Durable miniature gas composition detector having fast response time

• US 9,818,937 B2
• Filed: 12/29/2015
• Issued: 11/14/2017
• Est. Priority Date: 03/29/2013
• Status: Active Grant

• Current Assignee: STMicroelectronics International N.V. (STMicroelectronics NV)
• Original Assignee: Stmicroelectronics Pte Limited (STMicroelectronics NV)
• Inventors: Le Neel, Olivier, Shankar, Ravi
• Primary Examiner(s): Campbell, Shaun
• Application Number:
  US14/982,600
• Publication Number:
  US 20160111635A1
• Time in Patent Office: 686 Days
• Field of Search: None
• CPC Class Codes: G01N 27/74 of fluids G01N24/00 takes precedence
• CPC Class Codes: H01L 21/8234 MIS technology , i.e. integration processes of field effect transistors of the conductor-insulator-semiconductor type
• CPC Class Codes: H10N 50/85 Magnetic active materials
• CPC Class Codes: H10N 52/01 Manufacture or treatment
• CPC Class Codes: H10N 52/101 Semiconductor Hall-effect devices
• CPC Class Codes: H10N 52/80 Constructional details
• CPC Class Codes: Y10T 29/4913 Assembling to base an electrical component, e.g., capacitor, etc.

Abstract

A miniature oxygen sensor makes use of paramagnetic properties of oxygen gas to provide a fast response time, low power consumption, improved accuracy and sensitivity, and superior durability. The miniature oxygen sensor disclosed maintains a sample of ambient air within a micro-channel formed in a semiconductor substrate. O₂ molecules segregate in response to an applied magnetic field, thereby establishing a measurable Hall voltage. Oxygen present in the sample of ambient air can be deduced from a change in Hall voltage with variation in the applied magnetic field. The magnetic field can be applied either by an external magnet or by a thin film magnet integrated into a gas sensing cavity within the micro-channel. A differential sensor further includes a reference element containing an unmagnetized control sample. The miniature oxygen sensor is suitable for use as a real-time air quality monitor in consumer products such as smart phones.

Claims

1. A method, comprising:

forming a miniature Hall effect sensor in a silicon substrate;

coating a glass substrate with a metal film;

patterning the metal film to form a mask;

etching a micro-channel in the glass substrate through the mask, the micro-channel having a micro-channel depth;

forming openings to the micro-channel; and

bonding the glass and silicon substrates.

2. The method of claim 1 wherein the silicon substrate includes one or more of monocrystalline silicon, polycrystalline silicon, amorphous silicon, or quartz.

3. The method of claim 1, further comprising forming transistors and logic circuits in the silicon substrate.

4. The method of claim 1 further comprising, before bonding, forming an integrated thin film permanent magnet on the glass substrate.

5. The method of claim 4 wherein forming the thin film permanent magnet includes forming a ferromagnetic film on an interior surface of the micro-channel.

6. The method of claim 5 wherein the ferromagnetic film includes FeCoNi.

7. The method of claim 5 wherein the ferromagnetic film has a thickness that is less than half of the micro-channel depth.

8. The method of claim 1 further comprising:

dicing the bonded substrates into sensor chips; and

assembling one or more of the sensor chips into an open package.

9. The method of claim 1 wherein the metal film is a bi-layer film having two metallic components.

10. The method of claim 9 wherein the bi-layer film includes chromium and gold.

11. The method of claim 9 wherein a thickness of one of the two metallic components is more than ten times greater than a thickness of the other metallic component.

12. A method, comprising:

forming a miniature Hall effect sensor on a silicon substrate;

forming micro-channels in a glass substrate;

exposing the micro-channels;

bonding the silicon and glass substrates together;

dicing the bonded substrates into sensor chips; and

assembling the sensor chips into packages with other integrated circuit chips.

13. The method of claim 12 wherein forming the miniature Hall effect sensor includes

forming, by epitaxially growth, a surface layer of n-type silicon in contact with the silicon substrate;

forming p-n junctions in the surface layer; and

forming contacts to the surface layer.

14. The method of claim 13 wherein exposing the micro-channels includes drilling a plurality of openings into the glass substrate to allow ambient air to fill the micro-channels.

15. The method of claim 14 wherein each of the openings has an area of 100 square microns.

16. The method of claim 12 wherein the bonding uses one or more of anodic bonding, metal eutectic bonding, or adhesive bonding.

17. The method of claim 12 wherein the assembling further includes arranging the sensor chips with the other integrated circuit chips in the packages and coupling selected ones of the chips using wire bonds.

18. A method, comprising:

forming integrated circuits in a first substrate, the integrated circuits including contact pads;

forming a gas sensing unit in a second substrate, the gas sensing unit including a gas-filled cavity and a thin film permanent magnet integrated with the gas-filled cavity;

bonding the first and second substrates; and

attaching wires to the contact pads to access the gas-filled cavity.

19. The method of claim 18, wherein forming the gas sensing unit further comprises patterning the gas-filled cavity using a metallic mask.

20. The method of claim 18 wherein the first substrate is crystalline and the second substrate is amorphous.