Krishna Rajan

Silver nanoparticle ink technology: state of the art

Printed electronics will bring to the consumer level great breakthroughs and unique products in the near future, shifting the usual paradigm of electronic devices and circuit boards from hard boxes and rigid sheets into flexible thin layers and bringing disposable electronics, smart tags, and so on. The most promising tool to achieve the target depends upon the availability of nanotechnology-based functional inks. A certain delay in the innovation-transfer process to the market is now being observed. Nevertheless, the most widely diffused product, settled technology, and the highest sales volumes are related to the silver nanoparticle-based ink market, representing the best example of commercial nanotechnology today. This is a compact review on synthesis routes, main properties, and practical applications.

Ionic liquid-enhanced soft resistive switching devices

Resistive switching phenomena are of paramount importance in the area of memory devices. In the present study, we have fabricated a simple resistive switching device using a solution processable nanocomposite based on silver nitrate and poly(vinylidene fluoride-hexafluoropropylene). The change in resistance is ascribed to an initial ionic conduction, followed by a non-continuous field induced filament formation. The switching device fabricated with the above-mentioned active matrix displayed a volatile switching behavior. The addition of room temperature ionic liquid plays a fundamental role in triggering permanent memory and reducing the set voltage range up to ten-fold. The change in switching behavior with respect to the applied voltage bias and compliance level set during electrical characterization was studied thoroughly. The present work also gives a glimpse into the importance of device architecture on resistive switching phenomena.

Wearable Intrinsically Soft, Stretchable, Flexible Devices for Memories and Computing

A recent trend in the development of high mass consumption electron devices is towards electronic textiles (e-textiles), smart wearable devices, smart clothes, and flexible or printable electronics. Intrinsically soft, stretchable, flexible, Wearable Memories and Computing devices (WMCs) bring us closer to sci-fi scenarios, where future electronic systems are totally integrated in our everyday outfits and help us in achieving a higher comfort level, interacting for us with other digital devices such as smartphones and domotics, or with analog devices, such as our brain/peripheral nervous system. WMC will enable each of us to contribute to open and big data systems as individual nodes, providing real-time information about physical and environmental parameters (including air pollution monitoring, sound and light pollution, chemical or radioactive fallout alert, network availability, and so on). Furthermore, WMC could be directly connected to human brain and enable extremely fast operation and unprecedented interface complexity, directly mapping the continuous states available to biological systems. This review focuses on recent advances in nanotechnology and materials science and pays particular attention to any result and promising technology to enable intrinsically soft, stretchable, flexible WMC.

Highly performing ionic liquid enriched hybrid RSDs

A simple two terminal planar resistive switching device (RSD) is fabricated with a 10 µm active gap. The active hybrid matrix is based on a PEO, Ionic Liquid and Silver Nitrate formulation which represents a perfect polymeric medium for the growth of a conducting filament, whose creation/destruction is due to the migration of silver ions within the matrix. Two different device configurations are compared based on the electrode symmetry. The first case includes a planar symmetric device with electron beam evaporated gold electrodes, while the second is based on a planar asymmetrical device with sputtered platinum and electron beam evaporated silver electrodes. The asymmetric device exhibits a continuous resistive switching up to 500 cycles by maintaining an outstanding on/off ratio of 104 throughout the test without any compromise in its retention. The fabrication of reliable soft (hybrid) materials is of paramount importance for the development of next generation wearable devices that must be stretchable and flexible; planar microelectronic systems, better than stacked ones, are compatible with high throughput production technologies such as printing, where uniformity is controlled on a higher scale in comparison to standard lithographic processes. The present work provides clear-cut evidence of the conducting filament formation/dissolution during the resistive switching process of a soft material. A detailed explanation is given on the formation and rupture of the same.