Combined absolute differential transducer

• US 7,057,247 B2
• Filed: 12/12/2001
• Issued: 06/06/2006
• Est. Priority Date: 12/12/2001
• Status: Active Grant

• Current Assignee: Kulite Semiconductor Products Inc
• Original Assignee: Kulite Semiconductor Products Inc
• Inventors: Kurtz, Anthony D., Ned, Alexander A.
• Primary Examiner(s): Hu, Shouxiang
• Application Number:
  US10/016,035
• Publication Number:
  US 20030107096A1
• Time in Patent Office: 1,637 Days
• Field of Search: 257417-419, 257/415, 257/684, 257/710, 438/53, 438 50- 51, 438/456
• US Class Current: 257/419
• CPC Class Codes: G01L 13/025 using diaphragms
• CPC Class Codes: H01L 21/2007 Bonding of semiconductor wafers to insulating substrates or to semiconducting substrates using an intermediate insulating layer H01L21/2011 takes precedence; bonding of semiconductor wafers to semiconductor wafers for junction formation H01L21/187

Abstract

There is disclosed a combined absolute differential pressure transducer which consists of two sensors made from the same wafer silicon and selected to be adjacent to each other on the wafer. Since the same pressure is applied to the boss side of both sensors and a second pressure is applied to the opposite side of the differential sensor, deflection and the stress of the second sensor is determined by the pressure difference across the deflecting portion of the sensor. To obtain the same stresses in the thin section of each sensor, the overall active area of each sensor is different. For the same thickness read, the absolute value of P₂−P₁ where P₂ is the pressure applied to the front side of the two sensors and P₁ is the pressure applied to the differential sensor through the metal tube is less than P₂ to obtain the same stress in each sensor a great active area in the differential sensor is required. Conversely, if the absolute value of P₂−P₁ is greater than P₂, then a smaller active area in the differential sensor is required. By choosing adjacent sensors with the same web thickness, but different size active areas the thermal co-efficient and the thermal sensitivity are controlled by the impurity concentrations of the P regions and by how well they match each other. Thus, the thermal properties of the two individual sensors are closely controlled and matched to each other resulting in an improved overall combined absolute differential transducer.

Claims

1. A combined absolute and differential pressure transducer, comprising:

first and second sensors each having a piezoresistive structure thereon and responsive to an applied force to produce an output according to the magnitude of said applied force, each of said sensors fabricated from a common wafer process to enable said sensors to be matched in regard to thermal properties, said first sensor having a cover member and operative to receive a first force to provide an absolute pressure output, said second sensor having a cover member having a port aperture therein to enable said second sensor to receive said first force as applied to said first sensor and a second force applied via said aperture to provide a differential output pressure, said first and second sensors having substantially equal diaphragm thicknesses and having substantially different active areas, so as to accurately measure both absolute and differential pressures simultaneously.

2. The combined absolute differential pressure transducer according to claim 1 wherein, said first and second sensors are included on separate substrates obtained from a common wafer with said common wafer process.

3. The combined absolute differential pressure transducer according to claim 1 wherein said first and second sensors are located on the same substrate having a common cover member.

4. The combined absolute differential pressure transducer according to claim 1 wherein the active area of said differential sensor is larger than the active area of said absolute sensor.

5. The combined absolute differential pressure transducer according to claim 1 wherein the active area of said absolute sensor is larger than the active area of said differential sensor.

6. The combined absolute differential pressure transducer according to claim 1 wherein said first and second sensors include:

a semiconductor diaphragm member having a top surface coated with an oxide layer,

P+ sensors fusion bonded to said oxide layer at a relatively central area of said diaphragm,

P+ finger elements fusion bonded to said oxide layer extending from said sensors to an outer contact location of said diaphragm member for each finger,

an external rim of P+ material fusion bonded and surrounding said sensors and fingers,

a glass cover member electrostatically bonded to said fingers and rim to hermetically seal said sensors and fingers of said diaphragm member, said glass cover having a cavity above said sensors and having a plurality of apertures, each aperture associated with a separate finger at said contact location wherein each contact location can be accessed via said associated aperture in said glass cover.

7. The combined absolute and differential pressure transducer according to claim 6 including a conductive glass fit mixture having gold particles located in said apertures in contact with said contact locations.

8. The combined absolute and differential pressure transducer according to claim 6 wherein each of said sensors is approximately 100×

100 mils with circular contact apertures each approximately 10 mils in diameter.

9. The combined absolute and differential pressure transducer according to claim 6 wherein each of said contact locations includes a centrally located area of platinum-titanium metalization.

10. The combined absolute and differential pressure transducer according to claim 1 wherein said first and second sensors are housed in a common header.

11. The combined absolute and differential pressure transducer according to claim 1 wherein at least one of said cover members is fabricated from PYREX.

12. The combined absolute and differential pressure transducer according to claim 1 wherein each of said sensors has a similar shape.

13. The combined absolute and differential pressure transducer according to claim 12 wherein each of said sensors is square.

14. The combined absolute and differential pressure transducer according to claim 1 wherein said first and second sensors are fabricated on a single chip having located thereon an absolute sensor pattern followed by a differential sensor pattern.

15. The combined absolute and differential pressure transducer according to claim 1 further comprising a header, wherein said header is fabricated from an iron-nickel-cobalt alloy.

16. The combined absolute and differential pressure transducer according to claim 1 wherein said first and second sensors are fabricated from silicon and said cover members are fabricated from glass.

17. The combined absolute and differential pressure transducer according to claim 1 wherein said piezoresistive structures are dielectrically isolated piezoresistive elements forming a Wheatstone bride array.

18. The combined absolute and differential pressure transducer according to claim 17 wherein said piezoresistive elements are P+ silicon elements.

19. The combined absolute and differential pressure transducer according to claim 18 wherein said dielectric isolation is achieved with silicon dioxide.