100 GHz Operation of a Resonant Tunneling Logic Gate MOBILE Having a Symmetric Configuration Koichi Maezawa 1 , Hirokazu Sugiyama 1 , Shigeru Kishimoto 1,2 and Takashi Mizutani 1,3 1 Graduate School of Engineering, Nagoya University 2 Venture Business Laboratory, Nagoya University 3 Institute for Advanced Research, Nagoya University Furo-cho, Chikusa-ku, Nagoya-shi 464-8603, Japan Tel& Fax:+81-52-789-5455 maezawa@ieee.org ABSTRACT Resonant tunneling logic gate MOBILE (Monostable-Bistable Transition Logic Element) is a high-speed logic gate exploiting the negative differential resistance of resonant tunneling diodes (RTDs). In this paper, we propose a novel variation of the MOBILE, called a Sym- metric MOBILE (SMOBILE), which is promising for ultrahigh frequency operation, since it can operate at double-clock rate. 100 GHz operation of the SMOBILE is demonstrated with complementary 50 GHz clocks for circuits fabricated on InP substrates. I Introduction Resonant tunneling logic gate MOBILE (Monostable- Bistable Transition Logic Element) is a high-speed logic gate exploiting the negative differential resistance of res- onant tunneling diodes (RTDs)[1, 2]. The MOBILE fea- tures edge-trigger and latching function as well as short switching time. Various high speed ICs have been already demonstrated using MOBILEs, which includes DFF and ADCs[3, 4, 5, 6, 7, 8, 12]. In this paper, we propose a novel variation of the MOBILE, called a Symmetric MOBILE (SMOBILE), which can operate at double-clock rate. 100 GHz op- eration of the SMOBILE is demonstrated with comple- mentary 50 GHz clocks for circuits fabricated on InP sub- strates. II Operating principle of MOBILE In this section, we briefly explain the operating princi- ple of the MOBILE and some difficulties in designing MOBILE operating at ultrahigh frequency range (≥100 GHz). These clarify the features of the SMOBLE. There are three aspects to the operating principle of the MOBILE: 1) to employ the monostable-to-bistable transition of a circuit consisting of two NDR devices con- nected serially, 2) to drive this circuit by oscillating the bias voltage to produce the transition, and 3) the NDR device(s) having the third terminal to modulate their peak currents. Figure 1 shows the load curves for the cir- cuit. As shown in Fig. 1 (a), the number of stable points is one when the bias voltage is smaller than twice the peak voltage (2V p ). This stable point splits into two branches, S1 and S2 (Fig. 1 (b)), when the bias voltage increases through 2V p . A small difference in the peak current be- Current Fig. 1: Operating principle of the MOBILE tween the two NDR devices determines the circuit’s state after the transition. For example, a larger peak current in the driver device results in the stable point S1 (dotted lines). With the oscillatory varying of the bias voltage, the circuit forms a logic gate. This oscillatory bias volt- age works as a clock. To modulate the effective peak current a parallel circuit of an RTD and a FET is used for the NDR device. This mode of operation has several advantages. For example, edge-trigger and latching func- tion are unique characteristics of the MOBILE, and can be applied for several circuits. The MOBILE has a potential for ultrahigh-speed switching exploiting the high-current density and low in- trinsic capacitance of RTDs. However, there are some 46 MB1.5 12:15 pm – 12:30 pm 0-7803-9558-1/06/$20.00 ©2006 IEEE