CN101221143A - Micro-nano humidity transducer production method - Google Patents

Abstract

The invention relates to a novel method for preparing micro-nano humidity sensor, including the following steps: A, making a layer or a plurality of layers of plane metal micro-electrodes on an insulating underlay by a micro-processing technology; B, putting sensing nanometer material into electric medium solvent and leading the material to be diffused uniformly to be made into a suspension liquid containing the nanometer material through ultrasound, taking a small amount of the suspension liquid and dipping the suspension liquid into the micro-electrode, determining a frequency range of a control signal needed to be applied for generating positive dielectric electrophoresis in the system according to the dielectric properties of the material to be controlled and the solvent selected to be used, and selecting a proper frequency value; applying an alternating current signal with the same frequency at two ends of the electrode to lead the sensing material between the two ends of the electrode to be arranged sequentially in the middle of the electrode along the electric field line direction under the effect of the positive dielectric electrophoresis to form the arrangement and bridge connection of the nanometer sensing materials in the micro-electrode structure; C, pin packaging a sensing structure to make a final micro-nanometer humidity sensor after the solvent is removed completely by volatilization or other ways.

Description

A kind of micro-nano humidity transducer production method

Technical field

The present invention relates to a kind of preparation method of sensor, especially a kind of preparation method of micro-nano humidity transducer belongs to micro-nano sensing manufacture technology field.

Background technology

The sensitive material that nano material is considered to have preeminent performance, when adopting nanostructured as sensitive element structure electric sensor, usually need and to arrange or be connected across between two electrodes as the nanostructured of sensing material, its characteristic is spread out of with the variation of the measuring object form with electric signal so that utilize.So selectively nano material is placed to appointed positions, be to receive the problem that at first will solve in the sensor preparation process.

The following several method of general employing in the disclosed at present technical information:

First method is that the suspending liquid that will contain sensing material is coated on the substrate of carrying out electrode, and oven dry has the part material and is connected across by chance between two electrodes then.But distribution of material of doing up by this method and orientation all are in a mess, and the selectivity of dispensing area is also poor.

Second method be from an electrode to another electrode directional growth sensing material, although this process is controlled, also there is the selective problems of catalyst contamination and difference in this method, the kind of the nano material that can grow also is restricted in addition.

The somebody controls by instrument target material is put into the position of design in advance in addition, and this method needs long time, expensive instrument and vacuum environment, and also very big for the operation easier of nano material.So there is not very big commercial value.

Summary of the invention

Purpose of the present invention: be to overcome in the micro-nano sensor production deficiency of existing material location technology, propose new technology and control nano material, orientation problem such as come simply and effectively to finish the cross-over connection of sensing material and arrange.

The preparation method of this micro-nano humidity transducer is characterized in that:

A, at first on dielectric substrate, make one or more layers planar metal electrode by micro-processing technology;

B, then the sensing nano material is put into a kind of dielectric solvent, and make its diffusion evenly make the suspending liquid that contains nano material by ultrasonic; The hanging drop that takes a morsel is gone in the middle of the microelectrode, according to the dielectric property of being controlled material and selected solvent, determine in this system, to produce positive dielectrophoresis phenomenon and will apply the frequency range of controlling signal, select a suitable frequency values, apply the ac signal of a same frequency at the electrode two ends, make therebetween sensing material under the positive dielectrophoretic force effect along the electric field line direction orderly being arranged in the middle of the electrode, form nanosensor material arranging and cross-over connection in the microelectrode structure;

C, remove solvent fully in modes such as volatilizations after, carry out the sensing arrangement lead packages and make final micro-nano humidity transducer.

This controlling is not subjected to the conductive characteristic of material own, and the restriction of material shape etc. is applicable to all nano structural materials in principle; This material can be metal oxide or high molecular polymer.

The carrier that simultaneously can select a kind of dielectric solvent to control as material arbitrarily in actual applications, often adopts deionized water, ethanol or acetone to make dielectric solvent.

Make micro-nano humidity transducer according to above technical scheme, the method for making sensor by dielectrophoresis technology has following advantage:

1, this controlling is not subjected to the conductive characteristic of material own, and the restriction of material shape etc. is applicable to all nanostructureds in principle; The carrier that can select a kind of dielectric solvent to control as material arbitrarily in actual applications, often adopts deionized water, ethanol, acetone etc. in principle.

2, the sensing material regularity of distribution is orderly, and the locating area selectivity is good;

3, production equipment and environmental requirement are not high, and production cost is lower.

