A junctionless tunnel field effect transistor with low subthreshold slope

we demonstrate the design of a triple gate n-channel junctionless transistor that we call a junctionless tunnel field effect transistor (JLTFET). The JLTFET is a heavily doped junctionless transistor which uses the concept of tunneling, by narrowing the barrier between source and channel of the device, to turn the device ON and OFF. Simulation shows significant improvement compared to simple junctionless field effect transistor both in I _ON/I _OFF ratio and subthreshold slope. Here, junctionless tunnel field effect transistors with high-k dielectric and low-k spacers are demonstrated through simulation and shows an ON-current of 0.25 mA/μm for the gate voltage of 2 V and an OFF current of 3 pA/μm (neglecting gate leakage). In addition, our device shows optimized performance with high I _ON/I _OFF (～10⁹). Moreover, a subthreshold slope of 47 mV/decade is obtained for a 50 nm gate length of simulated JLTFET at room temperature which indicates that JLTFET is a promising candidate for switching performance.     

Integration and characterization of MFISFET using Pb5Ge3O11

Abstract

The first MFIS FETs PMOS using Pt/Pb₅Ge₃O₁₁/ZrO₂/n-Si structure has been successfully fabricated. The PGO thin film was deposited by spin on method. Single phase PGO with strong c-axis orientation and low leakage current was obtained on ZrO₂ substrate. Pt was used as top electrode and the gate stack was dry etched using chlorine chemistry. Using CMOS compatible process, the integration of MFIS FETs is simple and reliable. I_D-V_G and I_D-V_D were characterized on 10 × 10 μrn (L × W) devices. The memory window obtained is about 1.3V with 200nm PGO and 13nm ZrO₂. It is also found that memory window is less dependent on device sizes.     

Microstructure and dielectric properties of ferroelectric barium strontium titanate ceramics prepared by hydrothermal method

Ba _x Sr_1-x TiO₃, nanoparticles with different Ba compositions were synthesized by a hydrothermal method. The mechanism of hydrothermal reactions was discussed based on DTA/TG, XRD and TEM characterizations. The result showed that perovskite structure was developed through the mutual diffusion between the intermediate phases and TiO₂ phase. The grain size of the Ba_0.77Sr_0.23TiO₃ (BST77) powders was about 20–40 nm. BST ceramics were made from the hydrothermal-derived BST powders and the dielectric properties of the BST ceramics were measured. Due to the small grain size and active surface energy of the BST powders prepared by hydrothermal method, the BST ceramics showed low sintering temperature. It was found that the BST77 ceramics sintered at 1280 °C showed dielectric constant peak dispersion which was believed to be caused by dimension domino effect.     

C-Axis Oriented MOCVD YMnO3 Thin Film and Its Electrical Characteristics in MFIS FeTRAM

Yttrium manganate (YMO) thin films were prepared on SiO₂ buffered silicon as a candidate for ferroelectric transistor random access memory (FeTRAM). The films were deposited by flash evaporated MOCVD at low temperature and post annealed to crystallize the c-axis oriented hexagonal YMO phase. It is found that oxygen content and substrate temperature are major parameters determining c-axis orientation. For the electrical characteristics, P_r (remnant polarization) ～2 μ C/cm² and ? (dielectric constant) ～ 20 are obtained in Pt/YMO/Pt structures. It is also found that a top buffer layer of 30 nm ZrO₂ helps to reduce the leakage current of Pt/top buffer/YMO/SiO₂/Si stack to 10^{? 7} A/cm² and improves the C-V memory window from 0.2 V to 2 V.     

Effect of seed layers on dielectric properties of Ba(Zr0.3Ti0.7)O3 thin films

The Barium zirconium titanate Ba(Zr_0.3Ti_0.7)O₃ thin films were prepared on Pt/Ti/SiO₂/Si substrates with seed layers at the BZT/Pt interface by sol–gel process. Microstructure and structure of thin films were examined. Dielectric properties of thin films with various seed layers thicknesses were investigated as a function of frequency and direct current electric field. The tunability and dielectric constant of BZT thin films increased with increasing seed layer thickness from 0 to 20 nm, while it decreased with a further increase in thickness above 20 nm, meanwhile, the leakage current showed the similar tendency at applied electric field of 250 kV/cm. The optimized seed layer thickness for BZT thin films plays an important role in maintaining the high tunability and low leakage current, which are suitable for microwave device applications.     

