Estimation of the long-term stability of piezoresistive LTCC pressure sensors by means of low-frequency noise measurements

Abstract

In this paper we present the results of an investigation of the long-term stability of piezoresistive LTCC-based pressure sensors with the main emphasis on the effects of accelerated ageing. Noise spectroscopy was considered as a possible method for predicting the stability of the sensors’ characteristics. The experiments showed that the stability of the sensors’ offset voltage clearly relates to the low-frequency noise of the output signal: a lower noise level corresponds to a better long-term stability. An additional important finding is that the accelerated ageing that was carried out through the pressure cycling does not cause any significant increase in the sensors’ signal noise. This result suggests that the performed pressure loadings do not introduce some critical cracks in the thick-film sensing resistors, which may adversely influence the sensors’ stability. Moreover, the experiments revealed that the poor stability of the sensors, which was manifested in noticeable changes in the offset voltage and the sensitivity of some sensors after the overload pressure cycles, comes from defects that are not detectable using typical characterisation measurements and long-term stability tests. Since the unstable sensors always have a higher low-frequency noise of the output voltage in comparison with the stable sensors, the noise measurements can be described as a successful pre-screening test for a relatively quick assessment of the sensors’ long-term stability.