Field-effect transistor-based sensing device

Abstract

A field-effect transistor (FET)-based sensing device is disclosed. The FET-based sensing device has a shell, an FET-based sensor mounted in the shell and a reference electrode mounted to the shell. The reference electrode has a flat surface made of gold and is located above an active face of an FET-based sensing chip of the FET-based sensor. Gold is not easily ionized metal ion in the electrolyte solution and has a good electrical conductivity which is better than that of stainless steel and that of copper-nickel alloy. Furthermore, an electric field with area-to-area constituted between the flat surface and the active face of the FET-based sensing chip and the electric field is evenly distributed in the electrolyte solution. Therefore, the sensing result of the present invention can be more accurate.

Description

[0001] FIELD-EFFECT TRANSISTOR-BASED SENSING DEVICE

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims the benefit of United States provisional application filed on February 23, 2024 and having application Ser. No. 63 / 557,043, the entire contents of which are hereby incorporated herein by reference.

[0004] BACKGROUND OF THE INVENTION

[0005] 1. Field of the Invention

[0006] This present invention is related to a biosensor, and more particularly to a field-effect transistor-based sensing device.

[0007] 2. Description of the Prior Arts

[0008] With reference to Fig. 6, a conventional Field-effect transistor (FET)-based sensing device is illustrated. The conventional FET-based sensing device includes an FET-based sensor 50 and a conventional needle-type reference electrode 60. The conventional needletype reference electrode 60 is located above an active face 51 of the FET-based sensing sensor 50.

[0009] An electrolyte solution 70 is supplied on the active face 51 of the FET-based sensing sensor 50 and the conventional needle-type reference electrode 60 also dips in the electrolyte solution 70. Since the conventional needle-type reference electrode 60 is electrically connected to the FET-based sensing sensor 50, the FET-based sensing sensor 50 may obtain a more accurate sensing signal accordingly. However, since an oxidation-reduction reaction occurs between the electrolytic solution 70 and the conventional needle-type reference electrode 60 is made of copper-nickel alloy, the metal ions are greatly generated from ionizing the conventional needle-type reference electrode 60 to affect an ion concentration in the electrolyte solution 70.

[0010] To avoid metal ions being greatly generated from ionizing the conventional needle- type reference electrode 60 in the electrolyte solution 70 to further affect the sensing result, the conventional needle-type reference electrode 60 is generally made of stainless steel. However, the electrical conductivity of stainless steel is lower than that of copper-nickel alloy. In addition, since an end of the conventional needle-type reference electrode 60 aligns the active face 51 of the FET-based sensing sensor 50, an electric field with point-to-area is constituted but is not evenly distributed in the electrolyte solution 70. Therefore, the sensing accuracy of the FET-based sensing device is still not good enough.

[0011] To overcome the shortcomings, the present invention provides a new Field-effect transistor-based sensing device to mitigate or to obviate the aforementioned problems.

[0012] SUMMARY

[0013] An objective of the present invention is to provide a field-effect transistor (FET)- based sensing device.

[0014] The FET-based sensing device includes: a shell having a tank; an FET-based sensor mounted in the shell and having an FET-based sensing chip located in the tank of the shell; and a reference electrode mounted to the shell, electrically connected to the FET-based sensing chip and having a flat surface located in the tank and located above an active face of the FET-based sensing chip, wherein the flat surface is made of gold.

[0015] Based on the foregoing description, the present invention mainly provides the reference electrode having a flat surface made of gold. Gold is not easily ionized metal ion in the electrolyte solution and has a good electrical conductivity which is better than that of stainless steel and that of copper-nickel alloy. Furthermore, an electric field with area-to- area constituted between the flat surface and the active face of the FET-based sensing chip and the electric field is evenly distributed in the electrolyte solution. Therefore, the sensing result of the present invention can be more accurate.

