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Bend & Shape Flexible Integrated Circuits

The world of electronics is full of clever designs and ICs, but they are mostly non-flexible and rigid implementations of the engineer’s circuit idea. This is typically not very conducive to many of the applications in which the circuit will be used. The circuit may be placed on or inside human body, in clothing, or on some surface that is not straight, flat, and full of sharp angles. Much of the analog world we live in has softer lines, curves, and bends that move and change.

How do we adapt to these needs? Some developers are working with materials like graphene, which is both flexible and conductive. It is a lattice of pure carbon just a single atom thick. Other developers have chosen to pursue silicon sliced extremely thin, to a thickness less than the hair on your head. But silicon is a brittle material, especially at these thicknesses.

John Rogers, a material scientist at the University of Illinois at Urbana-Champaign has numerous patents covering silicon fabrics. These stretchable fabrics retain silicon's electrical performance while allowing flexibility. Rogers' company, MC10, is furthering the cause of biological sensors that can fit the shape of the heart, brain, and other organs of the body.

Flex sensors in silicon are combined with stretchable fabrics and rubber that stretches more than 200 percent.
(Source: MC10)

Flex sensors in silicon are combined with stretchable fabrics
and rubber that stretches more than 200 percent.
(Source: MC10)

Now the world of innovative electronic solutions can literally fit in the palm of your hand. You can have circuitry on your brain or under your skin. Besides biological applications, circuits (not merely sensors) can be embedded in or along the contours of steel cables. An obvious application is on the cables of a suspension bridge. Stress could be monitored and engineers could be warned of any potential failure.

Wireless, flexible sensors
Some designs have even gone to inkjet-printed circuitry on a paper-based material.[1] One technique like this uses inkjet-printed RFID circuits on flexible paper substrates. This gives the designer the advantages of low-cost and environmentally friendly RFID sensing.

Engineers have used inkjet-printed antenna configurations at frequencies as high as 7 GHz with good results.

A U-shaped dipole antenna can be printed by inkjet onto a paper or other flexible substrate.
(Source: Reference [1])

A U-shaped dipole antenna can be printed by inkjet onto a
paper or other flexible substrate.
(Source: Reference [1])

This antenna is printed on paper. Additional circuitry is printed for ICs, sensors, passive components, and a power source.

The inkjet-printed wireless sensor transmitter can be printed on a paper substrate with support components.(Source: Reference [1])

The inkjet-printed wireless sensor transmitter can be printed
on a paper substrate with support components.
(Source: Reference [1])

One use for this technology has been implemented in the “smart shoe.” The implementation needs no battery, since it is in an RFID configuration on a paper substrate. This is a remarkable enhancement to autonomous, wearable sensing applications that work over a relatively long range.

This technology has been taken one step further in that an asynchronous wireless link has been created between these flexible RFID imprinted tags and a wireless sensor network (WSN) with only a basic protocol. Connecting a simple RFID reader to the more complex WSN in this way has significant cost-savings ramifications.

Healthcare
One of the biggest areas of focus with potentially the most benefit to mankind is the use of flexible circuits in and on the human body. Second skin, neuroscience, water soluble circuits, and intra-cardiac imaging catheters are only a few of the amazing things that flexible electronic circuitry has brought to the industry.

John Rogers’ team is also involved in electronic skin that can contain temperature sensors, light detectors, and other integrated components in a rubberized sheet. This sheet can be applied as one would a temporary tattoo. It can bend and stretch with no damage to the circuitry. It can also be washed off after it serves its purpose. Less than a micron thick, there is no need for a polymer backing. The electronics are stamped directly onto the skin and sealed with a spray-on bandage.

Doctors can measure electrical conductivity or the spread of heat across the skin. They can identify levels of hydration as well as send small electrical currents to stimulate muscles as part of a physical therapy treatment program.

Neuroscience can also benefit from this technology. It has been demonstrated in the lab that an animal’s behavior can be modified by using a light flash in a technique called optogenetics. This reprograms the brain’s neurons in a specific area to respond to light. Micro-LED devices are small and less invasive than fiber-optic cables implanted into the brain and then connected to a cumbersome helmet linked to a laser.

Each square LED is 5 microns thick and 50 microns square. Four of these are put into a thin, flexible polymer sheet and then layered with other sheets containing sensors that monitor temperature, light, and electrical activity. The entire device is a tongue-depressor-shaped object that measures 10 microns thick — thinner than a spider web!

