pH sensor and manufacturing method
Disclosed is a pH sensor comprising a carrier ( 10 ) comprising a plurality of conductive tracks and an exposed conductive area ( 40 ) defining a reference electrode connected to one of said conductive tracks; a sensing device ( 30 ) mounted on the carrier and connected at least one other of said conductive tracks; an encapsulation ( 20 ) covering the carrier, said encapsulation comprising a first cavity ( 22 ) exposing a surface ( 32 ) of the sensing device and a second cavity ( 24 ) exposing the exposed conductive area, said second cavity comprising a reference electrode material ( 42 ) and an ion reservoir material ( 44 ) sharing at least one ion type with said reference electrode material, the reference electrode material being sandwiched between the exposed conductive area and the ion reservoir material. A method of manufacturing such a pH sensor is also disclosed.
1. A pH sensor comprising:
a carrier comprising a plurality of conductive tracks and an exposed conductive area defining a reference electrode connected to a first track of said plurality of conductive tracks;
a sensing device mounted on the carrier and connected to at least a second track of said plurality of conductive tracks;
an encapsulation covering the carrier, said encapsulation comprising:
a first cavity exposing a surface of the sensing device, and
a second cavity exposing the exposed conductive area, said second cavity comprising a reference electrode material and an ion reservoir material sharing at least one ion type with said reference electrode material, the reference electrode material being sandwiched between the exposed conductive area and the ion reservoir material.
2. The pH sensor of claim 1 , further comprising:
a layer impermeable to the at least one ion type in the ion reservoir material over the second cavity.
3. The pH sensor of claim 1 , further comprising:
a first contact pad connected to the sensing device via the second track; and
a second contact pad connected to the exposed conductive area via the first track.
4. The pH sensor of claim 1 , wherein the sensing device comprises a transceiver, the pH sensor further comprising:
an antenna on the carrier connected to the second track.
5. The pH sensor of claim 4 , wherein the exposed conductive area is connected to the sensing device via the first track.
6. The pH sensor of claim 1 , wherein said encapsulation further comprises:
a first fluid channel laterally extending from an edge of said encapsulation to the second cavity.
7. The pH sensor of claim 6 , wherein said encapsulation further comprises:
a second fluid channel laterally extending from said edge to the first cavity.
8. The pH sensor of claim 7 , wherein the first fluid channel and the second fluid channel maintain a permanent electrical connection between the sensing device and the reference electrode.
9. The pH sensor of claim 7 , wherein the first fluid channel and the second fluid channel are formed simultaneously.
10. The pH sensor of claim 1 , wherein the carrier is a printed circuit board.
11. The pH sensor of claim 1 , wherein the sensing device comprises an ion sensitive field effect transistor (ISFET) having its gate exposed in the first cavity.
12. The pH sensor of claim 11 , wherein the gate of the ISFET comprises Ta 2 O 5 .
13. The pH sensor of claim 1 , further comprising:
a sharp tip configured to insert the pH sensor into a substance.
14. The pH sensor of claim 13 , wherein a fluid channel is off-centered compared to the sharp tip.
15. The pH sensor of claim 1 , wherein the exposed conductive area comprises a gold-plated copper layer.
16. The pH sensor of claim 1 , wherein the reference electrode material comprises Ag and AgCl and the ion reservoir material comprises chloride ions.
17. The pH sensor of claim 16 , further comprising:
an ion-selective membrane impermeable to the at least one ion type in the ion reservoir material over the second cavity.
18. The pH sensor of claim 1 , wherein the reference electrode is formed during a packaging process.
19. A method of manufacturing a pH sensor comprising:
providing a carrier having on its surface a plurality of conductive tracks, a first exposed conductive area connected to one of said conductive tracks and a second exposed conductive area;
fixating an integrated circuit die to the second exposed conductive area, said integrated circuit die comprising an exposed pH-sensitive surface;
encapsulating the resultant structure in a protective resin;
forming first and second cavities in said protective resin, the first cavity exposing the pH-sensitive surface and the second cavity exposing the first exposed conductive area;
depositing a reference electrode material over the first exposed conductive area; and
depositing an ion reservoir material sharing at least one ion type with said reference electrode material over said reference electrode material.
20. The method of claim 19 , wherein said encapsulating step and said forming step are performed simultaneously.