Metal Insulator Semiconductor Capacitors Research Articles

Impedance spectroscopy of Au/TiO2/n-Si metal-insulator-semiconductor (MIS) capacitor

In this study, the electrical properties of Au/TiO2/n-Si metal-insulator-semiconductor (MIS) capacitor were investigated by impedance spectroscopy (IS) technique. Impedance measurements were performed in the frequency range of 10 Hz-1 MHz for various bias voltages. The Cole-Cole plots show a single dielectric relaxation. The equivalent circuit was estimated from the shape of the Cole-Cole plots. The equivalent circuit of the MIS capacitor consists of a parallel resistor (Rp) and capacitor (Cp) in series with a resistor (Rs). It is observed that the Cole-Cole plots indicate a semicircle. The parameters of the equivalent circuit were determined by fitting the impedance measurement data. While the Rp value decreases with increasing the bias voltage, the Cp and Rs value are almost independent of the bias voltage. From the variation of log(Rp) with log(V), the dominant conduction mechanism of the MIS capacitor was determined as space-charge limited current (SCLC) mechanism.

Modeling of Organic Metal–Insulator– Semiconductor Capacitor

In this paper, we demonstrate the principle of operation of a metal-insulator-semiconductor (MIS) capacitor based on undoped organic semiconductor. In spite of low charge concentration within the semiconductor, this device exhibits a capacitance variation with respect to applied gate voltage $V_g$, resembling the capacitance-voltage $C$-$V$ characteristics of a traditional doped semiconductor based MIS capacitor. A physics based model is developed to derive charge concentration, surface potential $\psi_s$ and the capacitance of organic MIS capacitor. The model is validated with TCAD simulation results and is further verified with experimental results obtained from fabricated organic MIS capacitor consisting of poly(4-vinylphenol) and poly(3-hexylthiophene-2,5-diyl) as insulator and semiconductor, respectively.

Threshold voltage extraction for organic thin film transistor in linear region using asymmetric metal insulator semiconductor capacitive test structure

Metal Insulator Semiconductor (MIS) capacitors are commonly used as a test structure for characterization of semiconductor/insulator interface. However, MIS devices do not provide useful information in strong accumulation or inversion mode as the capacitance saturates to a constant value. An MIS capacitor with area asymmetry on the other hand, exhibits a gate voltage dependent capacitance in strong accumulation mode and can be used to obtain additional useful information about the semiconductor/insulator interface. The present work describes the use of asymmetrical metal–insulator–semiconductor device for characterization of the threshold voltage in metal–insulator–organic test structures. Simulation results are presented to show that the threshold voltage extracted from these devices not only matches with that extracted from current–voltage characteristics of organic thin film transistors in the linear region but is also much less sensitive to source contact resistance. The experimental results obtained with pentacene as active semiconductor and poly-vinyl-phenol as the dielectric are also presented to demonstrate the operation and merits of the proposed technique.

PEALD of HfO2 Thin Films: Precursor Tuning and a New Near-Ambient-Pressure XPS Approach to in Situ Examination of Thin-Film Surfaces Exposed to Reactive Gases.

A bottom-up approach starting with the development of new Hf precursors for plasma-enhanced atomic layer deposition (PEALD) processes for HfO2 followed by in situ thin-film surface characterization of HfO2 upon exposure to reactive gases via near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) is reported. The stability of thin films under simulated operational conditions is assessed, and the successful implementation of HfO2 dielectric layers in metal-insulator-semiconductor (MIS) capacitors is demonstrated. Among the series of newly synthesized mono-guanidinato-tris-dialkyl-amido class of Hf precursors, one of them, namely, [Hf{η2-(iPrN)2CNEtMe}(NEtMe)3], was representatively utilized with oxygen plasma, resulting in a highly promising low-temperature PEALD process at 60 °C. The new precursors were synthesized in the multigram scale and thoroughly characterized by thermogravimetric analyses, revealing high and tunable volatility reflected by appreciable vapor pressures and accompanied by thermal stability. Typical ALD growth characteristics in terms of linearity, saturation, and a broad ALD window with constant growth of 1.06 Å cycle-1 in the temperature range of 60-240 °C render this process very promising for fabricating high-purity smooth HfO2 layers. For the first time, NAP-XPS surface studies on selected HfO2 layers are reported upon exposure to reactive H2, O2, and H2O atmospheres at temperatures of up to 500 °C revealing remarkable stability against degradation. This can be attributed to the absence of surface defects and vacancies. On the basis of these promising results, PEALD-grown HfO2 films were used as dielectric layers in the MIS capacitor device fabrication exhibiting leakage current densities less than 10-7 A cm-2 at 2 MV cm-1 and permittivities of up to 13.9 without postannealing.

