Si metal–oxide semiconductor field effect transistor with 70-nm slotted gates for study of quasi-one-dimensional quantum transport

Abstract

We have fabricated dual-gate Si metal–oxide semiconductor field effect transistor devices in which the lower gate is slotted and the upper gate, separated by 45 nm of SiO2, is planar. By appropriate adjustment of the potentials on the two gates, the field lines from the upper gate are pinched, creating an inversion layer about one-half the slot width. The resist patterning was done by x-ray lithography, using a mask that combined crystallographic-template/sidewall-shadowing techniques with UV lithography. The slotted lower gate was produced by lift-off. The metallization was a sandwich structure of Cr/W/Cr which permitted high-temperature annealing. Very high mobilities, ∼15 000 cm2 /V s at 4.2 K, were achieved as a result. The combination of high mobility and extremely narrow inversion channel (∼30 nm) yields very clear structure in the conductance as a function of gate voltage, which cannot be accounted for by either localization effects or universal conductance fluctuations. Although these oscillations may be related to one-dimensional subband effects, the magnetic field independence of the oscillations is not understood. At very high (12 T) magnetic fields an anomalous magnetoresistance has been seen.