Carola Strandman

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.

Field emitting structures intended for a miniature x-ray source

The concept of a miniature X-ray source is presented. The source consists of a micromachined field-emitting cathode and an anode. Electrons emitted from the cathode are accelerated towards and into the anode where their deceleration produces X-rays. The energy of the X-rays is controlled by the voltage applied to the electrodes, and the dose rate by the emission current. A tentative medical application is discussed and candidate field emission structures are investigated. Spectra from different anode materials have been collected using diamond cold cathodes.

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.

A production process of silicon sensor elements for a fibre-optic pressure sensor

Abstract Silicon micromachining has been used for small-scale production of sensor elements for a fibre-optic pressure sensor. Each sensor is integrated with a guide wire for insertion of catheters during balloon dilatation of constricted arteries of the heart. The manufacturing process of the sensor elements is described in detail. It consists of four lithographic steps and five etch steps. The sensor elements have been manufactured using anisotropic etching of slowly dissolving {100} silicon planes in KOH. The sensor elements are supported by a carrier for use of a micromanipulator when assembling the sensor. The dimensions of the sensor elements are 55 μ × 76 μm × 1240 μm, and the resulting guide-wire pressure sensor has an outer diameter of 0.36 mm. Critical element dimensions determing the sensor performance have been identified, and resulting etch depth variations are presented. It is shown that the sensor elements could be produced with sufficient accuracy using time etching of {100} planes. The yield of the total manufacturing process is about 40%. The sensor is a commercial product and the production volume of sensor elements is 10 000 units/year.

Electrochemical Detection Based on Redox Cycling Using Interdigitated Microarray Electrodes at µL/min Flow Rates

The influence of convection on the degree of redox cycling at interdigitated microarray electrodes in a flow system was investigated in the end column detection mode for flow rates below 20 mu L/min. It was found that the degree of redox cycling increased

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.

Method for the determination of the angular dependence during dry etching

Process simulation is going to play an ever increasing role in the development, process optimization, and production of integrated circuit devices, yielding shorter development times and reduced costs as compared to traditional development methods. One of the most notorious problems one faces in topography simulations in particular is the determination of the erosion/growth rates of materials exposed to a variety of complex physicochemical processes. The latter evolve continually to satisfy the needs of the ever advancing microelectronic industry, while our understanding about these processes is often incomplete and insufficient for their description. Existing theoretical models, which are often semiempirical, include a set of fitting parameters which are generally unknown and their determination in most cases involves guesswork. Another much more pragmatical approach to the problem is to measure these etch/growth rates directly in situ in the production equipment and feed the data into a topography simul...

Modelling of fibre holding elements in silicon

The mechanical behaviour of a fibre holding system is studied analytically and by using finite element analysis (FEA). The system consists of anisotropically etched v-grooves in which optical fibres are passively aligned and fixed by flexible holding beam

Decreasing the optical path length in an optoelectronic module using silicon micromachining

In order to decrease the optical path length of an optoelectronic module, two ways of achieving silicon mirrors with trenches defining the mirror size are presented: dicing, and dry etching. The dicing was performed with a Disco DAD 361 dicing machine. To define the dry etched trench UV-lithography on electrodeposited resist was used. The electrodeposition was performed using commercially available positive photoresist PEPR 2400 from Shipley Ltd.

Silicon fusion bond interfaces resilient to wet anisotropic etchants

The bond interface in silicon microsystems is sensitive to the subjection to wet anisotropic etchants. Fusion bond interfaces of bonded wafers resilient to potassium hydroxide or tetramethyl ammonium hydroxide etching are obtained using wafers of oxidized silicon bonded to oxidized silicon, where the bond oxide is removed by trifluoromethane plasma etching. Other investigated bond configurations initiate severe damages during etching.