Plastic-Compatible Low Resistance Printable Gold Nanoparticle Conductors for Flexible Electronics

Abstract

Low resistance conductors are crucial for the development of ultra-low-cost electronic systems such as radio frequency identification tags. Low resistance conductors are required to enable the fabrication of high-Q inductors, capacitors, tuned circuits, and interconnects. The fabrication of these circuits by printing will enable a dramatic reduction in cost, through the elimination of lithography, vacuum processing, and the need for high-cost substrates. Solutions of organic-encapsulated gold nanoparticles many be printed and subsequently annealed to form low resistance conductor patterns. We describe a process to form the same, and discuss the optimization of the process to demonstrate plastic-compatible gold conductors for the first time. By optimizing both the size of the nanoparticle and the length of the alkanethiol encapsulant, it is possible to produce particles that anneal at low temperatures (Ͻ150°C) to form continuous gold films having low resistivity. We demonstrate the printing of these materials using an inkjet printer to demonstrate a plastic-compatible low resistance conductor technology.

Printed gold for electronic applications

“…The sheet resistance is in the order of 10 -2 -10 -3 /sq, comparable to that of bulk gold. 16 The high volatility of the hexylamine stabilising ligand (b.p.= 132°C) is considered to be the main contributing factor to obtaining such clear conductive films, as it is easily eliminated during thermal treatment.…”

“…The printed films should ideally be metallised at temperatures below 150°C, as low-cost flexible plastic substrates distort undesirably between 150 and 200°C. 16 Alternative methods of sintering such as laser, 17 ultraviolet 18 or microwave 19 irradiation can be used to minimise such thermal deformation.…”

“…The resulting films were found to adhere reasonably well onto the glass substrate, but can be used in conjunction with powders of other metals to improve colour and adhesion on ceramic or glassware. More recently, thiol stabilised nanoparticle materials have been inkjet printed onto plastic substrates to give conductive films when thermally cured at temperatures as low as 120°C 16,22 or when using a chemical oxidising agent to remove the thiol ligands at room temperature. 23 Further to the above, Johnson Matthey have collaborated in a number of projects concerned with the development of the next generation of metalbased inks for application in thin film electronic and photonic devices.…”

Sintering and consolidation of silver nanoparticles printed on polyimide substrate films

“…[1][2][3][4][5][6] Direct printing techniques including the ink-jet and microcontact printing processes can draw conductive lines directly patterned on the substrate in one step using silver, gold, or other nanoparticles. [7][8][9][10] In particular, if nanoparticles are used for direct printing, the conductive lines can be solidified at substantially decreased temperatures due to the extremely high surface free energy of nano-sized metal particles. 11,12 When the patterned nanoparticles are heated, sintering occurs below the melting temperature of the nanoparticles accompanied with consolidation and densification of the patterned parts.…”

Liposomes as nanoreactors for the photochemical synthesis of gold nanoparticles

“…Gold nanoparticles (AuNPs) have widespread applications in plasmonics, 1 biosensors, 2 electronics, 3 catalysis, 4 imaging and drug delivery. 5,6 A large number of methods have been developed and optimized for synthesizing AuNPs with defined sizes and shapes, 7,8 and typically involves the chemical reduction of Au (III) to Au (0).…”