Compensated semiconductor pressure sensor

• US 6,229,190 B1
• Filed: 12/18/1998
• Issued: 05/08/2001
• Est. Priority Date: 12/18/1998
• Status: Expired due to Term

• Current Assignee: Maxim Integrated Products, Inc. (Analog Devices, Inc.)
• Original Assignee: Maxim Integrated Products, Inc. (Analog Devices, Inc.)
• Inventors: Nasiri, Steven S., Bryzek, Janusz, Burns, David W., Cahill, Sean S.
• Primary Examiner(s): Lee, Eddie C.
• Assistant Examiner(s): Wilson, Allan R.
• Application Number:
  US09/216,073
• Time in Patent Office: 872 Days
• Field of Search: 257/254, 257/417-419, 438/50, 438/53
• US Class Current: 257/419
• CPC Class Codes: G01L 19/0038 being part of the housing other details about the housing G01L19/14
• CPC Class Codes: G01L 19/143 Two part housings
• CPC Class Codes: G01L 19/147 Details about the mounting of the sensor to support or covering means
• 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
• CPC Class Codes: G01P 2015/084 the mass being suspended at more than one of its sides, e.g. membrane-type suspension, so as to permit multi-axis movement of the mass
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48247 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/16151 Cap comprising an aperture, e.g. for pressure control, encapsulation
• CPC Class Codes: H01L 2924/16195 Flat cap [not enclosing an internal cavity]

Abstract

A semiconductor pressure sensor compatible with fluid and gaseous media applications is described. The semiconductor pressure sensor includes a sensor capsule having a semiconductor die and a silicon cap that is bonded to the semiconductor die. The semiconductor die includes a diaphragm that incorporates piezoresistive sensors thereon, and a stress isolation mechanism for isolating the diaphragm from packaging and mounting stresses. The silicon cap includes a cavity for allowing the diaphragm to deflect. The semiconductor pressure sensor further includes a pressure port that is hermetically attached to the semiconductor die. The sensor capsule and pressure port may be incorporated into a plastic housing. In one embodiment, the silicon cap is bonded to the semiconductor die to form an integral pressure reference. In an alternative embodiment, a second pressure port is provided for allowing gage or differential pressure measurements. A technique for incorporating the piezoresistive sensors is also described. An ASIC may be optionally attached to the silicon cap, and/or active electronic circuitry may be fabricated on the semiconductor die or silicon cap. Additional coatings may be optionally applied to the pressure port and semiconductor die for enhancing chemical resistance.

Claims

1. A semiconductor pressure sensor, comprising:

a sensor capsule including

a semiconductor die having

a diaphragm region to deflect responsive to applied pressure,

a nominally rigid rim region to support the periphery of the diaphragm region,

an outer frame region, and

a stress isolation region to couple the rim region to the outer frame region, and

a silicon cap that is bonded to the outer frame region of the semiconductor die to cover the diaphragm region; and

a pressure port hermetically attached to the sensor capsule.

2. The semiconductor pressure sensor of claim 1, wherein the silicon cap is bonded to the semiconductor die at a temperature ranging between 25°

C. and 550°

C.

3. The semiconductor pressure sensor of claim 1, wherein the silicon cap is bonded to the semiconductor die using aluminum and germanium.

4. The semiconductor pressure sensor of claim 1, wherein the silicon cap is bonded to the semiconductor die using gold and polycrystalline silicon.

5. The semiconductor pressure sensor of claim 1, wherein the silicon cap is bonded to the semiconductor die using gold and single-crystal silicon.

6. The semiconductor pressure sensor of claim 1, wherein the silicon cap is bonded to the semiconductor die using a glass bond.

7. The semiconductor pressure sensor of claim 1, wherein the pressure port is hermetically attached to the semiconductor capsule with a eutectic solder that includes gold and tin.

8. The semiconductor pressure sensor of claim 1, wherein pressure port is hermetically attached to the semiconductor capsule with a eutectic solder that includes tin and silver.

9. The semiconductor pressure sensor of claim 1 wherein the silicon cap includes a cavity for allowing the diaphragm to deflect within the cavity.

10. The semiconductor pressure sensor of claim 9 wherein the cavity contains a vacuum.

11. The semiconductor pressure sensor of claim 9 further comprising an additional pressure port for providing gage or differential pressure measurements.

12. The semiconductor pressure sensor of claim 1, wherein the pressure port is molded into a plastic housing.

13. The semiconductor pressure sensor of claim 1, further comprising an active electronic circuit mounted on the semiconductor capsule opposite the pressure port.

14. The semiconductor pressure sensor of claim 13, wherein the active electronic circuit includes one or more of the following circuits:

an electronic trimming circuit, a calibration circuit, and a signal conditioning circuit.

