Darshana Weerawarne | University of Colombo, Sri Lanka (original) (raw)

Papers by Darshana Weerawarne

Volume 1: Additive Manufacturing; Bio and Sustainable Manufacturing

The goal of this work is in situ monitoring of the functional properties of aerosol jet-printed e... more The goal of this work is in situ monitoring of the functional properties of aerosol jet-printed electronic devices. In pursuit of this goal, the objective is to develop a multiple-input, single-output (MISO) machine learning model to estimate the device functional properties in a near real-time fashion as a function of process parameters as well as 2D/3D features of line morphology. The aim is to use the MISO model for in situ estimation and thus, monitoring of line/device resistance in aerosol jet printing (AJP) process. To realize this objective, silver nanoparticle structures are printed by varying three process parameters: (i) sheath gas flow rate (ShGFR), (ii) exhaust gas flow rate (EGFR), and (iii) print speed (PS). Subsequently, line morphology is captured in situ using a high-resolution charge-coupled device (CCD) camera, mounted coaxial to the nozzle. Besides, utilizing 2D/3D quantifiers (introduced in the authors’ previous publications), the line morphology is further quan...

Volume 1: Additive Manufacturing; Manufacturing Equipment and Systems; Bio and Sustainable Manufacturing

The goal of this work is to forward a comprehensive framework, relating to the most recent resear... more The goal of this work is to forward a comprehensive framework, relating to the most recent research works carried out in the area of flexible and hybrid electronics (FHE) fabrication with the aid of aerosol jet printing (AJP) additive manufacturing process. In pursuit of this goal, the objective is to review and classify a wide range of articles, published recently, concerning various aspects of AJP-based device fabrication, such as material synthesis, process monitoring, and control. AJP has recently emerged as the technique of choice for integration as well as fabrication of a broad spectrum of electronic components and devices, e.g., interconnects, sensors, transistors, optical waveguides, quantum dot arrays, photodetectors, and circuits. This is preeminently because of advantages engendered by AJP process. AJP not only allows for high-resolution deposition of microstructures, but also accommodates a wide renege of ink viscosity. However, AJP is intrinsically complex and prone to...

2018 IEEE 68th Electronic Components and Technology Conference (ECTC)

The development of reliable Flexible Hybrid Electronics (FHE) that are light, wearable and confor... more The development of reliable Flexible Hybrid Electronics (FHE) that are light, wearable and conforming to the human body while still preserving full operational integrity requires among other an understanding of the fatigue behavior of interconnects such as traces on flexible substrates (Polyimide, Polyethylene Terephthalate, etc.). There are different loading modes of potential concern, such as tension, bending and peeling. The present study addresses effects of tension on aerosol printed AgNP (silver nano-particles) traces. These traces are nano-porous and as such inherently brittle, but the presence of a flexible substrate has major effects on their behavior. Electroplated Cu traces are included for reference. Major increases in electrical resistance were observed for even minor deformation but inspection by SEM did not reveal any damage, and the presence of the substrate prevents the detection of changes in trace properties through direct measurement of deformation vs. the applied loads. Studies of the evolution of damage were therefore limited to characterization of the resistance vs. variations in strain. Interpretations of results were further complicated by the time-dependent viscoelastic deformation of the substrate. Nevertheless, systematic trends are appearing.

2019 IEEE 69th Electronic Components and Technology Conference (ECTC)

Growing demand for wearable and disposable electronics leads to a need for cost effective and com... more Growing demand for wearable and disposable electronics leads to a need for cost effective and compact sensor designs and fabrication. Most of the devices are multi-layered and require a carrier substrate to hold the sensors. Paper substrates have gained attention since they have the potential to act as both the sensor and the substrate itself. Paper-based printed sensors have been demonstrated and shown functional. However, device fabrication on paper is challenging because of the surface roughness, bleeding, and incompatibility with high temperature sintering processes needed to achieve high conductivity. The conductivity of the interconnects is therefore usually relatively low and imposes performance limitations. Here we report, for the first time, highly conductive silver nano-particle interconnects printed on a paper substrate and sintered with a continuous wave laser. The printing process was identified and the laser sintering parameters were optimized to achieve a conductivity of approximately 67% of the bulk material. As an example of application, interdigitated electrodes were printed and laser sintered. The leakage current was monitored while aging at 50°C /85% RH conditions and exposing to water and artificial sweat.

