R.E. Oosterbroek

A micromachined pressure/flow-sensor

The micromechanical equivalent of a differential pressure flow-sensor, well known in macro mechanics, is discussed. Two separate pressure sensors are used for the device, enabling to measure both, pressure as well as volume flow-rate. An integrated sensor with capacitive read-out as well as a hybrid, piezo-resistive variant is made. The fabrication processes are described, using silicon and glass processing techniques. Based on the sensor layout, equations are derived to describe the sensor behavior both statically as well as dynamically. With the derived equations, the working range of the sensor and the thermal and time stability is estimated. The computed results of the stationary behavior are verified with the measured data. A good similarity in linearity of the pressure/flow relation is found. The computed hydraulic resistance, however, differs from the measured value for water with 21%. This difference can be explained by the high sensitivity of the resistance to the resistor channel cross-section parameter in combination with the difference between the rounded etched shape and the rectangular approximation. From fluid dynamics simulations, a working range bandwidth of about 1 kHz is expected. Thermal influences on the sensor signal due to viscosity changes are in the order of 2% flow signal variation per Kelvin. From these results, it can be concluded that the sensor can be used as a low cost, low power consuming flow and pressure-sensing device, for clean fluids without particles and without the tendency to coat the channel walls. If a high accuracy is wanted, an accurate temperature sensing or controlling system is needed.

Etching methodologies in -oriented silicon wafers

New methodologies in anisotropic wet-chemical etching of -oriented silicon, allowing useful process designs combined with smart mask-to-crystal-orientation-alignment are presented in this paper. The described methods yield smooth surfaces as well as high-quality plan-parallel beams and membranes. With a combination of pre-etching and wall passivation, structures can be etched at different depths in a wafer. Designs, using the -crystal orientation, supplemented with pictures of fabricated devices, demonstrate the potential of using -oriented wafers in microsystem design.

Selective Wafer Bonding by Surface Roughness Control

Selective wafer bonding is presented as a technique for fabrication of microelectromechanical systems (MEMS) devices with movable, contacting elements, e.g., micromachined valves. The selectivity of the wafer bonding is obtained by tailoring the wafer surface microroughness. The adhesion parameter is used as the design rule for the wafer bonding technique. The technique is demonstrated with bulk micromachined check valves and a pressure actuated normally closed valve, but can be used for fabricating MEMS devices using surface micromachining processes as well. For these valves the selective fusion bonding technique turned out to be a convenient way to bond different wafer layers and a promising fabrication step with a high, reliable product yield.

Micromachining of \lbrace111\rbrace plates in oriented silicon

We introduce a new way to micromachine \lbrace111\rbrace oriented plates on \lbrace001\rbrace silicon wafers by anisotropic wet chemical etching. The process involves double-sided wafer-processing. Precision alignment, however, is only required at one side.

Designing, simulation and realization of in-plane operating micro-valves, using new etching techniques

Design, simulation, fabrication and measurement results of a new method to fabricate in-plane oriented micro valves with use of an-isotropic wet chemical etching techniques are reported. The method is very engaging due to the simplicity, low demands on cleanroom resources, high accurate controllability and wafer-thickness independence. Integration in micro systems is facilitated by the unique possibility to obtain in-plane working devices. Performed analytical and numerical simulations as well as measurements of a duckbill valve demonstrate the functionality.

A differential viscosity detector for use in miniaturized chemical separation systems

We present a micromachined differential viscosity detector suitable for integration into an on-chip hydrodynamic chromatography system. The general design, however, is applicable to any liquid chromatography system that is used for separation of polymers. The micromachined part of the detector consists of a fluidic Wheatstone bridge and a low hydraulic capacitance pressure sensor of which the pressure sensing is based on optical detection of a membrane deflection. The stand-alone sensor shows a resolution in specific viscosity of 3/spl times/10/sup -3/, in which specific viscosity is defined as the increase in viscosity by a sample, relative to the baseline viscosity of a solvent.

Utilizing the {111} plane switch-over etching process for micro fluid control applications

In this paper, new possibilities are shown to fabricate micro structures with use of a simple anisotropic wet chemical etching method. The method is very accurate, cheap and puts low demands on cleanroom facilities. Due to the possibility to obtain structures like valves which have their entrance and exit channels in one wafer in-line, the method might be very valuable for integration of different fluid handling components such as valves, channels and pumps. Several structures are fabricated and a summation of other possible designs is given. These show that exploitation of the well-known anisotropic etching methods in alkaline solutions can result in more sophisticated structures than used up to now.

New design methodologies in -oriented silicon wafers

New methodologies in anisotropic wet-chemical etching of oriented silicon allowing useful process designs combined with smart mask-to crystal-orientation-alignment are presented. The described methods yield smooth, etch-step free surfaces as well as high-quality plan-parallel beams and membranes. With a combination of pre-etching at different depths and passivation steps, structures can be etched at different levels in a wafer. Design rules using the < 100 >-crystal orientation, supplemented with examples demonstrate the high potential of using < 100 > oriented wafers in microsystem design.

Silicon and glass micromachining for μTAS

This chapter explores the micromachining of fluidic structures in silicon, and presents several examples of demonstrated functionality of devices in silicon. An often-used method for micromachining of silicon is anisotropic wet chemical etching. This is the most frequently used for the fabrication of membranes for pressure sensors. Such membranes may also serve as check valves or membranes in micropumps. The main advantage of anisotropic etching is the limited design freedom in the fabrication of channels with sharp bends but this method also allows the largest degree of freedom of structural design. Glass shows excellent chemical and optical properties and allows a variety of design possibilities. To obtain the desired microstructures in glass, batch fabrication techniques similar to those used for silicon micromachining, based on photolithography, can be used. Those processes help in achieving features with a size down to several tens of nanometers. So this method is useful for shallow structures. To fabricate micron and nano-scale structures with high yield and quality, high demands are put on the purity, uniformity of materials and surfaces and on the cleanness of the fabrication processes and fabrication environment, such that cleanroom environments and materials like silicon and glass become desirable, not only for prototype systems but also for commercial applications.

A Micro Viscosity Detector for Use in Miniaturized Chemical Separation Systems

A novel micromachined differential viscosity detector is presented that is suitable for integration with an on-chip hydrodynamic chromatography system. Viscosity detection is demonstrated using a prototype that shows a resolution in the specific viscosity of 3.0*10−3.