CN104237357A - Sensing element, preparation method and sensor - Google Patents
Sensing element, preparation method and sensor Download PDFInfo
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- CN104237357A CN104237357A CN201310231991.XA CN201310231991A CN104237357A CN 104237357 A CN104237357 A CN 104237357A CN 201310231991 A CN201310231991 A CN 201310231991A CN 104237357 A CN104237357 A CN 104237357A
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Abstract
The invention provides a sensing element. The sensing element comprises a substrate and a source electrode and a drain electrode which are fixed to the substrate. A graphene film is electrically connected between the source electrode and the drain electrode. The sensing element is characterized in that there is a cavity between the graphene film and the substrate. The invention also provides a preparation method of the sensing element, the sensing element prepared by the preparation method and a sensor. Through the above technical scheme, conductivity of graphene in the sensor is raised greatly.
Description
Technical field
The present invention relates to bio-instruments engineering field, particularly, relate to a kind of sensing element, sensing element that a kind of preparation method of sensing element, this preparation method obtain and a kind of sensor.
Background technology
Field effect transistor is a kind of electronic component being controlled electric current by field effect, there is grid (gate), source electrode (source) and drain electrode (drain) three terminals, the electric field produced by the voltage putting on grid carrys out the size of current circulated in the raceway groove of control linkage source electrode and drain electrode.The raceway groove of conventional field effect transistor is made up of heavily doped silicon.
Along with the development of nanosecond science and technology, various novel low-dimension nano material, such as silicon nanowires (SiNW), carbon nano-tube (CNT), Graphenes (graphene) etc., arouse widespread concern with the character of its uniqueness (surface effect, bulk effect and quantum size effect etc.).Compare with traditional material, nano material has less size, higher specific surface area, more excellent electrical properties, better biocompatibility etc.When the raceway groove of conventional field effect transistor is substituted by nano material, namely nano material field effect transistor is constituted, such as silicon nanowires field effect transistor (SiNW-field effect transistor), carbon nanotube field-effect transistor (CNT-field effect transistor), graphene field effect transistor (Gra-field effect transistor) etc.
Graphene is a kind of emerging carbon nanomaterial, and have that conductivity is high, physical strength is large, the physical and chemical performance that electrochemical stability etc. are excellent, makes it have unique application advantage in high-sensitivity detection field, cause people and pay close attention to greatly.Graphene is the planar crystal of individual layer atomic building, each atom from the teeth outwards, the change of external environment, all by directly affecting all carbon atoms forming Graphene, makes it extremely sensitive to the response at interface, and simultaneously unique structure makes it have outstanding detection sensitivity.Highly sensitive nitrogen monoxide (NO) the gas detect chip based on Graphene developed at present, has the high detection sensitivity of single NO molecule, shows that Graphene has huge potentiality as detection chip sensitive element.
Although each atom from the teeth outwards this characteristic imparts the high detection sensitivity of the Graphene change of environment to external world, but need Graphene to transfer on passive base material in conventional sensors method for making, inevitably cause base material to the doping of Graphene, reduce the mobility of charge carrier in Graphene, have a strong impact on the detection sensitivity of sensor.
Summary of the invention
In order to improve the sensitivity of sensor further, the invention provides a kind of sensing element, sensing element that a kind of preparation method of sensing element, this preparation method obtain and a kind of sensor.
Applicant finds Graphene sensing element Graphene being departed from substrate, make hanging shape, it can be made to avoid and the close contact of base material and being doped, can improve the sensitivity of sensor further, resulting in the present invention.
To achieve these goals, on the one hand, the invention provides a kind of sensing element, this sensing element comprises substrate and the source electrode that is fixed on this substrate and drain electrode, and be electrically connected with graphene film between source electrode and drain electrode, it is characterized in that, between graphene film and substrate, there is cavity.
On the other hand, the invention provides a kind of preparation method of sensing element, wherein, the method comprises the steps:, and (1) adheres to graphene film on substrate; (2) on the substrate that attached to graphene film, form source electrode and drain electrode, and form electrical connection between source electrode and graphene film and between drain electrode and graphene film; (3) make the surperficial step-down of the substrate under graphene film, to make the surface of the substrate under graphene film be separated with graphene film, form cavity; And source electrode and drain electrode are fixed on substrate.
