Steve Reyntjens

A review of focused ion beam applications in microsystem technology

In this paper the possibilities of focused ion beam (FIB) applications in microsystem technology are reviewed. After an introduction to the technology and the operating principles of FIB, two classes of applications are described. First the subject of FIB for microsystem technology inspection, metrology and failure analysis is outlined. A procedure for cross sectioning on samples is presented, as well as some examples of how this technique can be applied to study processing results. The second part of the paper is on the use of FIB as a tool for maskless micromachining. Both subtractive (etching) and additive (deposition) techniques are discussed, as well as the combination of FIB implantation of silicon with subsequent wet etching. We will show the possibility to fabricate three-dimensional structures on a micrometre scale, and give examples of recent realizations thereof.

Design and processing experiments of a new miniaturized capacitive triaxial accelerometer

Abstract A new accelerometer design is presented, which enables accelerations to be measured along three axes by using only one seismic mass. Two versions have been designed. The larger version has an input range of ± 8 g and a relative capacitance change of about 200% (full scale). The smaller version has an input range of ±10 g and a relative capacitance change of about 100% (full scale). The dimensions are 5 mm × 4.8 mm × 1.4 mm and 2.2 mm × 2.0 mm × 1.3 mm, respectively. The chosen technology is bulk micromachining, so the seismic mass is fabricated in an anisotropic wet etch step. The etchant is aqueous KOH, saturated with isopropyl alcohol. A 〈110〉 strip corner undercutting compensation technique has been adapted. It is shown that a full three-axis accelerometer can be fabricated in silicon by adapting the state-of-the-art micromachining tools.

RASTA-real-acceleration-for-self-test accelerometer: a new concept for self-testing accelerometers

Abstract This paper reports a new innovative concept for built-in self-test systems for accelerometers. Most existing designs are based on electrostatic forces acting directly on the seismic mass, or on a thermal or piezoelectric displacement of the seismic mass. This new self-test concept is based on deliberately inducing inertial forces on the seismic mass, by imposing a known acceleration. This gives a more realistic emulation of the physical quantity that an accelerometer is supposed to measure. A “built-in shaker” is incorporated into the sensor chip. The emphasis of this contribution is on the concept of this new self-test, and on the differences with other, existing self-test systems. Furthermore, the working principle, design and fabrication of a silicon bulk micromachined accelerometer are presented. The device is the first prototype to incorporate our new self-test principles. Our intention is to use this device for a practical evaluation of the presented ideas and concepts. The sensor is fabricated in an MPW bulk micromachining process, with focused ion beam (FIB) post-processing to obtain three-dimensional features, essential to its operation. Finally, a few preliminary measurement results are added to demonstrate some of the different aspects of the device.

The characterization of a miniature silicon micromachined capacitive accelerometer

The merit of extremely small capacitive accelerometers has been widely recognized. However, with decreasing size, the characterization of and readout circuitry for these devices become increasingly complex. In this contribution, the design and processing of a miniature silicon micromachined capacitive accelerometer are presented, as well as the typical difficulties for measuring extremely small capacitances and the solutions to these problems. The obtained results are discussed.

Integrating electro-discharge machining and photolithography: work in progress

This paper presents work in progress on the integration of micro-electro-discharge machining and photolithography. It is the aim to combine these two technologies in one microsystem. The case study of an inclinometer is used to verify the possibilities of such an integration. First the inclinometer principle is briefly introduced. Also a technique to compare the mechanical performance to the calculated values is given. Then, the specific problems of manufacturing this device with electro-discharge machining and photolithography are discussed. The following aspects of inter-process compatibility are discussed: surface quality aspects, process compatibility, and inter-process alignment.

Production of seismic mass suspensions in silicon by electro-discharge machining

Currently, nearly all microcomponents are fabricated by technologies such as etching, deposition, or other photolithographic techniques. In this way, the main emphasis has been in trying to fabricate micromechanic devices from a two-dimensional image. The major challenge for the future will be the development of real three-dimensional microstructures. Electro-discharge machining is a so-called non-conventional machining technique, whereby material is removed through the erosive action of sparks. As shown in this paper, electro-discharge machining proves to be a versatile technique that is very well suited for machining complex microstructures.

Remote sensors with self-test: New opportunities to improve the performance of physical transducers

When addressing the question on how to operate sensors in a remote environment, i.e., in non-accessible places, the issue of reliability becomes of extreme importance. Especially in the case where miniaturisation is essential, often the physical geometries become that small that the sensor performance degrades to yield only very weak signal levels. Matching circuits are an essential element. Monitoring physical quantities from a remote and difficult to access location requires high standards for the sensors and their circuits involved: it is essential that the data remains reliable at all times. This is a hard requirement, and many sensors used in such applications cannot cope with such severe specifications, as there are: low drift, high stability in time, immunity to cross sensitivies, etc. This paper focuses on a double solution: first by adding circuitry improving the intelligence of the entire sensor system. Secondly, it is shown how the sensor design in itself can be modified to improve the interface circuit performance. An essential element is the addition of built-in self-test features to verify the correct operation of the sensor at any given moment in time. Crucial in these novel developments is that the measurand itself is used to verify the operation of the sensor, and not a related actuation as is done in many existing devices.

RASTA: the real-acceleration-for-self-test accelerometer

The working principle, design and preliminary measurement results of an innovative silicon bulk micromachined accelerometer with built-in self-test are reported. Unlike previous devices, this new design uses a real acceleration for its self-test. This is realized by an embedded structure: the actual accelerometer is suspended in an additional frame, and can be actuated electromagnetically.

The NanoPirani — Presumably the World’s Smallest Pressure Sensor

This abstract reports an extremely miniaturized pressure sensor, with an active area of a mere 10 × 1 µm2. Its working principle is similar to Pirani-type vacuum sensors. However, unlike vacuum sensors, the working range of the device is around atmospheric pressure.