MOSFET Inversion Layer Research Articles

Coulomb-limited mobility in 4H-SiC MOS inversion layer as a function of inversion-carrier average distance from MOS interface

The Coulomb-limited mobility (μCoulomb) of Si-face 4H-SiC MOSFETs with nitrided gate oxide is experimentally evaluated. μCoulomb is experimentally determined using samples with various acceptor concentrations by varying the body bias. It is found that the depletion-charge and surface-carrier densities in the inversion layer can be utilized to well formulate μCoulomb. In addition, μCoulomb is investigated as a function of the inversion-carrier average distance from the MOS interface (ZAV), and it is established that ZAV can universally describe μCoulomb in the inversion layer of Si-face 4H-SiC MOSFETs with nitrided gate oxide.

Evaluation of carrier scattering properties and doping deep level donors in the inversion layer of SiC MOSFETs

Evaluation of carrier scattering properties and doping deep level donors in the inversion layer of SiC MOSFETs

Effects and mechanisms of RIE on SiC inversion layer mobility and its recovery

We report the use of hydrogen annealing to implement the substantial recovery of the a-face (1 1 2¯ 0) crystal structure and the 4H SiC MOSFET inversion layer mobility following material degradation by reactive ion etching (RIE). The results impact the processing of SiC trench MOSFETs where the a-face sidewall forms a significant portion of the conducting semiconductor channel.

Plasmons-Enhanced Minority-Carrier Injection as a Measure of Potential Fluctuations in Heavily Doped Silicon

Well-known apparent electrical silicon bandgap narrowing in a heavily doped region of a bipolar transistor is observed by means of an enhanced minority-carrier injection experiment. In the region of interest, plasmons-induced potential fluctuations are existent in nature and hence constitute the origin of apparent bandgap narrowing. In this letter, we extract the underlying potential fluctuations directly from the enhanced minority-carrier injection experiment published in the literature. The core of the extraction lies in a combination of the two existing theoretical frameworks. First, the Gaussian distribution can serve as a good approximation of potential fluctuations. Second, no change can be made in the real bandgap between fluctuating conduction- and valence-band edges. Extracted potential fluctuations come from plasmons, as verified by our published temperature dependences of plasmons limited mobility in the inversion layer of MOSFETs as well as theoretical calculation results on bulk silicon. More importantly, this letter can deliver potential applications in the modeling and simulation area of nanoscale FETs (MOSFETs, FinFETs, and so forth) and bulk semiconductors.

Study on Fabrication and Fast Switching of High Voltage SiC JFET

SiC devices have excellent properties such as ultra low loss, high withstand voltage, large capacity, high frequency, and high temperature operation compared with Si devices. The SiC JFET is expected to be appropriate for the power device because a JFET has no oxide-semiconductor interface in the channel region and does not use the low mobility SiC MOSFET inversion layer as a channel. Forward I-V up to 4A for SiC VJFET, Gate voltage from 2V to 3.5V by step 0.5V. Reverse I-V characteristics up to 4500V (VG=-8V) for SiC VJFET, Gate voltage from-4V to-8V by step-2V. Turn-off characteristics are studied and fast turn-off time of 136ns at room temperature under DC voltage of 600V is successfully demonstrated.

An Analytical Model of the First Eigen Energy Level for MOSFETs Having Ultrathin Gate Oxides

In this paper, we present an analytical model for the first eigen energy level (E0) of the carriers in the inversion layer in present generation MOSFETs, having ultrathin gate oxides and high substrate doping concentrations. Commonly used approaches to evaluate E0 make either or both of the following two assumptions: one is that the barrier height at the oxide-semiconductor interface is infinite (with the consequence that the wave function at this interface is forced to zero), while the other is the triangular potential well approximation within the semiconductor (resulting in a constant electric field throughout the semiconductor, equal to the surface electric field). Obviously, both these assumptions are wrong, however, in order to correctly account for these two effects, one needs to solve Schrodinger and Poisson equations simultaneously, with the approach turning numerical and computationally intensive. In this work, we have derived a closed-form analytical expression for E0, with due considerations for both the assumptions mentioned above. In order to account for the finite barrier height at the oxide-semiconductor interface, we have used the asymptotic approximations of the Airy function integrals to find the wave functions at the oxide and the semiconductor. Then, by applying the boundary condition at the oxidesemiconductor interface, we developed the model for E0. With regard to the second assumption, we proposed the inclusion of a fitting parameter in the wellknown effective electric field model. The results matched very well with those obtained from Li’s model. Another unique contribution of this work is to explicitly account for the finite oxide-semiconductor barrier height, which none of the reported works considered.

