High K Dielectrics

Abstract
The preparation and microwave
dielectric properties Cal(Lil/􀀳bz/3)o.8nI.lI03-'
ceramic filled polymer composites for microwave
substrate applications is discussed in this paper.
The prediction of the dielectric properties of
polymer-ceramic composites using different
theoretical models is also discussed. A Coplanar
Waveguide Monopole Antenna is designed and
fabricated using epoxy-CLNT polymer-ceramic
composite and compared its response with
standard FR-4 epoxy.

The work presented in this paper focuses on the
effects of high leakage current in field effect transistors and the
possible ways to play down with the leakage currents. This paper
combines density functional theory and non equilibrium Green’s
function formalism to perform atomic scale calculation of tunnel
currents through SiO2, HfO2, Ta2O5, ZrO2 and Dy2O3 dielectrics
in MOSFETs. The tunnel currents for different bias voltages
applied to Si/Insulator/Si systems have been obtained along with
tunnel conductance v/s bias voltage plots for each system and the plots have been analyzed with reference to the presently used
bulk Si/SiO2/Si systems that have SiO2 as the gate dielectric
material. The results justify the use of high dielectric constant
materials as gate dielectric in FET devices so as to enable further
downscaling of MOSFETs with reduced gate leakage currents
thereby enabling ultra large scale integration.

The ferroelectric Ca doped (Ba 0.9575 La 0.04 X 0.0025 ) (Ti 0.815 Mn 0.0025 Nb 0.0025 Zr 0.18 ) 0.99 O 3 was prepared by a high-temperature solid state reaction technique. For the understanding of the electrical and dielectric property, the relation between the crystal structures, electrical transition and ferroelectric transitions with increasing temperature (-160 to 35°C) have been analyzed. Xray diffraction analysis of the powders suggests the formation of a single-phase material with monoclinic structure. Capacitance and tanδ of the specimens were measured in the temperature range from -160 to 35°Cat frequencies 1 kHz -1 MHz. Detailed studies of dielectric and electrical properties indicate that the Curie temperature shifted to higher temperature with the increase in frequency. Moreover, the dielectric maxima dropped down rapidly initially and the dielectric peaks became extremely broad. The AC conductivity increases with increase in frequency. The low value of activation energy obtained for the ceramic samples could be attributed to the influence of electronic contribution to the conductivity.

Butyl rubber (BR)-single walled carbon nanotube (SWCNT) (BR-SWCNT) composites were prepared by
solution mixing process to evaluate its electromagnetic interference (EMI) shielding efficiency in the X
and Ku band (8.2–18 GHz) frequency range for flexible electrostatic discharge shielding applications.
Shielding properties of BR improved with SWCNT addition and EMI shielding effectiveness of about
9–13 dB was obtained for the composite with 8 phr of SWCNT loading in the measured frequency range.
The experimental results reveal that absorption was the dominating shielding mechanism. The dielectric
properties, conductivity and skin depth of BR-SWCNT composite were found to increase with SWCNT
loading and were observed to be significant factors influencing EMI shielding properties of the developed
composite

We report the results of the studies on crystal structure, electronic structure and dielectric properties of Er 1-x La x FeO 3 (ELFO) (x ¼ 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) orthoferrites synthesized by co-precipitation method. Rietveld refinement of the XRD data confirms the orthorhombic crystal structure for all the samples. The study of Fe L 3,2-edge X-ray Absorption spectroscopy shows the presence of Fe-ions in 3 þ valence state in all the samples. Investigations on the dielectric behavior of ELFO samples over the wide frequency range of 20 Hz to 5 MHz show the increment in the dielectric constant with La-doping. ErFeO 3 has the lowest value of dielectric constant whereas LaFeO 3 has the highest value of dielectric constant among all the samples. Effect of grain and grain boundary contribution on the dielectric behavior is studied using complex dielectric permittivity. The observed colossal dielectric behavior in LaFeO 3 is attributed to the combined contribution from the intrinsic dielectric constant of the material and that due to the modification in the microstructure.