15. The semiconductor pressure sensor of claim 1 further comprising integrated circuitry co-fabricated within the sensor capsule.

16. The semiconductor pressure sensor of claim 1 wherein the stress isolation region includes:

a first member including a first end coupled to a frame region of the semiconductor die, and a second end; and

a second member including a first end coupled to the second end of the first member, and a second end coupled to a rim region of the semiconductor die.

17. The semiconductor pressure sensor of claim 16 wherein a first wall etch defines the first member and a second wall etch, in combination with the first wall etch, defines the second member.

18. The semiconductor pressure sensor of claim 9 wherein the diaphragm includes:

a first silicon region of a first conductivity type and a second silicon region of a second conductivity type surrounding the first silicon region; and

a stress-sensitive diffused resistive element formed on the deformable member in the first silicon region.

19. The semiconductor pressure sensor of claim 18 further comprising second, third, and fourth resistive elements, said resistive elements formed on diaphragm in the first silicon region.

20. The semiconductor pressure sensor of claim 19 wherein the resistive elements are connected in a Wheatstone bridge configuration.

21. The semiconductor pressure sensor of claim 18 wherein the first conductivity type is an N−

semiconductor material and the second conductivity type is a P−

semiconductor material.

22. The semiconductor pressure sensor of claim 18 wherein the silicon region of the first conductivity type is connected to a voltage that is higher than or at the same potential as the resistive element potential.

23. The semiconductor pressure sensor of claim 9 further comprising:

a boss coupled to a first side of the diaphragm along an axis of the diaphragm; and

a plurality of piezoresistors disposed on a second side of the diaphragm in regions not occupied by the boss along the axis.

24. The semiconductor pressure sensor of claim 23, wherein first and second piezoresistors are placed in regions of highest tensile stress along the axis to increase sensitivity of applied pressure.

25. The semiconductor pressure sensor of claim 24, wherein third and fourth piezoresistors are placed in regions of highest compressive stress along the axis to increase sensitivity of applied pressure.

26. The semiconductor pressure sensor of claim 23, wherein the plurality of piezoresistors are oriented perpendicular to the axis.

27. The semiconductor pressure sensor of claim 1 further comprising a media coating over the pressure port and exposed areas of the sensor capsule.

28. The semiconductor pressure sensor of claim 1 wherein the silicon cap and the semiconductor die are bonded together to form a bond region, and wherein the semiconductor die includes a doped region covered by an oxide layer that electrically couples a first region located on one side of the bond region and a second region located on the opposite side of the bond region.

29. A semiconductor pressure sensor, comprising:

a sensor capsule including a semiconductor die and a silicon cap that are bonded together, the semiconductor die including

a diaphragm region to deflect responsive to applied pressure, the diaphragm region including an epi-layer of a first conductivity type adjacent a top die surface and a buried layer of a second conductivity type adjacent the epi-layer and an opposing bottom diaphragm surface, the buried layer being a portion of a substrate of the second conductivity type, the buried layer portion of the substrate being adjacent the surface of the substrate opposite the bottom die surface,

a nominally rigid region coupled to the periphery of the diaphragm region, the rigid region including the epi-layer, the buried layer, and the substrate, and

a piezoresistive sensor with a first portion in the diaphragm region and a second portion in the rigid region, the piezoresistive sensor including

a diffused region of the second conductivity type extending from the top die surface to the buried layer,

an epi-pocket formed by the portion of the epi-layer that is surrounded by the diffused region, and

a piezoresistor of the second conductivity type formed in the epi-pocket adjacent the top die surface;

a pressure port hermetically attached to the sensor capsule with a eutectic solder; and

a housing that houses the sensor capsule and the pressure port.

30. The semiconductor pressure sensor of claim 29, wherein the semiconductor die further includes a plurality of piezoresistive sensors connected in a Wheatstone bridge configuration for providing an output signal in direct proportion to applied pressure.

31. The semiconductor pressure sensor of claim 29, wherein the silicon cap includes a cavity such that an intergal vacuum reference is formed when the semiconductor die and the silicon cap are bonded together.

32. The semiconductor pressure sensor of claim 29, wherein the housing is made from one the following plastic materials:

liquid crystal polymer and epoxy resin.

35. The semiconductor pressure sensor of claim 29 wherein the epi-pocket is connected to a voltage that is higher than or at the same potential as the piezoresistor potential.

