# US 12,216,010 B2 · Flexible devices incorporating electronically-conductive layers, including flexible wireless LC sensors

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- Number: US 12,216,010 B2
- Document ID: US12216010B2
- Status: Granted
- Kind: B2
- Application number: 17/801,740
- Filed: 2021-02-26
- Published: 2023-03-16
- Granted: 2025-02-04
- Earliest claimed: 2020-02-28
- Assignees: The University Court of the University of Edinburgh; Heriot-Watt University
- Applicants: The University Court of the University of Edinburgh; Heriot-Watt University
- Inventors: Philip James Walton Hands; Vasileios Mitrakos; Lisa Miriam MacIntyre; Marc Philippe Yves Desmulliez
- Web page: https://patentgrep.com/patent/US12216010B2

## CPC

- G01L 1/146: {for measuring force distributions, e.g. using force arrays (G01L1/148 takes precedence)}
- H05K 1/165: {incorporating printed inductors}
- G01L 1/144: {with associated circuitry (G01L1/146 and G01L1/148 take precedence)}
- H05K 3/02: in which the conductive material is applied to the surface of the insulating support and is thereafter removed from such areas of the surface which are not intended for current conducting or shielding
- H05K 3/4673: {Application methods or materials of intermediate insulating layers not specially adapted to any one of the previous methods of adding a circuit layer (similar methods for protective coatings H05K3/28)}
- H05K 3/4682: {Manufacture of core-less build-up multilayer circuits on a temporary carrier or on a metal foil}
- A61B 2562/0247: Pressure sensors
- A61B 2562/12: Manufacturing methods specially adapted for producing sensors for in-vivo measurements
- A61B 2562/164: the sensor is mounted in or on a conformable substrate or carrier
- H05K 2201/0133: Elastomeric or compliant polymer
- G01L: MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE (weighing G01G)
- H05K: PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D)

## Abstract

There is described a method of producing a flexible structure and sensor devices incorporating the former, such as wireless LC sensors, that comprises a plurality of thin-film layers of elastomeric material and at least one layer of micro-wrinkled electrically conductive material. The method includes steps leading to 2D wrinkled metallised polydimethylsiloxane (PDMS) layers enabling considerable flexibility with negligible bending failure for angles up to 180 degrees.

## Claims

### Claim 1

A method of producing a flexible structure that comprises a plurality of thin-film layers of elastomeric material and at least one layer of micro-wrinkled electrically conductive material, the method comprising:
a) applying a selective anti-adhesion treatment process to a carrier substrate whereby an outer peripheral region of the substrate provides a strong adhesion region and the area of the substrate within the outer peripheral region provides an anti-adhesion central region;
b) forming, on the carrier substrate, a first plurality of successive thin-film layers of PDMS, each of the successive thin-film layers of PDMS having a smaller ratio of crosslinking agent to base material and hence a higher Young's modulus than a preceding one of the thin-film layer of PDMS;
c) forming, on the last-formed thin-film layer of PDMS, a first thin-film layer of Parylene;
d) placing the carrier substrate in an organic solvent for a first period of time to induce swelling in the first plurality of thin-film layers of PDMS;
e) forming, on the first thin-film layer of Parylene a first further thin-film layer of PDMS;
f) forming by vacuum deposition, on the first further thin-film layer of PDMS, a second thin-film layer of Parylene in which a permanent micro-scale wrinkled surface morphology is generated as a consequence of diffusion of the organic solvent from the first plurality of thin-film layers of PDMS during said vacuum deposition, thus providing a first micro-scale wrinkled Parylene layer;
g) forming and patterning a first layer of electrically conductive material on the first micro-scale wrinkled Parylene layer such that the first patterned electrically conductive material has a micro-scale wrinkled surface morphology conforming to that of the first micro-scale wrinkled Parylene layer, thus providing a first micro-scale wrinkled electrically conductive pattern layer.

### Claim 2 (depends on 1)

The method of claim 1, wherein the selective anti-adhesion treatment process applied to the carrier substrate comprises a process whereby the outer peripheral region of the substrate is made highly hydrophilic and the central area of the substrate within the outer peripheral region is made highly hydrophobic.

### Claim 3 (depends on 1)

The method of claim 1, wherein the organic solvent and the first period of time are selected to induce a degree of swelling in the first plurality of thin-film layers of PDMS that causes the permanent micro-scale wrinkled surface morphology to be generated in the first further thin-film layer of PDMS.

### Claim 4 (depends on 1)

The method of claim 1, wherein the organic solvent is n-methyl-2-pyrrolidone, dioxane, dimethyl carbonate, pyridine or dimethylformamide.

### Claim 5 (depends on 1)

The method of claim 1, wherein the first further thin-film layer of PDMS has a Young's modulus equal to that of the last-formed layer of the first plurality of thin-film layers of PDMS.

