Vacuum, temperature, and time dependencies of field-emission current for RF-MEMS applications Kiyotaka Yamashita a, * , Winston Sun a , Benoit Charlot a , Kuniyuki Kakushima b , Hiroyuki Fujita a , Hiroshi Toshiyoshi a a IIS, University of Tokyo, 4-6-1 Komaba, Meguroku, Tokyo, 153-8505, Japan b Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, Japan Available online 8 February 2007 Abstract We propose to utilize the field-emission (FE) effect on a novel micro-machined device to modulate the incoming radio-frequency sig- nal for RF-MEMS (r adio-f requency m icro-e lectro-m echanical s ystem) applications. In this paper, we present some preliminary results such as pressure and temperature dependencies of the FE current. We also notice that by annealing the device inside the vacuum chamber at 200 °C for 20 min, large FE current (85 nA) at low voltage (3 V) can be produced. The leakage current was reduced by employing a silicon-on-insulator (SOI) wafer with thicker buried-oxide layer. Fabrication procedures and experimental results will be discussed. Ó 2007 Elsevier B.V. All rights reserved. Keywords: RF-MEMS; Field-emission; Vacuum micro-electronics 1. Introduction The information age has popularized the use of wireless devices from its rudimentary military and aerospace appli- cations to the nowadays commonly-used mobile phones. Other wireless applications such as radio frequency identi- fication (RFID) in security system, wireless LAN (local area network), embedded biomedical instrumentations, and ITS (intelligent transportation system) for worldwide land and sea navigation, etc. One of the ultimate goals of wireless technology is to establish the ubiquitous computer network. This requires further device miniaturization, higher precision in the frequency spectrum selectivity, and more effective packaging method to reduce production cost. Conventional RF-MEMS mechanical filters [1,2] utilize capacitive coupling for both excitation and detection. However, as the device downsizes, the rapidly diminishing capacitance reduces the signal-to-noise ratio and thus makes detection difficult. In addition, direct capacitive cou- pling often associate with undesirable issues such as imped- ance mismatch and small fan-out. A new signal detection method for very small mechanical displacement is needed. Recent vacuum micro-electronics achievements [3,4] on the FE effect provide many research opportunities to RF engineers. Micro or nano-mechanical resonators have the advantages of high Q-factor, batch fabrication capabilities, and well-established MEMS processes. We can foresee that as the micro-fabrication technologies advance, dimensions such as the FE tip radii and the emitter–collector gap will continue to decrease, which are essential factors to provide a reliable source of FE current. This work investigates the possibilities of signal detection on a RF-MEMS device embedded with micro or nano-resonator by adopting the FE effect and utilizing the micro-fabrication and vacuum micro-electronics technologies. 2. Field-emission for detecting oscillation The conceptual operation principle for our proposed device is illustrated in Fig. 1a. Frequency signal picked 0167-9317/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2007.01.185 * Corresponding author. E-mail address: kiyo@iis.u-tokyo.ac.jp (K. Yamashita). www.elsevier.com/locate/mee Microelectronic Engineering 84 (2007) 1345–1353