First realization of the piezoelectronic stress-based transduction device.

We present the first realization of a monolithically integrated piezoelectronic transistor (PET), a new transduction-based computer switch which could potentially operate conventional computer logic at 1/50 the power requirements of current Si-based transistors (Chen 2014 Proc. IEEE ICICDT pp 1-4; Mamaluy et al 2014 Proc. IWCE pp 1-2). In PET operation, an input gate voltage expands a piezoelectric element (PE), transducing the input into a pressure pulse which compresses a piezoresistive element (PR). The PR resistance goes down, transducing the signal back to voltage and turning the switch 'on'. This transduction physics, in principle, allows fast, low-voltage operation. In this work, we address the processing challenges of integrating chemically incompatible PR and PE materials together within a surrounding cage against which the PR can be compressed. This proof-of-concept demonstration of a fully integrated, stand-alone PET device is a key step in the development path toward a fast, low-power very large scale integration technology.

It's time to reinvent the transistor!

A breakthrough in materials could refresh and sustain the information technology revolution.

Gating of a three-leg molecule.

We study the use of a simple three-leg molecule, triphenylene, as a transistor. This configuration allows increased voltage gain to be achieved. We analyze control of the transport between electrodes attached to two of the legs by a gate closely coupled electrostatically to the third leg, using self-consistent density functional calculations. In spite of the close coupling, the maximum voltage gain was less than unity, and this was attributed to efficient screening of the internal potential due to polarization of the molecular states. The transistor current vs. voltage characteristics were able to be reproduced using a simple electrostatic model.

The biphenyl molecule as a model transistor.

We study transport and charge control in a gated 4,4'-biphenyl diradical molecular transistor using self-consistent density-functional calculations. We track both electron-like and hole-like conduction and relate it to the field dependence of current-carrying pi-derived states. Owing to the coupling between the two benzene rings, the pi-states become segregated into extended, current-carrying states and localized states. Under application of the source/drain field, along the axis of the molecule, the localized pi-states become split, while the extended states become polarized and screen the field. The localized states act like isolated islands within the molecule--while they make a substantial contribution to the density of states, they make only a small contribution to transport.

An integrated logic circuit assembled on a single carbon nanotube.

Single-walled carbon nanotubes (SWCNTs) have been shown to exhibit excellent electrical properties, such as ballistic transport over several hundred nanometers at room temperature. Field-effect transistors (FETs) made from individual tubes show dc performance specifications rivaling those of state-of-the-art silicon devices. An important next step is the fabrication of integrated circuits on SWCNTs to study the high-frequency ac capabilities of SWCNTs. We built a five-stage ring oscillator that comprises, in total, 12 FETs side by side along the length of an individual carbon nanotube. A complementary metal-oxide semiconductor-type architecture was achieved by adjusting the gate work functions of the individual p-type and n-type FETs used.

Charge control in a model biphenyl molecular transistor.

We study charge control in a gated 4,4'-biphenyl diradical molecular transistor using ab initio density functional theory calculations. I-V curves and intrinsic gate capacitances were derived. We find charge control in this transistor to be strongly affected by polarization of the sigma-states of the molecule, leading to strong electrostatic coupling of the internal potentials to the source and drain electrodes, and relatively weak coupling to the gate. We suggest that this spatially dependent and anisotropic polarization is an essential element in the operation of molecular transistors.