Printing Electronic Features on Uneven Surfaces

A recently granted patent caught my eye because it made reference to a method of ink jet printing conductive inks onto non-uniform surfaces.  The patent was granted to the Cabot Corportion who currently provide a number of inkjet formulations for printed electronics applications.  This patent indicates that they have also been working on a system of direct printing which can compensate for the uneven surface of a substrate.

Patent details:

US8167393: Printable Electronic Features On Non Uniform Substrate And Processes For Making Same

Filing Information:
Inventor(s):    Karel Vanheusden, Chuck Edwards
Assignee(s):    Cabot Corporation

Filing date    13/01/2006
Issue date    01/05/2012
Prior Publication Data:     US20060158470 – 20/07/2006

Abstract:  A system and process for compensating for non-uniform surfaces of a substrate when direct printing traces is provided. The system and process provided herein measures the surface of a substrate and can determine whether the surface is substantially flat, rises or falls, or whether a mesa or valley is encountered. Depending on the surface feature (i.e., mesa, valley, falling or rising surface), the direct printing system can change the frequency of the printing timing signal, advance or retard the print timing signal, advance or retard the print data, or make repeated passes over certain areas. In addition, the process disclosed herein can determine whether two, three or all of the aforementioned steps for compensating for non-uniform substrates should be combined to most effectively and efficiently print on the non-uniform surface of the substrate as intended.

The invention seems to be primarily for printing on surfaces which have already received some printed circuit tracks or components and need to have additional conductive tracks to complete the device.  However, the text describes the situation where you might want to print directly onto an uneven or flexible substrate.  With a conventional printhead the drops will become more spaced out if the distance between the head and the substrate increases due to a downward slope.  If there was an upward slope then the drops will land closer together.

Various ways are described to overcome this problem and enable a uniform print density and line thickness to be achieved.  The distance between the printhead and the surface can be continually monitored with a laser interferometer so that the surface topography is mapped and used to control the drop delivery.

The patent has a huge number of document references and also contains a useful review of the background art associated with more traditional printing processes such as photolithography and screen printing.

This does seem to be a serious attempt at reducing the impact of an uneven surface on the reliability and quality of printed conductive tracks and I would be interested to hear from anyone who has looked at other ways of addressing this problem.


Printed electronics, tattoos and artificial skin

I came across a recent patent application from Nokia describing a haptic communication method in which labels or tattoos on the skin can be made to vibrate when triggered by a magnetic field.  In one example the magnetic field could be initiated by a mobile phone and the user could be alerted to incoming phone calls via the sensations induced on the users skin.

The patent application was published on 15th March 2012 as US20120062371

What is claimed is:
1. An apparatus comprising:
a material attachable to skin, the material capable of detecting a magnetic field and transferring a perceivable stimulus to the skin, wherein the perceivable stimulus relates to the magnetic field.
2. An apparatus according to claim 1, wherein the material comprises at least one of a visible image, invisible image, invisible tattoo, visible tattoo, visible marking, invisible marking, visible marker, visible sign, invisible sign, visible label, invisible label, visible symbol, invisible symbol, visible badge and invisible badge.
3. An apparatus according to claim 1, wherein the perceivable stimulus comprises vibration.

Several other claims go on to describe the material in more detail and indicate that it could comprise a ferromagnetic powder.

At about the same time The University of Cambridge were publishing in the Advanced Materials journal ( Vol 24, No. 12 pp. 1558-1565) an article on the progress made by researchers in the Cavendish Laboratory towards better flexible printed electronics materials.  The work was recently highlighted in the Research Features page and applications mentioned include artificial skin and interactive playing cards.  Many of these applications are a long way off yet but the groundwork to make them possible is progressing at a rapid rate.  The new circuits developed by Drs Kronemeijer and Gili exhibited the fastest operation published to date (a few hundred KHz) using a new class of ambipolar organic materials and reduced the power supply requirements by approximately one order of magnitude so that they can already be operated using a standard 9V battery.

If anyone would like to know more about the patent applications that are emerging in this highly competitive field then please contact me at IPScope (

Printed Electronics Patents Granted in 2011 – Kovio Inc

This is the third in the series covering patents granted during 2011 in the printed electronics field.

US7977240: Metal Inks For Improved Contact Resistance

Joerg Rockenberger, Yu Chen, Fabio Zürcher, Scott Haubrich

Kovio, Inc.