Ferroelectric phase transitions in sodium nitrite nanocomposites

The structure and dielectric properties of sodium nitrite and its solid solutions confined in porous glasses have been studied. The temperature dependences of the order parameter and the unit cell volume for NaNO₂ embedded into porous glasses with different pore sizes were studied by neutron diffraction in the ferro- and paraelectric phases. The characteristic sizes of nanoparticles are determined. It is shown that at a size of nanoparticles smaller than ~50 nm a crossover of the phase transition from first order to second order is observed. The effect of doping of sodium nitrite with potassium nitrite on the dielectric properties of the nanocomposite materials was studied and a strong lowering of the dielectric losses was observed.     

Chemical synthesis,structural characterization and electrical studies of nanoceria for CMOS applications

Cerium oxide nanoparticles were synthesized using cerium nitrate hexa hydrate and ammonium carbonate as precursors. Structural characterizations were done using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The crystallite size and lattice strain on the peak broadening of CeO₂ nanoparticles were studied using Williamson-Hall (W-H) analysis. The dielectric properties of nanocrystalline CeO₂ samples with different calcination temperatures, and frequencies have been studied over a temperature range from 303 to 423 K. It is found that the dielectric constant and dielectric loss for all temperatures have high values at low frequencies, which decreases rapidly as frequency is increased and attains a constant value at higher frequencies. The room temperature dielectric constant ε′ obtained for the as prepared CeO₂ nanoparticle sample is 61, which constitutes the highest value ever reported at low frequency. A.C. conductivity, which was derived from dielectric constant and loss tangent data, has a low value at smaller frequencies that increases as the frequency is increased. The dielectric constant and a.c. conductivity values are shifted upwards as the temperature is raised. However, these values are decreased as the annealing temperature is increased. The desired structural properties and high dielectric constant of nanophase CeO₂ make it as a promising material for the high dielectric constant dielectric gate in complementary metal oxide semiconducting (CMOS) devices.     

Effects of various oxide fillers on physical and dielectric properties of calcium aluminoborosilicate-based dielectrics

Physical and dielectric properties of LTCC (low temperature co-fired ceramics) materials based on a typical calcium aluminoborosilicate glass and various fillers such as Al₂O₃, BaTiO₃, CaTiO₃, TiO₂, ZrO₂, MgO and SiO₂ were investigated. Densification, crystallization and thermal and dielectric properties were found to strongly depend on the type of filler. The XRD patterns of Al₂O₃, BaTiO₃, CaTiO₃ and MgO samples demonstrated crystalline phases, CaAl₂Si₂O₈, BaAl₂Si₂O₈, CaTiSiO₅ and CaMgSi₂O₆, respectively, as a result of firing at 850 °C. For the sample containing CaTiO₃ filler, specifically, dielectric constant increased drastically to approximately 19.9. A high quality factor of >210 and a high TCE (temperature coefficient of expansion) of >8.5 ppm/°C were obtained for the composition containing MgO or SiO₂. Near zero TCF (temperature coefficient of frequency) was obtained for the samples containing TiO₂. The purpose of this work is to investigate the effects of various ceramic fillers on physical and dielectric properties and ultimately to provide the technical guidelines for the proper choice of filler in various LTCC systems.     

Low-temperature sintering of BaTiO3 with Mn-Si-O glass

In order to reduce sintering temperature and prevent adverse dielectric effects, pure BaTiO₃ powder with the addition of Mn-Si-O glass was sintered in the temperature range of 1175–1300°C. Microstructural observation showed that BaTiO₃ grains of the sintered samples only grew from the initial 400 nm to an average of 430 nm between 1175–1275°C for 1 h, or sintered at 1250°C as long as 27 h. Abnormal BaTiO₃ grains are not found in the sintered samples. The microstructure and phase analysis showed that the dielectric properties, tetragonality, and grain growth of BaTiO₃ are closely controlled by the formation of the liquid phase, newly formed Ba₂TiSi₂O₈ grains, and Mn solid solution in BaTiO₃ grains.     

