Circuits and Systems, 2013, 4, 157-164 http://dx.doi.org/10.4236/cs.2013.42021 Published Online April 2013 (http://www.scirp.org/journal/cs) Millimeter Wave Ring Oscillator Using Carbon Nano-Tube Field Effect Transistor in 150 GHz and Beyond Davood Fathi * , Baback Beig Mohammadi School of Electrical and Computer Engineering, Tarbiat Modares University (TMU), Tehran, Iran Email: * davfathi@modares.ac.ir Received January 10, 2013; revised February 10, 2013; accepted February 17, 2013 Copyright © 2013 Davood Fathi, Baback Beig Mohammadi. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ABSTRACT Carbon Nano-Tube Field Effect Transistors (CNTFETS) are the competitor of the conventional MOSFET technology due to their higher current drive capability, ballistic transport, lesser power delay product, higher thermal stability, and so on. Based on these promising properties of CNTFETs, a CNTFET-based millimeter wave ring oscillator operating around 150 GHz and beyond is introduced here in 32 nm technology node. To prevent overestimation, the CNT inter- connects between transistors are also included in simulation, which are assumed to be a single layer of ballistic metallic CNTs in parallel. For the sake of simplicity in RF design, the oscillator is based on CNTFET-based inverters. The in- verters with DC gain of 87.5 dB are achieved by proper design with the non-loaded delay around 0.6 ps, which is at least one order of magnitude better than the same 32 nm MOSFET-based inverters. The oscillator’s average power consumption is as low as 40 µW with the fundamental harmonic amplitude of around −6.5 dB. These values are, based on our knowledge, for the first time reported in the literature in CNTFET-based oscillator designs. Also, on the average, the performance of the designed oscillator is 5 - 6 times better than MOSFET-based designs. Keywords: CNTFET; CNT Interconnect; Millimeter Wave; Ring Oscillator 1. Introduction Carbon nanotubes (CNTs) have shown promising elec- trical and mechanical performance over the conventional materials used in semiconductor industry. Electrically, CNTs are divided into two major groups: metallic and semiconducting, based on their chirality [1]. The metallic CNTs are used as interconnect in the novel integration processes [2,3] and the semiconducting ones are used in the novel semiconductor devices, beyond the conven- tional silicon/GaAs based technologies, like Carbon Nano- Tube Field Effect Transistors (CNTFETs) [4]. The large mean free path and hence, the ballistic trans- port characteristic of CNTs [5] with high current density capability, combining with extraordinary mobility [6] and very low shot noise [7], leads to CNTFETs with accept- able and outstanding electrical characteristics like high transit and maximum frequency [8] and inherent linearity [9]. Here, we present a high performance, low power CN- TFET-based ring oscillator at 150 GHz and beyond with good THD. The amplitude of fundamental frequency of oscillation achieves around −6.5 dB which is to our knowledge 4 - 5 times better than the same MOSFET- based ring oscillators. The CNTFET used in this paper is a MOSFET-like CNTFET with gate length of 32 nm. In order to prevent overestimation of the ring oscillator per- formance, the CNT interconnects between CNTFETS are modeled and included in simulation, which have been arranged in a single layer of ballistic metallic CNTs. This paper is organized as follow. Section II includes explanations on the CNTFET and its model used in our simulations. In Section III we discuss the modeling of metallic CNTs as interconnects. CNT-based inverter de- sign and advantages over MOSFET-based inverters and its corresponding simulation results are represented in Section IV. Section V includes CNTFET-based ring os- cillator design and simulation results. Finally, Section VI concludes this paper. 2. CNTFET and Its Modeling There are several CNTFET models reported in literature [10-13]. The model used here is based on the [12,13]. * Corresponding author. Copyright © 2013 SciRes. CS