CN114624302B - PH sensor with high sensitivity on-chip integrated pseudo-reference grid and preparation method thereof - Google Patents

PH sensor with high sensitivity on-chip integrated pseudo-reference grid and preparation method thereof Download PDF

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CN114624302B
CN114624302B CN202210326643.XA CN202210326643A CN114624302B CN 114624302 B CN114624302 B CN 114624302B CN 202210326643 A CN202210326643 A CN 202210326643A CN 114624302 B CN114624302 B CN 114624302B
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pseudo
sensor
electrode
reference grid
chip
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CN114624302A (en
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张宇燕
肖梦梦
高云飞
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Beijing Yuanxin Carbon Based Integrated Circuit Research Institute
Xiangtan University
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Beijing Yuanxin Carbon Based Integrated Circuit Research Institute
Xiangtan University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/28—Electrolytic cell components
    • G01N27/30—Electrodes, e.g. test electrodes; Half-cells
    • G01N27/302—Electrodes, e.g. test electrodes; Half-cells pH sensitive, e.g. quinhydron, antimony or hydrogen electrodes

Abstract

The invention provides a high-sensitivity on-chip pH sensor integrated with a pseudo-reference grid and a preparation method thereof, wherein the pH sensor comprises: a silicon-based substrate; a dielectric layer on the surface of the silicon-based substrate; a source electrode and a drain electrode; a CNT channel layer; the pseudo-reference grid electrode is positioned on one side of the dielectric layer far away from the silicon-based substrate; and the passivation layer is arranged to wrap the surfaces of the source electrode and the drain electrode, so that only the CNT channel layer and the pseudo reference grid are exposed to the liquid environment when the pH sensor measures the pH value of the liquid. Compared with the design of a reference electrode with huge volume of the traditional pH sensor, the pH sensor with the pseudo-reference grid is integrated on the chip, the design of miniaturization and easy integration of the pH sensor can be realized based on the size effect, and the portable and real-time pH detection can be realized; meanwhile, the limit of Nernst can be broken through based on the size effect, and the design with high sensitivity is realized, so that the problems of the sensitivity and difficulty in integration of the traditional pH sensor are solved.

Description

PH sensor with high sensitivity on-chip integrated pseudo-reference grid and preparation method thereof
Technical Field
The invention relates to the technical field of pH sensors, in particular to a pH sensor based on a carbon nano tube type pH sensor, and specifically relates to a high-sensitivity on-chip pseudo-reference grid electrode integrated pH sensor and a preparation method thereof.
Background
The life body fluid maintains a stable pH range and is slightly changed, and the environment and life functions are greatly impaired. For example, when the pH of the body fluid is lowered from 6.9 to 6.5, the body fluid becomes acidic, in which case living cells of the human body are destroyed and tumors are easily formed. In fact, cancer breeds in an acidic environment, which also causes inflammation of blood cells, reduces oxygen content, destroys the metabolic state of cells, and hinders the functions of DNA and respiratory enzymes, thus blood coagulation, kidney, liver and sweat gland failure.
Thus, medical research and clinical real-time monitoring of biological fluids, sweat and blood is important. The current commercial pH sensor belongs to a primary battery system, and is generally composed of a chemical part and a signal transmission part by detecting the concentration of hydrogen ions in a measured object and converting the hydrogen ions into corresponding usable output signals, wherein the chemical part is used for converting chemical energy into electric energy, so that a measuring electrode and a reference electrode are needed to realize the pH sensor. The reference electrode is generally designed to be wrapped by a glass cylinder with the length of 10cm and the diameter of more than 1cm, and in the detection process, enough liquid needs to be detected, otherwise, too little body fluid cannot be detected, so that the reference electrode is not suitable for detecting a small amount of body fluid, and cannot meet the requirement of monitoring the body fluid of a human body at any time. Due to the volume design of the reference electrode, the existing pH sensor is difficult to miniaturize, expensive and difficult to realize portability design in a compatible manner with an integrated circuit. Furthermore, pH sensors based on the principle of galvanic systems are limited by the nernst equation, whose detection sensitivity is generally low, and are difficult to adapt to body fluid monitoring, which is complex and time-varying for the human body.
