System and method for a three-axis MEMS accelerometer

A three-axis accelerometer for determining components of an inertial force vector with respect to an orthogonal coordinate system, the accelerometer comprising:

• a sensor die made of a semiconductor substrate comprising:
• a frame element;
• a proof mass element;
• an elastic element mechanically coupling the frame and the proof mass, wherein the inertial force applied to proof mass induces stress in the elastic element;
• more than three stress-sensitive IC components, which are used for creating more than one sets of three stress-sensitive IC components and integrated into local areas of the elastic element;
• a digital signal processing circuit for processing of signals from stress-sensitive IC components;
• whereby stress-sensitive IC components generate signals resulting from the stresses in the elastic element and at least one set of three stress-sensitive IC components is used for determining an unknown applied force vector components and the remaining sets of three stress-sensitive IC components are used for increasing the accuracy and reliability of the three-axis accelerometer.

A method of determining three components of an unknown applied inertial force with respect to an orthogonal coordinate system and increasing accuracy of three-axis accelerometer, said method comprises the steps of:

• providing a semiconductor sensor chip having side 1 and comprising a frame element, a proof mass element and an elastic element mechanically coupling the frame and proof mass element;
• providing more than three stress-sensitive IC components each integrated into a local area of the elastic element;
• orienting the orthogonal coordinate system such that two axes are located in the plane of side 1 and the third axis is perpendicular to side 1;
• applying a known inertial force to the sensor chip along the orthogonal axes for calibration;
• determining the matrix of offsets and matrix of sensitivities of all stress-sensitive IC components to the orthogonal components of the known applied force;
• creating sets of independent systems of three equations based on a number of non-repeating combinations from the number of stress-sensitive IC components in threes;
• each independent combination of three stress-sensitive IC components corresponds to each independent systems of three equations;
• each independent system of three equations contains three unknown variables corresponding to orthogonal components of unknown applied force, (1×3) matrix of offsets and (3×3) matrix of sensitivities of the corresponding stress-sensitive IC components to orthogonal components of the known inertial force vector;
• determining three orthogonal components of the unknown applied inertial force by solving at least one independent system of three equations;
• increasing accuracy of determining three components of an applied inertial force by solving other independent systems of three equations and by averaging the results of independent solutions.