Design optimisation of high sensitivity MEMS piezoresistive intracranial pressure sensor using Taguchi approach

MEMS piezoresistive pressure sensors have been contemporarily used to measure intracranial pressure. Since an intracranial signal is of the pulsating type, the microsensor must be very sensitive to detect these changes. The sensitivity of the existing MEMS piezoresistive intracranial pressure sensors are in the range of 2 µV/V/mmHg to 0.17 mV/V/mmHg. Factors influencing the sensitivity and linearity of the sensor include the diaphragm thickness, the shape and placement of the piezoresistors, and the doping concentration. This paper will discuss the incorporation of these factors, which were tested to obtain higher sensitivity silicon-based piezoresistive intracranial pressure sensor, while maintaining the linearity of the sensor. In order to achieve this objective, the Taguchi robust design method of L27 orthogonal array was employed. The sensing outputs of these designs, with different combinations of factors were determined through simulations using COMSOL Multiphysics. The results indicated that the diaphragm thickness and perpendicular piezoresistors play important roles in the sensitivity performance of the MEMS piezoresistive intracranial pressure sensor. The findings also showed that the doping concentration of the piezoresistors have significant effect on the linearity performance of the sensor. Consequently, the design that consolidated the 3-turns (perpendicular) and 0-turn (parallel) meander shaped piezoresistors of 10¹⁷ cm⁻³ dopant concentration on a 2 μm diaphragm thickness was found to be the optimum design, with sensitivity of 0.1272 mV/V/mmHg and linearity of 99%. This design has been proven to be an improved version for the small diaphragm piezoresistive intracranial pressure sensor.