An improved compact gate C-V model for MOS devices with high-k gate dielectrics is proposed. The model accurately includes the effect of wave function penetration into the gate dielectric. It is based on making λ, the exponent of the Airy function solution of the eigenenergy, dependent on the characteristics of the dielectric material and on the substrate doping density. Comparison with experimental C-V data shows that the proposed model is more accurate than existing model which consider a constant value of λ for all dielectric materials and doping densities.

ZrO2/Ge is potential high-k dielectric candidate to replace silicon based devices. Controlling stress in zirconia film and stabilizing high dielectric constant phase is crucial for high-k application. A precise control of stress and phase selectivity in high-k thin films is demonstrated. Thin films of ZrO2 were grown by reactive sputter deposition. Wide range of
growth stress in thin films from -0.3 to -2.8 GPa can be tuned by growth rate control. Adatom incorporation into grain boundary was the dominant source of observed stress. Phase selectivity in zirconia was achieved by tuning growth parameters.

Al:HfO 2 is grown on III−V compound substrates by atomic layer deposition after an in situ trimethylaluminum-based preconditioning treatment of the III−V surface. After post-deposition rapid thermal annealing at 700°C, the cubic/tetragonal crystalline phase is stabilized and the chemical composition of the stack is preserved. The observed structural evolution of Al:HfO 2 on preconditioned III−V substrates shows that the in-diffusion of semiconductor species from the substrate through the oxide is inhibited. Al-induced stabilization of the Al:HfO 2 crystal polymorphs up to 700°C can be used as a permittivity booster methodology with possibly important implications in the stack scaling issues of high-mobility III−V based logic applications.

A triple metal double gate (TM-DG) MOSFET with high-k dielectrics has been proposed to overcome the short channel effects. We are using top and bottom metal gates with different work functions to screen the effect of drain (DIBL effect). It has been found that this is effective in reducing the short channel effects. The metal gates have been used to remove the poly silicon depletion of conventional double gate (DG) MOSFET due to aggressive scaling to sub 100 nm regimes. It has been observed that use of metal gate with different workfunctions along with high-k dielectric improves the carrier transport in the channel.

A triple metal double gate (TM-DG) MOSFET with high-k dielectrics has been proposed to overcome the short channel effects. We are using top and bottom metal gates with different work functions to screen the effect of drain (DIBL effect). It has been found that this is effective in reducing the short channel effects. The metal gates have been used to remove the poly silicon depletion of conventional double gate (DG) MOSFET due to aggressive scaling to sub 100 nm regimes. It has been observed that use of metal gate with different workfunctions along with high-k dielectric improves the carrier transport in the channel.

High gate leakage current, as a central problem, has decelerated the downscaling of minimum feature size of field effect transistors. In this paper, a combination of density functional theory and non equilibrium Green’s function formalism has been applied to the atomic scale calculation of tunnel currents through CeO2, Y2O3, TiO2 and Al2O3 dielectrics in MOSFETs. The tunnel currents for different bias voltages applied to Si/Insulator/Si systems have been obtained along with tunnel conductance v/s bias voltage plots for each system. The results are in agreement to the use of high dielectric constant materials as gate dielectric so as to enable further downscaling of MOSFETs with reduced gate leakage currents thereby enabling ultra large scale integration.
When used as dielectric, TiO2 exhibits extremely low tunnel currents followed by Y2O3 while CeO2 and Al2O3 exhibit high tunnel currents through them at certain bias voltages.

We present a detailed analysis of electrically active gate oxide defects on damascene CMOS devices with a HfO 2 gate dielectric and a TiN/W gate electrode. The interface state density (D it) and the trapped oxide charge (N it) are determined by 2 and 3-level charge pumping analysis on high-quality nMOS and pMOS transistors. Furthermore, we discuss the influence of the gate stack defects on the carrier mobility in the channel and correlate the reduction of the gate oxide defect density to a mobility improvement for both electrons and holes.