Ferroelectricity of 30 nm BaTiO3 ceramics prepared by high pressure sintering

BaTiO₃ ceramics with a grain size of 30 nm were prepared at 6 GPa, 1,273 K using a three-step high pressure sintering method. The sintered bulk is uniform and the relative density is above 96% of the theoretical value. Similar to normal BaTiO₃, successive phase transitions were observed in 30 nm BaTiO₃ ceramics by X-ray diffraction method with the change of temperature. After annealing in O₂, a broadened ferroelectric transition was obtained at 398 K and the relative dielectric constant is 1,700 at 10 kHz.     

Low operating temperature CO sensor prepared using SnO<Subscript>2</Subscript> nanoparticles

A low operating temperature CO (carbon monoxide) sensor was fabricated from a nanometer-scale SnO₂ (tin oxide) powder. The SnO₂ nanoparticles in a size range 10–20 nm were synthesized as a function of surfactant (tri-n-octylamine, TOA) addition (0–1.5 mol%) via a simple thermal decomposition method. The resulting SnO₂ nanoparticles were first screen-printed onto an electrode patterned substrate to be a thick film. Subsequently, the composite film was heat-treated to be a device for sensing CO gas. The thermal decomposed powders were characterized by field-emission scanning electron microscopy (FESEM), X-ray diffractometry (XRD), and surface area measurements (BET). The CO-sensing performance of all the sensors was investigated. The experimental results showed that the TOA addition significantly decreased the particle size of the resulting SnO₂ nanoparticle. However, the structure of the powder coating was crucial to their sensing performance. After heat-treatment, the smaller particle tended to cause the formation of agglomeration, resulting in the decline of surface area and reducing the reaction site during sensing. However, the paths for the sensed gas entering between the agglomerated structure may influence the sensing performance. As a CO sensing material, the SnO₂ nanoparticle (~12 nm in diameter) prepared with 1.25 mol% TOA addition exhibited most stable electrical performance. The SnO₂ coating with TOA addition >0.75 mol% exhibited sensor response at a relatively low temperature of <50°C.     

Fabrication and characterization of micropatterned barium titanate ceramics

A new patterning method combining electron beam (EB) lithography and electrophoretic deposition (EPD) for fabricating micropatterned barium titanate (BaTiO₃) thin films was investigated. At first, resist molds with high resolution were prepared using EB lithography on Pt/Ti/Si substrates. Then BaTiO₃ nanoparticles were deposited on the substrates by EPD from a transparent suspension of monodispersed BaTiO₃ nanoparticles; a mixed solvent of 2-methoxyethonal and acetylacetone with a 9:1 volumetric ratio was used as a dispersion medium. The nanoparticles with an average size of about 10 nm were synthesized at a low temperature of 90 °C by a high concentration sol-gel process. EPD layers superfluously deposited on the resist molds were mechanically polished away, followed by chemically removing the molds in a resist remover to leave micropatterns of BaTiO₃ nanoparticles on the substrates, which were finally sintered to yield micropatterned BaTiO₃ ceramic thin films. The method developed may be used to fabricate other micropatterned electroceramic thin films.     

Size dependence of THz region dielectric properties for barium titanate fine particles

Barium titanate (BaTiO₃) crystallites with various particle sizes from 22 to 500 nm were prepared by the two-step thermal decomposition method of barium titanyl oxalate. Various characterizations revealed that these particles were impurity-free, defect-free, dense BaTiO₃ particles. The powder dielectric measurement clarified that the dielectric constant of BaTiO₃ particles with a size of around 58 nm exhibited a maximum of over 15,000. To explain this size dependence, the THz region dielectric properties of BaTiO₃ fine particles, especially Slater mode frequency, were measured using the far infrared (FIR) reflection method. As the result, the lowest Slater mode frequency was obtained at 58 nm. This tendency was completely consistent with particle size dependence of the dielectric constant.     

