<title>Piezoresistive effect: stable enough for high-accuracy sensor applications?</title>

Abstract

To date, the usefulness of piezoresistive pressure sensors is still limited by their instability and inaccuracy. Therefore, the physical protection of the sensor elements and the robustness of the output signals with respect to environmental disturbances are important issues in the design and manufacturing of piezoresistive sensors. One approach to the encapsulation of small piezoresistive sensors is to adapt the passivation techniques commonly used in microelectronic manufacturing. An ideal passivation system is one that eliminates cross- sensitivities while not affecting the transfer behavior of the sensor. In reality, however, the same physical mechanisms that prevent cross-sensitivities will generally also modify the sensor's transfer function. The paper describes how accuracy and stability of non-encapsulated silicon pressure sensors can be optimized under consideration of mechanisms connected to environmental conditions like temperature and humidity. The performance of pressure sensors as a function of passivation layer properties and climatic conditions was experimentally studied. Valuation criteria were stochastic shares of the output voltage (noise). It was found that fast changes in the ambient climate induce significant measurement errors. Experimental results will be given that suggest new conclusions regarding the physics behind instabilities in piezoresistive sensors and yield approaches for improved sensor design.