Israel Mejia

Bio: Israel Mejia is an academic researcher from University of Texas at Dallas. The author has contributed to research in topics: Thin-film transistor & Thin film. The author has an hindex of 17, co-authored 84 publications receiving 910 citations. Previous affiliations of Israel Mejia include CINVESTAV.

Mobility model for compact device modeling of OTFTs made with different materials

Abstract: In this paper we present a new approach to model mobility in organic thin film transistors, OTFTs, which is used to analyze the behavior of mobility in devices made of poly(methyl methacrylate), PMMA, on poly(3-hexylthiophene), P3HT, recently reported by us. It is also used to discuss differences observed between OTFTs made with other polymers and oligomers. The method allows the calculation of the characteristic temperature and energy distribution of localized states (DOS) in the active layer, considering an exponential distribution. It is also shown that using the extracted DOS parameters as input DOS parameters in ATLAS simulator, it is possible to reproduce very well the device characteristics.

MIS polymeric structures and OTFTs using PMMA on P3HT layers

Abstract: In this paper we present a detailed characterization of metal–isolator–semiconductor MIS structures and organic thin film transistors (OTFTs) using poly(methyl methacrylate) (PMMA) as gate dielectric on top of a semiconductor poly(3-hexylthiophene) (P3HT) layer. The PMMA layer was spin coated from a 6% dilution of PMMA in anisole. The P3HT layer was spin coated from a 0.66 wt% dilution of P3HT in chloroform. OTFTs with upper gate were fabricated using photolithographic processes. The current density across the dielectric is below 1 × 10−6 A/cm2. The interface states density is below 1 × 1011 cm−2, while the flat band voltage shift is less than 0.5 V for bias stress in the range of ±20 V. Accumulation occurs for gate voltage below −10 V, allowing OTFTs to work in the voltage range below −30 V, with threshold voltage around −2.5 V. Mobility was 2.5 × 10−3 cm2/V s, which is among highest values reported for P3HT OTFTs working in this voltage range.

Impact of gate dielectric in carrier mobility in low temperature chalcogenide thin film transistors for flexible electronics

Abstract: Cadmium sulfide thin film transistors were demonstrated as the n-type device for use in flexible electronics. CdS thin films were deposited by chemical bath deposition (70°C) on either 100 nm HfO 2 or SiO 2 as the gate dielectrics. Common gate transistors with channel lengths of 40-100 μm were fabricated with source and drain aluminum top contacts defined using a shadow mask process. No thermal annealing was performed throughout the device process. X-ray diffraction results clearly show the hexagonal crystalline phase of CdS. The electrical performance of HfO 2 /CdS-based thin film transistors shows a field effect mobility and threshold voltage of 25 cm 2 V -1 s -1 and 2 V, respectively. Improvement in carrier mobility is associated with better nucleation and growth of CdS films deposited on HfO 2 .

Piezoelectric Biomaterials for Sensors and Actuators

Abstract: Recent advances in materials, manufacturing, biotechnology, and microelectromechanical systems (MEMS) have fostered many exciting biosensors and bioactuators that are based on biocompatible piezoelectric materials. These biodevices can be safely integrated with biological systems for applications such as sensing biological forces, stimulating tissue growth and healing, as well as diagnosing medical problems. Herein, the principles, applications, future opportunities, and challenges of piezoelectric biomaterials for medical uses are reviewed thoroughly. Modern piezoelectric biosensors/bioactuators are developed with new materials and advanced methods in microfabrication/encapsulation to avoid the toxicity of conventional lead-based piezoelectric materials. Intriguingly, some piezoelectric materials are biodegradable in nature, which eliminates the need for invasive implant extraction. Together, these advancements in the field of piezoelectric materials and microsystems can spark a new age in the field of medicine.

Charge injection in solution-processed organic field-effect transistors: physics, models and characterization methods.

