EA020321B1 - Sensitive pick up element - Google Patents

Abstract

The invention relates to technology of producing silicon micro and nano electronic devices. The invention can be used for manufacturing sensors for determining pH values of different biologic solutions and also as a constituent element of sensors for chemical and biological substances prepared by technology of silicon integrated microcircuits production. A sensitive pick up element comprises source electrodes of p-type 1 and n-type 2 and a general drain electrode 3, having regions p-type 4 and n-type 5, The electrodes are made on a dielectric layer 6 of a subsrate 7. The source electrode of p-type 1 is connected by the region of p-type 4 of the drain electrode 3 using nanowire 8, forming iono-sensitive field-effect transistor (FET) of p-type. The source electrode of n-type 2 is connected by the region of n-type 5 of the drain electrode 3 using nanowire 9, forming iono-sensitive field-effect transistor of n-type. Thus, the sensitive pick up element comprises two ion-sensitive FET of p-type and n-type made on the substrate dielectric layer. The nanowires 8 and 9 are dielectric coated. The drain 3 and source 1 and 2 electrodes are coated with an insulation layer 10. The technical result provides increasing sensitivity and spatial resolution of a sensitive pick up element.

Description

The invention relates to the field of manufacturing technology of silicon micro- and nanoelectronic devices. The invention can be used for the production of sensors for determining the pH value of various biological solutions, as well as a constituent element of the sensors of chemical and biological substances manufactured by the production technology of silicon integrated circuits.

Achievements of the silicon technology of VLSI make it possible to manufacture nanosized elements, on the basis of which it becomes possible to create qualitatively new sensor devices. Nanosized ion-sensitive field-effect transistors (ΙδΡΕΤ) are used as sensitive elements for sensors.

ΙδΡΕΤ is a MOS transistor structure where the analyzed electrolyte solution is used as the gate material. Depending on the acid-base properties of the measured solution, a change in the electrochemical potential occurs, the surface of the gate dielectric is recharged, and the conductivity of the transistor changes.

A large number of papers are published in the technical literature on the use of чувствδΡΕΤ ion-sensitive field effect transistors as sensitive elements of electronic sensors for chemical substances. In these works, the possibilities of using polycrystalline thin silicon films are considered [O1bbegdeg 1 .. Nosybayit Α.Ι. 8Sheoi UeyyuLu Y'IedgaYub №1po \\ 'ys // Hs1b EGGes! TgapmChop ,. 2006. Yo1. 7, No. 4. P. 37], miniaturization of the reference electrodes, the possibility of combining the manufacture of the sensor with the basic processes of planar technology for the manufacture of integrated circuits [Vegdue1b R. E1es! EbeyuU / Zepyuge apb Asyayga. 2003. Yo1. 8, No. 5, P. 9-11] and the possibility of forming nanoscale devices [Kuznetsov E.V., Rybachek E.N. Biosensors based on silicon nanowire field-effect transistors // Defense complex - to the scientific and technological progress of Russia. - M .: FSUE VIMI, 2010, No. 3, P. 85-90].

Known methods for the formation of sensors on ion-sensitive field effect transistors Ι8ΡΕΤ as sensitive elements are given in US applications I8 20090127589 (IPC Н01Ь 29/772, Н01Ь 21/50, С12М 3/00, publ. May 21, 2009) and И8 2011100810 (IPC Ο01Ν 7/414, Н01Ь 335, Н01Ь 29/772, published May 05, 2011). With their help, it is possible to simultaneously detect several types of test substances at once and build an array of sensors in which each sensitive element is functionalized for each type of analyte.

Known designs and methods for forming sensors on silicon nanowires (δί-ΝΛ ΡΕΤ), such solutions are described in US applications I8 2009152598 (IPC i01 29/00, H 21/00, publ. 06/18/2009) and υδ 2006054936 (IPC C30B 11/00, publ. March 16, 2006), as well as in the international application ΛΟ 2004034025 (IPC С12р 1/68; Ο01Ν 27/414; Ο01Ν 33/543, publ. 22.04.2004). The sensor consists of a nanoscale silicon wire located between the electrodes (drain and source). Before the analysis, the surface of the wire is functionalized with the necessary compounds that selectively interact only with the molecules of the analyte. A part of the analyte molecules introduced into the system through diffusion through the solution reaches the nanowire and binds to the surface of the wires. As a rule, under normal physiological conditions, most biomolecules have an electrostatic charge (for example, DNA is negatively charged, the resulting charge of the protein molecule is highly dependent on the pH of the solution). The Coulomb interaction between the charge of biomolecules and a nanowire leads to a change in the conductivity of the latter.