Description of drawings

Fig. 1 ~ 4 are at 1Vrms, and frequency is respectively the fitting a straight line synoptic diagram that impedance changes with humidity under 10KHz, 1KHz, 120Hz, the 100Hz condition;

Fig. 2 1Vrms, under the 10KHz condition, relative humidity direction from low to high, the curve synoptic diagram that omnidistance continuous 3 duplicate measurements impedances change with humidity;

Fig. 3 1Vrms, the positive and negative stroke curve synoptic diagram that impedance changes with humidity under the 1KHz condition;

The sensitivity analysis of the sensing arrangement among table 1 Fig. 1-4 under four different frequencies;

The repeatability analysis that table 2 Fig. 2 middle impedance changes with humidity.

Embodiment

Further set forth the present invention below in conjunction with accompanying drawing, and provide embodiment.

The preparation method of this micro-nano humidity transducer is as follows:

A, at first on dielectric substrate, make one or more layers planar metal electrode by micro-processing technology;

B, then the sensing nano material is put into a kind of dielectric solvent, and make its diffusion evenly make the suspending liquid that contains nano material by ultrasonic; The hanging drop that takes a morsel is gone in the middle of the microelectrode, according to the dielectric property of being controlled material and selected solvent, determines to produce positive dielectrophoresis phenomenon and will apply the frequency range of controlling signal in this system, selects a suitable frequency values.Apply the ac signal of a same frequency at the electrode two ends, make therebetween sensing material under the positive dielectrophoretic force effect along the electric field line direction orderly being arranged in the middle of the electrode, form nanosensor material arranging and cross-over connection in the microelectrode structure;

C, remove solvent fully in modes such as volatilizations after, carry out the sensing arrangement lead packages and make final micro-nano humidity transducer.

This controlling is not subjected to the conductive characteristic of material own, and the restriction of material shape etc. is applicable to all nano structural materials in principle; This material can be metal oxide or high molecular polymer, and the geometric configuration of material is sphere or clavate.

Simultaneously, the carrier that can select a kind of dielectric solvent to control as material arbitrarily in actual applications, often adopts deionized water, ethanol, acetone.

Now by adopting the ZnO nanostructured to further describe the present invention: navigate between the dull and stereotyped interdigital electrode configuration by dielectrophoresis technology, produce a kind of nm-humidity sensor as sensing material.

At first adopt micro-processing technology to make a dull and stereotyped interdigitation Ti/Au microelectrode.By the superficial growth layer of silicon dioxide insulation course of oxidation at silicon chip, the deposition one deck Ti of mode elder generation with evaporation deposits layer of Au more respectively on insulation course, spin coating is just dried by the fire post bake in (photoetching) glue, preceding baking, photoetching, development, back then, carries out the corrosion of Au, Ti again, finishes microelectrode and makes.

Nano material that then will be to be controlled is dissolved in the deionized water, then suspending liquid is put into the ultrasonic 20min in ultrasonic pond.Move into the electrode mesozone with the pipettor suspending liquid that takes a morsel.According to the dielectric property of deionized water and ZnO material, when the frequency of controlling AC signal was between 1KHz-10KHz, more negative dielectrophoresis phenomenon appearred in system, and when frequency was between 200KHz-2MHz, significantly positive dielectrophoresis phenomenon appearred in system.Adopting the DDS AWG (Arbitrary Waveform Generator) to apply frequency at the two ends of electrode is that 1MHz, amplitude are the sinusoidal ac signal of 8V, between electrode material being carried out positive dielectrophoresis controls, at room temperature volatilize fully until solvent, the ZnO nanostructured just has been positioned between the dull and stereotyped interdigitation electrode like this.

Conciliating absorption property because the ZnO nanostructured has good absorption to humidity, is a kind of good humidity-sensitive material.The ZnO nanostructured that is adopted adopts the sol-gel process growth, and the nanometer rods diameter of being grown is at 200nm, and length is at 10 μ m.

In the making of reality, this controlling is not subjected to the conductive characteristic of material own, and the restriction of material shape etc. is applicable to all nanostructureds in principle; The carrier that can select a kind of dielectric solvent to control as material arbitrarily in actual applications, often adopts deionized water, ethanol or acetone to make dielectric solvent in principle.

In order to check the effect of controlling, the sensing arrangement of made is carried out relative humidity test verification in addition.Needed standard humidity produces by the saturated solution method of salt in the experiment.Depress at a normal atmosphere, when experimental temperature is 25 ℃, get CuSO ₄, NaCl, CuCl ₂, NaBr, K ₂CO ₃, MgCl ₂Deng 6 kinds of saturated salt solutions, their rh value is respectively 97.6%, 75.29%, 68%, 57.57%, 43.16%, 32.78%, two incoming ends of sensing arrangement is connected to LCR bridge resistance measuring instrument carries out ac impedance measurement.