Meanwhile, the existing pH sensor also has the problems of liquid leakage and easy breaking, and cannot meet the requirements of portable real-time safety monitoring.
Disclosure of Invention
The invention aims to provide a micro-nano processed pH sensor with an on-chip integrated pseudo-reference grid, which achieves the micron level, realizes detection of a small amount of liquid based on a size effect, is easy to integrate with a rigid circuit board and a processing chip, realizes portable and safe real-time monitoring, and can break through the Nernst limit to realize high-sensitivity detection.
In another embodiment, the on-chip pseudo-reference grid pH sensor provided by the invention can break through the Nernst principle and has high sensitivity response.
According to a first aspect of the object of the present invention, there is provided a pH sensor with an on-chip pseudo-reference grid, comprising:
a silicon-based substrate defining a first surface and an opposing second surface;
a dielectric layer on the first surface of the silicon-based substrate;
a source electrode and a drain electrode which are positioned on one side of the dielectric layer far away from the silicon-based substrate, and are oppositely arranged and spaced;
the CNT channel layer is positioned on one side of the dielectric layer away from the silicon-based substrate and is positioned between the source electrode and the drain electrode;
the pseudo-reference grid electrode is positioned on one side of the dielectric layer far away from the silicon-based substrate; and
and the passivation layer is arranged to wrap the surfaces of the source electrode and the drain electrode, so that when the pH sensor measures the pH value of liquid, only the CNT channel layer and the pseudo reference grid are exposed to the liquid environment.
Wherein the dummy reference gate is not in contact with the source electrode, the drain electrode, and the CNT channel layer.
Wherein in a preferred embodiment, the metal material of the dummy reference gate is Au.
As an alternative example, the source electrode and the drain electrode are each a strip-shaped electrode of a certain thickness, and the dummy reference gate is located adjacent to an end portion of the strip-shaped electrode in the longitudinal direction and is arranged at a spacing.
As an alternative example, the dummy reference gate is a stripe-shaped electrode, and is disposed on the dielectric layer perpendicular to the source electrode and the drain electrode.
As an alternative example, the dummy reference gates are located in parallel with the longitudinal direction of the strip-shaped electrodes and are arranged at intervals.
As an alternative example, the thickness of the source electrode and the drain electrode is the same and is controlled to be 30-60nm; the thickness of the pseudo reference grid electrode is controlled to be 30-60nm.
As an alternative example, the thickness of the dummy reference gate is equivalent to the thickness of the source electrode and the drain electrode.
As an alternative example, the source and drain electrodes have a length of 30 μm or more and a width of 5 μm or more.
As an alternative example, the surface area of the pseudo-reference grid is less than or equal to 0.2535mm 2 。
As an alternative example, the pseudo reference gate, the source electrode and the drain electrode are all configured with independent and lead wires for signal extraction; the leads are all encapsulated and insulated.
According to a second aspect of the object of the present invention, a method for manufacturing a pH sensor with a pseudo-reference grid integrated on-chip is provided, characterized by comprising the steps of:
step 1, depositing SiO with a certain thickness on a silicon-based substrate 2 As a dielectric layer, si/SiO is formed 2 A structure;
step 2, depositing a CNT film on the upper surface of the dielectric layer;
step 3, the Si/SiO deposited with the CNT film is processed by a spin coater 2 Homogenizing the surface of the structure, exposing corresponding patterns by using a photoetching process, and performing CNT filmEtching to obtain a CNT channel layer;
step 4, exposing the source electrode (S), the drain electrode (D), the pseudo reference grid electrode (PRG) and the metal lead by using a photoetching machine, and depositing metal with a certain thickness by using a CVD process to form the source electrode (S), the drain electrode (D), the pseudo reference grid electrode (PRG) and the metal lead;
and 5, carrying out spin coating and exposure again, and packaging and insulating the source electrode (S), the drain electrode (D) and the metal lead, so that when the pH sensor measures the pH value of liquid, only the CNT channel layer and the Pseudo Reference Grid (PRG) are exposed to the liquid environment.
