The role of strain localization on the electrical behavior of flexible and stretchable screen printed silver inks on polymer substrates

Cahn, Gabe; Barrios, Alejandro; Graham, Samuel; Meth, Jeffrey S.; Αντωνίου, Αντωνία; Pierron, Olivier N.

doi:10.1016/j.mtla.2020.100642

Cited by 15 publications

(28 citation statements)

References 41 publications

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“…In the experiments, monotonic and cyclic straining methods as well as cyclic bending tests are used to induce microscale cracks in the thin films, and the associated changes in electrical resistance are analysed by four point probe (4PP) measurements (Gruber et al 2009;Lu et al 2010;Lambricht et al 2013;Sim et al 2013;Glushko and Cordill 2016;Kreiml et al 2019). In addition, characteristic properties like the crack onset strain (COS) are determined, and the evolution of the mechanical damage in terms of TTCs and localised necking is studied with optical microscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM) or confocal laser scanning microscopy (CLSM) methods (Renault et al 2003;Leterrier et al 2004;Cordill et al 2010;Jin et al 2011;Cordill et al 2015Cordill et al , 2016Etiemble et al 2019;Cahn et al 2020). For brittle film systems, SEM and optical observation methods are adequate because only TTCs form, and when combined with in-situ 4PP measurements, these are quite precise at determining the COS and crack spacing or density evolution as a function of applied strain or cycle.…”

Section: Introductionmentioning

confidence: 99%

Electrical and mechanical behaviour of metal thin films with deformation-induced cracks predicted by computational homogenisation

et al. 2021

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Motivated by advances in flexible electronic technologies and by the endeavour to develop non-destructive testing methods, this article analyses the capability of computational multiscale formulations to predict the influence of microscale cracks on effective macroscopic electrical and mechanical material properties. To this end, thin metal films under mechanical load are experimentally analysed by using in-situ confocal laser scanning microscopy (CLSM) and in-situ four point probe resistance measurements. Image processing techniques are then used to generate representative volume elements from the laser intensity images. These discrete representations of the crack pattern at the microscale serve as the basis for the calculation of effective macroscopic electrical conductivity and mechanical stiffness tensors by means of computational homogenisation approaches. A comparison of simulation results with experimental electrical resistance measurements and a detailed study of fundamental numerical properties demonstrates the applicability of the proposed approach. In particular, the (numerical) errors that are induced by the representative volume element size and by the finite element discretisation are studied, and the influence of the filter that is used in the generation process of the representative volume element is analysed.

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Section: Introductionmentioning

confidence: 99%

Electrical and mechanical behaviour of metal thin films with deformation-induced cracks predicted by computational homogenisation

et al. 2021

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“…Compared with conventional silicon-based electronic devices, flexible electronics devices can be made wearable and have the advantages of flexibility, conformality, and ultralight weight [12,13]. However, an important challenge in the development of these devices is maintaining electrical performance when the device has been bent, twisted, or stretched to a high strain, typically up to 30% for a wearable device [14].…”

Section: Introductionmentioning

confidence: 99%

“…A common conductive ink design consists of filler conductive particles or flakes, typically of silver, being embedded in a polymer binder. The electrical performance of such conductive inks has been characterized in a number of studies [14,19,24,25]. However, unlike polymer supported thin metal films, whose mechanical behavior is fairly well understood from numerous experimental [26][27][28][29][30][31][32][33][34][35][36][37] and modeling [38][39][40] studies, there is currently limited knowledge applied strain for 5025 ink deposited on TE11C substrate; (e) and (f) SEM images highlighting localized necking areas formed after 35% applied strain for 5025 ink deposited on PET substrate.…”

Section: Introductionmentioning

confidence: 99%

“…A FIB cut near a necked region showed a reduction in film height and silver flake fraction. Reprinted from [14], Copyright (2020), with permission from Elsevier. specific to the mechanical behavior of these composite conductive inks [14,24].…”

Section: Introductionmentioning

confidence: 99%

“…Reprinted from [14], Copyright (2020), with permission from Elsevier. specific to the mechanical behavior of these composite conductive inks [14,24]. An improved understanding of the inks' mechanical behavior will further the understanding of their electrical behavior under deformation and help inform their design.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Origins of strain localization in a silver-based flexible ink under tensile load

Li¹,

Pierron²,

Αντωνίου³

2021

Flex. Print. Electron.

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Flexible electronics often employs composite inks consisting of conductive flakes embedded in a polymer matrix to transmit electrical signal. Recently, localized necking was identified as a cause of a substantial increase in normalized resistance with applied strain thereby adversely impacting electrical performance. The current study explores two possible contributing factors for the formation of such localization – ink surface roughness and local variations in silver flake volume fraction. Uniaxial tension experiments of a DuPont 5025 type ink are used to inform a constitutive model implemented using Finite Element Method (FEM) on different substrates. Surface roughness was modeled by sinusoidal variation in ink height, whose amplitude and wavelength are informed by experimental laser profilometry scan data. Local flake fraction variation obtained from experimental measurements before applying any strain, were modeled as local variations in the elastic modulus according to an inverse rule of mixtures between the silver flake and acrylic binder material properties. The study identified that the ink height roughness is the most impactful contributor to the subsequent strain localization. The substrate elastic properties impact the number and magnitude of localization bands, with the stiffer substrate delocalizing strain and averting catastrophic crack formation seen with a more compliant substrate. The model incorporating surface roughness closely matches experimental measurements of local strain across different substrates. The study can inform designers of the adverse impact of ink surface roughness on localization and subsequent detrimental increase of the resistance.

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Large Area Ballistocardiography Enabled by Printed Piezoelectric Sensor Arrays on Elastomeric Substrates

Zalar,

Burghoorn,

Fijn

et al. 2024

Adv Materials Technologies

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Ballistocardiography (BCG) studies ballistic forces on the body generated during a heartbeat. As it is an unobtrusive detection method, that requires sensors measuring small dynamic forces. Piezoelectric sensors are ideal, but improvements in sensitivity are needed. Here, a universal method is demonstrated to obtain enhanced effective transverse charge constants by utilizing thin and long sensors fabricated upon compliant substrates. This approach is validated using the uniquely printable and patternable piezoelectric polymer, poly(vinylidene fluoride‐co‐trifluoroethylene) (P(VDF‐TrFE). Discrete sensors detect displacements of less than 1 µm, dynamic forces of ∼mN, and accelerations of ≈1 mm−1 s2. Since the sensor is screen‐printable, it is upscaled to a human‐sized array (60 × 90 cm, 255 sensors). High quality spatially resolved BCG measurements of a person is demonstrated in seated and supine positions. The obtained heart rate is verified using photoplethysmography. This development opens the door to ever‐more sensitive piezoelectric sensors, crucial for applications including and beyond healthcare.

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The role of strain localization on the electrical behavior of flexible and stretchable screen printed silver inks on polymer substrates

Cited by 15 publications

References 41 publications

Electrical and mechanical behaviour of metal thin films with deformation-induced cracks predicted by computational homogenisation

Electrical and mechanical behaviour of metal thin films with deformation-induced cracks predicted by computational homogenisation

Origins of strain localization in a silver-based flexible ink under tensile load

Large Area Ballistocardiography Enabled by Printed Piezoelectric Sensor Arrays on Elastomeric Substrates

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