[0016] Other objectives, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

[0017] BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Fig. 1 is a perspective view of a field-effect transistor (FET)-based sensing device in accordance with the present invention;

[0019] Fig. 2Ais a cross-sectional view of Fig. 1 taken along with line A-A;

[0020] Fig. 2B is a cross-sectional view of Fig. 1 taken along with line B-B;

[0021] Figs. 3A and 3B are two graphs depicting Vo- Vi characteristics of two reference electrodes, each of which dips in three different electrolyte solutions;

[0022] Figs. 4A to 4C are three graphs depicting Vo- Vi characteristics of two reference electrodes, each of which dips in three different electrolyte solutions, wherein an extended- gate of an FET-based sensing chip has been processed in silane evaporation;

[0023] Fig. 5A is a schematic view of a part of an FET-based sensing chip in accordance with the present invention;

[0024] Fig. 5B is a schematic view of a part of another FET-based sensing chip in accordance with the present invention;

[0025] Fig. 5C is a schematic view of a part of another FET-based sensing chip in accordance with the present invention;

[0026] Fig. 5D is a schematic view of a part of another FET-based sensing chip in accordance with the present invention; and

[0027] Fig 6 is a schematic cross-sectional view of a conventional field-effect transistor

[0028] (FET)-based sensing device in accordance with the prior art. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] With reference to Figs. 1 and 2A, a field-effect transistor (FET)-based sensing device in accordance with the present invention is shown. The FET-based sensing device includes a shell 10, an FET-based sensor 20, and a reference electrode 30.

[0030] The shell 10 has a tank 11 and a slot 12. The tank 11 is used to receive an electrolyte solution. In the present embodiment. The shell 10 is a cuboid. Atop opening 111 of the tank

[0031] 11 is formed through a top 100 of the shell 10 and is close to a first short side 101. The slot

[0032] 12 is formed through a second side 102 opposite to the first short side 101.

[0033] The FET-based sensor 20 is mounted in the shell 10 and has an FET-based sensing chip 21 located in the tank 11. The FET-based sensing chip 21 has an active face 211 for sensing changes of an ion concentration in the electrolyte solution. With reference to Fig. 5 A, the FET-based sensing chip 21 has a semiconductor body 210 and at least one FET element formed on the semiconductor body 210. Each of the least one FET element has a source electrode (S), a drain electrode (D) and a gate electrode (G). The source electrode (S), the drain electrode (D) and the gate electrode (G) are formed on the semiconductor body 210. The gate electrode (G) is exposed to be used as the active face 211 of the FET-based sensor 20. The source electrode (S) is electrically connected to a ground (GND). The drain electrode (D) is electrically connected to a drain voltage (VD). In one embodiment, with reference to Fig. 5B, the FET element may further have a sensing film 212 formed on the gate electrode (G). The gate electrode (G) with the sensing film 212 is used as the active face 211 of the FET-based sensor 20.

[0034] With reference to Fig. 5C, in another embodiment, the FET element may further have an extended gate (EG) The extended gate (EG) is electrically connected to the gate electrode (G). The extended gate (EG) is used as the active face 211 of the FET-based sensor 20. With further reference to Fig. 5D, a sensing film 212 is further formed on the extended gate (EG). The extended gate (EG) with the sensing film 212 constitutes the active face 211 of the FET-based sensor 20. In one embodiment, the FET-based sensing chip 21 has a plurality of the FET elements and the active face 211 of the FET-based sensor 20 is constituted by a plurality of the extended gates (EG) with the sensing films 212.

[0035] In one embodiment, the FET-based sensing chip 21 is mounted on a bottom 112 of the tank 11 of the shell 10. In one embodiment, the FET-based sensor 20 further includes a wiring substrate 22. The wiring substrate 22 has a substrate body 23, an extension part 24 and a plurality of contact pads 25. The substrate body 23 is mounted in the shell 10. The FET-based sensing chip 21 is mounted on the substrate body 23. The extension part 24 extends from the substrate body 23 and extends through the slot 12 of the shell 10. The contact pads 25 are formed on the extension part 24 and are electrically connected to the FET-based sensing chip 21. In one embodiment, the wiring substrate 22 may be a printed circuit board (PCB) and the contact pads 25 are gold fingers of the printed circuit board.

