WO2016022035A1

WO2016022035A1 - Apparatus comprising a self-assembled layer and method of surface modification

Info

Publication number: WO2016022035A1
Application number: PCT/RU2014/000587
Authority: WO
Inventors: Marina Nikolaevna KIRIKOVA; Alexander Alexandrovich BESSONOV; Elena Valerievna AGINA; Sergey Anatolievich Ponomarenko; Oleg Valentinovich BORSHCHEV; Mikhail Yurievich YABLOKOV; Aziz Mansurovich Muzafarov; Alla Borisovna GILMAN
Original assignee: Nokia Technologies Oy; Russian Academy of Sciences
Current assignee: Nokia Technologies Oy; Russian Academy of Sciences
Priority date: 2014-08-06
Filing date: 2014-08-06
Publication date: 2016-02-11
Anticipated expiration: 2017-02-06
Also published as: RU2017107564A; RU2733049C2; RU2017107564A3

Abstract

A film is disclosed. The film comprises a polymer substrate and a self-assembled layer (SAL) comprising an alkoxysilane-based oligomer chemically bonded to the polymer substrate. A method is also disclosed. The method comprises providing a polymer substrate, modifying a surface of the polymer substrate by depositing a self-assembling layer (SAL) comprising an alkoxysilane-based oligomer onto said surface.

Description

APPARATUS COMPRISING A SELF-ASSEMBLED LAYER AND METHOD OF

SURFACE MODIFICATION

TECHNICAL FIELD

[0001] The present application relates to microelectronics. In particular, the present application relates to films modified by a self-assembled layer (SAL) and methods of surface modification.

BACKGROUND

[0002] Polymers and silicone elastomers have been recently 15 implemented as a new class of substrates for printed and flexible microelectronics. The mechanical compliance of polymers and elastomers allows for novel flexible devices with changeable form factors. The electro-mechanical integrity of printed circuits relies on flexible functional layers that can sustain mechanical deformations without performance degradation. The functional layers 20 on flexible foils are typically fabricated by patterning via printing technologies such as screen printing, inkjet printing, flexography and gravure printing due to their simplicity, high speed and low cost.

[0003] The majority of polymers and elastomers widely used as substrates in printed electronics have a relatively hydrophobic and inert surface. 25 For example, the surface free energy of PDMS (poly(dimethilsiloxane)) that is a very popular material for the fabrication of flexible and stretchable devices appears to be less than 20 mN/m.

SUMMARY

30

[0004] In this section, the main embodiments of the present invention as defined in the claims are described and certain definitions are given. [0005] According to a first aspect of the present invention, an apparatus is disclosed. The apparatuscompnses a polymer substrate and a self-assembled layer (SAL) comprising an alkoxysilane-based oligomer chemically bonded to the polymer substrate.

[0006] The apparatusaccording to an embodiment may be a film. It may be, for example, a thin film with a thickness between land lOOOmicrometers.The apparatusmay be a film with a modified surface. According to an embodiment, the apparatus may comprise a film.

[0007] An oligomer may refer to any molecular complex that consists of a limited number of monomer units. By chemically bonded is meant connected via chemical bonds, for examplestrong chemical bonds such as covalent bonds and/or ionic bonds.

[0008] According to an embodiment, the film further comprises a metal layer chemically bonded to the SAL.

[0009] The metal layer may be bonded to the SAL via strong chemical bonds.

[0010] According to an embodiment, the metal layer comprises at least one of the following metals: silver, gold, copper, nickel and cobalt.

[0011] According to an embodiment, the polymer substrate comprises at least one of the following polymers: polydimethylsiloxane (PDMS), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), polyether ether ketone (PEEK), polycarbonate (PC), poly(methyl methacrylate) (PMMA), and polysulfone (PES).

[0012] According to an embodiment, the alkoxysilane-based oligomer comprises oligomer molecules with a variable chain length.Chain length and as a consequence molecular weight of oligomer affect the physical properties of the oligomer solution, which can be used for adjusting deposition conditions in process technology.

[0013] By chain length is meant herein the number of monomers in an oligomer molecule. In other words, according to the embodiment, the chain length of each molecule of the oligomer may vary from 2 to 1000 monomers. [0014] According to an embodiment, the characteristic size of the SAL is between 10 nanometers and 20micrometers, and the characteristic size of the substrate is between 1 and 1000 micrometers.

[0015] A characteristic size of the substrate and/or any layer is the smallest of the sizes in three dimensions of said substrate and/or layer. This size is commonly referred to as "thickness".

