Integrated released beam sensor for sensing acceleration and associated methods

• US 6,028,343 A
• Filed: 10/24/1997
• Issued: 02/22/2000
• Est. Priority Date: 10/24/1997
• Status: Expired due to Term

• Current Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Inventors: Chan, Tsiu Chiu, DeSilva, Melvin Joseph
• Primary Examiner(s): Tran, Minh Loan
• Application Number:
  US08/957,568
• Time in Patent Office: 851 Days
• Field of Search: 257/415, 257/417, 257/418, 257/419, 257/254, 73/579, 73/862.59
• US Class Current: 257/417
• CPC Class Codes: B81B 2201/018 Switches not provided for in B81B2201/014 - B81B2201/016
• CPC Class Codes: B81C 1/00246 Monolithic integration, i.e. micromechanical structure and electronic processing unit are integrated on the same substrate
• CPC Class Codes: B81C 2203/0735 Post-CMOS, i.e. forming the micromechanical structure after the CMOS circuit
• CPC Class Codes: G01P 15/135 by making use of contacts which are actuated by a movable inertial mass

Abstract

An integrated circuit and method are provided for sensing activity such as acceleration in a predetermined direction. The integrated released beam sensor preferably includes a switch detecting circuit region and a sensor switching region connected to and positioned adjacent the switch detecting circuit region. The sensor switching region preferably includes a fixed contact layer, remaining portions of a sacrificial layer on the fixed contact layer, and a floating contact on the remaining portions of the sacrificial layer and having only portions thereof directly overlying the fixed contact layer and in spaced relation therefrom in a normally open position and extending lengthwise generally transverse to the predetermined direction so that the floating contact contacts the fixed contact layer responsive to acceleration in the predetermined direction. The floating contact is preferably a released beam which is released by opening a window or removing unwanted portions of the sacrificial layer. The methods of forming an integrated sensor advantageously are preferably compatible with know integrated circuit manufacturing processes, such as for CMOS circuit manufacturing, with only slight variations therefrom.

Claims

1. An integrated sensor comprising:

a switch detecting circuit region; and

a sensor switching region connected to and positioned adjacent said switch detecting circuit region, said sensor switching region including;

a plurality of floating contacts positioned adjacent and lengthwise extending outwardly from said switch detecting circuit region for defining a plurality of released beams so that each of said plurality of released beams displaces in a predetermined direction responsive to acceleration, said plurality of released beams including at least two released beams lengthwise extending outwardly from said switch detecting circuit region to different predetermined lengths and at least two released beams lengthwise extending outwardly from said switch detecting circuit region to substantially the same predetermined lengths,

at least one fixed contact layer underlying said plurality of released beams,

remaining portions of at least one sacrificial layer positioned between said at least one fixed contact layer and each of said plurality of released beams, each of said plurality of released beams being positioned in spaced relation from said at least one fixed contact layer in a normally open position, the spaced relation forming by removal of unwanted portions of the sacrificial layer, said remaining portions of the at least one sacrificial layer including at least one concave surface underlying each of said plurality of released beams, and each of said plurality of released cantilever beams contacting said at least one fixed contact layer responsive to acceleration in a predetermined direction to form a closed switch position, and

at least one insulating support plate underlying said at least one fixed contact layer, and

wherein said switch detecting circuit region generates a signal responsive to the contact of said at least one of said plurality of released beams with said at least one fixed contact layer.

2. An integrated sensor as defined in claim 1, further comprising acceleration calibrating means associated with said released cantilever beam for providing a calibrated acceleration sensed by the integrated sensor.

3. An integrated sensor as defined in claim 2, wherein said acceleration calibrating means includes a predetermined length of said released cantilever so as to substantially correspond to a selected acceleration calibration threshold.

4. An integrated sensor as defined in claim 3, wherein the selected acceleration calibration threshold comprises a portion of said fixed contact layer substantially corresponding to a region of contact of said released cantilever beam with said fixed contact layer.

5. An integrated sensor as defined in claim 1, wherein the predetermined length of the outward extent of said released cantilever beam comprises a first predetermined length, wherein said fixed contact layer extends outwardly from said CMOS switch detecting circuit region a second predetermined length, and wherein the second predetermined length is greater than the first predetermined length.

6. An integrated sensor as defined in claim 1, wherein said insulating support layer comprises a nitride layer formed on a field oxide.

7. An integrated sensor as defined in claim 1, wherein the sacrificial layer comprises an oxide layer, and wherein the released cantilever beam comprises an integrally monolithic material having a generally uniform thickness extending substantially the entire length thereof.

8. An integrated cantilever sensor for sensing acceleration in a predetermined direction, the integrated sensor comprising:

a CMOS switch detecting circuit region; and

a sensor switching region connected to and positioned adjacent and extending outwardly from said switch detecting circuit region, said sensor switching region including;

an insulating support layer,

a fixed contact layer positioned on the insulating support layer,

remaining portions of a sacrificial layer positioned on portions of said fixed contact layer, the sacrificial layer comprising an oxide layer, and

a floating contact layer on said remaining portions of the sacrificial layer and having portions thereof directly overlying said fixed contact layer and in spaced relation therefrom in a normally open position and extending lengthwise generally transverse to the predetermined direction for defining a released cantilever beam, the released cantilever beam comprising an integrally monolithic material having a generally uniform thickness extending substantially the entire length thereof, the spaced relation forming from removal of unwanted portions of the sacrificial layer, said released cantilever beam contacting said fixed contact layer responsive to acceleration in the predetermined direction to form a closed switch position, and wherein said CMOS switch detecting circuit region generates a signal responsive to contact of said released cantilever beam with said fixed contact layer.

9. An integrated sensor as defined in claim 8, wherein said fixed contact layer comprises at least one of polysilicon and a metal.

10. An integrated sensor as defined in claim 9, wherein said released cantilever beam comprises at least one of polysilicon and metal.

11. An integrated sensor as defined in claim 10, wherein said released cantilever beam extends outwardly from the switch detecting circuit region a predetermined length, and wherein said remaining portions of the sacrificial layer includes at least one concave surface underlying said floating contact layer.

12. An integrated sensor as defined in claim 11, further comprising acceleration calibrating means associated with said released cantilever beam for providing a calibrated acceleration sensed by the integrated sensor.

13. An integrated sensor as defined in claim 12, wherein said acceleration calibrating means includes a predetermined length of said released cantilever so as to substantially correspond to a selected acceleration calibration threshold.

14. An integrated sensor as defined in claim 13, wherein the selected acceleration calibration threshold comprises a portion of said fixed contact layer substantially corresponding to a region of the contact of said released cantilever beam with said fixed contact layer.

15. An integrated sensor as defined in claim 14, wherein the predetermined length of the outward extent of said released cantilever beam comprises a first predetermined length, wherein said fixed contact layer extends outwardly from said CMOS switch detecting circuit region a second predetermined length, and wherein the second predetermined length is greater than the first predetermined length.

16. An integrated sensor as defined in claim 15, wherein said insulating support layer comprises a nitride layer formed on a field oxide.