Eloi Ramon

Inkjet patterning of multiline intersections for wirings in printed electronics.

Inkjet printed electronics using thermo-curable liquid inks exhibit particular geometrical characteristics in terms of regularity. This article presents a morphological analysis for inkjet printed multi line intersections that are critical structures for building circuits. We studied thin-film structures of silver conductive ink and printed by inkjet technology. Instability of the ink during printing causes the thickness irregularity of vertex, normally with peaks at these areas. We propose the usage of specific patterns for intersections as thickness regularity compensations. The results show that some patterns help to reduce this instability and improve the thickness regularity of intersections morphology.

All-inkjet printed organic transistors: Dielectric surface passivation techniques for improved operational stability and lifetime

Abstract We report about the use of a printed pentafluorothiophenol layer on top of the dielectric surface as a passivation coating to improve the operational stability of all-ink-jet printed transistors. Transistors with bottom-gate structure were fabricated using cross-linked poly-4-vinylphenol (c-PVP) as dielectric layer and an ink formulation of an amorphous triarylamine polymer as semiconductor. The resulting TFTs had low turn-on voltage (Vth

Inkjet printed antennas for NFC systems

Inkjet printing is one of the most promising techniques that could potentially revolutionize large area and organic electronics fabrication. At the moment, technology is still under development and some problems remain to be solved. Only few applications have been demonstrated with enough performance to be moved to industrial level. In this paper we present the study of a potentially successful inkjet printing application: a Near Field Communication Antenna. In our work we characterized an inkjet printing process and developed an antenna design to evaluate its potential. Fabricated antenna was tested on NFC systems and final results lead us to conclude that NFC antennas are a potentially successful inkjet printing application.

All-inkjet-printed thin-film transistors: manufacturing process reliability by root cause analysis

We report on the detailed electrical investigation of all-inkjet-printed thin-film transistor (TFT) arrays focusing on TFT failures and their origins. The TFT arrays were manufactured on flexible polymer substrates in ambient condition without the need for cleanroom environment or inert atmosphere and at a maximum temperature of 150 °C. Alternative manufacturing processes for electronic devices such as inkjet printing suffer from lower accuracy compared to traditional microelectronic manufacturing methods. Furthermore, usually printing methods do not allow the manufacturing of electronic devices with high yield (high number of functional devices). In general, the manufacturing yield is much lower compared to the established conventional manufacturing methods based on lithography. Thus, the focus of this contribution is set on a comprehensive analysis of defective TFTs printed by inkjet technology. Based on root cause analysis, we present the defects by developing failure categories and discuss the reasons for the defects. This procedure identifies failure origins and allows the optimization of the manufacturing resulting finally to a yield improvement.

Inkjet Printing Design Rules Formalization and Improvement

A process design kit (PDK) or Technology Design kit (TDK) is a set of files which describes manufacturing parameters that are relevant for the designers (fabrication layers, electrical parameters and design rules) for a certain technology of a given foundry. PDKs customize CAD/EDA tools used by designers, providing enough abstraction of technological details to facilitate the design of (organic electronics) circuits. Design rules are a set of geometric restrictions imposed to the different layers fabricated by the foundry that designers have to respect. By taking the geometric design rules into account, the design engineers address physical layout to develop devices and circuits without the need of a deep knowledge of process and materials. These rules guarantee their manufacturability and enable working circuits with an optimal balance of yield versus integration density. Design rules for inkjet printing are similar to general design rules for photolithographic processes but also need to cope with the failures related to additive printing of inks and related curing. In this paper, parameterizable cells (PCells) have been used to automate the generation of a complete set of structures to formalize and arrive at technology-independent design rules. A set of test vehicles has been designed, printed and characterized demonstrating the methodology to comprehensively capture the design criteria for inkjet printing technology. For improving design rules and scaling down device dimensions, we present a design approach that combines pre-patterned, high-resolution substrates with digital inkjet fabrication as a demonstration of the capabilities of combining inkjet with other fabrication technologies.

