Peter Enoksson

Low-temperature full wafer adhesive bonding

We have systematically investigated the influence of different bonding parameters on void formation in a low-temperature adhesive bonding process. As a result of these studies we present guidelines ...

Micromachined electrodes for biopotential measurements

We describe the microfabrication, packaging and testing of a micromachined dry biopotential electrode, (i.e., where electrolytic gel is not required). It consists of an array of micro-dimensioned, very sharp spikes, (i.e., needles) designed for penetration of human skin which circumvent high impedance problems associated with layers of the outer skin. The spikes are etched in silicon by deep reactive ion etching and are subsequently covered with a silver-silverchloride (Ag-AgCl) double layer. The electrode-skin-electrode impedance of dry spiked electrodes having a size of 4/spl times/4 mm/sup 2/ is reduced compared to standard electrodes using electrolytic gel and having a comparable size. Recorded low amplitude biopotentials resulting from the activity of the brain, (i.e., EEG signals) are of high quality, even for spiked electrodes as small as 2/spl times/2 mm/sup 2/. The spiked electrode offers a promising alternative to standard electrodes in biomedical applications and is of interest in research of new biomedical methods.

Micromachined flat-walled valveless diffuser pumps

The first valveless diffuser pump fabricated using the latest technology in deep reactive ion etching (DRIE) is presented. The pump was fabricated in a two-mask micromachining process in a silicon wafer polished on both sides, anodically bonded to a glass wafer. Pump chambers and diffuser elements were etched in the silicon wafer using DRIE, while inlet and outlet holes are etched using an anisotropic etch. The DRIE etch resulted in rectangular diffuser cross sections. Results are presented on pumps with different diffuser dimensions in terms of diffuser neck width, length, and angle. The maximum pump pressure is 7.6 m H/sub 2/O (74 kPa), and the maximum pump flow is 2.3 ml/min for water.

Micromachined flow-through filter-chamber for chemical reactions on beads

A new flow-through micromachined device for chemical reactions on beads has been designed, manufactured, and characterized. The device has an uncomplicated planar design and microfabrication proces ...

Deep wet etching of borosilicate glass using an anodically bonded silicon substrate as mask

Deep wet etching of borosilicate glass using an anodically bonded silicon substrate as mask is presented. Depths of m or more can be achieved very easily. The structured glass wafer can be bonded anodically on the same side to another silicon wafer, after having removed the bonded silicon mask. A lateral underetching 1.5 times larger than the depth was measured. An application using this masking technique is also presented. It consists of using the anodically bonded frame of a resonant silicon structure as a mask for deep glass etching to increase the gap between the glass wall and the resonator, thus yielding a high Q-factor.

A silicon resonant sensor structure for Coriolis mass-flow measurements

We present the first mass-flow sensor in silicon, based on the Coriolis-force principle. The sensor consists of a double-loop tube resonator structure with a size of only 9/spl times/18/spl times/1 mm. The tube structure is excited electrostatically into a resonance-bending or torsion vibration mode. A liquid mass flow passing through the tube induces a Coriolis force, resulting in a twisting angular motion phase shifted and perpendicular to the excitation. The excitation and Coriolis-induced angular motion are detected optically. The amplitude of the induced angular motion is linearly proportional to the mass flow and, thus, a measure thereof. The sensor can be used for measurement of fluid density since the resonance frequency of the sensor is a function of the fluid density. The measurements show the device to be a true mass-flow sensor with direction sensitivity and high linearity in the investigated flow range of as low as 0-0.5 g/s in either direction. A sensitivity of 2.95 (mV/V)/(g/s) and standard deviation for the measured values of 0.012 mV/V are demonstrated.

Low temperature full wafer adhesive bonding of structured wafers

In this paper, we present a technology for void free low temperature full wafer adhesive bonding of structured wafers. Benzocyclobutene (BCB) is used as the intermediate bonding material. BCB bonds well with various materials and does not release significant amounts of byproducts during the curing process. Thus void-free bond interfaces can be achieved. Cured BCB coatings have an excellent resistance to a variety of acids, alkalines and solvents and a high transparency for light across the visible spectrum, which makes it a good material for fluidic, optical and packaging applications. We demonstrate the fabrication of fluidic structures and the embedding of protruding surface structures. An important finding is that the pre-cured BCB coatings are extremely deformable and have a liquid-like behaviour during bonding.

A valve-less planar pump isotropically etched in silicon

The first valve-less diffuser fluid pump in silicon is presented. It consists of a planar double-chamber arrangement fabricated in a silicon wafer anodically bonded to a glass wafer. The pump uses fluid-directing diffuser - nozzle elements which have a depth of and a neck width of . The pump chamber diameter is 6 mm. Pump cavities and diffuser - nozzle elements are etched with an isotropic HNA silicon etch. Pumps with three different diffuser lengths are compared reaching a maximum pump capacity of and a maximum pump pressure of 1.7 m at a resonance frequency of 1318 Hz for methanol.

A high-stroke, high-pressure electrostatic actuator for valve applications

This paper presents a novel large-stroke electrostatic valve actuator for high-pressure applications. The combination of pressure balancing and flexible electrode structures ensures large flow gaps at a low actuation voltage. A simulation tool was built to evaluate the design parameters. Design specific, as well as general optimisations are performed. The model shows a 5.6 times (theoretical) performance improvement compared to earlier designs. A micromachined test structure was fabricated and evaluated. Measurement results are presented and discussed.

Highly sensitive triaxial silicon accelerometer with integrated PZT thin film detectors

This paper reports the first micromachined triaxial single-mass accelerometer with integrated piezoelectric thin film detectors. In addition, the design has a much higher sensitivity than previously presented approaches and is significantly smaller. The keystones of the performance are the use of the highly sensitive PZT material and the deep reactive ion etching (DRIE)-based process flow utilizing silicon-on-insulator (SOI) wafers. The accelerometer consists of a 1.2 mg seismic mass, supported by four 8 μm thick spokes. The charge sensitivity in the vertical direction is 22 pC/g and in the parallel direction 8 pC/g.