Carlos Zuniga

Optical properties of amorphous hydrogenated silicon nitride thin films

This paper presents a study of the optical properties of amorphous hydrogenated silicon nitride (a-Si3N4:H) films under deposition temperature influence. The films were deposited by low-frequency plasma-enhanced chemical vapor deposition at temperatures of 200, 300, and 400°C and 0.6-Torr pressure. The mixture gases were silane (SiH4), ammonia (NH3), and hydrogen (H2). The optical properties of the films samples were obtained by means of the transmittance spectra and from spectroellipsometry measurements. Then, the optical parameters of the films were determined using the Swanepoel, Cauchy, and Sellmeier models. The refractive index dispersion curves were well fitted with both the Cauchy and the Sellmeier theoretical model. The equivalence between the parameters that characterize the two models is established.

Physical and electrical characteristics of atomic-layer deposition-HfO2 films deposited on Si substrates having different silanol Si-OH densities

In this work, ultrathin HfO2 films, less than 6 nm in thickness, are deposited by atomic-layer deposition (ALD) on Si substrates that have a variable density of silanol (Si-OH) chemical bonds after oxidizing the Si surface using hot H2O2. Given the surface chemistry needed for proper ALD growth of HfO2, OH-last surfaces are needed in order to react with the Hf-based precursor during half-cycle of this reaction. The later is important for proper nucleation and uniform growth of ultrathin HfO2 by ALD. Depending on the immersion time of an initially HF-last Si surface in hot H2O2, ultrathin and nonstoichiometric chemical oxides SiOx are formed presenting a variable density of Si-OH bonds which are measured after Fourier-transform infra red spectroscopy. Following SiOx formation, HfO2 is directly deposited on these surfaces by ALD using water (H2O) and tetrakis-dimethylamino-hafnium as precursors. Metal–insulator–semiconductor (MIS) capacitors are then formed using both HfO2/Si and HfO2/SiOx/Si stacked structures and their electrical characteristics are evaluated. It is found that a variable density of Si-OH chemical bonds have an impact on the physical and electrical characteristics of these MIS structures by reducing their atomic surface roughness (Rrms) and gate leakage current density (Jg), and at the same time, increasing their flat band voltage (Vfb) for the same immersion times in H2O2. Obtaining the lowest Rrms, Jg, and Vfb are possible by using intermediate H2O2 immersion times between 4 and 8 min, which is also directly related to an intermediate Si-OH bond density.In this work, ultrathin HfO2 films, less than 6 nm in thickness, are deposited by atomic-layer deposition (ALD) on Si substrates that have a variable density of silanol (Si-OH) chemical bonds after oxidizing the Si surface using hot H2O2. Given the surface chemistry needed for proper ALD growth of HfO2, OH-last surfaces are needed in order to react with the Hf-based precursor during half-cycle of this reaction. The later is important for proper nucleation and uniform growth of ultrathin HfO2 by ALD. Depending on the immersion time of an initially HF-last Si surface in hot H2O2, ultrathin and nonstoichiometric chemical oxides SiOx are formed presenting a variable density of Si-OH bonds which are measured after Fourier-transform infra red spectroscopy. Following SiOx formation, HfO2 is directly deposited on these surfaces by ALD using water (H2O) and tetrakis-dimethylamino-hafnium as precursors. Metal–insulator–semiconductor (MIS) capacitors are then formed using both HfO2/Si and HfO2/SiOx/Si stacked struct...

Hermetic capacitive pressure sensors for biomedical applications

Purpose This paper aims to purpose the new design and fabrication scheme of Touch Mode Capacitive Pressure Sensor (TMCPS), which can be used in a wireless integrated resistor, inductor and capacitor circuit for monitoring pressure in biomedical applications. Design/methodology/approach This study focuses on the design, simulation and fabrication of dynamic capacitors, based on surface micromachining using polysilicon or aluminum films as the top electrode, both structural materials are capped with a 1.5 μm-thick polyimide film. Findings The design of microstructures using a composite model fits perfectly the preset mechanical behavior. After the full fabrication, the dynamic capacitors show complete mechanical flexibility and stability. Originality/value The novelty of the method presented in this study includes two important aspects: first, the capacitors are designed as a planar cavity within a rigid frame, where two walls contain channels which allow for the etching of the sacrificial material. Second, the electromechanical structures are designed using a composite model that includes a polyimide film capping for a precise pressure sensing, which also protects the internal cavity and, at the same time, provides full biocompatibility.

