Lars Tenerz

Fracture testing of silicon microelements in situ in a scanning electron microscope

Fracture testing of silicon cantilever beams (thicknesses 10–20 μm) was performed in situ in a scanning electron microscope by means of an equipment specially designed for this purpose. Beams of various sizes and orientations (〈011〉 and 〈001〉) were manufactured in Si (100) wafers by two different micromachining procedures. The beams were tested by simple bending to fracture, and a number of fundamental fracture parameters were determined from an analytical model of elastic fracture. To verify its validity, the model was utilized to evaluate an experimental E modulus, which was found to agree well with previous results. Fracture limits, fracture strains, and initiating flaw sizes were determined. The maximum fracture limit was very high; about 10 GPa. The strengths of different beams scattered from this value down to practically zero strength, with an average close to 4 GPa. The corresponding fracture strains and initiating flaw sizes were 6% and 3 nm, respectively (maximum strength), and 2% and 17 nm (ave...

Etching roughness for (100) silicon surfaces in aqueous KOH

The quality of vertical roughness produced by the etching of Si in aqueous KOH has been studied by varying several experimental parameters such as molarity, time of etching, temperature, and stirring. We note that at room temperature, unstirred etching is smoother at low and high molarities, and etch rate and roughness both peak near 5–6 M. With no stirring, roughness increases as a function of etch time, then levels off. With stirring, roughness decreases, especially around the peak etch rate near 5–6 M. For a fixed molarity like 5 M, unstirred etching becomes smoother with increasing temperature even as the etch rate increases rapidly. Such results suggest that masking by hydrogen bubbles or silicate etch products is the principle origin of vertical roughness. Bubble properties as a function of molarity and stirring (as determined from electrolysis experiments) are used to suggest a pseudo‐masking model to explain some roughness properties.

A batch-fabricated non-reverse valve with cantilever beam manufactured by micromachining of silicon

A batch-fabricated non-reverse valve has been manufactured in silicon with micromachining tools, i.e., electrochemical doping-selective etching in KOH and anisotropic etching in EDP. The valve simply consists of a cantilever beam that can take two positions, one letting a gas or a fluid through the valve, the other forced by the pressure to close on of the two inlet holes. The valve features fast response, small size, batch manufacturing and small dead volumes, and also shows an application of the mechanical strength of silicon. A simple theory is used to predict the basic characteristics of the valve.

Fabrication of three-dimensional silicon structures by means of doping-selective etching (DSE)

Abstract Despite its early discovery, doping-selective etching (DSE) of silicon sensor and actuator structures has not been widely used. The potential advantages of DSE are IC compatibility, new degrees of freedom in three-dimensional micromachining and full exploitation of the excellent mechanical properties of silicon. The mechanisms of DSE are both chemical and electrochemical in nature, and can be described as a ‘race’ between dissolution and passivation of the reaction products. The process has been monitored by studying the current-voltage characteristics of homogeneous silicon wafers. Model experiments on basic sensor structures, such as thin membranes and cantilever beams, have been performed. It is shown that the sequence in patterning the structures is crucial in determining the detailed geometry. This is partly expected due to the well-known anisotropy of alkaline etchants. Some as yet unreported effects of anisotropy will be subject to further investigations. Conclusively, DSE offers new and interesting possibilities in the fabrication of sensor and actuator elements.

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.

Fibre-optic sensors: A micro-mechanical approach

Abstract Fibre-optic sensors are examined from a micro-mechanical viewpoint. Theoretical expressions for the signal modulation of three basic designs are given, showing the relationship of geometrical parameters and optical transmission properties of multimode fibres. Intensity modulation is considered, together with various compensation schemes. The possibility of designing sensors with frequency output is pointed out. Design examples are given, together with measured performance data on sensor prototypes. One pressure sensor having an outer diameter of less than 0.5 mm for biomedical applications has been fabricated using silicon micro-machining. Another fibre-optic pressure sensor for industrial applications is described. Finally, a fibre-optic voltmeter based on a micro-mechanical light scanning element is described.

Pressure microsensor system using a closed-loop configuration

Abstract Pressure measurements in orthopaedics are hampered by the fact that the required measuring range is a factor of 20 higher than the common physiological range. A sensor system has been designed, based on a previously reported microsensor placed in a closed-loop configuration, in which the pressure across the microsensor membrane is kept constant. The backside of this membrane is connected to a pneumatic unit, with a high-pressure source and an electromagnetic valve, controlled by the output signal from the microsensor. The prototype system has excellent linearity, and a dynamic range of 67 dB, a 24 dB improvement compared with the open-loop system. Rise and fall times are 0.6 and 0.2 s, respectively, limited by the compliance and flow resistance of the pneumatic system. Recordings of intradiscal pressure have been made on animal carcasses, and on patients suffering from lumbar back pain. Intradiscal pressure measurements could, potentially, be valuable in the diagnosis and understanding of the pathogenesis of this disease.

Batch processing of laterally mobile structures in single-crystalline silicon

Abstract The introduction of elements free to move in the lateral wafer directions may have a great impact on the evolution of silicon micromechanics. Such laterally mobile structures allowing rotation and sliding motion can be used in sensor and actuator applications that have been inaccessible so far due to performance or cost limitations of present technology. This paper deals with the possibility of making these structures in single-crystalline silicon and outlines some fabrication processes using lamination of two oxidized wafers to form a sacrificial layer that will attach the mobile structure to the substrate, and a lamination of silicon surfaces to attach the overlay to the substrate. Both the mobile structure and the overlay will then have anisotropic properties, which gives new possibilities when designing three-dimensional mobile structures.

Silicon micromachined (2x2) opto coupler

Micromachining in silicon is a well established technique for manufacturing sensors and actuators. Another field is fiber alignment components such as V-grooves and reflecting mirrors. This work is aimed towards a batch fabricated opto coupler with the use of both V-grooves and perpendicular inflecting mirrors on the same silicon wafer, with a maximum utilization of the single crystalline lattice structure. Since both the (1 1 1) and (100)-etchstop planes are given by the crystal lattice structure, it is possible to obtain a well defmed 45 degree angle between the [1 10] and [100]-directions. The main function of the (2x2) coupler is that a perpendicular wall has a height that covers half the fiber core. The result is that half of the incoming light beam passes over the wall and the other half is reflected. There will obviously be some geometrical limitations for the distance between the fibers, which introduces optical loss that must be considered. The measured excess loss is 4dB above the theoretical limit.