On the other hand, present invention also offers the sensing element that above-mentioned preparation method prepares.
On the other hand, present invention also offers a kind of sensor, this sensor comprises above-mentioned sensing element and contrast electrode.
By technique scheme, the present invention improves the conductivity of the Graphene in sensor significantly.
Other features and advantages of the present invention are described in detail in embodiment part subsequently.
Accompanying drawing explanation
Accompanying drawing is used to provide a further understanding of the present invention, and forms a part for instructions, is used from explanation the present invention, but is not construed as limiting the invention with embodiment one below.In the accompanying drawings:
Fig. 1 is the schematic diagram adhering to graphene film process on substrate.
Fig. 2 is the schematic diagram in the process forming sensing element of the present invention.
Fig. 3 is the schematic diagram of the substrate that attached to graphene film.
Fig. 4 is the schematic diagram of the substrate sheltered with photoresist.
Fig. 5 is the schematic diagram of the substrate after exposure imaging, shows the region forming electrode.
Fig. 6 is the schematic diagram of the substrate defining electrode.
Fig. 7 is the schematic diagram of the substrate eliminating photoresist.
Fig. 8 is the schematic diagram being provided with liquid storage tank and being filled with liquid in liquid storage tank.
Fig. 9 is the schematic diagram having carried out the substrate after suitable etching in liquid storage tank with hydrofluorite.
Figure 10 is after eliminating the liquid in liquid storage tank and liquid storage tank, the schematic diagram of sensing element of the present invention.
Figure 11 is the schematic diagram of the sensing element of the present invention with liquid storage tank.
Figure 12 is the stereoscan photograph of sensing element of the present invention.
Figure 13 is the schematic diagram of sensor of the present invention.
Figure 14 is the variation relation result figure of conductivity G with contrast electrode voltage Vgate carrying out etching front and back sensing element with hydrofluorite.
Figure 15 is the relational result figure that the electric current in sensing element of the present invention changes along with the pH value difference of liquid sample.
Figure 16 a is that sensing element of the present invention is at the schematic diagram measuring the application in cell membrane potential.
Figure 16 b is the result figure of the cell membrane potential change that sensing element senses of the present invention arrives.
Description of reference numerals
The basic unit of surface layer 3 substrate of 1 graphene film 2 substrate
4 photoresists 5 form the region of source electrode
Region 7 source electrode 8 drain electrode of 6 formation drain electrodes
Sidewall 10 cavity of 9 formation liquid storage tanks
Embodiment
Below the specific embodiment of the present invention is described in detail.Should be understood that, embodiment described herein, only for instruction and explanation of the present invention, is not limited to the present invention.
The invention provides a kind of sensing element, this sensing element comprises substrate and the source electrode that is fixed on this substrate and drain electrode, and is electrically connected with graphene film between source electrode and drain electrode, it is characterized in that having cavity between graphene film and substrate.
Wherein, sensing element of the present invention can as the element of field effect transistor chemical biosensor.
Wherein, the substrate of the various materials that are electrically insulated that described substrate can use for the routine in sensor apparatus field, such as, have thermal oxide SiO
2at least one in the silicon substrate of layer, silicon dioxide substrate, silicon nitride board, silicon carbide substrate, silicate glass substrate, mica substrate and organic polymer substrate.Wherein, the size of substrate, thickness and shape also can be conventional selection.Such as, substrate can the square shape sheet substrate of long 4-7cm, wide 3-6cm, thick 0.1-0.3cm.
Wherein, described graphene film can be the graphene film that various routine uses, such as, graphene film for being obtained by the method for chemical gaseous phase deposition, also can for the graphene film obtained by the method for mechanical stripping.
According to sensing element of the present invention, wherein, the height of cavity can be 100-280nm, is preferably 120-260nm, is more preferably 140-240nm.Wherein, in the present invention, the height of cavity refers to the distance between graphene film and substrate.
