Micro electromechanical isolator

• US 6,417,743 B1
• Filed: 09/21/1999
• Issued: 07/09/2002
• Est. Priority Date: 09/21/1999
• Status: Expired due to Term

• Current Assignee: Teledyne Scientific & Imaging, LLC (Teledyne Technologies Incorporated)
• Original Assignee: Rockwell Science Center LLC
• Inventors: Mihailovich, Robert E., Yao, Jun J.
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): Glenn, Kimberly E
• Application Number:
  US09/400,125
• Time in Patent Office: 1,022 Days
• Field of Search: 333/192, 333/186, 333/189, 333/191
• US Class Current: 333/24.00C
• CPC Class Codes: H03H 9/462 Microelectro-mechanical filters

Abstract

The present invention relates to a micro electromechanical (MEM) isolator in which an input signal induces an output signal by means of electrically insulating mechanical motion. The MEM isolator device comprises a dielectric moveable platform suspended above a substrate by flexible beams. A drive and a control capacitor each have one electrode supported by the platform and one electrode supported by the substrate. Coupling between electrical and mechanical energies is achieved by providing an input signal to the drive capacitor to induce platform motion. When the input signal is fed to the drive capacitor, it actuates electrostatic motion of the platform resulting in a change in the value of the control capacitance. The change in the control capacitance is converted via a simple electronics circuit into an output that mirrors the input but is electrically isolated therefrom. The advantages of such a device include simple electrical isolation provided by the dielectric platform, built in signal-debounce inherent to the structure mechanics, and economical integration with silicon integrated circuits.

Claims

1. An isolator device for coupling a first signal to an output signal comprising:

A substrate;

A drive capacitor having opposing planar stationary and movable electrodes for converting said first signal to mechanical motion;

A control capacitor having opposing planar stationary and moveable electrodes for converting mechanical motion to an electrically isolated output signal responsive to said first signal; and

An electrically insulated microstructure having a selected mass and supported by a pair of beams above said substrate, said microstructure supporting said movable electrode of said drive capacitor and said movable electrode of said control capacitor so that movement of the movable electrode of said drive capacitor displaces said microstructure and said moveable electrode of said control capacitor, said microstructure determining the resonance frequency response of said isolator device.

2. The device of claim 1 further including an operational amplifier coupled to said control capacitor for converting changes in capacitance of said control capacitor to said output signal.

3. The device of claim 1 wherein said movable electrode of said drive capacitor is supported by said platform and said stationary electrode is supported by said substrate in alignment with said movable electrode such that application of said first signal to said stationary electrode actuates electrostatic motion of said movable electrode and said microstructure.

4. The device of claim 3 wherein said first signal is a digital signal.

5. The device of claim 4 wherein said microstructure, beams and moveable electrodes have a combined mass associated therewith, said mass limiting the motion of said microstructure in response to high frequency signal components of said first signal higher than said resonance frequency.

6. The device of claim 1 wherein said substrate comprises a silicon substrate coupled by an epoxy layer to a cap substrate.

7. The device of claim 6 wherein said cap substrate is coupled to said microstructure by said pair of beams.

8. An isolator device comprising:

A substrate;

An insulating movable coupling platform suspended above said substrate;

A first capacitor having a pair of opposing planar electrodes, one of said pair of electrodes supported by said coupling platform and a stationary one of said pair of electrodes supported by said substrate such that an applied digital signal to said first capacitor actuates electrostatic motion of said platform;

A second capacitor electrically isolated from said first capacitor having a pair of opposing planar electrodes, one of said pair of electrodes supported by said coupling platform and a stationary one of said pair of electrodes supported by said substrate such that motion of said platform changes the capacitance of said second capacitor; and

Circuit means for producing an output signal responsive to changes in said applied digital signal, said circuit means coupled to said second capacitor, said output signal having a resonance-limited frequency response.

9. The isolator device of claim 8 further comprising means for supporting said platform, said support means coupled to said substrate.

10. The isolator device of claim 8 further comprising a pair of beams for supporting said platform, said beams having a selected spring constant;

said isolator device having a resonance frequency determined by said beams and said platform where said resonance frequency determines a maximum data transfer rate.

11. The isolator device of claim 10 wherein said flexible beams each support at least one conductor for making an electrical connection to said movable electrode of said first and second capacitors.

12. In a signal transmission system, a system for mechanically coupling a first signal comprising a stream of digital pulses to an output electrical signal, said coupling system comprising:

A composite substrate having a silicon substrate coupled by an epoxy layer to a cap substrate;

A suspended platform coupled to said cap substrate by a pair of flexible supporting beams such that said platform is movable, relative to said composite substrate, the mass of said platform determining the resonance frequency response of said mechanical coupling system;

A drive capacitor having a planar stationary electrode coupled to said substrate and an opposing planar movable electrode coupled to said platform in proximity to said stationary electrode, at least one of said beams having an electrical conductor forming an electrical connection to said movable electrode;

said platform being laterally displaced in response to said first signal; and

Second means, coupled to said drive capacitor by said platform, for converting the lateral displacement of said platform to a second electrical signal responsive to said first signal, said second electrical signal being electrically isolated from said first signal.

13. The signal transmission system of claim 12 wherein said second converting means comprises:

A control capacitor having a planar stationary electrode and an opposing planar movable electrode, said stationary electrode of said control capacitor supported by said supporting means and said movable electrode of said control capacitor electrically isolated from said movable electrode of said drive capacitor, said movable electrode of said control capacitor supported by said platform in proximity to said stationary electrode of said control capacitor, at least one of said beams having an electrical conductor forming a connection to said movable electrode of said control capacitor such that lateral displacement of said platform changes the capacitance value of said control capacitor; and

A detection circuit coupled to said stationary and movable electrodes of said control capacitor for generating an output signal responsive to said change in the capacitance value of said control capacitor.

14. The signal transmission system of claim 12 wherein said support means comprises a silicon substrate coupled to said stationary electrodes by an epoxy layer.

15. A logical device having at least one input electrically isolated from an output, said logical device comprising:

A first micro electromechanical device having at least one electrical input coupled by a movable platform to an output;

A second micro electromechanical device having a stationary platform, said second micro electromechanical device providing a reference level; and

A comparator for comparing the output of said first micro electromechanical device with said reference level, said comparator having an output indicating the result of said comparison, said comparator having a first input connected to said first micro electromechanical device and a second input connected to said second micro electromechanical device.

16. The logical device of claim 15 wherein said electrical input further includes a drive capacitor having a stationary electrode coupled to said electrical input and a movable electrode coupled to said movable platform.

17. The logical device of claim 16 wherein said output further includes a control capacitor having a stationary electrode coupled to said comparator and a movable electrode coupled to said movable platform such that motion of said platform in response to an applied electrostatic force at said input changes the capacitance at said output of said second micro electromechanical device.

18. The logical device of claim 17 wherein said second micro electromechanical device further includes a reference capacitor having a pair of stationary electrodes, one of said stationary electrodes coupled to said movable electrode of said control capacitor and a second of said stationary electrodes coupled to coupled to said comparator;

each of said pair of stationary electrodes having dimensions substantially identical to the dimensions of said stationary and said movable electrode of said control capacitor.

19. The logical device of claim 18 wherein the size of said drive capacitor determines the resonate frequency of said logical device.