### Claim 6 (depends on 1)

The method of claim 1, wherein the carrier substrate is a silicon wafer.

### Claim 7 (depends on 1)

The method of claim 1, wherein a second micro-scale wrinkled electrically conductive pattern layer is formed by:
placing the carrier substrate in an organic solvent for a second period of time to re-induce swelling in the first plurality of thin-film layers of PDMS;
forming one or more additional thin-film layers of PDMS on the uppermost layer of the preceding structure;
forming by vacuum deposition, on the uppermost of the additional thin-film layers of PDMS, a third thin-film layer of Parylene in which a permanent micro-scale wrinkled surface morphology is generated as a consequence of diffusion of the organic solvent from the first plurality of thin-film layers of PDMS during said vacuum deposition, thus providing a second micro-scale wrinkled Parylene layer; and
forming and patterning a second layer of electrically conductive material on the second micro-scale wrinkled Parylene layer such that the second patterned electrically conductive material has a micro-scale wrinkled surface morphology conforming to that of the first micro-scale wrinkled Parylene layer, thus providing a second micro-scale wrinkled electrically conductive pattern layer.

### Claim 8 (depends on 1)

The method of claim 1, further comprising forming one or more additional layers of PDMS on the first micro-scale wrinkled electrically conductive pattern layer and patterning one or more of the one or more additional thin-film layers of PDMS to create a 3D microstructure.

### Claim 9 (depends on 8)

The method of claim 8, wherein the 3D microstructure is formed photolithographically.

### Claim 10 (depends on 8)

The method of claim 8, wherein the 3D microstructure comprises an array of individual frustum arrays and each of the first and second micro-scale wrinkled electrically conductive pattern layers comprises an array of individual inductive structures, and wherein each inductive structure of each micro-scale wrinkled electrically conductive pattern layer is aligned with a corresponding frustum array of the 3D microstructure and a corresponding inductive structure of the other micro-scale wrinkled electrically conductive pattern layer to provide an array of individual devices usable as wireless LC sensors.

### Claim 11 (depends on 1)

The method of claim 1, wherein each layer of electrically conductive material is patterned using photolithography.

### Claim 12 (depends on 1)

The method of claim 1, wherein the patterning of each layer of electrically conductive material provides an array of individual electrically conductive structures corresponding to an array of individual devices.

### Claim 13 (depends on 12)

The method of claim 12, wherein one or more of the individual electrically conductive structures has one or more physical parameters that is different from one or more of the other individual electrically conductive structures.

### Claim 14 (depends on 1)

The method of claim 1, wherein each layer of electrically conductive material is a metallic layer.

### Claim 15

A flexible structure that comprises a plurality of thin-film layers of elastomeric material and at least one layer of micro-wrinkled electrically conductive material, the structure comprising:
a first plurality of successive thin-film layers of PDMS, each of the successive thin-film layers of PDMS having a smaller ratio of crosslinking agent to base material and hence a higher Young's modulus than a preceding one of the thin-film layer of PDMS;
a first thin-film layer of Parylene;
on the first thin-film layer of Parylene, a first further thin-film layer of PDMS;
on the first further thin-film layer of PDMS, a second thin-film layer of Parylene having a permanent micro-scale wrinkled surface morphology, providing a first micro-scale wrinkled Parylene layer;
a first layer of electrically conductive material on the first micro-scale wrinkled Parylene layer having a micro-scale wrinkled surface morphology conforming to that of the first micro-scale wrinkled Parylene layer, providing a first micro-scale wrinkled electrically conductive pattern layer.

### Claim 16 (depends on 15)

The structure of claim 15, wherein the first further thin-film layer of PDMS has a Young's modulus equal to that of the last-formed layer of the first plurality of thin-film layers of PDMS.

### Claim 17 (depends on 15)

The structure of claim 15, further comprising:
one or more additional thin-film layers of PDMS on the uppermost layer of the preceding structure;
a third thin-film layer of Parylene having a permanent micro-scale wrinkled surface morphology, providing a second micro-scale wrinkled Parylene layer; and
a second layer of electrically conductive material on the second micro-scale wrinkled Parylene layer such that the second patterned electrically conductive material has a micro-scale wrinkled surface morphology conforming to that of the first micro-scale wrinkled Parylene layer, thus providing a second micro-scale wrinkled electrically conductive pattern layer.

### Claim 18 (depends on 15)

The structure of claim 15, further comprising one or more additional layers of PDMS on the first micro-scale wrinkled electrically conductive pattern layer, one or more of the additional layers of PDMS patterned to provide a 3D microstructure.

### Claim 19 (depends on 15)

The structure of claim 15, wherein each layer of electrically conductive material is patterned using photolithography.

### Claim 20 (depends on 15)

The structure of claim 15, wherein each layer of electrically conductive material is a metallic layer.