Filing date: 13 Feb 2009; Issue date: 12 Jul 2011


Metal ink compositions, methods of forming such compositions, and methods of forming conductive layers are disclosed. The ink composition includes a bulk metal, a transition metal source, and an organic solvent. The transition metal source may be a transition metal capable of forming a silicide, in an amount providing from 0.01 to 50 wt. % of the transition metal relative to the bulk metal. Conductive structures may be made using such ink compositions by forming a silicon-containing layer on a substrate, printing a metal ink composition on the silicon-containing layer, and curing the composition. The metal inks of the present invention have high conductivity and form low resistivity contacts with silicon, and reduce the number of inks and printing steps needed to fabricate integrated circuits.

Phil’s Comments:

Kovio Inc. is one of the leading companies involved in printed electronics devices and have made significant progress in printing complex electronic devices such as RFID’s in which not only the antenna but also the associated electronics is printed by a solution deposition process.

Here is an extract from the patent which explains the problem faced in any printing method for electronic devices:

In integrated circuits, the devices (e.g., TFT, capacitors, diodes, etc.) are generally connected to each other with metal lines (i.e., interconnects). Integrated circuits with good performance generally include interconnects with low resistivity, and thus not all metals are suitable for use as interconnects. Typical examples of suitable metals are Al, Cu, Au and Ag. Often, metals used for interconnects in integrated circuits do not form low resistivity contacts with the device electrodes (e.g., gate and source/drain electrodes), which are usually made with n+ and/or p+ doped silicon. Therefore, in order to fabricate integrated circuits with good performance, a contact layer formed between the n+/p+ silicon and the metal lines often provides relatively low resistivity between the devices and the interconnects. Typically, silicides are the preferred contact layers used in microelectronic devices, because they can provide ohmic contacts to heavily doped semiconductors (e.g. n+/p+ silicon and/or germanium).

This patent describes metal ink compositions that have high conductivity and low contact resistance and can therefore reduce the number of inks and printing steps required to manufacture a device.  The patent also describes a method which comprises (a) forming a layer comprising silicon and/or germanium on a substrate, (b) depositing (e.g., by printing) a metal ink composition on the silicon-containing layer, and (c) curing the metal composition. In general, the metal ink compositions comprise a bulk metal and a silicide-forming transition metal source.

More details are available in the full patent specification which can be found here.  Email me or leave a comment if you would like any further details.

Printed Electronics Patents Granted in 2011 – Conductive Ink

This is the second in the series covering patents granted during 2011 in the printed electronics field.

US7968011: Conductive Ink

Inventor(s): Gerardus Cornelis Overbeek, Michael Arnoldus Jacobus Schellekens, Alfred Jean Paul Bückmann

Assignee(s): DSM IP Assets B.V.

Filed: 6 Mar 2007; Issued: 28 Jun 2011

Abstract: A conductive ink comprising 10 to 75 wt % of at least one solvent comprising ≦20 wt % water; 0 to 50 wt % of at least one radiation curable material having a Mn in the range of from 50 to 10,000 g/mol; 5 to 70 wt % of at least one polyurethane having a Mw in the range of from 4,000 to 70,000 g/mol, 0 to 5 wt % of isocyanate-reactive component(s) bearing ionic or potentially ionic water-dispersing groups and a free isocyanate group content <0.5 wt % and 20 to 85 wt % of a conductive material.

The claims provide more details around the various components but rather than copying the claims I’ll explain in simple English.

The problem being solved by this invention is the lack of a common binder that can be used across a range of different conductive ink materials.  The inventors have provided a polyurethane based binder which they have found can be used to create inks suitable for flexography, gravure and ink-jet printing.  The method does not require high temperature curing and leads to good conductivity. Claim 1 requires that a UV radiation curing material is also included with the binder and this gives additional improvements in film properties and faster printing speeds.

The conductive materials are described as any form of conductive particle and the scope is very broad, including nanoparticles of silver or copper.  The particles can be flakes, fibres, nanotubes or mixtures, the particles can be silver coated.

The system requires a solvent which can be alcohol based (e.g. ethanol, iso-propanol, etc.) or any from a broad range of esters, ethers, ketones, etc. and preferably contains less than 10% water.

Any reader interested in the full formulation should refer to the patent for details of the preferred formulations.