Graphene has attracted a great deal of interest in the past several years.[1–5] New physics has been predicted and observed, such as ultrahigh carrier mobility,[6] electron-hole symmetry and quantum hall effect,[2, 4, 7–9] and the strong suppression of weak localization.[10–12] For mainstream logic application, graphene nanoribbons (GNRs), as thin strips of graphene or unrolled carbon nanotubes, are predicted to be semiconducting due to edge effects and quantum confinement.[13–15] Recent experimental studies have also demonstrated that GNRs can effectively function as a semiconducting channel for roomtemperature field-effect transistors.[16–22] By varying the width of GNRs at selected points, it is also possible to create graphene quantum dots within a GNR for single electron transistors.[23] These studies represent important advances in GNR based electronics. However, most of the efforts to date employ a silicon substrate as a global back gate and silicon oxide as the gate dielectrics. While such a device has led to many interesting scientific discoveries, it will be of limited use for practical applications due to the high gate switching voltage required and the inability to independently address multiple units on the