Stretchable electronics

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Wrapped around this cardiac balloon catheter are temperature and EKG sensors and LEDs. The wires are stretchable coils. It is manufactured with a lift-off MEMS process. The etched silicon is then stretched and attached to a polymer backing. Silicon usage is minimized over the substrate and the ensemble is quite flexible, to survive inflation and deflation of the balloon. Stretchable Electronics.jpg
Wrapped around this cardiac balloon catheter are temperature and EKG sensors and LEDs. The wires are stretchable coils. It is manufactured with a lift-off MEMS process. The etched silicon is then stretched and attached to a polymer backing. Silicon usage is minimized over the substrate and the ensemble is quite flexible, to survive inflation and deflation of the balloon.

Stretchable electronics, also known as elastic electronics or elastic circuits, is a group of technologies for building electronic circuits by depositing or embedding electronic devices and circuits onto stretchable substrates such as silicones or polyurethanes, to make a completed circuit that can experience large strains without failure. In the simplest case, stretchable electronics can be made by using the same components used for rigid printed circuit boards, with the rigid substrate cut (typically in a serpentine pattern) to enable in-plane stretchability. [1] However, many researchers have also sought intrinsically stretchable conductors, such as liquid metals. [2]

Contents

One of the major challenges in this domain is designing the substrate and the interconnections to be stretchable, rather than flexible (see Flexible electronics) or rigid (Printed Circuit Boards). Typically, polymers are chosen as substrates or material to embed. [3] When bending the substrate, the outermost radius of the bend will stretch (see Strain in an Euler–Bernoulli beam, subjecting the interconnects to high mechanical strain. Stretchable electronics often attempts biomimicry of human skin and flesh, in being stretchable, whilst retaining full functionality. The design space for products is opened up with stretchable electronics, including sensitive electronic skin for robotic devices [4] and in vivo implantable sponge-like electronics.

Stretchable Skin electronics

Mechanical Properties of Skin

Skin is composed of collagen, keratin, and elastin fibers, which provide robust mechanical strength, low modulus, tear resistance, and softness. The skin can be considered as a bilayer of epidermis and dermis. The epidermal layer has a modulus of about 140-600 kPa and a thickness of 0.05-1.5 mm. Dermis has a modulus of 2-80 kPa and a thickness of 0.3–3 mm. [5] This bilayer skin exhibits an elastic linear response for strains less than 15% and a non linear response at larger strains. To achieve conformability, it is preferable for devices to match the mechanical properties of the epidermis layer when designing skin-based stretchy electronics.

Tuning Mechanical Properties

Conventional high performance electronic devices are made of inorganic materials such as silicon, which is rigid and brittle in nature and exhibits poor biocompatibility due to mechanical mismatch between the skin and the device, making skin integrated electronics applications difficult. To solve this challenge, researchers employed the method of constructing flexible electronics in the form of ultrathin layers. The resistance to bending of a material object (Flexural rigidity) is related to the third power of the thickness, according to the Euler-Bernoulli equation for a beam. [6] It implies that objects with less thickness can bend and stretch more easily. As a result, even though the material has a relatively high Young's modulus, devices manufactured on ultrathin substrates exhibit a decrease in bending stiffness and allow bending to a small radius of curvature without fracturing. Thin devices have been developed as a result of significant advancements in the field of nanotechnology, fabrication, and manufacturing. The aforementioned approach was used to create devices composed of 100-200 nm thick Si nano membranes deposited on thin flexible polymeric substrates. [6]

Furthermore, structural design considerations can be used to tune the mechanical stability of the devices. Engineering the original surface structure allows us to soften the stiff electronics. Buckling, island connection, and the Kirigami concept have all been employed successfully to make the entire system stretchy[ [7] , [8] ].

Mechanical buckling can be used to create wavy structures on elastomeric thin substrates. This feature improves the device's stretchability. The buckling approach was used to create Si nanoribbons from single crystal Si on an elastomeric substrate. The study demonstrated the device could bear a maximum strain of 10% when compressed and stretched. [9]

In the case of island interconnect, the rigid material connects with flexible bridges made from different geometries, such as zig-zag, serpentine-shaped structures, etc., to reduce the effective stiffness, tune the stretchability of the system, and elastically deform under applied strains in specific directions. It has been demonstrated that serpentine-shaped structures have no significant effect on the electrical characteristics of epidermal electronics. It has also been shown that the entanglement of the interconnects, which oppose the movement of the device above the substrate, causes the spiral interconnects to stretch and deform significantly more than the serpentine structures. [7] CMOS inverters constructed on a PDMS substrate employing 3D island interconnect technologies demonstrated 140% strain at stretching. [9]

