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The gate-induced band-to-band tunneling in carbon nanotube field effect transistors (CNFETs) is studied by solving the Poissson and carrier transport equations self-consistently. The transmission coefficient through the bandgap has been calculated using the Wentzel–Kramers–Brillouin (WKB) approximation. The device parameters of CNFETs with uniformly doped source/drain (S/D) regions have been investigated to find the parameter window to observe subthreshold slope (SS) of less than 60 mV/dec. It is demonstrated that the band-to-band tunneling (BTBT) current can be significantly enhanced by reducing the thickness of inter-layer oxide (t int) between the substrate and carbon nanotube (CNT). With a thin t int of 10 nm (SiO2) and optimized S/D doping concentrations, a steep SS of less than 60 mV/dec can be achieved.

We investigated the effect of thermal cycling on the operational performance of YBa 2 Cu 3 O 7−δ (YBCO) direct current superconducting quantum interference devices (DC-SQUIDs) fabricated onto 24 • SrTiO 3 (STO) bicrystal substrates. The devices under investigation consist of directly coupled DC-SQUID magnetometer configurations. Thin films having 200 nm thicknesses were deposited by dc-magnetron sputtering and device patterns were made by a standard lithography process and chemical etching. The SQUIDs having 4 μm-wide grain boundary Josephson junctions (GBJJs) were characterized by means of critical currents, peak-to-peak output voltages and noise levels, depending on the thermal cycles. In order to achieve a protective layer for the junctions against the undesired effects of thermal cycles and ambient atmosphere during the room temperature storage, the devices were coated with a 400 nm thick YBCO layer at room temperature. Since the second layer of amorphous YBCO is completely electrically insulating, it does not affect the operation of the junctions and pick-up coils of magnetometers. This two-layered configuration ensures the protection of the junctions from ambient atmosphere as well as from the effect of water molecules interacting with the film structure during each thermal cycle.

a b s t r a c tThe signal performances of YBa 2 Cu 3 O 7−ı (YBCO) direct current superconducting quantum interference devices (DC-SQUIDs) have been investigated as a function of the thin film structure affected by the growth process. YBCO thin films of 200 nm thicknesses were deposited by DC magnetron sputtering using different deposition rates between 1.0 nm/min and 2.0 nm/min onto 24• bicrystal SrTiO 3 (STO) substrates. The thin film samples were subsequently analyzed by XRD and AFM in order to determine their crystalline structures and surface morphologies respectively. The 67 pH directly coupled DC-SQUIDs with 4 m-wide bicrystal Josephson junctions were fabricated, and characterized with respect to their device performances. The variations in the critical current (I c ), the voltage modulation depth ( V) and the noise performance of DC-SQUIDs were reported. The SQUIDs having relatively low deposition rate of 1.0 nm/min was observed to have larger voltage modulation depth as well as higher critical current than that of the samples having larger rate of 2.0 nm/min. The better noise performances were observed as the film deposition rate decreases. The results were associated with the thin film structure and the SQUID characteristics.

The device parameters of carbon nanotube field effect transistors (CNFETs) with doped source/drain junctions have been studied in order to realize lower off-state leakage current (I OFF) while keeping better on-state current (I ON). It is demonstrated that, when the power supply voltage (V dd) is greater than the bandgap (E g) of CNTs, optimized doping concentration showing the lowest I OFF exists. On the other hand, when V dd is smaller than E g , I OFF monotonically decreases as doping concentration decreases, although the aggressively lowered doping concentration results in lower I ON .