Steven K. Volkman

Progress Toward Development of All-Printed RFID Tags: Materials, Processes, and Devices

Printed electronics provides a promising potential pathway toward the realization of ultralow-cost RFID tags for item-level tracking of consumer goods. Here, we report on our progress in developing materials, processes, and devices for the realization of ultralow-cost printed RFID tags. Using printed nanoparticle patterns that are subsequently sintered at plastic-compatible temperatures, low-resistance interconnects and passive components have been realized. Simultaneously, printed transistors with mobilities >10/sup -1/ cm/sup 2//V-s have been realized using novel pentacene and oligothiophene precursors for pMOS and ZnO nanoparticles for nMOS. AC performance of these devices is adequate for 135-kHz RFID, though significant work remains to be done to achieve 13.56-MHz operation.

Printed electronics: the challenges involved in printing devices, interconnects, and contacts based on inorganic materials

Printed electronics represent an emerging area of research that promises large markets due to the ability to bypass traditional expensive and inflexible silicon-based electronics to fabricate a variety of devices on flexible substrates using high-throughput printing approaches. This article presents a summary of work to date in the field of printed electronics and the materials chemistry involved. In particular, the focus is upon the use of metal- and metal oxide-containing inks in the preparation of contacts and interconnects. The review discusses the challenges associated with processing these types of inks and ways to successfully obtain the desired features.

Quantification of thin film crystallographic orientation using X-ray diffraction with an area detector.

As thin films become increasingly popular (for solar cells, LEDs, microelectronics, batteries), quantitative morphological and crystallographic information is needed to predict and optimize the films electrical, optical, and mechanical properties. This quantification can be obtained quickly and easily with X-ray diffraction using an area detector in two sample geometries. In this paper, we describe a methodology for constructing complete pole figures for thin films with fiber texture (isotropic in-plane orientation). We demonstrate this technique on semicrystalline polymer films, self-assembled nanoparticle semiconductor films, and randomly packed metallic nanoparticle films. This method can be immediately implemented to help understand the relationship between film processing and microstructure, enabling the development of better and less expensive electronic and optoelectronic devices.

Printed organic transistors for ultra-low-cost RFID applications

Printed electronics provides a potential pathway toward the realization of ultra-low-cost radio frequency identification (RFID) tags for item-level tracking of consumer goods. Here, we report on our progress in developing materials and processes for the realization of printed transistors for low-cost RFID applications. Using inkjet printing of novel conductors, dielectrics, and organic semiconductors, we have realized printed transistors with mobilities >10/sup -1/cm/sup 2//V-s. AC performance of these devices is adequate for 135-kHz RFID, and, with further optimization, 13.56-MHz RFID appears to be within reach. We review the performance of these devices, and discuss optimization strategies for achieving the ultimate performance goals requisite for realizing ultra-low-cost printed RFID.

Printed electronics for low-cost electronic systems: Technology status and application development

In recent years, printing has received substantial interest as a technique for realizing low cost, large area electronic systems. Printing allows the use of purely additive processing, thus lowering process complexity and material usage. Coupled with the use of low-cost substrates such as plastic, metal foils, etc., it is expected that printed electronics will enable the realization of a wide range of easily deployable electronic systems, including displays, sensors, and RFID tags. We review our work on the development of technologies and applications for printed electronics. By combining synthetically derived inorganic nanoparticles and organic materials, we have realized a range of printable electronic ldquoinksrdquo, and used these to demonstrate printed passive components, multilayer interconnection, diodes, transistors, memories, batteries, and various types of gas and biosensors. By exploiting the ability of printing to cheaply allow for the integration of diverse functionalities and materials onto the same substrate, therefore, it is possible to realize printed systems that exploit the advantages of printing while working around the disadvantages of the same.

