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Method of forming conductors at low temperatures using metallic nanocrystals and product

a technology of metallic nanocrystals and conductors, applied in the field of forming conducting metallic films, can solve problems such as incompatibility with plastic substrates

Inactive Publication Date: 2007-08-02
RGT UNIV OF CALIFORNIA
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The invention provides a method for creating metallic nanoparticles that can be used to form electrical conductors on plastic carriers at low temperatures. The method involves depositing a composition of organic molecule-encapsulated metallic nanoparticles onto a substrate, evaporating the solvent, annealing the nanoparticles to evaporate the organic molecules, and sintering or melting the nanoparticles to form the conductor pattern. The use of nanoparticles allows for the formation of low-resistance conductors on plastic substrates. The invention also provides a composition of metallic nanoparticles that are compatible with plastic carriers and can be used for printing low-resistance conductors.

Problems solved by technology

), which is not compatible with plastic substrates.

Method used

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  • Method of forming conductors at low temperatures using metallic nanocrystals and product
  • Method of forming conductors at low temperatures using metallic nanocrystals and product
  • Method of forming conductors at low temperatures using metallic nanocrystals and product

Examples

Experimental program
Comparison scheme
Effect test

example 1

Nanocrystal Synthesis

[0045] The synthesis of the gold nanoclusters followed that reported by Murray et al., Longmuir, 14, 17 (1998). The length of the alkanethiol molecules used as the encapsulant was varied, and the size of the resulting nanocrystal was adjusted by controlling the relative mole ratio of the encapsulant and gold. In brief, 1.5 g of tetroactylammonium bromide was mixed with 80 mL of toluene and added to 0.31 g of HAuCl4:xH2O in 25 mL of deionized (DI) water. AuCl4− was transferred into the toluene and the aqueous phase was removed. A calculated mole ratio of an alkanethiol was added to the gold solution. Thiols with lengths ranging from 4 carbon atoms to 12 carbon atoms were used. For crystals with larger diameters (˜5 nm average diameter), a thiol:gold mole ratio of 1 / 12:1 was used. For smaller diameters, nanocrystals (˜1.5 nm average diameter), a thiol:gold mole ratio of 4:1 was used. Sodium borohydride mixed in 25 mL of water was added into the organic phase wit...

example 2

Heating Tests

[0046] The gold nanocrystals were redissolved in toluene to form saturated solutions. To measure resistance, the solutions were then micropipetted onto an insulating substrate (either plastic or SiO2) and allowed to air dry. To confirm plastic compatibility, several commercial plastics were used. Commercial polyester films (the smooth side of 3M inkjet transparencies and the uncoated side of laser printer transparencies) generally had deformation temperatures in the range of 150°-180° C., where we defined the deformation temperature as the temperature at which the film underwent dramatic contraction. Typically, these films showed significant degradation in transparency at temperatures 10°-20° C. lower, which therefore represented an upper bound on the usable temperature range for these materials, depending on their application. Therefore, these films were used only for the lower temperature tests. For these tests, the micropipetted film was dispensed on the uncoated s...

example 3

Annealing

[0047] A ramped anneal was performed to determine the various transition temperatures. The thiol burn-off temperature was determined visually, by a rapid transition of the film color from black to gold, accompanied by a sublimation of the thiol in the form of a black smoke. Upon further annealing, the film underwent a color transition from a dull golden color to a shiny gold. This indicated the nanocrystal melting temperature. At this point, the film achieves a low-resistance state. Resistivity of the films were measured using a 4-point probe and an HP4156 Semiconductor parameter analyzer. FIG. 11 is a table showing the results of the annealing tests. From this table, it is apparent that the required anneal temperature is a strong function of the encapsulant carbon chain length. Nanocrystals encapsulated in dodecanethiol anneal at 170° C.-200° C., which is not plastic compatible. However, by reducing the carbon chain length to four or six, it is possible to obtain nanocry...

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Abstract

Metallic nanoparticles are provided which can be used in forming metallic film conductors at reduced temperatures compatible with plastic carriers for the film conductors. This is realized by using a lower molecular weight organic encapsulant of the nanoparticle and thereby reducing the temperature at which the organic encapsulant evaporates. Further, the sintering or melting temperature of the metallic nanoparticle is reduced by using a lower sized nanoparticle, thereby increasing the particle surface area relative to the particle volume and thus reducing the required heat and melting temperature of the particle.

Description

RELATED APPLICATIONS [0001] This is a continuation-in-part of Serial No. PCT / US2004 / 005161, filed Feb. 19, 2004, the priority of which is claimed under 35 USC 120 and 365(c), which is incorporated by reference herein in its entirety. Priority is claimed pursuant to 35 USC 119(e) and 365(c) of provisional application Ser. No. 60 / 449,191, filed Feb. 20, 2003, which is incorporated by reference herein in its entirety.BACKGROUND OF THE INVENTION [0002] This invention is directed to forming conducting metallic films using organic-encapsulated metallic nanoparticles deposited out of a solution or suspension and more particularly the invention is directed to a method of forming metallic nanocrystals or particles for use in forming the metallic film. [0003] There has been growing interest in the development of printed organic electronics technologies, which are expected to see use in low-cost, flexible displays and disposable electronics applications. Low-cost RFID (radio frequency identifi...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): B22F3/10B22F1/0545B22F1/102H01B1/22H05K1/09H05K3/12
CPCB22F1/0022B22F1/0062B22F9/24B22F2998/10B82Y30/00H01B1/22H01L2924/19042H05K3/1241H05K1/097H01Q9/27B22F1/0085B22F3/1021B22F1/0545B22F1/102B22F1/142
Inventor SUBRAMANIAN, VIVEKHUANG, DANIELVOLKMAN, STEVENLIAO, FRANK
Owner RGT UNIV OF CALIFORNIA
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