As an alternative embodiment, the dummy reference gate (PRG) is an Au metal electrode, and the thickness thereof is equivalent to the thicknesses of the source electrode (S) and the drain electrode (D).
Therefore, the pH sensor with the on-chip integrated pseudo-reference grid in combination with the technical scheme utilizes the Carbon Nano Tube (CNT) as a channel material, and metal Au is used as the on-chip pseudo-reference grid, so that the novel pH sensor is designed to reach the micron level, and the problems that the traditional pH sensor cannot be miniaturized and integrated on a PCB and an SOC due to a huge reference electrode are solved. The preparation process is compatible with the CMOS semiconductor preparation process, avoids using a huge reference electrode, realizes miniaturization and can be repeatedly used.
The pH sensor with the pseudo-reference grid integrated on the chip, provided by the invention, has the advantages that the pseudo-reference grid can be adsorbed with hydrogen ions, and the capacitance values are different under different pH solutions, so that the detection of the pH value is realized. Compared with the prior art adopting the design of the traditional huge reference electrode, the detection process of the prior art needs enough liquid to be detected in quantity to realize effective detection, and the liquid to be detected cannot be detected if the liquid to be detected is too small, but the pH sensor designed by the invention can be integrated and manufactured by micro-nano processing, the detection liquid can be very little, and the pH detection of the liquid to be detected with very little uL level can be detected.
Meanwhile, the primary battery system of the traditional commercial pH sensor is limited by a Nernst equation, the sensitivity of the primary battery system is generally low, and the sensor designed by the invention has the characteristic of high sensitivity by utilizing ion adsorption and double-electric-layer effect.
Drawings
The drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures may be represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. Embodiments of various aspects of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:
fig. 1 is a schematic diagram of a pH sensor with an on-chip integrated dummy reference gate according to an exemplary embodiment of the invention.
Fig. 2 is a schematic drawing of the metal lead out of the pH sensor of the embodiment of fig. 1 in accordance with the present invention.
Fig. 3a, 3b are schematic diagrams of source, gate and pseudo-reference gate distributions for different examples of pH sensors with on-chip integrated pseudo-reference gates according to exemplary embodiments of the present invention.
FIG. 4 is a schematic illustration of a process flow for preparing the pH sensor of the embodiment of FIG. 1 according to the present invention.
Fig. 5 is a schematic diagram of the measurement principle of the pH sensor of the embodiment of fig. 1 according to the present invention.
Fig. 6 is a schematic diagram of the application of a gate voltage and a scan voltage during measurement of the pH sensor of the embodiment of fig. 1 in accordance with the present invention.
FIG. 7 is a schematic diagram of transfer curves of different concentrations of pH obtained during measurement by the pH sensor of the embodiment of FIG. 1 according to the present invention.
Fig. 8 is a schematic diagram of the sensitivity test results of the pH sensor according to the embodiment of fig. 1.
Fig. 9 is a schematic diagram of the continuous detection result of the pH sensor according to the embodiment of fig. 1.
Fig. 10 is a schematic diagram of the sensitivity comparison of a pH sensor according to the embodiment of fig. 1 with a solution of the same pH value tested with a non-gold-on-wafer pseudo-reference gate electrode (gold wire).
Fig. 11 is a plot of area versus sensitivity for a dummy reference gate PRG of a pH sensor according to the embodiment of fig. 1.
Detailed Description
For a better understanding of the technical content of the present invention, specific examples are set forth below, along with the accompanying drawings.
Aspects of the invention are described in this disclosure with reference to the drawings, in which are shown a number of illustrative embodiments. The embodiments of the present disclosure are not necessarily intended to include all aspects of the invention. It should be understood that the various concepts and embodiments described above, as well as those described in more detail below, may be implemented in any of a number of ways, as the disclosed concepts and embodiments are not limited to any implementation. Additionally, some aspects of the disclosure may be used alone or in any suitable combination with other aspects of the disclosure.