Sol-gel Synthesis and Photoluminescence Characterization of Ba2SiO4:Eu2+ Green Phosphors for White-LED Application

In this paper, Ba₂SiO₄:Eu²⁺ green phosphor was synthesized by sol-gel method. TGA-DTA, XRD, SEM and PL spectra were used to characterize the as-prepared phosphors. The phosphors are composed of nanoparticles with 60 nm grain size and exhibit green light with a broad peak around 500 nm. The relationship between crystal growth, morphology and luminescent properties was studied. The structure and luminescence properties of phosphors synthesized in different conditions were also discussed.     

Improved energy density and dielectric properties of P(VDF-HFP) composites with TiO<Subscript>2</Subscript> nanowire clusters

Dielectric composites are of great demand in the micro-electronics industry. To enhance the energy storage density of the composites, TiO₂ nanowire clusters was synthesized by a hydrothermal method and incorporated into the P(VDF-HFP) polymer matrix in this work. The microstructure, dielectric properties of the prepared film were discussed and the effects of TiO₂ loading on the energy density were investigated. The results shows that the TiO₂ clusters were tightly blended to the P(VDF-HFP) matrix owing to the dopamine-modified interface. The dielectric constant increased with the loading of TiO₂, the maximum dielectric constant reached 12.04 with 7.5 vol% TiO₂ loading at 1 kHz, as compared to 5.01 for the neat P(VDF-HFP). The enhanced dielectric constant was attributed to the interface polarization originated from the large interface area between the TiO₂ nanowire and polymer matrix. The discharged energy density of the composite significantly increased to 1.35 J/cm³ with 7.5 vol% TiO₂ nanowire clusters, which was two times higher than that of the neat P(VDF-HFP) at the same condition. The findings of this work can shed a light on improving the energy density of energy storage device via morphology modification.     

Neodymium substituted Bi4Ti3O12 nanostructures through self-assembly

For the sake of fabricating the ultrahigh density ultralarge scale integration (ULSI) memory chips, the ferroelectric nanostructures fabricated through self-assembly are studied. In this paper, we synthesized the neodymium substituted Bi₄Ti₃O₁₂ nanostructures on Pt/Ti/SiO₂/Si substrates. The method we used here was spin coating precursors with a series of different concentrations on the substrates and then annealing at 750 °C in the oxygen atmosphere to get the self-patterning nanoparticles. In order to avoid the influence of the Pt/Ti/SiO₂/Si substrates to the largest extent, the substrates were annealed first for different time in oxygen atmosphere to select appropriate conditions. Scanning probe microscope, and X-ray diffraction were used to detect the morphology and the crystalline structure of the nanoparticles respectively. The well-separated Bi_3.15Nd_0.85Ti₃O₁₂ particles have a typical lateral size about 100–150 nm and height about 20–25 nm. XRD reveals pyrochlore phase in the low concentration samples. The lower the precursor’s concentration, the higher the excess of Bi element is needed to form the pure perovskite nanoparticles.     

Characterization of PT ferroelectric thin films on porous silica for pyroelectric IR detectors

Ferroelectric PbTiO₃ thin films were deposited on Pt/DS/PS/SiO₂/Si substrates by sol–gel technique. Porous silica (PS) thin film was used as thermal-insulation layer and dense silica (DS) thin film was a buffer layer to reduce surface roughness of PS layer. Root mean square surface roughness can be effectively reduced from 9.7 to 3.5 nm after PS buffer layer was prepared. The average grain size of PT thin films decreased slightly with increasing thickness of porous silica. Dielectric constant of PT increased from 107 to 171 at 1 KHz as thickness of PS layer increased from 0 to 2,000 nm. PT thin film prepared on 2,000 nm porous silica exhibited good dielectric property. The leakage current density was less than 1.6?×?10^-6 A/cm² when the applied electrical field was 200 kV/cm. The composite film is suitable for preparing pyroelectric IR detectors.     