Kirigami is built around the concept of folding and cutting in 2D membranes. This contributes to an increase in the tensile strength of the substrate, as well as its out-of-plane deformation and stretchability. These 2D structures can subsequently be turned to 3D structures with varied topography, shape, and size controllability via the Buckling process, resulting in interesting properties and applications. [7] [9]

Energy

Several stretchable energy storage devices and supercapacitors are made using carbon-based materials such as single-walled carbon nanotubes (SWCNTs). A study by Li et al. showed a stretchable supercapacitor (composed of buckled SWCNTs macrofilm and elastomeric separators on an elastic PDMS substrate), that performed dynamic charging and discharging. [10] The key drawback of this stretchable energy storage technology is the low specific capacitance and energy density, although this can potentially be improved by the incorporation of redox materials, for example the SWNT/MnO2 electrode. [11] Another approach to creating a stretchable energy storage device is the use of Origami folding principles. [12] The resulting origami battery achieved significant linear and areal deformability, large twistability and bendability.

Medicine

Stretchable electronics could be integrated into smart garments to interact seamlessly with the human body and detect diseases or collect patient data in a non-invasive manner. For example, researchers from Seoul National University and MC10 (a flexible-electronics company) have developed a patch that is able to detect glucose levels in sweat and can deliver the medicine needed on demand (insulin or metformin). The patch consists of graphene riddled with gold particles and contains sensors that are able to detect temperature, pH level, glucose, and humidity. [13] Stretchable electronics also permit developers to create soft robots, to implement minimally invasive surgeries in hospitals. Especially when it comes to surgeries of the brain and every millimeter is important, such robots may have a more precise scope of action than a human.

Tactile Sensing

Rigid electronics doesn't typically conform well to soft, biological organisms and tissue. Since stretchable electronics is not limited by this, some researchers try to implement it as sensors for touch, or tactile sensing. One way of achieving this is to make an array of conductive OFET (Organic Field Effect Transistors) forming a network that can detect local changes in capacitance, which gives the user information about where the contact occurred. [14] This could have potential use in robotics and virtual reality applications. [6] [7] [5] [8] [9]

See also

Related Research Articles

A nanowire is a nanostructure in the form of a wire with the diameter of the order of a nanometre. More generally, nanowires can be defined as structures that have a thickness or diameter constrained to tens of nanometers or less and an unconstrained length. At these scales, quantum mechanical effects are important—which coined the term "quantum wires".

<span class="mw-page-title-main">Young's modulus</span> Mechanical property that measures stiffness of a solid material

Young's modulus is a mechanical property of solid materials that measures the tensile or compressive stiffness when the force is applied lengthwise. It is the modulus of elasticity for tension or axial compression. Young's modulus is defined as the ratio of the stress applied to the object and the resulting axial strain in the linear elastic region of the material.

<span class="mw-page-title-main">Flexible electronics</span> Mounting of electronic devices on flexible plastic substrates

Flexible electronics, also known as flex circuits, is a technology for assembling electronic circuits by mounting electronic devices on flexible plastic substrates, such as polyimide, PEEK or transparent conductive polyester film. Additionally, flex circuits can be screen printed silver circuits on polyester. Flexible electronic assemblies may be manufactured using identical components used for rigid printed circuit boards, allowing the board to conform to a desired shape, or to flex during its use.

<span class="mw-page-title-main">Stiffness</span> Resistance to deformation in response to force

Stiffness is the extent to which an object resists deformation in response to an applied force.

A thin film is a layer of material ranging from fractions of a nanometer (monolayer) to several micrometers in thickness. The controlled synthesis of materials as thin films is a fundamental step in many applications. A familiar example is the household mirror, which typically has a thin metal coating on the back of a sheet of glass to form a reflective interface. The process of silvering was once commonly used to produce mirrors, while more recently the metal layer is deposited using techniques such as sputtering. Advances in thin film deposition techniques during the 20th century have enabled a wide range of technological breakthroughs in areas such as magnetic recording media, electronic semiconductor devices, integrated passive devices, light-emitting diodes, optical coatings, hard coatings on cutting tools, and for both energy generation and storage. It is also being applied to pharmaceuticals, via thin-film drug delivery. A stack of thin films is called a multilayer.

Organic semiconductors are solids whose building blocks are pi-bonded molecules or polymers made up by carbon and hydrogen atoms and – at times – heteroatoms such as nitrogen, sulfur and oxygen. They exist in the form of molecular crystals or amorphous thin films. In general, they are electrical insulators, but become semiconducting when charges are injected from appropriate electrodes or are introduced by doping or photoexcitation.