According to sensing element of the present invention, wherein, the floorage of cavity can be the 70-99% of the area of graphene film, is preferably 75-95%, is more preferably 80-90%.Wherein, the floorage of cavity refers to the projected area of cavity in the plane parallel with graphene membrane surface.
Wherein, the distance between source electrode and drain electrode can be 500-5000nm, is preferably 750-4000nm, is more preferably 1000-3000nm.Wherein, the distance between source electrode and drain electrode refers to the distance between adjacent source electrode and drain electrode between immediate 2.Wherein, source electrode and drain electrode can be the electrode used conventional in field effect chemical biosensor field, such as can for the metal electrode obtained by hot evaporation or ion beam evaporation, the material of metal electrode can be at least one in platinum, gold and chromium, and the thickness of electrode can be 30nm-150nm.Source electrode and the connection be provided with between drain electrode and substrate for fixing.
Present invention also offers a kind of preparation method of sensing element, wherein, the method comprises the steps:, and (1) adheres to graphene film on substrate; (2) on the substrate that attached to graphene film, form electrode, described electrode comprises source electrode and drain electrode, and forms electrical connection between source electrode and graphene film and between drain electrode and graphene film; (3) make the surperficial step-down of the substrate under graphene film, to make the surface of the substrate under graphene film be separated with graphene film, form cavity; And source electrode and drain electrode are fixed on substrate.
Wherein, described graphene film can be the graphene film that various routine uses, such as, graphene film for being obtained by the method for chemical gaseous phase deposition, also can for the graphene film obtained by the method for mechanical stripping.
Wherein, the operation of substrate adhering to graphene film can be realized by the mode pressed on substrate by graphene film.
Wherein, under preferable case, reference literature (Li X S, Cai W W, An J H, et al.Large-area synthesis of high-quality and uniform graphene films on copper foils.Science, 2009,324:1312 – 1314) method, by the method growing graphene of chemical gaseous phase deposition in copper substrate; Then have in the copper substrate of Graphene in growth and apply one deck photoresist; Just be coated with photoresist again and grow to have in the copper substrate of Graphene and copper etching liquid (mixed solution of such as ferric trichloride and hydrochloric acid) and etch; Etching completely after, the remaining photoresist being attached with Graphene to be attached on substrate and to press; Then dissolve removing photoresist, retain graphene film on substrate, namely obtain the substrate being attached with graphene film.
Wherein, can position the graphene film on substrate under an optical microscope based on interference effect and mark its border, Raman spectrum can also be utilized to identify further its number of plies.
Preparation in accordance with the present invention, wherein, under preferable case, in step (1), substrate comprises basic unit and is attached to the surface layer in basic unit, and is attached on the surface layer of substrate by graphene film; Basic unit is silicon chip, and surface layer is silicon dioxide layer.Under this preferable case, substrate can directly be prepared by the mode of being carried out being oxidized by silicon chip, also be easy to carry out positioning the graphene film on substrate under an optical microscope based on interference effect and marking its border, and surface layer directly can form cavity by the etching of SiO 2 etch liquid (as hydrofluorite).
Preparation in accordance with the present invention, wherein, under preferable case, in step (2), the substrate regions that substrate forms source electrode comprises the region that covered by graphene film and not by region that graphene film covers; The substrate regions that substrate forms source electrode comprises the region that covered by graphene film and not by region that graphene film covers; Distance between source electrode and drain electrode is 500-5000nm, is preferably 750-4000nm, is more preferably 1000-3000nm.
Wherein, under preferable case, substrate is formed in the substrate regions of electrode, the region covered by graphene film and the area ratio in region do not covered by graphene film are 0.3-1.7:1, are preferably 0.5-1.5:1, are more preferably 0.8-1.2:1.