[0016] According to an embodiment, the SAL further comprises head groups comprising at least one of the following chemical groups or derivatives thereof: -SH, -SeH, -NH₂ , -OH, -COOH, -COOCH₃, -CN, and -SO3H.

[0017] Head groups refer to the chemical groups that are located at the surface of the SAL or inside of the SAL, and not at the interface between the SAL and the polymer substrate. For example, if a metal ink comprising metal particles is deposited onto the SAL, the head groups may serve to interact with metal ink particles, e.g. by chemisorption. The head groups can be head groups of oligomers comprised in the SAL.

[0018] According to an embodiment, the SAL further comprises anchor groups comprising alkoxysilane.

[0019] Anchor groups refer to the chemical groups that are located at the interface between the SAL and the polymer substrate or inside the SAL in a proximity to the interface. The anchor groups can react with the surface of the polymer substrate and/or with each other under certain conditions. Their function can be, for example, to link the SAL and the polymer substrate and/or make the SAL thicker due to their interconnections. The anchor groups can be anchor groups of oligomers comprised in the SAL. For example, the anchor groups may be selected from -Si(OCH₃)3 and -Si(OC₂H5)₃.These anchor groups can form strong covalent bond with hydroxyl groups on the polymer surfaces irrespective of the chemical nature of the polymer, for examplethey can be used with both PEN and PDMS substrates despite their different chemical structure. Anchor groups may be alternatively chosen fromchlorosilanes and phosphor-containing derivatives.

[0020] According to an embodiment, the components of the apparatusare flexible. [0021] Flexible components of the apparatusaccording to the invention may be used e.g. in fabrication of flexible microelectronic devices.

[0022] In an exemplary embodiment, the metal layer comprises ink comprising nanoparticles.

[0023] Ink comprising nanoparticles is a commercially available productwhich is commonly used in printed electronics. Chemical bonds are formed between metal nanoparticles and SAL head groups on molecular level.

[0024] According to an embodiment, the SAL is positioned on the polymer substrate according to a pattern.

[0025] The pattern may be a pre-determined pattern wherein some parts of the polymer substrate surface are covered by the SAL which is chemically bonded to it, while other parts of the polymer substrate remain uncovered. The metal layer may be positioned on the SAL according to the same or a different pattern.

[0026] According to an embodiment, the apparatusaccording to the present invention is used in a microelectronic device. Such device may be an integrated circuit, adisplay, a photovoltaic cell, accumulator batteryor a sensor.

[0027] According to a second aspect of the present invention, a method is disclosed. The method comprises: providing a polymer substrate; modifying a surface of the polymer substrate by depositing a self-assembling layer (SAL) comprising an alkoxysilane-based oligomer onto said surface.

[0028] The method according to this embodiment may be, but not limited to, a method for polymer surface modification, or a method for pre- treatment of polymers.

[0029] The polymer substrate may comprise, for example, PDMS and other siloxanes, PET, PEN, PI, PEEK, PC, PMMA, and/or PES. The SAL may comprise, for example, head groups including -SH, -SeH, -NH₂, -OH, -COOH, - COOCH3, -CN, and/or -SO3H. The oligomer-comprising SAL may be synthesized by using any anhydrous organic solvents such as, for example, tetrahydrofuran, dioxane, ethanol, methanol etc., in the presence of acetic acid (or other organic acid). Temperature of synthesis could be varied from 50° to 120°C. [0030] According to an embodiment, the method further comprises plasma treating the polymer substrate to create hydroxyl groups on the surface of the polymer substrate prior to modifying the surface of the polymer substrate.

[0031] The plasma treatment may be, for example, treatment by 0₂ plasma. It may be performed, for example, by corona discharge treatment or ionized oxygen or high-efficiency plasma. Plasma treatment creates hydroxyl groups on the polymer surface which induces efficient deposition of the SAL thereon.

[0032] According to an embodiment, the SAL is deposited by at least one of the following techniques: spin-coating, inkjet printing, spray-coating, slot- die coating, dip-coating, bar-coating, and drop coating.

[0033] According to an embodiment, the SAL is deposited in a liquid phase.

[0034] Liquid phase SAL can be used e.g. in printed electronics. Liquid phase solutions from which it is prepared enable using large scale fabrication methods such as inkjet printing, drop-casting, spin-coating etc. All these techniques can use liquids with different levels of viscosity in the technical process.

[0035] According to an embodiment, the SAL comprising an alkoxysilane-based oligomer is deposited according to a pattern.

[0036] The deposition according to a pattern can result in a patterned SAL, which subsequently may be used in patterned metal ink deposition.

