Flexible Hybrid Electronics is an emerging technology which has the potential to reshape the next generation electronics industry.
Introduction
In the last few decades, the modern semiconductor industry has revolutionized every aspect of human life. The remarkable miniaturization offered by micro- and nano-scale electronics has paved the way to integrate millions of circuits, sensors and logic elements on a small-area silicon microchip. This has not only replaced old, bulkier electronics systems with small and smart Integrated Circuits (ICs) but also enabled us to discover new application paradigms. Within a short span of time, countries like Taiwan, Korea, Singapore and Malaysia have experienced unprecedented economic growth thanks to the electronics industry in general and the IC industry in particular. There lies a huge possibility and investments that Turkey can also mimic the success stories of the above-mentioned countries to keep pace with the knowledge-based world economy and fulfill its local commercial and consumer needs.
Typically, an electronic system is ascribed by the trend commonly known as SWaP-c (Size, Weight, and Power — cost). In the recent years, the electronics industry is undergoing a new trend of the transformation from reliance on its traditional rigid forms to even more sophisticated and complicated forms with added functionalities such as flexibility, bendability and stretchability [1]. Despite the phenomenal benefits of performance and integration density offered by silicon ICs, manufacturing flexible and largearea electronics remains a huge challenge. On contrary, printed flexible electronics mainly employ flexible materials and printing technologies for manufacturing large-area electronics. Nevertheless, the efficiency and reliability of printed flexible electronics remain inferior to that of silicon ICs and of the discrete electronics on standard Printed Circuit Boards (PCBs). Major confrontations arise from logic, built-in memory, analog front ends circuits and power management units, thereby, limits the widespread adoption of printed flexible electronics. Flexible Hybrid Electronics (FHE) augments the strengths of two distinct technologies, i.e. using flexible printed electronics for sensing purposes and silicon ICs for data processing and communication. Complementing printed flexible electronics in conjunction with silicon ICs yields versatile technology that can be deployed in a diverse range of applications such as:
wearable health monitoring [2], structural health monitoring [3,4], predictive maintenance [5], automotive [6], consumer electronics, display technologies [7,8], transportation and logistics. These are the emerging domains that employ FHE extensively, as is highlighted in Figure 2.
Why Flexible Hybrid Electronics?
Flexible Hybrid Electronics (FHE) is an emerging technology which has the potential to reshape the next generation electronics industry. It constitutes an innovative frontier that enables the integration of sensing elements, thin silicon ICs, data processing and communication units, and power supply on non-traditional flexible substrates. Furthermore, it will aid to usher the novelty in terms of the configuration of sensors, the integration and medium of electronics, and above all the introduction of ubiquitous sensing in terms of the internet of things (IOT). Figure 3 represents the system-level implementation of FHE employing both printed electronics and silicon ICs. According to a forecast by the market research agency IDTechEx, the value of the printed flexible and organic electronics sector will escalate from $31.7 billion in 2019 to $ 73.3 billion industry by 2029 [10].
State-of-the-art FHE based systems are not only lightweight and stretchable but also conformable and bendable as well. These added properties are designated by the new form factors for the new-generation FHE systems, which differ considerably from those of their traditional rigid counterparts. Moreover, flexibility, cost-effectiveness and large area manufacturing capability are the key enablers of FHE systems, which make them an attractive alternative to rigid and expensive silicon ICs. The standard Fabrication process for microelectronics comprises photolithography, vacuum deposition and etching techniques, which is why it is termed a subtractive process. Henceforth, scaling up to large-area is expensive and wasteful. Whilst, the printed electronics is an additive form of processing, utilizing solution-based materials patterned on flexible substrates by means of printing technologies. Selective deposition of materials eliminates the need for photolithography and etching processes, thereby reduces the cost. Large-area, high volume and roll-to-roll manufacturing are the vital merits of printed electronics [11].
Fundamental Blocks of FHE
A FHE system primarily consists of printed sensors that serve to sense and convert physical quantities such as temperature, pressure and humidity, as well as chemical concentrations to electrical signals. These electrical signals can undergo further processes such as amplification, buffering and noise reduction by thinned ICs. Additionally, ICs provide on-chip data storage and communication capability through printed/integrated antennas. In order to power up the system, either printed/discrete batteries or energy-harvesting units are available. All these components are then integrated on flexible substrates. Figure 3 presents the basic FHE system, highlighting the key components [9].
Design and Development of a FHE System
The design and development cycle of a FHE system is undertaken by sensor specifications, conception, simulation and design verification and is heavily dependent on printing techniques for the fabrication of sensors. Afterwards, the sensing module is integrated and assembled with ICs and other discrete components for the purpose of signal conditioning and processing. Finally, the packaged FHE prototypes are tested and characterized, as shown in the design cycle in Figure 4.
Over the last decade, the evolution of printing techniques has assisted in rapid advancement and innovation in the realm of FHE. The choice of substrate materials, compatible inks/adhesives and various printed techniques (as shown in Figure 5 and 6) are the primary parameters involved in the development of the printing process for any specific printed electronics application.
