THREE-AXIS INTEGRATED MEMS ACCELEROMETER

• US 20060272413A1
• Filed: 06/04/2005
• Published: 12/07/2006
• Est. Priority Date: 06/04/2005
• Status: Active Grant

• Current Assignee: Nickolai Belov, Vladimir Vaganov
• Original Assignee: Nickolai Belov, Vladimir Vaganov
• Inventors: Belov, Nickolai, Vaganov, Vladimir
• Granted Patent: US 7,318,349 B2
• Time in Patent Office: Days
• US Class Current: 73/514.10
• CPC Class Codes: G01P 15/123 by piezo-resistive elements, e.g. semiconductor strain gauges
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: G01P 2015/084 the mass being suspended at more than one of its sides, e.g. membrane-type suspension, so as to permit multi-axis movement of the mass

Abstract

3D accelerometer for measuring three components of inertial force (or acceleration) vector with respect to an orthogonal coordinate system, which has high sensitivity due to a big proof mass located within a cavity beneath the surface of the sensor die. The size of the cavity and the size of the proof mass exceed the corresponding overall dimensions of the elastic element. The sensor structure occupies a very small area at the surface of the die increasing the area for ICs need to be integrated on the same chip.

Claims

1. 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 having side 1 and opposite side 2, die made of a semiconductor substrate comprising;

a frame element;

a proof mass element having overall dimensions;

an elastic element having overall dimensions and mechanically coupling the frame element and the proof mass element on side 1, wherein an inertial force applied to the proof mass element induces stress in the elastic element;

at least one cap mechanically coupled to the frame element from at least the side 2 of the sensor die, and

whereby;

the semiconductor substrate consists of layer 1 and layer 2 of semiconductor materials attached to each other and has at least one cavity at the interface between the layer 1 and layer 2, the cavity has overall dimensions and the overall dimensions of the cavity in the plane of side 1 of the sensor die exceed the corresponding overall dimensions of the elastic element and

at least two overall dimensions of the proof mass element exceed the corresponding overall dimensions of the elastic element.

2. A three-axis accelerometer of claim 1, further comprising a proof mass, thickness of which exceeds the frame thickness but is less than the combined thickness of the frame and the cap coupled to the side 2 of the sensor die.

3. A three-axis accelerometer of claim 1, wherein the elastic element has at least one opening in its thickness dimension.

4. A three-axis accelerometer of claim 1, wherein the elastic element has at least two portions of different thickness.

5. A three-axis accelerometer of claim 1, where the elastic element in the sensor chip has the shape chosen from the group of shapes consisting essentially of:

ring, perforated ring, n-sided faceted geometry, beams, tethers, springs and combinations of these shapes.

6. A three-axis accelerometer of claim 1, wherein the elastic element contains at least one stress concentrating element having a shape selected from a group of shapes consisting essentially of:

V-groove, trapezoidal groove, a groove with the sidewalls forming an angle in the range of 85 degrees to 95 degrees with the surface of the elastic element, pyramid, prism, ridge, rim, boss, mesa and combinations of these shapes.

7. 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 having side 1 and opposite side 2, die made of a semiconductor substrate comprising;

a frame element consisting of part 1 having thickness and part 2 having uniform thickness smaller than thickness of part 1 and surrounded by part 1;

a proof mass element;

an elastic element having thickness and mechanically coupling the frame element and the proof mass element on side 1 of the sensor die, wherein the inertial force applied to proof mass induces stress in the elastic element;

mechanical-stress sensitive IC components located on elastic element;

at least one electronic circuit coupled to accelerometer,

whereby at least one electronic circuit is integrated within part 2 of the sensor die frame.

8. A three-axis accelerometer of claim 7 further comprising at least one electronic circuit integrated within proof mass element on the surface 1 of the sensor die.

9. A three-axis accelerometer of claim 7, wherein at least one electronic circuit providing one or more functions from a group of functions consisting essentially of:

sensing inertial force, sensing acceleration, sensing vibration, sensing tilt, providing reference signals, signal conditioning, signal amplification, multiplexing, signal filtering, analog-to-digital conversion, analog-to-frequency conversion, acceleration dependent oscillation, signal processing, synchronization, voltage stabilization, current stabilization, memory, temperature compensation, digital interface, power management, transmitting and receiving radio-signals.