[0037] The method of any of the abovementioned embodiments may be used in a metal nanoparticle deposition process.

[0038] The method of any of the abovementioned embodiments may be used in a microelectronic device fabrication process.

[0039] As it is clear to a skilled person, the methods according to these embodiments are not limited to the mentioned techniques, and they are indicated for exemplary purposes only.

[0040] According to a third aspect of the present invention, an apparatus is disclosed. The apparatus comprises: at least one processor; at least one memory coupled to the at least one processor, the at least one memory comprising program code instructions which, when executed by the at least one processor, cause the apparatus to perform the methods according to any of the abovementioned embodiments.

[0041] According to a fourth aspect of the present invention, an apparatus is disclosed. The apparatus comprises means for providing and holding a substrate, and means for modifying a surface of the polymer substrate by depositing a SAL comprising an alkoxysilane-based oligomer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] For a more complete understanding of example embodiments of the present invention, reference is now made to the following descriptions taken in connection with the accompanying drawings in which:

[0043] FIGURES la and lb show apparatusesaccording to embodiments of the present invention;

[0044] FIGURE 2 shows a method according to an embodiment of the present invention;

[0045] FIGURE3 is a chart demonstrating improved adhesion of a metal ink to a polymer surface. DETAILED DESCRIPTON OF THE EMBODIMENTS

[0046] Exemplary embodiments of the present invention and its potential technical effectsare explainedwith reference to Figures 1 through 3 of the drawings.

[0047] Figs, laand lb show apparatuses according to an embodiment of the present invention. According to the exemplary embodiments of Fig. la and lb, the apparatus is a film. It is clear to a skilled person that the film shown in these figures is an exemplary implementation of the present invention, and the apparatus according to the present inventionis not limited to the structure shown herein.

[0048] In Fig.l, the film comprises a substrate 101 which can comprise any appropriate polymer material, for example PDMS and other siloxanes, PET, PEN, PI, PEEK, PC, PMMA, or PES.Theabovementionedmaterialscanserveassubstratese.g. forflexibledevices. Inthefilmaccordingtothepresentinventionstheirqualitiessuchaswettabilityandsurfa ceenergyareimprovedbytheadditionoftheSALcomprisinganalkoxysilane- basedoligomer.

[0049] The film further comprises a self-assembled layer (SAL) 102 comprising an alkoxysilane-based oligomer chemically bonded to the polymer substrate 101. The alkoxysilane-based oligomer may comprise oligomer molecules with a variable chain length. The SAL 102 may comprise anchor groups and head groups 104. These can be anchor and head groups of the oligomer. An anchor group may comprise -Si(OCH3)₃ and/or -Si(OC₂H₅)3. A head group 104 may comprise -SH, -SeH, -NH₂ , -OH, -COOH, -COOCH3, -CN, and -SO3H.

[0050] The chemical bonds 103 between the SAL 102 and the polymer substrate 101 are schematically shown with broken lines. These bonds may be implemented via anchor groups of the oligomer, such as a group comprising oxygen (as shown by the letter O on the leftmost part of the bonds 103). It is clear that the figure is only a schematic representation and size proportions are not observed. The head groups 104 are also schematically shown with broken lines on top of the SAL 102. All of the components of the film may be flexible.

[0051] A role of SAL in the film of the present invention can be to improve the printability of metal ink by surface energy modulation and to enhance the adhesion force of the ink to polymer substrates by binding at molecular level. In order to achieve sufficient adhesion the anchor groups of SAL molecules are chemically bonded to the polymer surface while the head groups are exposed to be able to interact with metal layer particles, for example to interact with metal ink via chemisorption.

[0052] Oligomer-based SAL has a strong linkage to the surface due to the numerous bonds of anchor alkoxysilane groups and, as a consequence, the possibility to form denser and more uniform layers with head groups, such as functional thiol groups, located on top of it. This facilitates reaction of the oligomer SAL with metal nanoparticles which bond to multiple head groups faster and form stronger bonds. [0053] The oligomer moleculesmay be synthesized by means of partial hydrolysis of 3-mercaptopropyltrimethoxysilane, HS-(CH₂)3-Si(OCH3)3 with acetic acid in ethanol or methanol solution.

