Microelectromechanical scalable bulk-type piezoresistive force/pressure sensor

Patent metadata

Field	Value
Publication number	US-10724909-B2
Application number	US-201815894770-A
Country	US
Kind code	B2
Filing date	Feb 12, 2018
Priority date	Feb 21, 2017
Publication date	Jul 28, 2020
Grant date	Jul 28, 2020

Abstract

A microelectromechanical force/pressure sensor has: a sensor die, of semiconductor material, having a front surface and a bottom surface, extending in a horizontal plane, and made of a compact bulk region having a thickness along a vertical direction, transverse to the horizontal plane; piezoresistive elements, integrated in the bulk region of the sensor die, at the front surface thereof; and a cap die, coupled above the sensor die, covering the piezoresistive elements, having a respective front surface and bottom surface, opposite to each other along the vertical direction, the bottom surface facing the front surface of the sensor die. A conversion layer is arranged between the front surface of the sensor die and the bottom surface of the cap die, patterned to define a groove traversing its entire thickness along the vertical direction; the piezoresistive elements are arranged vertically in correspondence to the groove and the conversion layer is designed to convert a load applied to the front surface of the cap die and/or bottom surface of the sensor die along the vertical direction into a planar stress distribution at the groove, acting in the horizontal plane.

First claim

What is claimed is:

1. A microelectromechanical sensor, comprising:
a sensor die of semiconductor material having a first surface and a second surface extending in a horizontal plane and having a thickness along a vertical direction transverse to the horizontal plane;
a plurality of piezoresistive elements integrated in the sensor die at the first surface;
a cap die coupled to the sensor die and covering the plurality of piezoresistive elements, the cap die having a first surface and a second surface opposite the first surface along the vertical direction, the second surface of the cap die facing the first surface of the sensor die; and
a conversion layer arranged between the first surface of the sensor die and the second surface of the cap die, the conversion layer including a groove traversing an entire thickness of the conversion layer along the vertical direction,
wherein the plurality of piezoresistive elements are vertically arranged with respect to the groove, wherein the conversion layer is configured to convert a load applied in the vertical direction to at least one of the first surface of the cap die or a second surface of the sensor die into a planar stress distribution in the sensor die at the groove acting in the horizontal plane.

2. The microelectromechanical sensor according to claim 1 wherein the groove has a longitudinal main extension in the horizontal plane and the stress distribution defines a maximum planar stress in a direction transverse to the longitudinal main extension, and a minimum planar stress in a direction parallel to the longitudinal main extension of said groove.

3. The microelectromechanical sensor according to claim 2 wherein the plurality of piezoresistive elements include:
at least a first piezoresistive element extending in the horizontal plane parallel to the longitudinal main extension of the groove; and
at least a second piezoresistive element extending in the horizontal plane transverse to the longitudinal main extension of the groove,
the microelectromechanical sensor further comprising electrical connections defining a current path through the longitudinal extension of the first and second piezoresistive elements.

4. The microelectromechanical sensor according to claim 3 wherein the piezoresistive elements further comprise:
at least a third piezoresistive element extending in the horizontal plane parallel to the longitudinal main extension of the groove; and
at least a fourth piezoresistive element extending in the horizontal plane transverse to the longitudinal main extension of the groove,
wherein the electrical connections are configured to define a Wheatstone bride that includes the first, second, third and fourth piezoresistive elements.

5. The microelectromechanical sensor according to claim 3 wherein the applied load is configured to cause a resistance variation in the first piezoresistive element and a corresponding, opposite, resistance variation in the second piezoresistive element.

6. The microelectromechanical sensor according to claim 1 wherein the cap die is bonded to the sensor die by a bonding layer, wherein the bonding layer is interposed between the conversion layer and the second surface of the cap die.

7. The microelectromechanical sensor according to claim 1 wherein the cap die covers the first surface of the sensor die except for an exposed area of the first surface;
the microelectromechanical sensor further comprising electrical contact pads formed on the first surface of the sensor die at the exposed area, wherein the electrical contact pads are electrically coupled to the plurality of piezoresistive elements by electrical connections in the sensor die.