Near-Field Chipless-RFID System With High Data Capacity for Security and Authentication Applications

A high data capacity chipless radio frequency identification (chipless-RFID) system, useful for security and authentication applications, is presented in this paper. Reading is based on the near-field coupling between the tag, a chain of identical split-ring resonators (SRRs) printed on a (typically flexible) dielectric substrate (e.g., liquid crystal polymer, plastic, and paper), and the reader. Encoding is achieved by the presence or absence of SRRs at predefined (equidistant) positions in the chain, and tag identification (ID) is based on sequential bit reading. Namely, the tag must be longitudinally displaced, at short distance, over the reader, a microstrip line loaded with an SRR and fed by a harmonic signal. By this means, the harmonic signal is amplitude modulated, and the (ID) code is contained in the envelope function, which can be obtained by means of an envelope detector. With this system, tag reading requires proximity with the reader, but this is not an issue in many applications within the domain of security and authentication (e.g., secure paper for corporate documents and certificates). Several circularly shaped 40-bit encoders (implemented in a commercial microwave substrate), and the corresponding reader, are designed and fabricated as proof-of-concept demonstrators. Strategies for programming the tags and a first proof-of-concept chipless-RFID tag fabricated on plastic substrate through inkjet printing are included in this paper.

Frequency scan technique for inkjet-printed chipless sensor Tag reading

A novel technique for the remote reading of chipless capacitive sensor Tags and one of its possible applications is presented. For this purpose, a frequency agile reader has been developed using Software Defined Radio (SDR) architectures, capable of scanning with high precision a frequency range given by an external user and extracting the resonant frequency of a Tag. The capacitive sensor Tag has been implemented on a plastic substrate using inkjet printing techniques. In order to demonstrate the feasibility of the technique, the reader analyzes the Tags backscatter response and gets its resonant frequency in a case study of a moisture sensor application.

Inkjet printed metal insulator semiconductor (MIS) diodes for organic and flexible electronic application

All inkjet printed rectifying diodes based on a metal-insulator-semiconductor (MIS) layer stack are presented. The rectifying properties were optimized by careful selection of the insulator interlayer thickness and the layout structure. The different diode architectures based on the following materials are investigated: (1) silver/poly (methylmethacrylate-methacrylic acid)/polytriarylamine/silver, (2) silver/polytriarylamine/poly (methylmethacrylate-methacrylic acid)/silver, and (3) silver/poly (methylmethacrylate-methacrylic acid)/poly-triarylamine/poly(3,4-ethylenedioxythiophene) poly (styrenesulfonate). The MIS diodes show an averaged rectification ratio of 200 and reasonable forward current density reaching 40 mA cm−2. They are suitable for a number of applications in flexible printed organic electronics.

A Systematic Study of Pattern Compensation Methods for All-Inkjet Printing Processes

Inkjet printed electronics is a promising technology for low-cost, flexible, and large area manufacturing of electronic systems. This paper presents a complete characterization methodology, automated and capable of extracting key technology parameters from a large amount of samples. We used this methodology to extract viable compensation strategies for a particular printer, ink, and substrate, analyzing more than a half million structures with a very low human interaction. The results show a promising improvement in yield and fidelity of printed patterns, when using an optimal compensation pattern. As an example, the fabrication yield for 120-μm width-40-μm separation structures raised from less than 10% up to 100% after applying compensations.

METHODOLOGY AND TOOLS FOR INKJET PROCESS ABSTRACTION FOR THE DESIGN OF FLEXIBLE AND ORGANIC ELECTRONICS

Inkjet printing is a promising and challenging technique that could potentially revolutionize large area and organic electronics fabrication. Inkjet systems are designed to construct devices and circuits drop by drop, which would lead to a new paradigm in electronics fabrication. However, inkjet technology for Printed Electronics is still under development and several challenges remain. While there is significant progress being made in the development of electronic devices, such as transistors or sensors, there is a lack of work on circuit and system level design. Designing devices and circuits implies a wide knowledge of process aspects, requiring a complex interaction among concepts, tools and processes coming from different science and engineering disciplines. An explicit methodology is needed to separate design from fabrication in a similar way as in silicon design, to design devices and systems without a deep knowledge of process and materials; thus making it possible to open up inkjet technology to a larger community and undergo more rapid design implementations. In this paper we present the main aspects of such a methodology and we discuss the key topics on inkjet technology that allow us to propose these new specific steps.