16/02/2012

What’s the principle of electrochemical sensors microns

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1 - INTRODUCTION 

The chemical and biochemical sensors, electrochemical fuel coniiaissent now, as all sensors, a conceptual and technological revolution. This is mainly due to two factors:

- The increasing severity of environmental NameBrowse, food, pharmaceutical, security indiistrielle, home automation ...

- Needs microsensors fabulous bio-compatible or not for medical monitoring and diagnosis.

- The generalization of process automation in the industrial process engineering.

- The second most recent downturn, but in the power of the miniaturization of microelectronics technologies is widespread.

This last point, which determines the possibilities for increasing the production of sensors is very important because it leads noiivelIes ideas on the constitution and methods of use thereof.

Niacrocapteurs an idea that is, sensors centimeter, often with electronic rather difficult (the glass electrode is an excellent example) and used in a unique way it needs to present individual perfomlances remarkable sensitivity and selectivity are reversible particularly appropriate to replace micro-sensors, millimeter, at least, by methods of mass production and iitilisés often together. This mass production is planned a number of properties of the reduction and improved reliability at a very low colit and in particular a natural ability with the clutch traitenient signal integratedSony VGP-BPS13 battery circuits (since this is mass production accordingly cliissique).

This Possibility opens up two important consequences:

- To facilitate First, the analytical signal can correct the disruptive effects of artifacts such as the influence of temperature or other stimuli. This gives the sensors can react spontaneously, ie, "smart".

- Second, the ability to manage multiple sensors to multiplex excerpt from a network in which each element is not responding correctly to the various components of a mixture, but may create by calculating the analytic signal corresponding to each pure. Chemometrics and this is the best known example is to create networks of olfactory recognition (the "electronic nose") (2). This is an opportunity because it is the duty importarite absolutely necessary for sensors chimiclues selectivity, a problem that has time and again their development, which does not dissolve naturally, instead, and the simple reduction triggers. Unlike the Sony VAIO VGN-FW21L battery

Biology and biochemistry and their reactions are, of course, selectively couples each participating enzyme / substrate and anticorpsfantigène contains only small molecules and ions can be distinguished too close, "recognized", easily. The combination of imperfect network microsensors with signal processing circuit, a powerful solution to this problem that will definitely take some weight connected in the coming years.

II - Methods of miniaturization

The current trend towards miniaturization of sensors, chemical, electrochemical, and others.

Miniaturization methods use a combination of techniques, microelectronics, chemical impregnation strong as it is shaped to form three-dimensional structures of metal compounds, semiconductor or dielectric. To run, siiccessivernent, operatioris deposition or erosion of materials in an appropriate sequence of rnicrozoiies are defined by photolithographic methods. A brief summary of the main methods used for the production microsensors is here.

All methods rely on the ability of miniaturization is able to transmit to the projection of light, the image of an opaque mask for defining the shapes of substrates to be processed (usually silicon wafers was here or quartz). The result is photoresist, the photoresist obtained. The HP Mini 1000 battery parts are UV reticiilation cohesion and chemical insolubility strengthened or weakened formatioii hydrophilic groups, are qii'elles second "negative" or "positive". This leads to a selective dissolution of the reasons are more soluble. This geometry allows the "open" window in the shape of the mask defines the access and possibly underlying matter. This is the basis of the production technology "plane" of silicon integrated circuits. for example, silica dissolves provided to facilitate access to silicon, which can then in the following treatment (corrosive attack on the various deposits) have by hydrofluoric acid.

The size Microsensors for common sub-micron resolution, this procedure is usually sufficient, and it is not necessary, except for the LIGA technique, which will see below, using the methods of limitation with rayonnen X-ient or beams electrons used in microelectronics integration very high. Therefore, the reasons are not more than a few Microns in height.

The sample is deposited on a horizontal plate (traction control) rotates at a speed in a controlled temperature conditions assessedby. In this way, the viscosity of the resin results in a repeatable controlled thickness. This is the spin-coating. The units are comparable in size to dust, like all these other micro-fabrication operations are usually in "clean rooms" sprinkled.

