Self-Mixing Model of Terahertz Rectification in a Metal Oxide Semiconductor Capacitance

This paper presents a compact model for metal oxide semiconductor (MOS) capacitors, based on a time-dependent solution for the surface potential. This enables modeling of the frequency dependence of MOS capacitors, which is not possible with existing compact models. The model is implemented in Verilog-A, and is verified against two-dimensional (2-D) numerical device simulations with DESSIS.

Metal oxide semiconductor (MOS) capacitors were fabricated based on oxygen-terminated p-type (100) oriented diamond and SiO2 grown by atomic layer deposition. A detailed electrical characterization consisting of I–V, C–V, and C–F was performed in order to analyze the electrical properties of the structure. The MOS capacitor presented no detectable leakage current in forward and very low leakage current in reverse sustaining at least 6 MV/cm without degradation. The C–V measurements showed depletion and deep depletion regimes in forward and accumulation regimes in reverse, with a low density of interface states of ∼1011 cm−2 along the diamond bandgap. The latter results were further validated by conductance and capacitance vs frequency measurements.

An unbalanced magnet (UM) is commonly employed in ionization magnetron sputtering (IMS) in order to increase the ionization rates of sputtering species. In this paper, sputtering using an UM is compared with that using a balanced magnet (BM) during the deposition of Ti thin layers. Ti layers were fabricated on the top of polycrystalline silicon (poly-Si) gate electrodes of antenna metal oxide semiconductor (MOS) capacitors with various thicknesses of gate SiO2 layers ranging from 25 to 80 Å, and the durability of the gate SiO2 layers was monitored by current–voltage (I–V) measurements. It was found that the MOS capacitors with thin SiO2 layers fabricated with the UM were much more damaged than those fabricated with the BM. This characteristic became more marked for thinner SiO2 layers. Its origin was investigated by monitoring the current injected from the plasma to the substrate using a specially designed electrical configuration, and was explained as follows. Electrons are carried toward substrates by curvature drift originating from the diverging magnetic field perpendicular to the substrate. This causes the accumulation of electrons on the gate SiO2 thin layers where the diverging magnetic field is developed at the beginning of discharge, i.e., before the uniform Ti deposition starts to occur. Consequently, the accumulated electrons break the gate SiO2 layer. These results suggest that a new design of magnetic fields for the UM is needed so that the magnetic field does not reach the substrate. It is particularly important to keep the diverging magnetic fields away from the substrates at the beginning of discharge.

In n-type 4H-SiC, over-oxidation of an implanted surface-near, Gaussian nitrogen-profile results in MOS capacitors, which possess a distinctly reduced density of interface states Dit and an undesirable large negative flatband voltage UFB. Their values are determined by the implantation parameters and the thickness of the oxide layer. The negative flatband voltage can strongly be compensated in the case that a Gaussian aluminum-profile is co-implanted prior to the oxidation. Depending on the conditions of the Al implantation, UFB can be controlled within a wide range. Secondary ion mass spectrometry analyses reveal that the implanted N and Al atoms are mobile in the oxide layer during the oxidation process and are partly accumulated at the SiC/SiO2 interface.

The electrical properties of hafnium oxide (HfO2) gate dielectric as a metal–oxide–semiconductor (MOS) capacitor structure deposited using pulse laser deposition (PLD) technique at optimum substrate temperatures in an oxygen ambient gas are investigated. The film thickness and microstructure are examined using ellipsometer and atomic force microscope (AFM), respectively to see the effect of substrate temperatures on the device properties. The electrical J–V, C–V characteristics of the dielectric films are investigated employing Al–HfO2–Si MOS capacitor structure. The important parameters like leakage current density, flat-band voltage (Vfb) and oxide-charge density (Qox) for MOS capacitors are extracted and investigated for optimum substrate temperature. Further, electrical studies of these MOS capacitors have been carried out by incorporating La2O3 into HfO2 to fabricate HfO2/La2O3 dielectric stacks at an optimized substrate temperature of 800 °C using a PLD deposition technique under oxygen ambient. These Al–HfO2–La2O3–Si dielectric stacks MOS capacitor structure are found to possess better electrical properties than that of HfO2 based MOS capacitors using the PLD deposition technique.