2020 IEEE 70th Electronic Components and Technology Conference (ECTC)

Aerosol jet printing has been emerging as an attractive circuit fabrication technique in flexible... more Aerosol jet printing has been emerging as an attractive circuit fabrication technique in flexible and wearable radio frequency (RF) electronics due to the capabilities it provides beyond conventional fabrication techniques. In this paper, the effect of AJP process parameters on the printability of transmission lines on Kapton and LCP was investigated in details. Better wettability for the used ink on LCP has contributed to better line definition. The effect of sintering temperature and laser sintering power on the conductivity of transmission lines on both substrates was also studied. Employing Laser sintering has increased the conductivity significantly: 30% versus 10% of the silver bulk conductivity. However, the adhesion of the laser sintered lines on Kapton was very weak where all the lines fell off the substrate. On the other hand, the adhesion of the laser sintered lines on LCP was very good and passed multiple times of the tape test.Mircostrip lines were designed and fabricated on both substrates. The insertion loss for lines on LCP is around 0.32 dB/mm while on the Kapton samples is around 0.38 dB/mm at 40 GHz.

Journal of Micro and Nano-Manufacturing, 2021

Aerosol jet printing (AJP) is a direct-write additive manufacturing technique, which has emerged ... more Aerosol jet printing (AJP) is a direct-write additive manufacturing technique, which has emerged as a high-resolution method for the fabrication of a broad spectrum of electronic devices. Despite the advantages and critical applications of AJP in the printed-electronics industry, AJP process is intrinsically unstable, complex, and prone to unexpected gradual drifts, which adversely affect the morphology and consequently the functional performance of a printed electronic device. Therefore, in situ process monitoring and control in AJP is an inevitable need. In this respect, in addition to experimental characterization of the AJP process, physical models would be required to explain the underlying aerodynamic phenomena in AJP. The goal of this research work is to establish a physics-based computational platform for prediction of aerosol flow regimes and ultimately, physics-driven control of the AJP process. In pursuit of this goal, the objective is to forward a three-dimensional (3D) ...

2020 IEEE 70th Electronic Components and Technology Conference (ECTC), 2020

The focus of this paper is to study the reliability of a wearable electrocardiogram sensor leadse... more The focus of this paper is to study the reliability of a wearable electrocardiogram sensor leadset under tight bending conditions using numerical simulations and experiments. In these simulations, appropriate material models are selected and fitted for each material layer, including a hyperelastic model for TPU, an elastic-plastic model for PET, and linear elastic models for the silver ink, carbon ink, and dielectric layers. The results from the numerical simulations are compared and validated using an analytical model as well as experimental data. Recommendations are made for acceptable operating conditions of the leadset.

2019 IEEE 69th Electronic Components and Technology Conference (ECTC), 2019

Inkjet printing of conducting traces offers well established advantages and disadvantages as an a... more Inkjet printing of conducting traces offers well established advantages and disadvantages as an alternative to electroplating of interconnects in flexible electronics. Assessment and optimization of their reliability is, however, often more complicated than commonly recognized. This is the case for an approach based on the deposition of silver nano-particle inks onto mesoporous PET substrates. In this case heating leads the trace resistance to drop not only because of the shrinkage and cure of the organic matrix holding the particles together, but also because some of that matrix 'disappears' into the substrate pores. The substrates can however only sustain relatively brief excursions above their glass transition, nominally 75°C, so it is not always practical to sinter the traces completely by conventional means. That has consequences such as ongoing reductions in resistance over time or under cyclic loading. Laser sintering does however offer the opportunity for much better fusing of the particles without excessive heating of the PET. The present work addresses effects of sintering parameters such as time/temperature and power/speed in oven and laser sintering, respectively, on the initial resistance and its evolution in subsequent low cycle fatigue testing. Interconnects of an average width of 80 µm and thickness of 550 nm were printed and post processed by one of two different sintering techniques: a) Convection oven sintering, and (b) Laser sintering. The resulting resistances were quantified, and samples finally subjected to tensile cycling with amplitudes of 1-2% and in-situ monitoring of the resulting resistance changes using a four-point probe. As expected, the resistance increased in each cycle as the substrate was stretched and it decreased again during unloading. However unlike for other kinds of traces, even though a remaining viscoelastic strain on the substrate prevented the complete elimination of the strain on the trace, the resistance of oven sintered traces usually ended up slightly lower after each cycle than before it. This effect was stronger for higher strain amplitudes, but it could be reduced or eliminated by longer preceding sintering of the traces. While a reduction in resistance may seem preferable to an increase, an even better solution would be a lower initial resistance that remained insensitive to subsequent fatigue cycling. This could be achieved by laser sintering, but careful optimization was required as too low a power did not prevent further resistance drops in cycling while too high ones led to significant degradations in fatigue resistance.