2 - The deposition of thin films (about qiielqiies inicromètres or less)

The method is by far the most widely used is the CVD (Chemical Vapor Deposition). In a reactor with thick walls and generally low pressure (LPCVD), the substrates to be treated in the presence of gases that react in contact with them while traveling in the desired material. To operate at a lower temperature, the Dell Latitude E5500 battery energy can be generated using a plasma (PECVD) or photon (EECVD). The polysilicon, commonly used in the microstructures, is then by the reaction of SiH 4 to 400 ° C is reached, while the silica at 450 ° C, by the action of a mixture of 0 2 S and that this process is often used for the deposition of a dielectric material is to determine the starting point for the treatment of a silicon substrate ERI, the tnermique its oxidation in a dry atmosphere of oxygen or wet, which allows growth of the single silica extremely smooth.

Another method, the growth of oxide layers, is very simple for now is that the soaking method

Approach is based on a sol-gel. Metal alkoxides are immersed in an appropriate alcohol and as a sample to be coated milieii precurseurs.L in the solution and then slowly extracted, to obtain a steam bath desired by hydrolysis-polycondensation, Co ~ IC. A trriiteinent therniique is therefore necessary to convert the gel into oxidized compounds. The having a thickness of 100 to 300 nm. The spin-coating has already been described for distributing the photoresist. There is also widespread,in particular, for distributing polymers in a solvent which is then evaporated dissolved.

For the deposition of metals, is the most common method of thermal evaporation. Sealing is carried into the chamber at low pressure (0 to ~ 1 Torr) obtained by Joule effect evaporation (tungsène resistance wire or molybdenum) is performed. The object is directed towards the source of metal atoms. 2 shows that the deposit is a metal pattern on the surface of the resin on the entire surface. Remove the resin layer by immersion in a solvent, it breaks at the junction of the thin window. This method is a widely used method of "lift-off." Other methods that the thermal process is used to piilverisation atom, such as ion bombardment (sputtering) or electronically.

3 - Deposits of thick film materials

In its natural form, screen printing is a process that an opaque pattern on a transfer gate cutting wires on a substrate with a paste which is forced by the free part of himself, is established. With its principle, the method requires no photolithography processes, but the lateral resolution is much lower. Cooking also helps solidify the paste, which is passed through the system. This is a process widely used for ceramic inserts.

Pulp (or ink) are sensitive to light with respect to current, is now the process of photolithography.

4 - The erosion of the material (etching) (3-5)

It is gas or ion faqon niilieu (erosion by plasma) or is carried out in a liquid medium (chemical erosion) is.

In the first method, substances are extracted ion bombardment photolitho graphiees windowing. For layers of resin, this attack can withstand, while deep wells can be dug by a few hundred nanometers, with a small surface. Erosion can be mechanical, when management essentiellenient ions from the surface of an electronic box, inert materials, such as argon ions.

It may be the chemical nature, when the reactive molecules are used. Siliciiim erosion is achieved by a

SFG + Cl 2 plasma and that of silica from a CF4 + H2 plasma.

In the second of these methods is the liquid medium to attack the name of the etchant. The attack is done by simply soaking in the milieii. This is an oxidative corrosion, if the attack is rapid, resulting in an isotropic solution, and if it is slow, which differ by a resolution in the anisotropic crystal planes of single crystals Etch rates vary widely (6-7). To monocrystalline silicon, in the usual manner quickly etchant CP-4A, nitric acid mélande, hydrofluoric acid and acetic acid, while a 44% potassium hydroxide has a strong action anisotropic 85oC. In the latter case, the erosion rate plans <Ill> tens to hundreds of times lower Plans, the <1 IO> and <100>. If the level is, the silicon wafers are processed, wherein the plane <100> practice window whose sides are parallel to the plane obtained <1 10>, for example, shaped slots of inclination with respect to vertical openings, 35 '3.

The use of masks with an appropriate form, several levels of attack and the shape of the window, it is possible with this method

Anisotropic resolution three-dimensional shapes to build, but are limited in height to the thickness of a few micrometers of the resin. 3 by reference numeral 7, which is the principle of generating a beam of high silica.

5 - Production process according to the method of microobiets sacrifice layers

Play on the stack of layers, usually by CVD, dielectric materials (SiO2, Si3N4) or metal (Al) or silicon polycristaIlin and use of selective solvent, it is possible, some of them are dissolved in dissolving insoluble material parts.