The (Sr1xAx)2(Zn1xBx)Si2O7 ceramics (A5Ca, Ba and
B5Co, Mg, Mn, Ni) were prepared by the conventional solidstate
ceramic route and their structure and microwave dielectric
properties were investigated. The majority of the compositions
have an akermanite-type structure except for A/B5Ba/Zn and
Sr/Ni. A structural change is observed from tetragonal to monoclinic
with the increase in Ba21 content at the Ca-site. When
Zn21 was completely replaced by Ni21, a mixture of SrSiO3 and
NiO phases resulted instead of the solid solution Sr2NiSi2O7.
The variation of cell parameters and cell volumes of
(Sr1xAx)2(Zn1xBx)Si2O7 was studied for various compositions
(x) in the range 0–1. Excellent dielectric properties (er58.4,
Quf5105 000 GHz (at 12.628 GHz) and sf551.5 ppm/1C)
were obtained for the composition Sr2ZnSi2O7 when sintered
at 14751C/2 h. Addition of 2 wt% of SrTiO3 to Sr2ZnSi2O7
decreased the sf value to 13 ppm/1C with er58.8,
Quf560 000 GHz (at 12.585 GHz). Thus, a composite of
Sr2ZnSi2O7 and SrTiO3 is a possible material for millimeterwave
communication systems and as microwave substrates.

We demonstrate high performance chemical bath deposited CdS thin-film transistors (TFTs) using atomic layer deposited ZrO2 based high-k gate dielectric material. Our unique way of isolation of the CdS-based TFTs devices yielded significantly low leakage current as well as remarkable lower operating voltages (<5 V) which is four times smaller than the devices reported on CdS-based TFTs using SiO2 gate dielectric. Upon thermal annealing, the devices demonstrate even higher performance, including μFE exceeding 4 ± 0.2 cm2 V−1S−1, threshold voltage VT of 3.8 V, and Ion-off of 104–105, which hold much promise for applications in future electronic and optical devices.

The effect of constant voltage stress (CVS) on Pt/La 2 O 3 /n-Ge MOS devices biased at accumulation is investigated and reported. It is found that the stress induced leakage current (SILC) initially increases due to electron charge trapping on pre-existing bulk oxide defects. After 10 s approximately, a clear decay of SILC commences which follows a t Àn power law, with n lying between 0.56 and 0.75. This decay of SILC is not changed or reversed when the stressing voltage stops for short time intervals. The effect is attributed to the creation of new positively charged defects in the oxide because of the applied stressing voltage, while other mechanism such as dielectric relaxation proposed in the past is proved insufficient to explain the experimental data.

We have demonstrated the fabrication of highly continuous and smooth CdSe semiconductor films containing self-assembled nanocrystals (NCs) using a simple, low cost solution-processed deposition technique. The impact of thermal annealing and ethanedithiol (EDT) treatment on oleate capped CdSe NCs films is illustrated. Post deposition EDT treatment enhances strong electron coupling between NCs by reducing the inter-particle distance, which enhances four orders of magnitude of photocurrent in the pn-device. Mild thermal annealing of NC films cause large redshift and significant broadening. Our findings suggest that NCs with short-range organic ligands are suitable for high-performance Thin-Film-Transistors and next generation high-efficiency photovoltaics.

