An integrated circuit apparatus (100, 200, 1200) comprising: an integrated circuit substrate (110, 209, 1230); a cavity; a suspended membrane (120, 203) forming a wall of a chamber that is at least partially in the cavity and that has a variable volume for containing gas, the membrane (120, 203) having a plurality of openings (124, 126, 207, 208) therein configured and arranged to pass gas into and out of the chamber, the membrane (120, 203) being configured and arranged to move and thereby change the volume of the chamber in response to an actuation force applied to the membrane (120, 203), the membrane (120, 203) comprising a top metal electrode (201, 1244); an actuator configured and arranged to cause movement of the membrane (120, 203) relative to the cavity, in response to an electrical control signal carried in the integrated circuit substrate (110, 209, 1230), and thereby change the volume of the chamber and generate a gas pressure inside the chamber that is different than a gas pressure outside the chamber, wherein the top metal electrode (201, 1244) and a bottom metal electrode (202, 1239) are operated to actuate the membrane (120, 203) with a bias applied to the top metal electrode (201, 1244) and the bottom metal electrode (202, 1239); and a sensor configured and arranged to detect, in response to the change in volume, a frequency-based characteristic of the membrane (120, 203) and therein provide an indication of the gas pressure in the chamber, wherein an impedance indicated between the top metal electrode (201, 1244) and the bottom metal electrode (202, 1239) is used as an indication of the frequency-based characteristic of the membrane (120, 203), wherein the integrated circuit substrate (110, 209, 1230) comprises a CMOS circuit and the bottom metal electrode (202, 1239) on the integrated circuit substrate (110, 209, 1230) connects to a CMOS top metal layer by means of an interconnect via. an integrated circuit substrate (110, 209, 1230); a cavity; a suspended membrane (120, 203) forming a wall of a chamber that is at least partially in the cavity and that has a variable volume for containing gas, the membrane (120, 203) having a plurality of openings (124, 126, 207, 208) therein configured and arranged to pass gas into and out of the chamber, the membrane (120, 203) being configured and arranged to move and thereby change the volume of the chamber in response to an actuation force applied to the membrane (120, 203), the membrane (120, 203) comprising a top metal electrode (201, 1244); an actuator configured and arranged to cause movement of the membrane (120, 203) relative to the cavity, in response to an electrical control signal carried in the integrated circuit substrate (110, 209, 1230), and thereby change the volume of the chamber and generate a gas pressure inside the chamber that is different than a gas pressure outside the chamber, wherein the top metal electrode (201, 1244) and a bottom metal electrode (202, 1239) are operated to actuate the membrane (120, 203) with a bias applied to the top metal electrode (201, 1244) and the bottom metal electrode (202, 1239); and a sensor configured and arranged to detect, in response to the change in volume, a frequency-based characteristic of the membrane (120, 203) and therein provide an indication of the gas pressure in the chamber, wherein an impedance indicated between the top metal electrode (201, 1244) and the bottom metal electrode (202, 1239) is used as an indication of the frequency-based characteristic of the membrane (120, 203), wherein the integrated circuit substrate (110, 209, 1230) comprises a CMOS circuit and the bottom metal electrode (202, 1239) on the integrated circuit substrate (110, 209, 1230) connects to a CMOS top metal layer by means of an interconnect via.