Packaging high-pressure sensors

J. Muchow, A. Kretschmann, R. Henn, K. Skrobanek, S. Finkbeiner, H.-R. Krauss, Influence of process variation on the functionality of a high pressure sensor, Design, Test, Integration and Packaging of MEMS/MOEMS, DTIP 2002, SPIE Proc 4755, Bellingham WA, USA, 2002, 143-148. 

Fig. 7.4.8 shows the results of endurance testing of a metal thin-film high-pressure sensor with the design shown in Fig. 7.4.7. Typical deviations from the ideal characteristic can be seen. The sensor has been tested in a gasoline direct injection car for 162000 km. The deviation is shown for pressures up to 140 bar and temperatures between —40 and 140 °C. Hysteresis can be seen for increasing and decreasing pressures at each measuring temperature. The maximum deviation of about 0.3% FSD demonstrates the long-term stability of the sensor package design and the thin-film technology.

The rate of sampling with piezoelectric sensors is limited by their physical characteristics and present technology to the millisecond range for applications in the liquid phase. The technique is versatile in that it can be used in a variety of locations. The solid state electronics necessary to operate the piezoelectric sensor are easily miniaturized, and data can be recorded continuously or periodically. A small computer with a reasonable memory could easily record data over long times. There may be some problems in deep-sea locations, simply because of the complications in packaging the sensor for high-pressure environments, although this problem may be surmountable. 

To develop any sensor with the potential to replace the piezoresistive pressure sensor, it is essential to impart the ability to detect the same physical quantity from very low to high pressure, to employ micromachining technology, and to produce a simple one-chip package [11]. If these goals can be achieved, the prospect of combining reduced cost with a many-fold increase in the number of pressure sensor applications per vehicle may no longer be a dream. 

Since the sensor is intended to detect very low pressures of 5 kPa, reduction in the sensing element error is important to achieve high accuracy. We therefore put some ideas into designing the sensing element glass base and the package [2]. 

While physical microsensors, i e sensors which measure physical parameters, such as temperature, pressure, acceleration etc, have reached already a high state of art, the development of chemical microsensors or analytical microprobes for the identification and quantification of chemical compounds has so far shown much less success The reason for that can be seen in the fact that in contrast to most physical sensors such as an acceleration sensor which are carefully packaged and protected from the outside, the very nature of the... 

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