In this paper, based on recent research on BaTiO3 (BT) nanoparticles, BT/P(VDF-HFP) nanocomposites,
frequency-dependent dielectric properties of such a material system with high energy density have
been investigated as functions of the volume fraction of the nanoparticles at room temperature by several
theoretical models. For single domain and single crystals of BT, a Debye type of dissipation and soft mode
theory have been adopted to obtain a more precise frequency-dependent dielectric spectrum of BT. For nanodielectric
composites, among the others, Wiener Rule, Lichtenecker model, Maxwell–Wagner model, Yamada,
andmodified Kernermodel were applied to evaluate the frequency-dependent dielectric spectrum of nanocomposites.
A simple rule of mixture for the dielectric loss tangent was obtained using Lichtenecker logarithmic
rule. The results from theoretical calculations are compared with the experimental data. For the dielectric
constant, Lichtenecker model, Maxwell–Wagner model, and Yamada model show reasonable agreements with
the experimental data up to 50% volume fraction of the nanoparticles. At the higher volume fraction of the
nanoparticles, the experimental data show a decreasing trend of the dielectric constant of the composites due
to an increase in porosity of the system. In this case, a three-phase model (nanoparticles/pores/matrix) was
developed to predict dielectric properties of the system at higher volume fraction of the nanoparticles (up to
80 %). The results showed reasonable agreements for a wide range of frequency. This theoretical study provides
an essential information on dielectric properties of polymer-based BT nanocomposites with a wide frequency
range instead of the trial-and-error strategy of experiments and can be used for designing high energy density
dielectric materials in the future.

The (Sr 1Àx A x) 2 (Zn 1Àx B x)Si 2 O 7 ceramics (A 5 Ca, Ba and B 5 Co, Mg, Mn, Ni) were prepared by the conventional solidstate ceramic route and their structure and microwave dielectric properties were investigated. The majority of the compositions have an akermanite-type structure except for A/B 5 Ba/Zn and Sr/Ni. A structural change is observed from tetragonal to monoclinic with the increase in Ba 21 content at the Ca-site. When Zn 21 was completely replaced by Ni 21 , a mixture of SrSiO 3 and NiO phases resulted instead of the solid solution Sr 2 NiSi 2 O 7. The variation of cell parameters and cell volumes of (Sr 1Àx A x) 2 (Zn 1Àx B x)Si 2 O 7 was studied for various compositions (x) in the range 0-1. Excellent dielectric properties (e r 5 8.4, Q u  f 5 105 000 GHz (at 12.628 GHz) and s f 5 À51.5 ppm/1C) were obtained for the composition Sr 2 ZnSi 2 O 7 when sintered at 14751C/2 h. Addition of 2 wt% of SrTiO 3 to Sr 2 ZnSi 2 O 7 decreased the s f value to À13 ppm/1C with e r 5 8.8, Q u  f 5 60 000 GHz (at 12.585 GHz). Thus, a composite of Sr 2 ZnSi 2 O 7 and SrTiO 3 is a possible material for millimeterwave communication systems and as microwave substrates.

Resistive random access memory (RRAM) is a promising emerging nonvolatile memory which offer high density integration in the form of cross-bar array design. Selector devices are a vital requirement to suppress the cross-talk issue. In this letter, we are going to demonstrate the coexistence of resistive switching (RS) and threshold switching (TS) in an ultrathin 2-nm Aluminium oxide (AlO x )-based crossbar RRAM devices. Depending on current level the device itself can switch from TS to RS mode with a nonlinearity of >10 2 . Stable TS of >10 3 cycles has been achieved at 10 nA. Achievements of this letter offers the usability of 2-nm AlO x RRAM devices as a selector and as a memory device for high density crossbar array integration.

Electrical and physical properties of a metal-oxide-semiconductor [MOS] structure using atomic layer-deposited high-k dielectrics (TiO 2 /Al 2 O 3 ) and epitaxial GaAs [epi-GaAs] grown on Ge(100) substrates have been investigated. The epi-GaAs, either undoped or Zn-doped, was grown using metal-organic chemical vapor deposition method at 620°C to 650°C. The diffusion of Ge atoms into epi-GaAs resulted in auto-doping, and therefore, an n-MOS behavior was observed for undoped and Zn-doped epi-GaAs with the doping concentration up to approximately 10 17 cm -3 . This is attributed to the diffusion of a significant amount of Ge atoms from the Ge substrate as confirmed by the simulation using SILVACO software and also from the secondary ion mass spectrometry analyses. The Zn-doped epi-GaAs with a doping concentration of approximately 10 18 cm -3 converts the epi-GaAs layer into p-type since the Zn doping is relatively higher than the out-diffused Ge concentration. The capacitance-voltage characteristics show similar frequency dispersion and leakage current for n-type and p-type epi-GaAs layers with very low hysteresis voltage (approximately 10 mV). PACS: 81.15.Gh.

