764 IEEE ELECTRON DEVICE LETTERS, VOL. 31, NO. 7, JULY 2010 FinFACT—Fin Flip-Flop Actuated Channel Transistor Jin-Woo Han, Jae-Hyuk Ahn, and Yang-Kyu Choi Abstract—Nanoelectromechanical system technology is applied for a complementary metal–oxide–semiconductor device to pro- vide a novel function. Based on an independently controlled double-gate FinFET, the fin of the proposed transistor is sus- pended by replacing the solid-state gate dielectric with a gas-state gate dielectric, which enables flip-flop actuation of the fin. Flip-flop actuation of the fin is accomplished via electrostatic force from two separated gates, representing a binary mechanical state of the fin. It is anticipated that the virtues of the reported device can be exploited in transformable circuit units and digital memory transistors. Index Terms—Complementary metal–oxide–semiconductor, Fin Flip-flop Actuated Channel Transistor (FinFACT), indepen- dently controlled double-gate FinFET, nanoelectromechanical system (NEMS). I. I NTRODUCTION O VER the course of the past three decades, unprecedented evolution of information technology (IT) has dramati- cally changed our lifestyles. A key element of the IT revolu- tion has been the continuing advancement of semiconductor technology based on metal–oxide–semiconductor field-effect transistors (MOSFETs). The main driving force of semicon- ductor development has been geometric scaling, which leads to reduced cost, improved microprocessor performance, and increased memory density. However, the revenue obtained by the scaling is increasingly diminished as MOSFET approaches the end point of the International Technology Roadmap for Semiconductors [1]. Thus, a novel paradigm is indispensable to ensure that silicon technology remains competitive. Since the invention of the thermal oxidation process, the SiO 2 gate oxide that insulates the gate electrode and channel has played a vital role in the development of MOSFETs. The silicon community has considered the replacement of SiO 2 to be impossible. As the gate electrode and channel are in a separated state, however, more functionalities and benefits that have been unrealizable thus far can already be attained. In a cantilever-type nanoelectromechanical system (NEMS) switch, for example, the cantilever beam (channel) [2], [3] is suspended over the drain electrode, and the cantilever switches on/off through the electrostatic force between the gate and the Manuscript received January 20, 2010; revised April 6, 2010; accepted April 7, 2010. Date of publication June 21, 2010; date of current version June 25, 2010. This work was supported in part by the Nano R&D program through the National Research Foundation of Korea funded by the Ministry of Education, Science and Technology under Grant 2009-0082583 and in part by the National Research Foundation of Korea funded by the Korean govern- ment under Grant 2009-0083079. The review of this letter was arranged by Editor J. Cai. The authors are with the Department of Electrical Engineering, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea (e-mail: ykchoi@ee.kaist.ac.kr). Color versions of one or more of the figures in this letter are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/LED.2010.2048093 Fig. 1. Schematic and SEM images of the FinFACT. (a) Schematic of a flipped or flopped state for the FinFACT and the tilted SEM image of (b) the initial straightened state, (c) the flipped or pull-up state, and (d) the flopped or pull- down state. beam. Thus, the standby leakage current approaches zero as the channel and the drain electrode are physically separated. The current flows through the contact between the cantilever and the drain electrode, and Joule heating can cause permanent stiction. Additionally, the suspended-gate MOSFET, another type of NEMS transistor, actuates its movable gate, enabling various applications such as low-power logic and memory [4], [5]. The suspended gate is attached to the substrate by electrostatic attraction force; however, because detachment of the gate from the substrate, namely, in what is known as a pull- off, relies solely on the mechanical restoration force of the gate, this aspect is difficult to control. This letter presents a novel 3-D transistor motivated by the independently controlled double-gate FinFET [6], [7]. The proposed device structure is similar to that of an independently controlled double-gate FinFET, except that the gate oxide is re- placed with an air gap. Thus, the structure features a suspended and movable channel (fin), as shown in Fig. 1(a). Prior research reported a movable-body (MB) microelectromechanical FET [8]. Its construction is similar to the present structure. The prior design used a movable beam, 50 μm, 4-μm width, and 180-nm air-gap width; however, the present structure is scaled down by roughly a hundred times, with an MB (fin) that is 500 nm long and 30 nm wide and with an air-gap width that is 10 nm. In the previous design [8], the spring force of the MB was too strong to retain a mechanically bent state. Therefore, the resonance of the body and possible data transmission applications were studied. In contrast, various spring forces are achieved, because the different fin widths can be defined by photolithography in this letter. A narrow fin, i.e., a low spring force, can hold a mechanically bent state; hence, it is likely feasible for memory and transformable logic devices. As the fin is actuated between flipped and flopped states, the proposed transistor is termed Fin Flip-flop Actuated Channel 0741-3106/$26.00 © 2010 IEEE Authorized licensed use limited to: Korea Advanced Institute of Science and Technology. Downloaded on June 28,2010 at 09:32:50 UTC from IEEE Xplore. Restrictions apply.