GB2578568A

GB2578568A - Compliant conductive device

Info

Publication number: GB2578568A
Application number: GB1815446.8A
Authority: GB
Inventors: Hussein Zakareya
Original assignee: Individual
Current assignee: Individual
Priority date: 2018-09-21
Filing date: 2018-09-21
Publication date: 2020-05-20
Also published as: GB201815446D0

Abstract

A polymeric substrate (eg PDMS) is attached to a poly-para-xylylene layer (eg parylene) and a conductive layer (eg a gold electrode) is attached to the parylene layer to form a laminate structure. The polymeric substrate surface and the poly-para-xylylene surface may be exposed to an oxygen plasma to enhance the bond strength between the layers of the laminate. The laminate may form a flexible electronic device such as a sensor for soft robotic applications.

Description

Compliant Conductive Device

FIELD OF THE INVENTION

This invention pertains generally to the field of compliant and flexible conductive and electronic devices, to substrates for use in making flexible conductive and electronic devices, to their use as force sensors and to methods of manufacture.

BACKGROUND OF THE INVENTION

There is considerable development in the field of flexible electronic devices. There remain some significant difficulties, particularly as regards the development of flexible conductive devices that are required to be conformable, such as sensors for soft robotic applications.

Devices having a conductive layer or patterned conductive layer on a polymer substrate suitable for a flexible application tend to suffer from cracking on flexing of the device or thermal expansion and contraction. This results in short lifetimes and/or inconsistent function.

PROBLEM TO BE SOLVED BY THE INVENTION

There is a need for improvements in flexible and conformable conductive devices, for example for use as force sensors.

It is an object of this invention to provide a substrate for use in the manufacture of a flexible conductive device which is durable and effective.

It is an object of this invention to provide a flexible conductive device which has a long lifetime and does not become irreparably damaged during normal use.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention, there is provided a flexible conductive or electronic device comprising: a polymer base; a poly-para-xylylene layer which is bonded to the polymer base by a first adhesive layer; and a -1 -conductive layer which is bonded to the poly-para-xylylene layer by a second adhesive layer.

In a second aspect of the invention, there is provided a substrate for use in the manufacture of a flexible conductive or electronic device, the substrate comprising: a polymer base; and a poly-para-xylylene layer which is bonded to the polymer base by a first adhesive layer.

ADVANTAGES OF THE INVENTION

The conductive device of the invention provides a flexible and even conformable substrate and a conductive, typically patterned, layer for a functional use such as a force sensor that is robust, survives flexing and thermal expansion and may be incorporated into other substrates for use.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides for an improved flexible conductive or electronic device and to a substrate for making such a device. The substrate according to one aspect comprises a polymer base and a poly-para-xylylene layer which is bonded to the polymer base by a first adhesive layer. Preferably a second adhesive layer is disposed on the poly-para-xylylene layer on the side opposing the side bonded to the polymer base. The flexible conductive device according to another aspect comprises the substrate above having a conductive layer (e.g. a patterned conductive layer) disposed thereon and bonded thereto by a second adhesive layer.

Preferably, the device and substrate are conformable.

The polymer base may be of any suitable base and may comprise one or more of PDMS, PI, polybutyrate, polycarbonate, PI'vIMA, am/ate, polyethylene, HDPE, LDPE, PET, TPU, polyurethane, PVC, PEI,PEN, PP, polystyrene, aliphatic or semi-aromatic polyamide, PTFE, PVDF or a blend thereof.

The polymer base preferably comprises a polymer and more preferably is a polymer having a Young's modulus of up to 5 GPa (e.g. polyimide -2 -being around 4 GPa), preferably up to 1 GPa and more preferably is a flexible material, e.g. having a Young's modulus of up to 1.5 MPa, more preferably up to 1.2 MPa, still more preferably up to 1 MPa and preferably at least 500 kPa, such as in the range 700 kPa to 1 MPa, e.g. 700 to 800 kPa.

Preferably, the polymer base comprises or is PDMS and/or PI (polyimide), more preferably PDMS (polydimethyl siloxane).

The polymer base may be of any suitable thickness but is preferably thin enough to achieve the desired flexibility or conformity. The polymer base may, for example, be in the range 0.5 to 200 pm. For example, the polymer base may be TPU having a thickness of 20 to 50 pm, or a polyimide having a thickness of 8 to 50 pm or a PET having a thickness of 0.5 to 50 pm.

Preferably, the polymer base, which is preferably PDMS, has a thickness of up to 1.5 mm, more preferably from 60 to 400 pm, still more preferably from 65 to 240 pm, such as from 80 to 170 pm, more preferably 85 to 110 pm. Alternatively, the polymer base (preferably PDMS) has a thickness in the range 135 to 155 pm.

The first adhesive layer and second adhesive layer can each be any suitable adhesive. This may be an adhesive layer created by plasma activation (e.g. Ar and/or 02 plasma activation) of the polymer. This has previously been done with PDMS (see, for example, Park, D., Shin, S. J., & Oh, T. S. (2017). Stretchable Characteristics of Thin Au Film on Polydimethylsiloxane Substrate with Parylene Intermediate Layer for Stretchable Electronic Packaging. Journal of Electronic Materials, 47(1), 9-17. https://doi.org/10.1007/s11664-017-5722-3) or may be a click chemistry bonding material.

The first adhesive layer and/or the second adhesive layer is preferably an 0, plasma activated surface. The reactive species generated by the 0, plasma attack the surface of the polymers, temporarily forming reactive bonds across their surface that easily bond to other polymers and metals. These bonds may include, but are not limited to, carbonyl groups, hydroxide groups, and other oxygen containing chain ends. In the case of PDMS this a SiO, silica-like layer may -3 -form underneath this reactive layer, as the reactive species attacks the siloxane backbone.

