Composite mass air flow sensor

• US 5,313,832 A
• Filed: 12/23/1991
• Issued: 05/24/1994
• Est. Priority Date: 12/23/1991
• Status: Expired due to Fees

• Current Assignee: Board of Regents of the University of Michigan (University of Michigan)
• Original Assignee: Ford Motor Company
• Inventors: Zanini-Fisher, Margherita, Stephan, Craig H.
• Primary Examiner(s): Goldstein, Herbert
• Application Number:
  US07/812,396
• Time in Patent Office: 883 Days
• Field of Search: 73/204.15, 73/204.23, 73/204.25, 73/204.26, 73/204.27, 338/25
• US Class Current: 73/204.26
• CPC Class Codes: G01F 1/6845 Micromachined devices

Abstract

A mass air flow sensor (MAFS) is disclosed wherein silicon members carrying a resistive film are bonded to a glass substrate and extend out over an air flow opening through the glass substrate. The silicon members may be either bridges across the air flow opening or cantilevered beams having one end bonded to the substrate and a second free end. Silicon frames around the air flow opening can also be provided, to which an environmental seal can be formed. A novel method of making such sensors includes providing the glass substrate with the air flow opening therethrough and aligning thereover a silicon wafer selectively passivated to define the silicon member(s) and any frame element. The glass and silicon wafers are bonded and subsequently anisotropically etched, after which the resultant bonded and etched assembly can be employed in accordance with known mounting techniques.

Claims

1. A mass air flow sensor comprising:

a generally planar glass substrate having an upper surface, a lower surface and an air flow opening formed therethrough perpendicular to the plane of the substrate;

a first silicon member having a bottom surface, a portion of the first silicon member extending over the air flow opening and a portion of the bottom surface of the first silicon member being bonded at a bonding site to an underlying portion of the upper surface of the glass substrate; and

an electrically heatable element comprising a resistive film on the first silicon member.

2. The mass air flow sensor of claim 1 wherein the first silicon member is a silicon beam cantilevered over the air flow opening.

3. The mass air flow sensor of claim 1 wherein the glass substrate has a peninsula extending into the air flow opening, the first silicon member being a beam of silicon cantilevered over the air flow opening from said bond site on the upper surface of the peninsula, the mass air flow sensor further comprising

a first electrically conductive lead extending on the upper surface of the glass substrate from electrical contact with the resistive film at a first electrical contact point on the peninsula to a first wire bond pad remote from the peninsula, and

a second electrically conductive lead extending on the upper surface of the glass substrate from electrical contact with the resistive film at a second electrical contact point on the peninsula to a second wire bond pad remote from the peninsula.

4. The mass air flow sensor of claim 1 wherein the resistive film consists essentially of metal selected from the group consisting of nickel and platinum.

5. The mass air flow sensor of claim 1 further comprising:

a second silicon member having a bottom surface, a portion of the second silicon member extending over the air flow opening and a portion of the bottom surface of the second silicon member being bonded at a second bonding site to an underlying portion of the upper surface of the glass substrate; and

a second electrical element comprising a second resistive film on the second silicon member.

6. The mass air flow sensor of claim 1 further comprising a passivating coating on the first silicon member and the glass substrate.

7. The mass air flow sensor of claim 1 wherein the first silicon member is a silicon beam which bridges the air flow opening.

8. The mass air flow sensor of claim 7 wherein each end of the silicon beam is bonded to the upper surface of the glass substrate on opposite sides of said air flow opening.

9. A mass air flow sensor comprising:

a generally planar glass substrate having an upper surface, a lower surface and an air flow opening formed therethrough;

a first silicon member having a bottom surface, a portion of the first silicon member extending over the air flow opening and a portion of the bottom surface of the first silicon member being bonded at a bonding site to an underlying portion of the upper surface of the glass substrate; and

an electrically heatable element comprising a resistive film on the first silicon member wherein the first silicon member is a silicon beam having a trapezoidal cross-section, being wider at the bottom surface than at the top surface, the resistive film being on the bottom surface.

10. A mass air flow sensor comprising:

a generally planar glass substrate having an upper surface, a lower surface and an air flow opening formed therethrough;

a first silicon member having a bottom surface, a portion of the first silicon member extending over the air flow opening and a portion of the bottom surface of the first silicon member being bonded at a bonding site to an underlying portion of the upper surface of the glass substrate;

an electrically heatable element comprising a resistive film on the first silicon member; and

a silicon frame spaced from the first silicon member and bonded to the upper surface of the glass substrate around the air flow opening.

11. A mass air flow sensor comprising:

a generally planar glass substrate having an upper surface, a lower surface and an air flow opening formed therethrough, a first peninsula and a second peninsula of the glass substrate extending generally parallel each other into the air flow opening;

a first electrically conductive lead extending on the upper surface of the glass substrate from a first electrical contact point on the first peninsula to a first wire bond pad remote therefrom;

a second electrically conductive lead extending on the upper surface of the glass substrate from a second electrical contact point on the first peninsula to a second wire bond pad remote therefrom;

a third electrically conductive lead extending on the upper surface of the glass substrate from a third electrical contact point on the second peninsula to a third wire bond pad remote therefrom;

a fourth electrically conductive lead extending on the upper surface of the glass substrate from a fourth electrical contact point on the second peninsula to a fourth wire bond pad remote therefrom;

a first silicon beam having a planar top surface, a planar bottom surface wider than its top surface and a trapezoidal cross-section, a portion of the bottom surface of the first silicon beam being bonded at a first bonding site on the first peninsula to an underlying portion of the upper surface of the glass substrate, covering the first and second electrical contact points, and a free end of the first silicon beam being cantilevered over the air flow opening;

a first resistive element comprising an elongate metal resistive thin film extending on the bottom surface of the first silicon beam from electrical contact with the first electrically conductive lead at the first electrical contact point toward the free end of the first silicon beam and back to electrical contact with the second electrically conductive lead at the second electrical contact point;

a second silicon beam having a planar top surface, a planar bottom surface wider than its top surface and a trapezoidal cross-section, a portion of the bottom surface of the second silicon beam being bonded at a second bonding site on the second peninsula to an underlying portion of the upper surface of the glass substrate, covering the third and fourth electrical contact points, and a free end of the second silicon beam being cantilevered over the air flow opening;

a second resistive element comprising an elongate metal resistive thin film extending on the bottom surface of the second silicon beam from electrical contact with the third electrically conductive lead at the third electrical contact point toward the free end of the second silicon beam and back to electrical contact with the fourth electrically conductive lead at the fourth electrical contact point; and

a silicon frame bonded to the upper surface of the glass substrate around the air flow opening remote from the first silicon beam and the second silicon beam, the silicon frame having a top surface coplanar with the top surface of the first silicon beam and the top surface of the second silicon beam.