Gate/insulator-interfacial-dipole-controlled current conduction in Al2O3 metal-insulator-semiconductor capacitors

Electric dipoles at a metal-gate/Al2O3 interface are found to control the current conduction in negatively biased Al2O3 metal-insulator-semiconductor (MIS) capacitors by effectively increasing the Al2O3 electron affinity near the gate and thereby reducing the barrier height against electron field emission from the gate. By carrying out space-charge-controlled field emission analysis, the Al2O3 effective electron affinity in Al-gate capacitors was found to be larger than that for the Au gate by 0.38 eV, and the value for the Ni gate was similar to that for the Au gate. The cross-sectional transmission-electron-microscope images of the samples revealed the presence of an approximately 3-nm-thick layer intervening between the Al gate and the Al2O3 film. This layer is likely to have formed Al/Al2O3 interfacial dipoles that caused the aforementioned shift of the Al2O3 effective electron affinity. It was also confirmed that the conventional Fowler–Nordheim tunneling analysis yields remarkably erroneous results under the presence of these dipoles. These findings not only form the basis for investigating the band alignment of metal-gate MIS capacitors, but also alert us to a possibility of unexpectedly large leakage currents in negatively biased metal-gate MIS field-effect transistors.

Electrical Characterization of MOCVD Grown Single Crystalline AlN Thin Films on 4H-SiC

We report on a very low density of interface traps at the AlN/4H-SiC interface estimated from capacitance-voltage (CV) analysis of metal-insulator-semiconductor (MIS) capacitors. Single crystalline aluminum nitride (AlN) films are grown by metal organic chemical vapor deposition (MOCVD). Current-voltage (IV) analysis shows that the breakdown electric field across the AlN dielectric is 3 MV/cm. By depositing an additional SiO2 layer on top of the AlN layer it is possible to increase the breakdown voltage of the MIS capacitors significantly without having pronounced impact on the quality of the AlN/SiC interface.

Net negative fixed interface charge for Si3N4 and SiO2 grown in situ on 000-1 N-polar GaN

The electrical properties and trapping characteristics of Si3N4 and SiO2 dielectrics grown in situ on (000-1) N-polar GaN by metal organic chemical vapor deposition are investigated in this paper. The fixed charges, densities of near-interface trap states, and interface trap density in N-polar Si3N4 and SiO2 metal insulator semiconductor capacitors (MISCAPs) are quantified using a capacitance-voltage measurement method which is assisted by ultraviolet illumination and applied voltage-stress. The fixed charges and trap states are located at or near the interface of Si3N4 (SiO2)/N-polar GaN as indicated by the linear relationship between the flatband voltage/hysteresis and the Si3N4 (SiO2) thickness. Positive flatband voltages were measured for both the N-polar Si3N4 and SiO2 MISCAPs which is a promising route toward realizing normally off GaN-based metal insulator semiconductor power devices. Net negative fixed charge densities of 2.9 × 1012 cm−2 and 3.3 × 1012 cm−2 are located at the interface of Si3N4/GaN (N-polar) and SiO2/GaN (N-polar), respectively. The origin of this net negative interface fixed charge is briefly discussed, and the trap densities with fast and slow emission rates are quantified in both the N-polar Si3N4 and SiO2 MISCAPs. This study is a step toward identifying suitable gate dielectrics that can be integrated into N-polar high electron mobility transistors for high-frequency and switching applications.

