Magnetic stimulus of ISFET-based sensor to enable trimming and self-compensation of sensor measurement errors
An ion sensor apparatus comprises at least one ion sensitive field effect transistor (ISFET) device configured to be exposed to a liquid, a reference electrode configured to contact the liquid to which the ISFET device is exposed, and at least one magnet configured to intermittently expose the ISFET device to a magnetic field. A processor is operatively connected to the ISFET device and the reference electrode. The processor modulates the magnetic field to produce a corresponding modulated output in resistance of the ISFET device, and modulation of a reported output value of the ion sensor apparatus.
1. A method of compensating for ion sensor measurement errors, the method comprising:
contacting a liquid with a portion of an ion sensitive field effect transistor (ISFET) device;
exposing the ISFET device to a modulated magnetic field to produce a corresponding modulated output in resistance of the ISFET device;
monitoring the modulated output to determine whether there is a difference between the modulated output and an expected output based on the modulated magnetic field;
determining an error compensation value when there is a difference between the modulated output and the expected output; and
applying the error compensation value to null the difference between the modulated output and the expected output over a period of time to maintain stability of ion sensor measurements.
2. The method of claim 1 , wherein the modulated magnetic field is from an electromagnet.
3. The method of claim 2 , wherein the electromagnet is selectively activated by a processor to expose the ISFET device to the modulated magnetic field.
4. The method of claim 1 , wherein the modulated magnetic field is from at least one permanent magnet.
5. The method of claim 1 , wherein the liquid comprises sea water, ground water, industrial chemicals, refined chemicals, or crude oil.
6. The method of claim 1 , wherein the ISFET device is configured to measure a pH of the liquid.
7. The method of claim 1 , wherein the ISFET device comprises:
a semiconductor substrate having a top surface;
a source and a drain located in opposing side portions of the semiconductor substrate;
a pair of electrical Hall contacts each located in opposing side portions of the semiconductor substrate that are adjacent to the side portions where the source and drain are located; and
a gate channel, which is sensitive to ions in the liquid, located in a top central portion of the semiconductor substrate between the source and the drain, and between the pair of electrical Hall contacts;
wherein the source, the drain, and the electrical Hall contacts are separate from each other and located below the top surface of the semiconductor substrate.
8. A method of compensating for ion sensor measurement errors, the method comprising:
contacting a liquid with a portion of an ion sensitive field effect transistor (ISFET) device;
exposing the ISFET device to a modulated magnetic field to produce a corresponding modulated output in resistance of the ISFET device, wherein the modulated magnetic field is produced by at least one magnet and a magnetic shield that intermittently exposes the ISFET device to the magnetic field produced by the at least one magnet;
monitoring the modulated output to determine whether there is a difference between the modulated output and an expected output based on the modulated magnetic field;
determining an error compensation value when there is a difference between the modulated output and the expected output; and
applying the error compensation value to null the difference between the modulated output and the expected output over a period of time to maintain stability of ion sensor measurements.
9. The method of claim 8 , wherein the modulated magnetic field is produced by at least one permanent magnet.
10. The method of claim 8 , wherein the liquid comprises sea water, ground water, industrial chemicals, refined chemicals, or crude oil.
11. The method of claim 8 , wherein the ISFET device is configured to measure a pH of the liquid.
12. The method of claim 8 , wherein the ISFET device comprises:
a semiconductor substrate having a top surface;
a source and a drain located in opposing side portions of the semiconductor substrate;
a pair of electrical Hall contacts each located in opposing side portions of the semiconductor substrate that are adjacent to the side portions where the source and drain are located; and
a gate channel, which is sensitive to ions in the liquid, located in a top central portion of the semiconductor substrate between the source and the drain, and between the pair of electrical Hall contacts;
wherein the source, the drain, and the electrical Hall contacts are separate from each other and located below the top surface of the semiconductor substrate.