Miniature pressure transducer for medical use and assembly method

• US 4,023,562 A
• Filed: 09/02/1975
• Issued: 05/17/1977
• Est. Priority Date: 09/02/1975
• Status: Expired due to Term

• Current Assignee: Case Western Reserve University
• Original Assignee: Case Western Reserve University
• Inventors: Ko, Wen H., Hynecek, Jaroslav, Yon, Eugene T.
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US05/609,382
• Time in Patent Office: 623 Days
• Field of Search: 128/2 R, 128/2 S, 128/2.05 D, 128/2.05 E, 128/2.05 P, 128/2.06 E, 128/2.05 R, 128/2 P, 73/398 R, 73/406, 73/408, 73/420, 73/DIG. 4, 29/577, 29/580, 29/590, 29/613, 29/25.35
• US Class Current: 600/561
• CPC Class Codes: A61B 5/03 Detecting, measuring or recording fluid pressure within the body other than blood pressure, e.g. cerebral pressure; Measuring pressure in body tissues or organs A61B5/205 takes precedence
• CPC Class Codes: G01L 19/0061 Electrical connection means
• CPC Class Codes: G01L 9/0054 integral with a semiconducting diaphragm

Abstract

A fluidtight, hermetically sealed, miniature transducer adapted to be inserted into the human body and useful for directly monitoring internal fluid or pneumatic pressures within the human body is disclosed. Semiconductor strain gauge elements constituting a piezoresistive bridge are formed by diffusion on the surface of one side of an integral flexible, rectangular, silicon diaphragm area of a single crystal silicon base. A single crystal silicon cover is eutectically bonded to the base by a metallic laminate seal. The base, cover, and seal define an evacuated fluidtight chamber containing the strain gauge elements. Electrical conductors, which include diffused conductor paths under an insulating oxide layer, extend from the piezoresistive bridge to contact pads outside the fluidtight chamber. The contact pads can be connected to a readout device for electrically measuring the pressure differential between the evacuated chamber and fluid external to the transducer as a function of time.

Claims

1. A transducer for measuring fluid or pneumatic pressure comprising a semiconductor base member, at least a portion of said base member being a thin flexible diaphragm, a piezoresistive bridge formed on a surface of a side of said diaphragm, said bridge having at least one electrical parameter which changes in response to flexing of said surface of said diaphragm, a cover member, a seal bonding said cover member to said base member, said members and said seal defining a fluidtight chamber containing said piezoresistive bridge, and electrical conductor means extending from said piezoresistive bridge to a point external to said fluidtight chamber, said conductor means including diffused conductor paths on said base member where said conductor means passes from said fluidtight chamber to said point external to said fluidtight chamber.

2. A transducer according to claim 1, wherein said base member and said cover member have generally identical thermal coefficients of expansion and contraction.

3. A transducer according to claim 2, wherein said fluidtight chamber is evacuated.

4. A transducer according to claim 3, wherein said seal and said base member are separated by a layer of electrical insulation material.

5. A transducer according to claim 4, wherein said insulation material covers said piezoresistive bridge and said conductor paths.

6. A transducer for measuring fluid or pneumatic pressure comprising a single crystal, silicon base member with an integral flexible diaphragm, a diffused piezoresistive bridge formed on a surface of said diaphragm, said bridge having at least one electrical parameter which changes in response to the deformation of said surface of said diaphragm, a single crystal, silicon cover member, a laminate seal bonding said cover member to said base member, said members and said seal defining an evacuated fluidtight chamber containing said piezoresistive bridge, and electrical conductor means extending from said piezoresistive bridge to a point external to said fluidtight chamber, said conductor means including diffused conductor paths on said base member where said conductor means passes from said fluidtight chamber to said point external to said fluidtight chamber.

7. A transducer according to claim 6, wherein said diaphragm is rectangular.

8. A transducer according to claim 7, wherein said diaphragm has a rectangle ratio of approximately 3:

1.

9. A transducer according to claim 6, wherein said laminate seal includes at least one metal alloy which eutectically bonds said cover member and said base member together.

10. A method of assembling a pressure transducer comprising the steps of:

forming a piezoresistive bridge and diffused conductor paths on the surface of one side of a generally planar semiconductor base member, at least a portion of said base member being a thin flexible diaphragm, said bridge having at least one electrical parameter which changes in response to flexing of diaphragm;

electrically connecting said piezoresistive bridge to one end of said diffused conductor paths;

forming a cup-shaped cover member, said cup member being composed of semiconductor material identical to that of the base member; and

eutectically bonding said members together with a metallic alloy seal such that said piezoresistive bridge is enclosed in a fluidtight evacuated chamber with said conductor paths extending from said fluidtight chamber to a point external to said fluidtight chamber.