Aluminium oxide thin film deposited by spray coating for p-type silicon surface passivation

A simple yet reproducible method to deposit high quality aluminium oxide (AlOx) film by spray coating is presented. Excellent thickness and refractive index uniformity is demonstrated. The AlOx film was found to be nearly stoichiometric with an oxygen to aluminium ratio of 1.7 from X-ray photoelectron spectroscopy (XPS) measurements. An interfacial layer with thickness of about 2 nm was observed in transmission electron microscopy analysis. The interfacial layer was determined to be aluminium silicate from XPS data. Electrical characterization of the films on Czochralski (Cz) p-type silicon yielded dielectric constant of 6.5 and mean breakdown field of 4.7 MV cm−1. Interface state density of 8.7×1010 eV−1cm−2 and fixed charge density of −5.5×1012 cm−2 were obtained from the electrical characterization of metal insulator semiconductor capacitors. The excellent interface quality with low interface state density and high negative charge is suitable for passivation of p-type silicon in solar cell applications. Effective surface recombination velocity of 12 cm s−1 and 48 cm s−1 were obtained for Cz p-type silicon surface for annealing temperature of 750°C and 790°C respectively without the use of capping layer.

Modeling the frequency response of organic metal-insulator-semiconductor capacitors

Substantial improvement of organic field effect transistors (OTFTs) toward circuit applications certainly demands stable device performance upon varying frequency and temperature. Organic metal-insulator-semiconductor (MIS) capacitor has been considered to be an efficient model system to predict the device performance of OTFT under the influence of frequency and temperature. In this study we show that the capacitance dispersion with respect to frequency and temperature in organic MIS capacitor device is an inherent property, which arises due to the low conductivity of the semiconductor along with Schottky type contact at the semiconductor-metal junction. In addition we propose an equivalent circuit model to explain the dispersion of capacitance with respect to frequency and temperature.

High-quality SiNx/p-GaN metal-insulator-semiconductor interface with low-density trap states

We report on a high-quality p-GaN metal-insulator-semiconductor (MIS) capacitors with sharp interface morphology and the lowest interface trap density by using SiNx as the gate dielectric layer. Transmission electron microscopy and x-ray photoelectron spectroscopy (XPS) analysis revealed a high-quality interface morphology with the effective removal of carbon and oxygen impurities. Better than the interface properties of Al2O3, SiO2, and CaF2/p-GaN metal-oxide-semiconductor (MOS) or MIS capacitors, the capacitance-voltage measurements of SiNx/p-GaN showed negligible electrical hysteresis after a two-step surface pre-treatment, leading to the lowest trapped charge density of 5 × 1010 cm−2. The interface state density distribution was also reduced to be ~1–2 × 1012 cm−2 · eV−1 at Et–Ev = 0.2–0.45 eV and 3–5 × 1012 cm−2 · eV−1 near the valance-band edge after the treatments. The achievement of the high-quality MIS interface was attributed to the suppression of the Mg-Ga-O interfacial disordered layer by the effective surface treatments and oxygen-free deposition process, which was usually observed at Al2O3/p-GaN MOS interface.

Effects of a photo-assisted electrochemical etching process removing dry-etching damage in GaN

We investigated the ability of a photo-assisted electrochemical (PEC) etching process to remove the damage that dry etching causes in the near-surface region of GaN samples. The process consists of anodic oxidation of the GaN surface and subsequent dissolution of the oxide with a chemical treatment, and the extent of the PEC reactions depends on the total charge density transferred in them. The PEC process was conducted for samples prepared with various dry-etching conditions followed by fabrication of Schottky barrier diodes (SBDs) and metal–insulator–semiconductor (MIS) capacitors. The PEC process greatly improved the barrier height, ideality factor, and reverse leakage current of SBDs. Capacitance–voltage measurements of MIS capacitors revealed that the densities of interface states and discrete traps were both reduced by the PEC process. The results obtained here show that the PEC process can remove dry-etching damage from the GaN surface.

Impact of remote oxygen scavenging on the interfacial characteristics of atomic layer deposited LaAlO3

In this paper, the influence of a remote interfacial layer (IL) scavenging method on the interfacial characteristics of LaAlO3 grown by atomic layer deposition (ALD) on Si substrates has been studied. After the fabrication of Pt/LaAlO3/Si and Pt/Ti/TiN/LaAlO3/Si metal-insulator-semiconductor (MIS) capacitors, the microstructures and electrical properties of these MIS capacitors have been comparatively investigated. High resolution transmission electron microscopy (HRTEM) analysis shows that the thickness of IL between LaAlO3 films and Si substrates is reduced by remote IL scavenging technique, contributing to lower equivalent oxide thickness (EOT) and to higher dielectric constant values. However, larger amount of oxygen vacancies and dangling bonds are induced in the MIS structure with IL scavenging reaction, resulting in a slight degradation of the gate leakage current-voltage and the breakdown characteristics.

