Abstract
Piezoresistive silicon pressure sensor samples were thermally cycled after being consecutively packaged to three different levels. These started with the absolute minimum to allow measurement of the output and with each subsequent level incorporating additional packaging elements within the build. Fitting the data to a mathematical function was necessary both to correct for any testing uncertainties within the pressure and temperature controllers, and to enable the identification and quantification of any hysteresis. Without being subjected to any previous thermal preconditioning, the sensors were characterized over three different temperature ranges and for multiple cycles, in order to determine the relative contributions of each packaging level toward thermal hysteresis. After reaching a stabilised hysteretic behaviour, 88.5% of the thermal hysteresis was determined to be related to the bond pads and wire bonds, which is likely to be due to the large thermal mismatch between the silicon and bond pad metallisation. The fluid-fill and isolation membrane contributed just 7.2% of the total hysteresis and the remaining 4.3% was related to the adhesive used for attachment of the sensing element to the housing. This novel sequential packaging evaluation methodology is independent of sensor design and is useful in identifying those packaging elements contributing the most to hysteresis.
Highlights
Piezoresistive single crystal silicon (Si) based sensors are widely used to measure pressure in numerous applications, including aerospace, oil and gas, and industrial [1,2,3,4]
To the authors’ knowledge, this study is the first to consecutively package the same sensing element (SE) to increasing levels in order to determine the relative contribution of the packaging elements to thermal increasing levels in order to determine the relative contribution of the packaging elements to thermal hysteresis
To the authors’ knowledge, this study is the first to do a systematic of increasing fitting orders on revealing thermal hysteresis, and to use the same fitting order on evaluation of increasing fitting orders on revealing thermal hysteresis, and to use the same fitting consecutively packaged sensors to compare the relative contributions of packaging elements
Summary
Piezoresistive single crystal silicon (Si) based sensors are widely used to measure pressure in numerous applications, including aerospace, oil and gas, and industrial [1,2,3,4] Their transduction mechanism is based upon the external pressure causing the deflection of a thinned section of Si that forms a diaphragm. Enhanced models, which account for both the anisotropy of Si and thermal effects on the piezoresistivity, have been recently published [13,14,15,16,17,18,19] This provides an excellent basis for initial sensor design, but cannot be solely relied upon to accurately predict the output of a complete pressure sensor. This is because the isolated sensing element (SE), which the theoretical models describe, cannot function as a practical pressure sensor if it is not mechanically supported and protected, and its electrical output made accessible to Sensors 2020, 20, 1727; doi:10.3390/s20061727 www.mdpi.com/journal/sensors
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