Self-Healing of Open Interconnect Faults for Reliable Large Area Electronic Systems

Lead Research Organisation: University of Cambridge
Department Name: Engineering

Abstract

Open circuit faults in interconnects can occur due to various reasons such as unexpected current spikes (e.g. during electrostatic discharge events), thermal stress, applied mechanical forces and fabrication faults. In the case of large area electronic systems (such as wearable electronics, active matrix systems on rigid and flexible substrates such as displays and image sensors) the occurrence of an open fault could make the system unusable. It is therefore of interest to improve the operational reliability of these systems.

To address this problem several passive and active approaches have been studied. Passive techniques such as adding redundancies, improving interconnect geometries and materials (e.g. meandering interconnects, stretchable interconnects etc.) make the electronic systems more fault tolerant. Active techniques imply the use of self healing mechanisms to completely restore electrical conductivity after the occurrence of the fault. One approach considers the encapsulation of conductive inks in dielectric shells (10.1002/adfm.201000159) embedded in the interconnect during fabrication. Upon the occurrence of an open circuit fault, the fracture in the interconnect also fractures the shells present in the local vicinity of the fault thereby spilling the conductive ink and immediately restoring conductivity. While this method provides a true healing of the fault, a downside is that the interconnect fabrication process flow must be modified to embed the shells.

We propose an alternate means to actively self heal open circuit faults using a dispersion of conductive particles in an insulating fluid. This dispersion is contained and isolated over each interconnect. When a current carrying interconnect experiences an open circuit fault, an electric field appears across the open gap. The field polarizes the conductive particles in the dispersion allowing some of them to chain up due to dipole-dipole attractive forces and create a bridge across the gap thereby healing the fault. The advantages of this approach is that the implementation does not disturb the existing techniques of fabrication of interconnects. The mechanism can be incorporated as an add-on feature.

A proof of concept of self healing using dispersion was demonstrated for printed circuits board (http://aip.scitation.org/doi/10.1063/1.4916513) but not for the much smaller length scales of integrated circuits using in large area electronic systems. The main goals of this proposal are (i) study and model the effectiveness of the self healing as we scale down particle size i.e. how quickly can we heal? how much current can the heal carry? (ii) to implement and demonstrate self healing of open faults at the much smaller length scales of interest on rigid and flexible substrates. (iii) Study the impact of the bending of a flexible substrate on the healing (iv) Implement self healing on integrated circuits used in large area electronic systems (thin film transistors on a rigid substrate) and study the performance of the circuit pre and post heal.

Apart from being of academic interest, this research would great help in developing modern manufacturing techniques that result in electronic circuits that last much longer. A wide variety of faults occurring in a wide variety of systems would benefit from this study eg. opens at solder joints in printed circuit boards, cracks in capacitive touch screen displays, open faults in photo-voltaic cell arrays, faults in foldable displays and wearable electronics etc. Certain critical systems such as health care devices, electronics used in satellites (where thermal stress is significant), electronics used to monitor dangerous or hard to reach environments etc. would operate with improved reliability. The research also has a direct impact on addressing social and environmental problems such e-wastes.

Planned Impact

This proposal permits advances in several strategic areas of significance to the UK economy and to maintaining UK as a leader in technology and innovation.
(i) Technology Impact: The answers to the questions raised in this proposal are the key to implementing the self-healing mechanism in integrated electronic circuits and systems, in particular - wearable electronics and large area electronic systems. However, the ideas could find an eventual implementation in any class of electronic systems (such as integrated circuit chips, printed circuit boards, etc.). For example,
(a) The use of electronic systems with the ability to repair themselves has a direct impact on space technology (http://www.ibtimes.co.uk/nasa-teams-stephen-hawking-help-prepare-tiny-spacecraft-epic-20-year-journey-1596130) and electronic system located in remote/hazardous environments (low maintenance required). The UK currently has a rapidly growing industry in satellite technology for space applications (https://www.gov.uk/government/publications/uk-space-industry-size-and-health-report-2016). The work from this proposal adds to the basket of technologies for the reliability of these systems
(b) The UK has put significant effort towards the development of large area electronics, flexible electronics and wearable electronics with the EPSRC Centre for Innovation and Manufacturing in Large Area Electronics (EPSRC CIMLAE) dedicated to this cause along with successful spinoffs such as Cambridge Display Technologies, Plastic Logic, FlexEnable etc. The answers to the questions raised by this proposal permit the development of reliable large area electronics, wearable electronics and flexible electronic systems with self repair capabilities. The EPSRC CIMLAE has agreed to provide a pathway to impact that allows me to directly engage with the industry (letter of support attached).

