An integrated capacitance bridge for high-resolution, wide temperature range quantum capacitance measurements

We have developed a highly-sensitive integrated capacitance bridge for quantum capacitance measurements. Our bridge, based on a GaAs HEMT amplifier, delivers attofarad (aF) resolution using a small AC excitation at or below kT over a broad temperature range (4K-300K). We have achieved a resolution at room temperature of 10aF per root Hz for a 10mV AC excitation at 17.5 kHz, with improved resolution at cryogenic temperatures, for the same excitation amplitude. We demonstrate the performance of our capacitance bridge by measuring the quantum capacitance of top-gated graphene devices and comparing against results obtained with the highest resolution commercially-available capacitance measurement bridge. Under identical test conditions, our bridge exceeds the resolution of the commercial tool by up to several orders of magnitude.Comment: (1)AH and JAS contributed equally to this work. 6 pages, 5 figure

Carbon nanotube circuits in the presence of carbon nanotube density variations

Carbon Nanotubes (CNTs) are grown using chemical self-assembly. As a result, it is extremely difficult to ensure exact positioning and uniform density of CNTs. Density variations in CNT growth can compromise reliability of Carbon Nanotube Field Effect Transistor (CNFET) circuits, and result in increased delay variations. A parameterized model for CNT density variation is presented based on experimental data extracted from aligned CNT growth. This model is used to quantify the impact of such variations on design metrics such as noise margins and delay variations of CNFET circuits. Finally, we analyze correlation that exists in aligned CNT growth, and demonstrate how the reliability of CNFET circuits can be significantly improved by taking advantage of such correlation