Title of Invention	"AN IMPROVED PROCESS FOR THE DEPOSITION OF A CONDUCTING POLYMER FILM ON AN INSULATING SUBSTRATES HAVING INTERDIGITED ELECTRODES"
Abstract	This invention relates to an improved process for the deposition of a conducting polymer film on an insulating substrate having interdigited electrodes. In the process, deposition of a conducting polymer film takes place on insulating substrate having planar metallic electrodes placed on them with large inter-electrode spacing. In a feature of the present invention, the conducting polymer films deposited on the preconditioned substrates as described in the invention, in the preferred range of composition exhibited good coverage of the interdigited electrodes and conductivity value of 9 orders of magnitude higher than the film deposited without pretreatment of the substrates.

Title of Invention

"AN IMPROVED PROCESS FOR THE DEPOSITION OF A CONDUCTING POLYMER FILM ON AN INSULATING SUBSTRATES HAVING INTERDIGITED ELECTRODES"

Abstract

This invention relates to an improved process for the deposition of a conducting polymer film on an insulating substrate having interdigited electrodes. In the process, deposition of a conducting polymer film takes place on insulating substrate having planar metallic electrodes placed on them with large inter-electrode spacing. In a feature of the present invention, the conducting polymer films deposited on the preconditioned substrates as described in the invention, in the preferred range of composition exhibited good coverage of the interdigited electrodes and conductivity value of 9 orders of magnitude higher than the film deposited without pretreatment of the substrates.