PH sensor with chip integrated pseudo-reference grid
The pH sensor integrated with the pseudo-reference gate on-chip in connection with the exemplary embodiment shown in fig. 1 includes a silicon-based substrate 10, a dielectric layer 20, a source electrode 31, a drain electrode 32, a pooling layer 33, a CNT channel layer 40, and a pseudo-reference gate 50.
Wherein the silicon-based substrate 10 defines a first surface and an opposing second surface, the first surface being a subsequently prepared growth surface for ease of illustration as shown in connection with fig. 1. The silicon-based substrate 10 may be P-type silicon.
Referring to fig. 1, a dielectric layer 20 is located on a first surface of a silicon-based substrate 10. As an alternative example, the dielectric layer 20 employs silicon dioxide as a deposition base for the carbon nanotube CNTs while achieving electrical insulation between the CNTs and the silicon-based substrate 10.
As in the example of fig. 1, the source electrode 31 and the drain electrode 32 are located on a side surface of the dielectric layer remote from the silicon-based substrate 10. The source electrode 31 is disposed opposite to and spaced apart from the drain electrode 32 with the CNT channel layer 40 deposited therebetween.
As in the example of fig. 1, CNT channel layer 40 is located on the side of the dielectric layer remote from the silicon-based substrate and is located between source electrode 31 and drain electrode 32. The CNT channel layer 40 has a thickness controlled to be 0.5-2nm.
The dummy reference gate 50 is located on a side of the dielectric layer away from the silicon substrate 10, and the dummy reference gate 50 is not in contact with the source electrode 31, the drain electrode 32, and the CNT channel layer 40.
As shown in fig. 2, the source electrode 31, the drain electrode 32, and the dummy reference gate 50 are each led to the corresponding three output electrodes 70 via the respective corresponding metal leads 60, thereby realizing signal output.
In an alternative embodiment, the output electrode 70 may be electrically connected to an external device, such as a microcomputer system, to output signals to the external device for signal analysis. In alternative embodiments, the output electrodes may be soldered to a processing chip or rigid wiring board for signal analysis processing.
It should be appreciated that the metal leads 60 are each subjected to an insulating encapsulation process and are insulated from the conductive portions during inspection.
As shown in fig. 3a, the dummy reference gate 50 is designed to be spaced apart from the source electrode 31 and the drain electrode 32, for example, the source electrode 31 and the drain electrode 32 are designed to be stripe-shaped electrodes having a certain thickness, and the dummy reference gate 50 is located adjacent to the end portions of the stripe-shaped electrodes in the longitudinal direction and is arranged to be spaced apart. For example, the dummy reference gate 50 is designed as a stripe-shaped electrode, and is disposed on the surface of the dielectric layer 20 perpendicular to the source electrode 31 and the drain electrode 32.
In the embodiment shown in fig. 3a, the source electrode 31, the drain electrode 32 may be designed to have the same length and width. Thus, the design and manufacture of the lead wire are facilitated when the lead wire is led out.
In connection with another example arrangement shown in fig. 3b, the dummy reference gates 50 are located parallel to each other in the longitudinal direction of the strip-shaped gate electrodes, the drain electrodes, and are arranged spaced apart. For example, in fig. 3b, the dummy reference gate 50 is designed so as to be shifted in the longitudinal direction, regardless of whether it is closer to the gate electrode or the source electrode, in order to facilitate the wiring design and manufacturing.
For example, in some examples, the source electrode 31 and the drain electrode 32 are designed to have the same length, and the dummy reference gate 50 is arranged parallel to the source electrode 31 and the drain electrode 32 with a gap therebetween in the longitudinal direction, so that the dummy reference gate is easily wired.
