AUTOFLEX - Automated Integration of Flexible Electronics

Lead Research Organisation: University of Cambridge
Department Name: Engineering


The increasing ubiquity of electronics has had a profound influence upon everyday life over the last forty years. The mobile
telephone is perhaps the most obvious example of this, as it allows someone to be constantly connected to a range of
electronic resources. This trend is continuing, and more and more everyday objects are becoming electronically enabled.
The challenge is to be able to add electronic functionality to objects with minimal impact upon cost, and this is being
addressed by the field known as 'large-area electronics' which looks at how electronic devices can be fabricated on a
diversity of surfaces (such as glass or plastics) over large areas. Although the large-area electronics industry has
historically been dominated by displays, it is now diversifying to other areas including printed logic, and it is this that will
allow electronic functionality to be added to everyday objects [Nathan, A., et al., Proc. IEEE, 100, 1486 (2012)].
The large-area electronic display industry has found it absolutely essential to be able to perform in-line testing (and
subsequent repair) of products for economic production [D. Hendricks, 'Inspection and test of flat panel displays', Proc.
SPIE, 2174, 107-115 (1994)]. This is a consequence of the very large areas over which display manufacture takes place,
and the statistical likelihood of a significant defect being present per unit area. The high value of the display backplane
means that testing and repair is economically essential.
A similar approach will be necessary in the next generation of large-area printed logic electronics. Although the use of low
cost materials and processes in the manufacture of printed logic means that the cost of an individual system for integration
into labels, novelty products, toys and games and similar applications is orders of magnitude lower than the display, there
is still an economic driver for testing, assuming that the cost of the test can be made to be sufficiently low. However,
whereas the testing of a display can be achieved economically using established techniques that employ probe cards and
multiple communication channels, this will not be true for printed logic where production speeds could be in excess of 1
million circuits per hour. Therefore, a step-change is required to be able to perform economical testing at such high rates,
and this is the focus of the research in this project.

Planned Impact

This project has the potential to have a broad impact across a diversity of fields.
In terms of the UK economy, the academic work on high-speed testing will have a direct impact upon the ability of the
industry partners in AUTOFLEX, all of whom are UK-based, to commercialise their printed logic technology and
manufacturing processes. However, by working with the Plastic Electronics Technology Centre (PETeC), the other Plastic Electronics Centres of Excellence, and the new EPSRC Centre for Innovative Manufacturing in Large-Area Electronics
(EPSRC-CIMLAE) it will be possible to open up the generic aspects of the high-speed device testing procedures to other
companies within the vibrant plastic and large-area electronics sector in the UK (
There is also a possibility that intellectual property generated in new high-speed testing methods could enable a spin-out
company to be formed, and this will be kept under review throughout the project in consultation with the University's
technology transfer operation, Cambridge Enterprise Ltd.
The AUTOFLEX project will also directly employ a post-doctoral research associate for 18 months, who will gain valuable
skills in device testing. However, the Principal Investigator, Dr Flewitt, also has an established working relationship with
employees of Pragmatic Printing Ltd. (PPL) who frequently use his lab facilities. He therefore frequently discusses
technical issues with PPL employees and employees of the other direct industrial partners, providing an important training
route. Through the EPSRC-CIMLAE and the Plastic Electronics Centres of Excellent, DR Flewitt will also be able to
engage with and disseminate knowledge to employees of non-participating industrial companies.
Finally, by enabling the commercialisation of large-area printed electronics, there will be a significant long-term benefit to
Society. As discussed in the 'Summary', this field will enable electronic functionality to be added ubiquitously to the world
in which we live. On one level, this will break down the barriers to the digital world that some sections of society currently
face due to the complexity of products such as mobile telephones and laptops. However, on another level, it will improve
the quality of life while reducing environmental impact. An example of this is in the food industry, where the integration of a
simple printed sensor, logic, display and battery at very low cost into packaging would permit 'use by' dates to be replaced
by a more accurate indication of whether the contents are still edible. The consequence of this measure alone would be a
significant reduction in food waste. Other applications include continuous health monitoring to allow greater healthcare in
the home and a resulting improved quality of life in old age, or new ways of validating identity electronically for a safe digital
Description The purpose of this project was to develop high speed testing concepts compatible with the inline manufacturing process for printed electronics being developed by the other partners in the AUTOFLEX project. The aim was to develope a testing scheme that could be scalable to 250,000 devices per hour. We achieved this goal by proposing a sub-circuit level testing approach to increase the speed of testing, where hexNOT inverters can be connected in a group by temporary tracks and tested in a group to establish the pass/fail criteria. We demonstrated, using simulation and then through experimental demonstration, that the hexNOT inverters can be tested using the Ring Oscillator (RO) circuit.

We demonstrated using circuit simulation that the measurement of amplitude and frequency of oscillation of ROs consisting of up to 10 devices are sensitive to variations in the devices under test. After establishing validity of the approach, experimental ROs were fabricated and optimum stages of ROs were experimentally determined. Using optimum 9 stage RO (3 blocks of hexNOT), the test was demonstrated on production wafers to pass and fail blocks of hexNOT structures across the wafers. In addition to establishing pass and fail methods, it was also demonstrated that the correlation between the voltage amplitude and frequency can be used to establish a Figure of Merit (MRO) of RO circuits. The MRO of tested RO circuits can be used as a qualitative method to bin and categorize the constituent devices. Moreover, we did preliminary testing on a method to measure the heat signature using a thermal imaging camera when a RO is under operation. This could potentially lead to a method to increase the resolution of testing .

In addition to technical development, we Developed a cost model and estimated cost of testing per unit/IC at the rate of 250,000 ICs per hour using the RO testing method. According to the cost model, using the RO testing the target can be achieved with reasonable quantity of equipment.
Exploitation Route The testing methodologies will be taken up by companies wishing to use printing for electronic device manufacture.
Sectors Electronics

Description This project made significant progress on understanding the importance of electronic testing within the fabrication processing of large-area electronics. Specifically, the work on testing methodologies for thin film transistor-based devices has been employed in part by the lead industrial partner, Pragmatic Printing Ltd. in their circuit designs. However, the greater impact has been that this project led on to further work on testing of devices with Pragmatic Printing Ltd. through a KnowledgeTransfer Partnership project between Cambridge University and Pragmatic Printing Ltd. The Knowledge Transfer Associate from this project went on to be employed by Pragmatic Printing, and we have continued to have regular discussions on device testing as a result.
First Year Of Impact 2015
Sector Electronics
Impact Types Economic

Description Innovate UK Contract Research and Development
Amount £56,503 (GBP)
Funding ID 102154 
Organisation Innovate UK 
Sector Public
Country United Kingdom
Start 04/2015 
End 09/2016
Description Knowledge Transfer Partnership
Amount £101,539 (GBP)
Funding ID KTP010131 
Organisation Innovate UK 
Sector Public
Country United Kingdom
Start 05/2016 
End 04/2018
Description Technology Strategy Board Contract Research & Development
Amount £56,503 (GBP)
Funding ID TS/M009645/1 
Organisation Innovate UK 
Sector Public
Country United Kingdom
Start 01/2015 
End 06/2016