Be carried out, as above, the flat objects, instead of actual three-dimensional. Parts are usually identified

The polysilicon layers and eliminated silice.La Figure 4 shows how to rotate a space, remove the circular symmetry. This is a technological revolution has introduced this method in recent years. It is represented by the generation of electrostatic micro-motor of several hundred microns in diameter.

6 - Process and Dar fabncation microobiets tithomaphie LIGA process. Galvanoformun Abdformund

Production methods described above have the disadvantage of allowing a limited relief. LIGA technology, of German origin, overcomes this disadvantage by UV radiation, but X-ray and polymethyl methacrylate resins suitable materials. Articles having a thickness of several hundred microns can be produced. Intense sources of X-rays are necessary to avoid lengthy operations are necessary, and we are therefore led to the use of synchrotron radiation. The method is expensive.

Production of items Dell Studio XPS 16 Battery made by the openings in the resin filler metal (Ni, Cu) deposited electrolytically. When many voices to be done, either by injecting a resin into the metal matrix and with this form, works in the negative, as a form where there is a new electrolytic growth of the property stated metal.A short, it should add a few special techniques, special production. This is the case for example the production of porous silicon for the anodic oxidation of silicon hydrofluoric acid environment. The erosion of the material in the form of a network of canals, is a few tens of nanometers to thermal oxidation plus.Par iitiliser stabilizes this structure as a porous. We know how important this is in electrochemistry. It is also the case of welding glass-silicon or silicon-silicon, welding can electrostatically (and chemical) when the plates of the material web is formed.

III - Micro Sensors

With the arsenal of the provision of micro-manufacturing process, you get the choice of micro-object.

The analysis of the literature shows that both channels are being used to miniaturize the sensors. The first is simply overwhelming Macro Sensors Ilne shown. The second is based on chemical sensitization or "functionalization" of devices based on oriented, reflected the transformation undergone by a recognition element (probe or receiver) in contact with species from a physical effect that always ends detects an electrical signal. This translation device called a transducer.

As it is rare that the conditions for the use of microsensors a comparable level of miniaturization required for the chip, an object size of millimeter wave sensors are in fact as a microsensor. Miniaturization technologies are not taken to extremes here.

A prime example is the classical Sony VGP-BPS13 batteries amperometric Clark electrode for the determination of dissolved oxygen by cathodic reduction itself. A planar realization of this sensor is based on Swiss Centre dtElectronique and Microtechnology is based. On a silicon substrate is oxidized to be deposited, surrounded by the use of conventional techniques of integrated circuits, the two electrodes, the thin layer has a silver cathode by an anode centrdle Ag / AgCl. A hydrogel used as an electrolyte is then passed through a silicone membrane, which is held guided ensures the penetration of oxygen.

emple is a micro-sensor d'oxygene gaseous zirconia is based. In this sensor, the solid electrolyte layer (here SCZ) is formed by screen printing. The flow of oxygen in the electrolyte CSZ, conductive O -, can be actuated to the cell in the system of diffusion through a porous platinum electrode 6. The reference electrode consists Ilne PdPdO.

A final example, the enzyme glucose electrode. It contains a reference electrode AdAgCl, a cathode, which is the reduction of hydrogen peroxide by the enzymatic reaction and the electrode against. Glucose polyiiréthane a membrane, the membrane keeping the glucose oxidase.

2 - Functionalization of microtransducers

Microtransducers were reviewed, dell inspiron 1300 batteries electronic components whose natural ability, the most interesting devices with piezoelectric materials and optical fibers to integrate. All are used in an aqueous medium, but only the electrochemical nature. Although the passive components, resistors and capacitors are widely used, these are the active components of field effect transistors current. The acronym FET (field effect transistors) is commonly used to identify and are used as sensors, ISFET (ion sensitive FET), if the ENFET ions for sensors and IMMUNOFET enzymes seen ( immunosensors) are determined. It is this kind of sensors, which show an example that the work of different types of functionalization.

A field effect transistor in silicon is a component niodification a MOSFET (FET semiconductor metal oxide) as

In a silicon wafer, typically p-type heavily doped two enclaves N (N +) are or drain and source of electrons that move in the network with the creation of a silica-drain oxide ~ i created C.et

The effect of the field in the semiconductor by an appropriate bias voltage between the surface and the surface which is applied niétallisation

Rear of the component. Metallizations other than the drain and the source (so-called contact "ohmic"), the input and output Stream ID is to be the analytical signal.