In other examples, the source electrode 31 and the drain electrode 32 are designed to have different lengths, and the dummy reference gate 50 is closer to a shorter electrode when arranged in parallel with the source electrode 31 and the drain electrode 32, so that a section is left in the length direction to be staggered with the source electrode 31 and the drain electrode 32, thereby facilitating wiring.
As shown in fig. 1, passivation layers, such as passivation layers formed by S1813 photoresist encapsulation, are further prepared on the surfaces of the source electrode 31 and the drain electrode 32 and the outer surface of the metal lead 60, so that the conductive region of the pH sensor is not affected by the solution environment when measuring the pH value of the liquid, and only the CNT channel layer and the dummy reference gate are exposed to the liquid environment.
As an alternative example, the thickness of the source electrode 31 and the drain electrode 32 is the same and controlled to 30-60nm. The thickness of the dummy reference gate 50 is controlled to be 30-60nm.
As a preferable example, the thickness of the dummy reference gate 50 corresponds to the thicknesses of the source electrode 31 and the drain electrode 32.
As an alternative example, the length of the source electrode 31 and the drain electrode 32 is designed to be 30 μm or more and the width is designed to be 5 μm or more. In designs employing the source electrode 31 and the drain electrode 32 of the same length or different lengths, the lengths of the source electrode 31 and the drain electrode 32 may reach 50 μm, 100 μm, or even more than 500 μm.
In alternative embodiments, the widths of the source electrode 31 and the drain electrode 32 may be designed to have the same size or different sizes.
In an alternative embodiment, the source electrode 31 and the drain electrode 32 may be metal Au electrodes, and the thickness is controlled to be 50-60nm.
The dummy reference gate 50 is preferably an Au electrode having a thickness of 50-60nm.
As shown in connection with fig. 2, the output electrode 70 (pad) may be sized 60 μm by 60 μm or more, with a thickness of 30nm or more.
In an embodiment of the present invention, the surface area of the control pseudo-reference gate 50 is 0.2535mm or less 2 To reach and exceed the Nernst limitSensitivity, i.e. when PRG area is less than or equal to 0.2535mm 2 When the pH sensor is used, the detection sensitivity of the pH sensor is more than or equal to 59.16mV/pH.
Therefore, compared with the design of a reference electrode with huge volume of the traditional pH sensor, the pH sensor with the on-chip pseudo-reference grid of the exemplary embodiment of the invention can realize the design of miniaturization and easy integration of the pH sensor based on the size effect, and realize portable and real-time pH detection; meanwhile, the limit of Nernst can be broken through based on the size effect, and the design with high sensitivity is realized, so that the problems of the sensitivity and difficulty in integration of the traditional pH sensor are solved.
Preparation method
The preparation process of the on-chip pseudo-reference grid integrated pH sensor as an alternative example comprises the following steps:
step 1, depositing SiO with a certain thickness on a silicon-based substrate 2 As a dielectric layer, si/SiO is formed 2 The total thickness of the structure is 300-400nm;
step 2, at SiO 2 Depositing a CNT film on the upper surface of the dielectric layer, wherein the thickness is controlled to be 0.5-2nm;
step 3, the Si/SiO deposited with the CNT film is processed by a spin coater 2 Carrying out spin coating on the surface of the structure, exposing corresponding patterns by using a photoetching process, and etching the CNT film to obtain a CNT channel layer;
step 4, exposing the source electrode (S), the drain electrode (D), the pseudo reference grid electrode (PRG) and the metal lead by using a photoetching machine, and depositing metal with a certain thickness by using a CVD process to form the source electrode (S), the drain electrode (D), the pseudo reference grid electrode (PRG) and the metal lead;
and 5, carrying out spin coating and exposure again, and packaging and insulating the source electrode (S), the drain electrode (D) and the metal lead, so that when the pH sensor measures the pH value of liquid, only the CNT channel layer and the Pseudo Reference Grid (PRG) are exposed to the liquid environment.
