Multi-mass MEMS motion sensor

A method of operating an inertial measurement unit comprising:

• operating an inertial measurement unit (IMU) having an integrated circuit connected to a first sensor having a first transducer and an inertial sensor having a proof mass, the IMU including an electrically conductive MEMS wafer having a frame, the MEMS wafer being fusion bonded on an inner side of an electrically conductive silicon cap wafer to form a wafer stack, wherein the electrically conductive MEMS wafer comprises a silicon-on-insulator (SOI) MEMS wafer having a device layer over an insulating layer that is over a silicon substrate, wherein the electrically conductive silicon cap wafer has an outer side with a plurality of electrical contacts, the wafer stack including the proof mass and the transducer patterned in at least a portion of the electrically conductive SOI MEMS wafer, said proof mass being positioned relative to at least one of a plurality of conductive silicon sensing electrodes in the wafer stack to sense a motion of the proof mass, the at least one of the plurality of conductive silicon sensing electrodes defining a capacitance gap between said at least one sensing electrode and the proof mass, and wherein the stack includes insulated conducting pathways extending from said electrical contacts, through the electrically conductive silicon cap wafer, and electrically connected with the electrically conductive MEMS wafer for conducting electrical signals between said plurality of conductive silicon sensing electrodes and the electrical contacts, the proof mass and the transducer being enclosed by at least the electrically conductive silicon cap wafer and by the frame of the electrically conductive MEMS wafer;
• and
• processing signals from the inertial sensor and the transducer wherein the integrated circuit includes circuitry connected to inertial sensor and the transducer to measure at least one of acceleration and angular rate.