Wherein, on substrate, can its border be determined by observation by light microscope by the region that graphene film covers and locate.The boundary in region covered at graphene film can select to comprise the region that covered by graphene film and the region that do not covered by graphene film as the substrate regions forming source electrode on substrate.After being selected in substrate regions substrate being formed electrode, can the substrate regions of formation electrode being exposed by the mode of conventional photoetch and shelter the substrate regions not forming electrode, then form electrode by hot evaporation or ion beam evaporation.Covert can also be removed after formation electrode.Wherein, source electrode and drain electrode can be the electrode used conventional in field effect chemical biosensor field, such as can for the metal electrode obtained by hot evaporation or ion beam evaporation, the material of metal electrode can be at least one in platinum, gold and chromium, and the thickness of electrode can be 0.03 μm-0.15 μm.Source electrode and the connection be provided with between drain electrode and substrate for fixing.Such as by metal electrode that hot evaporation or ion beam evaporation obtain, the region that covered by graphene film is included and not by region that graphene film covers owing to forming the region of electrode, defined the electrical links between electrode and graphene film by the region that graphene film covers on the one hand, do not defined between electrode and substrate for fixing connection by the region that graphene film covers on the other hand.
Preparation in accordance with the present invention, wherein, under preferable case, in step (3), by the mode of SiO 2 etch liquid and substrate contacts being made the surperficial step-down of the substrate under graphene film, and the condition of SiO 2 etch liquid and substrate contacts makes the surface layer under source electrode and drain electrode all do not corroded.Wherein, SiO 2 etch liquid is the hydrofluorite of concentration 21-22 % by weight.Wherein, the inert material of the liquid of resistance to SiO 2 etch (as dimethyl silicone polymer, PDMS) can be used on substrate, to form liquid storage tank, to hold SiO 2 etch liquid.This liquid storage tank can also be used for holding cleansing solution, to stop the effect of SiO 2 etch liquid, or the SiO 2 etch liquid of wash residual.
Preparation in accordance with the present invention, wherein, as a kind of highly preferred embodiment, in step (1), substrate comprises basic unit and is attached to the surface layer in basic unit, and is attached on the surface layer of substrate by graphene film; Basic unit is silicon chip, and surface layer is silicon dioxide layer, and thickness is 275-300nm and is greater than the height of cavity; In step (2), the substrate regions that substrate forms source electrode comprises the region that covered by graphene film and not by region that graphene film covers; The substrate regions that substrate forms source electrode comprises the region that covered by graphene film and not by region that graphene film covers; Distance between source electrode and drain electrode is 500-5000nm, is preferably 750-4000nm, is more preferably 1000-3000nm; By the mode of evaporation, the substrate regions of source electrode to be formed forms electrode; In step (3), by the mode of SiO 2 etch liquid and substrate contacts being made the surperficial step-down of the substrate under graphene film, and the condition of SiO 2 etch liquid and substrate contacts makes the surface layer under source electrode and drain electrode all do not corroded; SiO 2 etch liquid is the hydrofluorite of concentration 21-22 % by weight; By controlling the time of hydrofluorite and substrate contacts, make the floorage of cavity be the 70-99% of the area of graphene film, preferably 75-95%, is more preferably 80-90%, and the surface layer under source electrode and drain electrode is not all corroded.Under normal circumstances, can use the hydrofluoric acid dips graphene film 1-10 minute of concentration 21-22 % by weight, under hydrofluorite infiltration graphene film, also etch silicon dioxide forms cavity.Graphene film partial suspended is in surface.
Present invention also offers the sensing element that preparation method as above prepares.
Present invention also offers a kind of sensor, this sensor comprises sensing element as above and contrast electrode.
Below will be described the present invention by embodiment.Below by embodiment, the present invention is further described.In following examples, scanning electron microscope is purchased from HIT model S-4800.The tester of electrical properties is purchased from American AXON company model Axopatch200B electrical testing system.Agents useful for same is the analytical reagent be purchased.
Embodiment 1
With reference to figure 1-11, the present embodiment is used for illustrating that method according to the present invention prepares sensing element, i.e. deflocculated graphite alkene field effect device.