The closest in the set of essential features (prototype) of the invention is the technical solution set forth in US application υδ 2010129925 (IPC М01Ν 27/04; H01 21/02; H01 29/06, published on 05.27.2010). In this invention, the sensor element is made on the basis of an ion-sensitive field effect transistor consisting of a drain and source electrodes connected by a nanowire coated with a thin dielectric layer, the source and drain electrodes being isolated. The gate of the transistor is the analyzed medium. When using such a structure as a sensitive element of the sensor, the surface of the nanowire with a thin dielectric layer is prepared by functionalization with surface-active substances.

Obtaining the desired technical result is impeded by the imperfection of the design and the electrical circuit, which does not allow to increase the sensitivity of the sensor.

The main characteristics of the sensor are selectivity and sensitivity. Selectivity is provided by a functionalizing substance, and sensitivity depends on many parameters, including the design of the sensitive element. An object of the present invention is to provide a high-precision sensor for analyzing liquid media.

The technical result consists in increasing the sensitivity and spatial resolution of the sensor element for analyzing liquid media by measuring the electrochemical potential, including for measuring pH.

To achieve the above technical result, the sensor element of the sensor is made containing source electrodes of p-type and p-type and a common drain electrode having regions of rept and p-type, the electrodes are made on the dielectric layer of the substrate, the source electrodes are connected

- 1 020321 with the corresponding regions of the drain electrode by nanowires coated with a dielectric layer, the drain and source electrodes being isolated.

The claimed design differs from the prototype in that it contains a complementary pair of two ion-sensitive field-effect transistors of different conductivity types (p-type and η-type), and the drain electrodes of the transistors are interconnected. The use of a complementary pair of wire transistors with a common drain (topologically combined drain areas) as a sensitive element allows to increase the sensitivity of the sensor by more than 100 times in comparison with the prototype. The combination of the drain areas of the electrodes into a common electrode of transistors of different types of conductivity allows you to get an unexpected effect in increasing the sensitivity and spatial resolution, which is higher than when using two separate ion-sensitive field-effect transistors without combining the drain areas.

In particular cases of the invention, the substrate is made of silicon on the insulator or polysilicon on the insulator.

In particular cases of the invention, the stock and source electrodes are made of silicon or polysilicon.

In particular cases of the invention, the concentration of impurities in the drain, source electrodes is 10 ¹⁹ -10 ²¹ cm ^-3 .

In particular cases of the invention, the diameter of the nanowires is 5-100 nm.

In particular cases of the invention, the nanowire length is 50 nm-10 μm.

In particular cases of the invention, the distance between the nanowires connecting the drain and source electrodes is from 5 nm to 100 μm.

In particular cases of the invention, the nanowires can be both doped and unalloyed, and the concentration of the dopant in the nanowires is 10 ¹⁴ -10 ¹⁹ cm ^-3 .

In particular cases of the invention, both nanowires are doped with the same type of dopant.

In particular cases of the invention, nanowires have an equal concentration of dopant.

In particular cases of the invention, the nanowires have different dopants concentration.

In particular cases of the invention, both nanowires are doped with different types of dopants.

In particular cases of the invention, the dielectric layer deposited on the nanowires has a thickness of 5 to 200 nm.

In particular cases of the invention, the nanowire is located above the dielectric layer of the substrate.

In particular cases of the invention, the nanowire is located on the dielectric layer of the substrate.

In particular cases of the invention, the nanowire is partially buried in the dielectric layer of the substrate.

The invention is illustrated by drawings, where FIG. 1 - conditional image of the sensor element;

FIG. 2 - technological stages of the formation of the sensor element based on two nanowire transistors (Ι8ΕΕΤ) η- and p-type;

FIG. 3 - 1) an optical image of the sensor element of the sensor based on two nanowire Ι8ΕΕΤ η- and p-type; 2) image of the sensor element of the sensor obtained using a scanning electron microscope;

FIG. 4 - transfer characteristic of a sensitive element made on the basis of two ion-sensitive transistors η- and p-type formed on the structures of silicon on the insulator (a), polysilicon (b);

FIG. 5 - dependence of the gain of the nanowire sensitive element K on the molarity of the solution.

