Flat-band Shift Research Articles

Oxygen plasma-treated gold nanoparticle-based field-effect devices as transducer structures for bio-chemical sensing

EIS (electrolyte-insulator-semiconductor) sensors based on the functionalization of uncoated gold nanoparticles supported on a Si/SiO2 structure are presented. Oxygen plasma etching at moderate power (<200 W) provides a convenient and efficient way to remove organic capping agents from the gold nanoparticles without significant damage. Higher power intensities destroy the linkage between the SiO2 and the gold nanoparticles, and some of the gold nanoparticles are removed from the surface. The flat-band potential shift, i.e. the pH dependence of the gold-coated EIS sensors is similar (33 mV/pH) to the uncoated EIS pH-sensor. Lead, penicillin and glucose sensors were prepared by immobilization of β-cyclodextrin, penicillinase and glucose oxidase by various immobilization techniques.

Achieving 1nm capacitive effective thickness in atomic layer deposited HfO2 on In0.53Ga0.47As

A capacitive effective thickness (CET) value of 1.0nm has been achieved in atomic layer deposited (ALD) high κ dielectrics HfO2 on In0.53Ga0.47As∕InP. The key is a short air exposure under 10min between removal of the freshly grown semiconductor epilayers and loading to the ALD reactor. This has led to minimal formation of the interfacial layer thickness, as confirmed using x-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. The measured electrical characteristics of metal-oxide-semiconductor diodes of Au∕Ti∕HfO2(4.5nm)∕In0.53Ga0.47As showed a low leakage current density of 3.8×10−4A∕cm2 at VFB+1V, which is about eight orders of magnitudes lower than that of SiO2 with the same CET. The capacitance-voltage curves show an overall κ value of 17–18, a nearly zero flatband shift, and an interfacial density of states Dit of 2×1012cm−2eV−1.

Segregation of oxygen vacancy at metal-HfO2 interfaces

We perform first-principles calculations on metal-HfO2 interfaces in the presence of oxygen vacancies. Pt, Al, Ti, and Ag are considered as electrodes. It is found that oxygen vacancies are strongly attracted to the interface with binding energies of up to several eVs. In addition, the vacancy affinity of interfaces is proportional to the work function of metals, which is understood by the transition level of the vacancy and metal-Hf bonding. Interfacial segregation of vacancies significantly affects effective work functions of p metals. Our results are consistent with flatband shifts in p-type field effect transistors employing high-k dielectrics and metal gates.

The Quantization Impact of Accumulated Carriers in Silicide-Gated MOSFETs

We studied the electrical behavior of MOSFETs in both accumulation and inversion regions when the poly doping concentration was increased up to a level emulating the metallic limit for silicides. Our Poisson-Schrodinger simulations reveal a lower capacitance in the case of the silicided gate when compared with the ideal metal gate; as a consequence, the assumption that silicided gates behave like ideal metals leads to an overestimate of the extracted physical thickness of the insulator. We also showed that accumulation/depletion effects are still present in actual metal gates. Gate quantization produces a shift of the flatband voltage when compared with the classical value. This quantum shift increases as the polysicon doping increases, which is up to . However, for higher dopings, this flatband shift decreases and tends to disappear.

Interface characterization of ALD deposited Al2O3 on GaN by CV method

AbstractA high dielectric interface quality is the determining factor for high power GaN metal oxide semiconductor field‐ effect transistor (MOSFET) devices. We characterized 100 Å thick aluminum oxide (Al2O3) films deposited by ALD on MOCVD grown undoped GaN on sapphire. First we measured the leakage current and densification behaviour of the dielectric after annealing at different temperatures up to 900 °C and determined the polycrystalline phase change to be around 800 °C. Further we characterized the interface charges of both films according to the flatband shift, induced by over‐band gap UV light, showing the lowest interface charge density of 1.27 × 1011 cm–2 after thermal treatment at 850 °C. Additionally, we measured the AC conductivity and calculated the interface states density (Dit) of the upper half of the GaN bandgap, showing the lowest Dit of around 2×1010 cm–2 eV–1 at 2 eV above the valence band, while it remains higher around the band edge at 2.8×1011 cm–2 eV–1, after annealing at 750 °C. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Characterization of TBP containing polysiloxane membrane/insulator/semiconductor structures for hexavalent chromium detection

