Microelectromechanical system (MEMS) digital electrical isolator

• US 6,583,374 B2
• Filed: 02/20/2001
• Issued: 06/24/2003
• Est. Priority Date: 02/20/2001
• Status: Expired due to Term

• Current Assignee: Longitude Licensing Limited (Vector Capital Corporation)
• Original Assignee: Rockwell Automation Technologies Incorporated (Allen-Bradley Co., Inc.)
• Inventors: Kretschmann, Robert J., Harris, Richard D., Herbert, Patrick C., Knieser, Michael J., Dummermuth, Ernst H.
• Primary Examiner(s): Scott, J. R.
• Application Number:
  US09/788,928
• Publication Number:
  US 20020125117A1
• Time in Patent Office: 854 Days
• Field of Search: 200/181, 200/600, 257/415-420, 734/88--14, 73/39, 438/50, 438/52, 438/53, 333/101-108, 333/262, 335/5, 335/78, 324/17.R, 324/99.R, 324/259, 324/260, 310/306, 310/307, 310/309, 361/233, 361/234
• US Class Current: 200/181
• CPC Class Codes: H02N 1/008 Laterally driven motors, e.g. of the comb-drive type

Abstract

A microelectricalmechanical system (MEMS) digital isolator may be created in which an actuator such as an electrostatic motor drives a beam against a predefined force set, for example, by another electrostatic motor. When the threshold of the opposing force is overcome, motion of the beam may be sensed by a sensor also attached to the beam. The beam itself is electrically isolated between the locations of the actuator and the sensor. The structure may be incorporated into integrated circuits to provide on-chip isolation.

Claims

1. A micro-electro-mechanical system (MEMS) digital isolator, comprising:

a substrate;

an element supported by the substrate for movement between a first and second position with respect to the substrate, where at least a portion of the element between a first and second location on the element is an electrical insulator to electrically isolate the first and second locations from each other;

an actuator attached to the first portion of the element to receive an input electrical signal and exert a force dependent on the input electrical signal urging the element toward the second position;

a bias structure attached to the element to exert a predetermined opposite force on the element urging the element toward the first position; and

a sensor attached to the second portion of the element to provide an output electrical signal indicating movement of the element between the first position and the second position;

whereby an input signal of above a predetermined magnitude overcomes the opposite force to cause the element to move rapidly from the first to the second position to produce the output electrical signal electrically isolated from the input electrical signal;

wherein the sensor is selected from the group consisting of a capacitive sensor, a piezoelectric sensor, a photoelectric sensor, a resistive sensor, and an optical switching sensor.

2. The MEMS digital isolator of claim 1 wherein the actuator is selected from the group consisting of:

an electrostatic motor, a Lorenz force motor, a piezoelectric motor, a thermal-expansion motor, and a mechanical-displacement motor.

3. The MEMS digital isolator of claim 1 wherein the bias structure is selected from the group consisting of:

an electrostatic motor, a Lorenz force motor, a thermal-expansion motor, a mechanical-displacement motor, and a mechanical spring.

4. The MEMS digital isolator of claim 1 wherein the element is a beam attached to the substrate for sliding motion between the first and second positions.

5. The MEMS digital isolator of claim 4 wherein the beam moves with respect to the substrate along a longitudinal axis and including flexing transverse arm pairs attached at longitudinally opposed ends of the beam to extend outward therefrom to support the beam with respect to the substrate.

6. The MEMS digital isolator of claim 5 wherein the flexing transverse arms attached to the substrate at points proximate to the beam and where the flexing transverse arms include:

(i) cantilevered first potions having first ends attached to the beam and second ends attached to an elbow portion removed from the beam; and

(ii) cantilevered second portions substantially parallel to the first portions and having first ends attached to the substrate and second ends attached to the elbow portion;

whereby expansion of the first portion is offset by substantially equal expansion of the second portion to control the amount of stress in the beam.

7. The MEMS digital isolator of claim 5 wherein the flexing transverse arms attach to the substrate through a spring section allowing angulation of the end of the transverse arm with respect to the substrate.

8. The MEMS digital isolator of claim 5 wherein the beam and transverse arms are symmetric across a longitudinal axis.

9. The MEMS digital isolator of claim 5 including further a magnetic field crossing the beam and wherein at least one flexing transverse arm pair is conductive to receive an electrical signal and exert a force dependent on the electrical signal urging the beam toward a position.

10. The MEMS digital isolator of claim 5 including transverse extending primary capacitor plates attached to the beam and extending outward from the beam proximate to secondary capacitor plates.

11. The MEMS digital isolator of claim 10 wherein an effective area of the primary capacitor plates is equal across the longitudinal axis of the beam.