Frontiers in Optics 2016, 2016

Advances in Intelligent Systems and Computing, 2019

Aerosol jet printing (AJP) is a direct-write, additive manufacturing technique, which has emerged... more Aerosol jet printing (AJP) is a direct-write, additive manufacturing technique, which has emerged as the process of choice for the fabrication of a broad spectrum of electronics – such as, interconnects, sensors, transistors, electrodes, and antennae – toward consistent and uniform manufacture of flexible and hybrid electronic devices. The AJP has paved the way for rapid high-resolution device fabrication; it accommodates a wide range of ink viscosity and allows for material deposition with high placement accuracy, edge definition, and adhesion on non-planer surfaces. Despite the unique advantages and engendered strategic applications, the AJP process is intrinsically unstable and complex, prone to non-linear gradual drifts, which stem from process, machine, and metrical interactions. Consequently, real-time process monitoring and control, corroborated with physical models, is a burgeoning need.

Volume 2A: Advanced Manufacturing, 2019

Aerosol jet printing (AJP) is a direct-write additive manufacturing method, which has been utiliz... more Aerosol jet printing (AJP) is a direct-write additive manufacturing method, which has been utilized particularly for the fabrication of flexible and hybrid electronics (FHE). In spite of the advantages of AJP — e.g., high-resolution material deposition on nonplanar surfaces and accommodation of a wide renege of ink viscosity — AJP inherently is a complex process, prone to nonlinear process changes. Consequently, real-time process monitoring and control (with an understanding of the physics behind aerosol generation and transport) are inevitable. The overarching goal of this work is to establish a physics-based framework for process monitoring and closed-loop control (for correction) in AJP. In pursuit of this goal, the objective is to forward a CFD model to explain the underlying physical phenomena behind aerosol nebulization in AJP. To realize this objective, a 3D compressible, turbulent multi-phase flow CFD model is forwarded. The geometry of the pneumatic atomizer is modeled base...

Advanced Engineering Materials, 2020

Printed conductors are the main building blocks of printed flexible electronic circuits. With the... more Printed conductors are the main building blocks of printed flexible electronic circuits. With the advancement and growing demand for printed and flexible electronics, researchers are focused on assessing the mechanical reliability of interconnects. Even more important is, often, the electrical performance or the current‐carrying capacity of the interconnects. A mechanically reliable interconnect has limited use if it cannot meet the current‐carrying requirements. However, current‐carrying capacity curves and circuit design guidelines such as those available for conventional copper conductors have not yet been established for printed interconnects, i.e., there is a technological gap in this domain. The present work focuses on assessing the maximum allowed current through an aerosol jet printed silver nanoparticle‐based conductor on a 75 μm thick polyimide substrate. The temperature coefficient of resistance for the printed ink is experimentally determined. The effect of printed ink m...

Journal of Manufacturing Science and Engineering, 2020

Aerosol jet printing (AJP) is a direct-write additive manufacturing (AM) method, emerging as the ... more Aerosol jet printing (AJP) is a direct-write additive manufacturing (AM) method, emerging as the process of choice for the fabrication of a broad spectrum of electronics, such as sensors, transistors, and optoelectronic devices. However, AJP is a highly complex process, prone to intrinsic gradual drifts. Consequently, real-time process monitoring and control in AJP is a bourgeoning need. The goal of this work is to establish an integrated, smart platform for in situ and real-time monitoring of the functional properties of AJ-printed electronics. In pursuit of this goal, the objective is to forward a multiple-input, single-output (MISO) intelligent learning model—based on sparse representation classification (SRC)—to estimate the functional properties (e.g., resistance) in situ as well as in real-time. The aim is to classify the resistance of printed electronic traces (lines) as a function of AJP process parameters and the trace morphology characteristics (e.g., line width, thickness...