<span class="mw-page-title-main">Electroactive polymer</span>

An electroactive polymer (EAP) is a polymer that exhibits a change in size or shape when stimulated by an electric field. The most common applications of this type of material are in actuators and sensors. A typical characteristic property of an EAP is that they will undergo a large amount of deformation while sustaining large forces.

<span class="mw-page-title-main">PEDOT:PSS</span> Polymer

Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is a polymer mixture of two ionomers. One component in this mixture is made up of polystyrene sulfonate which is a sulfonated polystyrene. Part of the sulfonyl groups are deprotonated and carry a negative charge. The other component poly(3,4-ethylenedioxythiophene) (PEDOT) is a conjugated polymer and carries positive charges and is based on polythiophene. Together the charged macromolecules form a macromolecular salt.

Metal rubber is a broad, informal name for several conductive plastic polymers with metal ions produced by NanoSonic Inc. in cooperation with Virginia Tech. This self-assembling nanocomposite is flexible and durable to high and low pressures, temperatures, tensions, and most chemical reactions, and retains all of its physical and chemical properties upon being returned to a ground state. NanoSonic’s Metal rubber™ is an electrically conductive and flexible elastomer. It can be mechanically strained to greater than 1000% of its original dimensions while remaining electrically conductive. As Metal rubber can carry data and electrical power and is environmentally rugged, it can be used as a flexible and stretchable electrical conductor in the aerospace/defense, electronics, and bioengineering markets.

<span class="mw-page-title-main">Organic solar cell</span> Type of photovoltaic

An organic solar cell (OSC) or plastic solar cell is a type of photovoltaic that uses organic electronics, a branch of electronics that deals with conductive organic polymers or small organic molecules, for light absorption and charge transport to produce electricity from sunlight by the photovoltaic effect. Most organic photovoltaic cells are polymer solar cells.

<span class="mw-page-title-main">PHOSFOS</span> European optical sensing project

PHOSFOS is a research and technology development project co-funded by the European Commission.

Robotic sensing is a subarea of robotics science intended to provide sensing capabilities to robots. Robotic sensing provides robots with the ability to sense their environments and is typically used as feedback to enable robots to adjust their behavior based on sensed input. Robot sensing includes the ability to see, touch, hear and move and associated algorithms to process and make use of environmental feedback and sensory data. Robot sensing is important in applications such as vehicular automation, robotic prosthetics, and for industrial, medical, entertainment and educational robots.

Piezotronics effect is using the piezoelectric potential (piezopotential) created in materials with piezoelectricity as a “gate” voltage to tune/control the charge carrier transport properties for fabricating new devices.

Electronic skin refers to flexible, stretchable and self-healing electronics that are able to mimic functionalities of human or animal skin. The broad class of materials often contain sensing abilities that are intended to reproduce the capabilities of human skin to respond to environmental factors such as changes in heat and pressure.

<span class="mw-page-title-main">Borophene</span> Allotrope of boron

Borophene is a crystalline atomic monolayer of boron, i.e., it is a two-dimensional allotrope of boron and also known as boron sheet. First predicted by theory in the mid-1990s, different borophene structures were experimentally confirmed in 2015.

A two-dimensional semiconductor is a type of natural semiconductor with thicknesses on the atomic scale. Geim and Novoselov et al. initiated the field in 2004 when they reported a new semiconducting material graphene, a flat monolayer of carbon atoms arranged in a 2D honeycomb lattice. A 2D monolayer semiconductor is significant because it exhibits stronger piezoelectric coupling than traditionally employed bulk forms. This coupling could enable applications. One research focus is on designing nanoelectronic components by the use of graphene as electrical conductor, hexagonal boron nitride as electrical insulator, and a transition metal dichalcogenide as semiconductor.

<span class="mw-page-title-main">Soft robotics</span> Subfield of robotics

Soft robotics is a subfield of robotics that concerns the design, control, and fabrication of robots composed of compliant materials, instead of rigid links. In contrast to rigid-bodied robots built from metals, ceramics and hard plastics, the compliance of soft robots can improve their safety when working in close contact with humans.

Flexible silicon refers to a flexible piece of mono-crystalline silicon. Several processes have been demonstrated in the literature for obtaining flexible silicon from single crystal silicon wafers.

<span class="mw-page-title-main">Stéphanie P. Lacour</span> French neurotechnologist

Stéphanie P. Lacour is a French neurotechnologist and full professor holding the Foundation Bertarelli Chair in Neuroprosthetic Technology at the Swiss Federal Institute of Technology in Lausanne (EPFL). Lacour is a pioneer in the field of stretchable electronics and directs a laboratory at EPFL which specializes in the development of Soft BioElectronic Interfaces to enable seamless integration of neuroprosthetic devices into human tissues. Lacour is also a co-founding member and director of the Center for Neuroprosthetics at the EPFL Satellite Campus in Geneva, Switzerland.