Abstract: A high-mobility organic semiconductor employed as the active material in a field-effect transistor does not guarantee per se that expectations of high performance are fulfilled. This is even truer if a downscaled, short channel is adopted. Only if contacts are able to provide the device with as much charge as it needs, with a negligible voltage drop across them, then high expectations can turn into high performances. It is a fact that this is not always the case in the field of organic electronics. In this review, we aim to offer a comprehensive overview on the subject of current injection in organic thin film transistors: physical principles concerning energy level (mis)alignment at interfaces, models describing charge injection, technologies for interface tuning, and techniques for characterizing devices. Finally, a survey of the most recent accomplishments in the field is given. Principles are described in general, but the technologies and survey emphasis is on solution processed transistors, because it is our opinion that scalable, roll-to-roll printing processing is one, if not the brightest, possible scenario for the future of organic electronics. With the exception of electrolyte-gated organic transistors, where impressively low width normalized resistances were reported (in the range of 10 Ω·cm), to date the lowest values reported for devices where the semiconductor is solution-processed and where the most common architectures are adopted, are ∼10 kΩ·cm for transistors with a field effect mobility in the 0.1-1 cm(2)/Vs range. Although these values represent the best case, they still pose a severe limitation for downscaling the channel lengths below a few micrometers, necessary for increasing the device switching speed. Moreover, techniques to lower contact resistances have been often developed on a case-by-case basis, depending on the materials, architecture and processing techniques. The lack of a standard strategy has hampered the progress of the field for a long time. Only recently, as the understanding of the rather complex physical processes at the metal/semiconductor interfaces has improved, more general approaches, with a validity that extends to several materials, are being proposed and successfully tested in the literature. Only a combined scientific and technological effort, on the one side to fully understand contact phenomena and on the other to completely master the tailoring of interfaces, will enable the development of advanced organic electronics applications and their widespread adoption in low-cost, large-area printed circuits.

2D-Crystal-Based Functional Inks

Abstract: The possibility to produce and process graphene, related 2D crystals, and heterostructures in the liquid phase makes them promising materials for an ever-growing class of applications as composite materials, sensors, in flexible optoelectronics, and energy storage and conversion. In particular, the ability to formulate functional inks with on-demand rheological and morphological properties, i.e., lateral size and thickness of the dispersed 2D crystals, is a step forward toward the development of industrial-scale, reliable, inexpensive printing/coating processes, a boost for the full exploitation of such nanomaterials. Here, the exfoliation strategies of graphite and other layered crystals are reviewed, along with the advances in the sorting of lateral size and thickness of the exfoliated sheets together with the formulation of functional inks and the current development of printing/coating processes of interest for the realization of 2D-crystal-based devices.

The development of flexible integrated circuits based on thin-film transistors

Abstract: The use of thin-film transistors in liquid-crystal display applications was commercialized about 30 years ago. The key advantages of thin-film transistor technologies compared with traditional silicon complementary metal–oxide–semiconductor(CMOS) transistors are their ability to be manufactured on large substrates at low-cost per unit area and at low processing temperatures, which allows them to be directly integrated onto a variety of flexible substrates. Here, I discuss the potential of thin-film transistor technologies in the development of low-cost, flexible integrated circuits for applications beyond flat-panel displays, including the Internet of Things and lightweight wearable electronics. Focusing on the relatively mature thin-film transistor technologies that are available in semiconductor fabrication plants today, the different technologies are evaluated in terms of their potential circuit applications and the implications they will have in the design of integrated circuits, from basic logic gates to more complex digital and analogue systems. I also discuss microprocessors and non-silicon, near-field communication tags that can communicate with smartphones, and I propose the concept of a Moore’s law for flexible electronics. This Perspective discusses the potential of thin-film transistor technologies in the development of low-cost, flexible integrated circuits, evaluating the more mature technologies available today in terms of their potential circuit applications and the implications they will have in the design of integrated circuits.

New insights and perspectives into biological materials for flexible electronics

Abstract: Biological materials have robust hierarchical structures capable of specialized functions and the incorporation of natural biologically active components, which have been finely tuned through millions of years of evolution. These highly efficient architectural designs afford remarkable transport and mechanical properties, which render them attractive candidates for flexible electronic sensing technologies. This review provides a comprehensive overview of the fundamental aspects and applications of biological materials for flexible electronic devices and discusses various classes of biological materials by describing their unique structures and functions. We discuss the effect of the biological activity of biological materials on the improved properties in detail, because this effect overcomes the limited bioavailability and restricted morphology of materials generally encountered in traditional flexible electronic devices. We also summarize various approaches for the design and functionalization of natural materials and their applications in flexible electronic devices for use in biomedical, electron, energy, environmental and optical fields. Finally, we provide new insights and perspectives to further describe trends for future generations of biological materials, which are likely to be critical components (building blocks or elements) in future flexible electronics.