International Symposium on Microelectronics, 2019

Laser sintering of interconnects printed on flexible substrate with silver nanoparticle ink is st... more Laser sintering of interconnects printed on flexible substrate with silver nanoparticle ink is studied as an alternative to convection oven sintering. Interconnects of 80 μm and 250 μm line width are printed using an aerosol jet printer and sintered using an 830 nm continuous wave laser. A conductivity that is 4.5× higher than that of an oven sintered interconnect is achieved at optimal laser power and sintering speed set using a full factorial statistical design.

ACS Applied Electronic Materials, 2019

Transparent conductive meshes were fabricated by ink-jet printing on flexible substrates using a ... more Transparent conductive meshes were fabricated by ink-jet printing on flexible substrates using a percolation pattern created by random removal of conducting bonds from a regular square two-dimensional lattice. With this approach, a higher gain in optical transmittance than electrical conductivity loss is achieved above the percolation threshold. As a result of this, a figure of merit for the percolation pattern is improved with respect to a regular square mesh. The transmittance (T), sheet resistance (R), and figure of merit (F) on percentage of removed bonds for square lattices printed were measured. The gain of the figure of merit was observed in the range of removed bonds from 5% to 15% .

Journal of Manufacturing Science and Engineering, 2019

Aerosol jet printing (AJP) is a complex process for additive electronics that is often unstable. ... more Aerosol jet printing (AJP) is a complex process for additive electronics that is often unstable. To overcome this instability, observation while printing and control of the printing process using image-based monitoring is demonstrated. This monitoring is validated against images taken after the print and shown highly correlated and useful for the determination of printed linewidth. These images and the observed linewidth are used as input for closed-loop control of the printing process, with print speed changed in response to changes in the observed linewidth. Regression is used to relate these quantities and forms the basis of proportional and proportional integral control. Electrical test structures were printed with controlled and uncontrolled printing, and it was found that the control influenced their linewidth and electrical properties, giving improved uniformity in both size and electrical performance.

International Symposium on Microelectronics, 2018

In the presented work, electrical traces were directly printed on 2 mil thick polyimide flexible ... more In the presented work, electrical traces were directly printed on 2 mil thick polyimide flexible substrate by a dispenser system using two different silver pastes, SW 1400 paste from Asahi Co. and 125-13 HV paste from Creative Materials Co. The dispenser printing parameters were optimized to achieve the finest possible line width and the printing quality of both materials was investigated. The electrical behavior of the dispensed traces was investigated by monitoring the change in the electrical resistance of the test samples during fatigue cycling at different strains, strain percentage of 1.50%, 2.0%, and 2.5% for different number of cycles up to 1000 cycles. The life time of the dispensed traces versus the applied strain was modeled using Coffin-Manson relation setting 20% change in the initial resistance as the failure criteria. Based on the change in the trace resistance during testing, we concluded that the dispensed SW 1400 silver paste traces were less robust than the dispen...

Physical Review A, 2017

We experimentally and theoretically reinvestigate the significant third-harmonic enhancement via ... more We experimentally and theoretically reinvestigate the significant third-harmonic enhancement via plasma generation using time-resolved methods with two-color, copropagating femtosecond laser pulses. By measuring plasma densities with digital in-line holography and using carrier-resolved unidirectional pulse propagation equations to model the experiment, we show that a fifth-order nonlinearity contributes to third-harmonic generation mainly via phase matching. In particular, our study confirms that self-and cross-phase modulation including higher-order nonlinear processes can play a crucial role in harmonic-generation phase matching, which has recently been proposed by Weerawarne et al. [Phys. Rev. Lett. 114, 093901 (2015)] and should be potentially applicable to high-order harmonic generation.