[0054] Fig. l b shows a film according to another embodiment of the present invention. This film comprises some of the same elements as the film of Fig. la, namely a polymer substrate 101, a SAL 102 comprising an alkoxysilane- based oligomer chemically bonded to the polymer substrate, and chemical bonds 103 between the SAL 102 and the polymer substrate 101. However, the film according to this embodiment also comprises a metal layer 105 chemically bonded to the SAL 102, and the head groups 104 are now shown as bonds between the metal layer 105 and the SAL 102. Metals such as Ag, Au, Cu, Ni, Co and others can be used in the metal layer 105. Thiol functional groups may be used as head groups 104, in which case the bonds between the metal layer 105 and the SAL 102 are strong Me-S bonds (Me stands for metal).

[0055] In both of the above example embodiments of the present invention, the SAL 102 may be positioned or deposited onto the polymer substrate 101 in a pattern (not shown on the Figures). The metal layer 105 may also be positioned or deposited on the SAL 102 according to a pattern..

[0056] A technical effect of the apparatus according to one or more of the example embodiments is an improved printability and adhesion of a metal ink to it due to the self-assembled layer that comprises the alkoxysilane-based oligomer. Mechanical integrity of the SAL provides the effect of conformal and uniform covering of the surface by SAL, which can be used e.g. in flexible microelectronic devices. A patterned film according to one or more embodiments can be used in many microelectronic applications such as electrodes and interconnects in integrated circuits, shielding elements and sensors.

[0057] Fig. 2 shows a method according to an embodiment of the present invention. This method is suitable for modification of polymer substrates. According to the method, a substrate 201 is provided. The polymer substrate 201 may be pre-manufactured. The polymer substrate may be exposed to plasma treatment in an optional step. Plasma treatment creates hydroxyl groups 202 on the polymer surface which induces efficient deposition of the SAL 203 thereon. Then, the SAL 203 is deposited onto the polymer substrate 201, thereby modifying the surface of the polymer substrate 201. The SAL 203 deposition can be carried out from liquid phase by any applicable technique, for example, but not limited to, by spin-coating or inkjet printing, spray-coating, bar-coating, dip coating, drop coating, slot-die coating, and others. The SAL 203 deposition may be performed according to a pattern.

[0058] The polymer surface modification method results in a film with improved metal adhesion and wettability, which is suitable for further deposition of metal ink or other substances onto the SAL 203. If the SAL 203 is deposited according to a pattern, it may be used as part of a metal ink deposition method which may also include a cleaning step after the metal deposition in order to remove a residual ink which is not covalently attached to the surface in areas not covered by the SAL 203 pattern. Such methods as ultrasonic cleaning, mechanical removing and/or detaching by tape can be used for the cleaning step.

[0059] Fig. 3 shows an improvement in adhesion of silver ink to a polymer substrate according to an exemplary embodiment of the present invention. In this embodiment, two types of silver ink, water-based PSI-21 1 from PChem and organic-based CRSN2442 from Sun Chemical, were used for screen printing of a conductive pattern on the top of deposited SAL. The thickness of PSI-21 1 and CRSN2442 ink was 1.5±0.1 μηι and 15.0±1.0 μπι, respectively. After the curing of ink (2 min at 120°C for PSI-21 1 and 30 min at 150°C for CRSN2442) an adhesion enhancement for both PEN and PDMS substrates have been observed, according to the standard cross-hatch tape test BS 3900/ASTM D-3359/DIN 53151/ISO 2409. It was shown that modification of these polymers with SAL through spin-coating increases adhesion of both types of silver inks up to 90-100% compared to that on non-treated polymers (50%-80% for PEN and 0% for PDMS). Inkjet printing of oligomer-based SAL also led to the noticeable enhancement of adhesion reaching 80-90% in case of PEN substrate and up to 100% in case of PDMS.

[0060] In case of PDMS the thiol groups can form a strong covalent- like bond to the silver film, whereas only a weak van der Waals attraction should attach the silver film to the bare PDMS surface. [0061] A technical effect of the method according to one or more embodiments of the present invention is that it can result in a substrate with a modified surface which has an improved wettability compared to naturally hydrophobic polymer surfaces. A further technical effect provided by the method is that the modified surface can have a property of enhanced metal nanoparticle adhesion which may be used in deposition of inks and further fabrication of e.g. flexible microelectronic devices.The method according to one or more embodiments does not require dry conditions and inert atmosphere. The method can also provide the technical effectof a simple and cost-effective deposition of SAL on polymer substrates.

[0062] An apparatus in accordance with the invention may include at least one processor in communication with a memory or memories. The processor may store, control, add and/or read information from the memory. The memory may comprise one or more computer programs which can be executed by the processor. The processor may also control the functioning of the apparatus. The processor may control other elements of the apparatus by effecting control signaling. The processor may, for example, be embodied as various means including circuitry, at least one processing core, one or more microprocessors with accompanying digital signal processor(s), one or more processor(s) without an accompanying digital signal processor, one or more coprocessors, one or more multi-core processors, one or more controllers, processing circuitry, one or more computers, various other processing elements including integrated circuits such as, for example, an application specific integrated circuit (ASIC), or field programmable gate array (FPGA), or some combination thereof.