Preferably, the poly-para-xylylene layer is a parylene layer, more preferably a parylene-C layer.

The poly-para-xylylene layer preferably has a thickness in the range nm to 10 pm. It may comprise a single layer of poly-para-xylylene or a plurality of two or more layers of poly-para-xylylene bonded together, e.g. 3 layers of from 20 to 100 nm bonded by an adhesive such as the 0, plasma-derived adhesive referred to above. Preferably, the poly-para-xylylene layer has a thickness in the range 50 nm to 500 nm.

In the conductive device of the invention, the conductive layer may comprise a graphene, a graphite, a metal oxide, a metal alloy or a metal, which is preferably patterned as required (e.g. by screen printing, photolithography or shadow masking application techiniques).

The conductive layer preferably comprises a metal selected from one or more of zinc, aluminium, copper, gold, silver, platinum, chromium, tungsten or titanium. More preferably, the conductive layer comprises gold.

The conductive layer has a thickness of from 20 nm to 250 nm, preferably 50 nm to 150 nm.

The substrate and device as described herein may be manufactured by any suitable method known in the art.

The invention has been described with reference to a preferred embodiment. However, it will be appreciated that variations and modifications can be effected by a person of ordinary skill in the art without departing from the scope of the invention. -4 -

Claims

CLAIMS: 1. A flexible conductive or electronic device comprising: a polymer base; a poly-para-xylylene layer which is bonded to the polymer base by a first adhesive layer; and a conductive layer which is bonded to the poly-para-xylylene layer by a second adhesive layer.
2. A flexible device as claimed in claim 1, which is a conformable device.
3. A flexible device as claimed in claim 1 or claim 2, wherein the polymer base has a thickness of from 80 to 170 p.m.
4. A flexible device as claimed in claim 3, wherein the polymer base has a thickness of from 85 to 110 p.m.
5. A flexible device as claimed in claim 3, wherein the polymer base has a thickness of from 135 to 155 pm.
6. A flexible device as claimed in any one of the preceding claims, wherein the conductive layer comprises a graphene, a graphite, a metal oxide, a metal alloy or a metal.
7. A flexible device as claimed in 6, wherein the conductive layer compriess a metal selected from one or more of zinc, aluminium, copper, gold, silver, platinum, chromium, tungsten or titanium.
8. A flexible device as claimed in claim 7, wherein the conductive layer comprises gold. -5 -
9. A flexible device as claimed in any one of the preceding claims, wherein the conductive layer has a thickness of from 110 to 230 nm, preferably 125 to 225 nm, more preferably 130 to 180 nm.
10. A flexible device as claimed in any one of the preceding claims, wherein the polymer base comprises one or more of PDMS, PI, polybutyrate, PC, PMMA, acrylate, polyethylene, HDPE, LDPE, PET, TPU, polyurethane, PVC, PEI,PEN, PP, polystyrene, aliphatic or semi-aromatic polyamide, PTFE, PVDF or a blend thereof.
11. A flexible device as claimed in any one of preceding claims, wherein the polymer base comprises a polymer having a Young's modulus of up to 1.5 MPa.
12. A flexible device as claimed in any one of the preceding claims, wherein the polymer base has a Young's modulus of up to 1.5 MiPa.
13. A flexible device as claimed in any one of the preceding claims, wherein the polymer base comprises PDMS and/or PI.
14 A flexible device as claimed in any one of the preceding claims, wherein the polymer base comprises PDMS.
15. A flexible device as claimed in any one of the preceding claims, wherein the poly-para-xylylene layer is a parylene layer.
16. A flexible device as claimed in any one of the preceding claims, wherein the adhesive layer comprises adhesion with oxygen plasma.
17. A substrate for use in the manufacture of a flexible conductive or electronic device, the substrate comprising: a polymer base; and -6 -a poly-para-xylylene layer which is bonded to the polymer base by a first adhesive layer.
18. A substrate as claimed in claim 17, which further comprises disposed on the poly-para xylylene layer a second adhesive layer.
19. A substrate as claimed in claim 17 or claim 18, wherein the substrate is for use in manufacturing a flexible conductive or electronic device by deposition of a metal or metal oxide layer by shadow mask deposition.
20. A substrate as claimed in any one of claims 17 to 19, which is a conformable substrate.
21. A substrate as claimed in any one of claims 17 to 20, wherein the polymer base has a thickness of from 80 to 170 gm.
22. A substrate as claimed in claim 21, wherein the polymer base has a thickness of from 85 to 110 pm.
23. A substrate as claimed in claim 21, wherein the polymer base has a thickness of from 135 to 155 pm
24. A substrate as claimed in any one of claims 17 to 23, wherein the polymer base comprises one or more of PDMS, PI, polybutyrate, PI PMMA, acrylate, polyethylene, HDPE, LDPE, PET, TPU, polyurethane, PVC, PEI,PEN, PP, polystyrene, aliphatic or semi-aromatic polyamide, PTTE, PVDF or a blend thereof.
25. A substrate as claimed in any one of claims 17 to 24, wherein the polymer 30 base comprises a polymer having a Young's modulus of up to 1.5 MPa. -7 -
26. A substrate as claimed in any one of claims 17 to 25, wherein the polymer base has a Young's modulus of up to 1.5 MPa.
27. A substrate as claimed in any one of claims 17 to 26, wherein the polymer 5 base comprises PDMS and/or PI.
28. A substrate as claimed in any one of claims 17 to 27, wherein the polymer base comprises PDMS.
29. A substrate as claimed in any one of claims 17 to 28, wherein the poly-para-xylylene layer is a parylene layer. -8 -