The sensor sensor element (Fig. 1) contains p-type 1 and η-type 2 source electrodes and a common stock electrode 3 having p-type 4 and η-type areas 5. The electrodes are made on the dielectric layer 6 of the substrate 7. The source electrode p -type 1 is connected by the region of the p-type 4 of the drain electrode 3 by the nanowire 8, forming an ion-sensitive field-effect transistor of the p-type. The η-type source electrode 2 is connected by the η-type region 5 of the drain electrode 3 by the nanowire 9, forming an η-type ion-field transistor.

Thus, the sensor element (Fig. 1) contains two p-type and η-type ion-sensitive field effect transistors made on the dielectric layer of the substrate.

Nanowires 8 and 9 are dielectric coated. Stock 3 and source electrodes 1 and 2 are coated with an insulation layer 10.

- 2 020321

The p-type 4 and p-type 5 regions of the common stock electrode 3 are defined as the regions doped with the corresponding p-type and p-type impurities.

The manufacture of the sensor element is illustrated in FIG. 2.

Silicon substrates on an insulator made using the 8ΙΜΟΧ technology are used as the initial plates - the upper (working) layer of silicon 11 is 200 nm, under it (hidden) oxide layer 6 is 380 nm, the base is a silicon substrate 7.

The first stage is the formation of insulation and the working areas of the sensor element.

The working layer of silicon 8ί (11) is oxidized at 20-40 nm, a sacrificial layer of silicon nitride 70-100 nm is deposited on it. Using photolithography methods, the configuration of the drain-source electrodes of transistors is formed (a p-source electrode 2, a p-source electrode 1 and one common stock electrode 3 are formed, as well as wire structures (8 and 9) connecting the drain-source electrodes. Then, anisotropic plasma etching is removed nitride, oxide and silicon to the latent oxide 6 from areas not covered by the photoresist. After this operation, the wire width is equal to the width of the photolithographic mask (the smallest possible lithographic size), for example, 800 nm. For the thinning of the wire elements, a second photomask is formed, in which only the wire structures 8 and 9 are open, and silicon isotropically (laterally on both sides) etched under a layer of nitride and oxide (using them as a mask) at 300 nm. conduct plasma-chemical etching of nitride and oxide from wires 8 and 9. After these operations, the wire height is 200 nm — the thickness of the working layer of silicon 11, and the width is equal to the width of silicon left after side etching (200 nm) . Next, thermal oxidation of the wire at 150 nm is carried out with the formation of a layer of thermal oxide 10. After this operation, the resulting diameter of the oxidized silicon wire lying on the hidden oxide 6 is 50 nm. Then the sacrificial layer of nitride is removed from the areas of the electrodes.

The second stage is ion doping and the formation of isolation of the drain-source regions.

For this, a photolithographic mask is formed to dope the drain-source regions of pMOS transistors 2 and 5, ion phosphorus implantation and photoresist removal are performed. Then a photolithographic mask is formed to dope the drain-source regions of the rMOS transistors 1 and 4, ion boron implantation and photoresist removal are performed. After these operations, the deposition of silicon oxide with a thickness of 600 nm, to obtain a layer of 12.

The third stage is the formation of metallization. To do this, a photolithographic mask of the contact windows 13 in the insulating dielectric to the drain-source electrodes is created, plasma-chemical etching of silicon oxide in the windows to silicon and removal of the photoresist is carried out. Next, aluminum 14 is deposited with a thickness of 600-800 nm, a photolithographic mask of metal wiring is created, plasma-chemical etching of aluminum is carried out, and photoresist is removed. Then, layers 15 and 16 of a low-temperature oxide with a thickness of 800 nm and nitride with a thickness of 200 nm are applied. A photolithographic mask of the contact pads to the metal wiring is created, plasma-chemical etching of the layer 16 and the oxide of the contact pads 17 and the removal of the photoresist are carried out.

The fourth stage (final) is the preparation of the wire element to work as a sensitive element of the sensor.

