{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,23]],"date-time":"2026-04-23T03:45:19Z","timestamp":1776915919969,"version":"3.51.2"},"reference-count":99,"publisher":"MDPI AG","issue":"4","license":[{"start":{"date-parts":[[2021,2,16]],"date-time":"2021-02-16T00:00:00Z","timestamp":1613433600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001691","name":"Japan Society for the Promotion of Science","doi-asserted-by":"publisher","award":["16H06292"],"award-info":[{"award-number":["16H06292"]}],"id":[{"id":"10.13039\/501100001691","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100002241","name":"Japan Science and Technology Agency","doi-asserted-by":"publisher","award":["JPMJMI17F2"],"award-info":[{"award-number":["JPMJMI17F2"]}],"id":[{"id":"10.13039\/501100002241","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100002241","name":"Japan Science and Technology Agency","doi-asserted-by":"publisher","award":["JPMJCR1534"],"award-info":[{"award-number":["JPMJCR1534"]}],"id":[{"id":"10.13039\/501100002241","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100002241","name":"Japan Science and Technology Agency","doi-asserted-by":"publisher","award":["JST Industry-Academia Collaborative R&D"],"award-info":[{"award-number":["JST Industry-Academia Collaborative R&D"]}],"id":[{"id":"10.13039\/501100002241","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>A compact source is important for various applications utilizing terahertz (THz) waves. In this paper, the recent progress in resonant-tunneling diode (RTD) THz oscillators, which are compact semiconductor THz sources, is reviewed, including principles and characteristics of oscillation, studies addressing high-frequency and high output power, a structure which can easily be fabricated, frequency tuning, spectral narrowing, different polarizations, and select applications. At present, fundamental oscillation up to 1.98 THz and output power of 0.7 mW at 1 THz by a large-scale array have been reported. For high-frequency and high output power, structures integrated with cylindrical and rectangular cavities have been proposed. Using oscillators integrated with varactor diodes and their arrays, wide electrical tuning of 400\u2013900 GHz has been demonstrated. For spectral narrowing, a line width as narrow as 1 Hz has been obtained, through use of a phase-locked loop system with a frequency-tunable oscillator. Basic research for various applications\u2014including imaging, spectroscopy, high-capacity wireless communication, and radar systems\u2014of RTD oscillators has been carried out. Some recent results relating to these applications are discussed.<\/jats:p>","DOI":"10.3390\/s21041384","type":"journal-article","created":{"date-parts":[[2021,2,16]],"date-time":"2021-02-16T22:13:38Z","timestamp":1613513618000},"page":"1384","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":131,"title":["Terahertz Emitter Using Resonant-Tunneling Diode and Applications"],"prefix":"10.3390","volume":"21","author":[{"given":"Masahiro","family":"Asada","sequence":"first","affiliation":[{"name":"Institute of Innovative Research, Tokyo Institute of Technology, Tokyo 152-8552, Japan"}]},{"given":"Safumi","family":"Suzuki","sequence":"additional","affiliation":[{"name":"Department of Electrical and Electronic Engineering, Tokyo Institute of Technology, Tokyo 152-8552, Japan"}]}],"member":"1968","published-online":{"date-parts":[[2021,2,16]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"97","DOI":"10.1038\/nphoton.2007.3","article-title":"Cutting-edge terahertz technology","volume":"1","author":"Tonouchi","year":"2007","journal-title":"Nat. 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