deg/ mirrors together with well-defined v-grooves using wet anisotropic etching of silicon

The most commonly used microstructure for passive fiber alignment is the ordinary v-groove, defined by {111} planes on a (100) silicon wafer. The plane at the end of the groove, having a 54.7/spl deg/ angle to the surface, can be used as a reflecting mirror. For single-mode fiber applications, a 45/spl deg/ mirror is advantageous together with high accuracy in the position of the fiber, i.e. a smooth mirror and good control of the groove geometry is needed. Two techniques are presented to form 45/spl deg/ mirrors along with well-defined grooves in silicon, using the wet anisotropic etchants EDP and KOH. These techniques are used: (1) to reveal {110} planes on (100) silicon and (2) to make {111} mirrors on wafers that are cut 9.7/spl deg/ off the [100] axis. On (100) silicon, EDP without pyrazine gave the best result. The best mirror and groove reproducibility was found on off-axis cut silicon, using 36 wt.% KOH, with isopropyl alcohol added.

A lateral symmetrically bistable buckled beam

We have micromachined a lateral symmetrically bistable buckled beam for snap-in holding structures by oxidizing released beams micromachined on thick silicon-on-insulator wafers. The wafers were prepared by bonding and chemical mechanical polishing, and t

Precise mask alignment to the crystallographic orientation of silicon wafers using wet anisotropic etching

A design tool for fast and precise determination of the crystallographic orientation in (001) and (011) silicon wafers using anisotropic wet etching is introduced. The design takes advantage of the symmetric under-etching behaviour around, but not at (!), the -directions. The pattern needs to be etched only for a short time, and after a very quick optical inspection it can be used for aligning subsequent masks, using the same masking layer, more or less automatically. Two effects were investigated in a number of common anisotropic etchants: KOH, KOH with isopropyl alcohol (KOH/IPA), ethylenediamine based solutions (EDP), and tetramethyl ammonium hydroxide (TMAH). The precision of the method was found in most cases to be better than .

Passive silicon transensor intended for biomedical, remote pressure monitoring

Abstract A sensor is suggested for continuous monitoring of intraocular pressure and similar biomedical applications. The system consists of a capacitive pressure sensor determining the resonance frequency of a passive LC resonator. The resonance frequency is detected in a grid-dip configuration. The paper mainly deals with the capacitive sensor, which is fabricated in silicon, using a silicon fusion bond to seal the cavity. This process will minimize internal stress and provide the necessary conditions for a small temperature drift and stability over long periods of time. Experimentally, prototype sensors have been fabricated and evaluated in vitro . The results are promising and in accordance with theoretical expectations.

New shapes in (100) Si using KOH and EDP etches

Wet chemical etching in EDP, pure KOH and KOH with isopropyl alcohol (KOH/IPA) are known to etch different crystal planes with different etch rates. It is shown in this work that etching in EDP or KOH/IPA reverses the etch-rate ratios of (100) and (110) planes, as compared to etching in pure KOH. This can be used to reveal other relatively slow etching planes, other than (111), to be used in new structures. V-grooves, retro-reflector ridges and mesa structures were fabricated bounded by (110) planes with 45 degrees angles to the (100) surface. Also, by using a corner-compensated mask aligned in the (100) direction and etched in pure aqueous KOH, free-standing cubic studs bounded by (100) planes were fabricated.

A system for wireless intra-ocular pressure measurements using a silicon micromachined sensor

A system for the continuous monitoring of intra-ocular pressure is described. The sensor is intended for permanent implantation, integrated with an artificial lens. The system consists of a capacitive pressure sensor, determining the resonance frequency of a passive LC network, and a detector, based on the grid-dip technique. The passive pressure sensing element is micromachined from two silicon wafers and connected to a gold-wire coil. Prototype sensors have been evaluated experimentally in vitro. Pressure has been measured remotely, with promising results.

THE IOP-IOL. A PROBE INTO THE EYE

Abstract. The intraocular lens (IOL) implant can be looked upon as a probe into the space of the eye. Adapting that view, it is logical to furnish the IOL‐probe with biomedical sensors that would explore its environment. A sensor is presented for continuous monitoring of intraocular pressure (IOP), incorporated in the haptics of an IOL. The sensor consists of a capacitative spiral circuit, needing no energy, correlating its resonance frequency to the actual IOP. This resonance frequency is remotely and non‐invasively detected by an external device located in a spectacle frame.

Bulk silicon holding structures for mounting of optical fibers in v-grooves

A set of micromachined structures for holding optical fibers in anisotropically etched v-grooves has been produced. The structures are made of bulk silicon and formed in the same etch step as the aligning v-grooves, using the photovoltaic electrochemical etch-stop technique (PHET). It is a selective etch method where n-type silicon etches and p-type are passivated by combining an illuminated pn-junction and an electrochemical cell using KOH as electrolyte. The structures were produced in a variety of shapes, based on cantilever beams and doubly clamped bridges. The structures substantially facilitated the mounting of the fibers into the v-grooves. Certain structures could even push the fibers down into position in the grooves.

Etch rates of crystallographic planes in Z -cut quartz—experiments and simulation

The anisotropic etching behaviour of monocrystalline quartz is studied both experimentally and with computer simulations. The etch rate minima were identified as the crystal planes m, r, r(2), s an ...

Passive and fixed alignment of devices using flexible silicon elements formed by selective etching

Assembly systems consisting of aligning pits combined with flexible holding elements have been produced for both passive and fixed alignment of devices such as chips and optical fibres. The free-standing holding elements were fabricated in bulk silicon using the photovoltaic electrochemical etch-stop technique. The pits were oriented along the direction which resulted in square etch profiles and in underetching of the passivated silicon surface layer. The devices were inserted into the pits and positioned towards aligning corners and edges by specially designed tongues. The chips could be positioned with high precision on the wafer, in contrast to the fibres, due to uneven bottom surfaces of the grooves. Hence, the alignment method presented here is more suitable for chip positioning since the lateral position of the chips does not depend on the pit depth. The presented assembly systems are well suited for building hybrid microsystems, where different types of device are assembled onto a micromachined silicon substrate.