(ii) Strategic and Economic Impact: Large area electronic systems (including flexible and wearable electronics) are still being invented. All areas from manufacturing to applications have a lot of room for new ideas. Since the proposal targets a relatively new area of research (self-healing of open circuit faults) and applies it to a rapidly growing class of electronic systems (flexible, wearables and large area electronics) it forms a rich ground for generating intellectual property. It also promises new manufacturing methods. This would have a ripple effect on jobs and economic growth.

(iii) Direct Social Impact: To gauge the potential impact of this proposal, I ran a user survey through a program called the i-team (https://iteamsonline.org/exploring-the-potential-of-self-healing-circuits-to-address-e-waste-in-the-developing-world/). The team sought to identify (by contacting potential users) the key pain points in technologies and society, and to seek out the pathways to generate maximum impact with this technology. This proposal permits advances in several strategic areas of significance to the UK economy and to maintaining UK as a leader in technology and innovation. Apart from the technology impact, a direct social impact was identified in the area of e-wastes. The add-on feature of this technology helps refurbish many mildly damaged electronic devices (eg. display touch screens) and permits recycling. Moreover, if the technology matures to eventual deployment in electronic systems, it would significantly increase their lifetime thereby reducing e-waste.
 
Description The key findings are:
1.) The understanding of the physics of the behavior of a dispersion (of sub-micron sized conductive particles that are encapsulated and homogeneously dispersed in an insulating fluid, here silicone oil) - in the presence of an electric field.
It was found that polarized particles first oscillated rapidly between the electrodes, like as though carrying a message to and fro (in fact they carry electrical charge). Then these polarized particles 'became aware' of the presence of each other and chained up to form a bridge. They could now carry the message, i.e. charge, more efficiently by transporting it along the chain - i.e. allowing a current to pass through. Initially many chains forms, tracing the electrostatic lines of force. Finally, heating results in sintering i.e. the fusion of particles, and only the fittest chain (i.e. the chain having least resistance) remains. This proves to be the case suitable for quickest charge tranfer (i.e. maximized current). A deeper physical implication is that this is a consequence of the maximum entropy production principle.

2.) The application of the above phenomenon to achieve self healing circuits that can stretch!
The stretching is the interesting part. When the electrodes are pulled apart, the chain snaps - but new particles fill in the break in the chain and increase its length. This essentially permits self healing interconnects with stretching without any stress developing in the chain! This paper of ours received a lot of publicity and an editor suggestion. We have provided a link to the media article.

3.) We have now shown that we can self heal thin film transistor based integrated circuits on flexible substrates.
Exploitation Route We have already been approached by two sectors of the industry - aerospace/space technology and neuroscience. Although both these discussions are at an early stage they have interesting potential.

The space industry is interested in online correction and repair of printed circuit boards if they experience failure due to thermal fluctuations.
In the area of neuroscience, the interest is towards the development of flexible caps with a fine array of micron size wires that electrically connect the inside of the cap to the outside.
Sectors Aerospace, Defence and Marine,Electronics,Healthcare

URL https://physics.aps.org/synopsis-for/10.1103/PhysRevApplied.11.014057
 
Description EPSRC CIMLAE 
Organisation University of Cambridge
Country United Kingdom 
Sector Academic/University 
PI Contribution Research on Self Healing Circuit
Collaborator Contribution 1. Discussions with Industry 2. Invitation to present our research at the INNOLAE 2019 conference. This conference was attended by people from industry and academia.
Impact 1. Discussions with Industry 2. Invitation to present our research at the INNOLAE 2019 conference. This conference was attended by people from industry and academia. 2. Invitation to present our research at the INNOLAE 2020 conference. This conference was attended by people from industry and academia.
Start Year 2018
 