Intracardiac catheters for electrophysiological interventions in atrial fibrillation cases[2] use intracardiac echocardiography (ICE) as an alternative to a fluoroscope (which has potentially harmful ionizing radiation) for guided imagery in these procedures.

Capacitive micromachined ultrasonic transducers (CMUT) create micro-linear (ML) and ring catheters. The CMUT is in a phased-array configuration running at 10 MHz.

An ML catheter (a) and a ring catheter (b). (Source: Reference [2])

An ML catheter (a) and a ring catheter (b).
(Source: Reference [2])

Click on the image for a short slide show of additional portions of the medical device.

Flexible electronic integrated circuitry holds a rich future in many areas of design. The applications are limited only by our imaginations. Please give us examples you know about or for which you would like to see designs.

References

  1. “Progress Towards the First Wireless Sensor Networks Consisting of Inkjet-Printed, Paper-Based RFID-Enabled Sensor Tags,” Vasileios Lakafosis, Student Member IEEE; Amin Rida, Student Member IEEE; Rushi Vyas, Student Member IEEE; Li Yang, Member IEEE; Symeon Nikolaou, Member IEEE; and Manos M. Tentzeris, Fellow IEEE.
  2. “Forward-Looking Intracardiac Imaging Catheters Using Fully Integrated CMUT Arrays,” Amin Nikoozadeh, Ömer Oralkan, Mustafa Gencel, Jung Woo Choe, Douglas N. Stephens, Alan de la Rama, Peter Chen, Feng Lin, Aaron Dentinger, Douglas Wildes, Kai Thomenius, Kalyanam Shivkumar, Aman Mahajan, Chi Hyung Seo, Matthew O’Donnell, Uyen Truong, David J. Sahn and Pierre T. Khuri-Yakub

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24 comments on “Bend & Shape Flexible Integrated Circuits

  1. Davidled
    August 27, 2013

    Flexible circuit is used for monitoring and tracking object. I think that this type technology is more useful for military solder who execute the risk mission. This figure shows the separated battery, but battery might be powered by from part of body such as heart.  

  2. samicksha
    August 27, 2013

    But these circuits keep high dependency on use and limit of bend as wrong treatment can can cause wrinkles further compression can also cause rippled conductors.

  3. Steve Taranovich
    August 27, 2013

    Since this technology is still in its infancy, I know there will be many revisions to improve it—just think of the original pace-makers and those that we have in 2013—-time perfects design.

  4. Davidled
    August 27, 2013

    Yes, I think that there is a limitation of flexible circuit.  For example, there is a heating including temperature range. I am not sure how they validate those types testing case including EMI. I believed that flexible circuit is getting developed as MEMS technology and chemistry material are being developed.

  5. Scott Elder
    August 27, 2013

    Here is a kickstarter project using a flexible display on a human.  Mobile advertising.  Great idea.

    http://www.kickstarter.com/projects/erogear/fos-a-truly-wearable-bluetooth-led-display-system?ref=category

  6. eafpres
    August 27, 2013

    Hi Steve–flexible and printed electronics is similar to MEMS in terms of market development–the hype cycle has been longer than usual, and it has taken longer than hoped for technology to catch up to the hype.

    I still don't see high functionality in printed or flexible electronics.  I think in the media the distinction between a printed circuit and an integrated electronic device (i.e., an IC or active device) is often blurred.  Although progress has been made on some passives, and some sensors and even printed batteries, the more complex ICs still have to be made as normal and attached/applied to the circuit.  That doesn't mean there aren't useful advances here, but it is still early days.

    I agree that health monitoring may be a good application.  If you had say a blood pressure patch that you could replace every month, and it sent data wirelessly to a device in your home that your health care provider could monitor, that might be better than a blood pressure cuff.  There are many more possible applications like this.  But I think it is a long way to something with enough useful functionality and enough durability to implant, such as a flexible device on/around your heart.  Likewise, I think environmetal issues are a barrier to applications like the bridge cable you mention–if that is of enough value, you can do it with a more rugged strain gage and wireless device and a 10-year battery.  Someday, perhaps you extrude a think casing on the cable that you can just connnect to at a known spacing and read out strain, but that seems distant.

  7. Steve Taranovich
    August 27, 2013

    @eafpres—It sure will be interesting to see what new and innovative ideas the next generation can make out of this technology. I was just at NASA Ames in California and I met a team of “small satellite” designers, they were an average age of 23 and they developed the PhoneSat—using a smart phone as a major part of a satellite design at a cost of $25K instead of $25M!

