Electronic skin and its evolution

Michael Berger has featured an article in the journal Advanced Materials, which reviews 25 years of work on e-skin (aka, electronic skin or artificial skin) in his Nov. 15, 2013 Nanowerk Spotlight series article ,

Advances in materials, fabrication strategies and device designs for flexible and stretchable electronics and sensors make it possible to envision a not-too-distant future where ultra-thin, flexible circuits based on inorganic semiconductors can be wrapped and attached to any imaginable surface, including body parts and even internal organs. Robotic technologies will also benefit as it becomes possible to fabricate electronic skin (‘e-skin’) that, for instance, could allow surgical robots to interact, in a soft contacting mode, with their surroundings through touch. In addition to giving robots a finer sense of touch, engineers believe that e-skin technology could also be used to create things like wallpapers that double as touchscreen displays and dashboard laminates that allow drivers to adjust electronic controls with the wave of a hand.

Here’s a link to and a citation for the 25-year review of work on e-skin,

25th Anniversary Article: The Evolution of Electronic Skin (E-Skin): A Brief History, Design Considerations, and Recent Progress by Mallory L. Hammock, Alex Chortos, Benjamin C.-K. Tee, Jeffrey B.-H. Tok, and Zhenan Bao. Advanced Materials Volume 25, Issue 42, pages 5997–6038, November 13, 2013 Article first published online: 22 OCT 2013 DOI: 10.1002/adma.201302240

© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The review article is behind a paywall but Berger’s synopsis offers a good overview* and tidbits such as this timeline (Berger offers a larger version) which includes important moments in science fiction (Note: Links in the caption have been removed),

Figure 1. A brief chronology of the evolution of e-skin. We emphasize several science fictional events in popular culture that inspired subsequent critical technological advancements in the development of e-skin. Images reproduced with permission: “micro-structured pressure sensor,”[18] “stretchable OLEDs,”[20b] “stretchable OPVs,”[21a] “stretchable, transparent e-skin,”[22] “macroscale nanowire e-skin,”[23a] “rechargeable, stretchable batteries,”[137] “interlocked e-skin.”[25] Copyright, respectively, 2010, 2009, 2012, 2005, 2010, 2013, 2012. Macmillan Publishers Ltd. “Flexible, active-matrix e-skin” image reproduced with permission.[26a] Copyright, 2004. National Academy of Sciences USA. “Epidermal electronics” image reproduced with permission.[390a] Copyright, American Association for the Advancement of Science. “Stretchable batteries” image reproduced with permission.[27] “Infrared e-skin” image reproduced with permission.[8b] Copyright 2001, IEEE. “Anthropomorphic cybernetic hand” image reproduced with permission.[426] Copyright 2006, IEEE. [downloaded from http://onlinelibrary.wiley.com.proxy.lib.sfu.ca/doi/10.1002/adma.201302240/full]

Figure 1. A brief chronology of the evolution of e-skin. We emphasize several science fictional events in popular culture that inspired subsequent critical technological advancements in the development of e-skin. Images reproduced with permission: “micro-structured pressure sensor,”[18] “stretchable OLEDs,”[20b] “stretchable OPVs,”[21a] “stretchable, transparent e-skin,”[22] “macroscale nanowire e-skin,”[23a] “rechargeable, stretchable batteries,”[137] “interlocked e-skin.”[25] Copyright, respectively, 2010, 2009, 2012, 2005, 2010, 2013, 2012. Macmillan Publishers Ltd. “Flexible, active-matrix e-skin” image reproduced with permission.[26a] Copyright, 2004. National Academy of Sciences USA. “Epidermal electronics” image reproduced with permission.[390a] Copyright, American Association for the Advancement of Science. “Stretchable batteries” image reproduced with permission.[27] “Infrared e-skin” image reproduced with permission.[8b] Copyright 2001, IEEE. “Anthropomorphic cybernetic hand” image reproduced with permission.[426] Copyright 2006, IEEE. [downloaded from http://onlinelibrary.wiley.com.proxy.lib.sfu.ca/doi/10.1002/adma.201302240/full]