The selection of printing technique depends mainly on ink properties (surface tension, viscosity, etc.) and printed feature dimensions (line width, line spacing). Moreover, ink and substrate compatibility have to be taken into consideration. Silicon ICs are an integral part of FHE [9]. Numerous methods and materials have been proposed for mounting ICs and discrete circuit components onto flexible substrates. In order to obtain thinned ICs, pre- and post-processing of silicon and silicon on insulator wafer is performed i.e selective removal of silicon by grinding, dry or wet etching, or chemical reaction. Apart from thinned ICs, other passive components such as resistors, capacitors and inductors, which are mostly surface mount devices (SMD) are directly integrated onto the flexible substrate to realize a fully functional circuit. Typically, silicon ICs and other SMD are connected to substrates via conductive adhesive or solder pastes with the help of pick & place assembly equipment.
For wireless power transmission, as well as for data communication, FHE mainly relies on printed flexible antennas, whereby the choice of antenna design and operating frequency depend upon the application. Various standards and printing techniques are well established to serve the communication modes for FHE. Viable substitutes to supply adequate power to operate sensors and circuits in FHE systems include printed batteries and on-chip energy harvesting and storage. These solutions not only eliminate the use of bulky rigid batteries, which hinder mechanical flexibility, but also it does not require also the requirement of ports and cables in case of rechargeable alternatives.
Constraints and Design Challenges in FHE
The fast pace of growth and ever-increasing demand for diverse application domains entail FHE to ensure stable and reliable operation under diverse environmental conditions. As FHE is still a growing and developing technology, the reliability of FHE is a major concern. Primarily owing to the durabilty of printed materials, performance of FHE alleviate, exacerbates further due to the added mechanical features of flexibility and stretchability. Moreover, process variation in the scale up roll-to-roll manufacturing of printed electronics is another factor that can degrade the performance of FHE. In order to ensure the robust and reliable operation of FHE, substantial mechanical and environment tests need to be performed, which include bending and twisting tests, repeated thermal cycling, exposure to high humidity and temperature conditions, and lifetime testing. To circumvent these constraints and challenges, there is ample room for innovation in design manufacturability and for the optimization of printed electronics. In spite of the current challenges at hand, FHE is envisioned to reshape the electronics industry in the near future, specifically when it comes to large-area sensing, wearable electronics and soft robotics. As a global leader in reinforcement, Kordsa aims to establish a transformative and innovative center for conducting research and development in the field of flexible hybrid electronics. This platform will undertake the design and development of printed electronics in combination with life sciences, so as to transform know-how to working prototypes, which is bound to contribute to the advancement of technology and living standards in all aspects. Our near-term goal is to instigate benchmark studies analyzing the feasibility of new and exciting application paradigms, such as wearable health care electronics, logistic tracking, and structural health monitoring
References
[1] W. S. Wong, M. L. Chabinyc, T.-N. Ng, A. Salleo, Flexible Electronics: Materials and Applications, Springer, New York 2009, pp. 143–181.
[2] Y. Khan, A. E. Ostfeld, C. M. Lochner, A. Pierre, A. C. Arias, Adv. Mater. 2016, 28, 4373.
[3] A. V. Quintero, F. Molina-Lopez, E. Smits, E. Danesh,J. van den Brand, K. Persaud, A. Oprea, N. Barsan, U. Weimar, N. De Rooij, Flexible Print. Electron. 2016, 1, 025003.
[4] D. Zymelka, K. Togashi, R. Ohigashi, T. Yamashita, S. Takamatsu, T. Itoh, T. Kobayashi, Smart Mater. Struct. 2017, 26, 105040.
[5] IDTechEx presentation Smart Manufacturing and A Connected Factory — The Status Quo Of A Brave New World In 2019
[6] Opportunities in The Automotive Industry: From Materials To Printed Electronics To Electric Vehicles
[7] J. Chen, W. Cranton, M. Fihn, Handbook of Visual Display Technology, Springer, Berlin/Heidelberg, Germany 2016.
[8] J. Kim, H. J. Shim, J. Yang, M. K. Choi, D. C. Kim, J. Kim, T. Hyeon, D. Kim, Adv. Mater. 2017, 29, 1700217.
[9] Y.Khan,A. Thielens, S.Muin,J. Ting, C.Baumbauer and A.Arias, Adv. Mater 2019,05279 DOI: 10.1002/adma.201905279
[10] R. Das, X. He, K. Ghaffarzadeh, Flexible, Printed and Organic Electronics2019–2029: Forecasts, Players & Opportunities, IDTechEx Research, Cambridge, UK 2018.
[11] Realizing Fully-Printed Electronics — State of Technology in 2018, Semi-flextech, oct 2018
[12] OE-A ROADMAP FOR ORGANIC AND PRINTED ELECTRONICS, 3rd EDITION
Written by
ATIA SHAFIQUE,
PH.D, Global Technology, Project Leader, Kordsa