Correlation-induced phase transitions in two-dimensional electron systems

Abstract : The electrons in inversion or accumulation layers of MOSFETs or in semiconductor-semiconductor interfaces show prominent many-body effects. A new theory off the correlation energy is developed for these electrons such that the results are applicable to a wide density range. The ground-state energy is obtained for all densities. It is continuous and convergent, but changes its analytical form at r sub s = 1.414. Associated with this change is a divergence of the compressibility that occurs at r sub s =1.989. Hence, around this r sub s, the system can be considered to be in a liquidlike state. In the (001) direction of silicon inversion layers, the two valleys, occupied equally by the electrons at high densities, may be populated unevenly due to electron correlations. This unbalance will cause a valley occupancy phase transition at r sub s =8.011, in close agreement with a recent experiment. Under a magnetic field, the susceptibility is enhanced nonlinearly when the density of electrons is reduced. This enhancement becomes very strong toward r sub s =13.0, beyond which a spin-polarized state is favored.

Quasi-Charge-Sheet Model for Inversion Layer Mobility in 4H-SiC MOSFETs

The mobility of electrons in the inversion layer of 4H-Silicon Carbide (SiC) MOSFETs is lower than the ideal value due to the various scattering mechanisms that takes place at the surface. These scattering mechanisms are strong function of both the interface-trapped charge density and inversion-layer electron density. In this work, we develop a quasi-charge-sheet model to quantify coulomb scattering due to interface trapped-charge in SiC MOSFET inversion layers and calculate the inversion layer electron mobility.

Phonon-Limited Electron Mobility Behavior and Inherent Mobility Reduction Mechanism of Ultrathin Silicon-on-Insulator Layer with (111) Surface and Ultrathin Germanium-on-Insulator Layer with (001) Surface

One-dimensional self-consistent calculations and relaxation time approximations are used to study the phonon-limited electron mobility behavior of the inversion layer at room temperature for ultrathin body Si(111) and Ge(001) layers in single-gate (SG) and double-gate (DG) silicon-on-insulator (SOI) and germanium-on-insulator (GOI) metal–oxide–semiconductor (MOS) field-effect transistors (FETs). Assuming a 5-nm-thick SOI layer, it is shown that intravalley phonon scattering (acoustic-phonon scattering) in the DG SOI MOSFET inversion layer is strongly suppressed within a range of medium and high effective field (Eeff) values; DG SOI MOSFETs have higher phonon-limited electron mobility than SG SOI MOSFETs. Many simulations strongly indicate that, for medium Eeff values, the suppression of acoustic-phonon scattering in a 5-nm-thick DG SOI MOSFET primarily stems from the reduction of the form factor (F00) value. Although similar phenomena are observed in approximately 7-nm-thick GOI layers with a Ge(001) surface, it is shown that there is little merit in using the Ge(001) surface for DG GOI MOSFETs.

Effects of Channel and Crystalline Orientations on the Electron Mobility in MOSFETs Fabricated on (114) and (5 5 12)-Silicon Substrates

This work reports the measurement of the electron mobility in the inversion layer of MOSFETs fabricated on Si(114) and Si(5 5 12), for medium and high effective transverse electric fields, Eeff. We studied the channel mobility in these surfaces as a function of the channel direction [1-4]. Results reveal the strong influence on electron mobility of the channel direction on high-index surfaces. It was noted that mobility on high index-surfaces is degraded when the channel direction goes far away from , but it is less affected when the channel runs parallel to this direction. Even though Si(0 0 1) has been the surface with the highest electron mobility reported, we found that mobility on Si(1 1 4) is higher than that on Si(0 0 1) when Eeff {greater than or equal to} 0.4 MV/cm.