Description Research Collaboration 
Organisation Indian Institute of Science, Bangalore
Department Department of Instrumentation
Country India 
Sector Academic/University 
PI Contribution Primary research was conducted at the University of Cambridge
Collaborator Contribution Expertise in certain experiments and methods
Impact Research Publications: 1.) https://link.aps.org/doi/10.1103/PhysRevApplied.11.014057 (Editors Suggested and Featured in Physics) 2.) ECS Trans. 2018 volume 85, issue 13, 825-831 (Invited) 3.) https://ieeexplore.ieee.org/abstract/document/8918026 4.) https://www.nature.com/articles/s41598-019-55801-8 Multidisciplinary: Electrical Engineering, Chemical Engineering, Physics I am involved with teaching three key courses at the University of Cambridge and the Indian Institute of Science (IISc) 1.) Analog Integrated Circuits (Cambridge and IISc) 2.) Paper 8 - Electrical Engineering (Cambridge) 3.) Semiconductor Device Physics (IISc) 3.) GM1- Technology for the Poorest Billion (Cambridge) 4.) Supervision of about 8 students per year at Cambridge) and about 6 students per year at IISc. - In all these courses, I have developed new teaching methods eg. open ended questions where the students have to design without any restrictions in using books, software etc. These ideas have been appreciated by the students in their feedback. - The close supervision of Cambridge students leads to more personal interaction with the students. This has led to interesting ideas on education methods across different cultures. - In the course GM1-Technology for the Poorest Billion, I engaged a team of students to work on engineering design problems related to water and healthcare. The market being developing countries such as India led the students to directly talk to educators, researchers and startups in India and understand the problems better. One of these may lead to a startup and result in direct economic impact. I have also initiated interesting research activities in biomedical engineering with researchers at both IISc and Cambridge.
Start Year 2018
 
Description Self Healing for Space Research - Indian Space Research Organization 
Organisation Government of India
Department Department of Space, Indian Space Research Organisation
Country India 
Sector Public 
PI Contribution The research funded by the project on self healing circuits is attractive to space agencies for interest in use in satellites or deep space mission. An employee from the Indian Space Research Organization has joined my lab as a research student and is being trained on the technology.
Collaborator Contribution The Indian Space Research Organization has fully funded a student - an employee of theirs who has joined my lab - for a PhD program. Apart from this, there has been research funding in various phases with cumulative support of about 70000 GBP.
Impact The following publication is in collaboration with the Indian Space Research Organization https://www.nature.com/articles/s41598-019-55801-8
Start Year 2019
 
Description Invited Talk at the EDTM 2020 Conference, Penang, Malaysia 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Invited Talk at the EDTM 2020 Conference, Penang, Malaysia
Year(s) Of Engagement Activity 2020
URL https://ewh.ieee.org/conf/edtm/2020/
 
Description Invited Talk at the India Nanotech 2020 Conference 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact The research work was presented as an invited talk at the India Nanotech 2020 conference held at Bangalore, India.
Year(s) Of Engagement Activity 2020
URL https://www.bengaluruindianano.in/
 
Description Invited Talk, IEEE International Conference in Emerging Electronics 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact Invited Talk on ''Self Healing Interconnects'' at the IEEE International Conference in Emerging Electronics, Dec 2018.
Year(s) Of Engagement Activity 2018
 
Description Presentation at the INNOLAE 2020 COnference 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact The research work was presented at the INNOLAE 2020 conference held at Cambridge, UK.,
Year(s) Of Engagement Activity 2020
 
Description Presentation at the Sparc 2020 Conference 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact The research work was presented at the Sparc 2020 conference held at Bangalore, India.,
Year(s) Of Engagement Activity 2020
 
Description Research Talk, Innovations in Large Area Electronics Conference 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact Research Talk on Stretchable Self Healing Circuits at Innovations in Large Area Electronics Conference, 2019
Year(s) Of Engagement Activity 2019
URL http://www-large-area-electronics.eng.cam.ac.uk/innoLAE2019