33. A semiconductor die, comprising:

a diaphragm region to deflect responsive to applied pressure, the diaphragm region including an epi-layer of a first conductivity type adjacent a top die surface and a buried layer of a second conductivity type adjacent the epi-layer and an opposing bottom diaphragm surface, the buried layer being a portion of a substrate of the second conductivity type, the buried layer portion of the substrate being adjacent the surface of the substrate opposite the bottom die surface;

a nominally rigid region coupled to the periphery of the diaphragm region, the rigid region including the epi-layer, the buried layer, and the substrate; and

a piezoresistive sensor with a first portion in the diaphragm region and a second portion in the rigid region, the piezoresistive sensor including

a diffused region of the second conductivity type extending from the top die surface to the buried layer;

an epi-pocket formed by the portion of the epi-layer that is surrounded by the diffused region; and

a piezoresistor of the second conductivity type formed in the epi-pocket adjacent the top die surface.

34. The semiconductor die of claim 33 wherein the first conductivity type is an N−

semiconductor material and the second conductivity type is a P−

semiconductor material.

36. The semiconductor die of claim 33 further comprising an oxide layer adjacent to the piezoresistor, a conductive layer adjacent to the oxide layer such that the oxide layer insulates the conductive layer from the piezoresistor, and an interconnect that electrically connects an end of the piezoresistor to the conductive layer.

37. The semiconductor die of claim 33 further comprising an outer frame region and a stress isolation region to couple the rigid region to the outer frame region.

38. A semiconductor pressure sensor, comprising:

a sensor capsule including a semiconductor die and a silicon cap that are bonded together, the semiconductor die including

a diaphragm region to deflect responsive to applied pressure, the diaphragm region including an epi-layer of a first conductivity type adjacent a top die surface and a buried layer of a second conductivity type adjacent the epi-layer and an opposing bottom diaphragm surface,

a nominally rigid region coupled to the periphery of the diaphragm region, the rigid region including the epi-layer, the buried layer, and the substrate,

an outerframe region,

a stress isolation region to couple the rigid region to the outer frame region, and

a piezoresistive sensor with a first portion in the diaphragm region and a second portion in the rigid region, the piezoresistive sensor including

a diffused region of the second conductivity type extending from the top die surface to the buried layer,

an epi-pocket formed by the portion of the epi-layer that is surrounded by the diffused region, and

a piezoresistor of the second conductivity type formed in the epi-pocket adjacent the top die surface;

a pressure port hermetically attached to the sensor capsule with a eutectic solder; and

a housing that houses the sensor capsule and the pressure port.

39. The semiconductor pressure sensor of claim 38, wherein the semiconductor die further includes a plurality of piezoresistive sensors connected in a Wheatstone bridge configuration for providing an output signal in direct proportion to applied pressure.

40. The semiconductor pressure sensor of claim 38, wherein the silicon cap includes a cavity such that an integral vacuum reference is formed when the semiconductor die and the silicon cap are bonded together.

41. The semiconductor pressure sensor of claim 38, wherein the housing is made from one the following plastic materials:

liquid crystal polymer and epoxy resin.

42. The semiconductor pressure sensor of claim 38 wherein the epi-pocket is connected to a voltage that is higher than or at the same potential as the piezorsistor potential.

43. A semiconductor die, comprising:

a diaphragm region to deflect responsive to applied pressure, the diaphragm region including an epi-layer of a first conductivity type adjacent a top die surface and a buried layer of a second conductivity type adjacent the epi-layer and an opposing bottom diaphragm surface;

a nominally rigid region coupled to the periphery of the diaphragm region, the rigid region including the epi-layer, the buried layer, and a substrate adjacent the buried layer and an opposing bottom die surface;

an outer frame region;

a stress isolation region to couple the rigid region to the outer frame region; and

a piezoresistive sensor with a first portion in the diaphragm region and a second portion in the rigid region, the piezoresistive sensor including

a diffused region of the second conductivity type extending from the top die surface to the buried layer;

an epi-pocket formed by the portion of the epi-layer that is surrounded by the diffused region; and

a piezoresistor of the second conductivity type formed in the epi-pocket adjacent the top die surface.

44. The semiconductor die of claim 43 wherein the substrate is of the second conductivity type and the buried layer is a portion of the substrate.

45. The semiconductor die of claim 43 wherein the first conductivity type is an N−

semiconductor material and the second conductivity type is a P−

semiconductor material.

46. The semiconductor die of claim 43 wherein the epi-pocket is connected to a voltage that is higher than or at the same potential as the piezoresistor potential.

47. The semiconductor die of claim 43 further comprising an oxide layer adjacent to the piezoresistor, a conductive layer adjacent to the oxide layer such that the oxide layer insulates the conductive layer from the piezoresistor, and an interconnect that electrically connects an end of the piezoresistor to the conductive layer.