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Design007-Dec2020

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84 DESIGN007 MAGAZINE I DECEMBER 2020 vendors selling thin 2-mil FR-4 cores with the dendrites facing out to increase voltage rating, where the PI film has a much higher dielec- tric rating and no need for outward-facing den- drites. The thin FR-4 cores are dry-filmed, imaged, developed, and then etched as normal, result- ing in a power ground plane, which is then laminated into a normal multilayer. The bur- ied capacitance is spread out evenly between the planes. The FR-4 or PI capacitive layer is very effective in suppressing spikes right at the source. The further away the capacitor is from the power pin of the chip, the less effective it is in suppressing the spikes or noise. Bur- ied capacitive FR-4 or PI laminate cores are an easy, low-cost, and effective solution to reduce power plane spikes and noise. FLEX007 John Talbot is president of Tramonto Circuits. To read past columns or contact Talbot, click here. Long known as the hardest of all natural materials, diamonds are also exceptional thermal conductors and electrical insulators. Now, researchers have discovered a way to tweak tiny needles of diamond in a controlled way to transform their electronic properties, dialing them from insulating, through semiconducting, all the way to highly conductive, or metallic. This can be induced dynamically and reversed at will, with no degradation of the diamond material. Their findings are reported this week in the Proceed- ings of the National Academy of Sciences. The paper is by MIT Professor Ju Li and graduate student Zhe Shi; Principal Research Scientist Ming Dao; Professor Subra Suresh, who is president of Nanyang Technological University in Singapore as well as former dean of engi- neering and Vannevar Bush Professor Emeritus at MIT; and Evgenii Tsymbalov and Alexander Shapeev at the Skolkovo Institute of Science and Technology in Moscow. The concept of straining a semiconductor material such as silicon to improve its performance found appli- cations in the microelectronics industry more than two decades ago. In a major advance in 2018, a team led by Suresh, Dao, and Yang Lu from the City University of Hong Kong showed that tiny needles of diamond, just a few hundred nanometers across, could be bent without fracture at room temperature to large strains. Key to this work is a property known as bandgap, which essentially determines how readily electrons can move through a material. In their latest simulations, the researchers show that diamond's bandgap can be gradually, continuously, and revers- ibly changed, providing a wide range of electrical properties, from insulator through semiconductor to metal. This early-stage proof-of-concept work is not yet at the point where they can begin to design practical devices, the researchers say, but with the ongoing research they expect that practical applications could be possible, partly because of promising work being done around the world on the growth of homogeneous diamond materials. (Source: MIT News Office) Turning Diamonds Into Metal

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