Methods, apparatus, and systems for fabricating solution-based conductive 2D and 3D electronic circuits

Patent metadata

Field	Value
Publication number	US-11066296-B1
Application number	US-201916547239-A
Country	US
Kind code	B1
Filing date	Aug 21, 2019
Priority date	Aug 21, 2018
Publication date	Jul 20, 2021
Grant date	Jul 20, 2021

Abstract

This work develops a novel microfluidic method to fabricate conductive graphene-based 3D micro-electronic circuits on any solid substrate including, Teflon, Delrin, silicon wafer, glass, metal or biodegradable/non-biodegradable polymer-based, 3D microstructured, flexible films. It was demonstrated that this novel method can be universally applied to many different natural or synthetic polymer-based films or any other solid substrates with proper pattern to create graphene-based conductive electronic circuits. This approach also enables fabrication of 3D circuits of flexible electronic films or solid substrates. It is a green process preventing the need for expensive and harsh postprocessing requirements for other fabrication methods such as ink-jet printing or photolithography. We reported that it is possible to fill the pattern channels with different dimensions as low as 10×10 μm. The graphene nanoplatelet solution with a concentration of 60 mg/mL in 70% ethanol, pre-annealed at 75° C. for 3 h, provided ˜0.5-2 kOhm resistance. The filling of the pattern channels with this solution at a flow rate of 100 μL/min created a continuous conductive graphene pattern on flexible polymeric films. The amount of graphene used to coat 1 cm 2 of area is estimated as ˜10 μg. A second method regarding the transfer of graphene material-based circuits with small features size (5 μm depth, 10 μm width) from any solid surface to flexible polymeric films via polymer solvent casting approach was demonstrated. This method is applicable to any natural/synthetic polymer and their respective organic/inorganic solvents.

First claim

What is claimed is:

1. A method of fabricating a 2D or 3D conductive pattern or circuit in a substrate having a length, width, and thickness including but not limited to millimeter and micrometer scales without requiring post-processing steps comprising:
a. providing a substrate with a predetermined pattern or circuit of three-dimensional structural features in the thickness of the substrate to create three-dimensional open or closed microchannels in directions of any of the length, width, and thickness of the substrate, the microchannels having surfaces; and
b. coating at least some of said microchannel surfaces of selected said microchannels by:
i. controlling flow of a liquid comprising viscous or solution-form carbon-based conductive materials or nano-materials, through the selected said microchannels to control filling of the selected channels with the liquid by one or more of:
1. flow direction;
2. flow volume;
3. flow rate;
4. concentration of particles in the solution;
5. size of the particles in the solution;
6. solution viscosity;
7. capillary action; and

ii. adhering the electrically-conductive components of the liquid at a controlled thickness and coverage of the surfaces of the selected said microchannels;

c. without needing any postprocessing using chemicals or lasers or use of elevated temperatures;

further comprising transferring the conductive three-dimensional pattern or circuit to a second substrate by:
a. placing a polymer solution over the conductive three-dimensional pattern;
b. curing the polymer solution in place to;
i. create a second substrate;
ii. promote adherence of the conductive three-dimensional pattern to the second substrate;

c. transferring the conductive three-dimensional pattern to the second substrate by separating the second substrate from the first substrate.

2. The method of claim 1 wherein the substrate with a predetermined pattern or circuit is at least one of:
a. flexible;
b. non-flexible;
c. solid;
d. rigid;
e. non-porous;
f. porous;
g. nondegradable;
h. degradable;
i. stretchable; and
j. hydrogel.

3. The method of claim 2 wherein the predetermined pattern
a. in a said non-flexible substrate is created by one of:
i. machining;
ii. photolithography;
iii. laser etching; or
iv. deep reactive ion etching; or

b. in flexible substrates by:
i. formation in flexible polymers without molds.

4. The method of claim 3 wherein the non-flexible substrate comprises:
a. silicon wafer;
b. Teflon;
c. Delrin;
d. glass;
e. wafer;
f. metal; or
g. biodegradable or non-biodegradable polymer based material.

5. The method of claim 1 wherein the predetermined pattern or circuit is created by:
a. creating a mold comprising:
i. a material capable of high resolution forming of three-dimensional microstructural features with heights, widths, and thicknesses on the order of several tens of micrometers to several hundreds of micrometers, the material comprising:
1. silicon;
2. Teflon;
3. superhydrophobic material; or
4. glass, metal or Delrin, and

b. transferring from the mold to the substrate a negative of the three-dimensional microstructural features of the mold to create the microchannels.

