Diamond semiconductor technology for RF device applications

This paper presents a comprehensive review of diamond electronics from the RF perspective. Our aim was to find and present the potential, limitations and current status of diamond semiconductor devices as well as to investigate its suitability for RF device applications. While doing this, we briefly analysed the physics and chemistry of CVD diamond process for a better understanding of the reasons for the technological challenges of diamond material. This leads to Figure of Merit definitions which forms the basis for a technology choice in an RF device/system (such as transceiver or receiver) structure. Based on our literature survey, we concluded that, despite the technological challenges and few mentioned examples, diamond can seriously be considered as a base material for RF electronics, especially RF power circuits, where the important parameters are high speed, high power density, efficient thermal management and low signal loss in high power/frequencies. Simulation and experimental results are highly regarded for the surface acoustic wave (SAW) and field emission (FE) devices which already occupies space in the RF market and are likely to replace their conventional counterparts. Field effect transistors (FETs) are the most promising active devices and extremely high power densities are extracted (up to 30 W/mm). By the surface channel FET approach 81 GHz operation is developed. Bipolar devices are also promising if the deep doping problem can be solved for operation at room temperature. Pressure, thermal, chemical and acceleration sensors have already been demonstrated using micromachining/MEMS approach, but need more experimental results to better exploit thermal, physical/chemical and electronic properties of diamond

Diamond microelectronic gas sensor for detection of benzene and toluene

We have applied diamond chemical sensor to detect benzene (C6H6) and toluene (C7H8), volatile organic compounds and possible indication of environmental hazard and petroleum in soil/subsoil. Steady-state and transient responses of the sensor for both gases have been studied. These studies have shown that the sensor shows a large sensitivity, fast response, high selectivity, wider dynamic range, repeatable/reproducible response for benzene and toluene gases. The detection mechanisms of the sensor for both gases have been analyzed and models have been developed. Activation energy analysis of the sensor for both gases resulted in a very small values, confirming fast response and high sensitivity. Furthermore, the effects of structural properties of the sensor and temperature on gas sensing performance have been studied and a structurally optimum sensor has been presented in this study

PECVD diamond-based high performance power diodes

In this study, we have designed, fabricated, characterized, and analyzed plasma-enhanced chemical vapor deposition (PECVD) diamond-based Schottky diodes for high power electronics applications. We have elaborated four critical issues in the synthetic-diamond semiconductor technology: 1) growth, 2) doping, 3) Schottky contact, and 4) different device structures in order to achieve better performance parameters. We have obtained 500 V of breakdown voltage on one device and 100 A/cm/sup 2/ of current density on another device, optimized for different applications. These values are among the highest reported with the polycrystalline diamond-based devices. We have utilized different fabrication techniques for the growth of PECVD-diamond, different metals as a Schottky contact on diamond film and also optimized structural parameters such as diamond film thickness and doping concentration in order to achieve a high-performance power diodes. Analysis of the current conduction mechanisms of these devices in this study revealed a space-charge-limited current conduction mechanism in the forward bias region while thermionic field emission controlled current conduction mechanism in the reverse bias region. Performance parameters such as forward voltage drop, barrier height, and current density were analyzed as a function of temperature and type of metal Schottky contacts

Carbon-derived micro- and nanostructures for chemical sensing

Carbon-derived micro- and nanostructures for chemical sensing in air and liquid environments have been developed. Gas sensing rectifiers comprised of micro-electrodes on diamond layers for detection of H/sub 2/, O/sub 2/, CO, and hydrocarbon gases have shown high sensitivity and fast response time over a very wide temperature range (>600/spl deg/C). Detection mechanisms of these microsensors have also been studied. A novel microelectronic gas sensor utilizing carbon nanotubes for hydrogen detection has also been developed. The sensor exhibits diode behavior at room temperature with drastic current changes in the presence of hydrogen. Also, diamond microelectrode arrays for electrochemical sensing in liquid media have been achieved and exhibited higher sensitivity than the conventional planar diamond film and other microprobes. Carbon-derived structures have broad practical applications for chemical sensing and have been demonstrated to operate at temperature, dynamic range, sensitivity, and radiation with far better performance than those based on silicon and other materials

Mitochondria and Reactive Oxygen Species in Aging and Age-Related Diseases

Aging has been linked to several degenerative processes that, through the accumulation of molecular and cellular damage, can progressively lead to cell dysfunction and organ failure. Human aging is linked with a higher risk for individuals to develop cancer, neurodegenerative, cardiovascular, and metabolic disorders. The understanding of the molecular basis of aging and associated diseases has been one major challenge of scientific research over the last decades. Mitochondria, the center of oxidative metabolism and principal site of reactive oxygen species (ROS) production, are crucial both in health and in pathogenesis of many diseases. Redox signaling is important for the modulation of cell functions and several studies indicate a dual role for ROS in cell physiology. In fact, high concentrations of ROS are pathogenic and can cause severe damage to cell and organelle membranes, DNA, and proteins. On the other hand, moderate amounts of ROS are essential for the maintenance of several biological processes, including gene expression. In this review, we provide an update regarding the key roles of ROS–mitochondria cross talk in different fundamental physiological or pathological situations accompanying aging and highlighting that mitochondrial ROS may be a decisive target in clinical practice