Tunable 1/f Noise in CVD Bernal-Stacked Bilayer Graphene Transistors.

Low-frequency noise is a key performance-limiting factor in almost all electronic systems. Thanks to its excellent characteristics such as exceptionally high electron mobility, graphene has high potential for future low-noise electronic applications. Here, we present an experimental analysis of low-frequency noise in dual-gate graphene transistors based on chemical vapor-deposited Bernal-stacked bilayer graphene. The fabricated dual-gate bilayer graphene transistors adopt atomic layer-deposited Al2O3 and HfSiO as top-gate and back-gate dielectric, respectively. Our results reveal an obvious M-shape gate-dependent noise behavior which can be well described by a quantitative charge-noise model. The minimal area normalized noise spectral density at 10 Hz reaches as low as about 3 × 10-10 µm2·Hz-1 at room temperature, much lower than the best results reported previously for graphene devices. In addition, the observed noise level further decreases by more than 10 times at temperature of 20 K. Meanwhile, the noise spectral density amplitude can be tuned by more than 2 orders of magnitude at 20 K by dual-gate voltages.

Nanometre-thin indium tin oxide for advanced high-performance electronics.

Although indium tin oxide (ITO) is widely used in optoelectronics due to its high optical transmittance and electrical conductivity, its degenerate doping limits exploitation as a semiconduction material. In this work, we created short-channel active transistors based on an ultra-thin (down to 4 nm) ITO channel and a high-quality, lanthanum-doped hafnium oxide dielectric of equivalent oxide thickness of 0.8 nm, with performance comparative to that of existing metal oxides and emerging two-dimensional materials. Short-channel immunity, with a subthreshold slope of 66 mV per decade, off-state current <100 fA µm-1 and on/off ratio up to 5.5 × 109, was measured for a 40-nm transistor. Logic inverters working in the subthreshold regime exhibit a high gain of 178 at a low-supply voltage of 0.5 V. Moreover, radiofrequency transistors, with as-measured cut-off frequency fT and maximum oscillation frequency fmax both >10 GHz, have been demonstrated. The unique wide bandgap and low dielectric constant of ITO provide prospects for future scaling below the 5-nm regime for advanced low-power electronics.

Negative transconductance and negative differential resistance in asymmetric narrow bandgap 2D-3D heterostructures.

Two-dimensional layered black phosphorus is an ambipolar narrow bandgap semiconductor with excellent electronic properties. A heterostructure can be formed when black phosphorus is combined with a narrow bandgap n-type semiconductor, which can feasibly be modulated throughout the entire bandgap for both materials in momentum space, creating unique quantum tunneling devices. In this work, a black phosphorus and narrow bandgap n-type indium arsenide heterojunction is created with a broken-gap band alignment, forming two interband tunneling windows that can be modulated electrostatically. We observe simultaneous gate-tunable band-to-band tunneling induced negative differential resistance and negative transconductance in the heterointerface and the access region edge near the gate, respectively. Compared to the stringent conditions for realizing such abrupt heterojunctions with opposite doping polarities in conventional bulk semiconductors, layered two-dimensional materials provide unique opportunities for such quantum tunneling devices. Our results represent advances in the fundamental understanding of heterojunctions and will promote future applications in advanced electronics.

High-Performance CVD Bernal-Stacked Bilayer Graphene Transistors for Amplifying and Mixing Signals at High Frequencies.

Tunable bandgap can be induced in Bernal-stacked bilayer graphene by a perpendicularly electric displacement field. Here, we carry out a comprehensive study on the material synthesis of CVD Bernal-stacked bilayer graphene and devices for amplifying and mixing at high frequencies. The transistors show large output current density with excellent current saturation with high intrinsic voltage gain up to 77. Positive extrinsic forward power gain | S21|2 has been obtained up to 5.6 GHz as well as high conversion gain of -7 dB for the mixers. The conversion gain dependence on tunable on/off ratio of the transistors has also been discussed.