Piezoresistive strain concentrator

• US 7,392,716 B2
• Filed: 01/23/2006
• Issued: 07/01/2008
• Est. Priority Date: 11/30/2004
• Status: Active Grant

• Current Assignee: PCB Piezotronics of North Carolina, Inc. (Amphenol Corporation)
• Original Assignee: Endevco Corporation (Illinois Tool Works Inc.)
• Inventors: Wilner, Leslie Bruce
• Primary Examiner(s): Lefkowitz; Edward
• Assistant Examiner(s): DUNLAP, JONATHAN M
• Application Number:
  US11/338,519
• Publication Number:
  US 20060117871A1
• Time in Patent Office: 890 Days
• Field of Search: 737/54, 738/626.27
• US Class Current: 73/862.627
• CPC Class Codes: G01L 1/2231 the supports being disc- or ring-shaped, adapted for measuring a force along a single direction
• CPC Class Codes: G01L 19/141 Monolithic housings, e.g. molded or one-piece housings
• CPC Class Codes: G01L 9/0042 Constructional details associated with semiconductive diaphragm sensors, e.g. etching, or constructional details of non-semiconductive diaphragms details about the integration or bonding of piezoresistor in or on the diaphragm G01L9/0052 and G01L9/0057 respectively
• CPC Class Codes: G01L 9/0054 integral with a semiconducting diaphragm

Abstract

A piezoresistive device is provided for sensing mechanical input and converts mechanical movement of at least two relatively movable parts into an electrical output. A silicon substrate is provided that is oriented in the (100) plane and has an n-type impurity. A gap extends across a portion of the substrate. The gap defines the at least two relatively moveable parts. A flexible cross-section connects the at least two relatively moveable parts. The cross-section is made of the same material as the substrate. At least one strain sensitive element is provided on a surface of the silicon substrate, is aligned in a [110] direction and includes a p-type impurity. The strain sensitive element has two end portions interconnected by an intermediate neck portion. The neck portion is supported on a structure that concentrates strain. The structure extends across the gap and has vertical walls that extend to the cross-section in the gap. The structure is made of the same material as the substrate. At least one electrode is electrically connected to the end portions. The at least one electrode detects changes in electrical resistance between the end portions when the neck portion is subjected to stress in a direction of a current through the strain sensitive element that results from the relative movement of the at least two relatively moveable parts.

Claims

1. A piezoresistive device for sensing mechanical input and converting mechanical movement of at least two relatively movable parts into an electrical auto output, comprising:

a substrate of silicon carbide oriented in a (0001) plane, wherein silicon carbide is a single crystal material;

a gap extending across a portion of the substrate defining the at least two relatively moveable parts and a flexible cross-section that connects the at least two relatively moveable parts, the cross-section being made of a same material as the substrate;

at least one strain sensitive element at a surface at the substrate, the at least one strain sensitive element having two end portions interconnected by an intermediate neck portion, the neck portion being supported on a structure that concentrates strain, wherein changes are detected in electrical resistance when the neck portion is subjected to stress in a direction of current through the strain sensitive element resulting from relative movement, the structure extending across the gap and having vertical walls extending to the cross-section in the gap, the at least one strain sensitive element being made of the same material as the substrate, wherein the at least one strain sensitive element is a layer of silicon carbide; and

at least one electrode electrically connected to the end portions configured to detect changes in an electrical resistance between the end portions created when the neck portion is subjected to stress in a direction of a current through the at least one strain sensitive element that results from a relative movement of the at least two relatively moveable parts.

2. The device of claim 1, wherein the cross-section defines an elastic hinge parallel to the substrate.

3. The of claim 1, wherein the at least two relatively moveable parts tilt relative to each other about the elastic hinge portion of the cross-section.

4. The device of claim 1, wherein the device is included in at least one of, an accelerometer, pressure sensing device, catheter, microphone, weighing device, and a device to measure relative humidity.

