An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.

Semiconductor device, and manufacturing method thereof

The present paper proposes an improved charge control model of lattice-mismatched AlGaN/GaN HEMTs, valid over the entire operating region. The model for estimation of two-dimensional electron gas (2-DEG) sheet carrier concentration accounts for the strongly dominant spontaneous and piezoelectric polarization at the AlGaN/GaN heterointerface. The dependence of 2-DEG sheet carrier concentration on the aluminum composition and AlGaN layer thickness has been investigated in detail. Current–voltage characteristics developed from the 2-DEG model include the effect of field dependent mobility, velocity saturation and parasitic source/drain resistances. Close proximity with experimental data confirms the validity of the proposed model.

An accurate charge control model for spontaneous and piezoelectric polarization dependent two-dimensional electron gas sheet charge density of lattice-mismatched AlGaN/GaN HEMTs

Electro-thermal modeling of multifinger AlGaN/GaN HEMT device operation including thermal substrate effects.

We present detailed Monte Carlo based calculations of the electron dynamics in GaN–AlGaN heterostructures in the presence of strain polarization fields. The model consists of a fully numerical self-consistent solution of the Schrodinger–Poisson equation with a Monte Carlo transport model. The two-dimensional sub-band energies, wave functions and carrier scattering mechanisms are computed numerically and included within a Monte Carlo simulation. The electron energy, steady-state and transient drift velocity and band occupancy are calculated as a function of electric field for different AlGaN–GaN heterostructure compositions. The effect of piezoelectrically induced strain fields on the transport dynamics is examined. A field dependent mobility model is also developed from the Monte Carlo results.

Monte Carlo calculation of two-dimensional electron dynamics in GaN–AlGaN heterostructures

A new AlGaN/GaN heterostructure field-effect transistor (HFET) model, in the framework of the gradual channel approximation and based on Monte Carlo simulations of the electron transport properties, is presented. The effects on the dc HFET output characteristics arising from contact resistances, from the ungated access channels between the gate and the source and between the gate and the drain, and from self-heating are analyzed. By examining the channel potential, the ungated regions are shown to have nonlinear characteristics. The solution method uses implicit analytical relationships for the current in the gated and ungated segments of the channel that are connected by matching boundary conditions. Thermal effects on the transport parameters associated with self-heating are included self-consistently. The model results are in very good agreement with experimental data from AlGaN/GaN HFETs fabricated on sapphire substrates. The model also identifies several device design parameters that need to be adjusted to obtain optimized performance in terms of output current and transconductance.

AlGaN/GaN heterostructure field-effect transistor model including thermal effects

In this paper we present a general methodology, materials theory based modeling, for predicting device performance in technologically immature materials that can proceed relatively independently of experiment. The models incorporated within this general approach extend from a fundamental physics based, microscopic analysis to macroscopic, engineering based device models. Using this scheme, we have investigated the transport and breakdown properties of several emerging wide band gap semiconductor materials, i.e. GaN, InN, 3C-SiC, and 4H-SiC. The carrier drift velocities, mobilities, and impact ionization coefficients for these materials can be predicted using the materials theory based modeling method. Using these results, device level simulations can then be made. Here we report Monte Carlo and selfconsistent charge control modeling of GaN based devices. Comparison to experimental measurements is made when possible. Good agreement between the selfconsistent charge control model calculations and experiment is obtained. Some of the issues pertinent to heterostructure bipolar transistor modeling of GaN are discussed.

Materials theory based modeling of wide band gap semiconductors: from basic properties to devices

An OTP bit cell includes a latch circuit of cross-coupled inverters. A floating gate PMOS transistor is inserted in each of the inverters. One or the other of the floating gate PMOS transistors is programmed through an included programming circuit so that a differential output of the latch circuit provides a corresponding logic state that is the same each time when read. To program a selected floating gate PMOS transistor, appropriate write inputs are applied to the programming circuit while a high reference voltage to the OTP bit cell is raised to a level such that the selected floating gate PMOS transistor is programmed.

One-time-programmable bit cell with latch circuit having selectively programmable floating gate transistors

Extrinsic effects on the DC output characteristics of AlGaN/GaN HFETs with 1 m gate lengths are examined The devices investigated were fabricated on MOCVD-grown AlGaN/ GaN heterostructures on sapphire substrates An analytical model that takes into account parasitic resistances and thermal effects is constructed, and its results are compared with experimental data With parameters determined from characterization experiments on the same wafer and from independent theoretical results, the agreement between the data and the model predictions is found to be very good The model is then applied to performance predictions for devices with improved series resistances and heat sinking

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Extrinsic Performance Limitations of AlGaN/GaN Heterostructure Field Effect Transistors

Voltage regulation in charge pumps. A high voltage generation system includes a charge pump having an output voltage node and a regulated input voltage node. The high voltage generation system also includes a voltage regulator. The voltage regulator includes a capacitive attenuator in electrical communication with the output voltage node. The voltage regulator also includes a comparator in electrical communication with the capacitive attenuator and with a reference voltage source. The voltage regulator further includes a buffer in electrical communication between the comparator and the regulated input voltage node.

Agustinus Sutandi

Papers

Materials theory based modeling of wide band gap semiconductors: from basic properties to devices

One-time-programmable bit cell with latch circuit having selectively programmable floating gate transistors

Extrinsic Performance Limitations of AlGaN/GaN Heterostructure Field Effect Transistors

Voltage regulation in charge pumps

Extrinsic performance limitations of AIGaN/GaN heterostructure field effect transistors