Silicon capacitive pressure transducer with increased modulation depth

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Implementing the potentialities of silicon capacitive pressure sensors requires the solution to a number of design-technology and structure-circuitry problems. This work demonstrates the application of three-electrode capacitive transducers in silicon capacitive pressure sensors. IC technology is shown to provide the best possibility for fabricating three-electrode capacitive transducers with linear dependence of relative impedance versus the diaphragm deflection and, hence, versus applied pressure, the electrodes being flat. It is proposed to position a movable electrode on the diaphragm. It is shown that the real dependence of the relative impedance versus applied pressure in the case of capacitive sensors with a plane diaphragm can be approximated by a straight line with sufficient precision. The area of the electrodes being 0.25 times the area of the diaphragm, the approximation error is less than 1%, while the relative deflection of the centre of the diaphragm varies from −1.0 to 0.8. The sensitivity in this case is only 15% less than the highest possible one for capacitive transducers with flat electrodes. When the relative deflection of the centre of the diaphragm varies in the ranges −1.0–0 and 0–0.3, the approximation error is less than 0.2%. Experimental results are in good agreement with a theoretical analysis of silicon sensors with plane diaphragms.