{"id":1964,"date":"2010-07-13T16:54:06","date_gmt":"2010-07-13T20:54:06","guid":{"rendered":"https:\/\/wpmu2.mit.local\/?p=1964"},"modified":"2010-07-13T16:54:06","modified_gmt":"2010-07-13T20:54:06","slug":"nano-enabled-cold-cathodes-for-high-frequency-vacuum-amplifiers","status":"publish","type":"post","link":"https:\/\/wpmu2.mit.local\/nano-enabled-cold-cathodes-for-high-frequency-vacuum-amplifiers\/","title":{"rendered":"Nano-enabled Cold Cathodes for High-Frequency Vacuum Amplifiers"},"content":{"rendered":"<div class=\"page-restrict-output\"><p>The continued demand for very wideband communications and the increased need for wireless channel capacity have led to the exploration of new regions of operation.\u00a0 In particular, the broad minimum in atmospheric absorption that occurs between 200GHz and 300 GHz is largely under-utilized because of a lack of high-bandwidth and high-power amplifiers in this frequency range that are compact and efficient.\u00a0 The core of the vacuum amplifier technology that we propose is a field-emitter-array (FEA) cathode that implements individual emitter ballasting to mitigate the effects of the emitter tip radii spread in the performance of the cathode.\u00a0 Specifically, emission currents are extremely sensitive to tip radii variation due to the exponential dependence of the emitted current on the tip radius of the emitter<sup>&nbsp;[<a href=\"#footnote_0_1964\" id=\"identifier_0_1964\" class=\"footnote-link footnote-identifier-link\" title=\"R. Gomer, Field Emission and Field Ionization, American Institute of Physics, New York, 1961.\">1<\/a>]<\/sup>. Unfortunately, tip radii distribution in FEAs has long tails<sup>&nbsp;[<a href=\"#footnote_1_1964\" id=\"identifier_1_1964\" class=\"footnote-link footnote-identifier-link\" title=\"M. Ding, G. Sha, and A. I. Akinwande, &ldquo;Silicon Field Emission Arrays With Atomically Sharp Tips: Turn-On Voltage and the Effect of Tip Radius Distribution,&rdquo; IEEE Transactions on Electron Devices, vol 49, No. 12, Dec. 2002, pp. 2333 &ndash; 2342.\">2<\/a>]<\/sup>.\u00a0 By limiting the current from each emitter, it is possible to prevent destructive emission from the sharper tips while allowing higher overall current emission because of the emission of the duller tips.\u00a0 Ungated FETs are ideal to individually ballast each emitter because they behave like current sources and can be fabricated with high emitter density FEAs<sup>&nbsp;[<a href=\"#footnote_2_1964\" id=\"identifier_2_1964\" class=\"footnote-link footnote-identifier-link\" title=\"L. F. Vel&aacute;squez-Garc&iacute;a, B. Adeoti, Y. Niu, and A. I. Akinwande, &ldquo;Uniform High Current Field Emission of Electrons from Si and CNF FEAs Individually Controlled by Si Pillar Ungated FETs,&rdquo; Technical Digest IEEE International Electron Device Meeting, Washington DC, USA, Dec. 2007, pp. 599 &ndash; 602.\">3<\/a>]<\/sup>.\u00a0 We have developed the technology for massive FEAs that are individually ballasted using vertical ungated FETs (Figure 1). We have demonstrated fully-controlled electron emission with currents as high as 0.6 A and with no damage to the cathode (Figure 2).<\/p>\n\n\t\t<style type=\"text\/css\">\n\t\t\t#gallery-1 {\n\t\t\t\tmargin: auto;\n\t\t\t}\n\t\t\t#gallery-1 .gallery-item {\n\t\t\t\tfloat: left;\n\t\t\t\tmargin-top: 10px;\n\t\t\t\ttext-align: center;\n\t\t\t\twidth: 50%;\n\t\t\t}\n\t\t\t#gallery-1 img {\n\t\t\t\tborder: 2px solid #cfcfcf;\n\t\t\t}\n\t\t\t#gallery-1 .gallery-caption {\n\t\t\t\tmargin-left: 0;\n\t\t\t}\n\t\t\t\/* see gallery_shortcode() in wp-includes\/media.php *\/\n\t\t<\/style>\n\t\t<div id='gallery-1' class='gallery galleryid-1964 gallery-columns-2 gallery-size-medium'><dl class='gallery-item'>\n\t\t\t<dt class='gallery-icon landscape'>\n\t\t\t\t<a href='https:\/\/wpmu2.mit.local\/wp-content\/uploads\/2010\/07\/Velasquez_Cathode_2010_Fig1.jpg'><img width=\"300\" height=\"183\" src=\"https:\/\/wpmu2.mit.local\/wp-content\/uploads\/2010\/07\/Velasquez_Cathode_2010_Fig1-300x183.jpg\" class=\"attachment-medium