Achievements and Open Issues Toward Embedding Tactile Sensing and Interpretation into Electronic Skin Systems (original) (raw)
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A New Technology for Elastic Electronic Circuits and Assemblies for Biomedical Applications
2006
Electronic circuits for implantation in the human body or for use as intelligent band aid should ideally be stretchable and elastic for user comfort reasons. In this contribution the initial results of an MID (Moulded Interconnect Device) technology will be presented, showing the feasibility of simple functional stretchable electronic circuits. In the developed technology rigid or flexible standard components are interconnected by meander shaped electroplated metallic wires and embedded by casting or molding in a stretchable substrate material. The meander design was supported by mechanical simulations in order to minimize the stress in the metal during deformation. In this way stretchability of the circuits above 100% in one direction has been demonstrated. A simple stretchable thermometer circuit with 4 components embedded in Dow Corning Silastic ® PDMS silicone material has been built and proper operation has been demonstrated.
2009
A growing need for ambient electronics in our daily life leads to higher demands from the user in the view of comfort of the electronic devices. Those devices should become invisible to the user, especially when they are embedded in clothes (e.g. in smart textiles). They should be soft, conformable and to a certain degree stretchable. Electronics for implantation on the other hand should ideally be soft and conformable in relation to the body tissue, in order to minimize the rejecting nature of the body to unknown implanted rigid objects. Conformable and elastic circuitry is an emerging topic in the electronics and packaging domain. In this contribution a new low cost, elastic and stretchable electronic device technology will be presented, based on the use of a stretchable substrate. The process steps used are standard PCB fabrication processes, resulting in a fast technology transfer to the industry. This new developed technology is based on the combination of rigid standard SMD components which are connected with 2-D spring-shaped metallic interconnections. Embedding is done by moulding the electronic device in a stretchable polymer. The reliability of the overall system is improved by varying the thickness of the embedding polymer, wherever the presence and type of components requires to. Manufacturability issues are discussed together with the need for good reliability of the stretchable interconnections when stress is applied during stretching.
The FASEB Journal
Stretchable electronics facilitate increased design freedom of electronic products. Representative appli-cations can be found in health care, wellness and functional clothes, integrated electronics in stretchable parts and products. Typically, small rigid semiconductor islands are interconnected with thin metal conduc-tor lines on top of a highly deformable substrate, such as a rubber material. A key requirement on these products is the ability to withstand large deformations during usage without losing their integrity (i.e., large stretchability). During stretching, the adhesion of the interconnects to the rubber substrate is of major importance from a reliability point of view. Experimental observations show that delamination between the metal conductor lines and the stretchable substrate may eventually lead to short circuits while also the delaminated area could result in cohesive failure of the metal lines. To characterize the copper-rubber interface, peel tests are performed. E...
Stress Analysis of a Stretchable Electronic Circuit
Nowadays the research in electronic product has developed tremendously in order to offer human comfort in various applications such as medical, fabric and consumer applications. Starting from printed circuit board which is rigid, recent electronic products need to consider flexible and stretchable circuit board as a substrate in order to provide flexibility in product design. This paper presents a study on stress behavior of a stretchable electronic circuit using a plastic material as a substrate and a formulated polymer with Ag fillers as conductive ink. The data from tensile tests were implemented in the finite element simulation using ANSYS to simulate stress behavior of the circuit under mechanical loading. The material model was further used in predicting several design of electric circuit such as a zigzag and a horseshoe shape. The simulation and the experimental results show good agreement between them.
Design and Fabrication of Elastic Interconnections for Stretchable Electronic Circuits
IEEE Electron Device Letters, 2007
For biomedical and textile applications, the comfort of the user will be enhanced if the electronic circuits are not only flexible but also elastic. This letter reveals a simple mouldedinterconnect-device technology for the construction of elastic point-to-point interconnections, based on 2-D spring-shaped metallic tracks, which are embedded in a highly elastic silicone film. Metal interconnections of 3-cm long were constructed with an initial resistance of about 3 Ω, which did not significantly increase (< 5%) when stretched. A stretchability above 100% in one direction has been demonstrated.
