The effect of the geometry aspect ratio on the silicon ellipse-shaped surroundinggate field-effect transistor and circuit

The silicon (Si) surrounding-gate metal-oxide-semiconductor field-effect transistor (MOSFET) has ultimate gate structures and is a potential candidate for use in next-generation high-performance nano-devices. However, because of limitations of the fabrication process, theoretically ideally round shape of the surrounding gate may not always guarantee. These limitations may lead to the formation of an ellipse-shaped surrounding gate with major (a) and minor (b) axes of different lengths. In this study, the effect of the geometry aspect ratio, a/b, on the dc and ac characteristics of the 16 nm gate ellipse-shaped surrounding-gate MOSFETs and circuits is examined by using a three-dimensional coupled device-circuit simulation technique. The dependences of electrical characteristics on the geometry aspect ratio are evaluated with reference to various device characteristics and the circuit properties, including the circuit gain, the 3 dB bandwidth, the unity-gain bandwidth, the rise/fall time and the delay time. In analog circuits, the device with an aspect ratio of less than 1 is promising because the short-channel effect is suppressed. However, for a digital circuit configuration, the transient response of the circuit relies on the charge/discharge capability of the transistor. Thus, a device with a large aspect ratio, such as 2, will be more suitable for digital applications.