A hexavalent chromium-sensitive EMIS sensor (electrolyte membrane insulator semiconductor sensor) is prepared by deposition of a tributylphosphate (TBP) ionophore-containing siloprene membrane on a Si/SiO 2/Si 3N 4 structure. The developed EMIS sensor was studied by means of impedance spectroscopy, capacitance–voltage, X-ray photoelectron spectrometry and FT-IR spectroscopy. From the flat-band shift of the EMIS structure, the nersntian response to the anionic species Cr 2O 7 − was demonstrated. The linear range of detection is 10 − 4 M to 10 − 1 M and the detection limit is 10 − 5 M. Sulfate and chloride anions are shown not to be interfering whereas carbonate ions present a pK pot equal to 0.19.

Growth and Properties of Gadolinium Oxide Dielectric Layers on Silicon Carbide for High-K Application

We investigated the growth, interface formation as well as the structural and electrical properties of crystalline gadolinium oxide (Gd2O3) directly grown on 6H-SiC(0001) substrates by molecular beam epitaxy. The Gd2O3 layers were found to grow epitaxially resulting in the formation of flat (111) oriented layers with the cubic bixbyite type of structure. X-ray photoelectron spectroscopy measurements reveal a silicate-like Gd2O3/SiC interface. Furthermore, conduction and valence band discontinuities at the Gd2O3/6H-SiC interface were estimated with 1.9 eV and 1.2 eV, respectively. The fabricated capacitors exhibit suitable dielectric properties at room temperature; such as a dielectric constant of ε = 22, a leakage current of 10-8 A/cm2@1V and breakdown fields &gt; 4.3 MV/cm for layers with 14 nm thickness. The CV measurements exhibit only small negative flat band shifts and a very small hysteresis, resulting from fixed charges or interface trap levels in the range of 1x1012 cm-2. These properties make Gd2O3 suitable for high-k application also for SiC.

Improved high-field reliability for a SiC metal–oxide–semiconductor device by the incorporation of nitrogen into its HfTiO gate dielectric

Materials with high dielectric constant (k) have been used in SiC-based metal–oxide–semiconductor (MOS) devices to reduce the electric field in the gate dielectric and thus suppress a high-field reliability problem. In this work, high-k gate dielectrics HfxTi1−xO2 and HfxTi1−xON are applied in SiC MOS devices and an ultrathin thermally grown SiO2 is used as an interlayer between SiC and the high-k materials to block electron injection from SiC into the low-barrier high-k materials. Incorporating nitrogen into the Hf-Ti oxide (by adding nitrogen gas during its sputtering) stacked with a SiO2 interlayer (HfxTi1−xO∕SiO2) results in a better gate dielectric for the MOS capacitor, such as smaller frequency dispersion in the capacitance-voltage curve, less oxide charges, and better interface quality. Moreover, the nitrogen incorporation increases the dielectric constant of the oxide, but causes higher dielectric leakage, which can be suppressed by the SiO2 interlayer. High-field stress under constant electric field is performed on the stacked/nonstacked Hf-Ti oxides and oxynitrides, and it turns out that the two oxynitrides show a much smaller flatband shift and a less stress-induced leakage current compared with the two oxides. Based on these results, the HfxTi1−xON∕SiO2 stack could be a promising high-k gate dielectric for SiC MOS devices with enhanced reliability.

Sequential thermal treatments of SiC in NO and O2: Atomic transport and electrical characteristics

Sequential thermal oxidations and oxynitridations of SiC were performed using O218 and NO. The resulting films were characterized by x-ray photoelectron spectroscopy, ion beam analyses, and capacitance-voltage measurements. The best electrical characteristics were obtained from films directly grown in NO. A subsequent oxidation in O2 degraded the interface due to negative flatband-voltage shift, removal of N, and formation of C compounds, while a further annealing in NO brought the flatband shift in the C-V curves to rather moderate figures. This shift is related to competitive processes taking place during dielectric film formation which are discussed.

