1,720,982 research outputs found
The influence of interface states at the Schottky junction on the large signal behavior of copper-gate GaN HEMTs
No full textThe large signal characteristics of Cu-gate and Ni/Au-gate AlGaN/GaN high-electron-mobility transistors (HEMTs) were compared. The tested devices were fabricated on two different parts of the same wafer following the same fabrication steps, the only difference being in the Schottky contact material. Comparison of the direct-current (DC) and radio frequency (RF) characteristics points out a critical drain current collapse in the Cu-gate devices, with detrimental effects on the RF performance, whereas the Ni/Au-gate HEMTs performed properly during DC, pulsed, and RF measurements. Investigations on the drain current transients and on the I D-V GS characteristics, obtained by pulsed signals, suggest the presence of an acceptor trap density in the AlGaN barrier, beneath the Cu Schottky gate contact, responsible for the poorer performance of the Cu-gate device; an activation energy of 430 meV was extracted. This defectivity seemed to be due to a copper diffusion event, activated by thermal stress induced in the sample during the plasma-enhanced chemical vapor deposition (PECVD) of SiN. Numerical simulations carried out on the tested structure qualitatively support the presence of a trap density explaining the nature of the observed drain current transients
Trapping phenomena in field-plated high power GaAs pHEMTs
No full textThis paper presents the results obtained both by experimental measurements and numerical simulations carried out on state-of-the-art field plated GaAs-based pHEMTs.The effect of the field-plate length on DC and RF operation will be discussed showing that the adoption of an optimal field-plate structure can significantly boost the device RF power performance, resulting in power density up to 2W/mm measured at 2 GHz
Metal-oxide barrier extraction by Fowler-Nordheim tunnelling onset in Al2O3-on-GaN MOS diodes
No full textInvestigation of the properties of Al2O3-on-GaN metal-oxide-semiconductor diodes is reported. A new method is shown to calculate the metal-oxide barrier height based on the onset of the Fowler-Nordheim tunnelling current regime in direct bias. The Ni/Al2O3 barrier was extracted, for the first time with this method, and it was found to match other reports in the literature. The dependence of the effectiveness of this method on the oxide thickness is discussed. The breakdown field for Al2O3 was also measured and found to be in agreement with previous reports
Simulation of graphene base transistors with bilayer tunnel oxide barrier: Model calibration and performance projection
No full textA simulation study of the graphene base transistor is presented based on the most recent experimental results involving a novel double-layer emitter-to-base insulator made of TmSiO and TiO2. The simulations are based on a 1-D quantum transport model with the effective mass approximation, and reproduce well the experiments both in terms of current levels and common-base current gain α. Performance projections are then investigated: with transparent graphene, the cutoff frequency is predicted to increase from 1MHz to 100MHz by reducing the thickness of TmSiO from 1 nm to 0.5 nm. In order to go beyond this limit towards the THz range, a material with a lower barrier height than TmSiO should be considered. A technological breakthrough boosting the graphene interface quality is also needed in order to obtain acceptable values of α, which are still low
Graphene base heterojunction transistor: An explorative study on device potential, optimization, and base parasitics
No full textThe Graphene-Base Heterojunction Transistor (GBHT) is a novel device concept with a high potential for analog high-frequency RF operation, in which the current is due to both thermionic emission and tunneling. In this paper we study through numerical simulations the influence of previously uninvestigated aspects of Si- and Ge-based GBHTs - namely, crystallographic orientation and doping density values - on the device performance; a comparison with an aggressively scaled HBT structure is then reported. The simulations are carried out with an in-house developed code based on a 1-D quantum transport model within the effective mass approximation and the assumptions of ballistic transport with non-parabolic corrections and ideal semiconductor-graphene interface. We show that crystallographic orientation has a negligible effect on the GBHT performance. The doping density values in the GBHT emitter and collector regions can be tailored to maximize the device performance: the Si device shows better overall performance than the Ge one, yielding a peak cut-off frequency fT higher than 4 THz together with an intrinsic voltage gain above 10, or even higher fT at the cost of a lower gain. The Si-based GBHT can potentially outperform the SiGe HBT by a 2.8 higher fT. For a Si-based GBHT with a circular active region of diameter 50-100 nm, a theoretical balanced value for fT and fmax above 2 THz can be achieved, provided the base parasitics are carefully minimized
Evaluation and Numerical Simulations of GaN HEMTs Electrical Degradation
No full textIn this letter, the effects of dc stress on GaN high-electron-mobility transistors' performance are investigated by means of experimental measurements and numerical simulation. A degradation of both dynamic (pulsed I-V) and static characteristics (dc) has been observed on stressed devices, and it has been experimentally related to the formation of an electron trap in the AlGaN barrier layer. Numerical simulations carried out on the tested structure by introducing a trapping region at the gate edge of the device barrier confirm the experimentally observed device degradation. The worsening of the dynamic performance is induced by both an increase in trap concentration and/or depth of the trapping region while the degradation of the dc characteristics can be explained by an increase in the trapping-region depth
Simulations of Graphene Base Transistors with Improved Graphene Interface Model
No full textA simulation study of the graphene base heterojunction transistor (GBHT) is presented based on a novel realistic graphene-Si interface model, calibrated on the experimental graphene-Si Schottky diodes, whose current-voltageerature characteristics are well reproduced. The GBHT simulations predict fT in the tens-of-gigahertz range and confirm the need for an improved quality of the graphene interface for the terahertz operation to be reached
Design of GaN HEMTs for Power Switching Operation
No full textA model based on the key parameters of the device, such as the 2DEG carrier concentration and its mobility, as well as the active area geometry, will be presented and discussed
Impact of crystallographic orientation and impurity scattering in Graphene-Base Heterojunction Transistors for Terahertz Operation
No full textThe influence of the crystal orientation on the performance of silicon-based Graphene-Base Heterojunction Transistors (GBHTs) for terahertz operation is investigated by means of an in-house developed simulator based on quantum transport coupled with Poisson equation. The effect of impurity scattering is included, finding that terahertz operation is possible even considering the reduction of the mobility due to dopants
Graphene-base heterojunction transistors for post-CMOS high-speed applications: Hopes and challenges
No full textWe compare through numerical simulations a Si GBHT and a SiGe HBT: the fT limit of GBHTs is
predicted to be more than twice as high as for HBTs assuming a transparent graphene/Si interface; if a more realistic
interface model extrapolated from existing experiments is used, the fT limit drops by about two orders of magnitude
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