Full Text	This invention relates to an improved process for the deposition of a conducting polymer film on an insulating substrate having interdigited electrodes. In particular it relates to a process for the deposition of a conducting polymer film on insulating substrate having planar metallic electrodes placed on them with large inter-electrode spacing. Conducting polymers are finding, increasing number of applications in electronic devices such as chemical sensors, opto-electronic devices such as light emitting diodes, photocells, etc. In these devices, it is often found that the metallic contacts have to be made with the polymeric films, which have to be in thin film form and placed at certain distance with each other. Further, these metallic electrodes are usually deposited in the interdigited configuration on insulating substrates such as glass, alumina, silicon oxide etc. with an inter-electrode gap ranging from 0.01 mm to 1.0 mm. Conducting polymers are usually deposited by electrochemical polymerization process in which the substrates have to be conducting. When such substrates having interdigited electrode substrates are used for electrochemical process, the conducting polymer gets deposited only on the metallic portions and leaves behind discontinuity due to the inter-electrode gap. This gives a large resistance and such films cannot be used for the devices such as sensors. If the interdigited electrodes are deposited on top of metallic substrates having conducting polymers, the device gets shorted and gives no response. The prior art for the deposition of conducting polymer films on insulating substrates (Indian Patent no. 190556 ) comprises, first forming a complex of a strong electron acceptor with polymer containing ether or alcohol groups, blending the same with another polymer, dip-coating the substrate in the blend solution, drying and exposing the same to vapours of appropriate monomer so as to form the conducting polymer film. This process may be used for depositing conducting polymer films on interdigited electrode coated substrates. However, it is limited to those conducting polymers having only certain dopant ions such as chlorine, bromide, nitrate and sulfate. In certain applications, it is desired to incorporate other dopant ions as well. Further, the thickness of the conducting polymer obtained cannot be below certain value (2 to 3 urn). However in some applications such as sensors [Radhakrishnan et al, Adv. Mater. Optics and Electronics, 6 (1996) p. 151] the thickness of the polymer film is desired to be low. Such films may be formed by electrochemical technique but the electrodes have to be continuous without gaps which is not possible for interdigited electrodes coated substrates. It is essential to overcome the above drawbacks in order to fabricate a device using conducting polymers, which have wider range of dopants and hence better response characteristics. The main objective of the present invention is to provide an improved process for depositing a conducting polymer film on insulated substrates having interdigited electrodes. Accordingly the present invention provides an improved process for the deposition of a conducting polymer film on an insulating substrate having interdigited electrodes which comprises; cleaning the substrate by known methods, placing the cleaned substrate in an evacuated chamber, depositing a thin film of gold platinum or their alloys having interdigited comb-like configuration having inter-electrode spacing in the range of 0.01 mm to 1 mm under vacuum conditions by conventional methods, removing the substrate from the chamber and placing it in a 0.1 M solution of a strong electron acceptor in a polar solvent such as herein described adding drop wise monomer used for synthesis of conducting polymer, rinsing and drying the substrate, placing the above substrate as a working electrode in an electrochemical cell containing 0.1M -0.5M solution of electrolyte, 0.1 M monomer, platinum counter electrode and a saturated calomel reference electrode, depositing the conducting polymer film by applying a d.c. voltage ranging from 6 to 9 to the working electrode for a period ranging from 100 to 400 seconds, rinsing the above film in water and drying the same to obtain the desired conducting polymer film on insulating substrate having interdigited electrodes. In an embodiment of the present invention, the substrate used for the deposition of conducting polymer film is insulating or semi conducting having receptivity in the range of 106 to 1015 ohm-cm and is selected from the group consisting of glass plates, silicon oxide films, single crystal silicon covered with insulating layers, insulating polymer films, glazed alumina disks and insulating substrates having smooth surface. In an another embodiment of the present invention, the strong electron acceptor used in the solution for dipping the substrate is a Lewis acid selected from the group consisting of cupric chloride, ferric chloride, nickel chloride, aluminum chloride, nitrates of copper, iron and other transition metals, ammonium persulfate, sodium persulfate and potassium persulfate and chromate's of sodium and potassium. In yet another embodiment of the present invention, the monomer used for the preparation of conducting polymer film is selected from heterocyclic compound selected from the group consisting of pyrrole, thiophene and furan, and macro cyclic compound selected from the group consisting of phthalocyanine, porphyrin and nitrogen containing derivative selected from aniline, pyridine and toluedine. In yet another embodiment of the present invention, the electrolyte used for the deposition of the conducting polymer film is selected from the group consisting of perchlorates, sulphates and fluoroborates of tertiary butyl salts of ammonium. In a feature of the present invention , the conducting polymer films deposited on the preconditioned substrates as described in the invention, in the preferred range Decomposition exhibited good f coverage of the interdigited electrodes and conductivity value of 9 orders of magnitude higher than the films deposited without pretreatment of the substrates. The invention is described herein below by the following examples, which are illustrative only and should not be construed to limit the scope of the invention in any manner. EXAMPLE -1 Clean glass slides (microscopic grade) were placed in a vacuum chamber ( added 2.8 g. of pure pyrrole. The conducting polymer films were deposited by applying 0.7 V (Vs SCE) to the electrodes for 180 s. The substrates were removed, rinsed in water and dried to obtain conducting polymer deposited on interdigited electrodes having high coverage and conductivity. The properties of these films are given in Table - 1. EXAMPLE - 2 Clean glass slides were placed in a vacuum chamber and the gold films having interdigited comblike pattern were deposited in the same manner as described in Example-1. These substrates were dipped in the preconditioning solution containing 50 ml of water, 1.0 ml of hydrochloric acid and 0.5 ml aniline to which were added dropwise ammonium persulfate aqueous solution (0.5 g / 10 ml) and kept for 5 min. The substrates were taken out, rinsed and dried and then placed in the electrochemical cell which has been described in Example - 1. The electrolyte used contained 4.0 ml of aniline dissolved in a mixture of n-methyl pyrrolidone (50 ml) and water (50 ml) to which were added 8.0 ml of concentrated hydrochloric acid. The conducting polymer was deposited by applying a potential of 0.9 V (Vs SCE) for 300 s. The films were rinsed and dried. The properties of these films are given in Table-1. EXAMPLE - 3 The glass slides having the interdigited gold film electrodes were prepared in the same manner as described in Examples 1 and 2. These were then dipped in the pre-treatment solution containing 4.0g ferric nitrate dissolved in 100 ml distilled water to which were added dropwise 0.5 ml pyrrole. The substrates were taken out, rinsed with water and dried. These were then placed in the electrochemical cell, which has been described in Examples 1 and 2. The electrolyte used contained a mixture of n- methyl pyrrolidone (50 ml) and water (50 ml) to which were added 2.15 ml of sulfuric acid, 2.8 ml of pyrrole and 0.5 g of copper phthalocyanine. The conducting polymer films were deposited on the interdigited electrodes by applying a potential of 0.7 V (Vs SCE) for 180 s. The films were rinsed in water and dried. The properties of these films are indicated in Table - 1. TABLE -1 (Table Removed) * The coverage was measured by recording transmittance(T)in the inter-electrode zone at wavelength of 550 nm and taking coverage=l-T # The conductivity was measured across the inter-electrode gap. It is seen from the data given in Table - 1 that the preconditioning of the substrates and depositing the conducting polymer film by the process described in the present invention leads to better coverage of the interdigited electrodes, (inspite of the gap present) with the conducting polymer as well as higher conductivity in the films. We Claim: 1. An improved process for the deposition of a conducting polymer film on an insulating substrate having interdigited electrodes which comprises; cleaning the substrate by known methods, placing the cleaned substrate in an evacuated chamber, depositing a thin film of gold 'platinum or their alloys having interdigited comb-like configuration having inter- electrode spacing in the range of 0.01 mm to 1 mm under vacuum conditions by conventional methods, removing the substrate from the chamber and placing it in a 0.1 M solution of a strong electron acceptor in a polar solvent such as herein described adding drop wise monomer used for synthesis of conducting polymer, rinsing and drying the substrate, placing the above substrate as a working electrode in an electrochemical cell containing 0.1M -0.5M solution of electrolyte, 0.1 M monomer, platinum counter electrode and a saturated calomel reference electrode, depositing the conducting polymer film by applying a d.c. voltage ranging from 6 to 9 to the working electrode for a period ranging from 100 to 400 seconds, rinsing the above film in water and drying the same to obtain the desired conducting polymer film on insulating substrate having interdigited electrodes. 2. An improved process as claimed in claim 1 wherein, the substrate used for the deposition of conducting polymer film is insulating or semi conducting having resistivity in the range of 106 to 1015 ohm-cm and is selected from the group consisting of glass plates, silicon oxide films, single crystal silicon covered with insulating layers, insulating polymer films, glazed alumina disks and insulating substrates having smooth surface. 3. An improved process as claimed in claims 1-2, wherein the polar solvent is methanol or water, 4. An improved process as claimed in claims 1 to 3 wherein, the strong electron acceptor used in the solution for dipping the substrate is a Lewis acid selected from the group consisting of cupric chloride, ferric chloride, nickel chloride, aluminum chloride, nitrates of copper, iron and other transition metals, ammonium persulfate, sodium persulfate and potassium persulfate and chromate's of sodium and potassium. 5. An improved process as claimed in claims 1 to 4 wherein, the monomer used for the preparation of conducting polymer film is selected from heterocyclic compound selected from the group consisting of pyrrole, thiophene and furan, and macrocyclic compound selected from the group consisting of phthalocyanine, porphyrin and nitrogen containing derivative selected from aniline, pyridine and toluedine. 6. An improved process as claimed in claims 1 to 5 wherein, the electrolyte used for the deposition of the conducting polymer film is selected from the group consisting of perchlorates, sulphates and fluoroborates of tertiary butyl salts of ammonium. 7. An improved process for deposition of a conducting polymer film on an insulated substrate having interdigited electrodes substantially as herein described with reference to the examples.