1. sensitivity

Under 1Vrms, 10KHz condition, the sample environment of different relative humidity is switched by the order that relative humidity increases progressively in elder generation, writes down six measured values.The proceeding measurement of successively decreasing by relative humidity again comes and goes and measures 3 times, obtains 6 groups of measured values.Getting frequency respectively is 1KHz, 120Hz, 100Hz, the operation above repeating.Repeatedly measured value corresponding to each rh value under the same measuring condition is average in addition, obtain the actual measurement mean value of three positive revesals, the line linearity match of going forward side by side, we can obtain under four different frequencies, AC impedance is with the fitting a straight line of relative humidity variations, shown in Fig. 1-4.

The sensitivity analysis of the sensing arrangement among table 1 Fig. 1 under four different frequencies

Test frequency	The fitting a straight line equation	Sensitivity K Ω/RH%	Degree of correlation R
				f＝10KHz	Y＝2982.61838-28.5291 4x	-28.52	R＝-0.99
f＝1KHz	y＝10641.06644-120.864 74x	-120.86	R＝-0.91
				f＝120Hz	y＝12643.22544-144.569 75x	-144.56	R＝-0.90
f＝100Hz	y＝12887.8662-146.9076 3x	-146.90	R＝-0.90

Can see that from table 1 under different test frequencies, the slope of each bar fitting a straight line all is a negative value, illustrate that the AC impedance of sensing arrangement reduces significantly gradually along with the increase of test environment relative humidity.The absolute value of the slope of fitting a straight line is the sensitivity of sensing arrangement.Can see the reduction along with test frequency, it is big that the absolute value of the slope of fitting a straight line becomes, and illustrates that sensing arrangement increases the sensitivity of relative humidity; Simultaneously, the related coefficient size has minor fluctuations with the reduction of test frequency and is tending towards diminishing, but overall numerical value is higher, illustrates that sensing arrangement all has stability preferably under different test frequency conditions, and can be more stable under high frequency condition.

2. repeated

Under 1Vrms, 10KHz condition, the relative humidity of pressing test environment direction is from low to high done omnidistance continuous 3 duplicate measurementss, and the curve that the impedance of humidity sensor structure changes with humidity as shown in Figure 2.As we can see from the figure, sensing arrangement has better repeatability.

Table 2 is the repeatability analyses with the humidity variation of Fig. 2 middle impedance, obtains the mean value and the standard deviation of 3 measurements earlier, further can obtain relative standard deviation.

The repeatability analysis that table 2 Fig. 2 middle impedance changes with humidity

Relative humidity RH%	Measure for the first time K Ω	Measure for the second time K Ω	Measure K Ω for the third time	Mean value K Ω	Standard deviation K Ω	Relative standard deviation 100%
							32.78	1955	2024	1969	1982.66	36.47	1.83
43.16	1883	1975	1894	1917.33	50.24	2.62
							57.57	1380	1399	1294	1357.66	55.94	4.12
68	1023	1014	934	990.63	48.47	4.89
							75.29	825	763	650	746.23	88.35	11.83
97.6	191	229	210	210.30	19.25	9.15

Can see that from table 2 along with test environment relative humidity increases, it is big that the relative standard deviation of measurement result is tending towards becoming, and illustrates that under low moisture conditions the degree of closeness between the impedance measurements of sensing arrangement is good more, repeatability is good more.

3. humidity hysteresis and response time

Under the condition of 1Vrms, 1KHz, the first sequential testing that increases progressively by rh value is once successively decreased the direction test once by opposite humidity again.Can obtain the positive and negative stroke curve that impedance changes with humidity, as shown in Figure 3.The last curve in position is the humidity incremental impedance change curve (positive stroke) of sensing arrangement among the figure, successively decrease impedance variation curve (revesal) relatively with following humidity, can see, for same humidity measurement point, the always a little higher than measured value in revesal of measured value in positive stroke, and the response time in positive stroke is always short than the response time in revesal, may be owing to moisture absorption than the easy reason of dehumidification.In same test stroke, no matter be positive stroke or revesal, moisture absorption and dehumidification are all very fast during low humidity, and during high humility, the beginning moisture absorption is very fast, slack-off near saturated moisture absorption, this is consistent with the multilayer adsorption theory.

