Durable miniature gas composition detector having fast response time
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. O 2 molecules segregate in response to an applied magnetic field, thereby establishing a measureable 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.
1. A gas micro-sensor comprising:
a micro-channel formed within a solid carrier, the micro-channel configured to contain a gas sample;
a magnet disposed adjacent to the micro-channel and positioned to apply a magnetic field to the gas sample; and
a semiconductor-based differential Hall effect sensor positioned adjacent to the micro-channel and responsive to a momentary change in the magnetic field within the micro-channel.
2. The micro-sensor of claim 1 wherein the Hall effect sensor is configured to measure a Hall voltage in response to segregation of gas atoms in the magnetic field.
3. The micro-sensor of claim 1 , further comprising a reference apparatus in which a Hall voltage is measured and compared with a control voltage from an unmagnetized reference sensor.
4. The micro-sensor of claim 1 wherein a portion of the micro-channel is a gas-sensing cavity containing a paramagnetic gas sample.
5. The micro-sensor of claim 1 wherein a strength of the magnetic field is within the range of 1-100 μTesla.
6. The micro-sensor of claim 1 wherein the solid carrier is made of glass and the micro-sensor further comprises a silicon substrate bonded to the glass.
7. A method of detecting a paramagnetic gas, the method comprising:
applying a magnetic field to a miniature gas-sensing cavity within a carrier, the miniature gas-sensing cavity equipped with a miniature Hall effect sensor;
introducing a gas sample into the miniature gas-sensing cavity via a micro-channel; and
measuring a Hall voltage indicative of a presence of the paramagnetic gas in the gas sample.
8. The method of claim 7 further comprising:
coupling a miniature reference element to the micro-channel so that the reference element is in fluid communication with the miniature gas-sensing cavity; and
comparing the measured Hall voltage to a measured reference voltage of the reference element in which no magnetic field is applied.
9. The method of claim 7 wherein the paramagnetic gas is oxygen.
10. A miniature oxygen detector, comprising:
two patterned substrates bonded together to form a micro-channel;
a permanent magnet positioned to apply a magnetic field across the micro-channel; and
a Hall effect sensor positioned adjacent to the micro-channel.
11. The detector of claim 10 wherein the permanent magnet is external to the micro-channel.
12. The detector of claim 10 wherein the permanent magnet is a magnetic thin film integrated into the micro-channel.
13. The detector of claim 12 wherein the magnetic thin film is made of FeCoNi.
14. The detector of claim 10 wherein one of the two patterned substrates is crystalline and the other of the two patterned substrates is amorphous.
15. The detector of claim 10 wherein both substrates are crystalline.
16. The detector of claim 10 wherein the Hall effect sensor is formed in a crystalline silicon substrate.