5. A piezoresistive device for sensing mechanical input and converting mechanical movement of at least two relatively movable parts into electrical output, comprising:

a substrate of silicon carbide oriented in a (0001) plane, wherein silicon carbide is a single crystal material;

a gap extending across a portion of the substrate defining the at least two relatively moveable parts and a flexible cross-section that connects the at least two relatively moveable parts, the cross-section being made of a same material as the substrate;

at least two strain sensitive elements at a surface of the substrate and connected in series, each of the at least two strain sensitive elements having two end portions interconnected by an intermediate neck portion across said gap, each neck portion being supported on a corresponding structure that concentrates strain, wherein chances are detected in electrical resistance when the neck portion is subjected to stress in a direction of current through the strain sensitive element resulting from relative movement, the corresponding structure extending across the gap and having verticle walls extending to the cross-section in the gap, the at least two strain sensitive elements being made of the same material as the substrate, wherein each strain sensitive element is a layer of silicon carbide; and

at least one electrode electrically connected to the end portions configured to detect changes in an electrical resistance between the end portions when the neck portions are subjected to stress in a direction of a current through the at least two strain sensitive elements that results from a relative movement of the at least two relatively moveable parts.

6. The device of claim 5, wherein the cross-section defines an elastic hinge parallel to the substrate.

7. The device of claim 5, wherein the at least two relatively moveable parts tilt relative to each other about the elastic hinge portion of the cross-section.

8. The device of claim 5, wherein six strain sensitive elements are provided on the surface of the substrate of silicon carbide and connected in series.

9. The device of claim 8 wherein each strain sensitive element has a small width of about 4 microns.

10. The device of claim 5, wherein the device is included in at least one of, an accelerometer, pressure sensing device, catheter, microphone, weighing device, and a device to measure relative humidity.

11. A piezoresistive device for sensing mechanical input and converting mechanical movement of at least two relatively movable parts into electrical output, comprising:

a substrate of silicon carbide oriented in a (0001) plane;

wherein silicon carbide is a single crystal material;

a triple-bossed diaphragm on one side of the substrate the triple-bossed diaphragm having a rim, diaphragm extending across the rim, a central boss and two outer bosses on either side of the central boss and inside of the rim;

four gaps extending across a portion of the substrate defining the at least two relatively moveable parts and flexible cross-sections extending between corresponding gaps such that two of the gaps are located outside the outer bosses and two of the gaps are located on either side of the central boss and inside of either outer boss;

four strain sensitive element pairs provided at a surface of the substrate around the gaps, each pair having two strain sensitive elements connected n a series, each of a strain sensitive element having two end portions interconnected by an intermediate neck portion, the neck portion being supported on a corresponding structure that concentrates strain, wherein changes are detected in electrical resistance when the neck portion subjected to stress in a direction of current through the strain sensitive element resulting from relative movement, the four strain sensitive element pairs extending across the gap and having vertical was extending to the cross-section in the corresponding gap, the four strain sensitive element pairs connected as a bridge circuit, wherein each strain sensitive element is a layer of silicon carbide;

electrical connections to the bridge circuit configured to measure an unbalance resulting from changes in a resistance of the four strain sensitive element pairs caused by tilting of the outer bosses in response to pressure applied perpendicular to the device and

a support a single, crystal material and configured to provide mechanical rigidity and electrical connection.

12. The device of claim 11 wherein the cross-section defines an elastic hinge parallel to the substrate.

13. The device of claim 11, wherein the at least two relatively moveable parts tilt relative to each other about the elastic hinge portion of the cross-section.

14. The device of claim 11, further comprising an insulated crossover at the gage level on the substrate such that the strain sensitive elements are connected to terminals at the corners of the rim in a bridge circuit sequence such that adjacent legs of the bridge have opposite senses of strain.

17. The device of claim 11, wherein the strain sensitive elements are sealed to a surface mount terminal by thermocompression bonds.

18. The device of claim 11, wherein the device is included in at least one of, an accelerometer, pressure sensing device, catheter, microphone, weighing device, and a device to measure relative humidity.

15. The device of rim 11, further comprising a torsion bar conduction path from the tilting boss to the terminal on the rim.

16. The device of dawn 11, further comprising a reference cavity sealed by thermocompression bonds to capture a reference pressure.