Y-junction based carbon nanotube ͑CNT͒ transistors exhibit interesting switching behaviors, and have the structural advantage that the electrical gate for current modulation can be formed by any of the three constituent branches. In this letter, we report on the gating characteristics of metallic Y-CNT morphologies. By measuring the output conductance and transconductance we conclude that the efficiency and gain depend on the branch diameter and is electric field controlled. Based on these principles, we propose a design for a Y-junction based CNT switching device, with tunable electrical properties. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2213013͔ While conventional silicon microfabrication technology encounters barriers to further development due to difficulties in miniaturization and increased cost, carbon nanotubes ͑CNTs͒ show promise for a molecular electronics 1,2 based technology. CNTs ͓both single walled nanotubes ͑SWNTs͒ and multiwalled nanotubes ͑MWNTs͔͒ can be synthesized to be either semiconducting or metallic. 3 Consequently, they can be used in a wide variety of electronics including diodes, transistors, and high frequency devices. 4 The ultimate aim is an integrated nanoelectronics system, with the advantages of reduced power consumption, radiation hardness, and faster speeds of operation, which incorporates CNTs as both active devices and interconnects. The electrical and thermal conductivity 5 properties of both SWNTs ͑Ref. 6͒ and MWNTs ͑Ref. 7͒ have been well explored. While clean SWNTs ͑diameter ϳ1 nm͒ can be described as quantum wires due to the ballistic nature of electron transport, 8 the transport in MWNTs ͑diameter in the range of 2 -100 nm͒ is found to be diffusive/quasiballistic. 7 On this basis, Coulomb blockade 9 and field effect 10 phenomena have been used for demonstrating nanotube based transistors. While extremely important in elucidating fundamental properties, the above experiments have used external electrodes made through conventional lithographic processes to contact the nanotubes and do not truly represent nanoelectronic circuits. Additionally, the well known metal oxide semiconductor field effect transistor ͑MOSFET͒ architecture is used, where the nanotube serves as the channel between the electrodes ͑source and drain͒, and a SiO 2 / Si based gate modulates the channel conductance. In other demonstrations of electrical switching, cumbersome atomic force microscope ͑AFM͒ manipulations 11 of nanotube properties have been utilized.It would, therefore, be very attractive to propose different types of electronic elements and paradigms of switching, to harness functionalities peculiar to CNT forms 12 such as Y and T junctions. 13 In addition to the nanometer size of these devices, there is also the additional feature of having a selfcontained gate, i.e., in a switching device, the gate does not have to be separately fabricated but forms a part of the structure. In earlier experiments, rectification, 14 switching, and logic gates 15 were demonstrated in Y-shaped CNTs...