Margaret K. Joyce

Gravure Printing of ITO Transparent Electrodes for Applications in Flexible Electronics

The possibility to directly pattern indium-tin-oxide (ITO) layers at ambient conditions by printing has many benefits. Printing, being an additive process, would greatly reduce the amount of energy, labor and material used by the current manufacturing processes to deposit and pattern ITO. In this work, gravure printability of ITO nanoparticles on polyethylene terephthalate (PET) was studied. A wide range of sheet resistivites and film thicknesses was obtained by varying the specifications of the gravure cells. From the regression analysis of the results, a good estimation of sheet resistivity of the printed films at different gravure cell volumes and aspect ratios (AR) was achieved. The films also showed transparency above 95% in the visible light region. In addition, printed ITO films were assessed for mechanical flexibility and the results compared to commercially available sputtered ITO films on PET. The electrical performance of printed ITO layers was not deteriorated with bending in contrast to the sputtered films. Therefore, printed ITO films can be of great benefit for applications in flexible electronics such as organic photovoltaics (OPV), liquid crystal displays (LCD), organic light-emitting diodes (OLED), touch screens, biosensors and utilization in the field of energy efficiency, especially in buildings.

Screen Printing of Multilayered Hybrid Printed Circuit Boards on Different Substrates

This paper reports on the successful fabrication of a multilayered hybrid printed circuit board (PCB) for applications in the consumer electronics products, medical technologies, and military equipment. The PCB was fabricated by screen-printing silver (Ag) flake ink, as metallization layer, and UV acrylic-based ink, as dielectric layer, on different substrates such as paper, polyethylene terephthalate, and glass. Traditional electronic components were attached onto the printed pads to create the multilayered hybrid PCB. The feasibility of the hybrid PCB was demonstrated by integrating an embedded microcontroller to drive an liquid-crystal display (160 × 100 pixels). In addition, the amount of the ink spreading after printing, the effect of bending on the printed lines, and the effect of the roughness of the substrates on the resistance of the printed lines was investigated. It was observed that the resistance of the lines increased by ≈1.8%, after 10000 cycles of bending, and the lowest resistance of 1.06 Ω was measured for the 600 μm printed lines on paper, which had a roughness of 0.175 μm. The advantage of fabricating PCBs on flexible substrates is the ability to fold and place the boards on nearly any platform or to conform to any irregular surface, whereas the additive properties of printing processes allow for a faster fabrication process, while simultaneously producing less material waste in comparison with the traditional subtractive processes. The results obtained show the promising potential of employing screen printing process for the fabrication of flexible and light-weight hybrid PCBs.

Printed electrochemical based biosensors on flexible substrates

A flexible substrate electrochemical biosensor was successfully printed on a polyethylene terephthalate (PET) film with silver (Ag) electrodes using silver nanoparticle based ink. The electrochemical impedance spectroscopy (EIS) response of the printed sensor for detecting low concentrations of bio/chemical species revealed a very high sensitivity at pico molar (pM) concentration levels of D-Proline, Sarcosine, Cadmium sulphide (CdS) and Potassium chloride (KCl). The impedance response of the biosensor towards these species was analyzed and is reported in this paper.

A novel fully printed and flexible capacitive pressure sensor

A novel fully printed flexible capacitive pressure sensor was fabricated using conventional screen and gravure printing techniques. The sensor was successfully printed on a flexible polyethylene terephthalate (PET) substrate with silver (Ag) nanoparticle (NP) ink as the metallization layer and polydimethylsiloxane (PDMS) as the dielectric layer. The capacitive response of the sensor demonstrated a percentage change of 5 % and 40 % for minimum and maximum detectable compressive forces of 800 kPa and 18 MPa, respectively when compared to the base capacitance of 26 pF. At the minimum detectable pressure, the stability measurements resulted in a maximum variation of ± 0.15 % from the average capacitance value of 28 pf. The response of the printed device demonstrated the feasibility of employing traditional printing techniques for the fabrication of flexible pressure sensing devices.

