<italic>In Situ</italic> Observation of Metal Properties in a Piezoresistive Pressure Sensor

Relative Contributions of Packaging Elements to the Thermal Hysteresis of a MEMS Pressure Sensor

“…For a typical full-scale output (FSO) of 20 mV/V, this value can be expressed as 0.26%FSO. Unlike the work of Sandvand et al [21], wherein only the last cycle was used to determine the fitting coefficients, in this study, it was chosen to include all thermal cycles in the calculation of hysteresis. Taking this approach therefore includes the first few data points of the first cycle, which in the third and fourth order plots, can be seen to not follow the trend of the hysteresis in the later cycles.…”

“…Therefore, various packaging elements are required to transform the SE into a functioning sensor, but these may themselves affect the diaphragm deflection and/or the measured voltage output of the SE. While considering the SE alone was acceptable in the past, researchers and designers are recognizing the need to account for the effects of packaging elements as significant performance drivers for complete piezoresistive pressure sensors [20,21], particularly where devices are required to operate with higher precision and stability over longer operational lifetimes and within more demanding operating environments.…”

“…However, due to manufacturing tolerances and the assembly sequences, packaging will rarely impose perfectly balanced stresses that remain constant with time. The combined effects of most of these dependencies can be eliminated if the temperature of the SE is known and a mathematical fitting function [21,31] is applied to the raw voltage output to correct for any thermal contributions to the pressure signal. When the effects of these stresses cannot be compensated away, their effects will be falsely misinterpreted as pressure inputs that the sensor is designed to measure and will therefore negatively impact the performance of the sensor.…”

“…There have been a number of published studies on thermal hysteresis of piezoresistive pressure sensors [21,31,34,35]. All investigated fully packaged sensors, and to the authors' knowledge, none have investigated the relative contributions of the packaging elements involved in a particular design Sensors 2020, 20, 1727 3 of 19 to the overall hysteresis.…”

“…Unfortunately, neither details of the number of pressure and temperature cycles used to obtain the fitting function, nor its mathematical description, were presented. Sandvand et al [21] used a linear regression applied to the third thermal cycle to measure the hysteresis effect due to a 0.8 µm-thick Aluminium (Al) metallisation layer deposited directly on top of the piezoresistors in an absolute SE designed for pressures up to 100 kPa. These SEs were glass frit bonded to a Si stress isolation layer, which itself was glass frit bonded to a TO-8 header.…”