[0036] The reference electrode 30 is mounted to the shell 10 and is electrically connected to the FET-based sensing chip 21 through the wiring substrate 22. As shown in Fig, 5, the reference electrode 30 is electrically connected to a reference voltage (VREF). The reference electrode 30 has a body 31, a flat surface 32 and a contact pin 33. The flat surface 32 is located in the tank 11 and located above the active face 211 of the FET-based sensing chip 21. The flat surface 32 is made of gold. In one embodiment, the flat surface 32 is larger than or equal to and substantially parallel to the active face 211 of the FET-based sensing chip 21. In addition, the flat surface 32 is a geometric shape without sharp comers, such as a circle.

[0037] The body 31 is formed of a plate-shape and may be a circle plate. In one embodiment, the body 31 may be made of stainless steel, copper-nickel alloy, or polyamide. A gold layer 311 may be mounted around the body 31 as the flat surface 32 of the reference electrode 30. In another embodiment, the body 31 is made of gold to provide the flat surface 32 of the reference electrode 30.

[0038] With further reference to Fig. 2A, the contact pin 33 of the reference electrode 30 integrally extends from the body 31 through the tank 11 and is mounted on the substrate body 23. Therefore, the reference electrode 30 is electrically connected between the FET- based sensing chip 21 and at least one of the contact pads 25 on the substrate body 23. The contact pin 33 fixes the position of the flat surface 32 in the tank 11 and a distance between the flat surface 32 of the reference electrode 30 and the active face 211 is also fixed.

[0039] With further reference to Fig. 2B, the tank 11 of the shell 10 has a bottom opening 113 opposite to the top opening 111. A seal ring 114 corresponding to the bottom opening 113 is mounted on the substrate body 23 of the wiring substrate 22 and is mounted around the FET-based sensing chip 21 to seal the bottom opening 113 of the tank 11.

[0040] The comparison experiments are made to compare the plate-shaped reference electrode 30 as described and shown in Figs. 1 to 2B with the conventional needle-type reference electrode 60 as shown in Fig. 6. Three electrolyte resolutions with different pH values (pH6, pH7, pH8) are respectively supplied on the FET-based sensing chip 21. After one electrolyte resolution with pH6 is supplied on the FET-based sensing chip 21 (DEVICE NO. CT23-63-11) one end of the conventional needle-type reference electrode 60 dips in the electrolyte resolution with pH6. After then, the FET-based sensing chip 21 senses changes of the ion concentration in the electrolyte solution with pH6 for 11 times. As shown in Fig. 3A, a plurality of Vo- Vi curves (pH6-l to pH6-ll) of sensing signals from the FET- based sensing chip 21 are then obtained. The same sensing operations are repeated. As shown in Fig. 3A, a plurality of Vo-Vi curves (pH7-l to pH7-ll) of sensing signals for the electrolyte solution with pH7 and a plurality of Vo-Vi curves (pH8-l to pH8-ll) of sensing signals for the electrolyte solution with pH8 are also obtained. After then, using the same electrolyte resolutions with different pH values (pH6, pH7, pH8) and the same FET-based sensing chip 21 (DEVICE NO. CT23-63-11) but the conventional needle-type reference electrode 60 is replaced by the plate-shaped reference electrode 30 of the present invention to repeat the sensing operations as mentioned above. With further reference to FIG. 3B, a plurality of Vo- Vi curves (pH6-l to pH6-ll), (pH7-l to pH7-ll) and (pH8-l to Ph8-ll) of sensing signals for the electrolyte solutions with pH6, pH7 and pH8 are obtained.

