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Preface

Science means constantly walking a tightrope between blind faith and curiosity; between expertise and creativity; between bias and openness; between experience and epiphany; between ambition and passion; and between arrogance and conviction – in short, between an old today and a new tomorrow¹.

Heinrich Rohrer

(Swiss Physicist)

Radio has made people smarter since its discovery in the late 1800s. Now scientists are trying to make radios smart to make life even easier. Electromagnetic propagating waves in the range of 30 kHz–300 GHz are called radio waves, and electrical equipment handling these propagations are generally called radio or radio frequency (RF) devices. Human life is dependent on RF electronics in our everyday routine. TV and radio broadcast, mobile phone communication, the Internet, microwave heating and so on are an integral part of our daily life, implicitly or explicitly.

Radio equipment can be an active device (that uses an active power source for operation), like a mobile phone or a television set, or passive equipment (that does not use an active power source for operation or data storage, but scavenges a part of an interrogating energy source), like a contactless credit card, or an anti-theft RFID label in a supermarket.

Communication, connectivity and surveillance are the major fields that utilize most of the RF electronics in this era. This may involve the connectivity between two individuals separated in two continents or between two electrical devices in a same drawing room. The advent of the Internet of things (IoT), backed by 5G communication technologies, has intensified this demand by providing connectivity to almost all our daily utility accompaniments. However, all this electrical equipment, whether active or passive, requires electrical switches, beginning with the initial need for power, and these span the entirety of the internal RF circuitry. These switches operate in different domains, ranging from electrical power switches to different relays, selectors, limit switches and RF switches.

Among these, RF switches play a key role in their domain and are unique with respect to required performances. These are used not only in wireless communications, but also in smart RF sensors and actuators of the future. RF switches allow electronic reconfiguration of device parameters such as operating frequency in a filter, radiation pattern in an antenna and so on, in order to make these devices more efficient. They are present in all communication systems and allow, in summary, signal multiplexing or regulation, so as to reconfigure, or dynamically control, the system. Today’s technological solutions for RF switching (solid-state semiconductor switches and RF micro-electromechanical-systems [MEMS]) need some improvements to meet the emerging requirements, in which the most desired innovation is non-volatile operation, i.e. operating without any energy requirements for maintaining an impedance state. Such a broadband solution, based on a flexible and low cost approach, is eagerly awaited.

Conductive bridging random access memory/metal insulator metal (CBRAM/MIM) switches are a new innovation of memory technology, which has also been identified as a potential non-volatile RF switching solution in the recent years. The primary target of this book, and the core concept of the studies presented herewith, is to introduce the idea of a new generation of electronically reconfigurable, solid-state and passive RF-microwave devices based on integrated CBRAM/MIM switching technology. We will present our work and results, focusing on the development of a new technology of low-cost non-volatile RF switches with both high performance and flexibility of implementation.

We demonstrate the basic principle of CBRAM/MIM RF switches and give proof of concept realizations of integration of this technology into passive RF and microwave devices, such as electronically rewritable chipless RFID tags, which are often referred to as the “rewritable RF barcodes of the future”, electronically pattern steerable antennas, electronically reconfigurable filters and single pole double throw (SPDT) switches on classic as well as flexible substrates. The necessary analysis and theoretical validations of these concepts are also presented with these results.

We take this work as a humble beginning for a new innovation of electronically reconfigurable and non-volatile passive RF and microwave devices, which is dedicated to the future, and nurtured from deeply within our heart, with our passion and wide-eyed dreams for the betterment of current science and technology. Our investigations and findings are organized into four chapters in this book, as described below.

In Chapter 1, a general idea of the motivation for and background of the need for a non-volatile RF switch is discussed in detail. A review of prominent RF switching technologies is presented, along with the state of the art of research in CBRAM/MIM RF switch technology. The requirement of non-volatile RF switches and the reasons for the choice of CBRAM/MIM technology for this are also explained in detail.

Chapter 2 states the real-world implementation challenges of a low-cost non-volatile RF switching technology and describes our efforts to overcome these limitations. We present in this chapter the design and optimization process of CBRAM/MIM based Coplanar waveguide (CPW) RF switches on classic as well as flexible paper substrates, using simple and low-cost methods, compatible with mass industrial production. Discussion of electrical equivalent models, time stability and other interesting features are also given in addition in this chapter. An application example of these switches in SPDT configuration is also included in this chapter.

Chapter 3 focuses on the design and development of solid-state electronically rewritable chipless RFID tags, which may be informally called “rewritable RF barcodes”. In this chapter, we describe in brief the principle of chipless RFID and present the design and realization of electronically rewritable chipless RFID tags on classic and flexible substrates. Electrical equivalent model analysis and advantages of using the proposed integrated CBRAM/MIM switches for chipless RFID applications are discussed in detail.

Chapter 4 explains the application of the proposed CBRAM/MIM RF switch technology to electronically reconfigurable filter and antenna models using simple and low-cost methods. We present the implementation of reconfigurable band-stop filters, backed by theoretical discussions and electrical model analysis. We also discuss the extension of the proposed techniques to other filter topologies and the mitigation of current limitations of realized filters in futuristic designs. Application of CBRAM/MIM RF switches for electronically reconfigurable antennas for radiation pattern steering is also presented affirmatively in this chapter. We conclude this chapter by discussing the advantage of using the proposed RF switch technology for reconfigurable antenna and filter applications.

This book also has an appendix, which contains some interesting outcomes of a control experiment for observing the filament formation in CBRAM/MIM switches.

Jayakrishnan METHAPETTYPARAMBU PURUSHOTHAMA

Etienne PERRET

Arnaud VENA

November 2021

1 1 Heinrich Rohrer Quotes. (n.d.). BrainyQuote.com. Retrieved July 9, 2020, from BrainyQuote.com web site: https://www.brainyquote.com/quotes/heinrich_rohrer_736250.