Proceedings of The National Academy of Sciences
Electronic systems that offer elastic mechanical responses to highstrain deformations are of growing interest because of their ability to enable new biomedical devices and other applications whose requirements are impossible to satisfy with conventional wafer-based technologies or even with those that offer simple bendability. This article introduces materials and mechanical design strategies for classes of electronic circuits that offer extremely high stretchability, enabling them to accommodate even demanding configurations such as corkscrew twists with tight pitch (e.g., 90°in Ϸ1 cm) and linear stretching to ''rubber-band'' levels of strain (e.g., up to Ϸ140%). The use of single crystalline silicon nanomaterials for the semiconductor provides performance in stretchable complementary metal-oxide-semiconductor (CMOS) integrated circuits approaching that of conventional devices with comparable feature sizes formed on silicon wafers. Comprehensive theoretical studies of the mechanics reveal the way in which the structural designs enable these extreme mechanical properties without fracturing the intrinsically brittle active materials or even inducing significant changes in their electrical properties. The results, as demonstrated through electrical measurements of arrays of transistors, CMOS inverters, ring oscillators, and differential amplifiers, suggest a valuable route to high-performance stretchable electronics.
Design of metal interconnects for stretchable electronic circuits
Microelectronics Reliability, 2008
The trend of microelectronic products in the textile or medical field is toward higher functionality, miniaturization, application of new materials and a necessity for deformable electronic circuits for improving the comfort control. In this work, the design of flexible and stretchable interconnections is presented. These interconnections are done by embedding sinuous electroplated metallic wires in a stretchable substrate material. A silicone material was chosen as substrate because of its low stiffness and high elongation before break. Common metal conductors used in the electronic industry have very limited elastic ranges; therefore a metallization design is crucial to allow stretchability of the conductors going up to 100%. Different configurations were simulated and compared among them and based on these results, a horseshoe like shape was suggested. This design allows a large deformation with the minimum stress concentration. Moreover, the damage in the metal is significantly reduced by applying narrow metallization schemes. In this way, each conductor track has been split in four parallel lines of 15 lm and 15 lm space in order to improve the mechanical performance without limiting the electrical characteristics.
Stretchability—The Metric for Stretchable Electrical Interconnects
Micromachines
Stretchable circuit technology, as the name implies, allows an electronic circuit to adapt to its surroundings by elongating when an external force is applied. Based on this, early authors proposed a straightforward metric: stretchability—the percentage length increase the circuit can survive while remaining functional. However, when comparing technologies, this metric is often unreliable as it is heavily design dependent. This paper aims to demonstrate this shortcoming and proposes a series of alternate methods to evaluate the performance of a stretchable interconnect. These methods consider circuit volume, material usage, and the reliability of the technology. This analysis is then expanded to the direct current (DC) resistance measurement performed on these stretchable interconnects. A simple dead reckoning approach is demonstrated to estimate the magnitude of these measurement errors on the final measurement.
Stretchability of encapsulated electronics
Applied Physics Letters, 2011
Stretchable and flexible electronics offer the performance of conventional wafer-based systems but can be stretched like a rubber band, twisted like a rope, and bent over a pencil. Such a technology offers new application opportunities, in areas of surgical and diagnostic implements that naturally integrate with the human body to provide advanced capabilities, to curvilinear devices such as hemispherical "eyeball" cameras. In practice, stretchable and flexible electronic systems require encapsulation layers to provide mechanical and environmental protection. This paper establishes a simple, analytical model for the optimal design of encapsulation. V
Stretching-induced interconnect delamination in stretchable electronic circuits
Journal of Physics D: Applied Physics, 2011
Stretchable electronics offer increased design freedom of electronic products. Typically, small rigid semiconductor islands are interconnected with thin metal conductor lines on top of, or encapsulated in, a highly compliant substrate, such as a rubber material. A key requirement is large stretchability, i.e. the ability to withstand large deformations during usage without any loss of functionality. Stretching induced delamination is one of the major failure modes that determines the amount of stretchability that can be achieved for a given interconnect design. During peel testing, performed to characterize the interface behaviour, the rubber is severely lifted at the delamination front while at the same time fibrillation of the rubber at the peel front is observed by ESEM analyses. The interface properties are established by combining the results of numerical simulations and peeling experiments at two distinct scales: the global force-displacement curves and local rubber lift geometries. The thus quantified parameters are used to predict the delamination behaviour of zigzag and horseshoe patterned interconnect structures. The accuracy of these finite element simulations is assessed by a comparison of the calculated evolution of the shape of the interconnect structures and the fibrillation areas during stretching with experimental results obtained by detailed in-situ analyses.