<span class="mw-page-title-main">Chi Hwan Lee</span> American biomedical engineer, academic, and researcher

Chi Hwan Lee is an American biomedical engineer, academic, and researcher. He is the Leslie A. Geddes Professor of Biomedical Engineering and mechanical engineering, and by courtesy, of materials engineering, Electrical and Computer Engineering, and speech, language, and hearing sciences at Purdue University.

References

  1. ↑ Kim DH, Ahn JH, Choi WM, Kim HS, Kim TH, Song J, et al. (April 2008). "Stretchable and foldable silicon integrated circuits". Science. 320 (5875): 507–511. Bibcode:2008Sci...320..507K. doi: 10.1126/science.1154367 . PMID   18369106. S2CID   5086038.
  2. ↑ Yang JC, Mun J, Kwon SY, Park S, Bao Z, Park S (November 2019). "Electronic Skin: Recent Progress and Future Prospects for Skin-Attachable Devices for Health Monitoring, Robotics, and Prosthetics". Advanced Materials. 31 (48): e1904765. Bibcode:2019AdM....3104765Y. doi: 10.1002/adma.201904765 . PMID   31538370.
  3. ↑ Cataldi P (2020). "Graphene–Polyurethane Coatings for Deformable Conductors and Electromagnetic Interference Shielding". Advanced Electronic Materials. 6 (9): 2000429. arXiv: 2004.11613 . doi: 10.1002/aelm.202000429 .
  4. ↑ Cataldi P, Dussoni S, Ceseracciu L, Maggiali M, Natale L, Metta G, et al. (February 2018). "Carbon Nanofiber versus Graphene-Based Stretchable Capacitive Touch Sensors for Artificial Electronic Skin". Advanced Science. 5 (2): 1700587. doi: 10.1002/advs.201700587 . PMC   5827098 . PMID   29619306.
  5. 1 2 Kim DH, Lu N, Ma R, Kim YS, Kim RH, Wang S, Wu J, Won SM, Tao H, Islam A, Yu KJ, Kim TI, Chowdhury R, Ying M, Xu L, Li M, Chung HJ, Keum H, McCormick M, Liu P, Zhang YW, Omenetto FG, Huang Y, Coleman T, Rogers JA. Epidermal electronics. Science. 2011 Aug 12;333(6044):838-43. doi: 10.1126/science.1206157. Erratum in: Science. 2011 Sep 23;333(6050):1703. PMID 21836009.https://www.science.org/doi/10.1126/science.1206157
  6. 1 2 3 Lab-on-Skin: A Review of Flexible and Stretchable Electronics for Wearable Health Monitoring Yuhao Liu, Matt Pharr, and Giovanni Antonio Salvatore, ACS Nano 2017 11 (10), 9614-9635 DOI: 10.1021/acsnano.7b04898 https://pubs.acs.org/doi/10.1021/acsnano.7b04898
  7. 1 2 3 4 Wei Wu (2019) Stretchable electronics: functional materials, fabrication strategies and applications, Science and Technology of Advanced Materials, 20:1, 187-224, DOI: 10.1080/14686996.2018.1549460 https://www.tandfonline.com/doi/full/10.1080/14686996.2018.1549460
  8. 1 2 CS Materials Lett. 2022, 4, 4, 577–599 https://doi.org/10.1021/acsmaterialslett.1c00799 https://pubs.acs.org/doi/full/10.1021/acsmaterialslett.1c00799
  9. 1 2 3 4 Flexible and Stretchable Devices from Unconventional 3D Structural Design, Hangbo Zhao, Mengdi https://onlinelibrary.wiley.com/doi/abs/10.1002/9783527820153.ch10 Han
  10. ↑ Li X, Gu T, Wei B (December 2012). "Dynamic and galvanic stability of stretchable supercapacitors". Nano Letters. 12 (12): 6366–6371. Bibcode:2012NanoL..12.6366L. doi:10.1021/nl303631e. PMID   23167804.
  11. ↑ Li X (2012). "Facile synthesis and super capacitive behavior of SWNT/MnO2 hybrid films". Nano Energy. 1 (3): 479–487. doi:10.1016/j.nanoen.2012.02.011.
  12. ↑ Song Z, Ma T, Tang R, Cheng Q, Wang X, Krishnaraju D, et al. (2014). "Origami lithium-ion batteries". Nature Communications. 5: 3140. Bibcode:2014NatCo...5.3140S. doi: 10.1038/ncomms4140 . PMID   24469233.
  13. ↑ Talbot, David (March 22, 2016). "Controlling Diabetes with a Skin Patch". MIT Technology Review. Retrieved 2017-11-08.
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