12. The MEMS digital isolator of claim 10 wherein the capacitor plates attach to the beam between the attachment points of at least two of the flexing transverse arm pairs.

13. The MEMS digital isolator of claim 10 wherein the primary capacitor plates are positioned with respect to the secondary capacitor plates so as to draw the primary capacitor plates toward the secondary capacitor plates on one side of the beam while to separate the primary capacitor plates from the secondary capacitor plates on the other side of the beam with a given motion.

14. The MEMS digital isolator of claim 10 wherein the primary capacitor plates are positioned with respect to the secondary capacitor plates so as to draw the primary capacitor plates toward the secondary capacitor plates on both sides of the beam with a given motion.

15. The MEMS digital isolator of claim 10 wherein the beam includes a first and second micro-machined layer, the first of which is insulating to provide the portion of electrical insulator in a region where the second layer is removed.

16. The MEMS digital isolator of claim 1 wherein the portion of electrical insulator of the beam is between the actuator and the bias structure.

17. The MEMS digital isolator of claim 1 wherein the portion of electrical insulator of the beam is between the bias structure and the sensor.

18. The MEMS digital isolator of claim 1 wherein the element is supported for movement along a plane of the substrate.

19. The MEMS digital isolator of claim 1 wherein the first and second locations on the element communicate with stationary terminals attached to the substrate.

21. The isolated circuit module of claim 19 wherein the actuator of the mechanical digital isolator is attached to at least one output point of the integrated circuit.

28. The MEMS digital isolator of claim 1 including further a second sensor at the first portion of the element to provide a second output electrical signal indicating movement of the element to the second position, the second output electrical signal being electrically isolated from the output electrical signal.

29. The MEMS digital isolator of claim 28 including further a second actuator at the second portion of the element to receive a second input electrical signal and exert a force dependent on the second input electrical signal urging the element toward the second position.

20. An isolated circuit module comprising:

a substrate;

a plurality of interconnected solid state electronic devices formed on the substrate into an integrated circuit having input and output points;

a mechanical digital isolator also formed on the substrate and electrically attached to at least one of the integrated circuit input and output points, the mechanical digital isolator including;

(1) an element supported by the substrate for movement between a first and second position with respect to the substrate, where at least a portion of the element between a first and second location on the element is an electrical insulator to electrically isolate the first and second locations from each other;

(2) an actuator attached to the first portion of the element to receive an input electrical signal and exert a force dependent on the input electrical signal urging the element toward the second position;

(3) a bias structure attached to the element to exert a predetermined substantially fixed force on the element urging the element toward the first position; and

(4) a sensor attached to the second portion of the element to provide an output electrical signal indicating movement of the element to the second position, the output electrical signal being electrically isolated from the input electrical signal;

whereby an input signal of above a predetermined magnitude overcomes the fixed force to cause the element to move rapidly from the first to the second position.

22. The isolated circuit module of claim 20 wherein the sensor of the mechanical digital isolator is attached to at least one input point of the integrated circuit.

23. A method of providing electrical isolation of a digital signal to a circuit employing a MEMS digital isolator of a type having:

(i) a substrate;

(ii) an element supported by the substrate for movement between a first and second position with respect to the substrate, where at least a portion of the element between a first and second location on the element is an electrical insulator to electrically isolate the first and second locations from each other;

(iii) an actuator attached to the first portion of the element to receive an input electrical signal and exert a force dependent on the input electrical signal urging the element toward second position;

(iv) a bias structure attached to the element to exert a predetermined substantially fixed force on the element urging the element toward the first position; and

(v) a sensor attached to the second portion of the element to provide an output electrical signal indicating movement of the element to the second position, the output electrical signal being electrically isolated from the input electrical signal, the method comprising the steps of;

(1) identifying a logical threshold for an input signal beyond which a logical true is indicated and beneath which a logical false is indicated;

(2) adjusting the bias structure to exert a fixed force on the elements toward the first position sufficient so that the actuator cannot move the element toward the second position for input signals beneath the threshold; and

(3) providing an output logical true signal only with movement of the element to the second position.

24. The method of claim 23 wherein the biased device is an electrostatic motor and the force is adjusted by changing a voltage on the electrostatic motor.

25. The method of claim 23 wherein the threshold is a voltage level and wherein the actuator and bias structure are matched electrostatic motors and wherein the voltage on the bias structure is set to the threshold voltage level.

26. The method of claim 23 wherein the bias structure is a Lorenz force motor and the force is adjusted by changing a current through the Lorenz force motor.

27. The method of claim 25 wherein the threshold is a current level and wherein the actuator and bias structure are matched Lorenz motors and wherein the voltage on the bias structure is set to the threshold current level.