Full Text

This invention relates to an improved process for the deposition of a conducting polymer film on an insulating substrate having interdigited electrodes. In particular it relates to a process for the deposition of a conducting polymer film on insulating substrate having planar metallic electrodes placed on them with large inter-electrode spacing.
Conducting polymers are finding, increasing number of applications in electronic devices such as chemical sensors, opto-electronic devices such as light emitting diodes, photocells, etc. In these devices, it is often found that the metallic contacts have to be made with the polymeric films, which have to be in thin film form and placed at certain distance with each other. Further, these metallic electrodes are usually deposited in the interdigited configuration on insulating substrates such as glass, alumina, silicon oxide etc. with an inter-electrode gap ranging from 0.01 mm to 1.0 mm. Conducting polymers are usually deposited by electrochemical polymerization process in which the substrates have to be conducting. When such substrates having interdigited electrode substrates are used for electrochemical process, the conducting polymer gets deposited only on the metallic portions and leaves behind discontinuity due to the inter-electrode gap. This gives a large resistance and such films cannot be used for the devices such as sensors. If the interdigited electrodes are deposited on top of metallic substrates having conducting polymers, the device gets shorted and gives no response.
The prior art for the deposition of conducting polymer films on insulating substrates (Indian Patent no. 190556 ) comprises, first forming a complex of a strong electron acceptor with polymer containing ether or alcohol groups, blending the same with another polymer, dip-coating the substrate in the blend solution, drying and exposing the same to vapours of appropriate monomer so as to form the conducting polymer film.