Here’s an excerpt from the review article outlining the 1970s – 1990s period featuring some of the science fiction which has influenced the science (Note: Links have been removed),

The prospect of creating artificial skin was in many ways inspired by science fiction, which propelled the possibility of e-skin into the imagination of both the general public as well as the scientific community. One of the first science fiction books to explore the use of mechanical replacement organs was Caidin’s Cyborg in 1971, on which the famed Six Million Dollar Man television series about a man with a bionic replacement arm and eye was later based (1974).[4] Shortly after, at the beginning of the 1980s, George Lucas created a vision of a future with e-skin in the famous Star Wars series. In particular, he depicted a scene showing a medical robot installing an electronic hand with full sensory perception on the main character, Luke Skywalker.[5] Shortly after, in 1984, the Terminator movie series depicted humanoid robots and even a self-healing robot.[6] These fictitious renditions of e-skin took place against a real-life backdrop of vibrant microelectronics research that began bridging science fiction with scientific reality.

Early technological advancements in the development of e-skin were concomitant with their science fiction inspirations. In 1974, Clippinger et al. demonstrated a prosthetic hand capable of discrete sensor feedback.[7] Nearly a decade later, Hewlett-Packard (HP) marketed a personal computer (HP-150) that was equipped with a touchscreen, allowing users to activate functions by simply touching the display. It was the first mass-marketed electronic device capitalizing on the intuitive nature of human touch. In 1985, General Electric (GE) built the first sensitive skin for a robotic arm using discrete infrared sensors placed on a flexible sheet at a resolution of ≈5 cm.[8] The fabricated sensitive skin was proximally aware of its surroundings, allowing the robot’s arm to avert potential obstacles and effectively maneuver within its physical environment. Despite the robotic arm’s lack of fingers and low resolution, it was capable of demonstrating that electronics integrated into a membrane could allow for natural human–machine interaction. For example, the robotic arm was able to ‘dance’ with a ballerina without any pre-programmed motions.[8] In addition to the ability of an artificial skin to interact with its surroundings, it is equally critical that the artificial skin mimics the mechanical properties of human skin to accommodate its various motions. Hence, to build life-like prosthetics or humanoid robots, soft, flexible, and stretchable electronics needed to be developed.

In the 1990s, scientists began using flexible electronic materials to create large-area, low-cost and printable sensor sheets. Jiang et al. proposed one of the first flexible sensor sheets for tactile shear force sensing by creating silicon (Si) micro-electro-mechanical (MEM) islands by etching thin Si wafers and integrating them on flexible polyimide foils.[9] Much work has since been done to enhance the reliability of large sensor sheets to mechanical bending.[10] Around the same time, flexible arrays fabricated from organic semiconductors began to emerge that rivaled the performance of amorphous Si.[11]

Just before the turn of the millennium, the first “Sensitive Skin Workshop” was held in Washington DC under the aegis of the National Science Foundation and the Defense Advanced Research Projects Agency, bringing together approximately sixty researchers from different sectors of academia, industry, and government. It was discovered that there was significant industrial interest in e-skins for various applications, ranging from robotics to health care. A summary of concepts outlined in the workshop was compiled by Lumelsky et al.[12] In the early 2000s, the pace of e-skin development significantly increased as a result of this workshop, and researchers began to explore different types of sensors that could be more easily integrated with microprocessors.

I have written about e-skin a number of times, most recently in a July 9, 2013 posting about work on flexible sensors and gold nanoparticles being conducted at Technion-Israel Institute of Technology. This review helps to contextualize projects such as the one at Technion and elsewhere.

*To avoid redundancy ‘synopsis’ was replaced by ‘overview’ on Oct. 19, 2015.

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