Impedance spectroscopy of the metal-oxide semiconductor (MOS) system has played a central role in the development of silicon-based complementary MOS (CMOS) technology over the past 50 years [1, 2]. With current research interest into alternative semiconductor channels to silicon for MOSFET and tunnel FET technologies, the measurement and interpretation of the overall impedance of the MOS structure requires detailed analysis to separate and quantify the contribution of interface states, and near interface traps (border traps), on the capacitance and conductance response, and to separate the contribution of these electrically active defect states from the ac response of minority carriers in the case of genuine inversion of the semiconductor/dielectric interface. There has been considerable progress in recent years in reducing the interface state density (Dit) [3], [4], [5], in narrow gap InxGa1-xAs MOS structures to the point where genuine surface inversion can be observed for both n- and p-type In0.53Ga0.47As MOS capacitors, which is confirmed by analysis of the minimum capacitance of n- and p-type In0.53Ga0.47As MOS structure with doping concentration ranging from approximately 1x1016 to 1x1018 cm-3 [6]. In this presentation we will provide an overview of the experimental relationship between specific functions of the capacitance (C) and conductance (G) for the case of narrow band gap III-V MOS structures which exhibit genuine surface inversion, where the capacitance and conductance of the MOS system as a function of ac angular frequency (ω) are related, and in particular, the peak values of G/ω and −dC/dloge(ω) (≡− ωdC/dω) are equal, and that these peak magnitudes occur at the same value of ω [7]. The relationship is also confirmed by physics based ac simulations of MOS structures and through analysis of the equivalent circuit model in inversion. Results will be presented for InGaAs and InGaSb MOS structures (Al2O3 and Al2O3/HfO2 ALD oxides) where genuine inversion of the III-V/oxide surface is confirmed by the G/ω and −dC/dloge(ω) functions, which have peak values of Cox 2/2(Cox+Cd) when the surface is inverted (where Cox is the gate oxide capacitance and Cd is the maximum capacitance of the semiconductor surface in inversion). In the case of p type InGaSb MOS structures it is also notable that the accumulation frequency dispersion is very low (<0.7%/decade) indicating a reduced density of border traps at energies in the Al2O3 gate oxide aligning with the In0.3Ga0.7Sb valence band edge, which is approximately aligned with the lowest energy in the In0.53Ga0.47As conduction band gamma valley. Finally, experimental results and physics based simulations will be presented, which indicate that the peak values of G/ω and −dC/dloge(ω) in inversion for any MOS system which demonstrates an inversion response within the typically range of temperatures and ac signal frequencies employed in experiments, opens a route to determine the gate oxide capacitance in inversion (where the gate oxide field and gate leakage are reduced), and that the angular frequency associated with the peak values of the G/ω and −dC/dloge(ω) functions allows the determination of the minority carrier generation rate in the semiconductor, which is relevant to the leakage currents in MOSFETs and the optical performance in photonic applications. [1] E. H. Nicollian and J. R. Brews, MOS Physics and Technology. New York, NY, USA: Wiley, 1982 [2] E. H. Nicollian and A. Goetzberger, “The Si-SiO2 interface—Electrical properties as determined by the metal-insulator-silicon conductance technique,” Bell Syst. Tech. J., vol. 46, no. 6, pp. 1055–1133, 1967. [3] É. O’Connor et al., J. Appl. Phys., vol. 109, no. 2, p. 024101, 2011. [4] H.-D. Trinh et al., Appl. Phys. Lett., vol. 97, no. 4, pp. 042903-1–042903-3, 2010. [5] T. D. Lin et al., “Realization of high-quality HfO2 on In0.53Ga0.47As by in-situ atomic-layer-deposition,” Appl. Phys. Lett., vol. 100, no. 17, p. 172110, 2012. [6] E. O'Connor, K. Cherkaoui, S. Monaghan, B. Sheehan, I. M. Povey, and P. K. Hurley, Appl. Phys. Lett 110, 032902 (2017) [7] Scott Monaghan, Éamon O’Connor, Rafael Rios, Fahmida Ferdousi, Liam Floyd, Eimear Ryan, Karim Cherkaoui, Ian M. Povey, Kelin J. Kuhn, and Paul K. Hurley, IEEE Transaction on Electron Devices, 61, 4176 (2014)

