Conductive Ink Development Dr Allen Reid, Commercial Director, NANOGAP

Masterclass: Future of Conductive Printing

• Current Status – Market Size – Types of Ink – Applications

• Market Drivers and Barriers

• CLIP Project – Objectives – Tasks – Achievements

• State of the Art Developments – NANOGAP stable and Multimodal Ag Dispersions – Intrinsiq Nano Cu – NANOGAP Ag Nanofibers – Market Round-up

• Conclusions

Conductive Ink Development

• 2012 market size: $2.86 billion, dominated by silver flake inks • 2018 forecast: $3.36 billion, of which $735 million is based on nano Ag and Cu

Current Status – Conductive Inks*

Conductive Material

Ink Type / Printing process

Applications Advantage Disadvantage

Silver Flake Predominantly Screen printing

Silicon PV, membrane switches, automotive, EMI shielding, screen heaters

Cost effective for many applications

Limited conductivity, thick films, surface roughness, difficult to photocure

Silver Nanoparticles

Predominantly Inkjet

Silicon PV, logic and memory, packaging, PCBs, RFID, OPV, sensors

Thin films, flexibility, high conductivity, rapid photocuring

High cost, can have poor adhesion

Copper Nanoparticles

Same as Ag NP, but lower cost

Can oxidise and lose conductivity

Silver Nanowires Screen, die-slot Tranparent Conductive Films for touchpanels, solid state lighting and PV

Compared to sputtered ITO, lower cost and improved conductivity

Difficult to inkjet print, Haze

* Adapted from IDTECHEX report: Conductive Ink Markets, 2012

• Silver flake inks for screen printing will continue to dominate with largest market share – Mature technology, competitive pricing, sufficient technical performance for most applications – However, PV is biggest market, and move towards ultra thin crystalline silicon PV may require the use of

inkjet printing with nanoparticle base inks

• Other emerging opportunities which require printing onto delicate or irregular shaped objects will also drive a move towards ink jet and and nanoparticle inks

• The ability to print onto cheap flexible substrates (polymer film, paper) requires low temperature sintering which is also driving a move towards nanoparticle inks

• For transparent conductive films (TCF) there is an overwhelming requirement for an alternative to sputtered ITO due to cost, supply and performance issues

– Silver nanowire / nanofiber inks can be formulated into inks and printed to form TCFs with technically superior conductive properties to ITO films for use in touch panels, solid state lighting and PV applications

Market Drivers

• Cost – Nanoparticle silver is significantly more expensive that

silver flake – However with market uptake and economies of scale

nanoparticle inks will become more cost competitive – Total in-use cost needs to be considered rather than a

price comparison of inks

• Technical – Long term stability of nanoparticle inks is a key concern

for large scale commercial uptake – High resolution printing e.g. 10 microns required for

transistor applications – Value chain integration including optimization of

conductive ink formulations for specific printing processes and products

Market Barriers

• Development, formulation, and feasibility of low cost inks

• Development of optimized inks for screen, flexo, rotary gravure and inkjet

• Optimization of inks for large area printing with high resolution, <50 microns

• Prepare demonstrators

CLIP: Conductive Low Cost Ink Project Objectives

CLIP: Conductive Low Cost Ink Project Ink Development Tasks

Materials USC and NANOGAP developed and supplied multi-modal Ag NP dispersions

IML supplied Cu nanoparticle dispersions

USC developed Ag coated Cu NP

AVL developed and supplied micro Cu flakes

Sirris developed and supplied Ag coated micro Cu flakes

Commercially sourced materials included: Ferro Ag coated Cu flake, Cabot Ag inkjet ink, DuPont Ag screen and flexo inks

Ink Formulation PRA developed screen and flexo inks based on: Cu flakes + Cu NP Cu flakes + Ag NP

Sirris developed inkjet inks based on: Ag NP dispersions Multi-modal Ag NP dispersions, Cu NP dispersions

Printing KTH performed inkjet trials with inks developed by Sirris

Sirris performed inkjet trials with inks developed by Sirris

Sirris performed aerosol jet trials with Ag dispersions supplied by USC / NANOGAP

Acreo performed screen and flexo trials with inks developed by PRA

• Screen and Flexo Inks (Cu flake + Cu NP) – Good Printing properties – Sheet Resistance after flash curing = 1 Ω∕ – Work on-going to optimise formulation to improve conductive properties – Raw material cost of inks ~230€/kg, so after adding process costs and margins

selling price is estimated at <500€/kg which compares favourably to commercial ink prices

• Inkjet Inks (NANOGAP / USC Uni-modal and Multi-modal Ag) – Good printing properties from all Uni-modal and multi-modal Ag inks – Sirris demonstrated lower sintering temperatures and improved conductivity of tri-

modal ink compared to equivalent multi-modal ink and commercial reference

• Aerosol Jet Inks (NANOGAP / USC Uni-modal and Multi-modal Ag) – Good printing properties from all Uni-modal and multi-modal Ag inks – On paper, bi and tri-modal inks achieved 3.5 to 4 x bulk Ag resistivity compared to

5 x for mono-modal – On PET, bi-modal ink achieved 4 x bulk Ag resistivity compared to 11 x for mono-

modal

• Potential cost savings in inkjet and aerosol jet printing are achievable through more efficient use of silver (level of conductivity achieved from weight of silver deposited) as a result of performance improvements