Use of a chemically modified clay as a replacement for silica in matte coated ink-jet papers

New techniques for modifying the surface of ink-jet papers are continuously being developed. The affordability of ink-jet printers has placed them in the forefront of home-use for digital printing technology. Thus, there is a demand on the paper substrate, whether coated or not, to respond to a variety of ink-jet operating conditions, while continuing to yield a product with high print quality.Coating formulations for ink-jet papers currently utilize precipitated or gelled silica with polyvinyl alcohol (PVOH) as the binder. This silica and PVOH formulation generates good optical, surface, and print qualities, yet leaves a lot to be desired from a runnability and coating preparation standpoint. The modified clay pigment offers potential as a substitute particle for the silica pigment in matte grades of ink-jet paper. The modified clay pigment offered significant improvements in coating preparation and runnability. The modified clay, however, could not match silica in producing the surface and bulk coating properties required for generating high print quality without the addition of a cationic additive.

A novel flexographic printed strain gauge on paper platform

A novel flexible printed strain gauge was fabricated successfully on a flexible paper substrate using flexography printing process. Silver (Ag) ink was printed on the paper substrate as metallization layer. The performance of the printed device was investigated by subjecting the strain gauge to a 3-point bend test, with a displacement of 1 mm and 2 mm at 3 Hz operating frequency for 500 cycles. The electro-mechanical response of the strain gauge for the 1 mm displacement demonstrated an overall resistance change of 6.4 % and 6.5 % for the base resistance and bend resistance, respectively after 500 cycles of bending. Similarly an overall resistance change of 87.97 % and 28.8 % was observed for the base resistance and bend resistance, respectively after 500 cycles of bending for 2 mm displacement. The response of the fabricated strain gauge, as a function of electrical resistance, is analyzed and presented in this paper.

Fully printed and flexible piezoelectric based touch sensitive skin

A fully printed piezoelectric based touch sensitive skin has been successfully fabricated using screen printing technique. The device, consisting of a 4×4 array of printed sensors and interconnect lines, was fabricated on a flexible polyethylene terephthalate (PET) substrate, using silver (Ag) ink. Screen printed polyvinylidene fluoride (PVDF), as a piezoelectric layer, was sandwiched between the printed Ag top and bottom electrode metallization layers. The effective polarization of the printed piezoelectric PVDF layer was verified using capacitance-voltage analysis. Piezoelectric-voltage analysis demonstrated the capability of the device to generate voltage peaks as high as 10 V as well as the ability to turn on location based light-emitting diodes (LEDs). The response of the touch sensitive skin is analyzed and presented in this paper.

Screen printed flexible capacitive pressure sensor

A novel flexible fully printed capacitive based pressure sensor was designed and fabricated using screen printing technique. Silver (Ag) ink and polydimethylsiloxane (PDMS) were printed on a flexible polyethylene terephthalate (PET) substrate as metallization and dielectric layers, respectively. The capacitive response of the sensor demonstrated a percentage change of 1 % and 3.6 % for compressive forces of 0.2 MPa and 2.4 MPa, respectively when compared to the base capacitance. The response of the pressure sensor is analyzed and presented in this paper.

Mechanical consequences of coating penetration

Light weight coated papers were evaluated by dynamic mechanical analysis. In addition, water treated papers were studied to separate the contribution from the wetting-drying cycle on the response and thickness of the sheet. Measurements in three-point bending were performed in both the glassy and rubbery regions of the binder. The influence of coating penetration on bending stiffness was determined. At low coat weights, the bending stiffness of the base paper increased linearly. This was attributed to the sandwich structure achieved. As the coat weights continued to increase, the bending stiffness reached a constant value, then began to decrease. The decrease in bending stiffness was determined to be caused by the influences of coating water in the base paper. At higher coat weights, sufficient coating water was present to interfere with fiber-to-fiber bonds and release dried in strains. Variations in coating penetration and coating layer thickness were studied by electron microscopy. The results show the possibility of using dynamic mechanical testing to monitor the depth of coating penetration and thickness of the coating layer.

Detection of heavy metals using fully printed three electrode electrochemical sensor

A flexible three electrode electrochemical sensor was successfully screen printed on a polyethylene terephthalate (PET) film. Silver (Ag) ink, silver/silver chloride (Ag/AgCl) ink and carbon ink was used for the counter, reference and working electrodes, respectively. The feasibility of the fully printed sensor for detecting very low concentrations of toxic heavy metal ions was demonstrated. The electrochemical impedance spectroscopy (EIS) response of the printed sensor revealed a very high sensitivity at nano molar (nM) concentration levels of lead nitrate (Pb(NO3)2) and cadmium nitrate (Cd(NO3)2). A percentage change of 18 %, in impedance, was observed for the 1 nM concentration of Pb(NO3)2 when compared with DI water. The response of the electrochemical sensor is analyzed and presented in this paper.