Three-dimensional vertical Si nanowire MOS capacitor model structure for the study of electrical versus geometrical Si nanowire characteristics

The unique physical, chemical, and electronic properties of rare earth oxides have been of immense interest to replace SiO2 as a dielectric material in metal–oxide–semiconductor (MOS)-based sensors applications to accurately measure the radiation dosage and increase sensor sensitivities in as diverse applications as space radiation, nuclear physics, medical diagnostics, radiation cancer therapy, and personal dosimetry devices. Hence, the electrical characteristics of oxides prior to and after irradiation of MOS-based devices are needed since they are the backbone of the devices such as MOSFETs and ICs. In addition, an understanding of the behaviour of high-k dielectric oxides in an MOS configuration is necessary since the radiation-induced damage occurs in the bulk oxide film and/or near the oxide–semiconductor interface resulting in creation of lattice defects. Hence, MOS structures with the rare earth oxides of Er2O3, Gd2O3, Yb2O3, and a transition metal oxide of HfO2 were produced by RF magnetron sputtering to determine (a) the structure of the films, (b) dielectric constants, (c) capacitance versus voltage behaviour of Er2O3, Gd2O3, Yb2O3, and HfO2 prior to and after irradiation of the devices in the dose range of 0–76 Gy. The experimental results were analysed with a theoretical framework on the energy band diagram and the radiation effects on the electrical characteristics of the MOS capacitors. The characteristics of the devices were evaluated by using effective oxide charge density ( $$ Q_{\text{EFF}} $$ ), variation in the oxide trapped charge density ( $$ \Delta N_{\text{ox}} $$ ), and interface trapped charge density ( $$ \Delta N_{\text{it}} $$ ). In addition, barrier height ( $$ \phi_{\text{b}} $$ ), image force barrier lowering ( $$ \Delta \phi_{\text{b}} $$ ), acceptor concentration ( $$ N_{\text{a}} $$ ) were calculated before and after irradiation and examined the nature of interface states. The radiation responses of the Er2O3 and HfO2 MOS capacitors did not show a stable behaviour with an increase in radiation dose due to possible neutral electron trap centres. Contrary to expectations, we infer that more negative charges are trapped in Gd2O3-based device than positive charges with an increase in radiation dose. The C–V curves of the Yb2O3 MOS capacitor shifted in the same direction at both 100 kHz and 1 MHz, and as expected, positive charge traps in the structure are more efficient than negative charges. The observed sensitivities of Yb2O3 MOS capacitors are 4–7 times higher than those of SiO2, and the sensitivities of the Yb2O3 MOS capacitors with a total radiation dose of 70 Gy were found to be around 28.08 mV/Gy at both 100 kHZ and 1 MHz frequencies. The Yb2O3 appears to be a promising dielectric candidate for developing a new generation of radiation sensors with an excellent interface quality when compared to rare earth mixed oxides such as silicates, transition metal oxides, and the silicates based on transition metals, Al2O3, and BiFeO3. Our review of the literature suggests that while the radiation damage has been assessed comprehensively based on the C–V characteristics, microstructural characterization of the irradiated films and their interfaces is lacking even though the quality of oxide/Si interface is the most important feature of the devices. The electrical data should be correlated with the inferences from XPS, AFM, TEM, XRD, and other techniques. Further progress requires selection and validation of material properties based on theoretical calculations and predications, utilization of diverse thin film processing and characterization techniques, determining the effect of thickness on the properties of MOS capacitors, a thorough understanding of the interfaces, effect of frequency on the MOS capacitors and the interface characteristics, effect of radiation on the physical, interfacial, and electrical characteristics of MOS capacitors, and preparation and characterization of sensors based on thin films of novel mixed oxides and silicates of different chemistries.