High gate leakage current, as a central problem, has decelerated the downscaling of minimum feature size of the field effect transistors In this paper, a combination of density functional theory and non equilibrium Green’s function formalism has been applied to the atomic scale calculation of the tunnel currents through CeO2, Y2O3, TiO2 and Al2O3 dielectrics in MOSFETs. The tunnel currents for different bias voltages applied to Si/Insulator/Si systems have been obtained along with tunnel conductance v/s bias voltage plots for each system. The results are in agreement to the use of high dielectric constant materials as gate dielectric so as to enable further downscaling of MOSFETs with reduced gate leakage currents thereby enabling ultra large scale integration. When used as dielectric, TiO2 exhibits extremely low tunnel currents followed by Y2O3 while CeO2 and Al2O3 exhibit high tunnel currents through them at certain bias voltages.

We report on the structural and electrical properties of Pr-based high-k dielectric films fabricated by solid-state reaction between metallic Pr and SiO 2 underlayers. A non-destructive depth profiling using synchrotron radiation excited photoelectron spectroscopy (SR-PES), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) were employed to examine the chemical composition and microstructure. Ab initio calculations were done to gain insight into the physical processes involved. SR-PES results indicate that Pr deposition at room temperature (RT) leads to the formation of a Pr silicide and a Pr oxide, what is in good agreement with the scenario expected from ab initio calculations. As revealed by TEM and electrical measurements, oxidation of the reacted structures, followed by annealing, results in a stacked dielectric composed of a SiO 2 -based buffer with an enhanced permittivity and a Pr silicate film with a high dielectric constant. The leakage current density of 10 À4 A/cm 2 was measured for stacks with capacitance equivalent thickness (CET) of 1.5 nm prepared by evaporation of the Pr layer on a 1.8 nm SiO 2 film, followed by oxidation in air ambient and annealing in N 2 atmosphere. The capacitance-voltage (C-V) curves exhibit a large flatband voltage (V FB ) shift indicating the presence of a positive charge in the stack. Switching away from the Al contacts to Au gate electrodes introduces a significant reduction of the V FB by 1.3 eV, what is much more than the change expected from the work function difference between Al and Au ($0.9 eV). This in turn implies that V FB is strongly affected by the gate interface electrode. r

The effective carrier mobility in HfO 2 -based n-and p-metal oxide semiconductor field-effect transistors and in their control SiO 2 devices has been investigated as a function of temperature for three different silicon crystal orientations ͑100͒, ͑111͒, and ͑110͒. For both HfO 2 and SiO 2 , the electron mobility is steadily reduced between these orientations, whereas the hole mobility exhibits the opposite trend. The mobility-temperature dependence follows a power law ϳ o T ␣ , and the exponent ␣ varies also systematically with Si orientation and carrier type. The main finding is the presence of two temperature ranges with specific exponent values ␣ 1 and ␣ 2 occurring only for holes and for the ͑100͒ and ͑111͒ orientations. This crossover with rising temperature is explained by the progressive scattering of Si light holes that form the first excited states above the heavy-hole ground state. The same observation in SiO 2 /Si͑100͒ points to scattering by acoustic phonons in bulk Si. In addition to the contribution of acoustic phonons, the systematic reduction of mobility in HfO 2 devices as compared to SiO 2 is attributed to remote soft optical phonon scattering. A detailed analysis allows us to determine the precise inversion charge density range ͑or effective electric field͒ where remote phonon scattering predominates.