Ink-jetted Silver/Copper conductors for printed RFID applications

Low-resistance printed conductors are crucial for the development of ultra-low cost electronic systems such as radio frequency identification tags. Low resistance conductors are required to enable the fabrication of high-Q inductors, capacitors, tuned circuits, and interconnects. Furthermore, conductors of appropriate workfunction are also required to enable fabrication of printed Schottky diodes, necessary for rectification in RFID circuits. Last year, we demonstrated the formation of low-resistance conductive printed structures using gold nanoparticles. Here we demonstrate, for the first time, technologies for formation of printed conductors using silver and copper nanoparticles. These are particularly advantageous for several reasons. First, both silver and copper offer a 2X reduction in sheet resistance over gold, resulting in improved interconnect performance and inductor Q. Second, the material costs associated with both silver and copper are expected to be significantly cheaper than gold. Third, the workfunction of silver enables the fabrication of all-printed Schottky diodes with a silver rectifying contact to many common printable organic semiconductors. Solutions of organic-encapsulated silver and copper nanoparticles may be printed and subsequently annealed to form low-resistance conductor patterns. We describe novel processes for forming silver and copper nanoparticles, and discuss the optimization of the printing/annealing processes to demonstrate plastic-compatible low-resistance conductors. By optimizing both the size of the nanoparticle and the encapsulant sublimation kinetics, it is possible to produce particles that anneal at low-temperatures (

A novel transparent air-stable printable n-type semiconductor technology using ZnO nanoparticles

We report on a novel, air-stable, printable, transparent, NMOS semiconductor technology using soluble ZnO nanoparticles. We demonstrate solution-processed transistors with mobility > 0.1 cm/sup 2//V/spl middot/s, which is the highest solution-processed NMOS mobility reported to date. The air-stability and transparency make this device an ideal candidate for low-cost printed displays and CMOS circuitry.

Inkjetted Organic Transistors using a Novel Pentacene Precursor

Pentacene is one of the most promising organic materials for organic transistor fabrication, since it offers higher mobility, better on-off ratio, improved environmental stability, and better reliability than most other organic semiconductors. However, its severe insolubility renders it useless for the solution-based fabrication of electronic devices. Solution-based processing is the key to enabling ultra-low-cost circuit fabrication, since it eliminates the need for lithography, subtractive processing, and vacuum-based film deposition. Using a recently developed soluble pentacene precursor, we demonstrate the first inkjet-printed pentacene transistor fabricated to date. This is achieved using a substrate-gated transistor structure in conjunction with an inkjetprinted pentacene precursor active layer. After deposition, the precursor is converted to pentacene via heating, through the decomposition of the Diels-Alder product. As the anneal temperature increases above 120°C, performance increases dramatically. The process is therefore compatible with numerous low-temperature plastics. As the anneal time is increased to several minutes, performance likewise increases through increased precursor decomposition. However, exposure to excess temperatures or times tends to degrade performance. This is caused by morphological and chemical changes in the pentacene film. Optimization of the anneal process alone has resulted in the demonstration of transistors with an on-off ratio of >10 5 and field-effect mobility of >0.01cm 2 /V-s, attesting to the great promise of this material.

A high-performance all-inkjetted organic transistor technology

We report on the highest performance all-printed transistors reported to date. Using nanoparticle-based printed contact, polymer dielectrics, and a printed soluble pentacene precursor semiconductor, we demonstrate all-inkjetted devices with mobilities >0.1cm/sup 2//V-s and on-off ratios as high as 10/sup 4/. The performance of these devices is comparable to control devices fabricated on silicon-substrates, and thus, these devices represent a significant step towards the realization of low-cost printed electronics.

Synthesis of 3-Substituted 1,4-Benzodiazepin-2-ones

The preparation of 3-substituted 1,4-benzodiazepines by benzodiazepine enolate alkylation has been explored. Employing this approach, multigram quantities of benzodiazepine 1 have been prepared for animal studies to evaluate a new approach for the treatment of the autoimmune disease systemic lupus erythematosus (SLE).