We report on experimental observations of room temperature low frequency capacitance-voltage (CV) behaviour in metal oxide semiconductor (MOS) capacitors incorporating high dielectric constant (high-k) gate oxides, measured at ac signal frequencies (2 kHz to 1 MHz), where a low frequency response is not typically expected for Si or GaAs MOS devices. An analysis of the inversion regions of the CV characteristics as a function of area and ac signal frequency for both n and p doped Si and GaAs substrates indicates that the source of the low frequency CV response is an inversion of the semiconductor/high-k interface in the peripheral regions outside the area defined by the metal gate electrode, which is caused by charge in the high-k oxide and/or residual charge on the high-k oxide surface. This effect is reported for MOS capacitors incorporating either MgO or GdSiOx as the high-k layers on Si and also for Al2O3 layers on GaAs(111B). In the case of NiSi/MgO/Si structures, a low frequency CV response is observed on the p-type devices, but is absent in the n-type devices, consistent with positive charge (&amp;gt;8 × 1010 cm−2) on the MgO oxide surface. In the case of the TiN/GdSiOx/Si structures, the peripheral inversion effect is observed for n-type devices, in this case confirmed by the absence of such effects on the p-type devices. Finally, for the case of Au/Ni/Al2O3/GaAs(111B) structures, a low-frequency CV response is observed for n-type devices only, indicating that negative charge (&amp;gt;3 × 1012 cm−2) on the surface or in the bulk of the oxide is responsible for the peripheral inversion effect.

ABSTRACTA simple low-power and low-area metal-oxide-semiconductor field-effect transistor-only fully differential 1.5-bit pipelined analog-to-digital converter stage is proposed and designed in Taiwan Semiconductor Manufacturing Company 0.18 μm-technology using BSIM3v3 parameters with supply voltage of 1.8 V in inexpensive digital complementary metal-oxide semiconductor (CMOS) technology. It is based on charge pump technique to achieve the desired voltage gain of 2, independent of capacitor mismatch and avoiding the need of power hungry operational amplifier-based architecture to reduce the power, Si area and cost. Various capacitances are implemented by metal-oxide semiconductor capacitors, offering compatibility with cheaper digital CMOS process in order to reduce the much required manufacturing cost.

The properties of metal-oxide semiconductor (MOS) capacitors with different chemical treatments have been examined in this study. A MOS capacitor consists of an Al2O3/n-GaN/AlN buffer/Si substrate. Four chemical treatments, containing organic solvents, oxygen plasma and BCl3 plasma, dilute acidic and alkali solvents, and hydrofluoric acid, were used to reduce the metal ions, native oxides, and organic contaminants. The n-GaN surface was treated with these chemical treatments before Al2O3 was grown on the treated n-GaN surface to reduce the interface state trap density (Dit). The value of Dit was calculated using the capacitance–voltage curve at 1 MHz. The Dit of a u-GaN surface was modified using various solutions, which further influenced the contact properties of GaN.

The nonuniformity of the induced leakage current in metal oxide semiconductor (MOS) capacitors has been investigated in an electron cyclotron resonance (ECR) system. For plasma-etched MOS capacitors with 5-nm-thick oxides, it is found that the leakage currents induced by plasma etching increase with increasing overetching time. However, additional E bd (breakdown field) degradation is not obvious as overetching percentage increases from 10% to 50%. A mechanism based on the antenna charging effect has been proposed to explain the E bd electrical characteristics. In accordance with the mechanism, the E bd degradation has been significantly reduced by first etching off a narrow peripheral edge around the gate pattern.

The impact of different interfacial layers (ILs) on the electrical performances of Au/Ti/HfO2/Ge0.9Sn0.1 metal oxide semiconductor (MOS) capacitors is studied. Parallel angle resolved x-ray photoelectron spectroscopy measurements show that germanium diffuses into the HfO2 layer when no IL is used. This results in an increase in the tin content at the interface and a high interface state density. We demonstrate that the use of an IL prevents germanium and HfO2 intermixing and improves the electrical performance of MOS capacitors. Several ILs are studied such as alumina (Al2O3) and plasma oxidized GeSn (GeSnOx) prior to HfO2 deposition. C–V measurements correlated with simulations made by a customized analytical model indicate an interface state density of 5 × 1011 eV−1 cm−2 for the HfO2/GeSnOx/Ge0.9Sn0.1 gate stack. This result is promising for the integration of high mobility GeSn channels in CMOS devices.

Characterization of interface defects in ALD Al2O3/p-GaSb MOS capacitors using admittance measurements in range from kHz to GHz

Memory characteristics of platinum nanoparticle-embedded MOS capacitors