This process may be used for depositing conducting polymer films on interdigited electrode coated substrates. However, it is limited to those conducting polymers having only certain dopant ions such as chlorine, bromide, nitrate and sulfate. In certain applications, it is desired to incorporate other dopant ions as well. Further, the thickness of the conducting polymer obtained cannot be below certain value (2 to 3 urn). However in some applications such as sensors [Radhakrishnan et al, Adv. Mater. Optics and Electronics, 6 (1996) p. 151] the thickness of the polymer film is desired to be low. Such films may be formed by electrochemical technique but the electrodes have to be continuous without gaps which is not possible for interdigited electrodes coated substrates.
It is essential to overcome the above drawbacks in order to fabricate a device using conducting polymers, which have wider range of dopants and hence better response characteristics.
The main objective of the present invention is to provide an improved process for depositing a conducting polymer film on insulated substrates having interdigited electrodes.
Accordingly the present invention provides an improved process for the deposition of a conducting polymer film on an insulating substrate having interdigited electrodes which
comprises; cleaning the substrate by known methods, placing the cleaned substrate in an
evacuated chamber, depositing a thin film of gold platinum or their alloys having interdigited
comb-like configuration having inter-electrode spacing in the range of 0.01 mm to 1 mm under vacuum conditions by conventional methods, removing the substrate from the chamber and placing it in a 0.1 M solution of a strong electron acceptor in a polar solvent such as herein described adding drop wise monomer used for synthesis of conducting polymer, rinsing and drying the substrate, placing the above substrate as a working electrode in an electrochemical cell containing 0.1M -0.5M solution of electrolyte, 0.1 M monomer, platinum counter electrode and a saturated calomel reference electrode, depositing the conducting

polymer film by applying a d.c. voltage ranging from 6 to 9 to the working electrode for a period ranging from 100 to 400 seconds, rinsing the above film in water and drying the same
to obtain the desired conducting polymer film on insulating substrate having interdigited electrodes.
In an embodiment of the present invention, the substrate used for the deposition of conducting polymer film is insulating or semi conducting having receptivity in the range of 106 to 1015 ohm-cm and is selected from the group consisting of glass plates, silicon oxide films, single crystal silicon covered with insulating layers, insulating polymer films, glazed alumina disks and insulating substrates having smooth surface.
In an another embodiment of the present invention, the strong electron acceptor used in the solution for dipping the substrate is a Lewis acid selected from the group consisting of cupric chloride, ferric chloride, nickel chloride, aluminum chloride, nitrates of copper, iron and other transition metals, ammonium persulfate, sodium persulfate and potassium persulfate and chromate's of sodium and potassium.
In yet another embodiment of the present invention, the monomer used for the preparation of conducting polymer film is selected from heterocyclic compound selected from the group consisting of pyrrole, thiophene and furan, and macro cyclic compound selected from the group consisting of phthalocyanine, porphyrin and nitrogen containing derivative selected from aniline, pyridine and toluedine.

In yet another embodiment of the present invention, the electrolyte used for the deposition of the conducting polymer film is selected from the group consisting of perchlorates, sulphates and fluoroborates of tertiary butyl salts of ammonium.
In a feature of the present invention , the conducting polymer films deposited on the preconditioned
substrates as described in the invention, in the preferred range Decomposition exhibited good
f coverage of the interdigited electrodes and conductivity value of 9 orders of magnitude higher than
the films deposited without pretreatment of the substrates.
The invention is described herein below by the following examples, which are illustrative only and should not be construed to limit the scope of the invention in any manner.
EXAMPLE -1
Clean glass slides (microscopic grade) were placed in a vacuum chamber (
added 2.8 g. of pure pyrrole. The conducting polymer films were deposited by applying 0.7 V (Vs SCE) to the electrodes for 180 s. The substrates were removed, rinsed in water and dried to obtain conducting polymer deposited on interdigited electrodes having high coverage and conductivity. The properties of these films are given in Table - 1.
EXAMPLE - 2
Clean glass slides were placed in a vacuum chamber and the gold films having interdigited comblike
pattern were deposited in the same manner as described in Example-1. These substrates were dipped in the preconditioning solution containing 50 ml of water, 1.0 ml of hydrochloric acid and 0.5 ml aniline to which were added dropwise ammonium persulfate aqueous solution (0.5 g / 10 ml) and kept for 5 min. The substrates were taken out, rinsed and dried and then placed in the electrochemical cell which has been described in Example - 1. The electrolyte used contained 4.0 ml of aniline dissolved in a mixture of n-methyl pyrrolidone (50 ml) and water (50 ml) to which were added 8.0 ml of concentrated hydrochloric acid. The conducting polymer was deposited by applying a potential of 0.9 V (Vs SCE) for 300 s. The films were rinsed and dried. The properties of these films are given in Table-1.
EXAMPLE - 3
The glass slides having the interdigited gold film electrodes were prepared in the same manner as described in Examples 1 and 2. These were then dipped in the pre-treatment solution containing 4.0g ferric nitrate dissolved in 100 ml distilled water to which were added dropwise 0.5 ml pyrrole. The substrates were taken out, rinsed with water and dried. These were then placed in the electrochemical cell, which has been described in Examples 1 and 2. The electrolyte used contained a mixture of n-

methyl pyrrolidone (50 ml) and water (50 ml) to which were added 2.15 ml of sulfuric acid, 2.8 ml of pyrrole and 0.5 g of copper phthalocyanine. The conducting polymer films were deposited on the interdigited electrodes by applying a potential of 0.7 V (Vs SCE) for 180 s. The films were rinsed in water and dried. The properties of these films are indicated in Table - 1.
TABLE -1