As a specific example, fig. 4 schematically illustrates one specific process for preparing a pH sensor with an on-chip pseudo-reference grid, comprising:
first, the Si/SiO deposited with the CNT film is aligned on a spin coater using S1813 photoresist 2 Homogenizing the surface of the two-layer structure, and then etching the CNT film by photoetching and oxygen plasma etching (RIE) to form a CNT channel layer, so that the CNT is a channel region;
then, exposing a source electrode, a drain electrode, a pseudo reference grid and a metal lead of the device by using a ultraviolet photoetching machine, and depositing metal with the thickness of 60nm by using a CVD (chemical vapor deposition) process to form the source electrode, the drain electrode, the pseudo reference grid and the metal lead;
finally, spin coating and exposure are carried out again, and the source electrode, the gate electrode and the metal lead of the device are encapsulated by using S1813 photoresist, so that the conductive area of the device is not influenced by the solution environment when the pH value of liquid is measured, and only the CNT channel layer and the pseudo-reference gate area are exposed, so that the sensor device with the on-chip pseudo-reference gate electrode is manufactured.
Wherein SiO is 2 The deposition of the layers and the deposition of the CNTs can be prepared using existing semiconductor micro-nano processes.
Preferably, the purity of the CNT thin film is preferably up to 99.99% or more of the carbon nanotubes of the network structure.
Wherein Si/SiO 2 The thickness of the two-layer structure is controlled between 300 nm and 400nm. The minimum length of the source electrode and the drain electrode is controlled to be more than 30 mu m, the minimum width is controlled to be more than 5 mu m, and the thickness is controlled to be more than 30 nm.
The source electrode and the drain electrode can be Au metal electrodes or Ti/Au metal electrodes, and the thickness is 30-60nm.
The pseudo reference grid electrode can adopt an Au metal electrode, and the thickness is 30-60nm.
In an embodiment of the present invention, the on-chip pseudo-reference grid pH sensor prepared by the method illustrated in fig. 4 is designed to have the following dimensions:
source electrode: 1714um long, 10um wide and 60nm thick;
drain electrode: 50um long, 6um wide, 60nm thick;
pseudo-reference gate: 1820um long, 20um wide, 60nm thick.
The output electrode (pad) has a size of 240 μm or more and a thickness of 40nm.
PH detection
In connection with the detection schemes shown in fig. 5 and 6, only a small amount of liquid to be detected, such as a solution to be detected or body fluid, is needed in the detection process, and in the detection examples below, since the size of the pH sensor prepared by the present invention is very small, for example, reaches the micrometer level, the pH detection of a very small amount of uL level of liquid to be detected can be achieved, for example, the pH detection of 5uL level of liquid to be detected can be achieved.
During detection, the liquid to be detected is dropped on the sensor surface, for example, covered on the source electrode, the CNT channel layer, the drain electrode and the pseudo-reference gate. The dummy reference gate 50 may adsorb hydrogen ions, thereby causing a change in its surface state. H in the environment of the solution to be detected + When the concentration is increased or decreased, the positive charge on the surface of the pseudo reference gate electrode is increased or decreased, so that the electric double layer capacitance of the pseudo reference gate electrode is changed, and therefore, a voltage difference is formed under the solution environments with different pH values.
Based on the principle, when the pH value of the solution is tested by using the pH sensor of the embodiment of the invention, a voltage V with a certain magnitude is applied between the source collector electrode and the drain electrode of the sensor DS A certain range of scanning voltage is applied to the pseudo-reference grid electrode, and the current flowing between the source electrode and the drain electrode is different according to the pH value of the solution. The pH of each concentration we can scan a transfer curve, the pH transfer curves of different concentrations will differ, based on the on-chip gold pseudo-reference electrode, we can find that the smaller the pH, the transfer curve moves in the positive direction, as shown in fig. 7. Wherein the pH sensitivity is defined as: taking the same Ids at each concentration, the Vgs will be different, so that different Vgs will be the result of a change in threshold voltage, whereby a function between Vgs and pH can be obtained, the slope of which is the sensitivity. In the example shown in fig. 7, we use ids=1e -8 A is an example of a sensitivity curve obtained based on values of Vgs obtained by scanning.