Determination of Interface-State Distributions in Polymer-Based Metal-Insulator-Semiconductor Capacitors by Impedance Spectroscopy

Information on localized states at the interfaces of solution-processed organic semiconductors and polymer gate insulators is critical to the development of printable organic field-effect transistors (OFETs) with good electrical performance. This paper reports on the use of impedance spectroscopy to determine the energy distribution of the density of interface states in organic metal-insulator-semiconductor (MIS) capacitors based on poly(3-hexylthiophene) (P3HT) with three different polymer gate insulators, including polyimide, poly(4-vinylphenol), and poly(methylsilsesquioxane). The findings of the study indicate that the impedance characteristics of the P3HT MIS capacitors are strongly affected by patterning and thermal annealing of the organic semiconductor films. To extract the interface-state distributions from the conductance of the P3HT MIS capacitors, an equivalent circuit model with continuum trap states is used, which also takes the band-bending fluctuations into consideration. In addition, the relationship between the determined interface states and the electrical characteristics of P3HT-based OFETs is investigated.

Characterization of Molybdenum Oxide Thin Films Grown by Atomic Layer Deposition

Molybdenum oxide (MoO3) thin films have been deposited using plasma-enhanced atomic layer deposition with molybdenum hexacarbonyl (Mo(CO)6) and oxygen plasma. Self-limiting growth was verified at a deposition temperature of 162°C and the growth rate was determined to be 0.76 A/cycle. It was found that the as-deposited amorphous thin films crystallized into β- or α-MoO3 during annealing temperatures from 300°C to 400°C in air. In addition, the optical bandgap (Eg) of the amorphous MoO3 was estimated to be 4 eV by transmittance spectral analysis. Moreover, metal-insulator–semiconductor capacitors based on p-type (100) silicon substrates were fabricated to investigate the electrical properties of MoO3. It was shown that the MoO3 thin films exhibit a good dielectric performance and that the dielectric constant of the amorphous MoO3 was determined to be about 17. Additionally, a low leakage current of 6.43 × 10−7 A/cm2 at 1 V was detected and the equivalent oxide thickness was calculated to be 10.5 nm. As a result, MoO3 thin films, as a new high-κ gate dielectrics system, might be a good candidate for metal-insulator–semiconductor field-effect transistors based on two-dimensional transition metal dichalcogenides, especially for metal oxide semiconductor field-effect transistors using molybdenum disulfide (MoS2) as channel material.

Non-volatile memory and negative photoconductivity in a metal-insulator-semiconductor diode with embedded Co nanoparticles

We describe a new metal-insulator-semiconductor (MIS) device in which cobalt based nano particles (NPs) in a core-shell structure (Co–core and Co3O4-shell) are embedded between a thermally grown SiO2 layer and a HfO2 film deposited by atomic layer deposition. Two additional structures were prepared for comparison. One had no NPs and the other included the Fe NPs, prepared using the same procedure as used for the Co film. All devices exhibited the classic behavior of a voltage variable MIS capacitor with or without a large hysteresis as in non-volatile memory (NVM) systems. However, only the device with the Co core-shell structure exhibits a negative photoconductivity (NPC) effect as well as NVM capabilities in both the capacitance-voltage (C-V) and current-voltage (I-V) characteristics. The dependence of C-V and current voltage I-V characteristics on illumination intensity and wavelength (from ultraviolet to near infrared) as well as on temperature was characterized. Illumination enhances the NPC effect as well as the flat-band voltage shift determined from C-V characteristics and hence the memory width. Illumination in the wavelength range of 735–780 nm caused a current decrease, at a given voltage, by up to a factor of two. The NPC effect stimulates an annihilation of the stored charges and therefore erases the system instantly at a small applied bias. The main cause of the NPC effect under illumination is the photo excitation of supplementary trap channels in the Co3O4 shell, which lowers the free carrier density and hence the conductivity of the MIS structure.