(1) with reference to figure 1, according to document (Li X S, Cai W W, An J H, et al.Large-area synthesis of high-quality and uniform graphene films on copper foils.Science, 2009,324:1312 – 1314) in method by the method for chemical gaseous phase deposition at the upper growing graphene of copper substrate (size is 4cm × 8cm, and thickness is 100 μm).The photoresist (PMMA950K, purchased from German ALLRESIST company) that spin coating one deck 300nm is thick on the copper sheet having Graphene, at 180 DEG C, baking makes solvent volatilize completely; Spin coating had the copper sheet of photoresist to put into copper etching liquid (solution containing 1mol/L ferric trichloride and 1mol/L hydrochloric acid) to be etched to copper and to react completely; Obtain the graphene film adhered on a photoresist.
(2) with reference to figure 3,280nm thermal oxide SiO will be had
2silicon chip (size is 3cm × 3cm, and thickness is 0.52cm, purchased from American sillicon Valley Microelectrics) as substrate, namely basic unit is silicon chip, surface layer is the substrate of silicon dioxide layer.Attachment graphene film is on a photoresist transferred on substrate, and pressing makes graphene film and substrates into intimate contact; Then by photoresist lysate (acetone), the photoresist of graphene membrane surface is dissolved, retain graphene film on substrate, obtain the substrate being attached with graphene film.Located under an optical microscope and mark boundaries based on interference effect, for determining the region forming electrode.
(3) with reference to figure 4 and Fig. 5, the substrate being attached with graphene film forms source electrode and drain electrode.Particularly, revolve the thick photoresist of Tu one deck 800nm (PMMA950K, purchased from German ALLRESIST company) at the substrate surface being attached with graphene film, be baked to solvent volatilization at 180 DEG C completely.According to the border of the graphene film marked under optical microscope, determine the region forming electrode, form the region that covered by graphene film in the region of electrode (width is the strip electrode of 2 μm) and the area ratio in region that do not covered by graphene film is 1:1, with electron beam exposure apparatus, the region forming electrode is exposed, development 10min in developer solution (4-methyl-2 pentanone and isopropyl alcohol press the mixed liquor of the volume ratio mixing of 1:5), dries up with nitrogen after fixing 10min in isopropyl alcohol; Expose the substrate regions forming electrode thus and shelter the substrate regions not forming electrode.
With reference to figure 6, in high vacuum conditions, according to document (" film preparing technology basis "; the vertical man (Japan) of numb Dill is outstanding, and Chen Guorong translates, Chemical Industry Press, 2009) method in, utilize the electron beam evaporation plating machine thick Au of Cr and 50nm that evaporation 5nm is thick successively on sample (namely exposing the substrate regions forming electrode and shelter the substrate of the substrate regions not forming electrode), obtain electrode, respectively as source electrode and drain electrode stand-by.
With reference to figure 7, remove the photoresist on the sample of the good electrode of evaporation, the electrical links between electrode and graphene film is defined by the region that graphene film covers, do not defined for fixing connection between electrode and substrate by the region that graphene film covers, the distance between source electrode and drain electrode is 2000nm.
(4) with reference to figure 8-11, on the substrate defining electrode, to be provided with the real estate of graphene film and electrode for bottom surface, (size is for 1.5cm × 1.5cm to form liquid storage tank to surround sidewall with PDMS, the degree of depth is 0.8cm), to make when liquid sealed up for safekeeping by this liquid storage tank, graphene film is soaked in liquid completely.In liquid storage tank, add SiO 2 etch liquid (hydrofluorite of concentration 22 % by weight), soak graphene film 5min, under hydrofluorite infiltration graphene film, also etch silicon dioxide forms cavity.The floorage recording cavity at observation by light microscope is 90% of the area of graphene film.
Structure substantially element is as shown in Figure 10 sensing element prepared by the present embodiment.Utilize its micromechanism of scanning electron microscopic observation, as shown in figure 12: be Graphene (Graphene) in dashed rectangle, both sides are source-drain electrode, and material is chromium gold (Cr/Au).Visible Graphene in hanging shape, leaves the distance that substrate is about 200nm under the support of both sides cr-au electrode.
Comparative example 1
Sensing element is prepared according to the method for embodiment 1, unlike, do not use SiO 2 etch liquid to etch, namely do not there is the sensing element of cavity.