In Figure 8 of the electron density of points (electron-rich zone N, P Band electron-poor). In the absence ofelectrical bias between the A and B, no current flows between drain and source, as there are now two pn junctions in opposition.

The application of a negative bias voltage VG on the grid in series, on the basis of the facearrière, the electric field pushes the electrons in the conduction band and is always equal to zero.

If we reverse this polarization, the electrons accumulate in the door (such as accumulation) in a very thin channel source.L between the drain and the occurrence of the drain current ID of a given VT- value of the gate voltage is obtained which guarantees that the threshold Dell XPS M1530 batteries voltage.

The removal of the metallization of the gate dielectric, the devices for electrical loads, which may be present to collect on the surface is bare or membrane recognition sensitizer. This is what is done wherein the liquid medium provided that the electrical continuity between the outer surface of the dielectric and the modified base with a reference electrode.

Occurs in the chain of possible VG, the voltage drop on the surface of the dielectric changed. When the type of attachment is "detected", then the receiving surface is fixed, causes a change of this document, which leads to a change in threshold SONY VGP-BPS9/B voltage VT and the translation of the VGID to generate characteristic of the sensor. Such devices can then Operation with a constant or VG ID.

This raises the question of functionalization. As we can see some dielectric properties? Given different answers to this question remains of which are relevant to other types of sensors as described above are used. The book will be consulted with profit Janata égard.a they are - last ROF ~ ~ idt are himiques ropriétésc the dielectric surface in aqueous media, the conventional dielectric (Si02, Si3N4, silicon oxi ...) hydrolyze s' superficiellenient the silanol Si - OH. This hydrolysis is also observed for other dielectrics such as Ta205 or Al203. The acid-base-X - OH, then the appearance of a positive surface charge at acidic pH leads formed (or more precisely, at pH values ​​below the point of zero charge PZC) for these surfaces form clusters X OH2 + and negative charge at higher pH-X group forming. The ionic equilibrium between the surface and the immersion solutions, in response to a potential proton Nernst, leading to 59 mV per pH unit. PH sensors of this type are currently on the Dell XPS M1210 Battery market, particularly in France.

b - ~ odt receptors and membrane inorraniaues

Many inorganic membranes for the detection of the membrane are promising ions.Une, for example coiistitiiée NASICON (Na 3 Zr2Si2P012) for the detection of alkali metal ions. Although other membranes and insoluble and are involved in ion exchange between himself and the solution, and, in principle, a Nernst response. This is particularly the case in LaF3 membrane or aluminosilicate glass. These membranes are generally used by good adhesion is an important parameter for the duration of the sensors, but unfortunately a relatively small number of Dell Inspiron 1420 Battery materials for such use.

c - ~ From odt and membrane receptor-organic

As a macro-electrodes, we are looking for immobilization of receptor molecules in an organic protective film. The best example is the reaction of PVC membranes of large molecules, including valynomicine, for the detection of potassium ions is known. The method has a greater diversity due to the large number of available molecules (ionophores complexing, chelating agents, crown ethers), but suffer in general have poor adhesion of the membranes on the substrate and a carrier inophores often insufficient in resin at home. There is also the problem of the dissolution of plasticizers (16). Finally, when the thick membrane siiffisamn-ient, we can reduce the conductivity as Dell Inspiron E1405 Battery gate insulator and an increase in reaction time.

D - ~ The ion lantationd

Some results were published in the field of use of ion implantation of artificial ion conduction. Examples include work by Pham of monovalent ions in the silica plant. Method suffers from a very limited number of possibilities and examined.

Recently, functionalization niethode insulating substrates has been proposed, in particular silicon by grafting onto the surface of the resulting string long with a temperature INADL group recognition silanized E ~. This is achieved by chemical reaction of these molecules with silanol groups, which is already established on the surface of a dielectric made treatment with chromic acid.

Regardless of the method was, can also be applied to the formation of coiiches released to be used to correct a large n ~ olecules biochemical and biological recognition.

All the functionalization of microsensors mCthodes microtransducers rkalisation was pretty good, but usually only expect malheureusenlent sklectifs douCs qualitCs the future, which is the claim of objects through the Collective fabriquCs mCthodes. We can then espCrer actuellernent these microsensors in the near future, problbmes rCponse many analytical chemists currently available.

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