10. A three-axis accelerometer of claim 7, wherein at least one electronic circuit comprises components used in other sensors chosen from the group of sensors consisting essentially of:

temperature sensor, magnetic sensor, radiation sensor, optical sensor, image sensor, humidity sensor, chemical sensor, pressure sensor, tactile sensor, force sensor, acoustic sensor, angular rate sensor, mass flow sensor.

11. A three-axis accelerometer of claim 7, wherein the stress sensitive IC components are chosen from the group consisting essentially of:

a piezoresistor, a p-n junction, a tunnel diode, a Schottky diode, a shear stress component, a piezoresistive Wheatstone bridge, a MOS transistor, a complementary pair of CMOS transistors, a bipolar transistor, a pair of p-n-p and n-p-n bipolar transistors, a bipolar transistor and at least one piezoresistor connected to transistor, a MOS transistor and at least one piezoresistor connected to transistor, a bipolar transistor circuit, and a CMOS transistor circuit.

12. A three-axis accelerometer for determining components of an inertial force vector with respect to an orthogonal coordinate system within a range of measurements, the accelerometer comprising:

a sensor die having side 1 and opposite side 2, die made of a semiconductor substrate comprising;

a frame element;

a proof mass element;

an elastic element having thickness and mechanically coupling the frame and the proof mass on side 1, wherein the inertial force applied to proof mass causes displacement of the proof mass element and induces stress in the elastic element not exceeding critical stress and the elastic element creates a restoring force applied to the proof mass;

at least one cap mechanically coupled to the frame element from at least side 2 of the sensor chip;

at least four mechanical stops having contact area and characterized by a specific sticking force per unit area originating within a contact area between a contact surface of stops and a contact surface of the other parts of accelerometer at the moment of contact;

whereby the at least four mechanical stops;

limit linear and angular displacements of a proof mass element caused by inertial force applied in any direction;

have contacting area smaller than the ratio of the restoring force at the moment of contact to the specific sticking force and;

have the distance between the contact surface of stops and a contact surface of the other parts of accelerometer greater than the displacement of the proof mass corresponding to the range of measurement plus the additional displacement of the proof mass creating the restoring force greater than the specific sticking force multiplied by the contact area of the stops and smaller than the displacement of the proof mass corresponding to the critical mechanical stress in the elastic element.

13. A three-axis accelerometer of claim 12, whereby:

a frame element consists of part 1 having thickness and part 2 having uniform thickness smaller than thickness of part 1 and surrounded by part 1; and

mechanical stops are located at the elements of the sensor microstructure chosen from the group consisting essentially of;

the cap mechanically coupled to the frame element from side 2 of the sensor chip;

the cap mechanically coupled to the frame element from side 1 of the sensor chip;

proof mass;

proof mass from side 2 of the sensor chip;

proof mass from side 1 of the sensor chip;

part 2 of the frame;

part 1 of the frame;

elastic element.

14. A three-axis accelerometer of claim 12, having the center of rotation of the proof mass, wherein the stops are located at such a distance from the center of rotation, which provides maximum stress in the elastic element at the moment of stop, as a result of forward displacement of the proof mass, equal to the maximum stress in the elastic element at the moment of stop, as a result of rotational displacement of the proof mass.

15. A three-axis accelerometer of claim 12, having the center of rotation of the proof mass, wherein the stops are located at such a distance from the center of rotation, which provides restoring force in the elastic element at the moment of stop, as a result of forward displacement of the proof mass, equal to the restoring force in the elastic element at the moment of stop, as a result of rotational displacement of the proof mass.

16. A three-axis accelerometer of claim 12, wherein at least one mechanical stop limits deflection of the proof mass caused by an inertial force applied in either of at least two orthogonal directions.

17. A three-axis accelerometer of claim 12, wherein at least one mechanical stop consists of two parts of different height, part 1 and part 2, part 1 limits displacement of the proof mass element under applied inertial force exceeding the measurement range in lateral X or Y directions and part 2 limits displacement of the proof mass element under applied inertial force exceeding the measurement range in normal Z direction.

18. A three-axis accelerometer of claim 15, wherein at least one mechanical stop is located inside a through-hole in the frame element and has the shape chosen from the group of shapes consisting essentially of:

mesa, pole, boss, cylinder, prism, ridge, comb structure and combinations of these shapes.

19. A three-axis accelerometer of claim 17, wherein the part 2 of at least one mechanical stop has the shape chosen from the group of shapes consisting essentially of:

mesa, pole, boss, lug, cylinder, ridge, rim and combinations of these shapes.