In some embodiments, the scan voltage applied by the dummy reference gate may be scanned in a sweep mode. In the detection process, the scanning voltage range can be within the range of-1V to 1V. For example, a scanning voltage of-0.6V to 0.4V is used, and the time is related. A total of 200 Ids points were collected at-0.6V with a voltage applied per second, thus obtaining a transfer curve.
Test comparison
The tests and analyses were performed on the basis of the pH sensor (CNT-FET) prepared in the previous examples.
The test procedure was based on the B-R buffer solution proposed by Britton and Robinson, i.e. a mixed solution of phosphoric acid, acetic acid and boric acid, to which different amounts of sodium hydroxide were added to prepare buffer solutions of different pH ranges as test samples.
Finally, the ionic strength was adjusted to 0.5000 by incorporating potassium chloride. The pH of the samples was measured at 22℃with a pH meter and the pH of the samples was 5.5, 6.1, 6.7, 7.2 and 7.9, respectively. All test solutions were formulated with deionized water (18.2 mΩ). All chemical reagents used in the configuration were of analytical reagent grade.
We plot the gate voltage V of the required pseudo-reference gate for the same source-drain current GS And the gate voltage V GS The graph is plotted against pH, as shown in FIG. 8, with pH on the abscissa and gate voltage V on the ordinate GS The slope of the curve is the sensitivity of the sensor detection response. As shown in fig. 8, the sensitivity of the pH sensor reached 108mV/pH and exhibited sensitivity exceeding the nernst limit over a wide pH range, while exhibiting good linearity and a wide range of stability.
In the example shown in fig. 8, there is a transfer curve at each pH, and after extracting the threshold voltage of the transfer curve, the functional relationship between the value of the threshold voltage and the pH is fitted, and the slope is the sensitivity. The sensitivity of the pH sensor prepared according to the embodiment of the invention reaches 108mV/pH by fitting and acquiring sensitivity in another way.
In combination with the schematic diagram of the continuous real-time detection results shown in fig. 9, the continuous detection of samples with 5 different pH values shows high consistency and can be used repeatedly.
Referring to fig. 10, the detection sensitivity of the pH sensor with the non-on-chip gold pseudo-reference gate electrode is compared with that of the pH sensor with the on-chip gold pseudo-reference gate electrode according to the embodiment of the present invention, wherein the pH sensor with the non-on-chip gold pseudo-reference gate electrode uses gold wire as the reference gate electrode, and in the comparison curve shown in fig. 10, the detection sensitivity of the pH sensor designed by the present invention is more than 2 times that of the pH sensor with the non-on-chip gold pseudo-reference gate electrode.
In the test result of the relation between the area and the sensitivity of the pseudo-reference electrode PRG shown in FIG. 11, the pseudo-reference electrode PRG of the pH sensor designed by the invention is less than or equal to 0.2535mm 2 When the pH sensor detects the sensitivity of more than or equal to 59.16mV/pH,59.16mV/pH is Nernst limit value.
Therefore, according to the pH sensor of the on-chip integrated gold pseudo-reference gate electrode, on one hand, the pH sensor which is prepared by integrating the Au pseudo-reference gate electrode on the chip and adopting a semiconductor process is adopted, so that high miniaturization and integration are realized, the problem that the on-chip integrated gold pseudo-reference gate electrode cannot be integrated due to the use of a huge reference electrode is avoided, and the pH sensor of the on-chip integrated gold pseudo-reference gate electrode is easy to integrate to a rigid circuit board and a processing chip, so that portable real-time monitoring is realized; aiming at the detection object, detection can be realized under the condition of obtaining a very small amount of liquid; on the other hand, the pH sensor which is prepared by integrating the Au pseudo-reference grid on the chip and adopting the semiconductor technology can break through the Nernst limit value based on the size effect, so that the sensitivity of the pH sensor is enhanced, and the problem of low sensitivity of the traditional pH sensor is solved.