[0041] As shown in Figs. 3A and 3B, the Vo-Vi curves (pH6-l to pH6-ll) for pH value 6 of Fig. 3B sensed by the FET-based sensing chip 21 with the plate-shaped reference electrode 30 are more concentrated than those (pH6-l to pH6-ll) of Fig. 3A sensed by the FET-based sensing chip 21 with the conventional needle-type reference electrode 60. The Vo- Vi curves (pH7-l to pH7-l 1) for pH value 7 of Fig. 3B sensed by the FET-based sensing chip 21 with the plate-shaped reference electrode 30 are more concentrated than those (pH7- 1 to pH7-ll) of Fig. 3A sensed by the FET-based sensing chip 21 with the conventional needle-type reference electrode 60, too. The Vo- Vi curves (pH8-l to pH8-ll) for pH value 8 of Fig. 3B sensed by the FET-based sensing chip 21 with the plate-shaped reference electrode 30 are also more concentrated than those (pH8-l to pH8-ll) of Fig. 3A sensed by the FET-based sensing chip 21 with the conventional needle-type reference electrode 60.

[0042] The gold layer 311 may be mounted around the body 31 of the reference electrode 30 by the plating gold process or the electroless nickel immersion gold (ENIG) process. The FET-based sensing chip 21 (DEVICE NO. CT23-63-11) uses a reference electrode 30 with the plated gold layer 311 to respectively sense the changes of the ion concentration in an electrolyte solution with pH6 for 11 times and also uses a reference electrode 30 with the ENIG layer to respectively sense the changes of the ion concentration in the electrolyte solution with pH6 for 11 times. With reference to Figs. 4A a plurality of Vo-Vi curves (PLATED GOLD-1 to PLATED GOLD- 11) and (ENIG GOLD-1 to ENIG GOLD- 11) of sensing signals for the electrolyte solution with pH6 are obtained and shown. The electrolyte solution with pH6 is replaced by electrolyte solution with pH7 to repeat the same sensing operations. As shown in Fig. 4B, a plurality of Vo- Vi curves (PLATED GOLD-1 to PLATED GOLD-11) and (ENIG GOLD-1 to ENIG GOLD-11) of sensing signals for the electrolyte solution with pH7 are obtained. The electrolyte solution with pH7 is replaced by electrolyte solution with pH8 to repeat the same sensing operations. As shown in Fig. 4C, a plurality of Vo-Vi curves (PLATED GOLD-1 to PLATED GOLD-11) and (ENIG GOLD-1 to ENIG GOLD-11) of sensing signals for the electrolyte solution with pH8 are obtained.

[0043] With reference to Figs. 4Ato 4C, the Vo-Vi curves for the same pH value sensed by the FET-based sensing chip 21 using the reference electrode 30 with the ENIG layer are not concentrated. However, the Vo-Vi curves for the same pH value sensed by the FET-based sensing chip 21 using the reference electrode 30 with the plated gold layer 311 are relatively concentrated.

[0044] Since the ion concentrations in three electrolyte solutions with pH6, pH7 and pH8 are different, the inflection points of the Vo-Vi curves for pH6, pH7 and pH8 should be different. As shown in Figs. 4Ato 4C, the inflection points of the Vo- Vi curves for pH6, pH7 and pH8 sensed by the FET-based sensing chip 21 using the reference electrode 30 with the plated gold layer 311 are obviously different. However, the inflection points of the Vo- Vi curves for pH6, pH7 and pH8 sensed by the FET-based sensing chip 21 using the reference electrode 30 with the ENIG layer are almost close.

[0045] Therefore, the sensing quality of the FET-based sensing chip 21 using the reference electrode 30 with the plated gold layer 311 is better than that of the FET-based sensing chip 21 using the reference electrode 30 with the ENIG layer.

[0046] Based on the foregoing description, the present invention mainly provides the reference electrode having a flat surface made of gold. Gold is not easily ionized metal ion in the electrolyte solution and has a good electrical conductivity which is better than that of stainless steel and that of copper-nickel alloy. Furthermore, an electric field with area-to- area constituted between the flat surface and the active face of the FET-based sensing chip and the electric field is evenly distributed in the electrolyte solution. Therefore, the sensing result of the present invention can be more accurate

[0047] Even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and features of the invention, the disclosure is illustrative only. Changes may be made in the details, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.