For this, a photolithographic mask of the windows to the wire elements is formed, so that the size of the window to the nanowire is less than the distance between the drain-source electrodes (1, 2, and 3). This makes it possible to form the insulation of 10 electrodes from the analyzed medium. The layers of low-temperature nitride 200 nm 16 and oxide 800 nm 15, the layer of insulating silicon oxide 12 and the layer of thermal oxide grown on the wire element at the first stage of formation 10 are removed through this mask. Depending on the type of arrangement of the nanowire element relative to the dielectric layer of the substrate (2) it is necessary to obtain, etched thermal oxide 10 to a different thickness.

When forming a nanowire partially buried in the dielectric layer or located on the dielectric layer of the substrate, etching to a thickness of approximately 150-300 nm is carried out.

When forming a nanowire located above the dielectric layer of the substrate, we etch to a thickness approximately equal to three thicknesses of thermal oxide 10, in this example, 450 nm.

After removal of the photoresist mask, a thin dielectric layer forms on the surface of the nanowire. In this example, a thin layer of silicon oxide (2 nm) was formed by the method of low-temperature plasma oxidation of the surface of a nanowire.

When forming sensitive nanowire sensor elements on polysilicon structures on an insulator, thermal oxidation of the initial silicon substrate to a thickness of 380 nm is carried out. A layer of polysilicon with a thickness of 200 nm is deposited on the oxidized surface of the substrate. As a result, we obtain a polysilicon structure on an oxide (insulator), the geometrical dimensions of which are similar to the dimensions of the structure made using the 8ΙΜΟΧ technology given earlier. The initial structure of polysilicon on the insulator consists of an upper working layer of polysilicon 11 with a thickness of 200 nm, located

- 3,020,321 of a 380 nm thick silicon oxide layer 6, which is located on the surface of the silicon substrate 7. Next, the same sequence of technological operations is carried out as before to form the sensitive element.

The sensitive elements of the sensors were made on two types of substrates - silicon on the insulator (SOI) and polysilicon on the insulator (Fig. 3).

In FIG. 4 shows the transfer characteristics (with variation in supply voltage) of the sensitive elements according to the invention, which were formed on SOI structures and on polysilicon structures on an insulator.

The claimed device is a sensor consisting of two nanowire transistors of p- and p-type, one of which works in the enrichment mode, the other - depletion. The drains of transistors are implemented as a common conclusion (Ivyh). The source areas of the p- and p-type transistors are divorced and correspond to the ground (ΟΝΏ) and power (Ipit) levels. The solution of the analyzed electrolyte (Ivh) is used as a common shutter. Ivh is determined using a gold reference electrode.

To study the characteristics of the sensor, a low-temperature ultrathin layer of silicon oxide in oxygen plasma was previously grown on the surface of silicon nanostructures.

As a confirmation of the declared characteristics of the sensor, experiments were conducted.

For the experiments, the preparation of buffer test solutions was a prerequisite. To prepare 1 M phosphate buffer solution, a sample of 8 g No. 01, 0.2 g KCl, 1.44 g No. 1 ₂ NRA ₄ , 0.24 g KN ₂ PO ₄ was dissolved in 1 liter of distilled water. Aliquots of phosphate buffered saline were titrated with KOH or HC1 for a given value using a pH meter.

At the first stage, the sensor was tested for operability in a gas medium (in air) and in a liquid (deionized water). The experiments were carried out at room temperature (T = 25 ° C). Next, 10 μl of 0.01 M buffer solution with a fixed pH value was applied to the surface of the sensing element. The volume of the test solution was selected experimentally, taking into account the area of spreading of the droplet and the rate of evaporation.

After stabilization of the transfer characteristic over time, the sensor was measured at the given parameters with a fixed pH value.

Then, in the absence of voltage supply, the sample was thoroughly washed with a mechanical dispenser in deionized water. After washing, a buffer solution of the same volume (10 μl) with the following fixed pH value was applied to the surface. So, for various pH values, transfer characteristics were obtained. The sensitivity of the sensor to pH was determined by the voltage shift Ivh on the reference electrode.

A change in the input potential of the sensor at the reference electrode corresponds to a change in the surface potential of the structure. And the change in the surface potential, in turn, reflects the change in the electrochemical potential and the recharging of the surface of the sensitive element.

As a result of the analysis of the transfer characteristics of the sensor, it was found that the gain of the sensitive element for silicon structures was from 30 to 150, for structures made on polysilicon, from 5 to 30. The gain can be varied by the supply voltage to achieve the maximum value. The maximum sensitivity for these structures to pH reaches 5 V / pH, due to the high value of the gain of the sensitive element. The sensitivity of the sensor reaches its maximum at the switching point of its transfer characteristic.