size-medium\" alt=\"Figure 1\" loading=\"lazy\" aria-describedby=\"gallery-1-1965\" srcset=\"https:\/\/wpmu2.mit.local\/wp-content\/uploads\/2010\/07\/Velasquez_Cathode_2010_Fig1-300x183.jpg 300w, https:\/\/wpmu2.mit.local\/wp-content\/uploads\/2010\/07\/Velasquez_Cathode_2010_Fig1.jpg 600w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a>\n\t\t\t<\/dt>\n\t\t\t\t<dd class='wp-caption-text gallery-caption' id='gallery-1-1965'>\n\t\t\t\tFigure 1: A massive array (1-million units in 1 cm2) of individually ballasted field-emitters using very high-aspect-ratio vertical ungated FETs.\n\t\t\t\t<\/dd><\/dl><dl class='gallery-item'>\n\t\t\t<dt class='gallery-icon landscape'>\n\t\t\t\t<a href='https:\/\/wpmu2.mit.local\/wp-content\/uploads\/2010\/07\/Velasquez_Cathode_2010_Fig2.jpg'><img width=\"300\" height=\"205\" src=\"https:\/\/wpmu2.mit.local\/wp-content\/uploads\/2010\/07\/Velasquez_Cathode_2010_Fig2-300x205.jpg\" class=\"attachment-medium size-medium\" alt=\"Figure 2\" loading=\"lazy\" aria-describedby=\"gallery-1-1966\" srcset=\"https:\/\/wpmu2.mit.local\/wp-content\/uploads\/2010\/07\/Velasquez_Cathode_2010_Fig2-300x205.jpg 300w, https:\/\/wpmu2.mit.local\/wp-content\/uploads\/2010\/07\/Velasquez_Cathode_2010_Fig2.jpg 600w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a>\n\t\t\t<\/dt>\n\t\t\t\t<dd class='wp-caption-text gallery-caption' id='gallery-1-1966'>\n\t\t\t\tFigure 2: Fowler-Nordheim (FN) plot of the data from an individually ballasted FEA cathode made of silicon with a resistivity equal to 178 \u2126.cm. The data of an unballasted FEA describes a straight line in the Fn plot. The bending of the curve for high voltages is direct evidence of current control.\n\t\t\t\t<\/dd><\/dl><br style=\"clear: both\" \/>\n\t\t<\/div>\n\n<hr>\r\nReferences<ol class=\"footnotes\"><li id=\"footnote_0_1964\" class=\"footnote\">R. Gomer, <em>Field Emission and Field Ionization<\/em>, American Institute of Physics, New York, 1961. [<a href=\"#identifier_0_1964\" class=\"footnote-link footnote-back-link\">&#8617;<\/a>]<\/li><li id=\"footnote_1_1964\" class=\"footnote\">M. Ding, G. Sha, and A. I. Akinwande, \u201cSilicon Field Emission Arrays With Atomically Sharp Tips: Turn-On Voltage and the Effect of Tip Radius Distribution,\u201d <em>IEEE Transactions on Electron Devices<\/em>, vol 49, No. 12, Dec. 2002, pp. 2333 \u2013 2342. [<a href=\"#identifier_1_1964\" class=\"footnote-link footnote-back-link\">&#8617;<\/a>]<\/li><li id=\"footnote_2_1964\" class=\"footnote\">L. F. Vel\u00e1squez-Garc\u00eda, B. Adeoti, Y. Niu, and A. I. Akinwande, \u201cUniform High Current Field Emission of Electrons from Si and CNF FEAs Individually Controlled by Si Pillar Ungated FETs,\u201d <em>Technical Digest IEEE International Electron Device Meeting<\/em>, Washington DC, USA, Dec. 2007, pp. 599 \u2013 602. [<a href=\"#identifier_2_1964\" class=\"footnote-link footnote-back-link\">&#8617;<\/a>]<\/li><\/ol><\/div>","protected":false},"excerpt":{"rendered":"<div class=\"page-restrict-output\"><p>The continued demand for very wideband communications and the increased need for wireless channel capacity have led to the exploration&#8230;<\/p>\n<\/div>","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[11],"tags":[4064,71,4202],"_links":{"self":[{"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/posts\/1964"}],"collection":[{"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/comments?post=1964"}],"version-history":[{"count":2,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/posts\/1964\/revisions"}],"predecessor-version":[{"id":1968,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/posts\/1964\/revisions\/1968"}],"wp:attachment":[{"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/media?parent=1964"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/categories?post=1964"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/tags?post=1964"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}