(Table Removed)
* The coverage was measured by recording transmittance(T)in the inter-electrode zone at wavelength
of 550 nm and taking coverage=l-T
# The conductivity was measured across the inter-electrode gap.
It is seen from the data given in Table - 1 that the preconditioning of the substrates and depositing the conducting polymer film by the process described in the present invention leads to better coverage of the interdigited electrodes, (inspite of the gap present) with the conducting polymer as well as higher conductivity in the films.

We Claim:
1. An improved process for the deposition of a conducting polymer film on an insulating
substrate having interdigited electrodes which comprises; cleaning the substrate by known
methods, placing the cleaned substrate in an evacuated chamber, depositing a thin film of
gold 'platinum or their alloys having interdigited comb-like configuration having inter-
electrode spacing in the range of 0.01 mm to 1 mm under vacuum conditions by conventional
methods, removing the substrate from the chamber and placing it in a 0.1 M solution of a
strong electron acceptor in a polar solvent such as herein described adding drop wise
monomer used for synthesis of conducting polymer, rinsing and drying the substrate, placing
the above substrate as a working electrode in an electrochemical cell containing 0.1M -0.5M
solution of electrolyte, 0.1 M monomer, platinum counter electrode and a saturated calomel
reference electrode, depositing the conducting polymer film by applying a d.c. voltage
ranging from 6 to 9 to the working electrode for a period ranging from 100 to 400 seconds,
rinsing the above film in water and drying the same to obtain the desired conducting polymer
film on insulating substrate having interdigited electrodes.
2. An improved process as claimed in claim 1 wherein, the substrate used for the
deposition of conducting polymer film is insulating or semi conducting having resistivity in
the range of 106 to 1015 ohm-cm and is selected from the group consisting of glass plates,
silicon oxide films, single crystal silicon covered with insulating layers, insulating polymer
films, glazed alumina disks and insulating substrates having smooth surface.
3. An improved process as claimed in claims 1-2, wherein the polar solvent is methanol
or water,
4. An improved process as claimed in claims 1 to 3 wherein, the strong electron acceptor
used in the solution for dipping the substrate is a Lewis acid selected from the group
consisting of cupric chloride, ferric chloride, nickel chloride, aluminum chloride, nitrates of
copper, iron and other transition metals, ammonium persulfate, sodium persulfate and
potassium persulfate and chromate's of sodium and potassium.
5. An improved process as claimed in claims 1 to 4 wherein, the monomer used for the
preparation of conducting polymer film is selected from heterocyclic compound selected
from the group consisting of pyrrole, thiophene and furan, and macrocyclic compound

selected from the group consisting of phthalocyanine, porphyrin and nitrogen containing derivative selected from aniline, pyridine and toluedine.
6. An improved process as claimed in claims 1 to 5 wherein, the electrolyte used for the
deposition of the conducting polymer film is selected from the group consisting of
perchlorates, sulphates and fluoroborates of tertiary butyl salts of ammonium.
7. An improved process for deposition of a conducting polymer film on an insulated
substrate having interdigited electrodes substantially as herein described with reference to the
examples.

Documents:

104-del-2001-abstract.pdf

104-del-2001-claims.pdf

104-del-2001-correspondence-others.pdf

104-del-2001-correspondence-po.pdf

104-del-2001-description (complete).pdf

104-del-2001-form-1.pdf

104-del-2001-form-19.pdf

104-del-2001-form-2.pdf

104-del-2001-form-3.pdf

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Patent Number

216983

Indian Patent Application Number

104/DEL/2001

PG Journal Number

13/2008

Publication Date

31-Mar-2008

Grant Date

24-Mar-2008

Date of Filing

31-Jan-2001

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110 001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	SUBRAMANIAM RADHAKRISHNAN	NATIONAL CHEMICAL LABORATORY, PUNE-411008, (MAHARASHTRA), INDIA
2	SHRIPAD DAGADOPANT DESHPANDE	NATIONAL CHEMICAL LABORATORY, PUNE-411008, (MAHARASHTRA), INDIA

PCT International Classification Number

C08J 7/18

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA