  The 1/f noise in pentacene thin film transistors has been measured as a
function of device thickness from well above the effective conduction channel
thickness to only two conducting layers. Over the entire thickness range, the
spectral noise form is 1/f, and the noise parameter varies as (gate voltage)-1,
confirming that the noise is due to mobility fluctuations, even in the thinnest
films. Hooge's parameter varies as an inverse power-law with conductivity for
all film thicknesses. The magnitude and transport characteristics of the
spectral noise are well explained in terms of percolative effects arising from
the grain boundary structure.