Multisubband Monte Carlo Study of Transport, Quantization, and Electron-Gas Degeneration in Ultrathin SOI n-MOSFETs

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper presents a new self-consistent multisubband Monte Carlo model for electronic transport in the inversion layer of decananometric MOSFETs. The simulator is 2-D in real space and in <formula formulatype="inline"> <tex>$\vec{k}$</tex></formula>-space and accounts for the electron-gas degeneracy in the <formula formulatype="inline"><tex>$\vec{k}$</tex></formula>-space. Simulation of nanoscale ultra-thin-body silicon-on-insulator MOSFETs shows that the subband structure and the carrier degeneracy strongly affect the transport properties and, in particular, the injection velocity and the channel back-scattering. </para>

Impact of Phonon-Limited Mobility Superiority in Double-Gate or Fin FET with a (111) Si and (001) Ge Surface Channel on Device Scaling

1D self-consistent calculations and relaxation time approximations are used to study the phonon-limited electron mobility of the inversion layer at room temperature for ultra- thin Si (111), Ge (001) and Ge (111) layers in single-gate (SG) and double-gate (DG) MOSFET's. Assuming a 5-nm-thick SOI layer, it is shown that intra-valley phonon scattering in the DG SOI MOSFET inversion layer is strongly suppressed within a range of medium Eeff value; DG devices have higher phonon- limited electron mobility than SG devices. The suppression of intra-valley phonon scattering in a 5-nm TSOI DG device primarily stems from the reduction of the form factor (F00) value within medium Eeff values. Similar aspects of electron mobility expected for SG and DG GOI MOSFET's are also discussed.

Features of phonon-limited electron mobility behavior of double-gate field-effect transistor with (111) Si surface channel

One-dimensional self-consistent calculations and relaxation time approximations are used to study the phonon-limited electron mobility of the inversion layer at room temperature for ultrathin body Si (111) layers in single-gate (SG) and double-gate (DG) silicon-on-insulator (SOI) metal-oxide-semiconductor field-effect transistors (MOSFET’s). Assuming a 5-nm-thick SOI layer, it is shown that intravalley phonon scattering (acoustic-phonon scattering) in the DG SOI MOSFET inversion layer is strongly suppressed within a range of medium effective field (Eeff) values; DG SOI MOSFETs have higher phonon-limited electron mobility than SG SOI MOSFET’s. Many simulations strongly suggest that the suppression of acoustic-phonon scattering in a 5nm TSOI DG SOI MOSFET primarily stems from the reduction of the form factor (F00) value within medium Eeff values.

Modeling Aspects of Sub-100-nm MOSFETs for ULSI-Device Applications

Ultrathin oxides (1-3 nm) are foreseen to be used as gate dielectric in complementary-MOS technology during the next ten years. Nevertheless, they require new approaches in modeling and characterization due to the onset of quantum effects. Predicting device characteristics including quantum effects requires solving of Schroumldinger's equation together with Poisson's equation. In this paper, Poisson's equation is solved in two dimensions (2-D) over the entire device using Green's function approach, while Schroumldinger's equation is decoupled using triangular-potential-well approximation. The carrier density thus obtained is included in the space-charge density of Poisson's equation to obtain quantum-carrier confinement effects in the modeling of sub-100-nm MOSFETs. The framework also consists of the effects of source/drain-junction curvature and depth, short-channel effects, and drain-induced barrier-lowering effect. The 2-D potential profiles thus obtained with above said effects form the basis for an estimation of threshold voltage. Using this potential distribution, the transfer characteristics of the device are also evaluated. The method presented is comprehensive in the treatment, as it neither requires self-consistent numerical modeling nor it contain any empirical or fitting expression/parameter to provide formulation for quantized-carrier effect in the inversion layer of MOSFETs. The results obtained show good agreement with available results in the literature and with simulated results, thus proving the validity of our model

Characteristics of a two‐dimensional integrated magnetic sensor for position sensing and motor control

AbstractTwo‐dimensional integrated magnetic sensors for position sensing were designed and fabricated with the standard 0.35‐µm CMOS process on silicon. One such type is the n‐type Hall sensor that uses an inversion layer under the gate oxide of the MOSFET. The Hall sensors were arrayed (64 × 64), and the control digital circuits and output amplifier were also integrated into the same chip. ‘One pixel’ was 50 × 50 µm, and the entire chip was 4.9 × 4.9 mm. The sensitivity of one of these sensors was 2.7 mV/(mA·kG). The two‐dimensional magnetic flux distribution was measured from the 5‐mm diameter Nd–Fe–B rare‐earth permanent magnet. About 42 s was required to measure one frame. The position of the magnet could be detected with the fabricated sensors. Magnetic sensors using an inversion layer in MOSFETs are useful for position sensing systems, but their noise characteristics, such as poor sensitivity, should be improved. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.