Ionizing Dose Effect of Thermal Oxides Implanted with Si+ Ions

Total ionizing dose effects of Si+ ion implantedthermal oxides are studied by 10 keV x-ray irradiation.Photoluminescence (PL) method is engaged to investigate nanostructuresof samples. Ar+ implanted samples are also studied by thesame way to provide a comparison. The results show that Si+implantation following with high temperature annealing can significantlyreduce the radiation induced flatband shift, which is caused by netpositive charge accumulation in oxides. This reduction is attributed tothe formation of Si nanoscale structures. Ar+ implantation is alsofound to reduce the radiation induced flatband shift, while it isdifferent that the reduction with Si+ implantation shows littledependence on implant dose of Ar+ ions. This is explained bypossible increase of recombination centres.

Evaluation of Dielectric Reliability of Ultrathin HfSiOxNy in Metal-Gate Capacitors

We have studied the electrical and breakdown characteristics of 5 nm-thick HfSiO x N y (Hf/(Hf + Si) =∼0.43, nitrogen content = 4.5-17.8 at.%) in Al-gate and NiSi-gate capacitors. For Al-gate capacitors, the flat-band shift due to positive fixed charges increases with the nitrogen content in the dielectric layer. In contrast, for NiSi-gate capacitors, the flat band is almost independent of the nitrogen content, which is presumably controlled by the quality of the interface between NiSi and the dielectric layer. The leakage current markedly increases with nitrogen content. Correspondingly, although the time-to-soft breakdown, t SBD , gradually decreases with increasing nitrogen content, the charge-to-soft breakdown, Q SBD , increases with the nitrogen content. For Al-gate capacitors, the Weibull slope of time-dependent dielectric breakdown (TDDB) under constant voltage stress (CVS) remains constant at ∼2 for a nitrogen content of up to 12.5 at.% and then decreases to unity at 17.8 at.%. This must be a condition critical to the formation of the percolation path for breakdown. In contrast, for NiSi gate capacitors, a Weibull slope smaller than unity was obtained, suggesting that structural inhomogeneity, involving defect generation, is introduced during the NiSi gate fabrication, but this negative impact is reduced with nitrogen incorporation.

Protein-Mediated Nanocrystal Assembly for Flash Memory Fabrication

For the first time, we demonstrate that a chaperonin protein lattice can be used as a template to assemble nanocrystal (NC) arrays for Flash memory fabrication. This provides a new approach that can incorporate different types of NCs from a colloidal suspension for Flash memory fabrication. Lead selenide and cobalt NC assemblies achieved through this method have a high density of 9.5times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 1.6times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively, as well as good distribution uniformity. Devices exhibit promising Flash memory functions, with a flatband shift of 0.5 under 8-V operation, endurance >10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> cycles, and retention time >10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4 </sup> s

Interfacial compound suppression and dielectric properties enhancement of F–N codoped ZrO2 thin films

Fluorine and nitrogen codoped ZrO2 is produced on p-type Si (100) wafers by cathodic arc deposition and the interfacial and dielectric characteristics of the thin films are investigated. F–N codoping is found to effectively suppress the interfacial compounds between ZrO2 and silicon and the dielectric properties are also improved. Negligible flatband shift and hysteresis are achieved, implying that the fixed charge centers in the thin films and the interfacial states are obviously reduced. The improvement can be attributed in part to the large electronegativity of F radicals that are chemically more active.

A Study of compressively strained Si0.5Ge0.5 metal-oxide-semiconductor capacitors with chemical vapor deposition HfAlO as gate dielectric

The interfacial and electrical properties of metal organic chemical vapor deposited HfAlO on compressively strained Si0.5Ge0.5 (ε-Si0.5Ge0.5) substrate without or with surface nitridation treatment were investigated. X-ray photoelectron spectroscopic analysis suggests that an interfacial layer containing GeOx, Hf silicate, and Al silicate exists on substrates with direct deposition of HfAlO, whereas an interfacial layer containing SiNxOy exists on substrates with surface nitridation prior to HfAlO deposition. The TaN∕HfAlO∕ε-Si0.5Ge0.5 capacitor with surface nitridation shows a larger permittivity of the entire gate dielectric with a thinner interfacial layer (in terms of equivalent oxide thickness), a smaller interface trap charge density, and less severe flatband shift as well as two orders of magnitude lower gate leakage in comparison with those capacitors without nitridation.