Nano-structured GeySi1-y:H Films Deposited by Low Frequency Plasma for Photovoltaic Application

In this work we present the study of fabrication, Ge incorporation, structure and electronic properties of nano-structured Ge y Si 1-y :H films with y>0.5 prepared by low frequency (LF) PECVD. Ge y Si 1-y :H films were deposited by LF PECVD at a frequency f= 110 kHz from SiH 4 +GeH 4 +H 2 gas mixture. SiH 4 and GeH 4 flows were varied to fabricate the films in wide range of 0 H =20 to 80. Structure of the films was studied by AFM and SEM with consequent image processing to extract statistical parameters such as grain distribution and mean values. Composition of the films was characterized by SIMS and EDX. Electronic properties were characterized by temperature dependence of conductivity, spectral dependence of optical absorption. Sub-gap absorption was characterized by Urbach energy, E U; and defect absorption, α D . We observed grain like nano-structure with Gauss distribution of grain diameters by both AFM and SEM measurements. The most interesting films had mean grain diameter = 24.0±0.7 nm, dispersion D=11.0±0.2 nm and fill factor FF=0.313, Ge content y=0.96-0.97(by SIMS and EDS). These films showed also the lowest values of Urbach energy E U = 0.030 eV and low defect absorption α D = 5×10 2 cm −1 (at photon energy hv = 1.04 eV) indicating on low density of localized states in mobility gap. Doped films have been also fabricated and studied. Finally we shall discuss application of the above films in photovoltaic devices.

Photodetector with giant internal current amplification: experiment and numerically calculated model

New silicon based optical sensors with a metal - insulator - semiconductor structure (MIS) are developed and investigated both theoretically and experimentally. The physical properties of these sensors are described with a model of MIS capacitor where a presence of depletion layer of electrons and an inversion layer of holes of a finite depth is taken into account. Two-level voltage bias provides a transient between two quasi-equilibrium inversion modes. This transient is applied both for storage and for readout of the input optical signal for quantitative measurements of a weak infra red radiation. Proposed simple readout procedure provides reading the integrated information with a significant amplification. The amplification (or the current transformation coefficient) is determined by the ratio of integration and readout times and it may exceed 104. A theoretical model is given to explain a behavior of the sensor under storage by thermo generated carries and by photo generated ones jointly. Numerical simulations are of an agreement with experimental investigations of proposed sensors.

Evaluation of interface-states density for MOSFETs fabricated on high-index (114) silicon surfaces

Metal-oxide-semiconductor field-effect transistor (MOSFET) devices were fabricated on high-index silicon (114) surfaces and their threshold voltage (Vth) and interface-states density (Dit) parameters were both evaluated for the first time. Even though MOSFET devices aligned at 0°, 30°, 60° and 90° off the equivalent [110] direction present two closely related average Vth values, Dit evaluation shows that for all channel orientations (0°, 30°, 60° and 90°), this high-index silicon (114) surface develops a high-quality interface with SiO₂ in which few electrons are trapped so that Dit as low as 10¹⁰ cm^-2eV^-1 can be obtained.

Performance of a MOHOS-type memory using np-HfO 2 and variable tunneling oxide thickness

We use HfO2 nanoparticles (np-HfO2 embedded in a spin-on glass SOG oxide matrix) as a charge trapping layer CTL in metal/oxide/high-k/oxide/silicon (MOHOS)-memories. This CTL is then deposited on ultra-thin layers of chemical oxide SiOx ≤2nm. Depending on the SiOx thickness, a trade-off in writing/erasing and data retention time characteristics is obtained.

Progressive-degradation and breakdown of W-La 2 O 3 MOS structures after constant voltage stress

In this paper, we report the progressive electrical degradation and consequent breakdown (both soft and hard-breakdown regimes) of thin W-La2O3 stacked films deposited on silicon substrates and their influence on the electrical characteristics of metal-oxide-semiconductor (MOS) devices. Initial electrical degradation of the MOS devices results in an increase of the gate oxide leakage current (mostly known as Stress-Induced Leakage-Current, SILC), with the devices practical effect being a monotonous shift in threshold voltage (¿Vth) after constant voltage stressing. Following the initial degradation of the gate oxide, both soft and hard-breakdown modes are detected and their influence on the electrical characteristics of the MOS devices are also obtained and compared.

Optical, structural and electrical properties of amorphous SiGeB obtained by LF PECVD

Results of characterization of amorphous silicon germanium borum deposited by low frequency plasma enhanced chemical vapor deposition are presented. The structure has been studied by IR and Raman spectrocopy. Transport of carriers has been studied by measurement conductivity dependence on temperature. The optical properties have been determined using Swanepoel’s method.