An intrinsically coupled HBT/RTD device enabling an adjustable peak-current-density

For the two terminal Resonant-Tunneling-Diode (RTD) the device functionality is dominated by the epitaxially grown layer sequence consisting of very thin layers, i.e. a variation of the barrier layer thickness shows an exponential impact on the RTD peak-current density. This is a major drawback for the use of RTD devices for circuit applications and has to be compensated by novel circuit architectures like the MOnostable BIstable Logic Element (MOBILE). The operation principle of a MOBILE is based on the comparison of the absolute RTD peak-current scaled by the RTD device area. By this method the exponential impact of epitaxial growth variations are reduced to less critical lateral scaling rules. But the design of programmable and/or multiple-valued logic functions is inhibited because the current is defined by the RTD area, only. In this work a novel HBT/RTD device is presented with a controllable peak-current density S/sub Peak/. The proposed intrinsically coupled HBT/RTD device enables a direct adjustment of the peak-current-density by the B/E input voltage and simplifies the MOBILE circuit topology. The RTD layer sequence is integrated inside the collector of the HBT directly at the B/C junction. By this way the charge accumulation n/sub BC/ at the RTD structure can be controlled by the bipolar effect which results in an intrinsically coupled device structure (n/sub BC/=f(V/sub BE/). The applicability of the RTD/HBT device combinations to circuit concepts based on programmable MOBILE threshold and Boolean gates and multiple-valued-logic is discussed. For multiple-valued-logic applications and programmable XNOR, XOR, NAND, NOR logic gates the achieved low RTD peak-voltages are of major importance while enabling level compatibility.