A study of the transfer characteristics of the sensor at different molarity values of the tested solutions made it possible to establish the dependence of the gain of the sensitive element on the molarity of the solution. In FIG. Figure 5 shows the dependence of the gain of the nanowire sensitive element K on the molarity of the solution.

The maximum sensitivity to pH of the studied structures will be achieved with a solution molarity of 10 ^-2 M. Thus, a sensitive element based on two n- and mercury nanowires can also be used as a sensor for determining the molarity of solutions.

Thus, the principle of operation of the sensor is based on tracking the change in voltage at the reference electrode (Ivh), which indicates the accumulation of charge on the surface of the sensitive element, depending on the acid-base properties of the analyzed medium. The functioning of the device is based on the following stages: sampling and preparation of a sample; transport operations with breakdown, measurement and processing of results.

Sampling and preparation of samples (analyzed solutions with a given pH value) was carried out using a pH meter. Transport operations and manipulations consisted in placing an experimental sample according to a measuring stand (electrical circuit) and applying test solutions using a variable volume mechanical dispenser. Detection and analysis of measurements was carried out using a semiconductor analyzer and processing of the obtained transfer characteristics, as a result of which the response of the system to a change in the pH value was recorded.

So, the sensor includes a recognition element (receptor layer), which is a material that can selectively interact with the analyte (in this case, ultra-thin 81O ₂ ),

- 4 020321 sensitive element, based on two nanowire transistors (the claimed device), which converts chemical or biological interaction into an electrical output signal and a data processing and display system.

The claimed device can operate as a sensor for determining the absolute pH value, and local relative changes in pH.

The high sensitivity of the sensor relative changes in pH concentration is of great importance for monitoring the progress of biochemical reactions. A sensor based on two nanowire transistors of p- and p-type allows you to determine the relative local change in pH (with a sensitivity of ~ 10 hydrogen ions [H +] in the vicinity of the sensitive element).

In order to expand the scope of the sensor, the surface of the nanowires can be functionalized with various surfactants to determine the specific interaction of the surface of the sensitive element with the analyte. So, after functionalization, the sensor can be used as a biosensor device with very high sensitivity.

The formation of polysilicon nanowire systems will significantly reduce the cost of devices.

Claims (14)

CLAIM 1. A sensitive element of the sensor for measuring the electrochemical potential in liquid media, containing p-type and p-type source electrodes and a common stock electrode having p-type and p-type areas, the electrodes are made on the dielectric layer of the substrate, the source electrodes are connected to the corresponding areas the stock electrode with nanowires coated with a dielectric layer, the stock and source electrodes being isolated. 2. The sensor element according to claim 1, characterized in that the substrate is made of silicon on the insulator or polysilicon on the insulator. 3. The sensitive element of the sensor according to claims 1, 2, characterized in that the drain and source electrodes are made of silicon or polysilicon. 4. The sensor element according to claims 1 to 3, characterized in that the concentration of impurities in the drain, source electrodes is 10 ¹⁹ -10 ²¹ cm ^-3 . 5. The sensor element according to claims 1 to 4, characterized in that the diameter of the nanowires is 5-100 nm. 6. The sensor element according to claims 1 to 5, characterized in that the length of the nanowires is from 50 nm to 10 μm. 7. The sensor element according to claims 1 to 6, characterized in that the distance between the nanowires connecting the drain and source electrodes is from 5 nm to 100 μm. 8. The sensor element according to claims 1 to 7, characterized in that the nanowires are doped, and the concentration of the dopant in the nanowires is 10 ¹⁴ -10 ¹⁹ cm ^-3 . 9. The sensor element according to claims 1 to 8, characterized in that both nanowires are doped with the same type of dopant. 10. The sensor element according to claims 1 to 7, characterized in that both nanowires are doped with different types of dopants. 11. The sensor element according to claims 1 to 10, characterized in that the dielectric layer deposited on the nanowires has a thickness of 5 to 200 nm. 12. The sensor element according to claims 1-11, characterized in that the nanowire is located above the dielectric layer of the substrate. 13. The sensor element according to claims 1 to 11, characterized in that the nanowire is located on the dielectric layer of the substrate. 14. The sensor element according to claims 1 to 11, characterized in that the nanowire is partially buried in the dielectric layer of the substrate.