Susanna Reggiani

Numerical investigation of the lateral and vertical leakage currents and breakdown regimes in GaN-on-Silicon vertical structures

A 2D TCAD-based approach is proposed to investigate the leakage current and breakdown regime of GaN/AlGaN/Si structures at different ambient temperatures. Deep-level traps originated by Carbon doping, impact-ionization generation and thermally activated Poole-Frenkel conduction have been modeled to assess the role of such physical mechanisms on the forward-bias leakage current. A good agreement with experimental data has been obtained by implementing conduction and valence mini-bands within the deeper transition layer created by conductive dislocation defects or by superlattice structures. A 2D isolation device has been investigated up to breakdown and, for the first time to our knowledge, we prove with 2D TCAD simulation that in GaN based devices both impact-ionization and Poole-Frenkel conduction effects must be taken into account to correctly match experimental data.

Leakage current and breakdown of GaN-on-Silicon vertical structures

A TCAD-based approach has been used to investigate the leakage current and breakdown regime of vertical GaN/AlGaN/Si structures at different ambient temperatures. A good agreement with experimental data has been obtained by implementing both trap-assisted and Poole-Frenkel conduction mechanisms into the buffer layers. The latter mechanisms have been proven to anticipate the onset of breakdown at high temperatures.

TCAD low-field mobility model for InGaAs UTB MOSFETs including quasi-ballistic corrections

A new approach for including quasi-ballistic effects into TCAD drift diffusion simulations of short-channel III-V MOSFETs at low longitudinal fields is presented. The model is based on the concept of ballistic mobility through a modified Matthiessen rule. It has been applied to double-gate thin-body InGaAs MOSFETs and benchmarked against multi-subband Monte Carlo simulations. Our results indicate that the model provides I-V characteristics in good agreement with Monte Carlo for channel lengths as short as 15 nm.

Analytical model of thin-body InGaAs-on-InP MOSFET low-field electron mobility for integration in TCAD tools

A simple analytical model of thin-body In_0.53Ga_0.47As-on-InP MOSFET low-field electron mobility suitable for integration in Technology-CAD (TCAD) tools is presented. Phonon, Coulomb and surface roughness scattering are accounted for. In order to characterize the phonon scattering contribution, an expression for the device effective thickness is derived from 1-D Schroedinger-Poisson simulations. The model is validated through comparison with experimental C_G-V_gs and I_d-V_gs curves collected on transistors with body thicknesses down to 5 nm.

Characterization and Modeling of High-Voltage LDMOS Transistors

This chapter introduces integrated power devices and their reliability issues. The lateral double-diffused MOS (LDMOS) transistors are widely used in mixed-signal circuit design as integrated high-voltage switches and drivers. The LDMOS with shallow-trench isolation (STI) is the device of choice to achieve voltage and current capability integrated in the basic CMOS processes. The electrical characteristics of the STI-based LDMOS transistors are reviewed over an extended range of operating conditions through experiments and numerical analysis. The high electric-field regime is explained to the purpose of investigating the effects on the electrical safe operating area (SOA) and device reliability under hot-carrier stress (HCS) conditions. A review of the HCS modeling is addressed to the purpose of understanding the degradation kinetics and mechanisms. TCAD simulations of HCS degradation are finally reported to explain the HCS effects on a wide range of biases and temperatures, confirming the experimental results.

A TCAD Low-Field Electron Mobility Model for Thin-Body InGaAs on InP MOSFETs Calibrated on Experimental Characteristics

A simple analytical low-field electron mobility model to be employed for technology computer-aided design of thin-body MOSFETs based on III-V compound semiconductors is presented. The scattering sources accounted for in the model are Coulomb centers, lattice vibrations (i.e., phonons), and surface roughness. The dependence of the thin-body effective thickness on the transverse electric field is calculated through 1-D Schrödinger-Poisson numerical simulations and is introduced in the model by means of an appropriate analytical function. Then, the free-electron density distribution is determined by considering both quantization effects and oxide-semiconductor interface traps. The model is calibrated on the experimental data collected on In0.53Ga0.47As-on-InP thin-body MOSFETs featuring body thicknesses as low as 5 nm. In particular, the model accurately reproduces CG-VGS characteristics, effective mobility against inversion layer charge plots, and IDS-VGS curves at low VDS.

Numerical study of GaN-on-Si HEMT breakdown instability accounting for substrate and packaging interactions

The electron and hole impact-ionization coefficients in AlxGa1-xN have been calibrated through a Chynoweth law by using a Monte Carlo theoretical study and experimental data at different ambient temperatures. The model has been used to investigate the breakdown characteristics in AlGaN/GaN HEMTs. The concurrent effect of charge trapping in the GaN buffer and impact-ionization generation in the device failure mechanism has been studied by simulating the off-state breakdown under a dc stress. The sensitivity of the AlGaN/GaN HEMT to parasitic charging in molding compound has been investigated by incorporating the passivation and encapsulation layers in the TCAD setup and implementing the conductivity losses in the mold compound at high temperature.

Graphene-base heterojunction transistors for post-CMOS high-speed applications: Hopes and challenges

We 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.

TCAD-based investigation on transport properties of Diamond-like carbon coatings for HV-ICs

A TCAD-based approach is proposed to investigate the most relevant transport mechanisms of diamond-like carbon (DLC) films at different biases and ambient temperatures. Starting from the band structure and boundary conditions of a metal-insulator-metal (MIM) device, the most relevant trap levels have been determined against experiments along with the Poole-Frenkel conduction effect. The affinity of the DLC under study has been extracted from experiments on the corresponding metal-insulator-semiconductor (MIS) diode. A clear polarization effect has been found in the measured C-V curves at different frequencies. The latter has been modeled in the TCAD tool via the Debye equation leading to a nice agreement with experiments.