An integrated circuit apparatus comprising: an integrated circuit substrate ; a cavity ; a suspended membrane 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 having a plurality of openings therein configured and arranged to pass gas into and out of the chamber , the membrane being configured and arranged to move and thereby change the volume of the chamber in response to an actuation force applied to the membrane , the membrane comprising a top metal electrode ; an actuator configured and arranged to cause movement of the membrane relative to the cavity , in response to an electrical control signal carried in the integrated circuit substrate , 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 and a bottom metal electrode are operated to actuate the membrane with a bias applied to the top metal electrode and the bottom metal electrode ; and a sensor configured and arranged to detect, in response to the change in volume, a frequency-based characteristic of the membrane and therein provide an indication of the gas pressure in the chamber , wherein an impedance indicated between the top metal electrode and the bottom metal electrode is used as an indication of the frequency-based characteristic of the membrane , wherein the integrated circuit substrate comprises a CMOS circuit and the bottom metal electrode on the integrated circuit substrate connects to a CMOS top metal layer by means of an interconnect via. an integrated circuit substrate ; a cavity ; a suspended membrane 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 having a plurality of openings therein configured and arranged to pass gas into and out of the chamber , the membrane being configured and arranged to move and thereby change the volume of the chamber in response to an actuation force applied to the membrane , the membrane comprising a top metal electrode ; an actuator configured and arranged to cause movement of the membrane relative to the cavity , in response to an electrical control signal carried in the integrated circuit substrate , 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 and a bottom metal electrode are operated to actuate the membrane with a bias applied to the top metal electrode and the bottom metal electrode ; and a sensor configured and arranged to detect, in response to the change in volume, a frequency-based characteristic of the membrane and therein provide an indication of the gas pressure in the chamber , wherein an impedance indicated between the top metal electrode and the bottom metal electrode is used as an indication of the frequency-based characteristic of the membrane , wherein the integrated circuit substrate comprises a CMOS circuit and the bottom metal electrode on the integrated circuit substrate connects to a CMOS top metal layer by means of an interconnect via. <EOS>