  8. eafpres
    August 27, 2013

    Hi Steve–Agree completely.  Although not apples to apples, your satellite example is exemplary of new paradigms available due to rapid technology advancement.  

  9. Steve Taranovich
    August 27, 2013

    Hi eafpres–yes, that's true–Apple and Android technology is pretty unique technology and advancing at an amazing pace due to clever design and consumer hunger for more data and functionality

  10. samicksha
    August 28, 2013

    I read study case on electronic tatto by Northwestern University, where they express the main challenge they faced was to make electronics as soft as skin. i.e mechanics behind the design for serpentine-shaped electronics makes the device as soft as the human skin. The design enables brittle, inorganic semiconductors to achieve extremely vast stretchability and flexibility.

  11. jkvasan
    August 29, 2013

    Steve, 

    Transient Electronics is in similar league except that it is bio-degradable and dissolves in body fluids. They can be programmed to disappear after a certain period of time.

    TE has great uses in defence too.

  12. Steve Taranovich
    August 29, 2013

    Thanks for the information about Transient Electronics. Dissolving solutions will help make these types of flexible technologies available in many more areas of usage.

  13. Steve Taranovich
    August 29, 2013

    Yes, @samicksha—I believe that universities will certainly add their creative young minds, guided by excellent montors, to make these solutions a reality in the near future.

  14. jkvasan
    August 30, 2013

    Steve,

    Just imagine a simple electronic device getting exactly near a cancerous tumor and delivering exact amount of chemotherapy drug. It could reduce the drug dosage to the optimum level, kills only the bad guys leaving the good ones. Great isn't it? If this technology becomes implementable in humans, it could be a game changer.

  15. Steve Taranovich
    August 30, 2013

    Yes Jay (sorry if I am being too familiar) I firmly believe these types of applications are realizable within in the next decade—we seem to progress in electronics technology innovations more and more quickly as time goes on—-are our creative minds evolving?

  16. RedDerek
    August 30, 2013

    @SteveT – I believe it is because more “tools” are available for engineers to use. Our technology is built off of previous levels of technology. The new stuff just allows one to think the next step by using the previous step. Just breaking down the problem in the reverse order.

    The proper order is to ask… How do we get to the moon? Then break the whole question down to smaller tasks – Use a rocket, how to make a rocket? Use a controlled explosion, how to make this? Etc. It is the basis for all engineering problem solving.

  17. jkvasan
    August 31, 2013

    Steve,

    Minds were evolving since darwin. My opinion is, this surge in innovations can be attributed to the ecosystem simultaneously evolving. For example, a medical or industrial innovation evolves first and the ecosystem for testing, certifying and maintaining it evolves in parallel.

  18. Steve Taranovich
    August 31, 2013

    RedDerek—you've captured the essence of innovative deign thinking that is not taught in most engineering schools!

  19. David Maciel Silva
    August 31, 2013

    Who among us did not need to make a PCB that would have to be flexible?

    I believe that everyone, long ago thought about making electronic circuits for driving LEDs, shirts, thought it was going to get a good bill money, but at that time it was not possible to develop the project.

    With this technology we can advance much in this regard, caps, shirts, and electronics self adhesive …

    Engineers at Stanford, had a major breakthrough in this direction ..

    http://efytimes.com/e1/fullnews.asp?edid=106425

  20. SunitaT
    August 31, 2013

    One use for this technology has been implemented in the “smart shoe.”

    @Steve, thanks for the post. I am curious to know more about smart shoe. What is the concept behind smart shoe and what are the applications of using smart shoe ?

  21. SunitaT
    August 31, 2013

    @Scott, thanks for sharing the link. I think flexible display will make all of advertisement object and companies will start paying individual for displaying their ads on the display.

  22. SunitaT
    September 6, 2013

    An electronic apparatus built utilizing flexible electronics has numerous benefits. The capability to wrap a circuit-board into a wanted shape permits very dense and effective layouts to be formed. Cameras with flexible electronic circuits are not restricted to one form, but could be shaped into additional dense designs.

  23. Brad_Albing
    September 21, 2013

    @Scott – Perhaps we should have shirts made that could show adverts for Planet Analog, Integration Nation, EDN, and EETimes. Seems like a good idea….

  24. Brad_Albing
    September 21, 2013

    @SunitaT – yep – it'll be intersting to see how this field develops.

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