Tunnel Diode/Transistor Integrated Circuits

As the minimum feature sizes in transistor technology are reached,circuit performance may also saturate. For this reason, it isimportant to consider new and extraordinary ways to extend theperformance of circuits. Integrated tunnel diodes enable a varietyof design alternatives for signal processing, analog-to-digitalconversion, communications, and memory. It is the goal of thiswork to analyze and explore the potential of tunneldiode/transistor (TDT) technology for increasing speed andreducing power dissipation beyond what can be achieved withtransistors alone.Circuit design requires accurate device models. In this work, aphysics-based small-signal equivalent circuit model for theresonant tunneling diode (RTD) has been developed, which unifiesprevious models by Brown et al. for quantum inductance andby Lake and Yang for quantum capacitance, and provides analyticexpressions for both the quantum inductance and quantumcapacitance. Further, two new TDT circuits: a TDT differentialcomparator and a TDT frequency translator have been invented.The TDT differential comparator is of special interest for use indirect digital synthesis applications. Circuit simulation shows apower dissipation of 3.5 mW/latch at 100-GHz clock frequency with60-dBc spur-free dynamic range (SFDR) can be obtained in the TDTcomparator. In comparison with the conventional transistorapproach, power is reduced by approximately 1.6x at the same speedand SFDR.The TDT frequency translator is of special interest for use incommunication systems for upconverting digital signals. Thecircuit consists of a transistor, a tunnel diode, and an inductor.The transistor provides input-output isolation and power gainrelative to prior art at the expense of the immunity to the inputvoltage variation.A scalable self-aligned contact process for fabrication of the TDTcircuits has been developed using InP-based RTD and doubleheterojunction bipolar transistor (DHBT). This novel approach usessilicon nitride sidewalls and a benzocyclobutene (BCB) etchback toform self-aligned emitter-base contacts. InP/InGaAs DHBTs havebeen fabricated and the test results demonstrate the feasibilityof this sidewall and etchback process. AlAs/InGaAs/InAs RTDs werealso fabricated and demonstrated a peak current density of 1.8mA/um^2 and a peak-to-valley current ratio of 1.8.