Parameter extraction of gate tunneling current in metal–insulator–semiconductor capacitors based on ultra-thin atomic-layer deposited Al2O3

Metal–insulator–semiconductor devices were fabricated using ultra-thin (6 nm) atomic layer deposited Al2O3. From Ig–Vg measurements, it was determined that the main conduction mechanisms for these devices are Ohmic conduction at very low electric fields (E 2 MV cm−1) and finally, just before breakdown, Fowler–Nordheim (E > 5 MV cm−1). From the accurate verification of these conduction mechanisms, physical parameters such as barrier height (ΦB), effective mass (m*) and energy trap level (ΦT) are extracted and could be used to effectively understand the performance and reliability of these devices under different substrate injection conditions.

Electrical Characterization of Defects Created by γ-Radiation in HfO2-Based MIS Structures for RRAM Applications

The γ-radiation effects on the electrical characteristics of metal–insulator-semiconductor capacitors based on HfO2, and on the resistive switching characteristics of the structures have been studied. The HfO2 was grown directly on silicon substrates by atomic layer deposition. Some of the capacitors were submitted to a γ ray irradiation using three different doses (16 kGy, 96 kGy and 386 kGy). We studied the electrical characteristics in the pristine state of the capacitors. The radiation increased the interfacial state densities at the insulator/semiconductor interface, and the slow traps inside the insulator near the interface. However, the leakage current is not increased by the irradiation, and the conduction mechanism is Poole–Frenkel for all the samples. The switching characteristics were also studied, and no significant differences were obtained in the performance of the devices after having been irradiated, indicating that the fabricated capacitors present good radiation hardness for its use as a RS element.

Anomalous ${C}$ – ${V}$ Inversion in TSVs: The Problem and Its Cure

The metal–insulator–semiconductor capacitor formed by a through-silicon via (TSV) with its insulating layer and the p-type Si substrate may show an anomalous inversion behavior in the ${C}$ – ${V}$ characteristic. The dominant cause is the presence of positive charges in the backside (BS) passivation layer. In this paper, a dedicated test structure is proposed and characterized to confirm this hypothesis. Furthermore, a charge-free oxide/nitride BS passivation layer for preventing the anomalous ${C}$ – ${V}$ inversion, proposed in our previous work, is validated by experimental results on TSV structures manufactured up to the complete BS metallization processing.

Study of Sn and Mg doping effects on TiO2/Ge stack structure by combinatorial synthesis

The effects of Sn and Mg doping of a TiO2 film on a Ge substrate were investigated to improve leakage current properties and Ge diffusion into the TiO2 film. For systematic analysis, dopant-composition-spread TiO2 samples with dopant concentrations of up to 20.0 at. % were fabricated by RF sputtering and a combinatorial method. X-ray photoelectron spectroscopy revealed that the instability of Mg doping of TiO2 at dopant concentrations above 10.5 at. %. Both Sn and Mg dopants reduced Ge diffusion into TiO2. Sn doping enhanced the crystallization of the rutile phase, which is a high-dielectric-constant phase, although the Mg-doped TiO2 film indicated an amorphous structure. Sn-doping indicated systematic leakage current reduction with increasing dopant concentration. Doping at Sn concentrations higher than 16.8 at. % improved the leakage properties (∼10−7 A/cm2 at −3.0 V) and capacitance–voltage properties of metal–insulator–semiconductor (MIS) operation. The Sn doping of TiO2 may be useful for interface control and as a dielectric material for Ge-based MIS capacitors.

An Organic Temperature Sensor Based on Asymmetric Metal Insulator Semiconductor Capacitor With Electrically Tunable Sensing Area

An area-asymmetric organic metal-insulator-semiconductor (AMIS) capacitor is described, which exhibits strong temperature dependence. The gate electrode in the device is made much larger than the top electrode so that a significant fraction of the capacitance comes from the channel. This contribution, being dependent on mobility, has a strong temperature dependence, giving rise to a capacitor with positive temperature coefficient. The advantage of the proposed device as a temperature sensor includes not only the simplicity of fabrication but the ability to electrically tune the effective sensing area using voltage and frequency as well. Experimental results obtained with poly-4-vinyl-phenol/pentacene-based AMIS capacitor show that temperature coefficient as large as 1.98 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> −2</sup> °C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> can be obtained at a gate voltage of −15 V and a measurement frequency of 1 kHz.