There are two approaches in high speed digital designs. One is the conventional approach using a CML/ECL scheme. But this approach has several problems for high speed operation. The Problems include speed limit of transistor, interconnection effect and large power consumption. To overcome these problems, an NDR(Negative Differential Resistance) approach using quantum devices has been investigated lately.
As a quantum device, RTD(Resonant Tunneling Diode) is selected for the NDR approach. RTDs have demonstrated extremely low switching time of 1.5 ps and the unique Negative Differential Resistance (NDR) characteristics based on quantum transport phenomena. Due to these features, the logic gates utilizing the NDR of RTDs have the advantages of low circuit complexity and low-power consumption with high speed operation. Therefore, these logic circuits have been widely investigated as a promising candidate for future high speed digital ICs. Among them, MOnostable-BIstable Logic transition Element (MOBILE) ICs, which consist of two resonant tunneling diodes in series and one 3-terminal device for current modulation, have been developed for high speed operation mainly based on the HEMT/RTD technology. However, HBTs, which have an advantage of enhancement-mode operation have not been widely used in MOBILE ICs compared with HEMT based technologies. So, MOBILE ICs using HBT/RTD technology are investigated in this thesis. Firstly, InP/InGaAs SHBT and RTD models for high speed digital circuit design have been successfully developed. Secondly, based on the small signal model of SHBT, gate delay of the conventional CML scheme is analyzed and confirmed by the fabricated 3-stage ring oscillator. Key parameters of gate delays are $C_{BCX}$, $C_{BE}$, $R_L$ and $R_B$. Lastly, the new high speed MOBILE ICs using an InP-based HBT/RTD integration technology are proposed and designed. Basic MOBILE, Current Mirror type MOBILE, Emitter Follower type MOBILE and Current Mode Logic type MOBILE are proposed. Among the proposed MOBILE ICs, the basic MOBILE ICs have been fabricated. The D-flip flop operation speed of the fabricated HBT/RTD MOBILE ICs has been confirmed up to 12.5 Gbps.
