Toward roll-to-roll printed power sources and control electronics

Dr. Jukka Hast, Dr. Kimmo Solehmainen and Marja Vilkman, VTT Technical Research Centre of Finland

To pave the way for commercialization of printed electronics and optics applications, two European Union-funded projects are developing roll-to-roll-based fabrication technologies.

In the first project, called FACESS (Flexible Autonomous Cost efficient Energy Source and Storage), roll-to-roll printed organic photovoltaics and energy storage devices are being developed. In the second one, Polaric (Printed, Organic and Large-Area Realisation of Integrated Circuits), the aim is to bring the performance of printed electronics to a new level by combining roll-to-roll compatible high-resolution steps in the transistor fabrication process, and to demonstrate the developed high-performance organic electronics in various consumer applications.

Traditionally, the primary function of printing has been the delivery of data and information for visual inspection and further interpretation by humans or machines. Nowadays, printing and other large-area R2R (roll-to-roll)-compatible processes enable cost-efficient mass manufacturing of electronics and other functionalities on large-area and flexible substrates such as plastic, paper and fabrics. Figure 1 shows one of the pilot machines for printed electronics at VTT Technical Research Centre of Finland.

Figure 1. Shown is a pilot printing machine for printed electronics. Images courtesy of VTT Technical Research Centre of Finland, Printed Functional Solutions.

New printable-functional materials, print-production processes and reading mechanisms are expanding the role and function of printing toward novel application fields. This is the opportunity gap between traditional paper, packaging and printing industry products, and ICT/ electronics industry products, and it can realize completely new types of applications and businesses; e.g., disposable sensors, simple “electronic” components and circuits, large-area functional paperlike intelligent products, smart packages, tag-and-code technology-based ICT and hybrid media services.

The market potential loaded to printed and organic electronics is extremely high. Several independent market analysts expect it to become a $250 billion to $300 billion market within 20 years. All electronic applications require power, a challenge that will be emphasized in printed electronics applications, where power sources also must be implemented on flexible form.

In the FACESS project, energy harvesting and storage are being tackled. The goal of the project partners – VTT Technical Research Centre and Suntrica Oy, both of Finland; Interuniversity Micro-Electronics Centre of Belgium; Commissariat à l’Energie Atomique of France; Politechnika Warszawska of Poland; Umicore SA of Belgium; and Coatema Coating Machinery GmbH and Coatema Maschinenbau GmbH, both of Germany – is to develop cost-efficient R2R production techniques for organic solar cell modules and rechargeable lithium batteries.

Also in development is an application-specific integrated circuit (ASIC) chip that would optimize and control the battery charge from the organic solar modules. To be flexible, the chip is thinned to 30 μm and interconnected on the flexible backplane. The plan is to use R2R-compatible production technologies to manufacture an energy storage foil of four printed organic solar cell modules comprising a 100-cm2 area, a printed battery and an interconnected ASIC to control the charge operation. Under AM1.5, a reference organic solar cell module can produce 250 mW of power to charge the battery. The battery size is approximately 30 cm2 and its capacity, between 1 and 3 mAh/cm2.

In Figure 2, four gravure-printed organic solar cell modules operate at 2.3 percent photon-conversion efficiency at air mass 1.5 illumination on a 15.5-cm² area per module. The modules are manufactured using commercially available conductive – and photoactive – polymers. The rechargeable lithium battery has anode and cathode electrodes screen-printed on aluminum and copper foils, and an assembled commercial separator foil. The battery produces ~40-mAh capacity. The 30-μm-thick ASIC is flip-chip-bonded using anisotropically conducting adhesive on the backplane substrate.

Figure 2. This energy storage foil is from the FACESS project.

All other components of the energy source built for the FACESS project are printed, except for the electronic part. This is because the performance limitations of printed electronic circuits force the use of traditional, silicon-based microchips for the control electronics. To enable wholly printed devices, the printed circuits must be improved significantly.

In response to this challenge, the partners launched POLARIC earlier this year. The new project is expected to lead to smaller transistor dimensions, with the aim of improving their performance and demonstrating their use in applications including printed radio frequency identification tags and active matrix displays.

The work is divided among the coordinator, VTT Technical Research Centre of Finland; AMO GmbH, 3D-Micromac AG, Fraunhofer-Gesellschaft IZM and micro resist technology GmbH, all of Germany; BASF, CSEM SA and Asulab, a division of The Swatch Group Research and Development Ltd., all of Switzerland; Cardiff University and Imperial College London, both of the UK; IMEC of Belgium; Joanneum Research Forschungsgesellschaft mbH of Austria; and Obducat Technologies AB of Sweden.

Figure 3 demonstrates state-of-the-art organic electronics (printed and lithographically prepared) and compares it to the performance required for operationally good enough organic circuits; i.e., the POLARIC target. In detail, the high performance of the organic circuits referred to means high speed (kilohertz to megahertz), low operating voltage (±<5 V), low power consumption and low parasitic capacitance. The POLARIC target of improved performance is indeed challenging. However, that level of performance is needed to enable substantial market penetration of organic electronics.

Figure 3. The POLARIC target is compared with the state of the art in organic electronics. R2R = roll to roll.

Besides improved performance, the manufacturing process of organic electronics must be suitable for large-scale production. Thus, another, equally important goal of the project is to develop further R2R printing methods; e.g., using R2R-compatible nanoimprinting technologies for short-channel configuration of the electrodes to produce components and circuits with extremely high yield. The project also will provide solutions for the fabrication of R2R tools, making serial replication viable. Finally, the circuit design, modeling and characterization of organic electronics will be developed to offer a toolbox similar to that of silicon-based microelectronics. Thus, it is justified to say that the project will revolutionize the way printed electronic circuits are made by combining large-area fabrication methods with high-performance organic electronic circuits on a scale not previously attempted.

After the FACESS and POLARIC projects, high-performing organic electronic building blocks and manufacturing platforms can be used in all areas of printed electronics, including sensors, memory, batteries, photovoltaics, lighting and any combination of these devices. By combining different functionalities and blocks on the same flexible foil, and integrating the whole process in a cost-efficient way, the huge market potential for printed electronics and optics will turn into reality.

Meet the authors

Dr. Jukka Hast is a senior research scientist; e-mail: jukka.hast@vtt.fi. Dr. Kimmo Solehmainen also is a senior research scientist; e-mail: kimmo.solehmainen@vtt.fi. Marja Vilkman is a research scientist; e-mail: marja.vilkman@vtt.fi. All three work at VTT Technical Research Centre of Finland, Printed Functional Solutions.