Superconducting Electronics

Superconducting electronics is considered a low-power alternative to traditional CMOS technology due to the ultrafast and low-power switching of the superconducting devices. In contrast to semiconductor circuits, superconducting digital circuits use magnetic flux quanta, also known as Single Flux Quanta (SFQ), to encode, process, and transport information.

Rapid Single Flux Quantum (RSFQ) logic is one of the first logic families that was proposed based on SFQ pulses. In this logic family, digital one and zero are encoded by the presence or absence of an SFQ pulse. RSFQ circuits in the current technology can work at a few tens of gigahertz. For example, a flip-flop has been demonstrated that operated at 750 GHz and circuits like microprocessors and analog-to-digital converters have been demonstrated for commercial and military applications.

Advantages of RSFQ:

* Quantum accurate representation of the digital information in the form of single quanta

* Extremely fast switching speed

* Lossless interconnect that allows long-distance data transmission at the speed of light

A major drawback of the conventional RSFQ logic is the static power dissipation in the bias resistors which can be a problem for larger circuits. As a result, different families of logic circuits based on SFQ pulses are currently being investigated, including ERSFQ, eSFQ, RQL, LV-RSFQ, and AQFP logic families.

I have designed and simulated a few basic building blocks using the RSFQ logic family, performed DRC/LVS for some components, and hope to go through all the steps necessary to design a chip using open-source tools.

Quantum-dot Cellular Automata

Quantum-dot cellular automata (QCA) is an emerging technology for building digital circuits at the nano-scale. It is considered an alternative to widely used complementary metal oxide semiconductor (CMOS) technology because of its key features, which include low power operation, high density, and high operating frequency. Unlike conventional logic circuits in which information is transferred by electrical current/voltage, QCA operates with the help of coulomb interaction between two adjacent QCA cells. A QCA cell is a set of four quantum-dots that are placed near the corners of a square. Due to the fact that clocking provides power and control of data flow in QCA, it is considered to be the backbone of QCA operation.

As part of my M.S. thesis:

• I proposed two new clocking schemes for QCA circuits: Ripple clock scheme and an enhanced ripple clock scheme.

• Designed and simulated a variety of digital circuits using proposed clock schemes.