A 330-500 GHz Zero-Biased Broadband Tripler Based on Terahertz Monolithic Integrated Circuits

A 330-500 GHz zero-biased broadband monolithic integrated tripler is reported. The measured results show that the maximum efficiency and the maximum output power are 2% and 194μW at 348 GHz. The saturation characteristic test shows that the output i dB compression point is about -8.5 dBm at 334 GHz and the maximum efficiency is obtained at the point, which is slightly below the 1 dB compression point. Compared with the conventional hybrid integrated circuit, a major advantage of the monolithic integrated circuit is the significant improvement of reliability and consistency. In this work, a terahertz monolithic frequency multiplier at this band is designed and fabricated.

Chemical Vapour Deposition Graphene Radio-Frequency Field-Effect Transistors

We report the dc and rf performance of graphene rf field-effect transistors,where the graphene films are grown on copper by using the chemical vapour deposition (CVD) method and transferred to SiO2/Si substrates.Composite materials,benzocyclobutene and atomic layer deposition Al2O3 are used as the gate dielectrics.The observation of n- and p-type transitions verifies the ambipolar characteristics in the graphene layers.While the intrinsic carrier mobility of CVD graphene is extracted to be 1200cm2/V·s,the parasitic series resistances are demonstrated to have a serious impact on device performance.With a gate length of 1 μm and an extrinsic transconductance of 72 mS/mm,a cutoff frequency of 6.6 GHz and a maximum oscillation frequency of 8.8 GHz are measured for the transistors,illustrating the potential of the CVD graphene for rf applications.

Wafer-Scale Gigahertz Graphene Field Effect Transistors on SiC Substrates

Wafer-scale graphene field-effect transistors are fabricated using benzocyclobutene and atomic layer deposition Al_(2)O_(3) as the top−gate dielectric.The epitaxial-graphene layer is formed by graphitization of a 2-inch-diameter Si-face semi-insulating 6H-SiC substrate.The graphene on the silicon carbide substrate is heavily n-doped and current saturation is not found.For the intrinsic characteristic of this particular channel material,the devices cannot be switched off.The cut-off frequencies of these graphene field-effect transistors,which have a gate length of 1µm,are larger than 800 MHz.The largest one can reach 1.24 GHz.There are greater than 95% active devices that can be successfully applied.We thus succeed in fabricating wafer-scale gigahertz graphene field-effect transistors,which paves the way for high-performance graphene devices and circuits.

A High Performance Terahertz Waveguide Detector Based on a Low-Barrier Diode

A Schottky barrier diode with low-barrier is presented, based on which a terahertz waveguide detector working at 500-600 GHz is designed and fabricated. By using the InGaAs/InP material system, the feature of the low barrier is obtained which greatly improves the performance of the detector. The measured typical voltage responsivity is about 900 V/W at 50-560 OHz and is about 400 V/W at 560 600 GHz. The proposed broadband waveguide detector has the characteristics of simple structure, compact size, low cost and high performance, and can be used in a variety of applications such as imaging, moleeuIar spectroscopy and atmospheric remote sensing.

fT=260 GHz andfmax=607 GHz of 100-nm-gate In0.52Al0.48As/In0.7Ga0.3As HEMTs with Gm.max=1441 mS/mm

The 100-nm T-gate InP-based InA1As/InGaAs high electron mobility transistors （HEMTs） with the width of 2×50 μm and source-drain space of 2.4 μm are systematically investigated. High indium （In） composition of InGaAs layer was adopted to acquire the higher mobility of the channel layer. A sandwich structure was adopted to optimize the cap layers and produce a very low contact resistance. The fabricated devices exhibit extrinsic maximum transconductance Gm.max = 1441 mS/mm, cutoff frequency fT = 260 GHz, and maximum oscillation frequency fmax=607 GHz. A semi-empirical model has been developed to precisely fit the low-frequency region of scattering parameters （S parameters） for InP-based HEMTs. Excellent agreement between measured and simulated S parameters demonstrates the validity of this approach.

Top-gated graphene field-effect transistors on SiC substrates

We report on a demonstration of top-gated graphene field-effect transistors(FETs) fabricated on epitaxial SiC substrate.Composite stacks,benzocyclobutene and atomic layer deposition Al2O3,are used as the gate dielectrics to maintain intrinsic carrier mobility of graphene.All graphene FETs exhibit n-type transistor characteristics and the drain current is nearly linear dependence on gate and drain voltages.Despite a low field-effect mobility of 40 cm2/(V s),a maximum cutoff frequency of 4.6 GHz and a maximum oscillation frequency of 1.5 GHz were obtained for the graphene devices with a gate length of 1 μm.