Embodiment 2
The present embodiment be used for illustrate sensing element (that is, deflocculated graphite alkene field effect device) electric property.
With reference to Figure 13, use sensing element prepared by embodiment 1, using two of Graphene two ends Cr/Au electrodes as source electrode and drain electrode, Ag/AgCl electrode as contrast electrode (that is, solution gate electrode (Vgate)), thus is assembled into sensor.
By grounded drain, the voltage Vsd(0.01-0.1V that source electrode is fixed), measure the variation relation of the conductance G between source electrode and drain electrode with grid voltage Vgate, to characterize the Electronic Transport Properties of Graphene.As shown in figure 14: in the sensing element (i.e. the sensing element of comparative example 1) of non-deflocculated graphite alkene, the hole of G-Vg curve is propped up with electronics Zhi Mingxian asymmetric, there is translation in the Graphene of dirac point relative intrinsic, show the Si/SiO that Graphene is subject to it and pastes on Vgate axle
2the doping impact of substrate; In the sensing element (i.e. the sensing element of embodiment 1) that Graphene suspends, record its G-Vg(and be one axis of symmetry crosses dirac point, is similar to the G-Vg curve of assertive evidence Graphene about vertical axisymmetric curve, conductance improves a lot before suspending.
Embodiment 3
The present embodiment is used for the electric property of sensing element of the present invention (that is, deflocculated graphite alkene field effect device) and the application in the change of measuring chemical substance in solution are described.
With reference to Figure 13, use sensing element prepared by embodiment 1, using two of Graphene two ends Cr/Au electrodes as source electrode and drain electrode, Ag/AgCl electrode as contrast electrode (that is, solution gate electrode (Vgate)), thus is assembled into sensor.
Apply voltage by the contrast electrode Ag/AgCl in solution, between source electrode and drain electrode (Cr/Au electrode), apply constant channel voltage simultaneously.In liquid storage tank, add sample solution, in sample solution, the change of charged ion concentration and kind by changing the concentration of electric charges of graphenic surface, thus can change the electric current of graphene field effect pipe.By detecting the change of Graphene electric current, the change of chemical substance in solution can be detected.
Based on above-mentioned Cleaning Principle, deflocculated graphite alkene field effect device is used for the change detecting pH value of solution.The pH value calibration solution (purchased from American Sigma company) of different pH value (pH is respectively 6,7,8 and 9) is added according to this in liquid storage tank, because in the sample to be tested solution of different pH value, the change of charged ion concentration and kind can change the concentration of electric charges of graphene membrane surface, and then change the electric current of graphene field effect pipe.As shown in figure 15, detect that corresponding change occurs the electric conductivity value of graphene field effect pipe, react very rapid and sensitive, change stepped between different pH value.
Embodiment 4
The present embodiment is used for the application of sensing element (that is, deflocculated graphite alkene field effect device) in cellular electrophysiologicalsensor detects is described.
As illustrated in fig 16 a, by applying constant channel voltage between the source electrode at Graphene two ends and drain electrode, the electric current that in graphene nanobelt, generation one is constant under this voltage.After in cell or tissue and device, Graphene forms close contact, when the film potential of cell changes, this small voltage is to by cr-au electrode, the electromotive force be applied on Graphene has an impact, and then the electric current making to flow through Graphene produces corresponding change, by detecting this curent change and then realizing the measurement of the action potential change in cell membrane.
Based on above-mentioned Cleaning Principle, as shown in fig 16b, by deflocculated graphite alkene field effect device (i.e. the sensing element of embodiment 1) for detecting the change of ground squirrel.Acute isolation animal cardiac muscle cell dispersal drop is added deflocculated graphite alkene field effect device liquid storage tank and carries out original cuiture.After cardiac muscle cells and graphene device form close contact, along with the spontaneous beat of cardiac muscle cell, graphene field effect pipe can be recorded to corresponding cardiac muscle cell born of the same parents' volta potential change, relative to the sensing element (i.e. the sensing element of comparative example 1) that Graphene does not suspend, the signal amplitude detected after suspension promotes greatly, demonstrates deflocculated graphite alkene field effect transistor and has very high detection sensitivity.