Variation of flatband potential of oxide nanocrystalline particles with core-shell structured semiconductor-MgO composites

SnO 2 thin films and particles show feeble solar cell performance and poor photocatalytic activity respectively. It has been reported that coating of a thin MgO layer on SnO 2 particles results in enhancement of both solar cell performance and catalytic activities. The promoting effect of MgO layer was owing to barrier effect where MgO acts as a barrier layer for charge recombination. We noticed negative shift of flatband (FB) potential of SnO 2 with the increase of pH values and coating of a thin MgO layer on SnO 2 particles. It is shown how the negative shift in FB potential may contribute to enhance the solar cell efficiencies and photocatalytic activity in addition to the barrier effect of MgO layer.

Enhanced electrical characteristics of Au nanoparticles embedded in high-k HfO2 matrix

We present experimental results for laser-induced Au nanoparticle (NP) embedded in a HfO2 high-k dielectric matrix. Cross-sectional transmission electron microscopy images showed that the Au NPs of 8nm in diameter were clearly embedded in HfO2 matrix. Capacitance-voltage measurements of Pt∕HfO2∕AuNPs∕HfO2 on p-type Si substrate reliably exhibited metal-oxide-semiconductor behavior with a large flatband shift of 4.7V. In addition, the charge retention time at room temperature was found to exceed 105h. This longer time was attributed to the higher electron barrier height via high work function of the Au NP.

Al/La2O3 Analysis of Post Metallization Annealed MISFET by XPS

La2O3 gated MISFETs with various heat treatments were fabricated and measured. High effective mobility was obtained using a Post Metallization Anneal (PMA) with Al gate electrodes. XPS analysis showed the formation of a thin Al2O3 interface layer between the Al and La2O3 during the annealing. The formation of the Al2O3 layer increased the EOT and shifted the flatband shift in the positive direction. The improvement of the effective mobility can be explained by less formation of oxygen vacancies.

Visualization of Progressive Breakdown Evolution in Gate Dielectric by Conductive Atomic Force Microscopy

To understand the breakdown (BD) mechanism in gate oxide of MOSFET, BD evolution is investigated by a conductive atomic force microscope. High electric fields of both polarities are applied to induce a pre-BD degradation and a BD transient. Structural hillocks and negative charges are simultaneously observed at both pre- and post-BD stages. The hillocks show stress-polarity dependence, and the height increases with BD evolution. A flat-band shift caused by negative charges does not depend on stress polarity. Lateral size of the hillocks and the electrical degradation remains similar throughout the BD evolution. Progressive structural evolution of dielectric BD is confirmed, where polarity-dependent Si deformation plays an important role.

Charge Trapping in High-k Gate Dielectrics: A Recent Understanding

Charge trapping in Hf-based high-k dielectrics, used in MOS transistor gate stacks, causes threshold voltage shift during constant voltage stress (CVS). It seemed to be very transient due to the presence of a large number of shallow traps and can be eliminated by applying a reverse direction electric field. Recent findings, however, suggest that deep traps significantly contribute to the reliability of various Hf- based high-k gate stacks. The origin of the deep traps and their dependence on O vacancy formation during dielectric deposition is discussed. Flatband shift and leakage current dependence on these deep traps is also outlined. We have experimentally observed trap levels from low temperature measurements assuring the presence of O vacancies in Hf- silicate based films. It is further shown that negative-U transition to deep defects is responsible for trap assisted tunneling under substrate injection. This has the potential to be the ultimate limiting factor for the long-term reliability of Hf-based high-k gate dielectrics.

Structural and electrical evolution of gate dielectric breakdown observed by conductive atomic force microscopy

To clarify the breakdown (BD) mechanism in the gate oxide of transistors, BD evolution from prebreakdown (pre-BD) stage to BD transient is investigated by conductive atomic force microscopy. High electric fields of both polarities are applied to induce pre-BD degradation. Structural hillocks are observed to be dependent on stress polarity. The height of hillocks increases with BD evolution while keeping a similar lateral size. Flatband shift caused by negative charge is observed independent of stress polarity. Lateral size of the electrical degradation is similar to that of the hillock throughout BD evolution. We attribute the hillocks to deformation of Si substrate at the pre-BD stage, where an electrothermal effect plays an important role.