Structural, dielectric and electrical studies of MgAl2−2xY2xO4 (x = 0.00–0.05) cubic spinel nano aluminate

Investigations were carried out on a series of MgAl_2-2xY_2xO₄ (x?=?0.00–0.05) nanoparticles prepared in steps of 0.01 by chemical co-precipitation method to study the effect of yttrium substitution at aluminum site on the structural, dielectirc and electrical properties. The single phase cubic spinel structure of all the samples was confirmed by X-ray diffraction (XRD). The Fourier transform infrared spectroscopy (FTIR) study shows two strong absorption bands in the frequency range 400–800 cm^?1, on the tetrahedral and octahedral sites respectively. Elemental analysis by Energy dispersive X-ray fluorescence (EDXRF) shows that samples are stoichiometric. The scanning electron microscopy (SEM) study reveals surface morphology of nanoparticles. Transmission electron microscopy (TEM) study shows the individual nanoparticles size and validates the nanocrystalline nature of the samples. The variation of dielectric permittivity at room temperature as a function of frequency (1 KHz to 1 MHz) suggests the dielectric dispersion due to Maxwell-Wagner Interfacial Polarization. AC conductivity study reveals that the conduction is due to small polaron hopping. The electrical modulus analysis shows that nanocrystalline MgAl_2?2xY_2xO₄ system exhibits non Debye type relaxation. The dc resistivity was found to increase with increase in yttrium content.     

Microwave-Hydrothermal Synthesis of Ni0.53Cu0.12Zn0.35Fe2O4/SiO2 Nanocomposites for MLCI

The nanocomposites of NiCuZnFe₂O₄-SiO₂ were prepared using Microwave-Hydrothermal method at 160°C/45 min.The as-synthesized powders were characterized using X-ray diffraction and Transmission Electron Microscope (TEM).The average particle size of the powders were found to be ～20 nm.The powders were densified at 900°C/30 min using Microwave sintering method. The sintered composite samples were characterized using XRD and Scanning Electron Microscopy (SEM). Crystallite size of the ferrites decreases with an increase of SiO₂ content. The density of the composites varies of 93–98% of theoretical density. The densities of the present composites were increasing with the addition of SiO_2. The bulk densities of the present composites were increasing with the addition of SiO₂. The structural changes in these samples were characterized using Fourier Transform Infrared Spectrometer (FTIR) in the 400–4000 cm^?1. The bands in the range of 580–880 cm^?1 show a slight increase in intensity, which could be ascribed to the enhanced interactions between the NiCuZnFe₂O₄ clusters and silica matrix. The resistivity of the sintered samples was increased with an addition of ferrite content. The real and imaginary parts of permittivity and permeability were measured in the frequency range of 1 MHz–1.8 GHz.The addition of SiO₂ alters the values of dielectric constant and permeability which is useful to the Multilayer Chip Inductors (MLCI) fabrication.     

Lead-free K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>NbO<Subscript>3</Subscript>–Bi<Subscript>0.5</Subscript>Li<Subscript>0.5</Subscript>ZrO<Subscript>3</Subscript>–BiAlO<Subscript>3</Subscript> ternary ceramics: Structure and piezoelectric properties

Lead-free perovskite (0.995–x)(K_0.5Na_0.5)NbO₃–x(Bi_0.5Li_0.5)ZrO₃–0.005BiAlO₃ ternary piezoelectric ceramics were projected and prepared by a conventional solid-state method. A research was conducted on the effects of (Bi_0.5Li_0.5)ZrO₃ content on the structure and piezoelectric properties of the ceramics. By combining the X-ray diffraction patterns with the temperature dependence of dielectric properties, a rhombohedral–orthorhombic–tetragonal phase coexistence was identified for the ceramics with 0.02 ≤ x ≤ 0.025, and a rhombohedral–tetragonal phase boundary was determined in the composition x = 0.03. Upon further increasing the (Bi_0.5Li_0.5)ZrO₃ content, the rhombohedral–tetragonal phase boundary transformed to a single rhombohedral structure with x ≥ 0.035. An obviously improved piezoelectric activity was obtained for the ceramics with compositions in and around the rhombohedral–tetragonal phase boundary, among which the composition x = 0.025 exhibited the maximum values of piezoelectric constant d ₃₃, and planar and thickness electromechanical coupling coefficients (k _p and k _t), of 252 pC/N, 0.366, and 0.466, respectively. In addition, the ceramic with x = 0.025 was found to possess a relatively high Curie temperature of 368 °C, suggesting it may have a prospect for applications at elevated ambient temperatures.