6. The method of claim 5 wherein the substrate comprises a film of a natural or synthetic polymeric material having preselected material properties comprising one or more of:
a. flexibility;
b. porosity in the approximate range of 1% to 90%;
c. biodegradability;
d. biocompatibility;
e. mechanical properties including porosity, pore size, and elasticity; and
f. 3D microstructure.

7. The method of claim 6 wherein the natural or synthetic polymeric material comprises:
a. gelatin;
b. collagen;
c. chitosan;
d. alginate;
e. PVA;
f. PLLA;
g. PLGA;
h. whey protein isolate;
i. cellulose acetate;
j. polysulfone; or
k. polystyrene.

8. The method of claim 1 wherein the predetermined pattern is created by forming a pair of films, each with a predetermined pattern in a patterned surface and sandwiching the films with patterned surfaces of each facing one another.

9. The method of claim 8 wherein the patterns on each patterned surface of each film are predetermined to form three-dimensional microchannels relative to the length, width, and thickness of the sandwiched pair of films, including some at least partially closed microchannels or formation of close patterns directly within a 3D hydrogel structure (via 3D printing or injection molding) and filling of these close patterns with conductive solution via microfluidic approach.

10. The method of claim 1 wherein the liquid comprises:
a. a solution of a solvent and a solute comprising an adjustable concentration of electrically conductive particles.

11. The method of claim 10 wherein the electrically-conductive particles are graphene-based.

12. The method of claim 1 wherein the liquid comprises:
a. liquid metal or metal nanoparticles dispersed in a solvent; or
b. carbon nanotubes or nanofibers.

13. The method of claim 11 wherein the graphene-based conductive components are preprocessed prior to the step of coating the substrate by one or more of:
a. heating or annealing at a temperature and for a time period;
b. sonicating; and
c. cooling;

at predetermined temperatures and time periods and whether in solution or not, or in powder form or not to tune the coating relative to different electrical, mechanical, or microstructural properties.

14. The method of claim 1 wherein the controlling flow comprises one or more of:
a. adjusting flow rate;
b. adjusting flow volume;
c. promoting capillary action;
d. at room temperature; and
e. without post processing.

15. The method of claim 1 wherein the controlling flow comprises a microfluidic system adapted to pump, push, or guide the liquid into said selected channels at the controllable direction, volume, rate, number of passes, and concentration.

16. The method of claim 1 wherein the microchannels are only partially filled.

17. The method of claim 1 further comprising:
a. coating or adhering another substance over the coating.

18. The method of claim 17 wherein the another substance comprises:
a. biological cells.

19. The method of claim 1 further comprising using the fabricated conductive pattern in the film for one of:
a. flexible electronics;
b. biomedical implants;
c. biomedical cell interfaces;
d. biosensors;
e. sensors;
f. portable energy harvesting;
g. electronic skin; or
h. wearable devices.

20. A method of fabricating a 2D or 3D conductive pattern or circuit in a substrate having a length, width, and thickness including but not limited to millimeter and micrometer scales without requiring post-processing steps comprising:
a. providing a substrate with a predetermined pattern or circuit of three-dimensional structural features in the thickness of the substrate to create three-dimensional open or closed microchannels in directions of any of the length, width, and thickness of the substrate, the microchannels having surfaces; and
b. coating at least some of said microchannel surfaces of selected said microchannels by:
i. controlling flow of a liquid comprising viscous or solution-form carbon-based conductive materials or nano-materials, through the selected said microchannels to control filling of the selected channels with the liquid by one or more of:
1. flow direction;
2. flow volume;
3. flow rate;
4. concentration of particl

Assignees

• Univ Iowa State Res Found Inc

Inventors

• Uz Metin
• Mallapragada Surya

Classifications

• H05K2203/0534

  Offset printing, i.e. transfer of a pattern from a carrier onto the substrate by using an intermediate member · CPC title

• H05K2203/0156

  Temporary polymeric carrier or foil, e.g. for processing or transferring · CPC title

• H05K2203/0113

  Female die used for patterning or transferring, e.g. temporary substrate having recessed pattern · CPC title

• H05K2201/0257

  Nanoparticles · CPC title

• H05K2201/0245

  Flakes, flat particles or lamellar particles · CPC title