8. The microelectromechanical sensor according to claim 1 , further comprising an isolation trench surrounding the groove and extending through the entire thickness of the conversion layer and through a surface portion of the sensor die and cap die.

9. The microelectromechanical sensor according to claim 8 wherein the isolation trench is configured to elastically decouple a sensing area of the sensor die integrating the plurality of piezoresistive elements from force/pressure loads externally applied at lateral sides of the sensor die and cap die in a direction that is parallel to the horizontal plane.

10. The microelectromechanical sensor according to claim 1 wherein the groove further extends within a surface portion of the cap die at the second surface.

11. The microelectromechanical sensor according to claim 1 wherein the sensor die and the cap die are made of monocrystalline silicon.

12. The microelectromechanical sensor according to claim 1 wherein the conversion layer is made of one of the following materials: Polysilicon, SiO 2 , Si 3 N 4 , Al 2 O 3 , ZrO 2 , TiB 2 , B 4 C, SiC, WC, AlN or BN.

13. The microelectromechanical sensor according to claim 1 wherein the groove is a closed square shape in the horizontal plane that defines a first active area of the conversion layer that is internal to the groove and defines a second active area of the conversion layer that is external to the groove, the first and second active areas being independently configured to convert the load applied to one of the first surface of the cap die or the second surface of the sensor die into the planar stress distribution.

14. The microelectromechanical sensor according to claim 1 wherein the load is a force or a pressure directly applied to at least one of the first surface of the cap die or the second surface of the sensor die.

15. A method comprising:
forming a sensor die of semiconductor material, the sensor die having first and second surfaces extending in horizontal planes and separated from each other by a thickness along a vertical direction that is transverse to the horizontal plane, wherein the sensor die includes a plurality of piezoresistive elements integrated at the first surface of the sensor die;
forming a conversion layer on a portion of the first surface of the sensor die, the conversion layer being located outward of the plurality of piezoresistive elements such that the piezoresistive elements are uncovered by the conversion layer; and
coupling a cap die to the conversion layer, the cap covering the plurality of piezoresistive elements of the sensor die,
wherein the conversion layer is configured to convert a load applied to at least one of the cap die or the sensor die into a planar stress.

16. The method according to claim 15 wherein conversion layer is formed from one of the following materials: Polysilicon, SiO 2 , Si 3 N 4 , Al 2 O 3 , ZrO 2 , TiB 2 , B 4 C, SiC, WC, AlN or BN.

17. The method according to claim 15 wherein forming the conversion layer comprises forming the conversion layer to include a through opening, the piezoresistive elements located at the through opening.

18. A MEMS device comprising:
a sensor die of semiconductor material having a first surface;
a plurality of piezoresistive elements integrated in the sensor die at the first surface;
a conversion layer on the sensor die, the conversion layer having a through opening, the plurality of piezoresistive elements located in the through opening; and
a cap die coupled to the sensor die and covering the plurality of piezoresistive elements,
wherein the conversion layer is configured to convert a load applied to the MEMS device into a planar stress.

19. The MEMS according to claim 18 wherein the through opening is a closed square shape.

20. The MEMS according to claim 18 wherein the conversio

Assignees

• St Microelectronics Srl

Inventors

• Abbasi Gavarti Mohammad
• Caltabiano Daniele
• Picco Andrea
• Pomarico Anna Angela
• Roselli Giuditta
• Braghin Francesco

Classifications

• G01L19/146

  using flexible element between the transducer and the support · CPC title

• G01L9/0002

  using variations in ohmic resistance (G01L9/0051 takes precedence) · CPC title

• G01L1/26

  Auxiliary measures taken, or devices used, in connection with the measurement of force, e.g. for preventing influence of transverse components of force, for preventing overload · CPC title

• G01L9/06

  of piezo-resistive devices · CPC title

• B81B1/00

  Devices without movable or flexible elements, e.g. microcapillary devices · CPC title