Dielectrophoresis technology is a kind of technology of controlling based on Maxwell Classical Electromagnetic Field theory.According to the dielectrophoresis theory, any material all can have certain dielectric property, and under the effect of extra electric field, they can be subjected in various degree (galvanic couple) polarization, are tending towards coming arranged distribution along the extra electric field direction.If the extra electric field space distribution is inhomogeneous, these polarized particulates will be subjected to a net effort, i.e. dielectrophoretic force, and then cause in various degree drift.According to electromagnetic theory, at extra electric field

Under the effect, dielectric particles polarizes, and forms dipole induced electricity, its dipole moment induced electricity

With

Be directly proportional

$\stackrel{\→}{P}\∝\stackrel{\→}{E}---\left(1\right)$

If there is certain electric-force gradient, then electric dipole is stressed in electric field

Can be expressed as

The radius of supposing particulate is r, and specific inductive capacity is ε _p, the specific inductive capacity of suspending liquid is ε _m, as can be known

$\stackrel{\→}{P}=4{\mathrm{\π\ϵ}}_m\frac{{\mathrm{\ϵ}}_p-{\mathrm{\ϵ}}_m}{{\mathrm{\ϵ}}_p+2{\mathrm{\ϵ}}_m}{r}^3\stackrel{\→}{E}---\left(3\right)$

Associating (2), (3) Shi Kede

Wherein V is the volume of particulate, E _RmsBe the root mean square of electric field, the real part of K (ω) theClausius-Mosotti factor, and

$K\left(\mathrm{\ω}\right)\≡\mathrm{Re}\left[\frac{{{\mathrm{\ϵ}}_p}^{*}-{{\mathrm{\ϵ}}_m}^{*}}{{{\mathrm{\ϵ}}_p}^{*}+2{{\mathrm{\ϵ}}_m}^{*}}\right]---\left(5\right)$

" * " expression composite dielectric constant value in the formula,

${\mathrm{\ϵ}}^{*}\≡\mathrm{\ϵ}-i\frac{\mathrm{\δ}}{\mathrm{\ω}}---\left(6\right)$

When practical application, (6) formula also will be considered the surface conductance of the electrostatic double layer that particulate and suspending liquid and particulate interface go out to form.For spheroidal particle, K (ω) ∈ (0.5 ,+1.0) is when k (ω)＞0, and particulate is subjected to graviational interaction and is tending towards strong electric field region, and we are referred to as positive dielectrophoresis, arrives behind the field intensity zone because the effect of gravitation, and particulate will no longer leave.

When k (ω)＜0, particulate is subjected to the repulsion effect and is tending towards weak electric field region, and we are referred to as negative dielectrophoresis, arrives a back, weak zone because dielectrophoretic force is very little or be zero, and particulate also will be no longer mobile.

Though (4) formula only is applicable to spherical particle, the particulate of prolate shape is easier to polarize along long axis direction, is more suitable for dielectrophoresis and controls, as DNA, nanotube and nano wire etc.So in a lot of experiments and using, people select bar material as controlling object.Because the value of K (ω) is by the frequency decision, so by changing electric field frequency, can realize the positive and negative dielectrophoresis in same system.According to the dielectric property of the material of being controlled with the dielectric solvent that is adopted, can determine in system, to produce the frequency range that the plus or minus dielectrophoresis will apply electric signal, so as long as apply the AC signal of an appropriate frequency and certain amplitude at the electrode structure two ends that set in advance, produce controlled electric field and electric-force gradient, just can make system be in positive dielectrophoresis state.Under positive dielectrophoretic force effect, particulate will attracted to the forceful electric power place, that is the edge of general electrode wedge angle, thereby can realize that the nanosensor material is in two interelectrode arrangement and cross-over connections.

Claims (2)

1. the preparation method of a micro-nano humidity transducer is characterized in that:

A, at first on dielectric substrate, make one or more layers planar metal microelectrode by micro-processing technology;

B, then the sensing nano material is put into a kind of dielectric solvent, and make its diffusion evenly make the suspending liquid that contains nano material by ultrasonic; The hanging drop that takes a morsel is gone in the middle of the microelectrode, according to the dielectric property of being controlled material and selected solvent, determines to produce positive dielectrophoresis phenomenon and will apply the frequency range of controlling signal in this system, therefrom selects a suitable frequency values; Apply the ac signal of a same frequency and certain amplitude at the electrode two ends, make therebetween sensing material under the positive dielectrophoretic force effect along the electric field line direction orderly being arranged in the middle of the electrode, form nanosensor material arranging and cross-over connection in the microelectrode structure;

C, remove solvent fully in modes such as volatilizations after, carry out the sensing arrangement lead packages and make final micro-nano humidity transducer.

2. the preparation method of a kind of micro-nano humidity transducer as claimed in claim 1, it is characterized in that: this controlling is not subjected to the conductive characteristic of material own, and the restriction of material shape etc. is applicable to all nano structural materials; Any carrier of selecting a kind of dielectric solvent to control as material; In actual applications, often adopt deionized water, ethanol or acetone to make dielectric solvent.

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