Physics of Hole Transport in Strained Silicon MOSFET Inversion Layers

A comprehensive quantum anisotropic transport model for holes was used to study silicon PMOS inversion layer transport under arbitrary stress. The anisotropic band structures of bulk silicon and silicon under field confinement as a twodimensional quantum gas are computed using the pseudopotential method and a six-band stress-dependent k.p Hamiltonian. Anisotropic scattering is included in the momentum-dependent scattering rate calculation. Mobility is obtained from the Kubo-Greenwood formula at low lateral field and from the fullband Monte Carlo simulation at high lateral field. Using these methods, a comprehensive study has been performed for both uniaxial and biaxial stresses. The results are compared with device bending data and piezoresistance data for uniaxial stress, and device data from strained Si channel on relaxed SiGe substrate devices for biaxial tensile stress. All comparisons show a very good agreement with simulation. It is found that the hole band structure is dominated by 12 wings, where mechanical stress, as well as the vertical field under certain stress conditions, can alter the energies of the few lowest hole subbands, changing the transport effective mass, density-of-states, and scattering rates, and thus affecting the mobility

Carrier effective mobilities in germanium MOSFET inversion layer investigated by Monte Carlo simulation

This paper presents the Monte Carlo studies of inversion mobility in Ge MOSFETs covering a wide range of bulk-impurity concentrations (10 14 cm −3–10 17 cm −3), and substrate bias (0–10 V). Carrier mobilities in Ge MOSFETs have obviously increased compared with those in Si MOSFETs. At low effective field, both electron and hole mobilities have increased over 100%; while at high effective field the increase is reduced due to the effect of surface roughness. Similar to Si MOSFETs, the carrier effective mobilities in Ge MOSFETs also have a universal behavior. The universality of both electron and hole mobilities holds up to a bulk-impurity concentration of 10 17 cm −3. On substrates with higher bulk-impurity concentrations, the carrier effective mobilities significantly deviate from the universal curves under low effective field because of Coulomb scattering by the bulk impurity.

Temporal and Spatial Current Stability of Smart Field Emission Arrays

Emission current stability and the spatial uniformity of field emission devices are improved when a lightly doped drain MOSFET (LD-MOSFET) is integrated with a field emission array (FEA). At comparable current levels, the emission noise (/spl Delta/I/I) decreased from 16.9% to 1.8%. Emission current fluctuation was reduced in the integrated device compared to the FEA device even in the presence of gases. Spatial current uniformity was achieved in the integrated MOSFET/FEA devices at different wafer positions and for different array sizes. The results are explained by a two-step field emission process, which consists of an electron supply step determined by the MOSFET inversion layer and an electron transmission step determined by the field emission barrier width. The device structure also results in low voltage control of emission current.

Calibration of a pH sensitive buried channel silicon-on-insulator MOSFET for sensor applications

The threshold voltage characteristics of a buried channel silicon-on-insulator MOSFET is examined in solutions of varying acidity. Experiments utilizing an integrated micro-fluidic channel exhibit a variation in threshold voltage that appears approximately linear with pH in the range from pH 4 to pH 7, with a sensitivity of ∼1 V per pH unit. Charge configuration changes in the vicinity of the MOSFET inversion layer due to protonation/deprotonation of the device surface is proposed as an explanation for the observed shifts in threshold voltage. When the pH range is expanded we observe a non-linear relationship bet- ween pH and the threshold voltage of the device, this behavior is explained in terms of deprotonation of the different species of the native oxide surface, Numerical simulations of the MOSFET demonstrate that the threshold voltage sensitivity corresponds to an additional surface positive fixed charge density of ∼ 1 × 1010 cm–2 for each pH unit. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A study into the broadening of the quantized inversion layer states in deep submicron MOSFETs

The one dimensional density-of-states (DOS) in the inversion layers of MOSFETs with ultra-thin gate oxides is known to broaden in energy due to gate leakage. The existing self-consistent formulation does not take the effects of this broadening into account. We have calculated the DOS as functions of energy and position. It is shown that if the energy broadening of the inversion layer states are much smaller than the separation between the inversion layer eigenenergies, the DOS can be expressed as a product of an energy-dependent and a position-dependent function. This provides the justification for the use of the existing formulation in devices where the broadening is not negligible and it becomes unnecessary to explicitly incorporate the broadening into the model. We also estimate the lifetimes of the quasi-bound inversion layer states from the calculated resonance widths. We find that the lifetimes of the higher energy states, instead of saturating, begins to increase with increasing energy. A qualitative explanation for this unusual behavior is also provided.