Claims

WHAT IS CLAIMED IS:

1. A field-effect transistor (FET)-based sensing device, comprising: a shell having a tank; an FET-based sensor mounted in the shell and having an FET-based sensing chip located in the tank of the shell; and a reference electrode mounted to the shell, electrically connected to the FET-based sensing chip and having a flat surface located in the tank and located above an active face of the FET-based sensing chip, wherein the flat surface is made of gold.

2. The FET-based sensing device as claimed in claim 1, wherein the flat surface is larger than or equal to the active face of the FET-based sensing chip.

3. The FET-based sensing device as claimed in claim 2, wherein the reference electrode has: a body made of stainless steel; and a gold layer mounted around the body to provide the flat surface.

4. The FET-based sensing device as claimed in claim 3, wherein the gold layer is formed by plating gold process or electroless nickel immersion gold (ENIG) process.

5. The FET-based sensing device as claimed in claim 2, wherein the flat surface is substantially parallel to the active face of the FET-based sensing chip.

6. The FET-based sensing device as claimed in claim 2, wherein the flat surface is geometry without sharp corners.

7. The FET-based sensing device as claimed in claim 2, wherein the shell has a slot; and the FET-based sensor has a wiring substrate having: a substrate body mounted in the shell and on which the FET-based sensing chip is mounted;an extension part extending from the substrate body through the slot of the shell; and a plurality of contact pads formed on the extension part and electrically connected to the FET-based sensing chip; and the reference electrode has a contact pin extending from the body and mounted on the substrate body of the wiring substrate and is electrically connected to at least one of the contact pads.

8. The FET-based sensing device as claimed in claim 7, wherein the tank has: a top opening formed through a top of the shell and close to a first side of the shell; and a bottom opening corresponding to the FET-based sensing chip; and a seal ring formed on the substrate body of the wiring substrate and around the FET- based sensing chip to seal the bottom opening of the tank.

9. The FET-based sensing device as claimed in claim 7, wherein the wiring substrate is a printed circuit board, and the contact pads are gold fingers of the printed circuit board.

10. The FET-based sensing device as claimed in claim 2, wherein the FET-based sensing chip comprises a semiconductor body and at least one FET element formed on the semiconductor body, wherein each of the at least one FET element comprises: a source electrode formed on the semiconductor body and adapted to electrically connect to a ground; a drain electrode formed on the semiconductor body adapted to electrically connect to a drain voltage; and a gate electrode formed on the semiconductor body; and the reference electrode is adapted to electrically connect to a reference voltage.

11. The FET-based sensing device as claimed in claim 10, wherein the gate electrode is used as the active face.

12. The FET-based sensing device as claimed in claim 10, wherein each of the at least one FET element further comprises a sensing film is formed on the gate electrode, wherein the gate electrode with the sensing film is used as the active face.

13. The FET-based sensing device as claimed in claim 10, wherein each of the at least one FET element further comprises an extended gate electrode electrically connected to the gate electrode, wherein the extended gate electrode is used as the active face.

14. The FET-based sensing device as claimed in claim 10, wherein each of the at least one FET element further comprises: an extended gate electrode electrically connected to the gate electrode; and a sensing film formed on the extended gate electrode, wherein the extended gate electrode with the sensing film is used as the active face.

15. The FET-based sensing device as claimed in claim 2, wherein the reference electrode has: a body made of copper-nickel alloy; and a gold layer mounted around the body to provide the flat surface.

16. The FET-based sensing device as claimed in claim 15, wherein the gold layer is formed by plating gold process or electroless nickel immersion gold (ENIG) process.

17. The FET-based sensing device as claimed in claim 2, wherein the reference electrode has: a body made of polyamide; and a gold layer mounted around the body to provide the flat surface.

18. The FET-based sensing device as claimed in claim 17, wherein the gold layer is formed by plating gold process or electroless nickel immersion gold (ENIG) process.

19. The FET-based sensing device as claimed in claim 2, wherein the reference electrode has: a body made of gold; and a gold layer integrally formed around the body.

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