[0063] The memory can include, for example, volatile memory, nonvolatile memory, and/or the like. For example, volatile memory may include Random Access Memory (RAM), including dynamic and/or static RAM, on-chip or off-chip cache memory, and/or the like. Non-volatile memory, which may be embedded and/or removable, may include, for example, read-only memory, flash memory, magnetic storage devices, for example, hard disks, floppy disk drives, magnetic tape, etc., optical disc drives and/or media, non-volatile random access memory (NVRAM), and/or the like. If desired, the different functions discussed herein may be performed in a different order and/or concurrently with each other. Furthermore, if desired, one or more of the above-described functions may be optional or may be combined.

[0064] Although various aspects of the invention are set out in the independent claims, other aspects of the invention comprise other combinations of features from the described embodiments and/or the dependent claims with the features of the independent claims, and not solely the combinations explicitly set out in the claims.

[0065] It is also noted herein that while the above describes example embodiments of the invention, these descriptions should not be viewed in a limiting sense. Rather, there are several variations and modifications which may be made without departing from the scope of the present invention as defined in the appended claims.

Claims

WHAT IS CLAIMED IS

An apparatus comprising:

a polymer substrate; and

a self-assembled layer comprising an alkoxysilane-based oligomer chemically bonded to the polymer substrate.

The apparatusof claim 1, further comprising a metal layer chemically bonded to the self-assembled layer.

The apparatusof claim 2, wherein the metal layer comprises at least one of the following metals: silver, gold copper, nickel and cobalt.

The apparatusof any one of claims 1 to 3, wherein the polymer substrate comprises at least one of the following polymers: polydimethylsiloxane, polyethylene terephthalate, polyethylene naphthalate, polyimide, polyether ether ketone, polycarbonate, poly(methyl methacrylate), and polysulfone.

The apparatusof any one of claims 1 to 4, wherein the alkoxysilane- based oligomer comprises oligomer molecules with a variable chain length.

The apparatusof any one of claims 1 to 5, wherein the characteristic size of the self-assembled layer is between 10 nanometers and 20micrometers, and the characteristic size of the substrate is between land lOOOmicrometers.

7. The apparatusof any of claims 1 to 6, wherein the self-assembled layer further comprises head groups comprising at least one of the following chemical groups or derivatives thereof: -SH, -SeH, -NH₂ , -OH, -COOH, -COOCH3, -CN, and -S0₃H.

The apparatusof any of claims 1 to 7, wherein the self-assembled layer further comprises anchor groups comprising alkoxysilane including methoxysilane and ethoxysilane.

The apparatusof any one of claims 1 to 8, wherein the components of the apparatusare flexible.

10. The apparatusof any one of claims 2 and 3, wherein the metal layer comprises ink comprises nanoparticles.

11. The apparatusof any one of claims 1 to 10, wherein the self- assembled layer is positioned on the polymer substrate according to a pattern.

12. Use of the apparatusaccording to any one of claims 1 to 11 in a microelectronic device.

13. A method, comprising:

providing a polymer substrate;

modifying a surface of the polymer substrate by depositing a self- assembling layer comprising an alkoxysilane-based oligomer onto said surface.

14. The method of claim 13, further comprising plasma treating the polymer substrate to create hydroxyl groups on the surface of the polymer substrate prior to modifying the surface of the polymer substrate.

15. The method of any one of claims 13 to 14, wherein depositing a self-assembling layer comprises depositing by at least one of the following techniques: spin-coating, inkjet printing, spray-coating, slot-die coating, dip-coating, bar-coating, and drop coating.

16. The method of any one of claims 13 to 15, wherein depositing a self-assembling layer is performed in a liquid phase.

17. The method of any one of claims 13 to 16, wherein depositing a self-assembling layer comprises depositing the self-assembling layercomprising an alkoxysilane-based oligomer according to a pattern.

18. Use of the method of any one of claims 13 to 17 to modify a polymer substrate in a metal nanoparticle deposition process.

19. Use of the method of any one of claims 13 to 17 in a microelectronic device fabrication process. 20. An apparatus comprising

at least one processor;

at least one memory coupled to the at least one processor, the at least one memory comprising program code instructions which, when executed by the at least one processor, cause the apparatus to perform the methods according to any of claims 13 to 17.