While the invention has been described with reference to preferred embodiments, it is not intended to be limiting. Those skilled in the art will appreciate that various modifications and adaptations can be made without departing from the spirit and scope of the present invention. Accordingly, the scope of the invention is defined by the appended claims.

Claims (10)

1. A high sensitivity on-chip pseudo-reference grid integrated pH sensor comprising:
a silicon-based substrate defining a first surface and an opposing second surface;
a dielectric layer on the first surface of the silicon-based substrate;
a source electrode and a drain electrode which are positioned on one side of the dielectric layer far away from the silicon-based substrate, and are oppositely arranged and spaced; the source electrode and the drain electrode are strip-shaped gold electrodes with certain thickness;
the CNT channel layer is positioned on one side of the dielectric layer away from the silicon-based substrate and is positioned between the source electrode and the drain electrode;
the pseudo-reference grid electrode is positioned on one side of the dielectric layer far away from the silicon-based substrate; and
a passivation layer disposed to wrap around the surfaces of the source and drain electrodes such that only the CNT channel layer and the dummy reference gate are exposed to a liquid environment when the pH sensor is measuring a liquid pH;
wherein the pseudo reference gate is not in contact with the source electrode, the drain electrode and the CNT channel layer;
the pseudo reference grid is a gold electrode, can be adsorbed with hydrogen ions, and has different capacitance values under different pH solutions, so that the detection of the pH value is realized.
2. The high sensitivity on-chip pseudo-reference grid pH sensor according to claim 1, wherein the pseudo-reference grid is located adjacent to the lengthwise ends of the source and drain strip gold electrodes and is disposed in a spaced apart relationship.
3. The high sensitivity on-chip pseudo-reference gate pH sensor of claim 2, wherein the pseudo-reference gate is a strip gold electrode disposed on the dielectric layer perpendicular to the source and drain electrodes.
4. The high sensitivity on-chip pseudo-reference grid pH sensor according to claim 1, wherein the pseudo-reference grid is located parallel to the longitudinal direction of the source and drain strip gold electrodes and is arranged at a distance.
5. The high sensitivity on-chip pseudo-reference gate pH sensor of claim 1, wherein the source electrode and drain electrode are the same thickness.
6. The high sensitivity on-chip pseudo-reference grid pH sensor of claim 1, wherein the pseudo-reference grid thickness is between 30-60nm.
7. The high sensitivity on-chip pseudo-reference gate pH sensor of claim 1, wherein the source and drain electrodes are 30 μm or more in length and 5 μm or more in width.
8. The high sensitivity on-chip pseudo-reference grid pH sensor according to any one of claims 1-7, wherein the pseudo-reference grid has a surface area of 0.2535mm or less 2 。
9. The high sensitivity on-chip pseudo-reference grid pH sensor according to any one of claims 1-7, wherein the pseudo-reference grid, source electrode and drain electrode are each configured with separate and leaded lines for signal extraction; the leads are all encapsulated and insulated.
10. A method of manufacturing a high sensitivity on-chip pseudo-reference grid pH sensor according to any one of claims 1-9, comprising the steps of:
step 1, depositing SiO with a certain thickness on a silicon-based substrate 2 As a dielectric layer, si/SiO is formed 2 A structure;
step 2, depositing a CNT film on the upper surface of the dielectric layer;
step 3, bySpin coater to deposit Si/SiO with CNT film 2 Carrying out spin coating on the surface of the structure, exposing corresponding patterns by using a photoetching process, and etching the CNT film to obtain a CNT channel layer;
step 4, exposing the source electrode, the drain electrode, the pseudo reference grid and the metal lead by using a photoetching machine, and depositing metal with a certain thickness by using a CVD process to form the source electrode, the drain electrode, the pseudo reference grid and the metal lead;
and 5, carrying out spin coating and exposure again, and packaging and insulating the source electrode, the drain electrode and the metal lead, so that when the pH sensor measures the pH value of the liquid, only the CNT channel layer and the pseudo reference grid are exposed to the liquid environment.
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