More than describe the preferred embodiment of the present invention in detail; but the present invention is not limited to the detail in above-mentioned embodiment, within the scope of technical conceive of the present invention; can carry out multiple simple variant to technical scheme of the present invention, these simple variant all belong to protection scope of the present invention.
It should be noted that in addition, each concrete technical characteristic described in above-mentioned embodiment, in reconcilable situation, can be combined by any suitable mode, in order to avoid unnecessary repetition, the present invention illustrates no longer separately to various possible array mode.
In addition, also can carry out combination in any between various different embodiment of the present invention, as long as it is without prejudice to thought of the present invention, it should be considered as content disclosed in this invention equally.
Claims (10)
1. a sensing element, this sensing element comprises substrate and the source electrode that is fixed on this substrate and drain electrode, and is electrically connected with graphene film between source electrode and drain electrode, it is characterized in that having cavity between graphene film and substrate.
2. sensing element according to claim 1, wherein, the height of cavity is 100-280nm, is preferably 120-260nm, is more preferably 140-240nm.
3. sensing element according to claim 1 and 2, wherein, the floorage of cavity is the 70-99% of the area of graphene film, is preferably 75-95%, is more preferably 80-90%; Distance between source electrode and drain electrode is 500-5000nm, is preferably 750-4000nm, is more preferably 1000-3000nm.
4. a preparation method for sensing element, wherein, the method comprises the steps:
(1) on substrate, graphene film is adhered to;
(2) on the substrate that attached to graphene film, form electrode, described electrode comprises source electrode and drain electrode, and forms electrical connection between source electrode and graphene film and between drain electrode and graphene film;
(3) make the surperficial step-down of the substrate under graphene film, to make the surface of the substrate under graphene film be separated with graphene film, form cavity; And source electrode and drain electrode are fixed on substrate.
5. preparation method according to claim 4, wherein, in step (1), substrate comprises basic unit and is attached to the surface layer in basic unit, and is attached on the surface layer of substrate by graphene film; Basic unit is silicon chip, and surface layer is silicon dioxide layer.
6. preparation method according to claim 5, wherein, in step (2), the substrate regions that substrate forms electrode comprises the region that covered by graphene film and not by region that graphene film covers; Distance between source electrode and drain electrode is 500-5000nm, is preferably 750-4000nm, is more preferably 1000-3000nm.
7. the preparation method according to claim 5 or 6, wherein, in step (3), by the mode of SiO 2 etch liquid and substrate contacts being made the surperficial step-down of the substrate under graphene film, and the condition of SiO 2 etch liquid and substrate contacts makes the surface layer under source electrode and drain electrode all do not corroded.
8. preparation method according to claim 4, wherein,
In step (1), substrate comprises basic unit and is attached to the surface layer in basic unit, and is attached on the surface layer of substrate by graphene film; Basic unit is silicon chip, and surface layer is silicon dioxide layer, and thickness is 275-300nm and is greater than the height of cavity;
In step (2), the substrate regions that substrate forms electrode comprises the region that covered by graphene film and not by region that graphene film covers; Distance between source electrode and drain electrode is 500-5000nm, is preferably 750-4000nm, is more preferably 1000-3000nm; By the mode of evaporation, the substrate regions of source electrode to be formed forms electrode;
In step (3), by the mode of SiO 2 etch liquid and substrate contacts being made the surperficial step-down of the substrate under graphene film, and the condition of SiO 2 etch liquid and substrate contacts makes the surface layer under source electrode and drain electrode all do not corroded; SiO 2 etch liquid is the hydrofluorite of concentration 21-22 % by weight; By controlling the time of hydrofluorite and substrate contacts, make the floorage of cavity be the 70-99% of the area of graphene film, preferably 75-95%, is more preferably 80-90%, and the surface layer under source electrode and drain electrode is not all corroded.
9. the sensing element that the preparation method in claim 4-8 described in any one prepares.
10. a sensor, this sensor comprises sensing element in claim 1-3 and 9 described in any one and contrast electrode.
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