CLIP: Conductive Low Cost Ink Project Ink Development Achievements

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0 20 40 60 80 100

Shee

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curing time at 120°C (first 20 mins), then 150°C (minutes)

dropspacing 20 µm, PEL, 1 Layer

mono tri commercial ink

State of the Art Developments: NANOGAP Stable Ag NP Dispersions

Inkjet Trials at PEL • Printed onto paper

with Xaar print head • Cured at 120oC for 2

minutes • Resistivity = 4.4x10-5

Ω.cm

NGAP FI Ag-4101 Ag Content (wt %) 30 Ag Mean Particle Size (nm)

40 - 60

Ag Particle Size Distribution (nm)

25-75 (95% wt)

Viscosity (cP) 8 - 10 Surface Tension (mN/m)

25 - 28

Carrier Liquid Ethylene Glycol & IPA

Surface Functionality PVP

Aerosol Jet Trials at Sirris • Printed onto paper and PET • Laser cured • On Paper, 5x silver bulk

resistivity • On PET, 11x silver bulk

resistivity

10 20 30 40 50 60 70 80 90 100 1100

25

50

75

100

125

Diameter (nm)

42,52±14,5 nm

40 nm Ag Nanoparticle dispersions with excellent long term stability available for ink

formulators

State of the Art Developments: NANOGAP Multi-modal Technology

• Multi-modal particle size distributions improve particle packing leading to improved sintering and conductivity

• Very small size (<1nm) AQC promote low temperature sintering

• Development samples currently under evaluation

Development Samples DS13 Bi-modal (40nm/6nm) in EG/IPA blend with

water at <3% DS15 Bi-modal (40nm/6nm) in EG with water at

<3% DS20 Bi-modal (40nm/6nm) in EG/IPA blend

with BYK 430 and water at <7% DS29 Tri-modal (40nm/6nm/<1nm) in EG/IPA

blend with water at 3%

Aerosol Jet Printing Trials at Sirris • Printed onto Paper and PET • Laser cured • For DS13, 4x silver bulk resistivity on PET and Paper • For DS29, 3.5x silver bulk resistivity on Paper

State of the Art Developments: Intrinsiq Nano Cu

• Nano Cu produced by Plasma Process

• Product is surface treated with organic coating (to promote dispersion, and reduce reactivity, but maintain electrical conductivity (patented process)

• Suitable for direct formulation into inkjet ink (size < 50nm)

– Formulated inks available – Between 1.5 and 5 x bulk Cu conductivity – Once sintered, the tracks can maintain performance, are

equivalent to PCB tracks and can be similarly treated for extended life

• Suitable for formulation with micron copper into screen print ink

• Potential for – Offset litho – Flexo – Gravure

• Coating process available for other metals – nickel and

silicon inks in development STEM image of nano copper with organic coating which encapsulates the nanoparticles

State of the Art Developments: NANOGAP Ag Nanofibers for TCF

TYPICAL CHARACTERISTICS

NanoFiber Diameter (nm) 80 – 120 (95% wt/wt)

NanoFiber Length (µm)

5 – 50 (95% wt/wt)

Mean NanoFiber Length (µm) 20-30

Surface Functionality PVP

5% wt dispersions available in the following liquids

NGAP NP Ag-3103-W Water

NGAP NP Ag-3103-E Ethanol

NGAP NP Ag-3103-EG Ethylene glycol

NGAP NP Ag-3103-IPA Isopropyl alcohol

NGAP NP Ag-3103-Bt Butanol

NGAP NP Ag-3103-B Benzyl alcohol

• Ag Nanofiber dispersions available to ink formulators

• Alternatives to ITO transparent conductive films are required for many opto-electronic applications including touch panels and solid state lighting

• Inks based on NANOGAP silver nanofibers have been used to prepare TCF with sheet resistance <50ohms/sq and total light transmission > 95%

State of the Art Developments: Market Round-up* (1)

• Dupont MicroCircuit Materials – Inks for thinner printed lines – Eliminating precious metal and replace with low cost conductors – Improving ink functionality e.g. for heaters and sensors – Printed conductors replacing wires e.g. heaters and automotive interiors – Inks for roll to roll printing

• Toyochem – Ultrafine, low temperature, low resistivity – Screen printing as alternative to photolithography and etching – UV cured inks – Alternatives to Ag

• Other companies working on thin lines and features <50 microns – Pchem – Creative Materials

* Principal Source : printedelectronicsnow.com

State of the Art Developments: Market Round-up* (2)

• NovaCentrix – Ag and Cu based nanoparticle inks – PulseForge Photonic curing system – Copper Oxide based inks reduce in-situ to Copper metal during PulseForge

Sintering

• SunChemical – Inks for thin film PV technology – Inks for OPV for BIPV market

• Metalonix – “liquid metal” inks composed of metal atoms that convert to metal at low

temperature following printing

• Other Conductive Inks – Vorbeck Graphene inks for screen, flexo, gravure – Bayer aqueous CNT Inks for inkjet, gravure and screen – PEDOT:PSS from Agfa and Clevios

* Principal Source : printedelectronicsnow.com

Conclusions

• Nano particle based inks for printed electronics has been one of the many over-hyped areas of nanotechnology, with the market growth failing to meet expectations over the last 10-20 years

• However, there is now good signs on the commercial uptake of nano particle based inks

• Innovation is solving technical problems and leading to improved products – Stable nano inks, – Efficient ,and high conductivity, – Low temperature sintering

• Cost issues are being addressed – With commercial uptake and scale up cost will fall and competive position will rise – Cheaper Cu systems now available – Must consider whole process cost and not jut price of ink

• Supply chain collaborations and strategic partnerships are key to success – Companies that make conductive particles are not necessarily the best ink formulators

Allen Reid

a.reid@nanogap.es +44 7980 866 656

www.nanogap.es